GB2089428A

GB2089428A - Control Valve Device for I.C. Engine Exhaust Gas Recirculation

Info

Publication number: GB2089428A
Application number: GB8135937A
Authority: GB
Original assignee: Pierburg GmbH
Current assignee: Pierburg GmbH
Priority date: 1980-12-13
Filing date: 1981-11-27
Publication date: 1982-06-23
Also published as: DE3047036C2; FR2496173A3; GB2089428B; DE3047036A1; FR2496173B3

Abstract

The position of the recirculation valve 11 is determined by a pair of spring-loaded diaphragms 18 and 20 subject in the chamber 19 between them to the suction downstream of a carburettor throttle valve and on their other sides to atmospheric pressure. The initial loading of the diaphragm 18 by a spring 31 is set by a sleeve 26 carried by the diaphragm 20 and the compression of a spring 32, biasing the diaphragm 20, at which the valve stem 13 is engaged by the screw 27 carried by the diaphragm 20 to close the valve 11 is set by screw adjustment. In operation, at high idling suction the diaphragm 20 causes the valve 11 to close via the screw 27, at low suction suction corresponding to high engine output the spring 31 biases the valve closed and at intermediate suctions the valve opening will be dependent upon the diaphragm areas and spring forces. <IMAGE>

Description

SPECIFICATION Control Device for an Exhaust-gas Return System The invention relates to a control device for an exhaust-gas return system for internal combustion engines, the system comprising a carburettor, a driver-actuated throttle valve and an exhaust-gas return line extending from the exhaust pipe to the induction pipe of the engine and bypassing the combustion chamber, the return line having a pneumatically actuated control valve responsive to the degree of suction in the induction pipe, downstream of the throttle valve and controlling the flow of returned exhaust gas in such a way that: when the engine is idling no exhaust gas is returned, with increasing engine torque exhaust gas is returned proportionately, but at full torque, no exhaust gas is returned.

Control devices of this kind serve for reducing the emission, in the exhaust gases, of toxic combustion products such as oxides of nitrogen, carbon monoxide and various hydrocarbons, by refluxing a portion of the exhaust gases through the engine.

A number of different control devices have already been developed and used for this purpose in motor vehicles.

For example, the German Offenlegungsschrift 20 11 464 describes an internal combustion engine equipped with an exhaust-gas return system. A return line extends from the exhaust pipe of the engine to the induction pipe, bypassing the combustion chambers. The return line contains a pneumatically actuated control valve which compares the absolute pressure in the induction pipe with a second pressure which depends on the angular position of the throttle valve. The control valve closes the exhaust-gas return line during idling of the engine, opens the line when the engine is delivering low and medium torques and closes the line again when the engine is delivering high torques and full torque.Assuming that the throttle valve is in the form of a conventional pivoted plate (a butterfly throttle valve), the second pressure is derived from a bore located in the wall of the induction pipe near the edge of the pivoted plate when this is in its engine-idling position (i.e. when the butterfly throttle valve is almost closed).

But this arrangement has several disadvantages which can prevent the exhaustgasreturn system from operating in the desired manner and can, under certain circumstances, upset the correct functioning of the carburettor.

The pneumatically actuated control valve, which is costly to manufacture and fault-prone in operation, suffers from imperfect sealing of the two pneumatic chambers. Furthermore, the diaphragms are subjected to the direct impingement of hot exhaust gases and consequently do not last long. When a diaphragm is punctured this allows atmospheric air to be aspirated into the induction pipe, upsetting carburettion or bringing the engine to a standstill.

In attempting to remedy the matter, in another known exhaust-gas return system an atmospheric chamber is interposed between the exhaust-gas control chamber and a chamber in which induction-pipe pressure prevails, so as to separate hot exhaust gases from the diaphragms. But this arrangement has the disadvantage that a second control line has to be provided for transmitting the induction-pipe pressure. This not only increases manufacturing costs but involves a risk of the lines being incorrectly connected, either during manufacture or during subsequent maintenance.

Finally, the bore in the induction pipe adjacent the throttle valve, when this is in its idling position, has to be positioned quite precisely, because its exact position determines the instants when the flow of returned exhaust gas begins and ceases.

The making of this bore is a costly and timeconsuming operation.

The intention in the present invention is therefore to provide a control device for an exhaust-gas return system, which is constructed in such a way that exhaust gas is returned to the engine at a rate of flow controlled so as to ensure efficient carburettion with adequately low concentrations of toxic substances in the exhaust gases, which is not costly to manufacture, which operates with only one pneumatic control chamber in the control valve and does not require an extra bore to be made in the induction pipe near the throttle valve.

The problem is solved, according to the invention, in that the control valve, which controls the flow of exhaust gas through the return line and has a conical valve head cooperating with a valve seat, has two flexible diaphragms enclosing between them a suction chamber which communicates through a control line with the induction pipe of the engine; the outside surfaces of the diaphragms being subjected to atmospheric pressure; the upper diaphragm having a greater working area than the lower diaphragm; and in that diaphragm plates of the lower diaphragm are fixed to the valve stem of the conical valve head; a conpression spring thrusting downwards on the upper plate of the lower diaphragm, the spring acting against any reduction in the volume of the suction chamber, the upper end of the compression spring acting to lift a thrust plate upwards against the lower end of a slider tube, which is axially adjustable in position in a centrepiece of the upper diaphragm; the centrepiece retaining the two diaphragm plates of the upper diaphragm; and in that a compression spring thrusts upwards against the lower diaphragm plate of the upper diaphragm, the lower end of the spring taking support on a shoulder of the housing of the suction chamber; this spring also acting against any reduction in the volume of the suction chamber.Preferably, the installed axial length of the spring of the lower diaphragm of smaller working area, with the conical valve head resting on its seat and with the upper diaphragm plate of the upper diaphragm of greater working area resting in contact with the cover, is adjustable, by screwing the slider tube in and out of the centrepiece; while the installed axial length of the spring of the upper diaphragm of greater working area, with the upper plate of the lower diaphragm resting in contact with the shoulder of the housing of the suction chamber and with the nose of the adjustment screw resting in contact with the upper end of the valve stem, is adjustable, by screwing the adjustment screw in and out of the slider tube.

The advantages of the control device of the present invention are that: The control device responds exclusively to a single variable quantity, ie induction-pipe suction downstream of the throttle valve. This quantity varies over a sufficiently wide range to ensure that, with the help of a suitably contoured conical valve head, the flow of returned exhaust gas can be controlled in the desired manner.

The absence of a second controlling variable, ie induction-pipe pressure measured where it is directly dependent on the angular position of the throttle valve, allows the control valve and the entire system to be of simple construction.

The absence of a second pressure chamber in the control valve also makes the control valve less costly to manufacture and gives it greater reliability.

The control valve has only one pneumatic connection, which therefore cannot be connected in the wrong place during manufacture and subsequent maintenance.

The fact that the installed axial lengths of the two springs can easily be adjusted greatly facilitates manufacture and reduces manufacturing costs.

An example of the invention will now be described in greater detail with the help of the drawing, in which: Figure 1 shows an internal combustion engine equipped with an exhaust-gas return system.

Figure 2 shows an exhaust-gas-return control valve, drawn to a larger scale.

The internal combustion engine 1 has a carburettor 3, a driver-actuated throttle valve 4, and induction pipe 2, a combustion chamber 7 and an exhaust pipe 5.

The exhaust pipe 5 communicates through an exhaust-gas return line 6, containing an exhaustgas-return control valve 8, with the induction pipe 2, the line 6 by-passing the combustion chamber 7. The control valve 8 communicates through a connection 10 (in Figure 2 this is shown at 24) and through a control line 10, with the induction pipe 2 of the internal combustion engine. The flow of returned exhaust gas is controlled by the control valve 8 with the help of a conical valve head 1 which cooperates with a valve seat 12.

Referring now to Figure 2, the flow of exhaust gas returned through the line 6 is controlled, as already mentioned, by a conical valve head 11 cooperating with a valve seat 1 2. The conical valve head 11 is formed, as shown best in Figure 2, on the lower end of a valve stem 13 which moves up and down in a guide of a guide pan 14.

The upper end of the valve stem 13, which is stepped as shown at 15, is fixed to the two diaphragm plates 1 6, 1 7 of a lower flexible diaphragm 1 8. The entire space between this and an upper flexible diaphragm 20 forms a suction chamber, indicated at 19. The suction chamber 1 9 communicates, as already mentioned, with the induction pipe 2 of the engine through the connection 24 and through the control line 10 shown in Figure 1. Under the lower diaphragm 18, as shown in Figure 2, the guide pan 14 contains an atmospheric chamber 22, and above the upper diaphragm 20, under a cover 23, there is a further atmospheric chamber 21. The suction chamber 19 is contained in a housing 34.The upper diaphragm 20 has a centrepiece 28 into which is screwed a slider tube 26, which is adjustable in position axially, relative to the centrepiece 28, by screwing in and out. The slider tube 26 moves up and down, with the movements of the upper diaphragm 20, in a lower guide 25 fixed to the housing 34. Screwed into the slider tube 26 is adjustment screw 27, which is adjustable in position axially, relative to the slider tube 26, by screwing in and out. The upper diaphragm 20 is retained between two diaphragm plates 29, 30 of the centrepiece 28. The lower end of the adjustment screw 27 passes freely through a central bore in a thrust plate 33, which thrusts upwards against the lower end of the -slider tube 26.Thrusting upwards against the lower diaphragm plate 29 of the upper diaphragm 20 is an upper compression spring 32, whose lower end takes support of a shoulder of the housing 34. Thrusting upwards against the thrust plate 33 is a lower compression spring 31, whose lower end takes support on the upper diaphragm plate 17 of the lower diaphragm 18. It will be observed that both the springs 32 and 31 act against any reduction in volume of the suction chamber 1 9. Furthermore, when the control valve 8 is at rest, ie when the parts are in the positions shown in Figure 2, the upper spring 32 holds the upper diaphragm plate 30 of the upper diaphragm 20 in contact with the cover 23, the lower spring 31, thrusting downwards, holding the conical valve head 11 down against its seat 12.

The installed axial length of the spring 31 of the lower diaphragm 18, with the conical valve head 11 resting on its seat 12 and with the diaphragm plate 30 resting in contact with the cover 23, is adjustable by screwing the slider tube 26 in and out of the centrepiece 28; the installed axial length of the spring 32, with the diaphragm plate 1 7 resting in contact with the shoulder of the housing 34, and with the screw 27 in contact with the valve stem 13, is adjustable by screwing the adjustment screw 27 in and out in the slider tube 26.

Let it be assumed, to begin with, that the engine 1 is idling. Under these circumstances there is a high degree of suction in the induction pipe of the engine, downstream of the throttle valve, and this suction is transferred, through the control line 10, and the connection 24, to the suction chamber 1 9 of the control valve 8, ie the absolute pressure in the suction chamber 1 9 is very low. Atmospheric pressure in the upper atmospheric chamber 21 therefore drives the upper diaphragm 20, which has the larger working area, downwards until the nose of the screw 27 makes contact with the upper end of the valve stem 13, the screw 27 subsequently holding the conical valve head 11 firmly down against the valve seat 12. No exhaust gas flows through the return line 6.

If the throttle valve 4 is now opened, so that the engine develops higher torgue, the absolute pressure in the induction pipe 2, and therefore in the suction chamber 19, rises. This lifts the two diaphragms 20 and 1 8 and lifts the conical valve head 11 off its seat 12, allowing exhaust gas to flow through the return line 6 into the induction pipe 4. The control valve 8 continues to open until the upper diaphragm plate 1 7 of the lower diaphragm 18 makes contact with the shoulder of the housing 34.

With further opening of the throttle 4 the increasing pressure in the suction chamber 19 allows the lower spring 31 to drive the lower diaphragm 1 8 downwards, driving the conical valve head 11 once more into contact with its seat 12 and closing the exhaust-gas-return control valve 8.

Claims

1. Control device for an exhaust-gas return system for internal combustion engines, the system comprising a carburettor, a driveractuated throttle valve and an exhaust-gas return line extending from the exhaust pipe to the induction pipe of the engine and by-passing the combustion chamber, the return line having a pneumatically actuated control valve responsive to the degree of suction in the induction pipe, downstream of the throttle valve and controlling the flow of returned exhaust gas in such a way that:: when the engine is idling no exhaust gas is returned, with increasing engine torque exhaust gas is returned proportionately, but at full torque, no exhaust gas is returned, the control device being characterised in that the control valve 8, which controls the flow of exhaust gas through the return line 6 and has a conical valve head 11 cooperating with a valve seat 12, has two flexible diaphragms 18, 20 enclosing between them a suction chamber 1 9 which communicates through a control line 10 with the induction pipe 2 of the engine; the outside surfaces of the diaphragms 1 8, 20 being subjected to atmospheric pressure; the upper diaphragm 20 having a greater working area than the lower diaphragm 18; and in that diaphragm plates 1 6, 17 of the lower diaphragm 18 are fixed to the valve stem 13 of the conical valve head 11; a compression spring 31 thrusting downwards on the upper plate 1 7 of the lower diaphragm 18, the spring 31 acting against any reduction in the volume of the suction chamber 10; the upper end of the compression spring 31 acting to lift a thrust plate 33 upwards against the lower end of a slider tube 26, which is axially adjustable in position in a centrepiece 28 of the upper diaphragm 20; the centrepiece 28 retaining the two diaphragm plates 29, 30 of the upper diaphragm 20; and in that a compression spring 32 thrusts upwards against the lower diaphragm plate 29 of the upper diaphragm 20, the lower end of the spring 32 taking support on a shoulder of the housing 34 of the suction chamber 19;this spring 32 also acting against any reduction in the volume of the suction chamber 1 9.

2. Control device as claimed in Claim 1 characterised in that the installed axial length of the spring 31 of the lower diaphragm 1 8 of smaller working area, with the conical valve head 11 resting on its seat 12 and with the upper diaphragm plate 30 of the upper diaphragm 20 of greater working area resting in contact with the cover 23, is adjustable, by screwing the slider tube 26 in and out of the centrepiece 28; while the installed axial length of the spring 32 of the upper diaphragm 20 of greater working area, with the upper plate 1 7 of the lower diaphragm 18 resting in contact with the shoulder of the housing 34 of the suction chamber 1 9 and with the nose of the adjustment screw 27 resting in contact with the upper end 1 5 of the valve stem 13, is adjustable, by screwing the adjustment screw 27 in and out of the slider tube 26.

3. Control device substantially as described with reference to the accompanying drawings.