A speed governed carburettor

Abstract

 A carburettor (10) with inbuilt governor for speed control of an engine which comprises a throttle valve (16) actuated by a diaphragm (20) responding via a fluid line (25) to air pressure varying with engine speed, and also comprising a device (26) responding to air pressure varying with engine speed and connected in a duct (27) serving to vent said fluid line, said device including valving means (31) to control the degree of venting of said fluid line depending upon the response of said device to air pressure changes.

Description

[0001] This invention relates to engine-speed governed carburettors, and especially those for incorporation upon engines required to maintain speed under changing load.

[0002] Various forms of governors have been proposed for this purpose, such as centrifugal systems and flag or diaphragm pneumatic systems. These systems sometimes utilise exposed linkages, and invariably rely upon an initial drop in engine speed with increased load and, therefore, have a less than instantaneous response. Furthermore, the known governors do not allow for varying fuel mixture, altitude, barometric pressure, temperature of the engine, carbon build-up, or eventual engine wear.

[0003] It is the object of the invention to provide a carburettor with an engine-speed governor which is of improved form.

[0004] In accordance with the invention there is provided an engine-speed governed carburettor for an engine comprising a housing defining a through passage for the supply of a working fluid to an engine, a movable throttle valve within said passage, a first pneumatic-responsive device connected to said throttle valve, a supply line connecting said device to a pneumatic source, means for venting to atmosphere said supply line, and a second pneumatic-responsive device operating in response to the speed of said engine to determine the degree of venting by said venting means so as to effect closing movement of said throttle valve with increasing speed of said engine.

[0005] The invention will be described more precisely with reference to the accompanying drawings in which:

Fig. 1 diagrammatically depicts a carburettor incorporating an engine-speed governor according to this invention;

Figs 2(A) and (B) depict a dynamic condition of the carburettor in a condition where the associated engine is fully loaded and rotating at its governed speed;

Figs 3(A) and (B) are similar views with the engine at its governed speed and in an unloaded condition; and

Figs 4(A) and (B) relate to a dynamic condition where the engine is unloaded and decelerating from its governed speed.

[0006] The carburettor 10 shown in Fig. 1, consists of an air intake chamber 11 having a venturi 12 where fuel is induced or injected via a passage 13 which being mixed with the air flow through the venturi 12 produces an induced working fluid in the throat 14 for delivery to the intake manifold 15 of an I.C. engine (not shown). A throttle valve 16 is axially movable along the throat 14 to control the flow of working fluid to the manifold 15. The throttle valve 16 may be of any kind, such as a poppet valve as shown, or a butterfly valve. The stem 17 of the poppet valve 16 is supported in a bearing 18 and is connected at its distal end 19 to a flexible diaphragm 20 which with an enclosing casing 21 defines an air chamber 22. Bias springs 23 and 24 of predetermined rate act upon the diaphragm 20 to maintain it in equilibrium. A vacuum line 25 connects the chamber 22 with the intake manifold 15 to create sub-atmospheric pressure within the chamber 22 during running of the engine serviced by the carburettor 10. Alternatively, the inlet 25A to the line 25 may be connected to any source of pneumatic pressure available on the engine, or accessory thereto. When connected as shown to the intake manifold 15 the air pressure at the manifold 15 fluctuates cyclically with engine operation, but within reasonable tolerances for adequate functioning of the governor. One source of relatively non-cyclically fluctuating pneumatic pressure is the crankcase of a 2-stroke engine.

[0007] As shown in Fig. 1, it will be noted that the chamber 22 is sealed and reduced pressure therein permits the diaphragm 20 to move upwardly to close the poppet valve upon the venturi 12. As is conventional, idling passages may be provided around the valve 16 for sufficient fuel intake to maintain the engine at idling speed. For simplicity of explanation the carburettor 10 is depicted purely diagrammatically in Fig. 1. The carburettor housing may be of a variety of forms without departing from the spirit of the invention, and may or may not enclose the casing 21. If necessary a check valve (not shown) may be incorporated within the supply line 25 to eliminate at least some of the cyclic fluctuations in pressure derived from the intake manifold 15.

[0008] In the form of governor so far described increasing engine speed will create reduced pressure within the supply line 25 which will result in a closing movement of the valve 16. However, the response is quite slow and excessive swings in engine speed occur about the desired preset governed speed. It has been found that this slow response can be avoided by the use of a supplementary pneumatic device 26 connected by fluid line 27 to the supply line 25. The device 26 includes a diaphragm 28 supported between helical springs 29 and 30 and supporting a poppet valve 31 co-operating with a valve seat 32. The device 26 has an internal chamber 33 connected by orifice 34 to atmosphere. Thus, it will be seen that depending upon the degree to which the valve 31 is removed from its seat 32 the fluid line 27, and therefore the supply line 25, will be more or less vented to atmosphere through the orifice 34. An upper chamber 35 above the diaphragm 28 is connected by airline 36 to a position of sub-atmospheric pressure in the cowling 37 housing the engine cooling fan 38 in say a small air-cooled engine (not shown). Therefore, the faster the rotation of the fan 38, the lower will be the air pressure in the line 36 to effect greater closing of the valve 31 upon its seat 32. In such a condition less venting of the supply line 25 occurs so that the diaphragm 20 in the carburettor 10 will be caused to rise and close its associated valve 16. With rising air pressure in the line 36, resulting from slowing of the engine, the poppet valve 16 in the carburettor 10 will move in an opening direction.

[0009] The carburettor of this invention will be found to have most merit when applied to small I.C. engines such as used with lawn mowers, marine craft, portable power tools, and the like. Adjustment to the governed speed is preferably effected through effecting a change in tension of the upper spring 24 within the carburettor 10. It is now common practice on engines for the above purposes to provide only two speed conditions i.e. slow speed (or idling) and operating speed. Any one of the many presently available controls for effecting the change in tension may be incorporated.

[0010] The condition of the carburettor 10 as depicted in Fig. 1 is consistent with the engine rotating at the governed speed without load. This condition corresponds to low speed for the engine. In operation the poppet valve 16 is continuously fluctuating about a position consistent with the governed speed, so that fractional changes to the throttle position occur in order to maintain essentially constant speed of the engine. As load on the engine increases, the engine speed will tend to slow which will effect opening of the valve 31 in the device 26 having the effect of greater venting of the supply line 25 whereby the diaphragm 20 moves towards equilibrium and opens the poppet valve 16 of the carburettor 10 to increase engine speed. The valve 16 will finally stabilise at an increased open condition capable of restoring engine speed at the selected level with the increased load. The supplementary pneumatic device 26 may, or may not, be integrally formed with the housing of the carburettor 10.

[0011] The condition shown by Fig. 2 relates to a fully loaded state of the engine which is travelling at its governed speed. The valve 31 of the device 26 is fully open so that the diaphragm 20 of the carburettor 10 is allowed to move under the tension of spring 24 to fully open the poppet valve 16. Should additional load be imposed upon the engine no response will occur in the diaphragm 20 nor the valve 16. Each of the graphs of Fig. 2(B), 3(B) and 4(B) plot resulting torque against engine revolutions with rising and falling of torque, as indicated by the arrows X, to meet changing loads.

[0012] Figs 3 and 4 show other conditions of the governed carburettor 10 firstly where the engine has reached its governed speed and is unloaded and secondly where the engine speed is falling from its governed speed and is unloaded. From the latter condition any further decrease in speed resulting from closing movement of the valve 16 will cause the diaphragm 28 of the device 26 to move downwardly and open the valve 31 thereby effecting consequential opening of the poppet valve 16 in the carburettor 10.

[0013] Whereas the supply line 25 has been described as being connected to a source of sub-atmospheric pressure, the invention is not limited thereto. The use of super-atmospheric pressure in the line 25, as well as in the supply line 36 to the device 26, will achieve similar operation of the carburettor 10 as described above, providing that a modified connection between the diaphragms 20 and 28 be made to their associated valve 16 and 31 whereby the valves open with upward displacement of their associated diaphragms.

[0014] The modification to the valves need only be confined to the linkage connection thereto from their associated diaphragms 20 and 28. Alternatively, the same effect may be achieved by locating the poppet valves 16 and 31 at the opposite side of the venturi 12 and the seat 32.

[0015] Whereas a preferred embodiment has been described in the foregoing passages it should be understood that other forms, modifications and refinements are feasible within the scope of this invention.

Claims

1. An engine-speed governed carburettor for an engine comprising a housing (12) defining a through passage (14) for the supply of a working fluid to an engine, a movable throttle valve (16) within said passage, a first pneumatic-responsive device (20) connected to said throttle valve, a supply line (25) connecting said device to a pneumatic source (25A), means (27) for venting to atmosphere said supply line, and a second pneumatic-responsive device (26) operating in response to the speed of said engine to determine the degree of venting by said venting means so as to effect closing movement of said throttle valve with increasing speed of said engine.

2. A governed carburettor according to claim 1, wherein said pneumatic source is a source of sub-atmospheric pressure.

3. A governed carburettor according to claim 1 or 2, wherein said pneumatic source is the interior of the intake manifold (15) of said engine.

4. A governed carburettor according to any one of the preceding claims, wherein said engine is a 2-stroke engine and said pneumatic source is the interior of the crankcase of said engine.

5. A governed carburettor according to claim 1, wherein said pneumatic source is a source of super-atmospheric pressure.

6. A governed carburettor according to any one of the preceding claims, comprising also a check valve positioned with said supply line to reduce cyclic fluctuations in the pressure derived from said pneumatic source.

7. A governed carburettor according to any one of the preceding claims, wherein said throttle valve is a poppet valve (16), and said first pneumatic-responsive device comprises a diaphragm (20) connected on one side with the poppet valve and exposed upon its opposite side to pressure from said pneumatic source.

8. A governed carburettor according to any one of the preceding claims, wherein said second pneumatic-responsive device comprises a diaphragm (28) connected on one side to valving means (31 and 32) and exposed on its opposite side to a source of air, the pressure of which varies with the speed of the engine, and said venting means is a fluid line (27) connecting said supply line to atmosphere via said valving means whereby venting of said supply line is reduced with increasing speed of said engine.

9. A governed carburettor according to claim 8, wherein said valving means is a poppet valve (31) and associated valve seat (32), and the pressure of said source of air is reduced with increasing speed of said engine.

10. An engine-speed governed carburettor substantially as hereinbefore described with reference to the accompanying drawings.

Drawing