CA1134689A - Fuel metering system for a two-cycle internal combustion engine - Google Patents
Fuel metering system for a two-cycle internal combustion engineInfo
- Publication number
- CA1134689A CA1134689A CA000359198A CA359198A CA1134689A CA 1134689 A CA1134689 A CA 1134689A CA 000359198 A CA000359198 A CA 000359198A CA 359198 A CA359198 A CA 359198A CA 1134689 A CA1134689 A CA 1134689A
- Authority
- CA
- Canada
- Prior art keywords
- fuel
- valve
- induction pipe
- metering system
- engine
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 239000000446 fuel Substances 0.000 title claims abstract description 72
- 238000002485 combustion reaction Methods 0.000 title claims abstract description 18
- 230000006698 induction Effects 0.000 claims abstract description 29
- 238000002347 injection Methods 0.000 claims abstract description 21
- 239000007924 injection Substances 0.000 claims abstract description 21
- 239000002828 fuel tank Substances 0.000 claims abstract description 7
- 239000000203 mixture Substances 0.000 claims description 8
- 230000006835 compression Effects 0.000 claims description 4
- 238000007906 compression Methods 0.000 claims description 4
- 230000000295 complement effect Effects 0.000 claims 1
- 238000000034 method Methods 0.000 abstract 1
- 230000001419 dependent effect Effects 0.000 description 5
- 238000010276 construction Methods 0.000 description 4
- 230000033001 locomotion Effects 0.000 description 3
- 238000000889 atomisation Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 1
- 230000005484 gravity Effects 0.000 description 1
- 230000007257 malfunction Effects 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 230000010349 pulsation Effects 0.000 description 1
- 230000002269 spontaneous effect Effects 0.000 description 1
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
- F02M69/00—Low-pressure fuel-injection apparatus ; Apparatus with both continuous and intermittent injection; Apparatus injecting different types of fuel
- F02M69/10—Low-pressure fuel-injection apparatus ; Apparatus with both continuous and intermittent injection; Apparatus injecting different types of fuel peculiar to scavenged two-stroke engines, e.g. injecting into crankcase-pump chamber
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
- F02M17/00—Carburettors having pertinent characteristics not provided for in, or of interest apart from, the apparatus of preceding main groups F02M1/00 - F02M15/00
- F02M17/02—Floatless carburettors
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
- F02M37/00—Apparatus or systems for feeding liquid fuel from storage containers to carburettors or fuel-injection apparatus; Arrangements for purifying liquid fuel specially adapted for, or arranged on, internal-combustion engines
- F02M37/04—Feeding by means of driven pumps
- F02M37/12—Feeding by means of driven pumps fluid-driven, e.g. by compressed combustion-air
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
- F02M59/00—Pumps specially adapted for fuel-injection and not provided for in groups F02M39/00 -F02M57/00, e.g. rotary cylinder-block type of pumps
- F02M59/02—Pumps specially adapted for fuel-injection and not provided for in groups F02M39/00 -F02M57/00, e.g. rotary cylinder-block type of pumps of reciprocating-piston or reciprocating-cylinder type
- F02M59/10—Pumps specially adapted for fuel-injection and not provided for in groups F02M39/00 -F02M57/00, e.g. rotary cylinder-block type of pumps of reciprocating-piston or reciprocating-cylinder type characterised by the piston-drive
- F02M59/107—Pumps specially adapted for fuel-injection and not provided for in groups F02M39/00 -F02M57/00, e.g. rotary cylinder-block type of pumps of reciprocating-piston or reciprocating-cylinder type characterised by the piston-drive pneumatic drive, e.g. crankcase pressure drive
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
- F02B75/00—Other engines
- F02B75/02—Engines characterised by their cycles, e.g. six-stroke
- F02B2075/022—Engines characterised by their cycles, e.g. six-stroke having less than six strokes per cycle
- F02B2075/025—Engines characterised by their cycles, e.g. six-stroke having less than six strokes per cycle two
Landscapes
- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Control Of The Air-Fuel Ratio Of Carburetors (AREA)
- Lubrication Of Internal Combustion Engines (AREA)
- Fuel-Injection Apparatus (AREA)
Abstract
ABSTRACT
A fuel Metering system for a two-cycle internal combustion engine comprises an induction pipe through which air is drawn and mixes with fuel entering through an injection orifice in the pipe. A diaphragm pump has a diaphragm separating first and second pump chambers, the first chamber being in communication with the crankcase of the engine and the second chamber being connected through a one-way valve to a fuel tank and through a pressure valve to the injection orifice in the induction pipe. The one-way valve and the pressure valve are adapted to permit fuel to pass from the tank to the pump and from the pump to the injection orifice, respectively. The system provides a simple method of metering fuel which is less complex than conventional carburettor and fuel injection systems and also eliminates the use of a float chamber which renders the system particularly suited to mobile applications such as chain saws, etc.
A fuel Metering system for a two-cycle internal combustion engine comprises an induction pipe through which air is drawn and mixes with fuel entering through an injection orifice in the pipe. A diaphragm pump has a diaphragm separating first and second pump chambers, the first chamber being in communication with the crankcase of the engine and the second chamber being connected through a one-way valve to a fuel tank and through a pressure valve to the injection orifice in the induction pipe. The one-way valve and the pressure valve are adapted to permit fuel to pass from the tank to the pump and from the pump to the injection orifice, respectively. The system provides a simple method of metering fuel which is less complex than conventional carburettor and fuel injection systems and also eliminates the use of a float chamber which renders the system particularly suited to mobile applications such as chain saws, etc.
Description
113~8~3 ,!
The invention relates to a fuel metering system for two-cycle internal combustion i.c. engines. Such engines are particularly suited for use in portable appliances, such as chain saws, although the invention may be employed with two-cycle i.c. engines of any size.
Fuel metering systems for two-cycle i.c. engines generally fall into the categories of carburettors and fuel-injection systems. In a carburettor system, a mechanical or electrical fuel pump supplies fuel to a float chamber in which a constant level is maintained by a float valve. From the float chamber the fuel passes through jets and into the engine, as a result of the partial vacuum in the induction pipe. In this connection, a throttle valve that meters the quantity of air is important. The throttle valve also covers and uncovers various fuel metering ports in the carburettor throat, at least in the idle or off-idle position of the throttle. In the case of a fuel injection system, the fuel is sprayed under high pressure into the induction pipe or directly into the combustion chamber and it is only possible to achieve precise metering of the very small quantities of fuel required for the combustion process by using complex mechanisms.
- Because of the large number of precisely machined components that they contain, both carburettor and fuel injection systems are expensive, of complex construction and, as a result of the large number of components involved, are vulnerable to malfunction. Thus, it is an object of the present invention to provide a fuel metering system for two-cycle i.c. engines that is reliable, relatively simple and can be produced at relatively low cost.
As here described, the fuel metering system consists essentially of a diaphragm pump in which the diaphragm separates two chambers, one of these chambers being acted upon by the pulsating pressure within the engine crankcase. The other chamber is connected to the fuel tank of the engine through a one-way valve and through a . ~
113~
pressure valve to the induction pipe for the combustion air. Since, in the normal course of events, the combustion mixture is drawn into a two-cycle i.c.
engine through the crankcase, and the position of the throttle valve controls the desired power output and also the pressure differentials in the crankcase, it is possible to meter the quantity of fuel that is injected in relationship to the quantity of combustion mixture that is drawn in regardless of the magnitude of this pressure differential, by means of the proposed system. At the same time, these pulsations that take place in the crankcase serve to transport the fuel from the fuel tank into the diaphragm pump. Thus, neither an additional pump nor a gravity feed system are necessary.
The pressure valve prsferably consists of a spring-loaded ball, the tension of the spring being adjustable externally. In this way, it is possible to regulate or adjust the injection time of the diaphragm pump, thus making it possible, for example, to precisely meter the idling fuel requirement.
In addition, by appropriate selection of the spring characteristics, spring tension, and the weight of the ball in the pressure valve, the valve opening interval can be made longer as the engine revolutions increase. This means that as the engine speed increases, the valve will remain open for a longer time, in order to compensate for the shorter injection time at increasing engine revolutions.
It is also advantageous that between the pressure valve and the induction pipe, preferably at the point where the fuel enters the induction pipe, there is a jet that limits the quantity of fuel that is injected when the engine is at full load. This jet may be infinitely variable or may be available in one of a number of interchangeable sizes.
At the point of entry of the fuel into the induction pipe, such pipe is preferably in the form of a venturi throat. Additional suction is thus created, which is dependent upon the speed of the air stream in the venturi ~13~
and can serve to adjust the quantity of fuel. The throttle valve is located in the induction pipe on the engine side of the point of entry of the fuel.
In this regard, the distance between the point of entry of the fuel and the throttle valve is not critical, since the position of the throttle valve has only an indirect effect on the quantity of fuel that is injected. Thus there are no special demands for precision with regard to the throttle valve construction.
It is further proposed that the point of entry of the fuel in the induction pipe be displaced by ninety degrees around the circumference of the pipe relative to the shaft of the throttle valve. This means that the fuel that is in~ected moves directly through the space between the throttle valve and the induction pipe and on into the engine, thereby making it possible to achieve a spontaneous reaction to changes in the position of the throttle valve.
~ oresees that in the area of the throttle valve, on the engine side of the point of entry of the fuel into the induction pipe, there is provided a groove so that the fuel that is injected on starting is passed directly to the narrowest place between the throttle valve and the induction pipe, so that atomisation is immediate and intensive. Such effect may be enhanced by provision of a cut-out in the edge of the throttle valve facing the groove.
More particularly, in accordance with the invention there is provided, a fuel metering system for a two-cycle internal combustion engine whlch lncludes an inductlon plpe through which alr 18 drawn and is mixed with fuel enterlng through an in~ectlon orlfice in said pipe, and a crank case through whlch said air mixed with said fuel is drawn for delivery to a combustlon chamber, comprising;
a diaphragm pump having a diaphragm 6eparating first and second pump 113'16~
chambers, sald first chamber belng ln communlcatlon with the crank case, and sald second chamber belng connected through a one-way valve to a fuel tank and through a pressure valve to sald ln~ectlon orlfice ln said lnduction pipe, said one-way valve permltting fuel to pass from said tank to said pump, and sald pre~sure valve permitting fuel to flow from said pump directly to said injectlon orifice against closing force of the pressure valve, upon operation of said engine.
Specific embodiments of the invention will now be described with reference to the accompanying drawings wherein:
Figure 1 is a schematic illustration of a fuel metering system according to a preferred embodiment of the invention;
Figure 2 is a cross-section on the line II-II of Flgure l; and Figure 3 shows the pressure curves for the pump stroke cycle.
Referrlng to Figure 1, induction pipe 8 is arranged between the internal combustion engine (not shown) and the air filter (not shown). The -3a-~.3~
combustion air required by the engine is drawn into the pipe through the air filter and moves in the direction of the arrow F. The induction pipe 8 has a venturi throat 13 into which a jet l2 of the fuel metering system discharges.
On the engine side of the venturi throat 13 there is located a throttle valve 14, rotatably mounted on the throttle valve shaft 16. The jet 12 is connected with one chamber 4 of a diaphragm pump 1 through a pressure valve 7, This pressure valve 7 consists of a ball 9 and a spring 10, the tension of the spring 10 being externally adjustable by means of an adjusting screw 11. The chamber 4 of the diaphragm pump 1 is also connected through a one-way valve to the fuel tank 6. The chamber 4 is limited by the diaphragm 2 of the spring diaphragm pump 1 and on the side of the diaphragm pump 2 opposite the chamber 4 there is a chamber 3 which is connected by a vacuum line 19 to the crankcase of the engine (not shown).
The fuel metering system that is shown operates as follows. Because of the vacuum developed in the low pressure line 19 connected to the crankcase of the engine,,the diaphragm 2 is forced into a series of reciprocating motions in phase with the pressure variations in the crankcase. This reciprocating motion causes fuel to be sucked from the fuel tank 6 through the one-way valve 5 and into the chamber 4 when the diaphragm moves to the right, and on the return stroke to the left the fuel is pumped from the chamber 4 against the closing pressure of the spring 10 in the valve 7, through the jet 12 and into the region 15 of the induction pipe 8. The quantity of fuel that is moved is directly dependent on the quantity of combustion air that is inducted, and this air mixes with the fuel and the mixture passes into the crankcase according to the position of the throttle valve 14, where it is pre-compressed by the movement of the piston on its downward stroke. Since - the compression pressure in the crankcase is directly dependent on the quantity of combustion mixture that is drawn in, whereas on the other hand the diaphragm pump 1 supplies a (luantity of fuel t;hat is directly dependent on the pressure in the crankcase, the pump ~ill supply a quantity of fuel that is directly dependent on the quantity of mixture that is drawn in. The greater the charge, the greater the pressure of pre-compression will be, and the greater will be the quantity of fuel that is injected by the diaphragm pump.
The desired power output of the internal combustion engine will be obtained simply by control of the throttle valve 1ll, which controls the volume of the charge. Direct control of the quantity of fuel by the throttle valve, as in the case of conventional carburettor systems, does not take place. Thus, there is no need for great precision in the construction of the throttle valve, and for this reason it can be simple and inexpensive.
Figure 2 shows a cross-section on the line II-II of Figure 1 and it can be seen therefore that there is a groove 17 in the wall of the induction pipe 8, displaced approximately ninety degrees relative to the throttle valve shaft 16; this serves the special purpose of delivering the fuel that is required for starting to the narrowest part of the throttle valve in the practically closed position, in order to acheive intensive atomisation by virtue of the extremely high air velocity found at this point. For this purpose, the throttle valve 14 may also be provided with a cut-out 18 facing the groove 17. At this point, mention should be made of the fact that the choke valve that is requird for conventional carburettors in order to provide a richer starting mixture is not necessary in the present case. In this particular fuel metering system, the fuel is automatically injected in greater quantities than normal when the throttle is opened on starting.
Figure 3 shows the time-pressure curves related to the crankcase of the internal combustion engine. The heavy line shows the development of pressure in the crankcase. By pre-tensioning the spring 10 of the pressure valve 7 to the pressure value Pl, the duration of the injection cycle can be 1~3~
limited to the time Tl, Appropriate adjustment of spring characteristicS
and pre-tension and the wei,~ht of the ball 9 will make it possible to prolong V ~
the injection time to the ~Lve T2 for example, as engine speed increases.
Compensation for the shorter injection times at increased speeds will be achieved thereby, whereupon the pressure curve that is associated with the quantity of fuel that is injected will approximate the curve shown by the broken line of Figure ~.
The fuel metering system that has been described is of simpler construction, and cheaper to produce than conventional carburettors and it is simpler to adjust over a wider ran~e of speeds. In addition, this fuel metering system is to all intents and purposes unaffected by position, since it does not incorporate a float chamber and therefore is suitable for mobile internal combustion engines, such as chain saw motors, for example.
The invention relates to a fuel metering system for two-cycle internal combustion i.c. engines. Such engines are particularly suited for use in portable appliances, such as chain saws, although the invention may be employed with two-cycle i.c. engines of any size.
Fuel metering systems for two-cycle i.c. engines generally fall into the categories of carburettors and fuel-injection systems. In a carburettor system, a mechanical or electrical fuel pump supplies fuel to a float chamber in which a constant level is maintained by a float valve. From the float chamber the fuel passes through jets and into the engine, as a result of the partial vacuum in the induction pipe. In this connection, a throttle valve that meters the quantity of air is important. The throttle valve also covers and uncovers various fuel metering ports in the carburettor throat, at least in the idle or off-idle position of the throttle. In the case of a fuel injection system, the fuel is sprayed under high pressure into the induction pipe or directly into the combustion chamber and it is only possible to achieve precise metering of the very small quantities of fuel required for the combustion process by using complex mechanisms.
- Because of the large number of precisely machined components that they contain, both carburettor and fuel injection systems are expensive, of complex construction and, as a result of the large number of components involved, are vulnerable to malfunction. Thus, it is an object of the present invention to provide a fuel metering system for two-cycle i.c. engines that is reliable, relatively simple and can be produced at relatively low cost.
As here described, the fuel metering system consists essentially of a diaphragm pump in which the diaphragm separates two chambers, one of these chambers being acted upon by the pulsating pressure within the engine crankcase. The other chamber is connected to the fuel tank of the engine through a one-way valve and through a . ~
113~
pressure valve to the induction pipe for the combustion air. Since, in the normal course of events, the combustion mixture is drawn into a two-cycle i.c.
engine through the crankcase, and the position of the throttle valve controls the desired power output and also the pressure differentials in the crankcase, it is possible to meter the quantity of fuel that is injected in relationship to the quantity of combustion mixture that is drawn in regardless of the magnitude of this pressure differential, by means of the proposed system. At the same time, these pulsations that take place in the crankcase serve to transport the fuel from the fuel tank into the diaphragm pump. Thus, neither an additional pump nor a gravity feed system are necessary.
The pressure valve prsferably consists of a spring-loaded ball, the tension of the spring being adjustable externally. In this way, it is possible to regulate or adjust the injection time of the diaphragm pump, thus making it possible, for example, to precisely meter the idling fuel requirement.
In addition, by appropriate selection of the spring characteristics, spring tension, and the weight of the ball in the pressure valve, the valve opening interval can be made longer as the engine revolutions increase. This means that as the engine speed increases, the valve will remain open for a longer time, in order to compensate for the shorter injection time at increasing engine revolutions.
It is also advantageous that between the pressure valve and the induction pipe, preferably at the point where the fuel enters the induction pipe, there is a jet that limits the quantity of fuel that is injected when the engine is at full load. This jet may be infinitely variable or may be available in one of a number of interchangeable sizes.
At the point of entry of the fuel into the induction pipe, such pipe is preferably in the form of a venturi throat. Additional suction is thus created, which is dependent upon the speed of the air stream in the venturi ~13~
and can serve to adjust the quantity of fuel. The throttle valve is located in the induction pipe on the engine side of the point of entry of the fuel.
In this regard, the distance between the point of entry of the fuel and the throttle valve is not critical, since the position of the throttle valve has only an indirect effect on the quantity of fuel that is injected. Thus there are no special demands for precision with regard to the throttle valve construction.
It is further proposed that the point of entry of the fuel in the induction pipe be displaced by ninety degrees around the circumference of the pipe relative to the shaft of the throttle valve. This means that the fuel that is in~ected moves directly through the space between the throttle valve and the induction pipe and on into the engine, thereby making it possible to achieve a spontaneous reaction to changes in the position of the throttle valve.
~ oresees that in the area of the throttle valve, on the engine side of the point of entry of the fuel into the induction pipe, there is provided a groove so that the fuel that is injected on starting is passed directly to the narrowest place between the throttle valve and the induction pipe, so that atomisation is immediate and intensive. Such effect may be enhanced by provision of a cut-out in the edge of the throttle valve facing the groove.
More particularly, in accordance with the invention there is provided, a fuel metering system for a two-cycle internal combustion engine whlch lncludes an inductlon plpe through which alr 18 drawn and is mixed with fuel enterlng through an in~ectlon orlfice in said pipe, and a crank case through whlch said air mixed with said fuel is drawn for delivery to a combustlon chamber, comprising;
a diaphragm pump having a diaphragm 6eparating first and second pump 113'16~
chambers, sald first chamber belng ln communlcatlon with the crank case, and sald second chamber belng connected through a one-way valve to a fuel tank and through a pressure valve to sald ln~ectlon orlfice ln said lnduction pipe, said one-way valve permltting fuel to pass from said tank to said pump, and sald pre~sure valve permitting fuel to flow from said pump directly to said injectlon orifice against closing force of the pressure valve, upon operation of said engine.
Specific embodiments of the invention will now be described with reference to the accompanying drawings wherein:
Figure 1 is a schematic illustration of a fuel metering system according to a preferred embodiment of the invention;
Figure 2 is a cross-section on the line II-II of Flgure l; and Figure 3 shows the pressure curves for the pump stroke cycle.
Referrlng to Figure 1, induction pipe 8 is arranged between the internal combustion engine (not shown) and the air filter (not shown). The -3a-~.3~
combustion air required by the engine is drawn into the pipe through the air filter and moves in the direction of the arrow F. The induction pipe 8 has a venturi throat 13 into which a jet l2 of the fuel metering system discharges.
On the engine side of the venturi throat 13 there is located a throttle valve 14, rotatably mounted on the throttle valve shaft 16. The jet 12 is connected with one chamber 4 of a diaphragm pump 1 through a pressure valve 7, This pressure valve 7 consists of a ball 9 and a spring 10, the tension of the spring 10 being externally adjustable by means of an adjusting screw 11. The chamber 4 of the diaphragm pump 1 is also connected through a one-way valve to the fuel tank 6. The chamber 4 is limited by the diaphragm 2 of the spring diaphragm pump 1 and on the side of the diaphragm pump 2 opposite the chamber 4 there is a chamber 3 which is connected by a vacuum line 19 to the crankcase of the engine (not shown).
The fuel metering system that is shown operates as follows. Because of the vacuum developed in the low pressure line 19 connected to the crankcase of the engine,,the diaphragm 2 is forced into a series of reciprocating motions in phase with the pressure variations in the crankcase. This reciprocating motion causes fuel to be sucked from the fuel tank 6 through the one-way valve 5 and into the chamber 4 when the diaphragm moves to the right, and on the return stroke to the left the fuel is pumped from the chamber 4 against the closing pressure of the spring 10 in the valve 7, through the jet 12 and into the region 15 of the induction pipe 8. The quantity of fuel that is moved is directly dependent on the quantity of combustion air that is inducted, and this air mixes with the fuel and the mixture passes into the crankcase according to the position of the throttle valve 14, where it is pre-compressed by the movement of the piston on its downward stroke. Since - the compression pressure in the crankcase is directly dependent on the quantity of combustion mixture that is drawn in, whereas on the other hand the diaphragm pump 1 supplies a (luantity of fuel t;hat is directly dependent on the pressure in the crankcase, the pump ~ill supply a quantity of fuel that is directly dependent on the quantity of mixture that is drawn in. The greater the charge, the greater the pressure of pre-compression will be, and the greater will be the quantity of fuel that is injected by the diaphragm pump.
The desired power output of the internal combustion engine will be obtained simply by control of the throttle valve 1ll, which controls the volume of the charge. Direct control of the quantity of fuel by the throttle valve, as in the case of conventional carburettor systems, does not take place. Thus, there is no need for great precision in the construction of the throttle valve, and for this reason it can be simple and inexpensive.
Figure 2 shows a cross-section on the line II-II of Figure 1 and it can be seen therefore that there is a groove 17 in the wall of the induction pipe 8, displaced approximately ninety degrees relative to the throttle valve shaft 16; this serves the special purpose of delivering the fuel that is required for starting to the narrowest part of the throttle valve in the practically closed position, in order to acheive intensive atomisation by virtue of the extremely high air velocity found at this point. For this purpose, the throttle valve 14 may also be provided with a cut-out 18 facing the groove 17. At this point, mention should be made of the fact that the choke valve that is requird for conventional carburettors in order to provide a richer starting mixture is not necessary in the present case. In this particular fuel metering system, the fuel is automatically injected in greater quantities than normal when the throttle is opened on starting.
Figure 3 shows the time-pressure curves related to the crankcase of the internal combustion engine. The heavy line shows the development of pressure in the crankcase. By pre-tensioning the spring 10 of the pressure valve 7 to the pressure value Pl, the duration of the injection cycle can be 1~3~
limited to the time Tl, Appropriate adjustment of spring characteristicS
and pre-tension and the wei,~ht of the ball 9 will make it possible to prolong V ~
the injection time to the ~Lve T2 for example, as engine speed increases.
Compensation for the shorter injection times at increased speeds will be achieved thereby, whereupon the pressure curve that is associated with the quantity of fuel that is injected will approximate the curve shown by the broken line of Figure ~.
The fuel metering system that has been described is of simpler construction, and cheaper to produce than conventional carburettors and it is simpler to adjust over a wider ran~e of speeds. In addition, this fuel metering system is to all intents and purposes unaffected by position, since it does not incorporate a float chamber and therefore is suitable for mobile internal combustion engines, such as chain saw motors, for example.
Claims (9)
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A fuel metering system for a two-cycle internal combustion engine which includes an induction pipe through which air is drawn and is mixed with fuel entering through an injection orifice in said pipe, and a crank case through which said air mixed with said fuel is drawn for delivery to a combustion chamber, comprising;
a diaphragm pump having a diaphragm separating first and second pump chambers, said first chamber being in communication with the crank case, and said second chamber being connected through a one-way valve to a fuel tank and through a pressure valve to said injection orifice in said induction pipe, said one-way valve permitting fuel to pass from said tank to said pump, and said pressure valve permitting fuel to flow from said pump directly to said injection orifice against closing force of the pressure valve, upon operation of said engine.
a diaphragm pump having a diaphragm separating first and second pump chambers, said first chamber being in communication with the crank case, and said second chamber being connected through a one-way valve to a fuel tank and through a pressure valve to said injection orifice in said induction pipe, said one-way valve permitting fuel to pass from said tank to said pump, and said pressure valve permitting fuel to flow from said pump directly to said injection orifice against closing force of the pressure valve, upon operation of said engine.
2. A fuel metering system according to Claim 1, characterized in that said pressure valve consists of a valve seat having an orifice therethrough and a spring-loaded ball biased against said seat to block said orifice, said orifice adapted to pass fuel when the pressure of said fuel is greater than the force of said spring acting upon said ball, and means for externally adjusting the compression of said spring.
3. A fuel metering system according to Claim 2, characterized in that the spring characteristics, compression adjustment of the spring and the weight of the ball are selected to open the pressure valve for increasing periods of time as the speed of the engine increases.
4. A fuel metering system according to any of claims 1, 2 and 3, characterized in that the injection orifice is formed as a jet to restrict the quantity of fuel injected into said induction pipe when the engine is under full load.
5. A fuel metering system according to any of Claims 1, 2 and 3, characterized in that in the area of said injection orifice in said induction pipe, said pipe is formed as a venturi throat.
6. A fuel metering system according to any of Claims 1, 2 and 3, characterized in that a throttle valve is provided in said induction pipe between said injection orifice and said engine.
7. A fuel metering system according to any of Claims 1, 2 and 3, characterized in that a throttle valve is provided comprising a valve plate mounted upon a shaft extending transversely of said induction pipe and located between said injection orifice and said engine, said orifice being displaced approximately ninety degrees in relation to the axis of said throttle valve shaft.
8. A fuel metering system according to any of Claims 1, 2 and 3, characterized in that a throttle valve is provided, comprising a valve plate mounted upon a shaft extending transversely of said induction pipe and located between said injection orifice and said engine, said induction pipe having a groove in the region of the induction pipe wall immediately adjacent said valve plate in its position of maximum closure of said pipe, whereby fuel mixture may pass through the opening defined by said groove and said valve plate.
9. A fuel metering system according to any of Claims 1, 2 and 3, characterized in that a throttle valve is provided, comprising a valve plate mounted upon a shaft extending transversely of said induction pipe and located between said injection orifice and said engine, said induction pipe having a groove in the region of the induction pipe wall immediately adjacent said valve plate in its position of maximum closure of said pipe, and said valve plate having a cut-out at the periphery thereof in a region facing said groove and complementary with said groove to form an opening through which fuel mixture may pass when said valve plate is in its position of maximum closure of said pipe.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP2934816.1 | 1979-08-29 | ||
| DE19792934816 DE2934816A1 (en) | 1979-08-29 | 1979-08-29 | Fuel supply for two=stroke IC engine - has membrane operated by crankcase pressure to draw fuel from tank via non-return valve |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1134689A true CA1134689A (en) | 1982-11-02 |
Family
ID=6079516
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000359198A Expired CA1134689A (en) | 1979-08-29 | 1980-08-28 | Fuel metering system for a two-cycle internal combustion engine |
Country Status (4)
| Country | Link |
|---|---|
| JP (1) | JPS5634950A (en) |
| CA (1) | CA1134689A (en) |
| DE (1) | DE2934816A1 (en) |
| SE (1) | SE8005874L (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE202009007558U1 (en) * | 2009-05-27 | 2010-10-14 | Makita Corp., Anjo | Electrically controlled carburettor |
| DE102016123774B3 (en) * | 2016-12-08 | 2018-02-01 | Makita Corporation | A carburettor for an internal combustion engine of an implement and method for controlling a fuel flow in an idling operation of a carburetor |
-
1979
- 1979-08-29 DE DE19792934816 patent/DE2934816A1/en not_active Withdrawn
-
1980
- 1980-08-21 SE SE8005874A patent/SE8005874L/en not_active Application Discontinuation
- 1980-08-28 CA CA000359198A patent/CA1134689A/en not_active Expired
- 1980-08-29 JP JP11852080A patent/JPS5634950A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| DE2934816A1 (en) | 1981-03-19 |
| SE8005874L (en) | 1981-03-01 |
| JPS5634950A (en) | 1981-04-07 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |