EP1049860A1

EP1049860A1 - Fuel injection pump

Info

Publication number: EP1049860A1
Application number: EP99964368A
Authority: EP
Inventors: Wolfgang Geiger; Walter Fuchs; Hubert Greif; Stephan Jonas
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1998-11-27
Filing date: 1999-11-24
Publication date: 2000-11-08
Anticipated expiration: 2019-11-24
Also published as: DE59911983D1; WO2000032919A1; KR20010034375A; JP2002531747A; US6413054B1; EP1049860B1; PL341910A1; DE19854766A1

Abstract

Disclosed is a fuel injection pump with a cam drive and an injection-adjusting piston which acts upon the cam drive in order to time the beginning of the injection. Said piston comprises at least one pressure chamber (17) at its face end. Said pressure chamber can either be connected to a pressure source (38) having a discharge line (36) via a control valve (29) or can be completely closed, whereby the control valve is actuated by an electromagnet, preferably a proportional electromagnet. High efficiency of the timing of the beginning of the injection is thereby achieved with little need for adjusting means; the advantage is that the injection-adjusting piston (15) is only axially charged and that friction forces are thus eliminated at the circumference of the injection-adjusting piston.

Description

Fuel injection pump

State of the art

The invention is based on a fuel injection pump according to the preamble of the main claim. In such a fuel injection pump, known from DE-OS 24 58 109, the pressure in the pressure chamber enclosed by the injection adjuster piston in the cylinder is controlled by a 2/3 directional control valve which connects the pressure chamber either to a pressure oil delivery pump or to a relief line . By means of the pressure oil introduced into the pressure chamber, the injection adjustment piston is displaced against the force of the spring and adjusted in accordance with the start of injection of the associated fuel injection pump. The control takes place in such a way that the spray adjustment piston is adjusted between a first position that opens the relief line and a second position that opens the pressure line by corresponding actuation of the 2/3 directional control valve. In an alternative embodiment, pressure-oil-absorbing cell chambers are provided between a drive member and a driven member of the fuel injection pump, the connection of which to an oil feed pump or to a relief channel is controlled by a 2/4 directional control valve. In one position of the 2/4 directional control valve, fuel is supplied to the oil pump by one of the pressure chambers supplied and fuel from the other of the pressure chambers via a relief line. If the 2/4 directional control valve is in a different position, the fuel is supplied and removed in the opposite direction. With this device, two different positions of the drive member relative to the driven member can be set according to the known design. In contrast, it is necessary to set intermediate positions precisely and also to maintain them in accordance with the specified operating parameters.

Advantages of the invention

The fuel injection pump according to the invention with the characterized features of the main claim has the advantage that the configuration of the valve member of the control valve as a slide makes it possible to control exact control of the inflow or outflow from the pressure chamber with low actuating forces. In particular, a previously set one can be closed by the control collar of the slide by closing the connecting line

Positioning of the injection plunger can be maintained. By closing the connecting line, the restoring forces transmitted from the cam ring to the injection adjustment piston, which occur during the respective pump piston delivery stroke of the fuel injection pump, are absorbed, since the volume which is enclosed in the cylinder by the injection adjustment piston is formed as a closed volume with the cooperation of the control valve and only evasive the injection adjusting piston is realized within the framework of the elastic compressibility of the enclosed hydraulic column. At the end of the respective delivery stroke of the pump pistons of the fuel injection pump, the injection adjustment piston assumes the previously desired position and thus controls the recommencement of injection in the desired exact manner. At most if in the In the meantime, a change in the start of spraying is required due to correspondingly changed operating parameters, the pressure in the pressure chamber can be changed by opening the pressure chamber to the pressure source or to the relief line. With the aid of the control slide, it is also possible to produce overflow cross sections of different sizes between the connecting line and the pressure line or relief line, so that the pressure change rate in the pressure chamber can be of different heights in accordance with the control of the control valve. This results in a very flexible control, by means of which, depending on the requirement, a desired quick and a large desired injection start adjustment can be achieved. Advantageously, the valve spool is adjusted by an electromagnet which adjusts the valve spool analogously or proportionally to a control value. In an alternative embodiment, the control slide can also be actuated in a clocked manner, which reduces the idle friction which counteracts an adjustment when the valve slide is deflected from longer stationary positions.

Characterized in that according to claim 2 of the control slide 2 frets, a control collar and a guide collar, it is hydraulic in the axial direction of the same size

Forces are applied so that the slide is only moved against the force of a return spring according to claim 3 by the electromagnet. In an advantageous development according to claim 7, both the pressure chamber, which is located on one side, are controlled by the control valve

Front side of the injection adjustment piston is located, as well as a second pressure chamber, which continues opposite on the other end side of the injection adjustment piston with pressurized medium by the pressure in these pressure chambers by appropriate design of the Control valve spool is complementarily controlled by controlling the pressure medium flow. According to claim 7, the control slide is advantageously equipped with two control collars which, in a central position, close the respective connecting lines between the control valve and the pressure chambers on the injection adjustment piston, so that it assumes a neutral position previously preset by the corresponding actuation of the control valve. If operating parameters change, a rapid, efficient adjustment of the injection adjustment piston can be brought about by supplying pressure medium in one pressure chamber and removing pressure medium from the other pressure chamber. Above all, the adjustment speed of the injection adjustment piston can also be increased here.

All of the exemplary embodiments have in common that the supply of pressure medium can take place directly into the pressure chambers without radially loading the injection adjustment piston. This lowers the frictional forces and wear and tear on the injection adjustment piston and its guide and ensures long functionality. Due to the direct feeding of pressure medium and a reclosing of the pressure chambers by the control slide, a minimal pressure medium requirement is maintained. A high level of adjustment is possible even at a low speed of the fuel injection pump, which drives a pressure medium pump at this speed, since the outflow losses are minimized. In particular in an embodiment according to claim 8, in which in one of the pressure rooms in addition to the

If a pressure spring feed is also provided, the injection adjustment piston can assume a preferred position of the injection start adjustment in the case of pressure medium delivery quantities that are not yet available, by means of which the starting of the internal combustion engine is favored. In In this position, the pressure chambers are advantageously closed by the control slide and the spray start adjustment piston has moved under the action of the spring and made possible by the leakage losses on the circumference of the injection adjustment piston into said preferred position.

In a particularly advantageous manner, it is possible to make a recess in the injection adjustment piston, which allows a coupling part which is connected to the cam drive to be inserted into the injection adjustment piston to such an extent that the contact surface between the coupling part and the injection adjustment piston lies in an area. which lies essentially in the injection piston axis. The return forces of the cam drive are thus directed axially onto the injection adjustment piston and it is avoided that the injection adjustment piston is exposed to tilting moments. In an advantageous further development, the contact surface can be arranged slightly offset from the spray adjustment piston axis, which has the advantage that in this way an automatic self-alignment of the

Injection-adjusting piston to the coupling part is ensured, so that the axis of the recess remains essentially coincident with the axis of the coupling part.

drawing

Two exemplary embodiments of the invention are shown in the drawing and are explained in more detail in the description. Show it

Figure 1 shows a first embodiment with only one pressure chamber controlled by the control valve and

Figure 2 shows a second embodiment with two complementary controlled by the control valve pressure chambers.

description The cam drive of a fuel injection pump has, in a known manner, a cam track on which rollers run, with relative motion being generated when the pump pistons roll, by means of which the pump pistons move back and forth

Movement. In the case of a reciprocating piston pump, this is a cam disc, and in the case of a radial piston pump, this is e.g. B. a cam ring 1, as indicated in Figure 1. This is rotatably mounted in a circular recess 2 in the housing 3 of the fuel injection pump. Pointing inwards, to the axis of the circular recess 2, the cam ring 1 has a cam track 4 on which rollers 6 mounted in a roller shoe 5 run and thereby radial movements caused by the cams 7 of the cam track onto the pump pistons 8, of which only here one is shown.

To actuate the cam ring 1 in its circumferential direction or to set a rotational position of the cam ring, a coupling part 11 is provided in the form of a radially projecting pin which is formed in one piece with the cam ring and which extends through an opening 12 in the wall of the circular recess 2 into a in the housing 3 of the fuel injection pump arranged cylinder 14 protrudes and is coupled there with an injection adjusting piston 15 which is longitudinally displaceable in a cylinder 14. The injection adjusting piston 15 has a first end face 16 which, together with the closed end of the cylinder 14, encloses a first pressure chamber 17 and has on its opposite side a second end face 18, which together with the closed end of the cylinder 14 there has a second pressure-relieved pressure chamber 20 includes. Between the closed end of the cylinder 14 and the second end face 18, a compression spring 21 is clamped, which axially loads the injection adjustment piston 15 in the direction of a preferred position. The coupling between the coupling part 11 and the injection adjustment piston 15 takes place via a radially oriented recess 22 in the injection adjustment piston 15 in the region of its central lateral surface. This recess is so deep that the pin 11 extends into the region of the longitudinal axis 23 of the injection adjusting piston and there has a line of contact 24 of its head-like end with the cylindrical part of the recess 22 surrounding it. Actuating forces from the pump piston 8 via the cams 7 in

Transfer circumferential direction to the cam ring and from this in turn in the longitudinal direction to the adjusting piston 15, thus axially attack the spray adjusting piston 15 and it is thus prevented that the piston is exposed to tilting movements due to these forces, the one-sided wear on the jacket contact surfaces with the cylinder 14 would cause. The line of contact can be substantially aligned with the injection piston axis, but it can also be slightly z. B. 2 to 6 mm radially offset from this axis thereof. This has the advantage that a small torque in the circumferential direction acts on the injection adjusting piston in such a way that the recess 22 aligns coaxially with the pin 11 and thus a preferred position of the pump piston is automatically maintained without additional guide means being required.

A pressure medium source, not shown here, is provided for actuating the injection adjustment piston. B. can be the fuel supply pump of the fuel injection pump, which delivers speed-dependent fuel to a suction chamber of the fuel injection pump, from which the fuel to be injected is then directed into the pump work chambers, compressed there and then for injection by the pump pistons 8 to the injection Valves is deployed. The per se speed-dependent pressure that the speed-dependent delivery pump generates can also cause speed-dependent control processes. For this purpose, the pressure is controlled more precisely by additional pressure valves and is now also available as an actuating medium

Injection start adjustment available. The fuel pressure is via a control valve 26 to the first pressure chamber 17 via a connecting line 27. This opens directly into the pressure chamber 17 without the inflowing fuel having any radial force and tilting moments on it

Injection adjusting piston 15 is generated and axially loaded exclusively by this hydraulic force against the force of the compression spring 21. The connecting line 27 ends at the other end in a valve cylinder 28 in which a control slide 29 is slidably arranged. This carries two frets on a shaft 30, a first collar in the form of a control collar 32 and a second collar in the form of a guide collar 33. The control collar 32 sits at the end of the shaft 30 and is loaded on its axial end face by a return spring 35 which is in contact with one another is supported on the closed end face of the valve cylinder 28 and lies in a space which is relieved by a relief line 36. Between the control collar 32 and the guide collar 33 there is an annular space 37 which is in constant communication with the pressure medium source, the suction space, of the fuel injection pump via a pressure line 38. On the side of the guide collar 33 facing away from the annular space 37, a further space is enclosed, which is also relieved of pressure by a relief line 36. On this side, the stem 30 leads out of the valve cylinder and is connected there to the armature of a proportional electromagnet (not shown further here), which causes the control slide 29 to be adjusted counter to the force of the return spring 25 in accordance with its energization. In the starting position shown, the control collar 32 has the Entry of the connecting line 27 in the valve cylinder 28 is closed. A certain pressure has set in this space, which is counteracted by the force of the compression spring 21, so that the adjusting piston 15 assumes a force-balanced resulting position.

If the setting of the pressure adjusting piston is to be changed from the position shown, the control slide 29 is actuated, for. B. to the left so that fuel from the pressure line 38 via the annular space 37 in the

Connection line 27 can flow and can increase the pressure in the first pressure chamber 17 until there is again a balance of forces with the compression spring 21. This adjustment is advantageously monitored by a sensor which detects the adjustment position of the cam ring 1, emits a signal to a control device which compares it with a setpoint value and gives a corresponding control signal to the proportional magnet of the control valve, which moves the control slide into the position for the respective adjustment of the adjusting piston moves the necessary position.

By moving the control slide 29 to the right, the first pressure chamber 17 will be relieved, so that under the action of the now reduced pressure and the prestressed force of the compression spring 21, the adjusting piston in turn

Adjustment of the force balance on it moves to the left. This adjustment is again detected by the rotation angle sensor, not shown further. The control can also be influenced by other parameters that are decisive for the start of spray setting.

This embodiment has the advantage that the inflow rate of pressure fluid can be influenced by the degree of opening of the connecting line from the annular space 37 to the first pressure space 17. Correspondingly quickly can with large The inflow cross section of the injection adjustment pistons can be adjusted, and a desired position of the injection adjustment piston can also be set exactly by means of an exact feedback of the injection start adjustment result with the electromagnetic intervention on the control valve 29 via the proportional solenoid. Effects in the intermediate area due to the delivery processes of the pump pistons 8 are absorbed by closing the connecting line 27. The start of injection adjustment device is simple in construction and easy to implement and has the advantage of a balanced force balance on the injection adjustment piston while avoiding radial forces. A long service life of the injection adjustment piston is achieved due to the low frictional forces.

In a further embodiment of the invention according to FIG. 2, a control slide 129 is now provided, which in principle is constructed similarly to the control slide according to FIG. 1. Here, however, both frets serve as control frets. There is also the control collar 32 adjoining the compression spring 35 and the collar previously used as a guide collar is now one

Control collar 133. Again, the pressure medium is supplied via the pressure line 38 in the center of the outer surface of the valve cylinder 28 into the annular space 37, which acts upon the control slide 8 in a force-balanced manner when pressure is applied. The pressure areas of the two frets are the same size. While, as in the exemplary embodiment according to FIG. 1, the first control collar 32 controls the first connecting line 27 into the first pressure chamber 17, the second control collar 133 now controls a second connecting line 127 into the second pressure chamber 120, which is now no longer basically relieved of pressure. In the neutral position shown, the control collars 32 and 133 close the respective openings of the connecting lines 27 and 127 into the valve cylinder 28. The two pressure chambers 17 and 120 are thus hydraulically locked and the position of the Injection adjustment piston 15 is fixed. The compression spring 121 can only be effective in the region of a position of the injection adjustment piston that goes beyond a preferred position.

To adjust the spray adjustment piston, the control slide 129 is now in turn z. B. actuated by a proportional magnet, for. B. to the left against the force of the spring 35. A connection between the annular space 37 and the first pressure chamber 17 is established so that hydraulic fluid can get into the first pressure chamber 17. At the same time, the connecting line 127 to the relief line 36 is opened by the second control collar 133, so that hydraulic fluid can escape from the second pressure chamber 120. This creates an imbalance of forces on

Adjusting piston of a pronounced size so that it moves very quickly to the right until a certain position of the injection adjusting piston 15 is fixed by correcting the position of the control slide 29. This process is also regulated via a control loop in which the injection start adjustment angles are queried and, in accordance with the deviation from a predetermined setpoint, the proportional magnet now actuates the opening of the connecting lines 27, 127 or is set to close them. For a reverse sequence of movements of the injection adjusting piston to the left, the control slide 129 is moved to the right, so that pressure medium can flow into the second pressure chamber 120 via the connecting line 127 and pressure medium can also escape from the first pressure chamber 17 via the connecting line 27 to the relief line 36. This in turn until the control slide 129 is brought back into the position locking the connecting lines 27, 127 via a feedback. Instead of a proportional control spool 29 or 129 can also be adjusted clocked with a pulse train that acts on the electromagnet and thus produces a quasi-analog adjustment of its armature, which in turn is coupled to the control spool. It can be easy

Axial vibrations are generated, which ensure that the spool is constantly in motion and hysteresis due to frictional forces is largely avoided.

With the compression spring 121 can be achieved that z. B. at the start of the internal combustion engine, which is supplied with fuel by the fuel injection pump and from which the fuel injection pump is driven, a preferred position can be set. When starting, the pressure chambers 17 and 120 are hydraulically locked according to Figure 2. The compression spring 121 can nevertheless move the injection adjustment piston 15 into a preferred position, because of a leakage flow along the lateral surface of the injection adjustment piston.

Even when the internal combustion engine starts operating at a low speed, fuel pressure is available with a gradually increasing delivery volume. Due to the design of the invention, which enables the pressure chambers to be locked hydraulically via the control valve, only the smallest amounts of hydraulic fluid or pressure fluid, in the given case fuel, are necessary in order to achieve the desired setting of the injection start adjustment piston. This guarantees the operability of the injection start adjuster even at low speeds, with very little control effort overall and with high life expectancy due to the radial loads on the injection adjustment piston avoided.

Claims

Expectations

1. Fuel injection pump with a cam drive (1, 5, 6, 8) for at least pump pistons (8) and a spray adjustment piston (15), which acts on the cam drive and serves to adjust the start of injection, which is operated by an electrically controlled control valve (26, 126) controlled pressure can be adjusted against a restoring force (21), the pressure valve (17) enclosed by the one end face (16) of the injection adjustment piston (15) in a cylinder (14) by the control valve (29) either with a pressure source (38 ) high level or with a relief room

(36) can be used, characterized in that the control valve (26, 126) as a valve member has a valve slide (26, 126) which can be displaced in a valve cylinder (28) and has a control collar (32, 133) through which one in the Valve cylinder (28) connecting line (27,

127) to the pressure chamber (17, 120) either with a pressure line (38) which comes into the valve cylinder (28) from a pressure source or with a relief line (36) leading away from the valve cylinder (28).

2. Fuel injection pump according to claim 1, characterized in that the valve slide (29) in addition to the control collar has a guide collar (33), between which and the control collar (32) an annular space (37) in the valve cylinder (28) is included, which is either permanently connected to the pressure line (38) or to the relief line (36).

3. Fuel injection pump according to claim 2, characterized in that the control slide (29, 129) is adjustable by an electromagnet against the force of a return spring (35).

4. Fuel injection pump according to claim 2, characterized in that the electromagnet adjusts the control slide against the force of the return spring according to a control value analog.

5. Fuel injection pump according to claim 2, characterized in that the electromagnet adjusts the control slide against the force of the return spring (35) clocked according to a control value.

6. Fuel injection pump according to claim 1 to 5, characterized in that the electromagnet is actuated by a control device which detects the injection adjustment parameters with a feedback element for the injection adjustment position of the cam drive.

7. Fuel injection pump according to one of the preceding claims 2 to 6, characterized in that the restoring force is a restoring spring (20).

8. Fuel injection pump according to one of the preceding claims 2 to 7, characterized in that the guide collar is designed as a second control collar (133) through which a second connecting line (127) opening into the valve cylinder (28) leads to a second , from the other end face (18) of the injection adjustment piston (15) in the cylinder (14) enclosed pressure chamber (120) leads, either with the pressure line (38) coming from a pressure source into the valve cylinder (28) or with the relief line (36) leading away from the valve cylinder (28), or is closed, whereby by the control collar ( 32) and the second control collar (133), the pressure chamber (17) and the second pressure chamber (129) complementary to one another with the pressure source (38) or the relief line (36) or both connecting lines (27, 127) in a middle position the control slide (129) are closed.

9. Fuel injection pump according to one of claims 2 to 8, characterized in that the annular space (37) with the pressure source (38) is permanently connected.

10. Fuel injection pump according to one of the preceding claims, characterized in that the injection adjusting piston (15) has a recess (22) in its lateral surface into which a coupling part (11) connected to the cam drive engages and thereby the adjustment of the injection adjusting piston (15) to the cam drive (1) transmitting contact surface (24) on the injection adjustment piston (25) is essentially in the area of the injection adjustment piston axis (23).

11. A fuel injection pump according to claim 10, characterized in that the contact surface (24) is arranged offset by approximately 2 to 6 mm from the injection adjusting piston axis (23).