GB2186920A

GB2186920A - Distributor-type fuel injection pump for internal combustion engines

Info

Publication number: GB2186920A
Application number: GB08704047A
Authority: GB
Inventors: Gerald Hofer
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1986-02-20
Filing date: 1987-02-20
Publication date: 1987-08-26
Also published as: DE3605364A1; FR2594492B1; GB8704047D0; JPS62197665A; GB2186920B; FR2594492A1

Abstract

In order to achieve a uniform static pressure in the pressure lines (31), by way of which an internal combustion engine is supplied by a distributor-type fuel injection pump, during the injection intervals the pressure lines (31) are relieved by way of a compensating port (43) and a valve (51) the suction chamber (8). During starting when air is present in the pump or the pressure lines 31, the valve (51) prevents relief, o that the pressure level in the pressure lines (31) at the end of each delivery stroke of the pump piston (3) is maintained and any enclosed air is compressed to injection pressure and thereby purged from the pump working chamber and from the pressure lines by being delivered with the fuel. After start-up pressure builds up in the suction chamber (8) and moves the valve (51) to a position connecting the compensating port (43) to the suction chamber (8). The valve may be in the form of a spring loaded ball valve or be constituted by the control sleeve (38). <IMAGE>

Description

SPECIFICATION Distributor-type fuel injection pump for internal combustion engines The invention relates to a distributor-type fuel injection pump.

In a known distributor-type fuel injection pump, pressure valves are provided in the pressure lines leading to the injection valves, in the region of the housing of the fuel injection pump, and these valves close off the connection to the pump working chamber following termination of the effective pump delivery stroke. In the pressure lines, quantities of fuel surging back and forth between the fuel injection valves and the injection pump are reflected atthe pressure valve.

Some injection systems for internal combustions which have direct fuel injection into the main combustion chambers do not have such pressure valves, but are provided with a so-called return-flow throttle by way of which the above-mentioned pressure oscillations of the fuel columns can be reduced in order to prevent after-injection at the fuel injection valves. In such an embodiment, the clearance volume or dead space at the highpressure side in particular is advantageously reduced. If air enters the system, particularly the pressure lines, in fuel injection systems of this type, for example, due to the fuel tank running dry, it is not possible to restart the internal combustion engine once the fuel supply tank has been re-filled, without bleeding the pressure lines manually.For this purpose, the connection to each of the injection valves must, for example, be disconnected. In such known fuel injection pumps, the air trapped between the pump working chamber and the injection valves is compressed during the delivery stroke of the pump piston but can expand again during the following suction stroke of the pump piston towards the pump suction chamber by way of the return flow throttle and the compensating groove. In particular, it is not possible to start the internal combustion engine under these conditions if the distributor-type fuel injection pump does not have a pre-feed pump delivering to a higher pressure level.

The present invention resides in a distributor-type fuel injection pump for an internal combustion engine comprising a distributor which is rotatingly driven in a guide cylinder and which is provided on its periphery with a distributor port connected to a pump working chamber which is defined by a pump piston driven in synchronism with the rotational movement of the distributor and which is connected to a fuel source during the suction stroke of the pump piston by way of suction ports controlled by the distributor, the distributor port being connected to one of a pluraiity of pressure lines during the delivery stroke of the pump piston depending on the respective rotational position of the distributor, which pressure lines lead, in the working range of the distributor port, from the guide cylinder to the individual injection valves of the internal combustion engine and are distributed about the periphery of the guide cylinder according to the number of said injection valves, the periphery of the distributor also having at least one compensating port which connects pressure lines in succession, depending on the rotational position of the distributor, to a relief line leading to a relief chamber, the connection to the relief chamber being controlled by a valve, the arrangement being such that the distributor port closes the connection to the pressure line, in particular during starting of the internal combustion engine, before the pump working chamber is connected to the fuel source on commencement of the suction stroke of the pump piston and the valve in the relief line is controlled in dependence on at least one operating parameter of the internal combustion engine, in that it is closed under starting conditions.

This has the advantage that, in cases where the fuel supply tank from which the fuel injection pump receives fuel is empty and in which air has got into the fuel injection pump and the pressure lines, automatic restarting is possible within a reasonable starting time, once the fuel supply tank has been refilled, without manual bleeding of the pressure lines being necessary.Due to the closure, in accordance with the invention, of the relief line connected to the compensating port, the compressed air, following a delivery phase of the pump piston, can no longer expand during the suction phase, so that a further volume of fuel enters the pressure line during the following pump piston delivery stroke and hence the air in the fuel injection pump is continually purged in the direction of the internal combustion engine by way of the injection valve with each subsequent pump delivery stroke.

However, even in the case of fuel injection pumps without any valves, or fuel injection pumps provided with pressure-equalizing valves in connection with compensating grooves, the invention is advantageous for rapid restarting.

In an advantageous embodiment according to the invention, a pressure which changes in dependence on speed is used to dispense with this particular starting condition, namely the closure of the relief line. To do this, the valve advantageously comprises a slide valve comprising a piston, whose end face is subjected to the speed-dependent pressure of the suction chamber of the distributor-type fuel injection pump. Once a particular pressure has been built up in the suction chamber following starting, pressure compensation takes place in the known way in the pressure lines during intervals between injection, which compensation opposes deviations in the quantity of fuel injected.

The valve may simply and advantageously be a non-return valve.

Although the solution according to the invention can be used for various types of distributor-type fuel injection pump, an advantageous embodiment is to be found in its use in distributor-type injection pumps. In such distributor-type fuel injection pumps, the condition for closing the relief line is advantageously detected by the position of an annular sleeve on starting, which is again a very simple and functionally reliable embodiment. A further advantageous embodiment comprises the fact that, in a fuel injection pump operating with injection timing by the cam drive, the phase in which both-the pressure line and the suction port are closed lies in the region of the top dead centre of the drive cams, the conditions for starting being taken into account when adjusting commencement of injection.

The invention is further described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 shows a first embodiment of fuel injection pump having a valve in the form of a slide valve in the relief line; Fig. 2 shows a valve which is in the form of a nonreturn ball valve, in the relief line of a second embodiment; Fig. 3 is a timing curve showing the cam lobe curve with the control times of the pressure line port and the suction port; and Fig. 4 shows a third embodiment of fuel injection pump with a valve in the relief line, which valve is formed by the quantity control member in the form of an annular spool of the fuel injection pump.

Referring to Fig. 1, a guide cylinder 2 is provided in a housing 1 of a distributor-type fuel injection pump. A pump piston 3 is disposed in the cylinder 2 and its end face in the guide cylinder encloses, together with a plug 5 whose end face is contiguous with the guide cylinder, a pump working chamber 6.

The pump piston is closely fitted in the guide cylinder 2 and its lower end projects into a suction chamber 8 enciosed in the housing of the distributor-type fuel injection pump and is positively connected to a cam disc 9 both with respect to rotation and with respect to reciprocation. The underside of the cam disc is provided with a cam track 10 by which it abuts against rollers 11. The rollers 11 are distributed on a roller ring 12 according to the diameter of the circular cam track, said ring being rigidly mounted but angularly adjustable by means of a pin 14. The pin 14 is displaceable by a piston 15 of an injection tinier which is subjected on the one hand to the force of a spring and on the other hand to the pressure of the suction chamber 8 filled with fuel, which pressure is fed by way of a line 19.This suction chamber is supplied by means of a fuel feed pump 16 with fuel from afuel supplytank 17. The fuel pressure in the suction chamber 8 alters in dependence on engine speed in that the feed pump 16 is driven in synchronism with speed and a pressure control relief valve 18 leads back from the pump outlet.

Injection timing in dependence on speed takes place in substantially the same way.

The cam disc 9 is driven by a drive shaft 20 by way of a coupling element 21 in synchronism with the speed of the drive shaft and thus in synchronism with the speed of the internal combustion engine supplied by the distributor-type fuel injection pump, and its cam track rides on the rollers 11, against which they are held by a spring (not shown). The cam disc 9 and the pump piston accordingly perform a reciprocating pumping and simultaneously rotating motion.

During the suction stroke of the pump piston, when said piston is rotated accordingly, at least one of several filling grooves 23, which are permanently connected to the pump working chamber, is in register with a suction port 25 which is connected by way of a fuel supply passage 26 to the suction chamber 8. In this way, the pump working chamber is filled during the suction stroke of the pump piston. During the following pump or delivery stroke of the pump piston, this connection is closed again by a further rotational movement of the pump piston and the fuel expelled from the working chamber by the pump piston is fed by way of an axial passage 28 in the pump piston and a radial bore 30 leading to a distributor groove 29 on the periphery of the pump piston, to one of several pressure lines 31 leading from the guide cylinder.

Said pressure lines 31 are distributed about the periphery of the guide cylinder according to the number of cylinders of the associated internal combustion engine to be supplied by the distributor-type fuel injection pump, and each leads by way of a respective return-flow throttle valve 32 to the corresponding fuel injection valve (not shown) of the internal combustion engine. It is also possible, however, to do without the return-flow throttle valve. It comprises a valve plate 34, which can be moved backwards and forwards between two stops by the fuel flow. One stop 35, which is on the pump side, forms a planar sealing surface with the valve plate 34, and the corresponding stop on the fuel injection valve side allows fuel to flow around the valve plate 34.When the valve plate 34 is in abutment with the one stop 35, there still exists a connection with the pump working chamber by way of an axial throttle bore 36 in the valve plate.

In order to control the quantity of fuel injected, an annular sleeve 38 is fluid tightly displaceably disposed on the outer surface of the pump piston and its upper end face 39 forms, for example, a control edge by way of which a spill port 45 connected to the longitudinal passage 28 is opened during the delivery stroke of the pump piston. When this spill port is opened, a corresponding reduction in pressure in the pump working chamber causes the delivery of fuel to the fuel injection valve or to the combustion chambers of the internal combustion engine to be terminated. Depending on the axial position of the annular sleeve 38, this occurs at an earlier or later instant, with a corresponding variation of the effective delivery stroke of the pump piston. The annular sleeve is adjusted by a governor, of which only the governor lever 41 is shown here, coupled to the annular sleeve 38.

The pump piston is further provided with at least one compensating port in the form of a longitudinal groove 43 which also co-operates with the pressure lines 31 issuing from the guide cylinder 2. The compensating port is alternatingly connected in succession to the individual pressure lines, which at this point of time are not being controlled by the distributor port or distributor groove 29. The individual pressure lines are then connected by way of this compensating port to an annular groove 44 on the periphery of the pump piston and by way of this annular groove to a relief line 46 issuing from the guide cylinder 2 and opening into a cylinder 47.

This cylinder is disposed in the pump housing parallel to the guide cylinder 2 and opens at one end into the suction chamber 8, and is closed at the other end by a pressed-in plug 48. A piston 50 of a slide valve 51 is disposed in the cylinder and a compression spring 52 is clamped between it and the plug 48, and presses the end face of the piston 50 against a stop. The depth to which the plug is pressed in determines the initial stress in the spring.

Starting from the suction chamber, the piston 50 is provided with a blind bore 54, from which a cross bore 55 leads to its surface. In the starting position shown, the outlet of the cross bore 55 is closed by the cylinder 47 but, as the pressure in the suction chamber 8 increases and the piston 50 is displaced accordingly against the force of the spring, it is moved into alignment with the relief line 46, which is thereby connected to the suction chamber 8.This operating position is established during normal operation of the fuel injection pump, so that, during the injection intervals, the individual pressure lines 31 are relieved until the pressure therein falls to the pressure in the suction chamber 8, which takes place by way of the connection between the compensating port 43 and relief line46. As a result, a uniform pressure level prevails on commencement of delivery of pressure into the pressure lines 31, thus preventing deviations in the quantity of fuel injected due to varying filling volumes.

When the internal combustion engine is started, the pressure in the suction chamber 8 is so low that the piston 50 has not yet opened the relief line 46 and is located on its stop 53. Hence the compensating ports have been prevented from functioning. If the reason why the internal combustion engine had stopped was due to the fact that the fuel supply tank 18 was empty and hence the suction chamber 8 was no longer filled or completely filled with fuel, then, during the following starting procedure, fuel will initially be fed by way of the feed pump 16, which is driven in synchronism with the drive shaft 20, into the suction chamber which, however, contains some air which, in the fuel injection pump described here, can only escape by way of the pump working chamber and the pressure line 31 if, for example, a screw plug 57, which is screwed into the plug 5, is unscrewed.In such an event, there is initially a high proportion of air in the pump working chamber 6, and this is compressed during the pump stroke of the pump piston and fed into a pressure line 31. As a result of the high compressibility of the air, and air usually does not escape from the fuel injection valve, whose opening pressure at the end of compression can, in accordance with the direct injection into the combustion chamber of the internal combustion engine as provided in this case, be approximately 800 bar. In Fig. 3,11 is the control time of the distributor groove 29 plotted against a corresponding cam lobe curve which the pump piston follows during the delivery stroke, that is the time in which the distributor groove 29 is connected to one of the pressure lines.The graph also contains horizontal dash-dotted lines which indicate the pump piston delivery stroke at which, depending on the load set, the spill port 45 of the longitudinal passage 28 is opened to terminate fuel injection.

One of the lines Ill shows the position for the fullload position of the annual sleeve 38, while the other position Ill' shows the position of the annular sleeve 38 in which the quantity of fuel to be injected for starting is to be delivered. It can be seen that the entire pump piston delivery stroke is used to delivery the quantity of fuel to be injected, and hence that the spill port 45 is not opened during the course of the stroke. When the pump piston is at top dead centre, the connection between the distributor groove and the corresponding pressure line 31 is broken and, after approx. 2" overlap Ü, the filling groove 23 is connected to the suction port 25, which is shown by the control time length I.During the following suction stroke of the pump piston, the previously controlled pressure line 31 hence remains closed, while the pump piston again sucks in fuel and/or air from the suction chamber by way of the fuel supply passage 26. During the following delivery stroke of the pump piston, this fuel/air mixture is fed into the following pressure line in the same way. During the following delivery strokes, the previously compressed air is compressed even more until the opening pressure is achieved at the fuel injection valve and the air can escape to the combustion chamber of the internal combustion engine. In this way, the fuel injection pump purges itself of air during the starting procedure.In the case of the return-flow throttle valve 32 in the pressure line 31 provided in this case, the air compressed during a delivery stroke of the pump piston in the pressure line would expand again if, as is provided for in normal operation, the compensating port 43 were to control said corresponding pressure line and relieve it in the direction of the suction chamber 8. This process is interrupted for the starting range by the valve 51 provided in this case in the form of a slide valve in the relief line 46, until a predetermined initial pressure has been achieved in the suctiQn chamber 8. Instead of the pressure of the suction chamber, which alters in dependence upon speed, a different speed signal or pressure medium having a similar behaviour can act on the piston 50. The purging process is still guaranteed even if, in place of the retu rn-flow throttle valve 32, there is no valve at all in the pressure line 31.

The distributor-type fuel injection pump is conventionally provided with an injection timing device, the above-described timing piston 15. Using this device, the instant of injection is brought forward as the speed increases. In a corresponding embodiment, particulartiming angles, which are optimum for the type of internal combustion engine in question, can be set for the starting operation.

This adjustment is taken into account by the control times of the distributor groove II and the filling grooves I, as can be seen in Fig. 3. Advantageously, the cam in the top dead centre has a relatively flat shape or is provided with a so-called dwell R, which also corresponds approximately to the degree of overlap 2" to 30 crank angle. In this way, the pump piston can deliver a maximum quantity of fuel to be injected for starting the internal combustion engine, with optimum adjustment of the instant of injection.

In the other operating ranges, the pump working chamber is, as can be seen under line Ill in Fig. 3, opened at a considerably earlier angle of rotation, such that, in this case, a sufficiently large rotational angular range is available for adjusting injection with regard to the control times of the distributor groove 29 and filling groove 23 (Il and 1).

In a variant of the embodiment of Fig. 1, a nonreturn valve 59 (Fig. 2) can be provided in place of the slide valve 51. In this case, a blind hole 47' is provided in place of the cylinder 47, which hole opens towards the suction chamber 8 and into which the initially uncontrolled relief line 46 opens.

From the direction of the suction chamber 8, a valve insert 58 is screwed in, into which a ball non-return valve 60 is integrated. The latter is subjected to pressure from the suction chamber 8 in the direction of opening. The opening pressure of the non-return valve 59 is less than the minimum normal running pressure in the chamber 8. Pressure oscillations in the relief line 46 are relieved to the pressure level of the suction chamber 8.

Athird embodiment is shown in Fig. 4, which shows only the pump piston 3' which is fitted into the guide cylinder 2' and, as in the embodiment according to Fig. 1, is reciprocatingly and simultaneously rotatingly driven, the piston also acting as a distributor during its rotational movement. This pump piston 3' also has filling grooves 23 which co-operate with the suction port 25 and are connected to the pump working chamber 6. Furthermore, the longitudinal passage 28' in the pump piston 3' is in the form of a slightly inclined blind bore and is connected at the end of the blind bore by way of a cross bore 61 to the spill port 45.

Said spill port 45 is controlled, as in the embodiment according to Fig. 1, by the annular sleeve 38. A connection leads from said longitudinal passage 28' to the distributor port in the form of a longitudinal groove 29 which successively controls different pressure lines 31 leading from the guide cylinder 2'.

Furthermore, a second passage 63 is provided in the pump piston 3' and connects the compensating port 43' to an outlet port 65, which is on a levei with the spill port 45 in the surface of the pump piston and is controlled together with the spill port 45 by the annular sleeve 38. The control point of this outlet port 65 is designated IV in Fig. 3.

As a result of this design, it can in turn be seen in Fig. 3 that, when the annular sleeve 38 is displaced upwards on starting in the direction of maximum quantity, the outlet port 65 remains closed. The compensating port 43 is hence prevented from functioning and the same automatic purging takes place as described in the embodiment according to Fig. 1.

This embodiment has the advantage that an additional valve provided in Figs. 1 and 2 is not required and that the cutting out of pressure compensation by way of the compensating port 43 actually does depend exclusively on the load position of the annular sleeve 38 and not on the additional auxiliary force of the pressure in the suction chamber 8. In this respect, the pressure in the suction chamber does not require any particular consideration for achieving the aim described here.

The present solution described with reference to a lifting piston distributor-type injection pump can also be used in other pump types. This can also be applied analogously to radially opposed plunger rotary distributor-type injection pumps.

Claims

1. A distributor-type fuel injection pump for an internal combustion engine comprising a distributor which is rotatingly driven in a guide cylinder and which is provided on its periphery with a distributor port connected to a pump working chamber which is defined by a pump piston driven in synchronism with the rotational movement of the distributor and which is connected to a fuel source during the suction stroke of the pump piston by way of suction ports controlled by the distributor, the distributor port being connected to one of a plurality of pressure lines during the delivery stroke of the pump piston depending on the respective rotational position of the distributor, which pressure lines lead, in the working range of the distributor port, from the guide cylinder to the individual injection valves of the internal combustion engine and are distributed about the periphery of the guide cylinder according to the number of said injection valves, the periphery of the distributor also having at least one compensating port which connects pressure lines in succession, depending on the rotational position of the distributor, to a relief line leading two a relief chamber, the connection to the relief chamber being controlled by a valve, the arrangement being such that the distributor port closes the connection to the pressure line, in particular during starting of the internal combustion engine, before the pump working chamber is connected to the fuel source on commencement of the suction stroke of the pump piston and the valve in the relief line is controlled in dependence on at least one operating parameter of the internal combustion engine, in that it is closed under starting conditions.

2. A distributor-type fuel injection pump as claimed in claim 1, in which there is a permanently open connection between the pump working chamber and the respective injection valve.

3. A distributor-type fuel injection pump as claimed in claim 1 or 2, in which the valve in the relief line comprises a slide valve, with a piston which is subjected to the force of a return spring and to a pressure which alters with the speed of the internal combustion engine.

4. A distributor-type fuel injection pump as claimed in claim 1 or 2, in which the valve is a nonreturn valve which is subjected in the opening direction to the pressure of the relief chamber which alters with the speed of the internal combustion engine.

5. A distributor-type fuel injection pump as claimed in claim 3, in which the pressure acting on the piston of the slide valve is the pressure in the relief chamber.

6. A distributor-type fuel injection pump as claimed in claim 4 or 5, in which the relief chamber comprises a suction chamber inside the distributortype fuel injection pump, which chamber serves as a fuel source for supplying the pump working chamber.

7. A distributor-type fuel injection pump as claimed in any preceding claim, in which the distributor comprises a reciprocatingly driven pump piston and has a passage issuing from the pump working chamber to which passage the distributor port is connected and which is connected to a spill port which is located on the periphery of a part of the pump piston projecting into the suction chamber of the distributor-type fuel injection pump, acting as the fuel source, and is opened or closed by an annular sleeve actuated by a governor in conjunction with the pump piston movement for variable pump delivery strokes of the pump piston.

8. A distributor-type fuel injection pump as claimed in claim 1 or 2, in which the distributor is in the form of a reciprocatingly driven pump piston and has a passage issuing from the pump working chamber, to which passage the distributor port is connected and which is connected to a spill port, which is located on the periphery of a part of the pump piston projecting into the suction chamber of the distributor-type fuel injection pump acting as the fuel source and is opened or closed by an annular sleeve actated by a governor in conjunction with the pump piston movementforvariable pump delivery stroke positions of the pump piston, and the compensating port is connected to an outlet port provided on the periphery of the part of the pump piston projecting into the suction chamber, which outlet port is closed by the annular sleeve when said sleeve is in an extreme position corresponding to the starting quantity adjustment, and is open in the other operating ranges.

9. A distributor-type fuel injection pump as claimed in claim 8, in which the compensating port is connected by way of a connection passage in the pump piston to the outlet port.

10. A distributor-type fuel injection pump as claimed in any preceding claim, in which the reciprocating motion of the pump piston is generated by a pump piston drive, provided with a drive cam, whose phase position with respect to the drive of the distributor-type fuel injection pump can be altered in dependence upon at least one operating parameter, and in which, under starting conditions, the rotational angle region in which both the pressure lines and the suction port are closed by the distributor is in the top dead centre range of the cams of the pump drive.

11. A distributor-type fuel injection pump as claimed in claim 10, in which the cams are provided with a dwell in the top dead centre region.

12. A distributor-type fuel injection pump, constructed and adapted to operate substantially as herein described, with reference to and as illustrated in the accompanying drawings.