GB2185600A - Fuel injection pump for an internal combustion engine - Google Patents

Abstract

A distributor-type fuel injection pump for internal combustion engines has, for the purposes of injection timing and adjusting the delivery quantity, an axially displaceable and rotatable control spool (26) which cooperates with a pump and distributor piston (15). In order to adjust the control spool, two hydraulic adjusting mechanisms (30,31) are provided, each of which is controlled by a baffle plate valve (32) which in turn is controlled by an electronic control device (65). <IMAGE>

Description

SPECIFICATION Fuel injection pump for an internal combustion engine The present invention relates to a fuel injection pumpforan internal combustion engine, ofthe type comprising a reciprocable and rotatably driven pump and distributor element.

In an injection pump ofthistype, known forexample from German Auslegeschrift No.21 45036,the axial and rotational positions of a control spool are controlled by two flyweight adjusters in conjunction with two adjustable governor springs in accordance with the respective operating conditions. Such mechanical adjusting devices are expensive and take up a relatively large amount of space in the pump housing.

In accordance with the present invention, there is provided a fuel injection pump for an internal combustion engine, comprising reciprocable and rotatably drivable pump and distributor element closing offa working chamber, a pump suction chamberaccommodating fuel under pressure, and a control spool which is both axially displaceably and rotatably disposed on the pump and distributor element and whose rotational and axial position is determined by a quantity adjusting device and by an injection timer, and which cooperates with passages, in the pump and distributor element leading to the working chamberforthe purposes of opening and closing the working chamber, the injection timer and the quantity adjusting device each comprising a hydraulic mechanism having an adjusting piston closing off a control pressure chamber, the control pressure chambers being supplied with fuel under pressure from the pump suction chamber, and each control pressure chamber being associated with a pressure control valve of the baffle plate valve type to control the effective control pressure.

In contrast to the prior art, a fuel injection pump in accordance with the present invention has the advantage that the hydraulic pressure ofthe fuel, which is already present in the pump suction chamber, is used to applythe adjusting forces, and that the hydraulic adjusting mechanisms controlled by the baffle plate valves have a stable structure and function free from hysteresis.

Byway of example only, a specific embodiment of the present invention will now be described, with re ferencetotheaccompanying drawings, in which Figure 1 shows a simplified longitudinal section of an embodiment of fuel injection pumpofthedes- tributortype in accordance with the present invention; and Figure 2is a cross section taken along the plane Il-I I in Figure 1 of the adjusting devices of the fuel injection pump shown in Figure 1.

In the distributor-type fuel injection pump shown, a housing 10 surrounds a pump suction chamber 11, which is supplied with fuel from a supply tank 13 bya delivery pump 12. In orderto adjust the pressure in the pump suction chamber 11, a pressure control valve 14 is connected in parallel with the delivery pump 12 and, once the internal combustion engine supplied with fuel by the injection pump has reached a particular speed, maintains the pressure in the pump suction chamber 11 at a predetermined level, for example 8 bar. A reciprocating and simultaneously rotatingly driven pump and distributor piston 15, which closes off a pump working chamber 16, serves to meter fusel delivery and injection quantities to the internal combustion engine.During the suction stroke ofthe pump and distributor piston 15, the pump working chamber 16 is filled with fuel from the pump suction chamber 11 by way of a suction line 17 and one of a pluarality of control grooves 18 in the piston 15. During the following compression stroke, and if the piston 15 has been rotated through a specific angular range, a quantity offuel to be injected is passed, with the suction line 17 closed, through a longitudinal bore 20, an outlet passage 21 and a delivery groove 22to one of a pluralityofan- gularly offset pressure lines 23, and through these is delivered to an injection nozzle (notshown in detail) at the engine cylinder ofthe internal combustion en gine.Theinletofthesuction line 17 isoffsetin relation to the, for example four, outlet passages 21 in such a way that either the inlet is connected to one of the control grooves 18 or the delivery groove 22 is connected to one of the pressure lines 23.

The longitudinal bore 20 in the piston 15 leads from the pump working chamber 16 to four uniformly angularly offset radial passages 25, and, longitudinally offset, to a radial passage 24. A control spool 26 is both axially displaceably and rotatably disposed on the piston 15 in the region of the passages 24 and 25. The left front face 27 of the control spool 26 cooperates with the passage 24. An oblique control face 28 is provided in the right front face of the control spool 26 and cooperates with the passages 25. The commencement of an injection process is determined by the cooperation of the front face 27 with the passage 24, and termination is determined by the cooperation of the oblique control face 28 with one ofthe passages 25.The effective compression stroke commences when the passage 24 is closed, on movement of the piston 15 from left to right, by the control spool 26, and terminates when the oblique control face 28 opens one of the passages 25. Commencement of injection can thus be altered by means of axial displacement of the control spool 26, and termination of injection can be altered by In order to adjust commencement and termination of injection, and hence also the volume ofthe quantities of fuel to be injected, to identical hydraulic adjusting mechanisms 30,31 are disposed in the housing 10 above the drive of the piston 15, each of which is associated with a pressure control valve in the form of a baffle plate valve 32.The parallel adjusting mechanisms 30,31 each have an adjusting piston 35,36 in a cylinder 33,34 with piston rods 37 to 40 projecting from each end face and penetrating through the facing walls of the cylinders 3334. The right-hand side of the adjusting pistons 35,36 each close off a control pressure chamber 41,42 respectively, and the left-hand sides each closes off a reference pressure chamber 43,44 respectively. Return springs 45,46 supported on cyiinders 33,34 re spectively and collars 47,48 respectively, press the adjusting pistons 35,36 to the right against the force of the pressure effective in the control pressure chambers 41,42.

The control pressure chambers 41,42 of the adjusting mechanisms 30,31 are each connected byway ofan opening 50 with a throttle to the pump sure tion chamber 11. The control pressure in each con trol pressure chamber4l 42, in conjunction with the force ofthe return springs 45,46, determines the position ofthe adjusting pistons 35,36. The control pressures are controlled by the baffle plate valves 32.

Such baffle plate valves, known for example from German Offenlegungsschrift No.31 09 560, have a baffle plate 52 which is pivotable about an axis 53 in a housing 51. An inlet nozzle 55 is directed towards the right-hand end of the baffle plate 52 from below and is connected byway of an inlet opening 56 to the control pressure chambers 41,42 ofthe adjusting mechanisms 30,31 respectively. At the opposite end, a pressure spring 57 presses on the baffle plate 52 from above. The inner chamber 54, which is kept un pressurised,ofthe baffle plate valve 32 is connected to asupplytank 13 bywayof an outlet58.

Each baffle plate valve 32 is provided with a permanent magnet 60 which acts byway of yoke parts 61,62 on an armature 63 connected to the pivotable baffle plate 52. The armature 63 is surrounded by a coil 64 which is controlled by an electronic control device 65.Depending on the size of the magnetic field ofthe coil 64 controlled by the control device 65 as a function of various operating parameters of the internal combustion engine such as speed,temperature, load and ambient pressure, or the like, as well as ofthe desired torque, the baffle plate 52 opens the opening ofthe inlet nozzle 55to agreater or lesser extent, such thatthethrottie combination of the inlet nozzles 55 and the throttles 49 leading from the pump suction chamber 11 into the control pressure chambers 41,42 respectively enable control pressuresto be built up which are smallerthanthe pressure in the pump suction chamber 11, but greaterthan the pressure in the inner chamber 54 of the baffle plate valves 33, which is kept unpressu rised by way ofthe outlet 58. The throttles 49, inlet nozzles 55 and baffle plates 52 are preferably seiected such that a control pressure of between 0 and approximately 1.5 bar can be obtained in the control pressure chamber41,42 during operation.

In cooperation with the unpressurised reference chambers 43,44 of the adjusting mechanisms 30,31 respectively, which are connected to the inner chamber 54 of each baffle plate valve housing 51 by way of an opening 67, and with the return springs 45, 46, the adjusting piston 35,36 respectively takes up a position according to the control pressure in the re spective control pressure chamber4l ,42. Due to the design ofthe baffle plate valve 32, the control pressures are proportional to the control currents fed to the coils 64 from the control device 65.The position ofthe adjusting pistons 35,36 is signailed to the control device 65 by a travel sensor, for example a potentiometer 68, which is actuated by an extension connected to each piston rod 39,40 and penetrating the housing 10.

The adjusting mechanism 31 controlling commencement of injection acts on a two-armed lever 71 which is pivotally mounted at 72 and whose upper, longer arm 73 is joined to the end ofthe piston rod 38, and whose shorter arm 74 engages in a groove 75 in the control spool 26 in orderto axially displace it.

In orderto control or regulate termination of injection and hence the volume of the delivery quantity, the other adjusting mechanism 30 acts with its piston rod 37 on a bell crank lever 77 which is pivotally mounted on a bearing pin 78. One arm 79thereof abuts against the end of the piston rod 37, and the other, fork-shaped, arm 80 longitudinally displaceably surrounds a lug 81 radially projecting from the control spool 26.

As relatively large injection quantities are required for starting the internal combustion engine, butthe pressure in the pump suction chamber 11 on starting is not high enough for a high control pressure to prevail in the control pressure chamber 41, a starting piston 85, which is axially aligned in a cylinder 84 in the housing 10 with respect to the adjusting piston 35 and its piston rod 37, can be displaced by a pressure spring 86, which starting piston 85 has a pinshaped extension 87 pointing towards the arm 79 of the bell crank lever 77. A soft pressure spring 88 is seated on the extension 87 and is supported on the starting piston 85 and the bell crank lever 77. The rearward reference chamber 88 is connected by way of a line 89 to the inner chamber 54 ofthe baffle plate valve 32 and is hence also pressureless.When the pump suction chamber 11 is pressureless, the pressure spring 86 displaces the starting piston 85 to the left, such that its extension 87 pivots the bell crank lever 77 in the direction towards an extension of the duration of injection.

In dependence on the position of an adjusting lever 90 and on the operation parameters transmitted by the internal combustion engine to the control device 65, the control device 65 feeds electricai currents to each coil 64 of the two baffle plate valves 32, which currents regulate predetermined positions of the baffle plate 52 such that proportional control pressures are built up in the control pressure chambers 41,42. At the same time, the control pressure chambers 41,42 are supplied with fuel from the pump suction chamber 11 by way ofthrottles 49 and their control pressures are determined by the outlet controlled by the baffle plate 52 through the inlet nozzles 55. As each adjusting mechanism 30,31 effects a separate movement of the displaceable and rotatable control spool 26, it is possible to adjustthe quantity of fuel delivered by the injection pump separatelyfrom the timing of commencement of injection in the entire speed range. The control device described is, as a result ofthe use of identical system parts, of simple construction and inexpensive to manufacture.

Claims (8)

1. Afuel injection pumpforan internalcombustion engine, comprising a reciprocable and rotatably drivable pump and distributor element closing off a working chamber, a pump suction chamber ac commodatingfuel under pressure, and a control spool which is both axially displaceably and rotatably disposed on the pump and distributor element and whose rotational and axial position is determined by a quantity adjusting device and by an injection timer, and which cooperates with passages, in the pump and distributorelement leading tothe working chamberfor the purposes of opening and closing the working chamber, the injection timer and the quantity adjusting device each comprising a hydraulic mechanism having an adjusting piston closing off a control pressure chamber, the control pressure chambers being supplied with fuel under pressure from the pump suction chamber, and each control pressure chamber being associated with a pressure control valve of the baffle plate valve type to control the effective control pressure.

2. Afuel injection pump as claimed in claim 1, wherein, on its side opposite the control pressure chamber, the adjusting piston of each adjusting mechanism closes off a reference pressure chamber, which has a relief pressure which is less than that of the pump suction chamber, and is acted upon a return spring acting against the control pressure.

3. Afuel injection pump as claimed in claim 2, wherein the control pressure chamber of each adjusting mechanism is connected by way of a throttle to the pump suction chamber.

4. Afuel injection pump as claimed in claim 3, wherein each baffle plate valve is provided with an inlet nozzle connected to the respective control pressure chamber and pointing towards the baffle plate, and each throttle and the throttle effect of the assoc iated inlet nozzle/baffle plate until enables a pressure to be obtained in each control pressure chamber which is smallerthan the pressure in the pump suction chamber, but greater than the pressure in the reference chamber.

5. Afuel injection pump as claimed in claim 4, wherein the baffle plate ofthe baffle plate valve is connected to an armature of a magnetic circuit, which is controlled by an electronic control device, which is influenced by the operating parameters of the internal combustion engine determiningthefuel/ air mixture formation.

6. Afuel injection pump as claimed in any of claims 1 to 5, wherein the adjusting pistons ofthe adjusting mechanisms are each connected to a travel sensorwhich is connected to the control device.

7. Afuel injection pump as claimed in any of claims 1 to 6, wherein the adjusting piston of each adjusting mechanism is provided with piston rods, penetrating both the control pressure chamber and the reference pressure chamber for the purposes of pressure compensation.

8. Afuel injection pump for an internal combustion engine, substantially as herein described, with reference to, and as illustrated in,the accompanying drawings.