GB2227105A - A fuel injection pump for internal combustion engines - Google Patents

Description

- 1 A 177 4

DESCRIPTION A Fuel Injection Pump for Internal Combustion Engines

This invention relates to fuel injection pumps for internal combustion engines.

In known fuel injection pumps, the respective control operations correspond to the different requirements placed on control quality, wherein the control operations are of either a mechanical or a hydraulic nature. In the known injection pumps, it is a matter of intervention in the hydraulic control and, more particularly, in the control of the commencement of delivery or commencement of injection, wherein an increase in the pressure of the control fluid brings forward the commencement of injection and a reduction in pressure retards it. Thus, in these pumps, the pressure of the control fluid is dependant upon rotational speed and is controlled with increasing pressure as the rotational speed increases. As is known, the higher the rotational speed, the earlier the commencement of injection, since, in absolute terms, because of the higher rotational speed, there is less time for the injection operation, which is compensated by said earlier commencement of injection. In the event of cold starting of the internal combustion engine, the cold starting characteristics of the diesel engine may also r 1 2 1 t k - 2 be improved by adjustment to advance commencement of injection. Thus, an arbitrary increase in control pressure fluid in the event of cold starting - that is, in a rotational speed range in which this control fluid pressure is relatively low - can also be used to obtain an adjustment to provide advanced commencement of injection.

In a known fuel injection pump of this type (DE-OS 29 25 418.0), if the engine is cold, that is in the event of a so-called cold start, the speeddependant pressure control of the control fluid, which is effected by way of a control pressure valve, is rendered inoperative in that the control valve closes in the discharge channel and the pressure control valve is, so to speak, put out of operaticn, so that the pressure of the control fluid increases correspondingly and effects adjustment to provide early commencement of injection. The specially designed pressure-control valve plays a considerable part in this control operation. In the manner of a conventional pressure-control valve, it has a control piston upon which a spring acts progressively in a stroke-dependent manner and, depending on the delivery quantity, which increases in dependence upon rotational speed, causes a correspondingly progressive change in pressure, wherein this control piston contains a throttle outflow by way of which a particular quantity 1, 3 - of control fluid may flow constantly into the outflow passage. When the control valve is closed, that is when the outflow passage is closed, the backing-up of the control fluid assists the spring so that the control piston closes its control opening and a corresponding increase in pressure is achieved in that control fluid does not flow off, which pressure increase causes the desired adjustment to provide early commencement of i n j e c t i o n.

In a further development of the pressure control operations towards the above-mentioned known fuel injection pump, the generic, load-dependent pressure control was developed by way of the adjusting sleeve in order to be then produced in large quantities.

Although the above-mentioned control has been very successful, manufacture of the pressure-control valve is expensive and the respective adjustment, that is adaptation to the engine characteristics, is difficult. On the other hand, load-dependant adjustment of the commencement of delivery should be clearly separated from speed-dependent adjustment, even if only to be able to carry out the various control operations. Basically, the speed-dependent adjustment of the commencement of injection must be maintained and load-dependent or temperature- dependent adjustment of the commencement of 1 injection may then only take place mechanically or, if it is to be effective hydraulically, by way of additional control intervention in the control fluid pressure. These so called device groups for the additional control are preferably independent elements.

In accordance with the present invention there is provided a fuel injection pump for an internal combustion engine having a governor which actuates a fuel injection quantity control member and which has an adjusting sleeve whose operating position conrresponds to the prevailing load and speed, a hydraulic injection timer in which the control pressure of a control fluid controlled by a pressure-control valve changes with increasing speed in accordance with the speed and hence changes the commencement of injection in accordance therewith, a reduction in the control pressure of the control fluid by additionally allowing the control fluid to flow off by way of a first outflow throttle of an outflow passage, which throttle is controllable in dependence upon load by the adjusting sleeve, a control valve in the outflow passage, and a second outflow throttle in the adjusting sleeve and connected tp the outflow passage, the arrangement being such that the second outflow throttle can be rendered inoperative at least on starting and at low rotational speed in order to achieve an adjustment to provide early commencement - 5 of delivery and such that the connection between the second outflow and the outflow passage exists at least at starting speeds.

Such an injection pump has the advantage that, despite sufficient independence of the device group's, two of the control operation which are always provided are combined into one device group or the pressurecontrol valve can be.made considerably more simple without a throttle outflow bore, and, advantageously, adaptation to the respective internal combustion engine is much more simple. Provided no load- dependent adjustment of injection is necessary or desired (which is only extremely infrequently the case), the throttle outflow provided in the adjusting sleeve may cooperate on its own with the outflow passage.

According to a preferred embodiment of the invention, the control valve is controllable in dependence upon temperature and can be closed off during warm up. This control may take place for example by way off an expansion-element regulator. It may, however, also take place by way of a temperature sensor for the engine temperature, which then actuates the control valve by way of a heating element or an electro-magnet.

According to yet another advantageous feature of the invention, the control valve is in the form of a 1 6 solenoid valve which is open when non-energised, since the flow quantity when the valve is open is relatively small and even the control pressures only reach the maximum intake chamber pressure of the injection pump.

According to a further advantageous embodiment of the invention, the control valve also acts as an excesspressure valve so that, even when the control valve is closed and the control fluid pressure is correspondingly high, excess pressure is prevented from arising.

According to yet another advantageous feature of the invention, the adjusting sleeve is a governor sleeve which is axially displaceable on a spindle containing a central relief bore as an outflow passage, which sleeve has two radial, axially differently disposed throttle bores for the ouflow of the control fluid, which cooperate with an annular groove disposed in the outer surface of the spindle and wherein the governor sleeve is acted upon on the cne hand by the force of flyweights driven in dependence upon rotational speed and, on the other hand, by the force of a governor spring, which force alters in dependence upon load.

While the throttle outflow for cold-starting adjustment must be open at least for starting speeds, and is preferably permanently open in order to prevent any additional control effect when the control valve not closed, the outflow throttle for load-dependent 1 1 k adjustment of injection is not normally opened until a corresponding load- dependent state has been reached, which state is usually above idling speed.

The invention is described furter hereinafter, by way of example only, with reference to the accompanying drawings, in which:- Fig. 1 is a longitudinal sectional view through a distributor-type injection pump contructed in accordance with one embodiment of the present invention; Fig. 2 is a longitudinal sectional view through an adjusting sleeve of the governor of the distributor-type injection pump on an enlarged scale; Fig. 3 is a simplified representazion of the hydraulic control circuit of the injection timing control of the distributor-type injection pump; and Fig. 4 is a function diagram of the commencement of i n j e c t i o n.

In the distributor-type injection pump, a pump piston 1, which also serves as a distributor, is set into reciprocating and simultaneously rotating motion by a drive shaft 2 and by means of a cam drive 3. With each pressure stroke of the pump piston 1, fuel is delivered from a pump working chamber 4 by way of a distributor-type longitudinal groove 5 to one of a plurality of pressure passages 6 disposed at uniform i 8 angular intervals about the pump piston 1. Each pressure passage 6 leads to a combustion chamber (not shown) of an internal combustion engine. Fuel is supplied to the pump working chamber 4, via an intake passage 7, from fuel filled intake chamber 8 disposed in the housing of the injection pump. During the intake stroke of the pump piston 1, the intake passage 7 is opened by longitudinal control grooves 9 in the pump piston 1. The number of control grooves 9 corresponds to the number of pressure passages 6 and hence to the number of pressure strokes executed per revolution of the pump piston. A solenoid valve 10 in the intake passage 7 is adapted to close the intake passage 7 in order to terminate injection, so that no fuel can pass from the intake chamber 8 into the pump working chamber 4 during the suction stroke of the pump piston 1.

The quantity of fuel to be injected, which is delivered into one of the pressure passages 6 per stroke, is determined by the axial position of a control sleeve 11 disposed about the pump piston 1. This axial position is determined by a governor 12 and an arbitrarily actuable adjusting lever 13, with evaluation of the prevailing rotational speed and load (the load may, for example, correspond to the position of the accelerator pedal of the motor vehicle).

The intake chambe 8 is supplied with fuel by a feed i pump 14. The feed pump 14 is driven by the drive shaft 2 and supplies fuel from a fuel tank 15 and an intake line 16. The output pressure of the feed pump 14, and hence the pressure in the intake chamber 8, is controlled by a pressure-control valve 17, wherein this pressure also increases as the rotational speed increases. The cam drive 3 and the governor 12 are disposed in the intake chamberr 8 and are hence subjected to this pressure on all sides and are lubricated by the fuel.

The cam drive 3 has a roller ring 19, which is mounted in the housing so as to be rotatable through a particular angle and in whose U-shaped cross section rollers 18 are mounted. An injection timing piston 22 is coupled, by way of an adjusting bolt 21, to the roller ring 19 so as to be nonrotatable therewith (the injection timing piston 22 is shown in the drawing rotated through an angle of 900, that is perpendicular to the plane of the drawing). A dog coupling is provided in the inner bore of the roller ring 19, in which coupling dogs 23 on the drive side mesh with dogs 24 on the output side of the pump and distributor piston 1, so that the pump and distributor piston 1 can execute a stroke movement independently of the drive shaft 2 during rotation. A face cam ring 25 disposed on the 0 J - 10 Pump piston 1 has face lobes cam 26 on its surface rolls along the rollers 18, wherein the number of face cams 26 in turn corresponds to the number of pressure passages 6. The face cam ring 25 is pressed by springs 27 onto the rollers 18 by way of its track.

The injection timing piston 22, which is axially displaceable tangentially to the roller ring 19, is acted upon in one direction of adjustment by a restoring spring 28 and in the,other direction of adjustment by the pressure of the intake chamber 8 prevailing in a chamber 29, which is transmitted by way of a throttle passage 31 in the injection timing piston 22. The direction of displacement of the injection timing piston is selected such that, when the fuel pressure in the intake chamber 8 increases as the roational speed increases, the face cam lobes 26 of the face cam ring 25 engage earlier with the rollers 18, as a result of which the commenccement of the stroke of the pump piston 1, and hence the commencement of fuel delivery, that is the commencement of fuel injection, takes place earlier relative to the angular position of the drive shaft 2. Thus, the higher the rotational speed, the earlier the commencement of injection.

The governor 12 is driven by way of a toothed gear 32, which is connected to the drive shaft 2 and drives a speed sensor 33 with flyweights 34, which act on the one j A - J hand on a governor onradjusting sleeve 35, which is axially displaceably mounted on a spindle 36, and, on the other hand, acts on a control lever system 38, which is also acted upon by a governor spring 37, which system articulates the control sleeve 11 for its stroke position. To do this, the control lever system 38 is pivotally mounted on a spindle 39. The pre- stress of the governor spring 37 can be altered by the adjusting lever 13 in such a way that, when the adjusting lever 13 is adjusted in the direction of increasing load, the pre-stress of the governor spring 37 increases, so that the control sleeve 11 is displaced further upwards, which, because of the resulting later opening of a spill passage 41 of the pump working chamber 4 during the compression stroke of the pump piston 1, results in an increase in the quantity injected. The quantity of fuel still in the pump working chamber 4 is always discharged when the mouths 42 of the spill passage 41 emerge from the control sleeve 11 during the compression stroke of the pump piston 1, and thus further delivery of fuel by the pump piston 1 takes place into the intake chamber 8.

In order to be able to alter the commencement of delivery to be dependent on load, as well as to be dependent on rotational speed only as described above, outflow throttles 43 and 44 are provided in the governor 1 j 2 - 12 sleeve 35 (as shown in more detail in Fig. 2). The throttles 43, 44 cooperate with an outflow passage 45 in the spindle 36, so that, in certain rotational speed or load states, which act by way of the adjusting lever 13, the governor spring 37 and the control lever system 38 on the governor sleeve 35 or which act by way of the load of the engine on the rotational speed, an adjustment of the governor sleeve 35 is effected, so that the resulting opening of the outflow passage 45, although throttled, reduces the pressure in the intake chamber 8 and the commencement of delivery is adjusted to a relatively later point. The outflow passage 45 is itself pressure-relieved by way of an outflow line 46. However, a solenoid valve 47, which is "non-energised when opeC, is disposed in this outflow line 46 and, when current is switched on, it closes the outflow line 46 and hence interrupts the outflow effect which would change the commencement of injection. The commencement of injection is then correspondingly determined by the pressure-control valve 17 only, so that the commencement of delivery is brought forward correspondingly.

In order to allow the above-mentioned speeddependent increase in pressure in the intake chamber 8 to take place, the pressure-control valve 17 has a control piston 48 which is acted upon by a control spring 49, in order to control a control port 51 of an k 13 outflow bore 52, which opens into the intake line 16. The control spring 49 has a correspondingly progressive characteristic, so that, depending on the speedconditioned delivery quantity of the feed pump 14, the control piston 48 opens the control put 51 to a greater or lesser extent. A relief line 54 leads from a spring chamber 53 of the control spring 49 to the intake line 16. The control pressure determined by this pressure control valve 17 and prevailing in the intake chamber 8 is thus determined by the delivery quantity of the feed pump 14, wherein this delivery quantity is reducible by the quantity flowing out through the outflow throttle 43 and or 44 of the suction chamber 8. Thus, the areater the quantity flowing off, the lower the pressure prevailing in the intake chamber 8, such that, given the same rotational speed, this outflow causes an adjustment to provide a later commencement of injecticn.

In order to illustrate this additional outflow, the governor sleeve 35 with the spindle 36 is shown on an enlarged scale in Fig. 2. In this case, the two outflow throttles 43 and 44 have different functions. While the outflow throttle 43 serves in a known way to control a load-dependent adjustment of injection, the outflow throttle 44 makes it possible to control commencement of injection in the event of cold starting. As can be seen c 'I 1 14 from this figure, the first outflow thrott-le 44 permanently overlaps an annular groove 55 disposed in the outer surface of the spindle 36. Thus, fuel can flow off by way of the outflow passage 45 even at starting speeds or low rotational speeds that is when the governor sleeve 35 is in its extreme left-hand position. The second outflow throttle 43 does not overlap the annular groove 55 until the governor sleeve 35 has moved a certain amount to the right, that is at low rotational speeds and low load. Since the outflow of fuel out of the intake chamber 8 is throttled, there is a corresponding reduction in pressure in the intake chamber, but no pressure collapse, so that the desired effect, that is a relative late adjustment of the commencement of injection, is obtainable without interrupting the ba-sic function of the speed-dependent adjustment to provide early commencement of delivery. As soon as the load changes, for example when the driver opens the throttle fully, the governor sleeve 35 is moved to the extreme left, the outflow throttle 43 is correspondingly closed and the comencement of injection is brought forward as desired, wherein the pressure in the intake chamber 8 is determined by the pressurecontrol valve 17 only.

These two control positions are shown as position a and position b in Fig. 3, wherein in position a the c 1 - outflow throttle 43 is closed, and in position b it is open.

These two control positions correspond to the curves a and b in the graph shown in Fig. 4. In this graph, the governor sleeve travel s is plotted along the ordinate and the rotational speed n is plotted on the abscissa. The dotted line c shows the transistion from one state to the other given a corresponding stroke s of the governor sleeve, which, as explained, is determined not only in dependence upon rotational speed, but also in dependence upon load.

When the solenoid valve 47, which is disposed in the outflow line 46 is energised, fuel cannot flow out of the intake chamber 8 either by way of the first outflow throttle 43 or by way of the second oAflow throttle 44. So that, the pressure in the intake chamber 8 is determined by the pressure-control valve 17 only, which, as described above, leads to a rise in the pressure level in the intake chamber 8, with a corresponding adjustment to provide early commencement of injection across the entire rotational speed range. This situation is desirable when then engine is cold and such an earlier commencement of injection provides extra time for preparing the fuel than is necessary when the engine is warm. This solenoid valve 47 may be triggered 1 j g --.

- 16 by a temperature sensor on the engine. As soon as a sufficient temperature has been reached, the magnet of the solenoid valve 47 is switched off so that the valve moves into the switching position shown. In Fig. 4, the characteristic at which the solenoid valve 47 is closed, that is the actual characteristic of the pressurecontrol valve 17, is shown by the dotted line d. Since, when the engine is cold, a loaddependent retardation of injection is not required, the closing of the outflow passage 45 and the outflow throttle 43, which determines the loaddependent adjustment of injection, is not disadvantageous.

c

Claims (7)

1. A fuel injection pump for an internal combustion engine having a governor which actuates a fuel injection quantity control member and which has an adjusting sleeve whose operating position conrresponds to the prevailing load and speed, a hydraulic injection timer in which the control pressure of a control fluid controlled by a pressure-control valve changes with increasing speed in accordance with the speed and hence changes the commencement of injection in accordance therewith, a reduction in the control pressure of the control fluid by additionally allowing the control fluid to flow off by way of a first outflow throttle of an outflow passage, which throttle is controllable in dependence upon load by the adjusting sleeve, a control valve in the outflow passage, and a secGnd outflow throttle in the adjusting sleeve and connected tc the outflow passage, the arrangement being such that the second outflow throttle can be rendered inoperative at least on starting and at low rotational speed in order to achieve an adjustment to provide early commencement of delivery and such that the connection between the second outflow and the outflow passage exists at least at starting speeds.

2. A fuel injection pump as claimed in claim 1, c - 18 in which the control valve is controllable in dependence upon temperature and can be closed while the internal combustion engine is warming up.

3. A fuel injection pump as claimed in claim 1 or 2, in which the control valve comprises of a solenoid valve which is open when non-energised.

4. A fuel injection pump as claimed in any of claims 1 to 3, in which the control valve is contructed additionally as an excess-pressure valve.

5. A fuel injection pump as claimed in any preceding claim, in which the adjusting sleeve is a governor sleeve which is axially displaceable on a spindle containing -a central relief bore and has two radial bores acting as the first and second outflow throttles, which cooperate with an annular groove disposed in the outer surface of the spindle and wherein the governor sleeve is acted upon the one hand by the force of flyweights which are driven in dependence upon rotational speed and, on the other hand, by the force of a governor spring whose force alters in dependence upon load.

6. A fuel injection pump as claimed in any preceding claim, wherein the second outflow throttle is permanently conneted to the outflow passage.

7. A fuel injection pump contructed and adapted to operate substantially as hereinbefore described with 1 6 4 reference to and as illustrate d in the accompanying drawings.

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Published 1990 at The Patent Office, State House. 66'71 High Holborn. London WC1R4TP. Further copies maybe obtained from The Patent Office Sales Branch, St Maxy Cray. Orpington. Kent BR5 3RD Printed by Multiplex techruques ltd. St Mary Crky. Kent. Con. 187 owe... --j -.I. -11 - -------