GB2057165A - Fuel injection pump for internal combustion engines - Google Patents

Abstract

The pump provides a suction chamber (8) and a control piston (3) for varying the engine injection timing in dependence on engine speed. The piston is normally biassed by a spring (5) in the retard direction but, at least over a certain speed range, is supplemented by fuel pressure from the suction chamber fed via a bore (13); the speed range concerned and degree of supplemental pressure being determined by a control valve (16) in response to, say, engine temperature sensed by a thermostat 17. <IMAGE>

Description

SPECIFICATION Fuel injection pump for internal combustion engines The invention relates to a fuel injection pump for internal combustion engines, having an adjusting piston for adjustment of the fuel injection timing device, the adjusting piston being displaceable, on its forward stroke, by a pressure in the working chamber proportional to the engine speed, and being displaceable, on its return stroke, against a restoring force in a restoring chamber, which force is variable in dependence upon engine parameters.

In a known fuel injection pump of this type, a spring which abuts against an adjustable abutment member serves as a restoring force. The abutment member is displaceable in dependence upon engine parameters. Since the variable controlling pressure must first displace the abutment piston before adjustment of the injection timing is effected by variation of the force of the spring, this system has a relatively slow response. The control system is a multiplicative system, in which one controlling parameter, that is, the pressure acting upon the abutment member, varies the second controlling parameter, namely, the restoring spring. This reciprocal influencing of the controlling parameters makes it difficult to determine individual quantities for different conditions, with all the resultant disadvantages in matching the requirements of the engine manu factu rer.

There is provided by the present invention a fuel injection pump for internal combustion engines, having an adjusting piston for adjustment of the fuel injection timing device, the adjusting piston being displaceable, on its forward stroke, by a pressure in the working chamber proportional to the engine speed, and being displaceable, on its return stroke, against a restoring force in a restoring chamber, which force is variable in dependence upon engine parameters, wherein pressurised fluid, whose pressure is variable, is employed as the variable restoring force.

As compared with the known art, the fuel injection pump according to the present invention has the advantage that the timing adjustment is additive in character and is therefore relatively easy to control and match. Thus, the injection timing can be advanced or retarded in dependence on engine parameters, in particular temperature, but also on load or boost pressure, or on other quantities. A further advantage of the invention is that its practical embodiment can be achieved merely by the addition of modules to a standard fuel injection pump. The module may be of simple or complex construction according to requirements.

Simplified view of a number of embodiments of the invention are shown in the accompany drawings, in which: Figures 1 and 3 are, respectively, views of two embodiments; Figure 2 is a graph showing retardation of the timing at low engine speeds, Figures 4, 6 and 7 relate to further embodiments, and Figure 5 is a graph similar to that of Figure 3.

An adjusting piston 3 engages via a pin 2 in the cam mechanism of a fuel injection pump 1 in order to adjust the timing of the commencement of injection. The adjusting piston 3 is displaceable by means of pressurised fluid in a working chamber 4 against the force of a return spring 5, whereby the further the piston is displaced towards the spring, the more the injection timing is advanced relative to the top dead centre of the piston of the engine. The 'plus' direction of the arrow denotes an advance of the timing, and the 'minus' direction denotes a retardation. Afuel feed pump 6 draws fuel from a fuel tank 7 and feeds it to a suction chamber 8 serving as an input chamber of the injection pump 1, from which chamber the fuel injection pump itself (not shown) is supplied with fuel and which is connected via a bore 9 in the adjusting piston 3 to the working chamber 4.This bore 9 has a throttle 10.

The feed pressure of the feed pump 6, and thus also the pressure in the suction chamber 8, are controlled by means of a pressure control valve 11 in dependence on engine speed, the pressure increasing in proportion to the engine speed. This engine-speeddependent pressure prevails also in the working chamber 4, so that, on an increase in engine speed and consequently also in pressure, the injection timing control piston 3 is displaced in the 'plus' direction, that is, the direction to advance the timing.

Figure 2 shows a graph in which the strokes of the adjusting piston (the ordinate) is shown against the engine speed n (the abscissa). / designates the injection timing characteristic, according to which the stroke, and therefore also the timing advance, increase as a linear function of engine speed. In many engines it is desirable or essential for starting, and particularly in order to achieve a fast run-up, to retard the commencement of injection when the engine is cold, or under other conditions, at least up to a predetermined engine speed, as is shown by the broken-line curve II in the graph.

According to the invention, adjustment of the injection timing is performed by variation of the fuel pressure in the restoring chamber 12 which receives the return spring 5. This chamber 12 has a connection 13, having a throttle 14, to the suction chamber 8.

In the first embodiment, shown in Figure 1, this throttle is arranged in the form of a bore 14 in the wall of the timing control piston 3, which, during its stroke movement, on completion of a predetermined stroke disconnects the bore 14 from the connection 13, and thereby disconnects the restoring chamber 12 from the suction chamber 8. In the position shown in the drawing, which corresponds to low engine speeds, however, the injection timing control piston 3 is displaced to the right, that is, in a direction to retard the timing, by the pressure created in the restoring chamber 12. This is possible because of the arrangement of a thermostatically controlled pressure control valve 16 in a by-pass line 15 leading from the restoring chamber 12.So long as this pressure control valve 16 is closed, the pressure in the suction chamber 8 and working chamber 4 builds up in the restoring chamber 12, so that the injection timing control piston 3 is displaced to the right, in a direction to retard the injection timing, assisted by the force of the spring 5. The thermostat 17 of the pressure control valve 16 may be heated either by means of an electrical heating filament or, alternatively, directly by the cooling water of the engine, in order to permit the flow of fuel via the ball valve 18.

According to how far the valve is opened, fuel is then able to flow from the restoring chamber, the consequent flow of fuel from the suction chamber 8 being determined by the cross-section of the throttle bore 14. Apart from the fact that the electrical heating of the thermostat 17 may be effected in dependence upon any desired engine parameters, in addition, instead of a thermostatically controlled valve 16, a valve controlled by other means may be used. When the valve 16 is fully open, the restoring chamber 12 is fully pressure-balanced, and only the return spring 21 acts in a direction to retard the timing.In order to obtain a predetermined controlling effect with the valve 16 notfully open, for example, in orderto prevent retardation at higher engine speeds and also to prevent loss of fuel via the throttle bore 14 at higher engine speeds while the valve 16 is open, at speeds in excess of the idling speed the throttle bore 14 is disconnected from the connection 13 by displacement of the timing control piston 3. Above a sufficient pressure in the restoring chamber 12 the valve opens in the manner of a pressure limiting valve.

In the second embodiment, shown in Figure 3, the injection timing control piston 3 is shown to a larger scale in order to clarify the method of control of the fluid flow effected by the timing control piston. The method of operation of this embodiment is fundamentally the same as that of the first embodiment, shown in Figure 1. In condradistinction and supplementarily to the latter, however, the connection 13 is controlled by means of an annular groove 19 in the injection timing control piston 3. From the annular groove 19 the throttle bore 14 branches off to the restoring chamber 12. On completion of a predetermined stroke in a direction to advance the timing, that is, to the left, the annular groove 19 is disconnected from the connection 13, so that the flow from the suction chamber 8 to the restoring chamber 12 is interrupted.Immediately following this disconnection a spill port 20 is opened by the annular groove 19 and now releases the pressure in the restoring chamber 12 via the throttle bore 14. In contrast to the first embodiment, in this second embodiment the restoring chamber 12 is relieved of pressure above a predetermined engine speed irrespective ofthe operating position ofthe pressure control valve 16. In this case, there is also connected in series with the return spring 5 a weaker spring 21, which, on starting, permits the injection timing control piston 3 quickly to assume a position to advance the timing when the pressure control valve 16 is inoperative, that is, on starting, when the timing control piston 3 is in a position to retard the timing.

When it then moves in a direction to advance the timing, it compresses the spring, until the timing control piston butts against the intermediate spring retainer 22 of the return spring 5. The subsequent injection timing response then corresponds once more to the charactertistic / in Figure 2. The characteristic produced by means of the spring 21 is shown by a dot-and-dash line II in Figure 2.

The characteristic Ill shows the configuration of the fuel injection timing characteristic with the valve 16 opened by the thermostat 17.

In the third embodiment, shown in Figure 4, fuel flows continuously via a connection 13 from the suction chamber 8 to the restoring chamber 12. In this connection there is arranged a preferably adjustable throttle 23. During normal operation, that is, when the internal combustion engine is warm, and preferably at speeds higher than starting speeds, fuel flows from the restoring chamber 12 via a by-pass line 24, in which there is arranged a pressure retaining valve 25. This pressure retaining valve 25 creates in the restoring chamber 12 a pressure which acts upon the piston 3, thereby providing a force to assist the force of the spring 5. This force is superimposed upon the force of the spring 5, and, since the pressure is constant and the superimposed force additively applied, it remains constant over the entire speed range.The forces acting upon the piston 3 in the direction of the resilient bias, namely, the pressure and the spring, are, at least at medium and high engine speeds, smaller than the hydraulic forces acting in the working chamber 4 upon the piston 3, so that a corresponding timing advance can be effected by the engine speed. According to this third embodiment, via second by-pass line 26 the pressure in the restoring chamber 12 can be reduced by a predetermined amount by a pressure control valve 27 arranged in this by-pass passage 26. The embodiment of a pressure control valve shown in Figure 4 operates as a thermostatic valve, having a bimetallic element 28, which is heatable by means of an electrical heating filament 29, and which, assisted by a spring 30, acts upon a valve member 31.When the heating filament 29 is cold, the spring 30 is relieved of pressure by the bimetallic element, so that fuel flows from the restoring chamber 12 via the by-pass line 26 before the pressure retaining valve 25 opens. The pressure in the restoring chamber 12 is therefore lower than during normal operation, with a consequent advance of the fuel injection timing control piston 3. Instead of a bimetallic valve 27, a solenoid-operated valve, a valve operated by an expansion element, our a mechanically operated valve, may be used.

In the graph shown in Figure 5, whose coordinates correspond to those of Figure 2, the normal timing characteristic is again designated as 1, that is, for a warm engine, without the effect of other engine parameters. A curve IV, shown by a broken line, corresponds to a timing advance and also, therefore, to the described method of operation of the pressure control valve 27.

In the fourth embodiment, shown in Figure 6, a valve operated by an expansion element serves as the pressure control valve 27'. Moreover, the crosssection 32 of the branch of the by-pass line 26 is controlled by the injection timing control piston 3 and is closed at speeds higher than a predetermined engine speed, that is, above a predetermined engine speed advance of the timing is cancelled in accordance with the curve IV shown by a broken line in Figure 5.

The fifth embodiment, shown in Figure 7, is fundamentally similar in principle. In this case the pressure control valve 27" is in the form of a slide valve whose valve spool 33 controls the by-pass line 26 via an annular groove 34. When the valve slide 33 is displaced, the by-pass line 26 is blocked. This displacement is effected by means of a control element, such as, for example, an expansion-type element 35, and also by pressurised fluid which is supplied from the working chamber 4 of the injection timing control piston 3 via a pressure line 36 to a chamber 37 into which one end face of the valve spool 33 extends. At its end remote from this chamber 37 the valve spool 33 is subjected to the force of a spring 38. As a result, the by-pass line 26 is blocked at speeds above a predetermined engine speed in the manner of a safety circuit, whereby the pressure in the restoring chamber 12 increases and the injection timing is correspondingly retarded.

Should it be desired to prevent complete cut-off of the fuel, then, as shown by broken lines, a branch 39 of the by-pass line 26 may be opened by the slide valve 33, or the annular groove 34; a throttle 40 being arranged in the branch line 39. Consequently, the pressure in the restoring chamber 12 in fact rises above the pressure created via the line 36; however, it remains below the pressure which would be created by the pressure retaining valve 25.

Claims (12)

1. A fuel injection pump for internal combustion engines, having an adjusting piston for adjustment of the fuel injection timing device, the adjusting piston being displaceable, on its forward stroke, by a pressure in the working chamber proportional to the engine speed, and being displaceable, on its return stroke, against a restoring force in a restoring chamber, which force is variable in dependence upon engine parameters, wherein pressurised fluid, whose pressure is variable, is employed as the variable restoring force.

2. Afuel injection pump according to claim 1, wherein additionally, a restoring spring is provided to assist the restoring force.

3. Afuel injection pump according to claim 1 or 2, wherein, in orderto vary the pressure, pressurised fluid, whose outflow from the chamber is controlled, is fed into the restoring chamber.

4. Afuel injection pump according to claim 3, wherein the pressurised-fluid feed is throttled.

5. A fuel injection pump according to any preceding claim, wherein the maximum pressure in the restoring chamber is limited by means of a pressure limiting valve.

6. Afuel injection pump according to any preceding claim, wherein the flow to and from the restoring chamber is controllable by the adjusting piston.

7. A fuel injection pump according to any preceding claim, wherein a pressure control valve, whose operation is dependent upon engine parameters, is arranged in the by-pass line.

8. Afuel injection pump according to claim 7, wherein the pressure control valve is operated by electrical means.

9. A fuel injection pump according to claim 7 or 8, wherein the valve is operated by temperaturedependent means, such as an expansion-type control element or a bimetallic element.

10. Afuel injection pump according to any preceding claim, wherein the pressurised fluid in the restoring chamber is drawn rom the source which also supplies the working chamber.

11. Afuel injection pump according to any preceding claim, wherein, at speeds in excess of a predetermined engine speed, the by-pass line from the restoring chamber is blockable by means of an engine-speed-dependent valve.

12. A fuel injection pump substantially as hereinbefore described with reference to Figures 1 or 2 and Figure 3 orto Figure 4,6 or 7 and Figure 5 of the accompanying drawings.