GB2167134A - Carburettor choke valve actuation - Google Patents

Abstract

The choke valve 3 is opened against a temperature dependent force by an actuator 4 having a pressure chamber 22 connected by a passage 13 to the passage 2 downstream of the throttle valve 10. A valve 27 connects the chamber 22 to a passage 15 when the valve is operated after initial movement of the rod 5 to provide choke valve opening a. A valve 16 operated in dependence on time from engine starting and engine and air intake temperatures connects the passage 15 to either the passage 17 or 18, 19. Connection to the passage 18, 19 provides greater choke valve opening (a1, Fig. 3). <IMAGE>

Description

SPECIFICATION Carburettor for internal combustion engines The invention relates to a carburettor for internal combustion engines with a controlled choke-valve, which is part of an engine-starting device, mounted to pivot eccentrically in the induction passage, the choke-valve being pivoted in the opening direction, against the influence of a flexible thermal positioner, by the current of aspirated air and by a pneumatic positioner which communicates, through a first channel, with the induction passage downstream of the throttle valve, the pneumatic positioner also having a second channel whose flow-cross-section is controlled, in dependence on the movements of the pneumatic positioner, by a valve for obtaining a 2-stage positioning movement.

Carburettors are known in which the controlled choke-valve is opened in successive stages by pneumatic positioners, to agree with different engine-operating conditions.

Thus from the German Offenlegungsschrift 22 20 988 it can be derived that just after engine starting, the best fuel-air mixture is obtained by first rapidly opening the choke-valve to a partly open position and then, after holding this setting for a period of time, slowly opening the choke-valve to a second predetermined position.

The German Offenlegungsschrift 24 17 449 describes a device which is intended to give optimal adaptation of mixture to engine requirements during acceleration after starting.

For this purpose the pneumatic positioner has two flexible disphragms. A first change in the pneumatic positioner occurs when one of the diaphragms is subjected, just after the engine starts, to suction taken from the induction passage at a location downstream of the throttle valve. Subsequently, when the throttle valve opens more to give more torque, a second change occurs in that a control drilling which had been located upstream of the throttle valve, in the induction channel, when the throttle valve was in its engine-idling position, now comes to be located downstream of the throttle valve, with the result that suction now also acts on the second diaphragm, causing the pneumatic positioner to shift.

This known device has the disadvantage that the control drilling has to be situated far enough away from the rim of the closed throttle valve to ensure that the throttle valve can open sufficiently for starting the engine, compared with its engine-idling position, without the control drilling coming to be downstream of the throttle valve, as otherwise the chokevalve is opened too far by the second shift.

On the other hand the German Offenlegungsschrift 22 02 988, already mentioned above, suggests nothing that could bring about a further opening of the choke-valve when the engine accelerates.

The intention in the present invention, starting from the kind of caburettor mentioned at the beginning, is to provide a device which opens the choke-valve as soon as the throttle valve opens even by a little, i.e. even before the throttle valve has opened to its full starting position.

The problem is solved by the provision of a carburettor for internal combustion engines with a controlled choke-valve, which is part of an engine-starting device, mounted to pivot eccentrically in the induction passage, the choke-valve being pivoted in the opening direction, against the influence of a flexible thermal positioner, by the current of aspirated air and by a pneumatic positioner which communicates, through a first channel, with the induction passage downstream of the throttle valve, the pneumatic positioner also having a second channel whose flow-cross-section is controlled, in dependence on the movements of the pneumatic positioner, by a valve for obtaining a 2-stage positioning movement, and in which, according to this invention, the second channel communicates, through a two-position 3-way valve which responds to engineoperating conditions, either with the induction passage upstream of the choke-valve or, when the 3-way valve is switched over, through a control drilling, with the induction passage at a location which is upstream of the throttlevalve when this is in its engine-idling position but downstream of the throttle-valve when this is opened.

This arrangement controls the combustible mixture in very accurate agreement with engine requirements, preventing excessive enrichment in the low-torque operation of a cold engine.

This improves the behaviour of the vehicle on the road, economises fuel and can, under certain circumstances, reduce obnoxious exhaust emissions. Moreover, the known pneumatic positioner can be adapted for use in the invention, favouring series manufacture and simplifying the keeping of stocks.

A practical example of the invention is shown in the drawing, and this will now be described in greater detail.

Figure 1 is a section through the carburettor.

Figures 2 and 3 show the pneumatic positioner of the carburettor of Fig. 1.

Fig. 1 shows a carburettor 1 with a controlled choke-valve 3 mounted to pivot eccentrically in the induction passage 2. The chokevalve 3 is part of a known kind of starting device which need not be described in detail here. The choke-valve 3 is pivoted towards a more open position by the current of air, against the influence of a flexible thermal positioning device (not shown). The choke-valve 3 is also influenced to open more by the pneumatic positioner 4 shown in Figs. 2 and 3.

The pneumatic positioner 4 acts, to open the choke-valve 3 more, through a pull-rod 5, a rocking lever 6, a connecting rod 7 and a lever 9, the lever 9 being fixed to the pivotshaft 8 to which the choke-valve is also fixed.

The pneumatic positioner 4 opens the chokevalve 3 more when low pressure occurs in the induction passage 2 downstream of the throttle valve shown at 10, which can be actuated at will by the operator of the engine.

A main fuel-supply system 11 communicates with the induction passage 2 at a location downstream of the choke-valve 3, an idling fuel supply system 12 communicating with the induction passage 2 at a location downstream of the throttle valve 10 is shown in full lines in its engine-start position, and in broken lines in its normal engine-idling position.

A first channel 13 leading directly to a first connection on the pneumatic positioner 4 branches off from the induction passage 2 at a location downstream of the throttle valve 10. From a second connection 14 on the pneumatic positioner 4, a second channel 15 leads to a two position 3-way valve 16 which responds to engine-operating conditions.

When the 3-way valve 16 is in its first position the channel 15 communicates, through the 3-way valve 16, with a channel 17 which communicates with the induction passage 2 at a point upstream of the choke-valve 3. When the 3-way valve 16 is in its other position the channel 15 communicates, through the 3-way valve 16, with a channel 18 which communicates, through a control drilling 19, with the induction passage 2 at a location which is downstream of the throttle-valve 10 when this in its engine-start position, but upstream of the throttle valve 10 when this is in its engine-idling position.

The pneumatic positioner 4, shown sectioned in Figs. 2 and 3, comprises a housing 20 which may be fixed to the carburettor and which contains a flexible diaphragm 21 to which is fixed the pull-rod 5. A cap 23 forms a suction chamber 22 behind the diaphragm 21. The forward face of the diaphragm 21, facing towards the right in Figs 2 and 3, is acted on by atmospheric pressure. When suction is applied in the suction chamber 22 this flexes the diaphragm 21 towards the left, pulling the pull-rod 5 towards the left and rocking the lever 6 anticlockwise. The connecting rod 7 rotates the lever 9 and the choke-valve shaft 8 anticlockwise, rotating the choke valve 3 itself anticlockwise. The diaphragm 21 is thrust towards the right by a spring 24, which thrusts against a diaphragm plate 25 of the diaphragm 21.

The pneumatic positioner 4 also contains an additional screwed-in valve 26 with a closure member 27 projecting forwards, i.e. towards the right, into the suction chamber 22, where it acts as a back-stop limiting leftwards move ment of the diaphragm 21. The closure mem ber 27 controls the flow-cross-section of a channel 28 leading from the suction chamber 22 to the second connection 14 for the chan nel 15, the channel 28 opening when induction-passage suction applied to the suction chamber 22 through the first channel 13 flexes the diaphragm 21 leftwards, against the spring 24, until the diaphragm plate 25 comes up against the closure member 27.

The opening of the channel 28 applies to the suction chamber 22, additionally, whatever pressure there may be in the channel 15, and this can be either high or low, depending on the switch-position of the two position 3-way valve 16, as determined by the action of a positioner 29, which responds to time elapsed after starting the engine, as well as to engine and air temperatures.

Before the cold engine is started, the known starting device has ensured that the choke valve 3 is held in its closed position by the flexible thermal positioner. The throttle valve 10 is in its engine-start position (full lines in Fig. 1). The 3-way valve 16 connects the channel 15 to the channel 17, i.e. to the in duction passage 2 upstream of the choke valve 3.

When the engine has been started it speeds up to high revolutions per minute, producing a high degree of suction in the induction pas sage 2 downstream of the throttle valve 10, the suction here being transmitted through the channel 13 to the suction chamber 22 of the pneumatic positioner 4. Consequently, the dia phragm 21 flexes towards the left, pulling the pull-rod 5 towards the left until the diaphargm plate 25 makes contact with the closure mem ber 27.

Further leftward flexing of the diaphragm 21 opens the additional valve 26, admitting high pressure air from the induction passage 2 up stream of the choke-valve 3, through the channels 17, 15 and the second connection 14, to the suction chamber 22. During this leftward flexing of the diaphragm 21 the choke-valve 3 is rotated anticlockwise, i.e. to wards a more open position, by the pull-rod -5, acting through the linkage 6, 7, 8, 9, the opening of the choke-valve 3 being arrested when the gap shown at "a" in Fig. 2 has been formed. This opening of the choke-valve 3, just after the engine has started, consider ably thins down the excessively rich starting mixture.

Very soon thereafter the throttle valve 10 is closed, to being down excessive engine speed, so that the control drilling 19 now comes to be positioned upstreat of the throttle valve 10. In the meantime the 3-way valve 16 has switched over to connect the pneumatic positioner 4 to the control drilling 19, but this does not change the position of the choke-valve 3 because high pressure is now also acting in the control drilling 19.

As soon as, in response to a requirement for higher torque, the throttle valve 10 is opened a little more, the control drilling 19 comes to be located downstream of the throttle valve 10, so that air flow at low pressure flows out through the additional valve 26 and the channel 15. This allows the diaphragm 21 to flex additionally leftwards, drawing the pullrod 5 towards the left, i.e. the pneumatic positioner 4 now adopts the position shown in Fig. 3, opening the choke-valve 3 to form the greater flow-gap "a,". This prevents excessive enrichment of the combustible mixture.

Claims (5)

1. A carburettor for internal combustion engines with a controlled choke-valve (3), which is part of an engine-starting device, mounted to pivot eccentrically in the induction passage, the choke-valve being pivoted in the opening direction, against the influence of a flexible thermal positioner, by the current of aspirated air and by a pneumatic positioner (4) which communicates, through a first channel (13) with the induction passage downstream of the throttle valve (10), the pneumatic positioner (4) also having a second channel (15) whose flow-cross-section is controlled, in dependence on the movements of the pneumatic positioner (4), by a valve for obtaining a 2stage positioning movement, characterised in that the second channel (15) communicates, through a two-position 3-way valve (16) which responds to engine-operating conditions, either with the induction passage (2) upstream of the choke-valve (3) or, when the 3-way valve (16) is switched over, through a control drilling (19), with the induction passage (2) at a location which is upstream of the throttlevalve (10) when this is in its engine-idling position but downstream of the throttle-valve (10) when this is opened.

2. A carburettor as claimed in Claim 1, characterised in that the 3-way valve (16) is switched over at the end of a predetermined time-delay after the engine has started.

3. A carburettor as claimed in Claim 1, characterised in that the 3-way valve (16) is switched over in response to engine temperature.

4. A carburettor as claimed in Claim 1, characterised in that the 3-way valve (16) is switched over in response to the temperature of the aspirated air.

5. A carburrettor substantially as hereinbefore described with reference to the accompanying drawings.