GB2089895A - Valve control of carburettor idling mixture systems - Google Patents

Abstract

A valve 12 opens to permit idling mixture flow to downstream of the carburettor throttle valve when its actuator diaphragm 37 is subject through an inlet 15 to the suction downstream of the throttle valve which occurs at idling. At lower and higher suctions the valve cones 32, 33 engage the seats 30, 31.The inlet 15 is connected, under the control of a selector valve (20), Fig. 1 (not shown), to the carburettor induction passage by a first passage (16) having inlets (17, 18) both of which are downstream of the throttle valve when closed but one of which becomes upstream when the throttle valve is opened or to a second passage (21) opening to the induction passage inlet or the atmosphere. The selector valve may be operated by an electromagnetic or suction actuator. The valve 12 closes at overrunning and when the ignition is switched off. <IMAGE>

Description

SPECIFICATION Carburettor The invention relates to a carburettor for internal combustion engines, with at least one main mixture-forming system for forming a fuel-air mixture whose rate of flow is controlled by a driver-actuated throttle valve situated in the induction pipe, and with an auxiliary mixtureforming system for forming an engine-idling mixture whose rate of flow depends on the setting of an adjustment screw and on the position of a valve which controls the flow of idling mixture through a mixture outlet into the induction pipe at a location downstream of the throttle valve.

Carburettors of this kind are required for internal combustion engines which are used mainly in motor vehicles.

In order to give the vehicle good behaviour on the road, with economical operation and a low concentration of toxic substances in the exhaust gases, the carburettor must be of high quality and must function efficiently. This requires that it must be equipped with special systems for the different modes of operation of the engine, in particular for starting, warming up, idling, medium power and full power operation.

A carburettor known from the German Offenlegungsschrift 19 64 766 has an auxiliary mixture-forming system for supplying combustible mixture to the engine when it is idling. During overrunning operation (i.e. when the vehicle is driving the enginer), when no mixture flows through the main mixture-forming system, an electromagneticaliy actuated valve interrupts the flow of mixture through the auxiliary mixtureforming system, in order to reduce the emission of unburnt hydrocarbons in the exhaust gases. But this carburettor produces an unpleasantly jerky operation of the engine, particularly at the beginning of overrunning. In attempting to remedy the matter, ignition is switched off.But in practice the abrupt and repeated engagement and disengagement of the auxiliary mixture-forming system, for example during a long downhill run at engine speeds in the region of the chanye-over point, produced abrupt changes in vehicle speed which the driver finds very unpleasant. A further disadvantage is that at the end of the journey the electromagnetically actuated valve cannot prevent the engine from "dieseling" (running on) after the ignition has been switched off, because switching off the ignition deprives the valve of electric current and consequently it cannot close.

The intenion in the present invention is therefore to equip a carburettor of the kind mentioned at the beginning with a device for interrupting the flow of combustible mixture through the auxiliary mixture-forming system, the device being less costly to manufacture than the previous electromagnetic device. It must function without it being necessary to switch the ignition on and off. It must not cause the engine to operate jerkily and it must prevent the engine from "dieseling" after ignition has been switched off.

Finally, the device must be compact in dimensions and simple in construction.

Starting out from a carburettor of the kind mentioned at the beginning, the problem is solved by the characteristics claimed in Claim 1. Further advantageous developments of the invention are described in the subsidiary claims. The advantages obtained are as follows: 1. The entire arrangement is constructively simple and compact.

2. The auxiliary mixture-forming system has a wide field of application and allows considerable adjustment in the vehicle factories.

3. The control device can be added to existing carburettors which are already equipped with auxiliary mixture-forming systems.

4. The arrangement for interrupting the flow of idling mixture can be used not only for overrunning operation of the engine but also for preventing "dieseling".

5. The control device, used in conjunction with a 2-way selector valve and a constricted orifice, ensures that the engine operates smoothly, i.e. not jerkily.

The invention will now be described in greater detail with the help of the example represented diagrammatically in the drawing, in which: Figure 1 is a section through the carburettor.

Figure 2 is a section through the double-action controller valve.

The carburettor shown in Figure 1 is assumed to be equipped with all the appropriate systems, although only those necessary for understanding the invention are shown here. The carburettor 1 has a main mixing-forming system 2, with a main mixture outlet 3 situated in a venturi-like portion 4 of the induction pipe. Downstream of this is a throttle valve 5 for actuation by the drive of the vehicle. In addition, the carburettor also has an auxiliary mixture-forming system 6 for when the engine is idling, with a mixture outlet 29 situated in the induction pipe at a location 8 downstream of the throttle valve 5.

The auxiliary mixture-forming system 6 comprises a by-pass channel 9 equipped with means for forming a fuel-air mixture, two conical nosed adjustment screws 7 and 10 for adjusting the fuel-to-air ratio of the mixture flowing through the by-pass channel 9, and for adjusting its rate of flow, and a double-action controller 11 for opening and closing the mouth of the mixture outlet 29 through which the by-pass channel 9 communicates with the induction pipe at the location 8 downstream of the throttle valve 5.

The double-action controller 11 comprises a double valve-head 12 actuated, through a valve rod 34, by a pneumatic positioner 1 3 whose flexible diaphragm 37 separates a working chamber 14 from an atmospheric chamber 39.

The working chamber 14 communicates through a connector 15, through a first line 1 6 containing a 2-way selector valve 20 and through two passages 17, 18 with the induction pipe of the carburettor. Of these two passages, the first 1 7 constantly communicates with the induction pipe at the location 8 downstream of the throttle valve 5. The second 18 8 of the two passages, on the other hand, communicates with the induction pipe at a location which is downstream of the throttle valve 5 when this is closed (i.e. in the region 8) but upstream of it when the throttle valve is open (i.e.

now in the region 19).

Alternatively, when the 2-way selector valve 20 is switched over, the working chamber 14 communicates through the connector 15, through the 2-way selector valve 20 and through a line 21 containing a constricted orifice 22 with the induction pipe in the region 1 9 upstream of the throttle valve 5, or directly with the external atmosphere. The 2-way selector valve 20 can be actuated by an electromagnetic actuator 24 responsive either to the clutch and gearbox of the vehicle, or to the ignition switch and engine speed.

Alternatively, if desired, the 2-way selector valve 20 can be actuated by a pneumatic actuator 23 responsive to the absolute pressure in the induction pipe in the region 8 downstream of the throttle valve 5.

The double action controller 11, shown sectioned in Figure 2, includes the valve 12 which opens and cioses the mouth of the mixture outlet 29 through which idling mixture leaves the bypass channel 9 to flow into the induction pipe at the location 8 downstream of the throttle valve 5.

In its lower portion the by-pass channel 9 communicates with a transverse channel 28 and this in turn communicates with a channel 26, which itself communicates through a passage 25 with the idling mixture outlet 29. Flow of mixture through the passage 25 is controlled by the valve 12. This has two valve-head cones 32, 33 cooperating with valve seats 30, 31. The valve rod 34, which is fixed to the double head valve 12, slides back and forth in the housing 27 of the double-action controller 11.

Fixed to the other end of the valve rod 34 are two diaphragm plates 35, 36 which retain between them a diaphragm 37 which separates the atmospheric chamber 39 contained in the housing 27 from the working chamber 14 which is contained in a housing cover 38. There are two compression springs 40 and 42. The first spring 40 acts between a shoulder of the cover 38 and the inner diaphragm plate 36.

When there is no suction in the working chamber 14, this spring 40 thrusts the inner valve head cone 32 into contact with its seat 30. The second compression spring 42 thrusts against a plug in the base of the cover 38 and against the base of a hollow slider 41 which slides back and forth in the cover 38, forwards movement of the slider 41, in the direction of the double head valve 12, being limited by contact between a shoulder 43 of the slider 41 and a step of the cover 38. The thrusts of the two springs 40 and 42 are related to each other in such a way that when a moderate suction is applied to the working chamber 14, atmospheric pressure in the chamber 39 lifts the cone 32 off its seat 30 until the inner diaphragm plate 36 makes contact with the forward nose of the hollow slider 41.With greater suction in the working chamber 14, the inner diaphragm plate 36 thrusts the slider 41 backwards, compressing its spring 42 and lifting its shoulder 43 off the step of the cover 38, until the outer valve-head cone 33 makes contact with its seat 31.

The arrangements illustrates functions as follows: When ignition is switched on, electric current flowing over the electromagnetic actuator 24 sets the 2-way selector valve 20 so that the working chamber 14 communicates through the line 16 and the passages 1 7, 1 8 with the induction pipe in the region 8 downstream of the throttle valve 5.

Consequently when the engine starter is engaged suction in the working chamber 14 lifts the inner valve cone 32 off its seat, against the influence of the first spring 40, until the inner diaphragm plate 36 makes contact with the nose of the slider 41.

Idling mixture therefore flows through the mixture outlet 29 into the induction pipe, allowing the engine to idle.

When the vehicle is overrunning the engine, with the throttle valve 5 in its fully closed position, a still greater degree of suction occurs in the working chamber 14, compared with engine-idling operation, and consequently atmospheric pressure in the chamber 39 thrusts the diaphragm 37 still further back, thrusting now against the influence of spring 42 as well as against spring 40, the slider 41 sliding back, so that the double valvehead 1 2 retracts, towards the right in Figure 2, until the outer cone 33 makes contact with its seat 31 , closing the passage 25. If the driver now opens the throttle valve 5, so that the engine delivers a driving torque, the pressure in the region 19 of the induction pipe, upstream of the throttle valve 5, reaches the working chamber 14 through the passage 18.Consequently the outer cone 33 now lifts away from its seat 31, allowing idling mixture to flow through the mixture outlet 29 into the induction pipe.

Supposing now that with the vehicle overrunning the engine, the throttle valve 5 being in its closed position, vehicle speed, and therefore engine speed, decreases until engine-idling speed is obtained. Under these circumstances the absolute pressure in the working chamber 14 increases until, at engine-idling speed, the outer valve cone 33 lifts from its seat 31, flowing idling mixture to flow through the mixture outlet 29 into the induction pipe in the region 8, and allowing the engine to idle. Finally, supposing that now ignition is switched off. This deprives the electromagnetic actuator 24 of current, with the consequence that the 2-way selector valve 20 switches over from the line 1 6 to the line 21, so that the working chamber 14 now communicates with the induction pipe upstream of the throttle valve 5, or communicates directly with the external atmosphere. The increased absolute pressure in the working chamber 14 drives the inner cone 32 into contact with its seat 30, preventing idling mixture from flowing through the mixture outlet 29 and preventing the enging from "dieseling", i.e. bringing the engine reliably to a stop.

Alternatively, the electromagnetic actuator 24 can, if desired, be arranged so that during decelerative overrunning, when engine speed drops to idling speed the electromagnetic actuator 24 responds to disengagement of the clutch, or to movement of the gear lever into neutral, by switching the 2-way selector valve 20 partly over from line 1 6 to line 21. This raises the absolute pressure in the working chamber 14 enough to lift the outer cone 33 off its seat, allowing the engine to idle. Under these circumstances the compression springs 40 and 42 can be selected to apply less thrust. The advantages obtained are that towards the end of decelerative overrunning, -when engine speed drops to idling speed the opening of the mixture outlet 29, to allow the engine to idle, is delayed by the effect of the constricted orifice 22 in the line 21, with the result that the transition from decelerative overrunning to idling takes place smoothly, i.e. without inconvenient jerks.

During engine-idling, when ignition is switched off this deprives the electromagnetic actuator 24 of current so that the flow of idling mixture is interruped and "dieseling" of the engine is prevented, as described before.

Pneumatic control of the 2-way selector valve 20 is a variant of the invention.

Claims (6)

1. A carburettor for internal combustion engines, with at least one main mixture-forming system for forming a fuel-air mixture whose rate of flow is controlled by a drive-actuated throttle valve situated in the induction pipe, and with an auxiliary mixture-forming system for forming an engine-idling mixture whose rate of flow depends on the setting of an adjustment screw and on the position of a valve which controls the flow of idling mixture through a mixture outlet into the induction pipe at a location downstream of the throttle valve, characterised in that the valve (12) is actuated by a pneumatic positioner (13) which closes the valve (12) whenever the absolute pressure in the working chamber (14) of the pneumatic positioner (13) exceeds or falls below the induction-pipe pressure, measured downstream of the throttle valve (5), corresponding to engine idling;; the working chamber (14) communicating through a line (16) and through two passages (17, 18) with the induction pipe of the carburettor; the first passage (17) being located in a region (8) of the induction pipe downstream of the throttle valve (5); the second passage (18) being located where it is downstream of the throttle valve (5) when this is closed but upstream of it, in another region (19) of the induction pipe, when the throttle valve (5) is open.

2. A carburettor as claimed in Claim 1, and in which the line (1 6) contains a 2-way selector valve (20) capable of switching over so that the working chamber (14) now communicates through a line (21), containing a constricted orifice (22), with the induction pipe in a region (19) upstream of the throttle valve (5).

3. A carburettor as claimed in Claim 2, and in which the 2-way selector valve (20) is actuated by a pneumatic actuator (23) responsive to the absolute pressure in the induction pipe in a region (8) downstream of the throttle valve (5).

4. A carburettor as claimed in Claim 2, and in which the 2-way selector valve (20) is actuated by an electromagnetic actuator (24) which responds either to the positions of the ignition switch and the clutch lever or gear lever, or to the position of the ignition switch and to engine speed.

5. A carburettor as claimed in Claim 1, wherein the valve (12) forms a structural unit (11) with the pneumatic positioner (13), the structural unit (11) having transverse channels (28) communicating with a channel (26) leading to a passage (25) which terminates in a mixture outlet (29); the flow of idling mixture through the passage (25) being controlled by two valve-head cones (32, 33) which cooperate with valve seats (30, 31); the valve-head cones 132,33) being fixed to a valve rod (34) which moves back and forth in the housing (27) of the pneumatic positioner (13); the other end of the valve rod (34) being fixed to the two diaphragm plates (35, 36) of a diaphragm (37) which separates a working chamber (14) of the cover (38) from an atmospheric chamber (39) of the housing (27); a first compression spring (40) thrusting against a shoulder of the cover (38) and against the inner plate (36) of the diaphragm (37) so as to thrust the inner valve--head cone (32) against its seat (30) when there is no suction in the working chamber (14); a second compression spring (42) thrusting against the cover (38) and a hollow slider (41) mounted to slide back and forth in the cover (38), so as to thrust the slider (41) forwards towards the diaphragm (37), this forwards movement being limited by contact between a shoulder (43) of the slider (41) and a step of the cover (38); the thrusts applied by the two springs (40, 42) being selected so that: : - moderate suction in the working chamber (14) lifts the inner valve-head cone (32) off its seat (30), until the inner diaphragm plate (36) makes contact with the forward nose of the slider (41), and so that - increased suction brings the slider (41) back, its shoulder (43) lifting off the step of the cover (38), until the outer valve-head cone (33) is retracted by the diaphragm (37) into contact with its valve seat (31).

6. A carburettor according to any of Claims 1 to 5 and substantially as described with reference to the accompanying drawing.