GB2063997A

GB2063997A - An Exhaust Gas Recycling Control Arrangement for Use with an Internal Combustion Engine

Info

Publication number: GB2063997A
Application number: GB8036522A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1979-11-17
Filing date: 1980-11-13
Publication date: 1981-06-10
Also published as: FR2470863A1; JPS636733B2; FR2470863B1; DE2946557C2; JPS5683545A; GB2063997B; DE2946557A1

Abstract

The exhaust recirculation valve 5 is opened by vacuum supplied to an actuator 7 when the valve 13 is open in response to less than a predetermined deflection of the control lever 26 of the fuel injection pump governor and less than a predetermined engine speed or less than a predetermined displacement of the governor sleeve 23. A switch 14 in the circuit of the solenoid of the valve 13 may be closed by the cam 42 at less than a predetermined deflection of the lever 26 and the switch 17 may be closed except when fuel under pressure from the governor chamber is permitted to flow to the switch actuator by the passages 30, 39, 40, when the governor sleeve port 38 registers with the groove 36. An engine speed between upper and lower predetermined values may cause closure of a circuit switch (48), Fig. 3 (not shown). A throttle valve (55), Fig. 5 (not shown), in the engine air intake 3 may be operated by a vacuum modified in dependence on the position of the lever 26. <IMAGE>

Description

SPECIFICATION An Exhaust Gas Recycling Control Device for Use With an Internal Combustion Engine The present invention relates to an exhaust gas recycling control device for use with an internal combustion engine.

In one known such control device, a centrifugal governor is provided, which acts on a fuel feed rate control device against the force of a control spring prestressed by an adjusting lever. With greater than a specific deflection of the adjusting sleeve of the centrifugal governor, a communication is formed between a suction chamber of an injection pump and an outlet line, in which a throttle for forming a control pressure is disposed, which pressure serves to actuate an exhaust gas return metering apparatus. The communication between suction chamber and outlet line is here continuously changed in accordance with the adjustment of the fuel feed rate control device, so that a control pressure which changes with the setting of the fuel feed rate control device is formed for the purpose of adjusting the exhaust gas return metering apparatus.The arrangement here is such that the exhaust gas recycling is suppressed at full load and supplied at part load.

This apparatus suffers, however, from the drawback that the speed-dependence of the fuel flow delivery for a constant setting of the fuel flow rate adjusting device is not allowed for. This property of the fuel injection pump leads to the result that, although the setting of the fuel flow rate adjusting device can still be used at low speeds as a control magnitude for the exhaust gas recycling rate, nevertheless even in the middle speed range for a constantly maintained setting of the fuel flow adjusting device fuel flow rates are Injected, for which an exhaust gas recycling should no longer take place having regard to the formation of soot and the performance of the internal combustion engine.Thus no assurance is provided that at all the operating points other than the start and running-up range of the internal combustion engine, a sufficiently high recycling rate of exhaust gas can be achieved with exploitation of the permissible limits.

According to the present invention, there is now provided an exhaust gas recycling control device for use with an internal combustion engine and comprising a fuel injection pump to feed fuel to such engine at a rate influenced by a setting member acting through a control spring on fuel feed rate control means of the pump, throttle means disposable in an exhaust gas retum duct of the engine and controlled by a throttle control device actuable under the control of switch means acted on by the setting member, the throttle control device being arranged to open the throttle means when and only when the setting member is in a position corresponding to less than a predetermined engine load and a limiting vatue is attained by a signal Indicative of rotational speed of the engine at least at constant load thereof.

A suitably designed and constructed embodiment of such a device provides the advantage that exhaust gas can be recycled to a much greater extent over a desired speed range at a considerably closer approach to the permissible limits of exhaust gas recycling.

It is especially advantageous for the signal to be given by the position of a control member of a mechanical speed transmitter coupled to the fuel feed rate control means. The signal deals with the low speed range of the characteristic field. In this range, the limitation of the exhaust gas recycling takes place solely with the use of the control member signal at too high fuel injection values.

By contrast, in the remaining regions of the characteristic field of the internal combustion engine, the limit for the exhaust gas recycling can be maintained with the adjusting lever signal in a very good approximation to the maximum permissible value.

Embodiments of the present invention will now be more particularly described by way of example with reference to the accompanying drawings, in which: Fig. 1 shows a first embodiment of the present invention in an auxiliary-force-actuated exhaust gas recycling apparatus controlled by the positions of the setting member of the flow control device and the control member of the speed transmitter, Fig. 2 shows the characteristic parameter field of an internal combustion engine operated with a device embodying the present invention, Fig. 3 shows a second embodiment of the present invention with control of an auxiliary force for actuating the exhaust gas recycling metering apparatus as a function of the presence of the setting member signal and of a signal indicative of a first or second speed threshold being exceeded, Fig. 4 shows a third embodiment of the present invention in a throttling damper disposed upstream of the entry of the exhaust gas recycling line into the intake pipe and capable of being actuated as a function of the position of the setting member, and Fig. 5 shows a fourth embodiment of the present invention in modification of the embodiment according to Fig. 4 and comprising an auxilTary-force-controlled throttle flap upstream of the inlet of the exhaust gas recycling line into the intake pipe.

A recycling of controlled quantities of exhaust gas to the induction pipe of an internal combustion engine proved to be effective for reducing the proportion of harmful substances in the exhaust gases of the internal combustion engine. In particular, in self-igniting internal combustion engines, the high NOx component can be reduced. These freely inducting internal combustion engines, governed by the fuel injection rate, are operated in the part-load range with a considerable air excess, which can be reduced by the admixing of returned exhaust gas.

The combustion is thereby so influenced that the harmful substances content of NOx is reduced.

The requirement therefore exists, in respect of the exhaust gas return rate, at all load and speed conditions of the intemal combustion engine to approach the maximum exhaust gas recycling rate permitted there as closely as possible.

In spite of various known and expensive control devices for the recycling of exhaust gas, the requfrement still remains to make such devices as simple and funct-ionally reliable as possible.

Particularly in small vehicles, as simple and as inexpensive as possible while still sufficiently effective a control of the exhaust gas recycling rate should be achieved possibly with some compromises being made to the approximation to the maximum permissible exhaust gas return rate.

An important criterion for the maximum permissible exhaust gas return rate is the level of fuel injection quantity per injection operation. In particular, for example, at full-load or during the start enrichment, the recycling of the exhaust gases should be suppressed in order to avoid any reduction of performance in these ranges. In the remaining ranges, a generally good result in respect of exhaust gas composition can be achieved with an appropriately adapted average exhaust gas return rate.

Referring now to the drawings, Fig. 1 shows a diagrammatically illustrated internal combustion engine 1 comprising an exhaust gas manifold 2 and an induction pipe 3. An exhaust gas return duct 4 branches off from the exhaust gas manifold 2 and leads into the induction pipe 3. An exhaust gas return control valve 5 is installed in the duct 4 and is actuated by an adjusting device comprising a pneumatic actuator 7, in which an operating chamber 8 is bounded by a control diaphragm 9, which is connected to the exhaust gas return control valve 5 and which is loaded by a spring 10 acting in the closing direction of the exhaust gas return control valve 5.

The operating chamber 8 is connected by a pressure duct 11 to an underpressure source 12 through a switching valve 13, which is magnetically actuable and in its ground position closes the pressure duct 11.

A first switch 14 and a pressure-sensitive switch 1 7 are connected in series in an electrical supply line or switching line 15 of the electromagnetically actuated switching valve 13, which can thus be actuated only when both these switches are closed.

Furthermore, a portion of a distributor injection pump is illustrated in the figure, although the use of the invention is not restricted to such a pump.

This by way of example comprises a reciprocating and simultaneously revolving pump piston 16 as fuel flow propelling and metering apparatus thus acting as distributor, the not-illustrated pump chamber of which is connectable through a relief ducat 20 to a pump suctIon chamber 18. The relief duct 20 emerges at the cylindrical face of the portion of the pump piston that penetrates into the pump suction chamber 18, the outlet opening being governed by a cylinnrical slide valve 19 associated with the pump piston 16. Depending upon the position of the cylindrical slide valve, the relief duct is opened and thereby the injection is terminated after a shorter or longer delivery stroke of the pump piston.

The cylindrical slide valve 19 is adjustable by means of a setting member in the form of a lever 21, which acts as fuel flow adjusting device and on the other end portion of which act a control spring 22 and a control sleeve 23 of a centrifugal governor 24. Instead of the control sleeve, some other adjusting element of a speed transmitter could be used.

The bias of the control spring 22 is adjustable through an eccentric 25 by means of an adjusting lever 26, by which the desired torque is put in.

The control sleeve 23 acts in known manner against the force of the control spring 22 on the lever 21. The control sleeve is adjusted by centrifugal weights 27, which are rotatably driven proportionally to the pump speed. Depending upon the bias of the control spring 22, the control sleeve is displaced to a greater or lesser extent at a specific rotational speed so that the sliding cylindrical valve 19 also adopts a higher or lower position relative to the pump piston 1 6. The positions of the control sleeve and the lever 21 and cylindrical slide valve 19 each represent a measure of the set load.

An axial bore 30 is provided in the support 29, on which the control sleeve 23 is slidable. The bore 30 leads out from the housing of the injection pump 6 into an outlet duct 39, which passes through a fixed throttle or constriction 31 to the fuel storage tank 32. From the latter, the pump suction chamber 18 is supplied with fuel by a delivery pump 34, the fuel pressure in the pump suction chamber 18 being controlled by a pressure control valve 35 connected in parallel with the delivery pump 34.

The end of the bore 30 leads into an annular groove 36 in the support 29 of the control sleeve 23. The control sleeve sliding on the support 29 here closes this annular groove at least in its starting position. The control sleeve 23 is furthermore provided with an opening 38 in its cylindrical wall which, from a specific deflection of the control sleeve onwards, comes into register with the annular groove 36, as a result of which fuel is enabied to flow back out of the suction chamber 18 through the bore 30 and the throttle 31 to the fuel storage tank 32.

From the duct 39 connecting the bore 30 to the fuel storage tank 32, a control duct 40 branches upstream of the constriction 31 to the pressure-sensitive switch 1 7. This switch is so constructed that, when a control pressure builds up at the constriction 31, that is when the control sleeve 23 has travelled a specific distance, the switch opens and the connection in the electrical supply line 15 is interrupted. The first switch 14, connected in series, is.actuated by a cam disc 42 rotated together with the adjusting lever 26. From a specific load setting onwards, the first switch is opened by the cam disc 42, eo that the connection in the electrical supply line 1 5 is interrupted also here.Only when both switches are closed can the switching valve 13 be actuated to result in opening of the exhaust gas return valve.

The operation of the device according to Fig. 1 will be explained in more detail by reference to the diagram in Fig. 2. The full lines in the diagram of Fig. 2 are the lines of constant position of the adjusting lever 26. In the medium speed range between 800 and 2200 revolutions per minute, these lines are to a coarse approximation parallel to the abscissa, the lowest line corresponding to idling and the uppermost to full load operation.

The fuel injection quantity per stroke is plotted along the ordinate. A broken line 44 represents the target curve for the fuel injection quantity, up to which exhaust gas recycling can take place.

The position of this curve is dependent upon the characteristics of the internal combustion engine and, at about 2000 revolutions per minute is situated approximately midway between full load injection quantity and idling injection quantity.

This line rises slightly towards decreasing rotational speeds, then falling away more steeply at about 700 revolutions per minute. A chaindotted line 45 represents one of the curves of constant adjusting lever position and closely approximates to the target curve 44. Also illustrated in the diagram is a second dashed curve 46, which indicates the injectIon quantity at constant control sleeve position or constant position of the cylindrical slide valve 1 9. Injection pumps which operate as initially described with bypass control have the property that the quantity of fuel injected increases relatively steeply with increasing speed for a constant position of the fuel flow adjusting element, i.e. the cylindrical slide valve 19.This is also shown by the curve 46, which starting from a relatively low injection rate at low speed rises relatively steeply at around 500 revolutions per minute and in the example illustrated here has already passed through the target curve 44 at 800 revolutions per minute.

The starting point of the curve 46 ideally lies below the target curve 44 and is highly suitable for a limiting of the exhaust gas return. Only the last portion of the curve reaches, while still at relatively low speed, fuel injection values at which an exhaust gas recycling must no longer take place. It is therefore not possible to use a specific setting of the control sleeve 23 as limiting value for the exhaust gas recycling. For that reason, the curve 46 for constant control sleeve position and also the curve 45 of a specific, constant adjusting lever position, are both used as limiting value for the exhaust gas return. Accordingly, the first switch 14 and the pressure-sensitive switch 1 7 are provided, which here have the function of an AND-gate.With the help of the described construction of control sleeve 23 and support 29, a control signal can be generated in a simple manner for the pressuresensitive switch 17. A corresponding signal could, of course, also be obtained with appropriately adapted travel pickups. As iong as the opening 38 is not in register with the annular groove 36, the pressuresensitive switch 17 remains closed. Also, for adjusting lever positions which are smaller than the adjusted position associated with the curve 45, the first switch 14 is closed. Accordingly, the switching valve 13 is opened and likewise also the exhaust gas return valve.If, in the speed range between about 400 revolutions per minute and 800 revolutions per minute according to the values given by way of example in Fig. 2, the control sleeve 23 is deflected sufficiently far that fuel can flow out through the bore 30, then the pressure-sensitive switch 1 7 is opened and independently of the position of the first switch 14 the electrical supply to the switching valve 13 is interrupted and this valve then closes. In this position, the operating chamber 8 of the pneumatic actuator 7 is vented so that the exhaust gas return valve is also brought into its closed position under the action of the compression spring 10. The same operation takes place in the range of speeds above about 800 revolutions per minute when a greater adjusting lever position is set than that which corresponds to the curve 45.In this case, the first switch 14 opens.

A modified form of embodiment of the governing of the switching valve 13 is illustrated in Fig. 3. Here also, the first switch 14 is provided in the electrical supply line 15, in like manner as illustrated in Fig. 1, in series with a second switch 48, which is governed by a comparator device 49, which receives at least one speed signal from a speed transmitter (not shown), which picks up the actual speed of the internal combustion engine. In the comparator device, the actual speed signal is compared in a known manner with a limiting speed value in such a way that, when the limiting value is exceeded, the comparator device 49 emits an output signal to open the switch 48. This limiting value can for example be at 2000 revolutions per minute as illustrated in Fig. 2 by the line 51.The comparator device 49 furthermore contains a second comparator, in which the actual speed is compared with a second, lower limiting value, and if the speed falls below this value, the switch 48 is likewise opened. This second, lower limiting value is indicated by line 52 in the diagram of Fig. 2.

It is however also possible, in internal combustion engines in which exhaust gas can be recycled even to the throttling-down speed, for the comparator device for the upper limiting value corresponding to the line 51 to be omitted. On the other hand, instead of the comparator device for the lower limiting value or as a supplement thereto, a pressure-sensitive switch 1 7 according to the embodiment of Fig. 1 may be provided in the electrical supply line 15. By means of the described combinations, it is possible to recycle exhaust gas in a specific region of the characteristic field of the internal combustion engine with a quite good approximation to the ideal values.

Fig. 4 shows a supplementary, additional apparatus for influencing the exhaust gas retum flow rates. Here, with the remainder of the construction being the same as in the examples of Fig 1 and 3, the exhaust gas retum control valve 5 is provided directly at the inlet of the exhaust gas retum duct 4 into the Induction pipe 3. The exhaust gas return control valve is here actuated In the same manner by a pneumatic actuator 7. In departure, a throttle damper or flap 55 is now provided upstream of the entry of the exhaust gas retum duct 4 into the induction pipe and connected by a linkage 56 to the adjusting lever 26.

With the linkage 56 appropriately adapted, the throttling damper or flap 55 can be so adjusted by the adjusting lever as a function of the adjusting lever position that when the exhaust gas return control valve is opened, the flow rate of the recycled exhaust gas can be continuously matched by throttling of the fresh air feed. For example, a small quantity of exhaust gas can be recycled at very light load and a large quantity of exhaust gas can be recycled at a higher load approximating to the limiting position of the adjusting lever 26 by the fresh air feed being more drastically throttied there.

Fig. 5 shows a form of embodiment modified from that of Fig. 4 and in which for the purpose of actuating the throttling damper or flap 55 in the induction pipe 3, a pneumatic actuator 57 is provided upstream of the entry of the exhaust gas return duct 4. This actuator may for example be connected through a control duct 58 to the pressure duct 11 between switching valve 13 and pneumatic actuator 7. Connected into the control duct 58 is a pressure control valve 59 which is govemed by a cam wheel 60 driven by the adjusting lever 26. The control spring 61 of the pressure control valve is adjusted according to the shape of the cam wheel 60. In numerous variations, the exhaust gas recycling rates can be adapted, when the exhaust gas return control valve 5 is opened, to the operating ranges available.

Furthermore, when the throttling damper or flap 55 is actuated with the aid of a pneumatic actuator 57 through the intermediacy of a pressure control valve 59, the possibility is offered also of effecting the adjustment of the throttling damper or flap as a function of the rotational speed or the induction pipe suction or by an appropriate combination of the named control signals. It is thus possible to achieve further adaptations of the exhaust gas recycling rate to the operating conditions of the internal combustion engine.

The adjusting of the exhaust gas return control valve can of course also be effected by hydraulics or by some other auxiliary force such as for example provided by an electric motor or actuating magneta With a pneumatic or hydraulic solution, it is also possible to provide the drive to the switching valve by pneumatic or hydraulic means just as it is also possible to realise the drive by electronic means. With the described devices, it is possible in a simple and functionally reliable manner to adapt the exhaust gas recycling rate to the various operating points of the internal combustion engine In such a manner that a close approximation to the maximum permissible exhaust gas recycling rate is assured each time.

Claims

1. An exhaust gas recycling control device for use with an internal combustion engine and comprising a fuel injection pump to feed fuel to such engine at a rate influenced by a setting member acting through a control spring on fuel feed rate control means of the pump, throttle means disposable in an exhaust gas retum duct of the engine and controlled by a throttle control device actuable under the control of switch means acted on by the setting member. the throttle control device being arranged to open the throttle means when and only when the setting member Is in a position corresooodlng to less than a predetermined engine load and a limiting value is attained by a signal indicative of rotational speed of the engine at least at constant load thereof.

2. A control device as claimed in claim 1, wherein the setting member Is mechanically coupled to cam means, the switch means comprising a switch operable by the cam means to control supply of auxiliary energy to the throttle control device.

3. A control device as claimed in claim 2, wherein said signal is given by the position of a control member of a mechanical speed transmitter coupled to the fuel feed rate control means.

4. A control device as claimed in claim 3, wherein said signal is produced by a connection which under the control of the control member is extendible between a suction chamber of the injection pump and an outflow duct thereof, the suction chamber in use being filled with fuel under pressure. and the outflow duct Is provided with a constriction therein and communicates upstream of the constriction with a pressuresensitive switch electrically connected in series with the switch operable by the cam means

5. A control device as claimed in claim 2, wherein said signai is provided by a transmitter adapted to be responsive to the rotational speed of the engine.

6. A control device as claimed in claim 5, comprising a further switch operable to control said supply of auxiliary energy to the throttle control device, and comparator means to compare said signal with a signal value corresponding to an upper limit value of the rotational speed and responsive to said signal value being exceeded by said signal to generate an output signal to set the further switch into a first setting thereof.

7. A control device as claimed in claim 6, comprising further comparator means to compare said signal with a signal value corresponding to a lower limit value of the rotational speed and responsive to said signal value exceeding said signal to generate an output signal to set the further switch into the first setting thereof.

8. A control device as claimed in either claim 6 or claim 7, wherein the further switch is electrically connected in series with the switch operable by the cam means.

9. A control device as claimed in claim 8, comprising a source of electrical current to supply said auxiliary energy to a switching valve controlling supply of actuating energy to the throttle control device.

10. A control device as claimed in claim 9, comprising a source of fluid atunderpressure to supply said actuating energy through the switching valve to an operating chamber of a pressure-sensitive setting means of the throttle control device.

11. An internal combustion engine comprising an exhaust gas feedback control device as claimed in any one of the preceding claims.

12. An engine as claimed in claim 11, comprising an induction pipe provided with a connection to an exhaust gas return duct and upstream of the connection with a throttle flap controllable in dependence on operational parameters of the engine.

13. An engine as claimed in claim 12, comprising a setting device to operate the throttle flap and to be actuated by auxiliary energy supplied in dependence on operational parameters of the engine.

14. An engine as claimed in claim 13, wherein the auxiliary energy to actuate the setting device is provided by a source of fluid at under-pressure controllable by a pressure control valve controlled in dependence on operational parameters of the engine.

1 5. An engine as claimed in any one of claims 11 to 14, comprising means to control the throttle flap in dependence on the position of the setting member acting on the fuel feed rate control means of the pump.

1 6. An internal combustion engine substantially as hereinbefore described with reference to and as illustrated by Fig. 1 of the accompanying drawings.

1 7. An internal combustion engine substantially as hereinbefore described with reference to and as illustrated by Fig. 3 of the accompanying drawings.

1 8. An internal combustion engine substantially as hereinbefore described with reference to and as illustrated by Fig. 4 of the accompanying drawings.

1 9. An internal combustion engine substantially as hereinbefore described with reference to and as illustrated by Fig. 5 of the accompanying drawings.

20. An engine as claimed in any one of claims 1 6 to 1 9 and substantially as hereinbefore described with reference to and as illustrated by Fig. 2 of the accompanying drawings.