GB2168761A

GB2168761A - Fixed choke carburettor

Info

Publication number: GB2168761A
Application number: GB08528368A
Authority: GB
Inventors: Anwar Abidin; Gunter Gilz; Dieter Thonnenssen
Original assignee: Pierburg GmbH; Robert Bosch GmbH
Current assignee: Pierburg GmbH; Robert Bosch GmbH
Priority date: 1984-12-07
Filing date: 1985-11-18
Publication date: 1986-06-25
Also published as: IT8548824A0; FR2574481A1; GB8528368D0; DE3444673A1; IT1200146B

Abstract

A fixed choke carburettor has a choke valve 4 operated by an electric actuator 5 under the control of an electric control device 6 which processes operating parameters alpha , lambda , n, T, of the carburettor and of an engine to which the carburettor is fitted, fed to it by sensors 3, 24. A main one of these parameters is the opening angle of a main throttle valve 2. The choke valve 4 is coupled by a linkage 6 to a profiled metering needle 17 which is axially movable in a jet 19 to vary the free cross-sectional area of the jet 19 to control the flow of fuel through a duct 10, 11 from a float chamber 20 to a main jet 12 in a mixing chamber 1. As the choke valve 4 is closed, the needle 17 is raised to increase the fuel flow. Rapid opening of the throttle valve 2 causes the control device 6 to close the choke valve 4 to some extent and accordingly the mixture is enriched by the multiplicative effect of the increase of vacuum at the main jet 12 owing to closure of the choke valve and the increase of fuel flow owing to the increase of area at the jet 19. <IMAGE>

Description

SPECIFICATION Fixed Choke Carburettor This invention relates to fixed choke carburettors, which are also known as fixed Venturi Carburettors, comprising a mixing chamberwith a main throttle valve at its downstream end, a choke valve at its upstream end and a fuel duct leading from a float chamber into the mixing chamber, a sensor which senses the instantaneous opening of the main throttle valve as an operating parameter of the carburettor and a control device which processes this opening and optionally other operating parameters of an engine to which the carburettor is, in use, fitted and controls the choke valve by means of an electrical actuator in dependence upon the parameter or parameters in particular to close the choke valve to enrich the mixture upon rapid opening of the main throttle valve.

Such a carburettor is disclosed in German Patent Specification No. 2 927 881. In this carburettor the fuel flow rate is varied exclusively by influencing the suction in the choke or Venturi. For some operating ranges, especially during acceleration and at the full load of the engine to which the carburettor is, in use, fitted, the choke valve must be closed in order to achieve the necessary suction to such an extent that incomplete induction in the cylinders of the engine occurs.

It is known from German Published Patent Applications Nos. 2 441131 and 3 113 681, to supply the fuel in fixed choke carburettors via a nozzle or jet in which an axially movable metering needle, which is coupled to the main throttle valve, is fitted. The effect of the needle in this arrangement, which does not have any choke valve control, must be amplified for some operating conditions. For example, an additional accelerator pump is necessary for rapid acceleration in order to achieve the mixture enrichment necessary for this purpose.

Furthermore, additional measures must be provided for cold starting.

The object of the present invention is to adapt a carburettor as initially described by simple measures in such a way as to make possible sufficient and rapid mixture enrichment in all operating ranges of the engine to which the carburettor is fitted without harmful loss of filling of the cylinders with fuel mixture and without additional aids, such as an accelerator pump or a valve for cold starting.

To this end, according to this invention, such a carburettor is characterised in that the fuel duct is provided above the level of the fuel in the float chamber with a nozzle objet the opening of which is controlled by a movable profiled needle and a mechanical control connection is provided between the needle and the choke valve or a member coupled to the choke valve whereby the needle is moved to increase the free flow cross-sectional area of the nozzle or jet when the operating parameters are such that the choke valve is closed by the control device.

This arrangement is extremely advantageous, since the mixture enrichment takes place in a multiplicative dependence upon the vacuum acting in the choke during induction and upon the free cross-section of the nozzle or jet. Thus, by relatively small adjustments of the choke valve, a large change to the mixture composition can be achieved.

This is extremely advantageous, for example, for acceleration of the engine, since no harmful losses of induction occur and also a separate accelerator pump is not required. Whereas, in the carburettor initially described the choke valve had to be closed for acceleration, for example by approximately 60 in the case of a butterfly valve, in the carburettor in accordance with the present invention a closure of the choke valve by, for example, approximately 30 is sufficient, so that on the whole considerably better operating conditions are established.This is particularly so since in the carburettor initially described the choke valve had to be partly closed even for a lambda control to the value 1, so that the further closure of the choke valve for acceleration purposes of necessity resulted in a loss of filling of the cylinders of the engine with fuel mixture, that is a loss of induction. This disadvantage can now be avoided, and the mixture enrichment with multiplicative dependence on the vacuum and jet area becomes very rapidly established when required. This applies also for the entire starting operation, including cold starting, for which no further actuating element for mixture enrichment is necessary.

Preferably, the mechanical control connection comprises a connecting rod pivotally connected between the profiled needle and an arm connected to the choke valve. This arrangement is particularly simple and is adequate for achieving mixture enrichment which is dependent upon both the choke vacuum and the area of the nozzle or jet.

For special functions it is furthermore preferred that the nozzle needle should have, at a thicker end, an end portion which engages in and closes the nozzle or jet when the choke valve is moved by the actuator as a function of operating parameters under specific operating conditions, for example over run, stopping, or speed limitation of an engine to which the carburettor is, in use, fitted.

In this manner the control device and the electric actuatorforthe choke valve can completely interrupt the fuel supply when this is desired and such an operating situation is determined by the control device. In this case, the choke valve may be rotated somewhat beyond its fully open position, in order to bring the end portion of the needle into engagement with the nozzle or jet.

Particularly favourable operating conditions arise in a further preferred example in which in a manner similar to that with the carburettor described in German published Patent Application No. 3 113 681, the fuel duct is connected via a main jet to the mixing chamber and also via an adjustable idling nozzle to an intake duct downstream of the main throttle valve. As a consequence a mixed pressure having a suction effect becomes established in the fuel duct. This pressure is dependent upon the pressure in the Venturi region and upon the intake duct pressure downstream of the main throttle valve. This mixed pressure can be adjusted by appropriate choice of the main jet and of the idling nozzle and can thus be adapted to particular requirements.

In this connection, it is furthermore advantageous to provide an air bypass leading from upstream of the choke valve via a nozzle into the fuel duct for supplying secondary air for assisting transport of fuel. The nozzle in the air bypass may be adjustable in cross-section. The magnitude of the supply of secondary air is then the amount required for satisfactory transport of the fuel.

In an advantageous example, the control device is arranged to control the opening of the choke valve in dependence upon other operating parameters consisting of, the temperature, speed and lambda value of an engine to which the carburettor is, in use, fitted. These operating parameters can be sensed in a simple manner by a sensor connected to the control device and then be processed for adjusting the choke valve by the electric actuator and also, indirectly, for adjusting the profiled metering needle to meet requirements.

In one practical example, the fuel duct leads to a main jet in a preliminary atomiser in the mixing chamber.

An example of a carburettor in accordance with the invention is illustrated in the accompanying drawings in which: Figure 1 is in a diagrammatic longitudinal section through the carburettor; and, Figure 2 is a detailed section to a much larger scale through the fuel metering nozzle or jet and needle of the carburettor.

A mixing chamber 1 is bounded downstream by a main throttle valve 2, in the form of a butterfly valve, with which there is associated a sensor 3, for example in the form of a rotary potentiometer, for sensing the magnitude of its opening. The mixing chamber 1 is bounded upstream by a choke valve 4, which is adjusted in opening position by an electric actuator 5. A control device 6 receives at its input information from the state sensor 3, which is in the present case the angular position of the main throttle valve 2, and optionally other operating parameters, namely in the present case the temperature T (for example the cooling water temperature) of an engine (not shown) to which the carburettor is fitted, the engine speed n and the lambda value, which is measured by a lambda probe 24 in an exhaust pipe 25.These and possibly other items of information relating to operating parameters of the carburettor or engine are processed in the control device 6, which in turn controls the electric actuator 5 for the choke valve 4 via a control connection 7.

In the choke or Venturi region 8 of the fixed choke carburettor, there is a preliminary atomizer 9, to whichthefuel is supplied.Afuel supplyduct 10 divides into a main duct 11 which leads via a main jet 12 into the preliminary atomizer 9, and into an idling duct 13 which leads via an idling outlet opening or jet 14 into an intake duct or manifold downstream of the main throttle valve 2. An idling adjustment screw 15 is associated with the idling outlet opening 14, so that an adjustable idling jet is formed by these two components. In the fuel duct 10, the main duct 11 and the idling duct 13, a mixed pressure becomes established, which is a function of the vacuum in the Venturi 8 and in the preliminary atomizer 9 and the vacuum in the region downstream of the main throttle valve 2.The mixed pressure can be adapted to suit requirements by appropriate choice or setting of the main jet 12 and of the adjustable idling jet. A mechanical control connection 16 in the form of a rod is pivotally connected to an arm of the choke valve 4 and is pivotally connected at its other end to a profiled metering needle 17 which is guided so that it can move axially. The metering needle 17 has, adjoining its profiled portion, that is at its thicker end, an end portion 18, which when engaged in a needle jet or nozzle 19 completely closes it as shown in Figure 2.

This function, which serves as a fuel shut-off during over-run, engine stopping or speed limitation, may for example be achieved by turning the choke valve 4 further clockwise somewhat beyond its completely opened position, in order that the end portion 18 shall enter the needle nozzle 19. On closing of the choke valve 4, the metering needle 17 is so adjusted according to the magnitude of the closure that a certain portion of the profiled region of the needle is situated in the throat of the needle nozzle 19, with the result that a smaller or a larger flow cross-section is obtained for the fuel, which is sucked out of a float chamber 20 with a float 21.

In the example illustrated, an air bypass 23, connected with the region upstream of the choke valve 4, provides venting of the float chamber 20 and also a feed of secondary air, which flows into the region of the fuel suction point in the fuel duct 10 via a nozzle 22, which in this example, is not fixed cross-section. This secondary air assists satisfactory transport of the fuel. If necessary or appropriate, the fixed nozzle 22 could be replaced by a nozzle of adjustable cross-section.

Claims

1. A fixed choke carburettor comprising a mixing chamber with a main throttle valve at its downstream end, a choke valve at its upstream end and a fuel duct leading from a float chamber into the mixing chamber, a sensor which senses the instantaneous opening of the main throttle valve as an operating parameter of the carburettor and a control device which processes this opening and optionally the operating parameters of an engine which the carburettor is, in use, fitted and controls the choke valve by means of an electrical actuator in dependence upon the parameter or parameters in particular to close the choke valve to enrich the mixture upon rapid opening of the main throttle valve, characterised in that the fuel duct is provided above the level of the fuel in the float chamber with a nozzle or jet the opening of which is controlled by a movable profiled needle and a mechanical control connection is provided between the needle and the choke valve or a member coupled to the main choke valve whereby the needle is moved to increase the free flow cross-sectional area of the nozzle or jet when the operating parameters are such that the choke valve is closed by the control device.

2. A carburettor according to Claim 1, in which the mechanical control connection comprises a connecting rod pivotally connected between the profiled needle and an arm connected to the choke valve.

3. A carburettor according to Claim 1 or Claim 2, in which the profiled needle has, at a thicker end, an end portion which engages in and closes the nozzle or jet, when the choke valve is moved by the actuator as a function of operating parameters under specific operating conditions, for example over-run, stopping, or speed limitation of an engine to which the carburettor is, in use, fitted.

4. A carburettor according to any one of Claims 1 to 3, in which the fuel duct is connected via a main jet to the mixing chamber and also via an adjustable idling nozzle to an intake duct downstream of the main throttle valve.

5. A carburettor according to Claim 4, in which there is an air bypass leading from upstream of the choke valve via a nozzle into the fuel duct for supplying secondary air for assisting transport of fuel.

6. A carburettor according to Claim 5, in which the nozzle in the air bypass is of adjustable crosssection.

7. A carburettor according to any one of the preceding Claims, in which the control device is arranged to control the opening of the choke valve in dependence upon other operating parameters consisting of, the temperature, speed and lambda value of an engine to which the carburettor is, in use, fitted.

8. A carburettor according to any one of the preceding Claims, in which the fuel duct leads to a main jet in a preliminary atomiser in the mixing chamber.

9. A carburettor according to Claim 1, substantially as described with reference to the accompanying drawings.