GB2199088A - A fuel injection pump for internal combustion engines - Google Patents

Abstract

A fuel injection pump of the distributor type wherein a pump piston (4) is driven in a simultaneously reciprocating and rotating manner, the piston being provided with a relief passage (14) connecting the pump working chamber (6) to a relief chamber (7) and the relief passage (14) having discharge ports (16) controlled by an annular spool (18) displaceable and rotatable on the pump piston. In order to achieve low injection rates each discharge port is extended in the axial direction by a rectangular recess (77) into the forward face (78) of which leads a longitudinal throttling groove 80 opened by registration with a control groove (51) in the end face of the annular spool (18) before final opening of the discharge port (16) occurs. By operating a device (52) for rotating the annular spool, the controlling effect of the throttling grooves (80), and hence the quite-idle control of the fuel injection pump, can be cut out. <IMAGE>

Description

DESCRIPTION A FUEL INJECTION PUMP FOR INTERNAL COMBUSTION ENGINES The present invention relates to a fuel injection pump for internal combustion engines. A fuel injection pump is disclosed in German Offenlegungschrift 32 18 275, in which grooves are provided in the annular spool, which issue diametrically from the end face of the annular spool and which, together with the end face of the annular spool, which serves as the first control edge, co-operte with one discharge port of the relief passage. The grooves thus have second control edges for controlling the connection between the pump working chamber and the relief chamber, before the first control edge becomes effective.The annular spool is not only ~ axially displaceable on the pump piston in dependence upon the adjustment of an injected fuel quantity regulator, but it can also be rotated by rotating device. By rotating the annular spool, the discharge port can become contiguous, during the delivery stroke of the pump piston at each or every second delivery stroke of said pump piston, with one of the diametrical grooves, depending on the number of grooves provided. Thus either the number of injections can be reduced, for example by half, or the high pressure delivery of the fuel injection pump can be prohibited altogether.Furthermore, it is possible to achieve a throttled discharge or "leakage" of fuel during each delivery stroke by reducing the width of the grooves, which serves to reduce the fuel injection rate in the low rotational speed range.

This acts as a so-called quiet-idle device, which allows the internal combustion engine to be operated for example during idling with reduced combustion noise. The throttling grooves, having a rectangular shape, are, relative to the rotation of the pump piston, disposed in front of the first control edge in a control-effective manner. For rotating the annular spool, the known means for preventing relative rotation has a rigid coupling with a crank arm, which is turned during idling operation of the internal combustion engine to cut out individual cylinders.

In this known fuel injection pump, problems do however occur with regard to controlling the quantity of fuel escaping by way of the throttle cross sections.

Problems are to be found in particular in continuously increasing the quantity of fuel from the transition from the idling range to the part-load range, in order that no load surges occur when load is introduced. For operation with a reduced fuel injection rate, it is disadvantageous, due to leakage by way of a throttle groove, that as many throttle grooves are required as there are delivery strokes carried oot by the pump piston per revolution.

In accordance with the present invention there is provided a fuel injection pump having a pump piston which is driven in a pump cylinder in a simultaneously reciprocating and rotating manner and which acts as a distributor of the delivered fuel quantity to a plurality of injection points, which pump piston defines a pump working chamber in the pump cylinder and contains a relief passage, which is disposed in the pump piston and leads from the pump working chamber to a first discharge port located on the periphery of the pump piston, the quantity of fuel delivered by the pump piston being altered by controlling the opening of a discharge port, by means of an annular spool which is axially displaceable inside the relief chamber and actuated by a fuel injection quantity regulator for setting the desired torque, which annular spool has control grooves, disposed on one end face and opening towards the inner surface of the annular spool to control the discharge port which spool can be rotated by a rotating device to influence the control effect of the control grooves, the pump piston also comprising a throttling connection groove, which is located upstream of the discharge ports wherein the control groove, which branches onto the surface of the inner annular of the annular spool, has a first boundary edge, as a first control edge, facing in the direction of the pump piston axis, which is contiguous with a second control edge which is one of the side edges of the control groove disposed in a direction parallel to the pump piston axis, and the discharge port is provided with a straight boundary edge, which faces in the direction of the delivery stroke of the pump piston, from which straight boundary edge a longitudinal throttling groove branches.

Preferably, only one throttle longitudinal groove is provided per discharge port and the control effectiveness of the throttle groove is maintained in a further region of adjustment of commencement of injection with the aid of the first and second control edges provided by the control groove.

Advantageously cut out can be effected continuously with increasing load by rotating the annular spool, thus obtaining a load-controlled, jerk-free transition from quiet-idling operation to part-load or load operation.

The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 illustrates a longitudinal section through one embodiment of a fuel injection pump according to the present invention; Fig. 2 is a section through the pump piston of the embodiment of Fig. 1; Fig. 3 illustrates a rotary drive of the annular spool in a section through a fuel injection pump according to the present invention and perpendicular to the pump piston axis; Fig. 4 is a plan view of part of the rotary drive of Fig. 3; Fig. 5 illustrates the function of the outer surface of the pump piston in the region of its control-effective part, with the associated control ports of the annular spool, which is displaceable on said part, and includes a piston elevation curve, according to one embodiment of the present invention; and Fig. 6 illustrates the function of the outer surface of the pump piston in the region of its control-effective part with the associated control ports of the annular spool, which is displaceable on this part, and including a piston elevation curve, according to another embodiment of the present invention.

In a housing 1 of a fuel injeciton pump shown in Fig. 1, a bushing 2 is disposed in whose inner bore 3, which forms a pump cylinder, a pump piston 4 is driven by a cam drive 5 in a simultaneously reciprocating and rotating manner. One end face of the pump piston defines a pump working chamber 6 and another part of the piston projects out of the inner bore 3 into a pump suction chamber 7, which forms a relief chamber which is enclosed in the housing 1.

The pump working chamber 6 is provided with fuel while the pump piston occupies its suction stroke or bottom dead centre position by way of longitudinal grooves 8 disposed in the outer surface of the pump piston and a suction bore 9, which issues from the pump suction chamber 7. The pump suction chamber is provided with fuel from a fuel tank (not shown) by way of a feed pump 11. A pressure-control valve (not shown) is used to control the pressure in the suction chamber in dependence upon rotational speed, in order, for example, to carry out a hydraulic speed-dependent adjustment of injection by way of a pressure, which IS controlled in dependence upon rotational speed. The stroke of the pump piston is adjusted to commence earlier as rotational speed increases.

A longitudinal passage 14 is disposed in the pump piston and leads from the pump working chamber 6. This passage is in the form of a blind bore and functions as a relief passage. A transverse bore 15 branches off from said passage and leads to two discharge ports 16 located on the periphery of the pump piston 4, and into a region in which the pump piston projects into the suction chamber 7. The discharge ports 16 are preferably diametrically opposed, which leads to a balanced hydraulic force on the pump piston. In this region, a quantity-adjusting member is disposed on the pump piston in the form of an annular spool 18, which is rotatable and displaceable on the pump piston and which controls the function of the discharge ports 16.

A radial bore 20 branches off from the relief passage 14, which runs preferably coaxially with respect to the pump piston axis, and leads to a distributor port 21 on the periphery of the pump piston. In the operating region of this distributor port, delivery lines 22 branch off in a radial plane from the inner bore 3, which lines are distributed about the periphery of the inner bore 3 in accordance with the number of cylinders of the associated internal combustion engine to be'provided with fuel. The delivery lines each lead by way of a valve 23, which is in the form of a known non-return valve or pressure-relief valve, to fuel injection points (not shown).As soon as the suction bore 9 is closed by the outer surface of the pump piston on commencement of the delivery stroke of the pump piston following a corresponding rotation thereof, fuel in the pump working chamber 6 is delivered to the fuel injeciton points by way of a relief passage 14, the radial bore 20 and the distributor groove 21. This delivery is interrupted if the discharge ports 16 are opened during the course of the pump piston stroke, by the annular spool 18, and are connected to the suction chamber 7. The remaining fuel displaced by the pump piston is then delivered to the suction chamber 7 only. The higher the annular spool 18 is displaced on the pump piston, with respect to the pump working chamber, the larger the quantity of fuel delivered by the pump piston.

The fuel injection quantity regulator 25 provided for adjusting the annular spool has a single-arm tensioning lever 26, pivotable about an axle 27, with its lever arm end connected to a governor spring arrangement 28. This arrangement comprises an idling spring 29, which is disposed between the head of a coupling member 30 and the tensioning lever, whereby the coupling member 30 is inserted through an opening in the tensioning lever, and its other end, which is remote from the head, is connected to a main governor spring 31.

The other end of this main governor spring 31 is in turn connected to a swivel arm 33, which is adjustable, by way of a shaft 34 which passes through the pump housing by an adjusting lever 35. The adjusting lever can be acutated by an operator as required between an adjustable full-load stop 36 and an adjustable idling stop 37. For example, the adjusting lever 35 is connected to the accelerator pedal, which is actuated by the driver of the vehicle which is fitted with the internal combustion engine and the injection pump, according to the torque required. In place of the simple spiral spring shown here, other governor spring arrangements can be used for the main governor spring, which may by multiple-stage and/or prestressed.

A two-arm starting lever 39 is pivotable about the axle 27, and one arm of the lever engages the annular spool 18 by way of a ball end 240 located in a transverse groove 41, disposed in a plane which is radial with respect to the annular spool 18. The other arm of the starting lever has a leaf spring 49, which acts as a starting spring on the tensioning lever 26. A regulating member 42 of a rotational-speed sensor, which is in the form of a centrifugal force regulating device 43 of a known type, acts on this lever arm of the starting lever 39.The centrifugal force regulating device 43 is driven is synchronism with the drive shaft 44 of the fuel injection pump by way of toothed-wheel gearing 245. As the rotational speed increases, the regulating member 42, starting lever 39 and annular spool 18 are displaced against the force of the starting spring 49 until the starting lever moves into abutment against the tensioning lever 26. In the course of this movement, the annular spool is moved from a highest position, which is closest to the pump working chamber, towards the pump piston drive side, in accordance with an adjustment to the starting quantity, and the excess quantity on starting is controlled.

If the starting lever moves into abutment against the tensioning lever, both levers can be pivoted against the force of the idling spring 29 until the main governor spring 31 becomes effective in the idling range. Depending on whether this spring is a variable-speed governor spring or an idling maximum-speed governor spring, when the set rotational speed is reached, the tensioning lever continues to be moved and the annular spool 18 is displaced in order to reduce the injection quantity.

A larger or smaller quantity of fuel will be injected, depending on the position of the adjusting lever 35, at a particular rotational speed.

For the purposes of adjustment, the axle 27 is mounted on a setting lever 246, which is pivotable about an axle 47, which is fixed to the housing, and which is held in abutment against an adjustable stop 48 by a spring.

The end face 19 of the annular spool 18 has radial control grooves 51 which, in accordance with the plan view in Fig. 2, are disposed at an angular distance of 900 from one another, for example symmetrically with respect to the point of action of the ball end 240. A rotating device 52 is provided which comprises an angle lever 53, one arm 54 of which has a sliding part 55 in the form of a ball end, which engages in a longitudinal groove 57 in the annular spool 18, opposite the ball end 40 of the st rting-lever 39.Other equivalent embodiments are possible, in which the sliding part is replaced by a fork or a longitudinal groove, and the longitudinal groove 57 in the annular spool is replaced by a projecting sliding part. - The angle lever 52 can be pivoted about axle 58, which is firmly mounted in the injection pump housing 1, and its other lever arm 59 is a U-shaped lug, whose end is also mounted on the axle 58 and which has a recess 60 in which an actuating arm 62 engages, which is eccentrically disposed on an end face 63 of a shaft 64, which is guided through the housing towards the outside thereof (Fig. 3). The shaft is disposed in a tight fit in an inner bore 65 of a bushing 66 in the pump housing wall and its outer end has a reduced diameter part 67, on which a hub 68 of an adjusting lever 69 is mounted.The regulating lever 69 is fixed in the axial direction by a lever 70, which is seated on the shaft 64 and which is connected to the outer end of the shaft 64 so as to be non-rotatable and is held in position by a nut 71. One end of a torsion spring 73 is fastened to the lever 70 and its other end is connected to the regulating lever 69 and is prestressed in such a way that the regulating lever 69 is in abutment with the lever arm 72 of the lever 70 and is thus connected to the shaft 64. Furthermore, a disc 74 is connected to the shaft at the point of transition from the reduced diameter part 67 to the part of the shaft issuing from the inner bore 65, so as to be non-rotatable thereto which disc has two arms 75. These arms engage in a recess 76 on the end face of the bushing 66. The width of the recess 76 determines the range through which the shaft 64 and the lever 70 can pivot, and its limiting edges act as stops for the arms 75.

The regulating lever 69 is connected to the adjusting lever 35 in such a way that the regulating lever 69 can be rotated in synchronism during the first part of the rotation of the adjusting lever 35 away from its idling stop 37. At the same time, the lever 69 turns the shaft 64 due to the connection to the lever 70 by way of the torsion spring 73. The angle lever 53 is pivoted accordingly and the spool 18 is rotated.

After an angle of rotation which is determined by the width of the recess 76, the rotation of the shaft 64 is prohibited, although the regulating lever 69 continues to rotate against the force of the torsion spring 73.

In this manner, a free-wheel action of the lever 69 is obtained.

In addition to the features of the annular spool 18, recesses 77 are provided in the outer surface of the pump piston, which extends the discharge ports 16 with a straight control edge 78 facing towards the pump working chamber. A longitudinal groove 80 branches from the edge 78, which is provided with a throttling cross section and is disposed on the outer surface of the pump piston, with either the whole of the longitudinal groove acting as a throttling groove, or only a part thereof, as illustrated more clearly in Fig. 5.

The two control grooves 51 are thus associated with the two recesses 77 having throttling longitudinal grooves 80, which are diametrically opposed on the pump piston.

In a four-cylinder distributor-type injection pump, one of the recesses 77 can be connected to one of the control grooves 51 during each of the four delivery strokes per revolution. This is illustrated in Fig. 5, along with the function of the pump piston outer surface and the surface of the inner ring 81 of the annular spool and in particular it shows the rectangular cross section with which the control grooves 51 open onto the inner ring 81, having the first control edge 82 which lies in a plane which is radial to the pump piston axis, and with contiguous limiting edges 83 and 84, which run in the axial direction, one of which, namely the left-hand limiting edge 83 serves as a second control edge. It also shows the piston lift curve 85, which the recesses 77 with the throttling longitudinal grooves 80 follow.

The dotted line indicates a position 77' in which the recess 77 is located when the pump piston is in the bottom dead centre position. Starting therefrom, the end of the throttling longitudinal grooves 80 is at a distance sv from the second control edge 82. This stroke corresponds to the prestressing stroke when the annular spool 18 is in the low-load position. During this stroke path, the pump piston prestresses the fuel in the pump working chamber in such a way that it achieves the injection pressure which is determined by the injection nozzle. During the following stroke, from the position of the recess 77, the throttling longitudinal groove 80 is connected to the pump suction chamber 7, since it is opened by the first control edge 82. By way of a subsequent leakage path of a stroke length hl, fuel flows into the suction chamber 7.In this way, the delivery rate of the pump piston is reduced in order to obtain, in a known manner, quiet running of the internal combustion engine. Following the stroke path hl, the recess 77 is opened by a first control edge 82 at FEL (end of delivery - idling) and the subsequent sudden enlargement of the discharge section causes the pump working chamber to be relieved to such an extent that fuel injection is terminated. This process is repeated every 900 angle of rotation of the pump piston, after the pump piston has drawn fuel into the pump working chamber, as represented by the downward flank of the cam lift curve 85.

If the internal combustion engine operates in a higher rotational speed range, the pump piston lift curve 85 or cam lift curve 85 is displaced towards the left, in Fig. 5, which represents an early commencement of injection. In this region, the second control edge 83, i.e. the left limiting edge of the control groove 51, becomes control-effective in that the throttling longitudinal groove 80 is also associated with the left side of the front edge of the recess 77.

The quiet-idle device realised in this way is only effective when the annular spool 18 is in the abovedescribed rotational position shown in Fig. 5, as is the case in the idling range of the internal combustion engine or in the lowest part-load range. By rotating the annular spool, the effect of the longitudinal groove 80 can be cut out, in such a way that only the front edge 78 of the recess 77 is control-effective. In-Fi. 5, the annular spool is rotated to the right in the direction of rotation of the piston, so that the throttle groove 80 can no longer be opened by the second control edge 83.

In Fig. 6, the throttle 60 is on the right-hand side of the front edge 78 of the recess 77 and is associated with the right-hand limiting edge 84 of the control groove 51 as the second control edge. In principle, the device operates in a similar way to that described above, although in this case, the annular spool is rotated in the opposite direction to effect cutout.

A second piston lift curve 85', which is obtained in the event of angular adjustment of the spool to provide an extremely early commencement of injection, is also shown.

In order to introduce load, when the quiet-idle device becomes effective, the stroke position of the annular spool can be adjusted from its idling position at fuel load. FEV represents termination of delivery at full load, where the recess 77 is connected to the control groove 51 by way of the front edge 78. Up to this position, an increasing injection delivery occurs, with increasing load, as in the prestressing stroke at the full injection rate before any leakage occurs by way of the longitudinal groove, and correspondingly more fuel is injected on the introduction of load. This injection function can be additionally modified through the position of the longitudinal groove 80 on the front edge 78, the shape of the control groove 51, and possibly, by selective partial rotation of the annular spool.

Claims (6)

1. A fuel injection pump having a pump piston which is driven in a pump cylinder in a simultaneously reciprocating and rotating manner and which acts as a distributor of the delivered fuel quantity to a plurality of injection points, which pump piston defines a pump working chamber in the pump cylinder and contains a relief passage, which is disposed in the pump piston and leads (/6) from the pump working chamber to a first discharge port located on the periphery of the pump piston, the quantity of fuel delivered by the pump piston being altered by controlling the opening of a discharge port by means of an annular spool which is axially displaceable inside the relief chamber and actuated by a fuel injection quantity regulator for setting the desired torque, which s ,s annular spool has control grooves disposed on one end face and opening towards the inner surface of the annular spool to control the discharge port which spool c can be rotated by a rotating device to influence the control effect of the control grooves, the pump piston also comprising a throttling connection groove, which is located upstream of the discharge ports wherein the control groove which branches onto the surface of the inner annulus of the annular spool has a first boundary '6s edge as a first control edge, facing in the direction of the pump piston axis, which is contiguous with a second control edge which is one of the side edges of the control groove disposed in a direction parallel to the pump piston axis, and the discharge port is provided with a straight boundary edge, which faces in the direction of the delivery stroke of the pump piston, e from which straight boundary edge a longitudinal throttling groove branches.

2. A fuel injection pump as claimed in claim 1, wherein the relief passage has at least two diametrically opposite discharge ports into which a transverse bore opens, which crosses the axial relief passage and which ports are connected to control grooves distributed on the annual spool depending of the distance of angular rotation between the delivery strokes cf the pump piston.

3. A fuel injection pump as claimed in claim 2, wherein two control grooves are provided, which supply four injection points per pump piston revolution and which are disposed at angular distances of 900 from one another on the annular spool.

24. A fuel injection pump as claimed in claim 3, wherein the control grooves are symmetrical to the axial guideway, against which the rotating device of the annular spool abuts, and are symmetrical to the point of action of an adjusting member of the fuel injection quantity regulator, whereby the adjusting member acts on guideways which are in a radial plane to the pump piston.

5. A fuel injection pump as claimed in any of claims 1 to 3, wherein the rotating device is connected to the adjusting lever of the fuel injection quantity regulator in such a way that, when the adjusting lever reaches a particular position of adjustment from its idling position, the annular spool maintains a final position of rotation.

6. A fuel injection pump substantially as hereinbefore described, with reference to and as illustrated in, the accompanying drawings.