FR2631388A1 - CARBURETOR WITH AUTOMATIC STARTER FOR INTERNAL COMBUSTION ENGINE - Google Patents

Abstract

The carburetor comprises an inlet duct for the air 2 mixed with the fuel to form the mixture and its opening is controlled by an air valve 3 and a duct for supplying the mixture to the engine 5, the opening of which is controlled by a butterfly valve 6; the carburetor further comprises an actuator 12 provided with a movable member 13 whose movement is controlled by the vacuum acting in the engine suction manifold and a transmission 14 between the movable member and the butterfly valve, this actuator comprises elastic means 22 capable of maintaining, in the absence of the vacuum, the movable member in a position to which corresponds a first predetermined opening angle of the butterfly valve, so that the opening angle of this The valve gradually decreases as the vacuum increases in the manifold, between the first quoted angle and a second predetermined angle to which the engine idle speed corresponds.

Description

Carburetor with automatic choke for internal combustion engine

  The invention relates to a carburetor for an internal combustion engine and in particular to a device for a carburetor of this type, by means of which the operations which are necessary to ensure correct engine speed can be carried out automatically during the period

  following the cold start of the engine.

  A carburetor to which the device according to the invention can be applied essentially comprises a duct - inlet of the air mixed with the fuel to form the mixture and the opening of which is controlled by an air valve and a duct supply of the mixture to the engine,

  the opening of which is controlled by a butterfly valve.

  Devices are known which make it possible to carry out, in automatic mode, the operations which are necessary to ensure correct engine speed in the period following the starting of the engine, when the latter is started at low temperature. As is known, when the engine is stopped, the air valve is normally maintained in its closed position and the butterfly valve is in a partially open position.

  to which corresponds a predetermined opening angle.

  In the period following the start of the engine, as we know, it is necessary that the opening of the air valve gradually increases while that of the butterfly valve gradually decreases to result in a configuration to which the engine idling speed, configuration which must be obtained when the engine temperature corresponds to the

operating temperature.

  Devices are known by means of which it is possible to respectively control the opening and closing of the air valve and of the butterfly valve, automatically, in the period following the starting of the engine; a device of a first type essentially comprises an actuator provided with a paraffin element and with a movable member whose movement is controlled by the increase in the volume of the paraffin contained in the capsule mentioned above when the temperature of the engine increases; a transmission of the appropriate type is arranged between these actuators and the two valves. In a device of a second type, the opening of the air valve is controlled by a first actuator comprising a bimetallic element and a movable member, connected to the valve by means of a transmission, and which moves when the engine temperature increases, by an action of the bimetallic element mentioned above. The device further comprises a second actuator provided with a paraffin element and with a movable member, the displacement of which determines the closing of the butterfly valve, by means of a

appropriate transmission.

  Carburetors provided with the devices of the first and second type described have some drawbacks. In itself, the flow rate and the richness of the mixture leaving the carburetor in the period following the start of the engine are not optimal to ensure a substantially constant engine speed throughout the period; in fact the above-mentioned speed increases at first abruptly enough to reach a maximum and then decreases until reaching the value of the idle speed. This is due to the fact that the law according to which vary the angles of the two butterflies, in the period indicated above, and under the control of the actuators defined first, does not correspond to the theoretical law which would be necessary to realize in the totality of the period a substantially constant engine speed. In fact, the closing of the butterfly valve started only after a certain time from the moment at which the engine is started, due to the inertia with which the actuators indicated first intervene and the characteristics of the transmissions which connect valve actuators; it therefore follows that in these first moments there is an excessively high flow mixture supply which determines a rather abrupt increase in the engine speed. Similarly, the closing of the butterfly valve also takes place with a certain delay with respect to the time of starting the engine, due to the inertia of the actuator which controls the rotation of the latter. The object of the present invention is to produce a carburetor of the type described first, provided with a device capable of automatically carrying out the operations necessary for starting the engine cold in the period following the instant. at which the engine is started, with which the drawbacks already mentioned can be eliminated and, in particular, making it possible essentially to obtain, from the moment of starting, a substantially constant engine speed which is kept unchanged until

  that it has reached engine speed.

  These aims are achieved by means of a carburetor for an internal combustion engine which comprises an air inlet duct mixed with the fuel to form the mixture and the opening of which is controlled by an air valve and a duct supply of the mixture to the engine, the opening of which is controlled by a butterfly valve, characterized in that it comprises a first actuator provided with a movable member whose movement is controlled by the vacuum acting in the suction manifold of the motor, and in proportion to the value of the vacuum itself, and a transmission between the movable member and the butterfly valve, said actuator comprising elastic means capable of maintaining, in the absence of vacuum, said movable member in a position to which corresponds a first predetermined opening angle of said butterfly valve, so that the opening angle of said butterfly valve gradually decreases when the vacuum at lies in the collector, between said first predetermined angle and a second predetermined angle

  to which the engine idling speed corresponds.

  Various other features and benefits of

  device the invention will emerge from the description

  detailed below. An embodiment of the invention is shown by way of nonlimiting example in the appended drawings in which: FIG. 1 represents a vertical section of a part of the carburetor of the present invention; 2 shows a side view, partially in section, of the part of the carburetor of the previous figure; FIG. 3 represents the appearance of some operating parameters as a function of time, from

  when the engine is started.

  The carburetor of the invention essentially comprises a body 1 in which an air inlet duct 2 is hollowed, in communication, for example, with an engine air filter, and the opening of which is controlled by a valve d 'air 3. The carburetor further comprises a chamber 4 into which is supplied the air from the duct 2 and the fuel sprayed from suitable spray jets (not shown). The carburetor then comprises a conduit for supplying the mixture to the engine, designated by 5, the opening of which is controlled by a butterfly valve 6 and which is in communication with the chamber 4 in which the mixture

is formed.

Z631388

  Suitably, the valves 3 and 6 scnz produced by means of a disc 7 secured to a perit oscillating shaft 8 supported, by means of suitable bearings, on the body 1 of the carburetor. The butterfly valve 6 is normally held in the closed position by the action of a spring 9 and its opening is controlled by the accelerator pedal, via an appropriate transmission (not shown) connected to a

appropriate crank 10.

  On the basis of the invention, the carburetor comprises a first actuator, designated as a whole by 12, which is provided with a movable member, suitably a rod 13, the displacement of which is controlled by the depression acting in the manifold suction (not shown) of the motor and in proportion to the value of the vacuum. A suitable transmission, indicated as a whole by 14, is interposed between the rod 13 and the butterfly valve 6, (Figure 2) transmission which can simply comprise an oscillating lever 15 provided with a fin 16 in a threaded hole which screws the threaded rod with an adjustable stop 17; the end of the rod 13 rests on this stop, as can be seen

clearly in the figures.

  The actuator 12 comprises elastic means capable of maintaining, in the absence of the aforementioned depression, the rod 13 in a position to which corresponds a first predetermined opening angle of the butterfly valve 6, for example the angle ai indicated in FIG. 2, the actuator further comprises an envelope 18, a deformable membrane 19 blocked in correspondence with a pair of edges of the envelope, and which is capable of defining therewith a chamber 20 in communication with the engine intake manifold, via an appropriate connection 21 and a pipe not shown; the actuator further comprises a helical spring 22 interposed between the casing and the membrane, so as to normally push the rod 13 against the stop 17. The carburetor then comprises a second actuator designated as a whole by 24 ,, provided with a movable member, for example a crank 25, integral with a small oscillating shaft 26 whose movement is controlled by an element sensitive to the temperature of the engine and in proportion to the value of the temperature. This sensitive element which is designated by 27 may simply consist of a bimetallic blade 28; a suitable transmission 29 is disposed between the blade and the small oscillating shaft 26 and another transmission, designated as a whole by 30, is disposed between the crank 25 and the air valve 3 and comprises

  essentially a crank 31 and a connecting rod 32 ..

  Suitably, the rotation of the small shaft 26, and therefore of the crank 25, can also be caused by a rod 33 whose movement is controlled by a pneumatic actuator 34 connected, as indicated below, to the manifold. motor suction; as can be clearly seen in FIG. 2, the rod 33 can be provided with a head 35 capable of cooperating with the fin 36 of a crank 37, which is also integral with the

small tree 26.

  According to an alternative solution, the second actuator 24, rather than comprising a temperature-sensitive element 27 consisting of a bimetallic blade 28, can comprise a paraffin capsule capable of controlling, via an appropriate transmission, the rotation of the small shaft 8, and therefore the closing of the

air valve 3.

  The operation of the carburetor of the invention, in the period following the starting of the engine, is carried out

as follows.

  As the engine has barely started, the vacuum which is immediately created in the suction manifold acts in the chamber 20 of the actuator 12, overcoming the elastic resistance of the spring 22 and therefore allows the lever 15 (FIG. 2 ), which controls the rotation of the butterfly 6, to rotate, clockwise in the figure, under the action of the spring 9; in this way there is control of the closing of the butterfly valve 6 from the opening angle ai indicated

initially in Figure 2.

  It can be seen that the shape of the depression inside the chamber-20 as a function of time, following the instant of starting the engine, presents the shape presented by the curve a of the figure. 3: there is thus a sudden increase in this depression, followed by a rather reduced increase thereof, until a substantially constant value is reached; due to this shape of the depression, the intervention of the actuator 12 to control the closing of the butterfly valve as a function of time is such that it produces a closing of the butterfly as a function of time which has the shape shown by curve b of Figure 3; there is in fact a first line bl of this curve, in which the opening angle a of the butterfly is reduced significantly in a much shorter time and a second line b2 in which the rotation of the opening angle as a function time is less marked, until an aperture angle value, indicated by af, is reached after a certain time from the moment when the engine started. We also meet in this same period the engine speed whose speed, which is indicated by the curve c, increases suddenly following the line cl of the curve, until a substantially constant value is represented represented by the line C2

of the curve.

  This favorable result, consisting in obtaining a substantially constant engine speed until the first moments following the start of the engine, is also attributable to the action exerted by the air valve 3, which, at the same time, opens gradually under the action of the second actuator 24. In fact, when the temperature of the engine increases, the bimetallic blade 28 controls, via the transmission 29, the rotation of the small shaft 26 which, in turn, determined the gradual opening of the valve 3. In addition, immediately after switching on the. motor, the actuator 34 which is connected to the motor intake manifold controls the translation of the rod 33 in order to determine a sudden and sensitive opening of the valve 3 to prevent drowning the motor. The combined action of the actuators 24 and 34 is therefore that of having first a sudden and sensitive opening of the valve 3 and, then, a subsequent opening, much more gradual than the previous one, which increases appreciably and in proportion to the increase. engine temperature. Consequently, the favorable result consisting in obtaining a substantially constant engine speed, as shown in curve c of FIG. 3, is attributable to the presence of the actuator 12 which controls the opening of the butterfly valve 6, substantially with a shape represented by the curve b; this result also depends also on the concomitant action of the air valve 3, the opening of which varies as a function of time,

  in a manner first described.

  The structure of the carburetor of the invention is very simple, which makes it reliable and allows it to be produced at low cost; in fact, the actuator which controls the butterfly valve 6 is a simple pneumatic actuator, well known and having a very simple structure; similarly, the actuator which controls the air valve 3 has a very simple structure and is of a

low cost.

  It is obvious that modifications and variants can be made to the embodiment described in the present invention, either in the form or in the arrangement of the different parts, without going beyond the ambit

of the invention itself.

Claims (7)

  1. Carburetor for internal combustion engine, comprising an air intake duct (2) mixed with the fuel to form the mixture and the opening of which is controlled by an air valve (3) and a duct (5 ) supplying the mixture to the engine, the opening of which is controlled by a butterfly valve (6), characterized in that it comprises a first actuator (12) provided with a movable member (13) whose movement is controlled by the depression acting in the suction manifold of the engine, and in proportion to the value of the depression itself, and a transmission (14) between the movable member and the butterfly valve, said actuator comprising elastic means (22) capable of maintaining, in the absence of vacuum, said movable member in a position to which corresponds a first predetermined angle (Ci) of opening of said butterfly valve, so that the opening angle of said valve butterfly gradually decreases when the depres sion increases in the manifold, between said first predetermined angle and a second predetermined angle (af) to which the idle speed of the engine.   2. Carburetor according to claim. 1, characterized in that said actuator comprises a casing (18), a deformable membrane (19) housed in said casing and capable of defining therewith a chamber (20) in communication with said suction manifold and a spring (22 ) interposed between said envelope and said membrane, and a movable stop (17) fixed to said membrane and acting on a member (15) of said transmission.   3. Carburetor according to claims 1 or 2,   characterized by the fact that it comprises a second actuator 263i388! 11 (24) provided with a movable member (26) whose movement is controlled by an element sensitive to the temperature of the motor (27) and in proportion to the value of the temperature and a transmission (30) between said movable member and said air valve, so as to gradually control the opening of said air valve when   the temperature of said motor increases.   4. Carburetor according to any one of   previous claims, wherein   said temperature sensitive element (27) of the second   actuator is a bimetallic blade (28).   5. Carburetor according to any one of   previous claims, wherein   said temperature sensitive element is a capsule paraffin.   6. Carburetor according to any one of   previous claims, wherein   said transmission between said movable member (13) and said butterfly valve (6) consists of a lever (15) integral with the valve, said lever being provided with a stop (17) on which said rod ( 13) and   whose position is adjustable relative to said lever.   7. Carburetor according to any one of   previous claims, characterized in that it   comprises a third pneumatic actuator (34) connected to said suction manifold and capable of controlling the movement of said movable member (26), to determine a sudden increase in the opening of said valve   immediately after starting the engine.