Patent Grant
7185623
This invention relates to carburetors, and more particularly to an air-fuel mixture enrichment circuit that facilitates engine starting.
Most engines require a mixture enrichment system to improve or even allow starting. An enrichment system is especially necessary when the engine is cold, or after the engine has been run out of fuel. The two common means of enrichment in the field of small engines are the choke and the primer.
The choke provides enrichment by closing off the front end of the air intake of a carburetor to allow a manifold vacuum to draw on all of the fuel passages that open to the air intake. The disadvantage of the choke is that the user must close the choke completely and then crank the engine until they hear a false start. The choke is then partially opened and the engine is cranked until it starts. When the engine is warmed up 30 to 40 seconds, the choke is opened fully. This operation is too complex for many users and results in many field returns and complaints.
The primer uses a manually operated bulb to inject fuel into the carburetor throat. The disadvantage of the primer is that a simple primer cannot regulate the amount of fuel injected into the carburetor throat which makes it easy for the user to over- or under-prime the engine, resulting in no start.
An improved enrichment system uses an auxiliary fuel pump coupled with the carburetor body. The auxiliary fuel pump provides enrichment by injecting fuel into the carburetor throat when starting the engine. To prevent over- or under-priming the engine, the auxiliary-fuel pump uses a pulse emitted from the engine's crankcase to control the fuel injection. This approach is described in more detail in U.S. Pat. No. 5,704,774, entitled “Carburetor Start Pump Circuit,” filed on May 24, 1996, which is hereby incorporated by reference in its entirety.
When using a system such as the auxiliary fuel pump described above, it may be desirable to deactivate the system when the engine warms up because a constant fuel-air ratio will have been obtained, and thus, there would be no need for additional fuel injection. However, often times, the user may forget to do so or may engage the system when the engine is already running and is warmed up or hot. This may result in the engine “conking out” or stalling due to too much fuel being injected into the carburetor throat while the engine is running.
Therefore, it is believed that an improved carburetor start pump circuit would be desirable.
The carburetor start pump circuit of the present invention serves to facilitate engine starting in a simple manner that is independent of manifold vacuums and capable of regulating the amount of fuel injected into the carburetor throat to ensure the engine is properly primed. It preferably has an auxiliary fuel pump mounted on a relatively standard carburetor body, a start pulse passage extending through the carburetor body to the auxiliary fuel pump, and a fuel circuit having an intake side which extends from a metering chamber of the carburetor body to the auxiliary fuel pump and a discharge side which is interconnected to the intake side and extends from the auxiliary fuel pump to a throttle bore in the air intake of the carburetor body. To prevent the engine from stalling, a restriction jet is placed within the start pulse passage to limit the amount of fuel that the auxiliary pump may discharge into the throttling bore when the engine transmits pulses at high frequencies.
An object of this invention is to provide an improved carburetor start pump circuit.
Further, objects and advantages of the invention will become apparent from the following detailed description and accompanying drawings.
Referring now in detail to the drawings, therein illustrated is a novel carburetor start pump circuit of the present invention. Turning to
Three passageways are bored into the carburetor body 10 from the top surface 13. The first is a pulse passageway 24 which opens into the starting pulse passageway 20. The second is a fuel intake passageway 22 which opens into the metering chamber (not shown) of the carburetor body 10. The third is a fuel discharge passageway 26 which opens into a throttle bore 14 of the air intake of the carburetor body 10.
Referring to
Turning to
The fuel pump gasket 40, which mounts on the carburetor body 10 on top of the fuel pump diaphragm 30, also includes a pair of holes 41 and 43 that are aligned with holes 21 and 23 in the carburetor body 10 to mount the gasket 40. The fuel pump gasket 40 also includes a fuel intake hole 42, a pulse hole 44, and a fuel discharge hole 46, respectively, that are aligned with the fuel intake passageway 22, the pulse passageway 24, and the fuel discharge passageway 26, respectively, in the carburetor body 10 when the fuel pump gasket 40 is mounted on the carburetor body 10.
The auxiliary fuel pump 12 includes a pump body 50 mounted on top of the main fuel pump 11, a start pump gasket 70 mounted on top of the start pump body 50, a start pump diaphragm 80 mounted on top of the start pump gasket 70 and a start pump cover 90 mounted on top of the start pump diaphragm 80. Holes 51 and 53 in the start pump body 52, holes 71 and 73 in the start pump gasket 70, holes 81 and 83 in the start pump diaphragm 80, and holes 91 and 93 in the start pump cover 90 are all aligned with the holes 21 and 23 in the carburetor body 10 to mount these components on the carburetor body 10.
The auxiliary pump body 50 as shown in
The auxiliary pump body 50 also includes a pulse passageway 54 bored through the auxiliary pump body 50 and a fuel discharge passageway 56 bored into the auxiliary pump body 50 from its bottom surface 58. The pulse passageway 54 is aligned with the pulse passageway 24 in the carburetor body 10 and the fuel discharge passageway 56 is aligned with the fuel discharge passageway 26 in the carburetor body 10. The fuel discharge passageway 56 opens to a discharge check valve chamber 65 bored into the auxiliary pump body 50 from the pumping chamber 60. A discharge check valve 66 is mounted in the valve chamber 65. The discharge check valve 66 is held close against its seat by a spring 68 positioned on the discharge side of the check valve 66. The spring force prevents fuel from being drawn out of the system by the carburetor manifold vacuum when the start pump 12 is shut off, i.e., when the throttle shaft 25 is rotated out of the start position and passageway 28 is no longer aligned with passageways 20 and 24. A calibrated jet 64 may be positioned on the inlet side of the discharge check valve 66. The calibrated jets 63 and 64 restrict the fuel flow into the engine to prevent an over rich condition at startup.
The auxiliary pump gasket 70 maintains a seal between the auxiliary pump body 50 and the auxiliary pump diaphragm 80. The gasket 70 includes a pulse hole 74 aligned with the pulse passageway 24 in the carburetor body 10 and a hole 75 aligned with the pumping chamber 60 in the auxiliary pump body 50 to allow the auxiliary pump diaphragm 80 to communicate with the pumping chamber 60.
The auxiliary pump diaphragm 80 transfers the force of the crank case pulse to the fuel in the pumping chamber 60 of the auxiliary pump body 50. The flat auxiliary pump diaphragm 80 includes a pulse hole 84 aligned with the pulse passageway 24 in the carburetor body 10.
The pump cover 90, which seals the stack of gaskets 40 and 70, diaphragms 30 and 80, and the auxiliary pump body 52, accepts the crank case pulse P and directs it to the auxiliary pump diaphragm 80.
In operation, the start pump 10 is activated by turning on the crank case pulse supplied to it. The crank case pulse P can be controlled with the throttle shaft as shown in
The pulse P travels up through the stack of the main fuel pump diaphragm 30 and the main fuel pump gasket 40, and then through the auxiliary pump body 52, diaphragm 80, and gasket 70 and on into the start pump cover 90. The pulse P moves the diaphragm 80 up and down which creates a corresponding vacuum and pressure in the pumping chamber 60 of the auxiliary pump body 50. The vacuum pulse opens the inlet check valve 62 and draws fuel I from the metering chamber (not shown) of the carburetor body 10. By drawing fuel from the metering chamber, the carburetor start pump circuit advantageously acts as an air purge or primer.
The fuel I passes through the carburetor body 10 through the main fuel pump diaphragm 30 and gasket 40, into the start pump body 50 and on into the pumping chamber 60 through the inlet check valve 62 and, optionally, through the calibrated metering jet 63. When the auxiliary pump diaphragm 80 is pushed down into the auxiliary pump body 50 by the crank case pulse P, the inlet check valve 62 is forced closed and the force of the crank case pulse P is transferred to the fuel forcing the fuel through the discharge check valve 66 and, optionally, first through the calibrated metering jet 64. The fuel must pass through the starting jet 64 and press open the spring 68 loaded check valve 66 to leave the pumping chamber 60. The spring 68 exerts a sufficient force on the check valve 66 to prevent it from being opened by a manifold vacuum and thus ensuring that fuel is not drawn through the carburetor start pump circuit unless the start pump 12 is receiving a pulse P.
The fuel D then exits the auxiliary pump body 50 through the discharge fuel passageway 56 and passes back through the main pump gasket 40 and diaphragm 30, and on through the fuel discharge passageway 26 into the throttle bore 14 in the carburetor body 10. When the engine is warmed up, the operator shuts off the start pump circuit and the engine begins normal operation.
As mentioned above, often times the operator may neglect to shut off the start pump circuit when the engine is warmed up or accidentally engage the start pump when the engine is already operating and warmed up. This may result in the engine stalling or “conking out” from too much fuel being discharged into the throttling bore 14. One approach to prevent the engine from stalling is to place a calibrated restriction or jet 85 anywhere along the path that the start pulse P travels, and preferably somewhere between the carburetor body 10 and the start pump cover 90 of the auxiliary fuel pump 12. As shown in
The jet 85 is positioned and calibrated such that the jet 85 tends to substantially choke off high frequency pulses P transmitted from the engine, thus substantially choking off the power to move the start pump diaphragm 80 at the high frequencies. In other words, when the engine starts to warm up, the jet 85 tends to substantially reduce the amount of fuel D that the auxiliary fuel pump 12 discharges into the throttling bore 24.
When the engine is being cranked, a low frequency pulse P, e.g., about 18 hz or about 800 rpm, is transmitted from the engine. At the lower frequency, a substantial portion of the pulse P will pass through the jet 85 sufficient to operate the start pump diaphragm 80. When the engine starts to warm up, it starts to supply a higher frequency pulse P, e.g., about 80 hz or about 5000 rpm. At this point, the engine will no longer need mixture enrichment. The jet 85 tends to choke off a substantial amount of the pulse P transmission to the start pump circuit sufficient to substantially decrease the operation of the start pump diaphragm 80. Thus, the start pump circuit will advantageously cease operation or at least substantially limit the amount of fuel D discharged into the throttling bore 24, preventing the engine from conking out or stalling.
In an alternative embodiment (see
Thus, the carburetor start pump circuit of the present invention provides many benefits over the prior art. While the above description contains many specificities, these should not be construed as limitations on the scope of the invention, but rather as an exemplification of one preferred embodiment thereof. Many other variations are possible.
Accordingly, the scope of the present invention should be determined not by the embodiments illustrated above, but by the appended claims and their legal equivalents.
This application is a continuation of U.S. application Ser. No. 10/162,458 filed Jun. 3, 2002 now U.S. Pat. No. 6,799,545, which application is incorporated herein by reference.
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| Number | Date | Country | |
|---|---|---|---|
| 20040261741 A1 | Dec 2004 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10162458 | Jun 2002 | US |
| Child | 10887152 | US |
