GB2216196A

GB2216196A - Fuel injection pump for internal combustion engines

Info

Publication number: GB2216196A
Application number: GB8904747A
Authority: GB
Inventors: Gerald Hofer
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1988-03-02
Filing date: 1989-03-02
Publication date: 1989-10-04
Anticipated expiration: 2009-03-02
Also published as: DE3806669A1; FR2628150A1; GB8904747D0; JPH01271653A; GB2216196B; DE3806669C2

Description

2216196

DESCRIPTION

FUEL INJECTION PUMP FOR INTERNAL COMBUSTION ENGINES The invention is based on a fuel injection pump for internal combustion engines.

In a known fuel injection pump, the pump working chamber is supplied by way of a variable inlet throttle which is disposed in a filling passage and which controls the quantity of fuel injected per delivery stroke Hence the pump working chamber is not completely filled with fuel upon the termination of the suction stroke during part load operation of the associated internal combustion engine, so that suction forces act upon a plug which, in this known fuel injection pump, is freely movable, and upon a control slide valve arrangement which comprises a control sleeve which is connected to a control piston, by way of a spring, which is a starting spring This leads to undesirable wear on the point at which the plug abuts against the stop pin The excess starting quantity is governed down by the control sleeve upon the commencement of pressurization in the control pressure chamber, this being effected by shortening of the effective delivery stroke of the pump piston by advancing the instant at which the control port is opened, although, in the known fuel injection pump, the delivery characteristic of the fuel injection cannot be adapted to the fuel requirement of the internal combution engine, particularly during operation under full load.

The invention resides in a fuel injection pump for an internal combustion engine, having a reciprocated and simultaneously rotated stepped pump piston, the larger diameter portion of which is guided in a guide cylinder and serves as a distributor, and the smaller diameter portion of which projects out of the guide cylinder, a displaceable control slide valve arrangement provided with a bore into which the smaller diameter portion of the pump piston enters from one end and a plug enters from the other end to enclose a pump working chamber, that end of the plug which is located outside the bore abutting against an adjustable stop pin which is located coaxially of the pump piston and is adjustable through a closure member of the housing of the fuel injection pump, the control slide arrangement being in the form of a control piston and being displaceable in a cylinder by means of a fixedly supported spring, said cylinder being closed at one end towards the guide cylinder and at the other end by the closure member, wherein the displacement travel of the control piston is limitable by at least one stop and the spring is disposed in a relief chamber which is enclosed by the control piston in the cylilnder and which is relieved of pressure by way of a relief passage, whereas that end of the control piston which is remote from the relief chamber defines a pressure control chamber in the cylinder, which control pressure chamber communicates with a pressure source having a rotational-speed-dependent pressure by way of a pressure line, and with a longitudinal passage which is located in the pump piston and leads from the end thereof which defines the pump working chamber, which longitudinal passage communicates with a control port in the outer surface of the pump piston, and communication between the control port and a chamber relieving the pump working chamber is controllable by a control edge on the control slide valve arrangement, which longitudinal passage is also connectible by way of at least one filling opening which opens in the region of the guide cylinder into the outer surface of that portion of the pump piston which serves as a distributor to at least one filling passage, opening into the guide cylinder, for feeding fuel during the suction stroke of the pump piston, and, during each pressure stroke of the pump piston, the longitudinal passage is connected, by way of a distributor port in the outer surface of the pump piston in the region of the guide cylinder, to one of a plurality of pressure passages which, distributed t around the pump piston, and which lead from the guide cylinder and are connectible to injection points of the internal combustion engine, and wherein the control slide valve arrangement, which is in the form of a control piston having the bore and the control edge, is sealingly displaceable in the cylinder, the drive end of the pump piston extends out of the guide bore and into an interior space filled with fuel where the outer surface of the pump piston has a control sleeve which is adjustable by means of an injected fuel quantity governor and which has a control edge which controls an outlet of the longitudinal passage into the interior space, and the effective point of opening of the pump working chamber is variable in dependence upon the rotational speed by way of the control port and the control edge on the control piston controlling the said control port.

Accurate control of the quantity of fuel injected is obtained by such a fuel injection pump The effective delivery stroke of the pump piston, acting upon a fuel column under constant delivery pressure, is geometrically adjustable by means of the cylindrical slide valve Rotational-speed-dependent adaptation of quantity of fuel, injected under full load, to the requirements of the internal combustion engine is obtained in a simple and readily adjustable manner by varying the termination of the delivery- effective stroke of the pump piston by using the spring as an adaptation spring At the same time, if a starting spring is disposed between the control piston and the plug, an excess starting quantity of fuel injected, made available in a similarly simple manner by means of the control piston, is shut off automatically upon starting of the internal combustion engine or at the commencement of operation of the fuel injection pump and, advantageously, is established in advance of the quantity of fuel injected under full load and hence advances the commencement of injection during starting This simplifies the construction of the commencement of injection timer which may then have a shorter working stroke Furthermore, an adaptation injection quantity established in advance of the actual quantity of fuel injected may be reduced as the rotational speed increases.

Advantageously, negative adaptation, that is, a quantity of fuel injected under full load for specific requirements in internal combustion engines, and increasing as the rotational speed increases, is obtained by the development in which the relief chamber is located at the guide cylinder end of the control piston, the spring is an adaptation spring, and the control pressure chamber is located at the i A closure member end of the control piston and has a compression spring which is interposed between the control piston and the plug, wherein that end of the cylinder which faces the guide cylinder serves as a stop for the control piston.

This in conjunction with the development in which the control port is opened by the control edge on the control piston when the control piston is abutting against the adaptation spring when the latter is not yet compressed, and is closed after a pre-stroke of the pump piston, the pre-stroke being varied in dependence upon the rotational-speed-dependent pressure in the pressure control chamber by compression of the adaptation spring.

The modified control piston is otherwise of the same construction in the basic construction of the fuel injection pump.

Advantageously, positive adaptation of the quantity of fuel injected, that is, a reduction in the quantity of fuel injected under full load as the rotational speed increases, can be obtained by varying the pre-stroke in conjunction with the development in which the control pressure chamber is located at the guide cylinder end of the cylinder and the adaptation spring is disposed between the control piston and the spring which serves as a stop for the control piston.

A A uniform termination of the high-pressure delivery by the pump piston of the fuel injection pump is obtained by the development in which an outlet port on the outer surface of the piston is connected to the longitudinal passage and, from a predetermined pump piston stroke (h FE) onwards, is connected to a relief line leading from the guide cylinder to a relief chamber, for the purpose of limiting the effective delivery stroke of the pump piston.

Hence it is possible to observe an accurate governing-down point by setting the cylindrical slide valve during full load in such a way that it opens the longitudinal passage only at a later stroke of the pump piston delivery stroke h FE The termination of delivery when the cylindrical slide valve is in its normal full load position is no longer determined by the cylindrical slide valve, but is determined by the connection of the outlet port to the flow-off passage Hence, upon attaining the maximum or governing-down speed, the cylindrical slide valve can pass through a small initial stroke until it opens the outlet port of the longitudinal passage The effects of oscillation and hysteresis during governing-down are reliably avoided in this manner, so that an accurate governing-down point is obtained By shutting off the relief of the pump working chamber upon attaining the pump piston delivery stroke h FE, a starting quantity is advantageously made available in addition thereto and is established after the quantity of fuel injected under full load with regard to the injection characteristic, that is, it has an injection-timing effect This is desirable in special cases of application.

In a further embodiment of the fuel injection pump, the spring is a starting spring and the control piston has, as a boundary edge, a first opening in the surface of the bore and the first opening communicates with a second opening in the surface of the bore by way of a connection passage extending in the control piston, which second opening is connectible to a flow-off passage, leading from the outer surface of the plug to a relief chamber, after the force of the starting spring has been overcome, the termination of delivery by the pump piston being determined by the point at which the control port is opened by the first opening after a predetermined pump piston stroke (h FE).

Negative adaptation of the quantity of fuel injected, that is, an increase in the quantity of fuel injected as the speed of the internal combustion engine increases, is achieved by modifying the construction of the readily interchangeable control piston in the fuel injection pump of the same basic construction The position of the starting quantity portion in the high-pressure delivery is then such that it follows the quantity of fuel injected under full-load without varying the commencement of injection.

Advantageously, rotational-speed-dependent, negative adaptation may be additionally obtained by.

means of a throttle which is provided in the course of the flow-off passage or by means of an adaptation spring which is disposed between the control piston and a fixed part of the fuel injection pump in addition to the spring serving as the starting spring, the deflection of which adaptation spring is limited by abutment of the control piston against the stop, and the termination of delivery is shifted towards a larger delivery-effective stroke (h FE) of the pump piston by the deflection of the adaptation spring after the force of the starting spring has been overcome.

The invention is further described, by way of example, with reference to the accompanying drawings, in which:- Fig l shows a first embodiment of the invention; Fig 2 is a control graph relating to the embodiment of Fig l; Fig 3 shows a variant of the embodiment of Fig l, having a separate starting piston for adjusting an excess quantity of fuel injected; Fig 4 shows a third embodiment of the invention, with negative adaptation; Fig 5 is a control graph for the embodiment of Fig 4; Fig 6 shows a variant of the embodiment of Fig 4; Fig 7 shows a fifth embodiment of the invention, with negative adaptation; and Fig 8 is a control graph for the fifth embodiment of Fig 7.

A pump piston 4 is disposed in a guide cylinder 2 of a cylinder liner 3 fitted in a housing 1 of a fuel injection pump, and is reciprocated and at the same time rotated by means not shown The pump piston is a stepped piston and its larger diameter portion 6 is in the form of a distributor and is guided in the guide cylinder 2 The smaller diameter portion 7 projects from the guide cylinder and into a cylinder 9 whose end is contiguous to the cylinder liner 3 in the housing of the fuel injection pump That end of the cylinder 9 which is remote from the cylinder liner 3 is tightly sealed by a closure member 10 which is located coaxially of the pump piston and is screwed into the housing 1 A stop pin 12 passes through the closure member 10 coaxially of the pump piston and is held in the closure member by screw-thread 13, which stop pin is adjustable and is fixable externally by means of a lock nut 14 The cylinder 9 is sealed towards the outside by means of a sealing ring 15 on the stop pin 12 A control piston 18 in the form of a sleeve 21 having a bore 22 is disposed in the cylinder 9 and is sealingly displaceable on the smaller diameter portion 7 of the pump piston A plug 24 enters the bore 22 at the opposite end and is also sealingly guided in the bore and encloses pump working chamber 25 between its end face and the end face of the smaller diameter portion 7 of the pump piston.

The plug 24 is held in abutment against the end face of the stop pin 12 by means of a compression spring 27 which is supported on the control piston 18 and which acts upon a spring abutment plate 28 connected to the plug The compression spring 27 acts as a starting srping.

The spring abutment plate 28 abuts against a flange 29 of the plug 24 or is a part thereof The flange 29 is the support point of an adaptation spring which abuts against a shoulder 31 of the control piston 18 and which may be, for example, a cup spring That end 26 of the control piston which faces the plug serves as a stop for the control piston on the flange 29 and hence directly on the stop pin 12, since the plug 24 is held in abutment against the stop pin by means of the compression spring 27 The end face 26 of the control piston 18 defines the I deflection of the adaptation spring 30 The control piston 18 divides the cylinder 9, defined between the closure member 10 and the cylinder line 3, into a control pressure chamber 32 located between the control piston and the cylinder liner, and a relief chamber 33 which is connected by way of a relief passage 34 to, for example, the suction side of the fuel feed pump 36 which delivers fuel from a fuel reservoir 37 into an interior space 38 of the fuel injection pump The fuel feed pump is driven in synchronism with the drive speed of the fuel injection pump and, together with a pressure control valve 39, forms a rotational-speed-dependent pressure in the interior space 38 in a known manner This interior space is in permanent communication with the pressure control chamber 32 by way of a pressure line 40.

A longitudinal passage 41 leads through the pump piston from the end face of the smaller diameter portion 7 of the pump piston and opens by way of a transverse bore 42 into the outer surface of a portion, extending into the interior space 38 of the larger diameter portion 6 of the pump piston at the drive end thereof The outlet 45 of the transverse bore 42, which forms the outlet of the longitudinal passage 41, is controlled by a control edge 43 disposed on a cylindrical slide valve or control sleeve 44 which is sealingly displaceable on the large diameter portion 6 of the pump piston The control spool 44 constitutes the quantity control element of -the fuel injection pump and is adjustable by a known governor (not further illustrated) by way of a governor lever 47 The higher the control 44 is adjusted, the longer the effective stroke of the pump piston is during the termination of delivery regulation, until the pump working chamber 25 is relieved to the interior space 38 by way of the longitudinal passage 41 by opening the outlet 45.

In order to fill the pump working chamber, a radial bore 48 branches from the longitudinal passage 41 in the region of the guide cylinder 2 to a filling port 50 which is provided in the larger diameter portion 6 of the pump piston and which, upon rotation of the pump piston during its suction stroke, comes into contact with a filling passage 51 which opens into the guide cylinder The filling passage 51 branches from the pressure line 40 and is closeable by means of a solenoid shut-off valve 53 The pressure line 40 and the pressure control chamber 32 are interconnected by way of a longitudinal groove 46 in the outer surface of the cylinder liner, whereby the filling passage 51 is connected to the pressure control chamber, and the longitudinal groove 46 is also closeable by means of the solenoid shut-off valve 53 Alternatively, instead of only one filling port and one filling passage port, a plurality of filling ports and filling passage ports may be distributed around the periphery of the pump piston.

However, in each case, the filling port 50 communicates permanently with an annular groove 52 in the outer surface of the larger diameter portion 6 of the pump piston, which serves as an outlet port of the longitudinal passage 41, wherein the annular groove 52, and hence the pump working chamber are connected to the filling passage 51 irrespective of the angular position of the pump piston after a delivery stroke h FE, and hence, in principle, terminating the high-pressure delivery of the pump piston.

Furthermore, a radial bore 54 branches from the longitudinal passage 41 to a distributor port 56 in the outer surface of the larger diameter portion 6 of the pump piston During each delivery stroke of the pump piston, this distributor port is alternately connected to one of a plurality of pressure passages 57 which are distributed around the periphery of the pump piston and which lead from the guide cylinder 2 to respective injection valves 58 on the internal combustion engine A pressure valve of known construction is fitted in each pressure passage 57, and in the injection intervals, each pressure passage 57 can be alternately relieved to a constant level between the pressure valve and the opening into the guide cylinder by means of a relief groove 59 which is disposed in the outer surface of the pump piston and which communicates permanently with the filling passage 51.

Finally, a transverse bore 61 branches from the longitudinal passage 41 and communicates with a control port 62 in the outer surface of that part of the smaller diameter portion 7 of the pump piston which is guided in the bore 22 As is shown in Fig l, this control port communicates with the control pressure chamber 32 at the commencement of the stroke of the pump piston and, during the course of the subsequent pump piston stroke of the magnitude hv, is closed by the end face, serving as a control edge 63, at the pump drive end of the control piston 18 The high-pressure delivery of the pump piston can only commence after this pre-stroke hv from bottom dead centre of the pump piston.

The fuel injection pump described above operates in the following manner:

I When the pump piston 4, driven by means not illustrated, is performing its suction stroke and the solenoid shut-off valve 53 has opened the filling passage, the pump working chamber is fully filled with fuel during each suction stroke of the pump piston.

The filling port 50 is then in communication with the filling passage 51 The distributor port 56 is connected to one of the pressure passages 57 during the subsequent delivery stroke, and communication between the filling port and the filling passage is interrupted Furthermore, the outlet 45 is closed when the cylindrical slide valve 44 is in its part load position, and the control port 62 is closed after a stroke hv when the control piston 18 abuts against the adaptation spring 30 after overcoming the force of the starting spring 27 A high pressure can then build up in the pump working chamber 25 and is propagated to the injection valve 58 by way of the longitudinal passage 41 and one of the pressure passages 57, thereby opening the injection valve 58 and triggering the injection of fuel If the internal combustion engine is operating in the range of part load, the outlet 45 is opened by the control edge 43 of the cylindrical slide valve 44 during the course of the subsequent delivery, before communication is established between the annular groove 52 and the 1. filling passage 51 From this point onwards, the remaining fuel delivered by the pump piston flows off into the interior space 38 The injection operation has ended However, if the internal combustion engine is operating under full load, communication between the annular groove 52 and the filling passage 51 is established after a pump piston stroke h FE and before the outlet 45 opens, whereby the pump working chamber is also relieved towards the pressure line 40 and the injection operation is terminated This has the advantage that a uniform termination of full load delivery or termination of fuel injection is achieved, and that the annular slide valve 44 can be displaced further towards the cylinder liner 3 than would be necessary to adjust the quantity of fuel injected under full load In the case of governing-down, the cylindrical slide valve must cover an initial stroke until the outlet 45 is opened at an earlier instant with the elimination of the control function of the annular groove 52, so that the fuel injection pump is governed down to zero during the course of further displacement of the cylindrical slide valve.

Advantageously, this prevents an oscillatory movement of the cylindrical slide valve, caused by the governing-down operation of the governor at the governing-down point, from affecting the commencement of governing-down, and the full load performance is fully maintained up to the desired governing-down point Hence the effects of hysteresis are also precluded.

The function is as follows for the purpose of producing an excess starting quantity when starting the internal combustion engine:

The pressure in the interior space 38 is at a very low level before the engine is started, so that the control piston 18 is abutting against the cylinder line 3 under the action of the compression spring 27, since the pressure required in the control pressure chamber 32 is absent, so that the control port 62 is closed by the control piston 18 during the course of the delivery stroke of the pump piston 18 and also remains closed Consequently, an excess starting quantity of fuel exceeding the quantity injected under full load is injected per delivery stroke of the pump piston This quantity is established before the quantity injected under full load, so that a quantity-conditioned advance of the commencement of injection is effected during starting Pressure builds up in the interior space 38 as the engine speed increases and then displaces the control piston 18 against the force of the starting spring 27 until it abuts against the adaptation spring 30 and holds the control port 62 open in the initial position of the pump piston.

The function described above is also established when an adaptation spring 30 is not provided on the control piston 18 In this case, after the build-up of pressure in the pressure control chamber 32, the control piston moves until it comes into abutment against the flange 29 However, if an adaptation spring is provided, as is shown in Fig l, the adaptation spring is compressed to a greater extent in conformity with the pressure in the control pressure chamber 32 as the rotational speed increases, until the end face 26 comes into abutment against the flange 29 The pre-stroke hv increases during the course of this operation, so that the effective delivery stroke of the pump piston decreases during full load as the rotational speed increases, until the final stroke h FE is reached.

Fig 2 is a control graph in which a stroke of the pump piston is plotted against the angle of rotation of the pump piston The characteristic strokes are also shown The stroke h FE is the stroke up to the termination of delivery by the pump piston or until the pump working chamber 25 is opened by way of the annular groove 52 A stroke hs is also shown which is larger than the termination of delivery stroke h FE and which characterises the position of the cylindrical slide valve in the full load position It will be seen from this that, in this instance, the opening of the outlet 45 by the cylindrical slide valve is no longer effective with respect to control Finally, the pre-stroke h, from which the high-pressure.

delivery from the pump working chamber commences, is plotted The excess starting quantity is added to the full load quantity, which is delivered between hv and h FE, from bottom dead centre of the pump piston up the height hv of the stroke The stroke hv is increased by compression of the adaptation spring in the sense of positive adaptation, this being shown by various small dashes in the graph, in conjunction with the arrow +AN in the direction of top dead centre OT.

This part of the illustration is omitted in Fig 2 if the adaptation spring 30 is not provided.

A variant of the embodiment of Fig 1 is shown in Fig 3, in which the compression spring 27, which is the starting spring in Fig 1, is omitted in a fuel injection pump of the same design Hence, displacement of the control piston 18 during rotational-speed-dependent build-up of pressure in the control pressure chamber 32 is-effected only against the force of the spring 30, whereby the stroke hv is varied Hence, as in the embodiment of Fig 1, I positive adaptation of the quantity of fuel injected under full load is achieved In order to obtain an excess starting quantity of fuel, the control of the maximum delivery stroke or of the uniform termination of delivery in the case of stroke h FE is then designed in such a way that the annular groove 52 has an associated relief line 64 which leads from the guide cylinder 2 and through which the working chamber can be relieved when the relief line 64 is in register with the annular groove 52 The relief line 64 leads into a cylinder 66 which is disposed in the housing 1 and parallel to the guide cylinder 2 and one end of which opens into the interior space 38 A starting piston 67 is displaceable in the cylinder 66 and can be brought into abutment against a stop 68, disposed at that end of the starting piston which faces the interior space of the pump, by means of a spring 69 which acts upon the rear of the starting piston 67, and, as the pressure in the interior space of the pump increases, is displaced away from the said stop against the force of the spring 69 When in the initial position, the mouth of the relief line 64 is closed by the outer surface of the starting piston.

From a predetermined pressure in the interior space after displacement of the starting piston, the mouth of the relief line is opened towards the interior I space 38 of the pump by a control edge 70 provided on the starting piston In this manner, the control function of the annular groove 52 is cancelled during starting in conjunction with the relief line 64 leading from the guide cylinder 2, so that the pump piston delivers fuel beyond the termination of delivery determined by the stroke h FE until the pump piston reaches top dead centre or until communication between the annular groove 52 and the filling passage 51 is established A further requirement in this connection is that the cylindrical slide valve 44 is moved towards the cylinder liner 3 into a starting position in which the outlet 45 is not opened over the stroke of the pump piston Advantageously, in this development, the excess starting quantity is added to the quantity injected under full load, so that the excess starting quantity does not affect the commencement of injection The starting piston and the spring 69 are designed in such a way that they keep the relief bore 64 open during entire normal operation A switching hysteresis can be obtained on the starting piston by constructing it with pressure stages by enlarging thesurface subjected to pressure, so that, after the starting piston has been raised from an initial position, the starting piston remains in its disengaged position even in the case of a pressure lower than the pressure initiating the deflection of the starting piston.

Fig 4 shows a variant of the embodiment of Fig.

3 In this embodiment, as in the embodiment of Fig 1 or Fig 3, the pump piston 4 ' is displaceable in the guide bore 2 of the cylinder liner 3 and has the longitudinal passage 41 which communicates with the filling port 56 which, in the present instance also, is advantageously in the form of a longitudinal groove, and with the filling port 50 which is also in the form of a longitudinal groove The cylindrical slide valve 44 is again displaceable on the larger diameter portion 6, extending into the interior space 38 of the pump piston and its control edge 43 controls the outlet 45 of the longitudinal passage.

Beyond the cylinder liner 3, the smaller diameter portion 7 ' of the pump piston enters the bore 22 of a control piston 18 ' and, together with the plug 24 inserted into the bore 22 from the other end, encloses the pump working chamber 25 as in the embodiment of Fig 1 The plug abuts against the stop pin 12 by way of the flange 29 and at the same time serves as a support point for a compression spring 27 ' which is no longer a starting spring in the present case The compression spring is supported on a shoulder 71 of the control piston 18 ' which is again sealingly displaceable in the cylinder 9 The shoulder 71 defines towards the closure member 10 a control pressure chamber 32 ' which communicates permanently with the interior space of the pump by way of a connenction line 72, analogously to the pressure line of Fig 1 A relief chamber 33 ' is defined by the other end of the control piston and the cylinder liner 3 The adaptation spring 30 ' abuts against a shoulder 73 at this end of the control piston 18 ', and the adaptation spring is supported at its other end on the end face 60 of the cylinder liner 3 or of the cylinder 9 and the control piston 18 ', acting as a stop, is displaceable by the maximum amount of adaptation travel A towards the adaptation spring In this embodiment, a transverse bore 61 ' leads from the longitudinal passage 41 and opens into a control port 62 ' in the form of an annular groove This annular groove has an associated, second annular groove 65 which is disposed in the wall of the bore 22 and whose other end communicates with the control pressure chamber 32 ' by way of one or a plurality of passages Alternatively, this connection serving to relieve the pump working chamber may be made to the relief chamber 33 ' Alternatively, one of the annular grooves 65 or 62 ' may be omitted, and only the openings of the bores 77 or of the transverse 61 ' bore may be provided The second annular groove 65 is associated with the control port 62 ' in such a way that, when the pump piston is in its initial position, they first are in register with one another from bottom dead centre onwards The control port 62 ' is then closed by the wall of the bore 22 from a pre-stroke hv onwards, so that high pressure can be built up in the pump working chamber 25 from this storke onwards, provided that the outlet 45 is also closed by the cylindrical slide valve 44.

A piston stroke curve is again plotted against the angle a of rotation of the piston in the control graph of Fig 5 In this graph, the stroke h FE characterises the termination of delivery after which the pump working chamber 25 is relieved by way of the open outlet 45 In the present embodiment, this termination of delivery is variable according to the adjustment of the cylindrical slide valve In addition to establishing the quantity of fuel injected under full load, the cylindrical slide valve also establishes the excess starting quantity by being displaced towards the cylinder liner 3 in a known manner The control graph of Fig 5 also shows the pre-stroke hv from which the effective delivery stroke of the pump piston commences, so that the quantity of fuel to be injected results from the difference between the stroke h FE and the pre-stroke hv Since the control pressure chamber 32 ' is subjected to higher pressure as the rotational speed increases, the control piston 18 ' is consequently displaced towards the cylinder liner 3 and hence reduces the pre-stroke hv In this manner, an additional adaptation quantity is established before the actual quantity of fuel injected and increases as the rotational speed increases, which finally corresponds to a negative adaptation While the adaptation quantity is established in advance of the basic quantity to be injected, the starting quantity is established after the quantity injected under full load and thus has no effect on the commencement of injection during starting.

The embodiment of Fig 5 is an alternative development of the embodiment of Fig 4 The embodiment of Fig 6 is modified relative to that of Fig 4 in that the control of the excesss starting quantity is initiated in a different manner In this case, the annular groove 52 ' is provided on the larger diameter portion 6 ' of the pump piston 4 " in a similar manner to that in the embodiment of Fig 3, the annular groove 52 ' being in permanent communication with the filling port 50 The annular groove 52 " is connected to the pump working chamber 25 by way of the filling ( port 50 and the longitudinal groove 41 Analogously to the relief line 64 of Fig 3, a relief line 76 branches from the guide cylinder 2 in a region between the annular groove 52 ' when the pump piston is in its bottom dead centre position and the entry of the filling passage 51 into the guide cylinder 2, and opens into a cylinder 66 in which a starting piston 67 is displaceable The starting piston is held in abutment against a stop 68 by means of a compression spring 69, for as long as the pressure in the interior space 38 is too low to deflect the starting piston from this position When in this position, the relief line 76 is closed and is only opened from a predetermined pressure in the interior space after the starting piston 67 has been deflected As in Fig 3, the effective delivery stroke of the pump piston is uniformly terminated from a termination of delivery stroke h FE when the relief line 76 is open, even when the cylindrical slide valve 44 is in its full load position or even in its starting position, in which positions the outlet 45 is opened only after the relief line 76 is opened This applies to normal operation During part load operation, the pump working chamber is relieved at-an earlier or later instant before the stroke h FE, corresponding to the position of the cylindrical slide valve 44 On the other hand, the relief line 76 is fully closed during starting, so that, with the cylindrical slide valve 44 in a corresponding position, an additional excess quantity of fuel serving as an excess starting quantity can follow the quantity of fuel injected under full load.

A fifth embodiment of the invention in accordance with Fig 7 is a modification of the embodiment of Fig l The control slide valve 18 " is of different design from that of the embodiment of Fig l and again separates a control pressure chamber 32 at the end facing the cylinder liner from a relief chamber 33 at the end facing the closure member The control piston 18 " comprises an inner sleeve 77 and an outer sleeve 78 which are rigidly connected to one another by, for example, electron beam welding The inner sleeve 77 has the bore 22 in accordance with the embodiment of Fig l, into which the smaller diameter portion 7 of the pump piston 4 enters from one end and a plug 24 ' from the other end, which plug, together with the pump piston, thus encloses the pump working chamber 25 in the bore 22 The plug 24 ' again has the flange 29 at the end thereof which extends out of the bore 22, where it also has the spring abutment plate 28 which serves-as an abutment for the compression spring 27 in the form of a starting spring whose other end is supported on a shoulder of the outer sleeve 78 Like the control piston 18 of Fig l, the outer sleeve 78 slides sealingly in the cylinder 9 and, together with the inner sleeve 77 and the cylinder liner 3, encloses the pressure control chamber 32 which communicates with the filling passage 51 and the pressure line 40 or the interior space 38 by way of the longitudinal groove 46 The piston 18 " is displaced towards the closure member 10 by the pressure prevailing in the pressure control chamber 32, until the end face 26 ', associated with the inner sleeeve 77 in the present embodiment, of the control piston comes into abutment against the flange 29.

An annular chamber 80 is formed between the inner sleeve 77 and the outer sleeve 78 and serves as a connecting passage between a first radial bore 81 and a second radial bore 82 through the wall of the inner sleeve 77 Alternatively, a plurality of radial bores may be provided instead of first and second radial bores and are then each located in a common radial plane to the axis of the pump piston The first radial bore opens into the bore 22 by way of a first opening 83, and the second radial bore opens into the bore 22 by way of a second opening 84 A control port 62 ", in the form of an annular-groove in the outer surface of the pump piston in the present embodiment, co-operates with the first opening 83 at the pump i piston end The control port 62 " is connected to the longitudinal passage 41 by way of a transverse bore 61 ' and communicates with the first opening 83 after a stroke h FE of the pump piston determining the termination of delivery after the pump piston has reached bottom dead centre When the control port 62 " is overlapping the first opening 83, fuel may flow from the pump working chamber into the annular chamber from where the fuel flows into an external annular groove 85 in the plug 26 ' by way of the second radial bore 82 and the second opening 84 The external annular groove communicates with a flow-off passage comprising a transverse bore 86, a bore 87 located in the plug and leading from the transverse bore 86, and an annular groove 88 which is provided in the plug 24 and into which the bore 87 opens and which is directly contiguous to the flange 29 The fuel flowing to this location can then escape into the relief chamber 33 by way of throttle openings 89 between the end face 26 ' of the inner sleeve 77 and the flange 29 of the plug.

It will be appreciated that the throttle opening may be disposed elsewhere in the flow-off passage, although it can be produced in a convenient manner in the case of the above arrangement Communication between the second opening 84 and the external annular groove 75 only exists for as long as the control piston 18 ' is in its illustrated end position in abutment against the flange 29 This can only be established when the pressure in the control pressure chamber 32 is sufficiently high to overcome the force of the starting spring 27.

While the pre-stroke was controlled by the control edge 63 in conjunction with the control port 62 in the embodiment of Fig l, which was also the case in the embodiments of Figs 2, 4 and 6, the control port 62 " controls the termination of delivery in conjunction with the first opening 83 in the present case In the case of the pump previously described, this is adjusted to a constant stroke h FE after the force of the starting spring 27 has been overcome However, the control piston 18 " is displaced towards the cylinder liner 3 during starting and with a low pressure in the control pressure chamber 32, to the second opening 84 is no longer in register with the external annular groove 65 and is closed by the plug 24 ' Nevertheless, the fuel cannot escape if the control port 62 " now reaches the first opening 83.

Hence, the high pressure delivery of fuel is continued and an excess starting quantity is injected This excess starting quantity follows the quantity injected under full load Since the termination of delivery has been established in this manner, it is unnecessary I to adjust the termination of delivery by means of an annular groove for termination of delivery in accordance with the annular groove 52 in the embodiment of Fig l, in conjunction with the filling passage 51 Nevertheless, in the embodiment of Fig 7, an annular groove 90 is provided in the large diameter portion 7 of the pump piston and communicates permanently with the filling port 50 However, in this case, the annular groove 90 of the filling port is displaced towards the control piston end and first communicates with the filling passage 51 upon the commencement of the stroke of the pump piston.

The overlap is then cancelled from a pre-stroke hv onwards, so that high pressure delivery from the pump working chamber 25 may be effected from this point onwards.

Based on the development of Fig 7 described above, an adaptation may also now be provided analogously to the embodiment of Fig l by disposing an adaptation spring 30 between the flange 29 and a shoulder 31, as is shown in Fig l The shoulder 31 is the end face of the outer sleeve 78 In such a case, a non-throttling flow-off groove is provided in the end 26 ' of the control piston instead of the throttle opening 89.

The control piston 18 " comes into abutment against the adaptation spring 30 after overcoming the force of the starting spring 27 When in this position, communication already exists between the first opening 83 and the external annular groove 85 in the plug 24 ' While the control port 62 ' communicates with the first opening 83 at a relatively early instant when the control piston is in this initial position, the pump working chamber is relieved at a later stroke of the pump piston as the pressure in the control pressure chamber 32 increases and the control piston 18 " is displaced towards the adaptation spring 30 In this manner, a quantity injected under full load increases as the rotational speed increases, and is added at the end of the main injection towards top dead centre OT This corresponds to a negative adaptation The relationship can again be seen from a control graph shown in Fig 8 in which a stroke of the pump piston is plotted against the angle o Z of rotation, and the pre-stroke hv up to which a high pressure delivery is still not effected and which is followed by the injection of fuel up to the stroke h FE The adaptation displacement travel of the control piston 18 " is indicated by the arrow -An The strokes correspond to the quantities of fuel injected The control of the quantity of fuel injected in the range of part load is effected by means of the cylindrical slide valve 44, as in the previous embodiments The throttle opening 89 in the end face 26 ' in the first-described variant of Fig 7 replaces adaptation by displacing the control piston 18 " towards the adaptation spring 30 Since the time taken for the flow-off quantity to flow through the throttle opening decreases as the rotational speed increases, the relief by way of the flow-off quantity decreases as the rotational speed increases, which corresponds to an increase in the quantity of fuel injected as the rotational speed increases, and hence also corresponds to negative adaptation Provided that the starting quantity is obtained by means of the control piston 18 or 18 ', it may be varied by adjusting the stop pin 12 in all the embodiments.

With a uniform basic construction of the pump and the variation of control ports in the pump piston or variation of the control piston, there are many possibilities of adapting the fuel injection pump to the various requirements of different internal combustion engines There is the advantage that only a small number of parts have to be interchanged, which add to the otherwise uniform construction of the fuel injection pump in the manner of a modular construction system Starting quantity requirmenets before or after the full load quantity can be met and, if desired, the injection of fuel may be advanced I automatically Positive as well as negative adaptation can be achieved Quantity drift as a result of setting of the piston or as a result of wear on the drive end of the pump piston or wear on the parts of the governor can be avoided by the correlation of the control of the pre-stroke to the control piston This applies particularly to the embodiments of Figs 1, 3, 4 and 6 A quantity drift, particularly a quantity drift of the quantity injected under full load, can compensate for wear on the parts of the governor by establishing a uniform termination of delivery after the stroke h FE Setting of the pump piston may also be compensated for in conjunction with the control of the pre-stroke by the control piston.

Claims

1 A fuel injection pump for an internal combustion engine, having a reciprocated and simultaneously rotated stepped pump piston, the larger diameter portion of which is guided in a guide cylinder and serves as a distributor, and the smaller diameter portion of which projects out of the guide cylinder, a displaceable control slide valve arrangement provided with a bore into which the smaller diameter portion of the pump piston enters from one end and a plug enters from the other end to enclose a pump working chamber, that end of the plug which is located outside the bore abutting against an adjustable stop pin which is located coaxially of the pump piston and is adjustable through a closure member of the housing of the fuel injection pump, the control slide arrangement being in the form of a control piston and being displaceable in a cylinder by means of a fixedly supported spring, said cylinder being closed at one end towards the guide cylinder and at the other end by the closure member, wherein the displacement travel of the control piston is limitable by at least one stop and the spring is disposed in a relief chamber which is enclosed by the control piston in the cylilnder and which is relieved of pressure by way of a relief passage, whereas that end of the control piston which is remote from the relief chamber defines a pressure control chamber in the cylinder) which control pressure chamber communicates with a pressure source having a rotational-speed-dependent -pressure by way of a pressure line, and with a longitudinal passage which is located in the pump piston and leads from the end thereof which defines the pump working chamber, which longitudinal passage communicates with a control port in the outer surface of the pump piston, and communication between the control port and a chamber relieving the pump working chamber is controllable by a control edge on the control slide valve arrangement, which longitudinal passage is also connectible by way of at least one filling opening which opens in the region of the guide cylinder into the outer surface of that portion of the pump piston which serves as a distributor to at least one filling passage, opening into the guide cylinder, for feeding fuel during the suction stroke of the pump piston, and, during each pressure stroke of the pump piston, the longitudinal passage is connected, by way of a distributor port in the outer surface of the pump piston in the region of the guide cylinder, to one of a plurality of pressure passages which, distributed around the pump piston, and which lead from the guide cylinder and are connectible to injection points of the internal combustion engine, and wherein the control slide valve arrangement, which is in the form of a control piston having the bore and the control edge, is sealingly displaceable in the cylinder, the drive end of the pump piston extends out of the guide bore and into an interior space filled with fuel where the outer surface of the pump piston has a control sleeve which is adjustable by means of an injected fuel quantity governor and which has a control edge which controls an outlet of the longitudinal passage into the interior space, and the effective point of opening of the pump working chamber is variable in dependence upon the rotational speed by way of the control port and the control edge on the control piston controlling the said control port.

2 A fuel injection pump as claimed in claim 1, in which the control pressure chamber is located at the guide cylinder end of the cylinder, and the spring is supported between the control piston and the plug which at the same time serves as a stop for the control piston.

3 A fuel injection pump as claimed in claim 2, in which the spring is an adaptation spring.

4 A fuel injection pump as claimed in claim 2, in which a starting spring is additionally disposed between the control piston and the plug.

A fuel injection pump as claimed in claim 1, in which the relief chamber is located at the guide cylinder end of the control piston, the spring is an adaptation spring, and the control pressure chamber is located at the closure member end of the control piston and has a compression spring which is interposed between the control piston and the plug, wherein that end of the cylinder which faces the guide cylinder serves as a stop for the control piston.

6 A fuel injection pump as claimed in any of claims 2 to 5, in which the control port is opened by the control edge on the control piston when the control piston is abutting against the adaptation spring when the latter is not yet compressed, and is closed after a pre-stroke of the pump piston, the pre-stroke being varied in dependence upon the rotational-speed-dependent pressure in the pressure control chamber by compression of the adaptation spring.

7 A fuel injection pump as claimed in claim 6, in which the control edge on the control piston is formed by the boundary edge of the mouth of a passage leading through the wall of the control piston.

8 A fuel injection pump as claimed in any preceding claim, in which an outlet port on the outer surface of the pump piston is connected to the I I longitudinal passage and, from a predetermined pump piston stroke (h FE) onwards, is connected to a relief line leading from the guide cylinder to a relief chamber, for the purpose of limiting the effective delivery stroke of the pump piston.

9 A fuel injection pump as claimed in claim 8, in which the outlet opening is an annular groove in the outer surface of the pump piston.

A fuel injection pump as claimed in claim 8 or 9, in which the relief line is opened, after the internal combustion engine has started, by a piston operable in dependence upon a rotational-speed- controlled pressure in the fuel-filled chamber.

11 A fuel injection pump as claimed in claim 2, in which the spring is a starting spring and the control piston has, as a boundary edge, a first opening in the surface of the bore and the first opening communicates with a second opening in the surface of the bore by way of a connection passage extending in the control piston, which second opening is connectible to a flow-off passage, leading from the outer surface of the plug to a relief chamber, after the force of the starting spring has been overcome, the termination of delivery by the pump piston being determined by the point at which the control port is opened by the first opening after a predetermined pump piston stroke (h FE).

12 A fuel injection pump as claimed in claim 11, in which an adaptation spring is disposed between the control piston and a fixed part of the fuel injection pump in addition to the spring serving as the starting spring, the deflection of which adaptation spring is limited by abutment of the control piston against the stop, and the termination of delivery is shifted towards a larger delivery-effective stroke (h FE) of the pump piston by the deflection of the adaptation spring after the force of the starting spring has been overcome.

13 A fuel injection pump as claimed in claim 12, in which the adaptation spring and the starting spring are supported on a flange or spring abutment plate of the stop pin.

14 A fuel injection pump as claimed in claim 11, in which the starting spring is supported on a flange or a spring abutment plate of the stop pin.

A fuel injection pump as claimed in any of claims 11 to 14, in which the flow-off passage opens into the relief chamber.

16 A fuel injection pump as claimed in any of claims 11 to 14, in which a throttle is provided in the course of the flow-off passage.

17 A fuel injection pump as claimed in any of claims 11 to 16, in which the connection passage is in the form of an annular chamber which is enclosed between an outer sleeve and an inner sleeve which are sealingly joined to one another and form the control piston.

18 A fuel injection pump for an internal combustion engine, constructed and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.

Published 1989 at The Patent Office, State House, 6671 HI 4 ghtolborn London W Cl R 4 TP Further copies maybe obtained from The Patent Ofice Sales Branch, St Mary Cray, Orplngton, Kent BR 5 3RD Printed by Multiplex techniques ltd, St Mary Cray, Kent, Con 1/87