GB1564894A - Carburettors having an acceleration pump - Google Patents

Description

(54) IMPROVEMENTS IN CARBURETTORS HAVING AN ACCELERATION PUMP (71) We, SOCIETE INDUSTRIELLE DE BREVES Er D'EThDEs S.I.B.E., a French Body Corporate, of 3 Villa E. Bergerat, 92200 Neuilly Sur Seine, France, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to carburettors for internal combustion engines provided with an acceleration pump comprising a variable volume chamber which is connected to a float chamber through a suction channel provided with a suction valve and to the part of the induction passage situated upstream of an operator operable throttle member, through a delivery channel provided with a delivery valve and a calibrated injection orifice which pump comprises a mobile pumping member partially limiting said variable volume chamber and actuated by means adapted to cause it to accomplish a fuel delivery stroke during opening movements of the throttle member, and a temperature responsive device for increasing the volume delivered by the pump to the inlet pipe when said temperature is lower than a predetermined value. Such a carburettor will be referred to as being "of the kind above defined".

The acceleration pump delivers an amount of liquid fuel to the induction passage of the carburettor during acceleration caused by opening of the main throttle member. The actuating means, coupled mechanically to the throttle member or actuated by variation of the depression which prevails downstream of the throttle member, move the pumping member (typically a diaphragm or piston) of the acceleration pump in the direction corresponding to fuel delivery.

The amount of fuel to be delivered to the inlet pipe by the acceleration pump may be lowered when the temperature increases.

Acceleration pumps are known in which the variable volume chamber is connected to the float chamber by a duct having a passage section controlled by a thermostatic element; part of the fuel contained in the variable volume chamber thus flows back towards the float chamber during the delivery stroke of the pumping member. But it is difficult to reach the accuracy desirable, for the thermostatic element must regulate an orifice of very small cross-sectional flow area, much smaller than the cross section of the injection orifice.

According to the invention, there is provided a carburettor of the above defined kind in which the temperature responsive device comprises a supplementary mobile pumping member, adapted to be actuated by the variations of the pressure downstream of the throttle member as long as said temperature has not exceeded the given value.

The supplementary member may particularly comprise a diaphragm, one face of which partially limits the variable volume chamber and the other face of which partially limits a work chamber connected to that part of the induction passage located downstream of the throttle member through a channel in which is disposed a temperature responsive valve subjected to said temperature and adapted to close the channel when the temperature exceeds the predetermined value.

The valve is typically a bulging bimetallic disc of the so-called "blistering" type whose curvature suddenly reverses when the temperature increases beyond the predetermined value, the valve then closing the channel.

The invention will be better understood from reading the following description of a carburettor which forms one particular embodiment thereof. The description refers to the single figure which accompanies it and shows, in elevation and partial crosssection, the elements concerned by the invention, the elements being illustrated in the position that they occupy during idling or when the engine is stopped, at a tem perature higher than the predetermined value.

The carburettor comprises an'induction passage 1 formed in a housing and provided with a throttle member 2 fixed on a shaft 3 and actuatable by the operator through a linkage (not shown), an air inlet 4 protected by a filter (not shown), and a venturi 5 in which opens a fuel delivery system (not shown). The carburettor is fed with fuel from a float chamber 6 with constant level N, in which the intake of fuel coming from a reservoir (not shown) is regulated by a valve (not :shown) actuated by a float 7.

The float chamber is maintained substan- tially at atmospheric pressure by a vent in its- upper part, The carburettor is provided with an ac celeration pump 8 which comprises a variable volume chamber 9, connected to float chamber 6 by a suction channel 10 provided with a suction valve 11 and to the induction passage 1 through a delivery chan nel 12 provided with a delivery ball valve 13 and a calibrated injection nozzle 14.

Chamber 9 comprises conventional means adapted for reducing its volume during the opening movements of the throttle member 2. In the embodiment shown, chamber 9 is limited by a flexible diaphragm 15 to which is fixed a push-rod 16. The diaphragm may be moved, against the action of a return spring 17, by a lever 18 pivoting about an axis 19, subjected to the action of a spring 20 mounted on a rod 21 hinged to a lever 20 fast with shaft 3 of the throttle mem ber 2, and in abutting connection with push rod 16.

Referring to the drawing, the variable volume chamber 9 comprises a second mobile wall which is in addition to that formed by diaphragm 15. The second wall is formed by a second diaphragm 25 form ing the mobile part of a pneumatic motor 26 whose work chamber 27, which contains a spring 28 biasing diaphragm 25 in the direction reducing the volume of chamber 9, is connected to the induction passage 1 downstream of the throttle member 2 by a channel. The channel comprises two sec tions 29a and 29b separated by a tempera ture responsive valve element 30 control ling the opening and the closing of the channel. The temperature responsive ele ment comprises a casing defining a cham ber 33 which contains a bulging bimetallic or "blistering" disc 31. The casing and the disc 31 which it contains are brought to a temperature representative of the tem perature of an engine associated with the carburettor by the cooling fluid of the latter flowing in a conduit 32. The bimetallic disc 31 has a curvature which reverses when its temperature exceeds a predetermined limit value; below this temperature the disc has the form shown in chain-dotted line, above the form shown in full line.

When disc- 31 is subjected to a tempera ture greater than the predetermined limit value (40"C to 500C for example) and has consequently the shape shown by a continuous line, it bears on an O-ring seal 34 and separates section 29a from section 29b.

When the temperature drops and becomes less than the predetermined limit value, the curvature of the disc is reversed and channel sections 29å and 29b communicate again.

A calibrated leak aperture 35, of small cross-sectional area (typically a few tenths of a millimeter in diameter) is disposed in channel section 29a connected permanently to work chamber 27 of pneumatic element 26. As soon as the channel 29a-29b is closed by thermostatic element 30, the leak brings the pressure in work chamber 27 of pneumatic element 26 quickly back to the atmospheric pressure. The mobile part of pneumatic element 26 is then retained in abutment either against a collar arranged inside chamber 9, as shown in the drawing, or against the central part of the mobile unit carried by membrane 15, through an abutment stud 40 of suitable length, fast with diaphragm 25. From this moment onwards, no fuel delivery to the induction passage may be caused by the pneumatic motor 26.

Operation of the device is as follows: when the engine is idling and is cold, the bimetallic disc 31 has the curvature shown by a chain-dotted line in the drawing and chamber 27 of pneumatic element 26 is subjected to the high level of depression prevailing in passage 1 downstream of throttle member 2; diaphragm 25 is maintained in the part of the work chamber 27 stiuated on the left of the figure and retains spring 28 under compression: chamber 9 has its maximum volume.

When the throttle valve 2 is opened to accelerate the engine, the two diaphragms 15 and 25 move towards one another, delivering a maximum amount of fuel to passage 1 through delivery channel 12: diaphragm 15 is moved by throttle member 2 through the mechanical linkage 1618-20- 21-22. Diaphragm 25 is moved by spring 28 rightwards (on the figure) due to the reduction of the depression transmitted to chamber 27 through channel 29a-29b.

If the temperature of the engine is above the predetermined value of the temperature responsive element 30, the bimetallic disc 31 assumes the curvature shown in full line and closes channel 29S29a; since the depression is no longer transmitted to work chamber 27, the atmospheric pressure is established therein. Diaphragm 25 assumes the position shown in the figure and will no longer act to deliver fuel to the induction passage.

Then if there occurs an acceleration, diaphragm 15 will act to deliver fuel to the induction passage and, consequently, will feed the smaller amount of fuel needed for the proper operation of the engine when hot.

Moreover, in these circumstances, the fuel contained in chamber 9 will not be wholly delivered to passage 1 through delivery channel 12, since abutment stud 40, and consequently diaphragm 25, will be driven back leftwards in the figure, simultaneously with an amount of fuel which will remain in chamber 9.

In a modified embodiment of the invention (not shown), abutment stud 40 is omitted. Then the device modulates the amount of fuel injected into induction passage 1 in dependence on the speed of acceleration and allows a favourable result to be obtained: in the case of sudden acceleration (stamping on the accelerator pedal by the driver), it is not desirable to inject the whole of the fuel contained in the variable volume chamber into the induction passage, for there is then the risk of faulty operation of the engine due to excessive richness upon a sudden acceleration, the pressure of the fuel in chamber 9 becomes sufficient to drive back membrane 25 by compressing spring 28 and thus maintains in the lefthand part of chamber 9 a certain amount of fuel. On the other hand, if the acceleration is slow, steady and spread out over a longer time, the pressure of the fuel is insufficient to compress spring 28 and there is fed to the engine a larger fraction of the fuel contained in the variable volume chamber, even the whole of the fuel.

WHAT WE CLAIM IS:- 1. A carburettor for internal combustion engine of the kind above defined, wherein said temperature responsive device comprises a supplementary mobile pumping member adapted to be actuated by the variations of the pressure downstream of the throttle member, as long as the temperature has not exceeded a predetermined value.

2. A carburettor according to claim 1, wherein said supplementary member comprises a diaphragm one face of which partially limits the variable volume chamber and the other face of which partially limits a work chamber connected to the part of the induction passage situated downstream of the throttle member through a channel in which is disposed a temperature responsive valve subjected to said temperature and adapted to close the channel when the temperature exceeds the predetermined value.

3. A carburettor according to claim 2, wherein the temperature responsive valve comprises a bulging bimetallic disc whose curvature reverses at said predetermined temperature to close said channel.

4. A carburettor according to claim 3, wherein a calibrated aperture of small crosssectional area connects said work chamber to the atmosphere.

5. A carburettor according to any one of the preceding claims, wherein said supplementary member is subjected to the action of a spring adapted to force it back in the direction corresponding to a fuel delivery stroke as far as an abutment position, against the action of the depression prevailing in the induction passage.

6. A carburettor according to any one of the preceding claims, wherein said supplementary member is disposed in the path of the first mobile pumping member so that the two members are capable of abutting as the first mobile pumping member travels through its delivery stroke.

7. A carburettor constructed and arranged substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. the position shown in the figure and will no longer act to deliver fuel to the induction passage. Then if there occurs an acceleration, diaphragm 15 will act to deliver fuel to the induction passage and, consequently, will feed the smaller amount of fuel needed for the proper operation of the engine when hot. Moreover, in these circumstances, the fuel contained in chamber 9 will not be wholly delivered to passage 1 through delivery channel 12, since abutment stud 40, and consequently diaphragm 25, will be driven back leftwards in the figure, simultaneously with an amount of fuel which will remain in chamber 9. In a modified embodiment of the invention (not shown), abutment stud 40 is omitted. Then the device modulates the amount of fuel injected into induction passage 1 in dependence on the speed of acceleration and allows a favourable result to be obtained: in the case of sudden acceleration (stamping on the accelerator pedal by the driver), it is not desirable to inject the whole of the fuel contained in the variable volume chamber into the induction passage, for there is then the risk of faulty operation of the engine due to excessive richness upon a sudden acceleration, the pressure of the fuel in chamber 9 becomes sufficient to drive back membrane 25 by compressing spring 28 and thus maintains in the lefthand part of chamber 9 a certain amount of fuel. On the other hand, if the acceleration is slow, steady and spread out over a longer time, the pressure of the fuel is insufficient to compress spring 28 and there is fed to the engine a larger fraction of the fuel contained in the variable volume chamber, even the whole of the fuel. WHAT WE CLAIM IS:-

1. A carburettor for internal combustion engine of the kind above defined, wherein said temperature responsive device comprises a supplementary mobile pumping member adapted to be actuated by the variations of the pressure downstream of the throttle member, as long as the temperature has not exceeded a predetermined value.

2. A carburettor according to claim 1, wherein said supplementary member comprises a diaphragm one face of which partially limits the variable volume chamber and the other face of which partially limits a work chamber connected to the part of the induction passage situated downstream of the throttle member through a channel in which is disposed a temperature responsive valve subjected to said temperature and adapted to close the channel when the temperature exceeds the predetermined value.

3. A carburettor according to claim 2, wherein the temperature responsive valve comprises a bulging bimetallic disc whose curvature reverses at said predetermined temperature to close said channel.

4. A carburettor according to claim 3, wherein a calibrated aperture of small crosssectional area connects said work chamber to the atmosphere.

5. A carburettor according to any one of the preceding claims, wherein said supplementary member is subjected to the action of a spring adapted to force it back in the direction corresponding to a fuel delivery stroke as far as an abutment position, against the action of the depression prevailing in the induction passage.

6. A carburettor according to any one of the preceding claims, wherein said supplementary member is disposed in the path of the first mobile pumping member so that the two members are capable of abutting as the first mobile pumping member travels through its delivery stroke.

7. A carburettor constructed and arranged substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.