GB2139284A - Apparatus for controlling the return of exhaust gases into the induction pipe of an internal combustion engine - Google Patents

Abstract

The gas-return valve 7 comprises a valve with a valve-head and a valve-stem. A spring-loaded diaphragm 9 is fixed to said valve stem, and on one face of the diaphragm there acts, in suction chamber 11, a suction derived through a transfer duct 13 from a pneumatic controller 14. The pneumatic controller 14 has two chambers 23, 24 separated by a diaphragm 19, the first chamber 24 of which communicating, firstly and permanently, with the transfer duct 13 and, secondly and alternatively in dependence upon, and as governed by, differences in instantaneous pressure, either, with the induction pipe 2 at a location upstream of the throttle valve 3, or, with atmosphere; the second chamber 23 being in permanent communication with a location on the downstream side of the throttle valve 3. In this way the pressures transmitted to the valve 7 through the transfer duct 13 from the pneumatic controller 14 are governed by differences in instantaneous pressures at locations on the upstream and downstream sides, respectively, of the throttle valve 3 in the engine induction passage. <IMAGE>

Description

SPECIFICATION Apparatus for controlling the return of exhaust gases into the induction pipe of an internal combustion engine The invention relates to apparatus for controlling the return of exhaust gases into the induction pipe of an internal combustion engine, with a gas-return valve interposed in an exhaust gas recirculation pipe.

The intention, in the operation of control devices of this kind, is to control the flo of the exhaust gas in dependence of engine load (the torque delivered by the engine), with a view to reducing the emission of toxic substances, particularly oxides of nitrogen, hydrocarbons and CO, into the surrounding atmosphere.

The beneficial effects of refluxing the ex- haust gases through the engine are well known and a variety of control devices are already known which can be installed in motor vehicles for this purpose.

The German Offenlegungsschrift 23 62 359 describes a very simple control device comprising a gas-return valve interposed in a gas-return passage, and a venting valve for communication with the external atmosphere, the venting valve being controlled by the throttle valve of the carburettor. A suction chamber communicating with the induction pipe is limited by a diaphragm which controls the gas-return valve. The venting valve controls the pressure in this chamber so that the exhaust gas is returned in the desired manner.

The German Patent Specification 23 1 5 734 describes a control device whose gasreturn valve is controlled by a diaphragm which is acted on by a pressure intermediate between induction-pipe pressure and atmospheric pressure, the intermediate pressure being controlled by a control valve responsive to exhaust-gas pressure.

Other control devices zre known for controlling exhaust-gas reflux to the engine, for example the device of the German Patent Specification 25 28 760. But this known device has a gas-return valve equipped with several diaphragms which require careful adjustment. Constructions of this kind are far more expensive to manufacture than those which have only one diaphragm.

On the other hand, the simpler constructions which are less expensive to manufacture have certain disadvantages which can impair the process of detoxicification and upset the good functioning of the engine. One source of trouble is wear in the venting valve resulting in incorrect control of the flow of returned gas. This is particularly troublesome when the engine is idling or operating in the near-idling condition. The proportion of air in the mixture in the induction pipe is falsified, upsetting the correct functioning of the carburettor, causing engine speed to fluctuate during idling and falsifying the composition of the exhaust gas.

The intention of the present invention is therefore to provide a control device which is free from three disadvantages.

Broadly stated the present invention provides apparatus for controlling recirculation of exhaust gases to the induction pipe of an internal combustion engine, with a gas-return valve interposed in an exhaust gas-return passage and comprising a valve with a valve-head and a valve-stem, the apparatus including, fixed to said valve stem, a spring-loaded valve diaphragm on one of whose faces there acts, in a suction chamber, a suction derived through a transfer duct from a pneumatic controller; and including means whereby the pressures transmitted through the transfer duct from the pneumatic controller are governed by differences in instantaneous pressure at locations on the upstream and downstream sides, respectively, of a driver controlled throttle valve in the induction passage of the engine.

The invention has the advantage that the gas-return valve has only one diaphragm, which does not suffer abrasion and which cannot falsify the proportion of air in the combustible mixture in the induction pipe.

Consequently engines speed does not fluctuate during idling and the proportion of CO in the exhaust gases remains constant over long periods.

The invention will now be described in greater detail with the help of the example shown in the drawing, in which: Figure 1 shows an internal combustion engine equipped with the control device of the invention.

Figure 2 is a section through the pneumatic controller, which is also shown in Fig. 1.

The engine 1 has an induction pipe 2 containing a throttle valve 3 which can be, for example, part of a carburettor (not shown) and the engine 1 has an exhaust pipe, shown at 4. A gas-return passage 5 branching away from the exhaust pipe 4 communicates with the induction pipe at a location 6 downstream of the throttle valve 3 and contains a gasreturn valve 7 for controlling the flow of exhaust gas returned to the engine. The gasreturn valve 7 comprises a valve-head 8 whose valve-stem is fixed to a spring-loaded valve diaphragm 9 contained in a housing 10.

The diaphragm 9 separate a lower atmospheric chamber from an upper chamber 11 to which suction can be applied. The diaphragm spring 12 in the suction chamber 11 thrusts the diaphragm 9 downwards, tending to close the gas-return valve 7. Suction in the upper chamber 11, above the diaphragm 9, tends to open the gas-return valve 7 against the influence of the spring 12.

The suction chamber 11 of the gas-return valve 7 communicates, through a transfer duct 13, with a pneumatic controller 14. The pneumatic controller 14 communicates through an upper duct 1 6 with the induction pipe 2 at a location 6 downstream of the throttle valve 3, and through a lower duct 1 5 with the induction pipe at a location upstream of the throttle valve 3. It will be observed that when the throttle valve 3 is opened the pressure at location 1 7 approaches equality with the pressure at location 6, which can be called "the induction pipe pressure".It can therefore be said that when induction pipe pressure is transmitted to the pneumatic controller 14, this can take place not only through the upper duct 16, but also through the lower duct 15, to a degree depending on the opening of the throttle valve 3.

The pneumatic controller 14, shown best in Fig. 2, has a housing 18 containing three chambers 22, 23, 24 separated by two diaphragms 20 and 19. The two diaphragms 20 and 1 9 are joined together by a rigid connecting piece 21, so that they move up and down together.

The upper chamber 22 communicates with the external atmosphere. The middle chamber 23 communicates through the upper duct 1 6 with the induction pipe 2 at the location 6 downstream of the throttle valve 3. The lowerchamber 24 communicates through the lower duct 1 5 with the induction pipe 2 at the location 1 7 upstream of the throttle valve 3, the lower chamber 24 also communicating with the suction chamber 11 of the gas-return valve 7 through the transfer duct 1 3.

A spring 25 in the lower chamber 24 thrusts the connecting piece 21, and therefore the two diaphragms 20, 19 upwards the atmospheric chamber 22. At its lower end the spring 25 is supported by a wedge-shaped support 32 which is adjustable in height with the help of a screw 33.

The connecting piece 21 is a hollow cylinder with an inner passage 28 whose base forms a valve-seat 26 for a spring loaded valve-plate 27 whose spring 30 thrusts the valve-plate 27 down towards its valve-seat 26. The upper end of the inner passage 28 is limited by an inserted filter 29, through which the inner passage 28 communicates with the external atmosphere.

Of the two diaphragms 1 9 and 20, the upper one 20 has the greater working area.

When the device is at rest, i.e. when the middle chamber 23 contains atmospheric pressure, the parts of the device are in the positions shown in Fig. 2, the valve-plate 27 resting in contact with its valve-seat 26, obturating the inner passage 28.

If suction is now applied to the middle chamber 23, i.e. if the pressure here drops below atmospheric pressure, then the atmospheric pressure acting on the upper chamber 22 thrusts the upper diaphragm 20 (of larger working area) downwards, the two diaphragms 20 and 19 moving downwards to gether, against the influence of the lower spring 25, and with further lowering of the pressure the valve plate 27 comes into con tact with the mouth 31 of the lower duct 15, obturating this duct. With still further lowering of the pressure the valve plate 27 is lifted from its valve-seat 26, against the influence of the upper spring 30, putting the lower cham ber 24 into communication with the external atmosphere.

When the engine is idling the pressure in the induction pipe 2 at the location 6, down stream of the throttle valve 3, is below atmo spheric pressure, this low pressure being transmitted through the upper duct 16 to the middle chamber 23 of the pneumatic control ler 14. Due to the fact that the upper dia phragm 20 has a larger working area than the lower diaphragm 19, the two diaphragms move downwards, against the influence of the lower spring 25, bringing the valve-plate 27 into contact with the mouth 31 of the lower duct 15, obturating this duct.

With further downwards movement of the two diaphragms 20, 1 9 and of the connecting piece 21, the valve-plate 27 is lifted off its valve-seat 26, putting the middle chamber 23 and therefore, through the transfer duct 13, the suction chamber 11 of the gas-return valve 7, into communication with the external atmosphere, so that no exhaust gas returns to the engine 1 through the gas return passage 5.

On the other hand, when the engine is running at full load (i.e. with the throttle valve wide open), the induction pipe pressure at the location 6, and thereforte in the middle cham ber 23, is not low enough to overcome the upwards thrust of the lower spring 25 and consequently, this spring lifts the connecting piece 21, lifting the valve-plate 27 out of contact with its valve-seat 26. Under these circumstances the lower chamber 24 no lon ger contains atmospheric pressure which now exists in the lower duct 1 5 due to the fact that the pressure at the location 1 7 now approaches equality with the pressure at the location 6.

This induction-pipe pressure also acts, through the transfer duct 1 3, in the suction chamber 11 of the gas return valve 7, but it is not low enough to overcome the influence of the diaphragm spring 1 2 and consequently the gas-return valve 7 is in its closed position.

Finally, when engine load is gradually re duced (i.e. the throttle valve 3 is gradually closed towards more and more moderate values, induction-pipe pressure decreases, so that the diaphragm 11 moves upwards against the influence of the spring 12, open ing the gas-return valve 7 more and more, as determined by the spring characteristics, up to a maximum.

When the engine is operating at moderate loads the connecting piece 21, moving down wards with decreasing induction -pipe pressure, produces an intermediate pressure partway between induction-pipe pressure and atymospheric pressure, the intermediate pressure increasing with decreasing induction-pipe pressure until the spring 1 2 in the gas-return valve 7, overcoming the lifting influence of the diaphragm, closes the gas-return valve 7.

Claims (5)

1. Apparatus for controlling recirculation of exhaust gases to the induction pipe of an internal combusgion engine, with a gas-return valve interposed in an exhaust gas-return passage and comprising a valve with a valve-head and a valve-stem, the apparatus including, fixed to said valve stem, a spring-loaded valve diaphragm on one of whose faces there acts, in a suction chamber, a suction derived through a transfer duct from a pneumatic controller; and including means whereby the pressures transmitted through the transfer duct from the pneumatic controller are governed by differences in instantaneous pressures at location on the upstream and downstream sides, respectively, of a driver controlled throttle valve in the induction passage of the engine.

2. Apparatus according to claim 1, and wherein the pneumatic controller has two chambers separated by a diaphragm, and wherein a first chamber of the pneumatic controller communicates firstly and permanently with the transfer duct and secondly, and alternatively, in dependence upon, and as goverened by, the said differences in instantaneous pressure either with the induction pipe at a location upstream of the throttle valve, or, with atmosphere; and wherein the second chamber of the pneumatic controller is in permanent communication with a location on the downstream side of the throttle valve.

3. Apparatus according to claim 2, wherein the diaphragm which separates the two chambers, is connected by a rigid hollow connecting piece to a second diaphragm which has a greater working area than the first diaphragm; one face of the second diaphragm being acted on, against the influence of a spring which is adjustable in position, by atmospheric pressure; and wherein the connecting piece contains a valve plate urged by a spring towards a valve seat, the connecting piece and the valve plate firstly; cooperating with the vlve seat which terminates an inner passage of the connecting piece, the inner passage communicating with the external atmosphere, and secondly; controlling the mouth of a duct which provides intercommunication betweenthe first chamber of the controller and the induction passage at a location on the upstream side of the throttle valve.

4. Apparatus as claimed in Claim 3, and wherein the spring is adjustable in position by meas of a wedge-shaped spring support cooperating with an inclined surface and held in position be an adjustment screw.

5. Apparatus according to claim 1, and substantially as described with reference to the accompanying drawings.