FR2481371A1 - HOT RESET VALVE FOR MEMBRANE CARBURETOR - Google Patents

Abstract

A HOT RESTART VALVE ASSEMBLY 64 FOR DIAPHRAGM CARBURETOR 10 INCLUDES A CONTROL CHAMBER 68 AND A VAPOR DISCHARGE CHAMBER 66 SEPARATED BY A DIAPHRAGM PRESSED BY A SPRING. THE VAPOR DISCHARGE CHAMBER COMMUNICATES WITH THE FUEL CHAMBER 26 OF THE CARBURETOR. A VAPOR DISCHARGE PORT 76 INCLUDES A NORMALLY OPEN 78 MOVABLE VALVE. THE CONTROL CHAMBER 68 CONTROLS THE CIRCULATION OF AIR IN THE CARBURETOR'S INTRODUCTION CHANNEL 14 THROUGH A SIGNAL PORT 94 AND ACTIVATES A MEMBRANE 70 TO WHICH THE VALVE 78 IS CONNECTED IN RESPONSE TO A FLOW OF AIR IN CHANNEL 14. WHILE THE ENGINE IS RUNNING, THE VALVE 78 IS TAKEN TO CLOSE THE EXHAUST PORT 76, AND WHEN THE ENGINE IS STOPPED, THE VALVE 78 OPENS TO EVACUATE THE VAPORS FROM THE CHAMBER A FUEL.

Description

The present invention relates to a carburetor with mem-

brane which can be rid of fuel vapors,

so as to facilitate start-up after a so-called "va-

por lock ". More particularly, the present invention

identifies a diaphragm carburetor cooperating with a pneumatically actuated valve to cause rapid evacuation

vapors contained in the carburetor fuel chamber

which accelerates the transfer of liquid fuel to the chamber, the metering of the fuel going towards the channel

îo of introduction, then the supply of fuel to the engine.

  Diaphragm carburetors are widely used in

internal combustion engines powered by liquid fuel.

In particular, diaphragm carburetors have found

Considerable applications in small devices powered by an internal combustion engine, such as mowers, weed knives, snow blowing machines and chainsaws. One of the main objectives of a manufacturer of devices of this kind is to have a compact, light engine, so as to minimize the total weight of the device. To receive this equipment, the motor manufacturers have developed compact, light and efficient motors. An internal combustion engine operates at temperatures

well above ambient temperatures. It is general-

2. compactly, as indicated above, and therefore the heat it releases tends to heat all the elements

that it contains or that are in its vicinity, in par

especially the carburetor. During engine operation, the fuel pump and the affected channels supply fuel to the carburetor chamber. Diaphragm carburetors generally use a diaphragm driving a valve in order to regulate the flow of the fuel introduced.

in the bedroom. This room has a consistent arrangement

  with a main nozzle and a reverse gear nozzle

slowed, and channels connecting the fuel chamber to a tank

nal of introduction into the carburetor for the fuel mixture

rant-air and its introduction into the engine.

As the engine warms up, the carburetor runs continuously, the fuel being transmitted to the carburetor and passing through it. This direct current of fuel allows

keep the carburetor temperature below

re to that of the engine. However, when stopped, the engine is at a high temperature, the temperature to which the carburetor is exposed without benefiting from a direct current of coolant. Therefore the temperature of the carburetor also rises. This stopping of the engine at a high temperature is at the origin of what is called in the

technical "vapor lock".

At a high temperature, the fuel in the carburetor chamber vaporizes and is trapped in this chamber;

the steam is then slowly evacuated through the nozzle nozzles

burant which communicate with the introduction channel. Such vaporization and the subsequent loss of fuel through the chamber decreases the volume of liquid fuel available in this chamber for restarting the engine. We found

that this lack of fuel prevented the restart of a mo-

explosion fuel equipped with a diaphragm carburetor. The room

Fuel bre is relatively small in most applications, i.e. on the order of a few cubic centimeters. It is well known that a temperature of only 650C is sufficient to vaporize the most volatile fraction of a normal mixture of gasoline. Therefore, after a vapor lock period, most of the fuel supplied to the chamber for restart will vaporize quickly, leaving virtually no fuel for startup. In addition, the pressure in the fuel chamber increases, preventing a

correct operation of the diaphragm actuator for the furnace-

fuel and therefore compromising the dosa-

fuel age for restarting the engine.

The present invention solves this problem.

lO me by providing a vent for the release of pressure from

steam and the evacuation of vapors from the chamber, which

starts transferring a new volume of liquid fuel

in the bedroom. This transfer can thus be considered as

performing the function of a refrigerant.

  A diaphragm carburetor for an internal combustion engine according to the present invention comprises a body defining an introduction channel in which a butterfly plate is pivotally mounted. Associated with the carburetor is a fuel chamber, a signal port for monitoring the air flow in the introduction channel, and a vapor exhaust port for communication between the fuel chamber and a discharge chamber of vapors from an assembly comprising an exhaust valve for hot restarting This valve assembly comprises a body defining a cavity in which is placed a membrane, which divides it into a control chamber and a vapor discharge chamber. The body of this assembly defines an orifice in which a valve is removably placed

normally open outlet, responding to a spring of -

stress and membrane. The valve is fixed to one end of the membrane so as to move to a closed position in response to the air flow passing through the introduction channel. The valve allows vapors

leave the room when the engine stops, but avoid

the air entering this room during operation

engine.

The present invention will be well understood during the

248137 I

4.

following description made in conjunction with the drawings below

seals in which: Figure 1 is a sectional view of a carburetor incorporating a discharge valve according to the present invention, where a valve and the carburetor are combined in the same structure; and Figure 2 is a sectional view of a variant

of the present invention.

In Figure 1, a carburetor 10 has more

main components, in particular a body 12

having a central part which defines an intro channel 14

air duction having a side wall 16. The body 12 contains

me a fuel pump 20 and defines a main line

fuel blade 18 comprising a connecting means 22 which

connects line 18 to a fuel source (not shown

tee). The body 12 defines a channel 24 which communicates the pump 20 with a fuel chamber 26, defined by the

  body 12, and a set 28-composed of a closing plate-

structure 30 and a membrane actuator 32 fixed to the body 12

  by a screw 34 and by similar screws (not shown).

The diaphragm actuator 32 has a rivet 36 located in the center. A lever 38 is pivotally mounted on an axis 40

and one of the arms of the lever abuts against the head of the rivet 36.

A biasing spring 42 extends between the arm of the

-25 sink just described and the carburetor body, when-

that the diaphragm is in the reference position re-

shown in Figure 1. Attached to the other arm of the lever 38 is a needle valve 44 seated in an opening 46 in the

body 12 at the junction of channel 24 and the fuel chamber

Rant 26 for controlling the fuel flow between the

nal 24 and the chamber 26. The body 12 and the wall 16 defined-

feels a main fuel nozzle 48 and fuel nozzles for idling 50 and 52. The body 12 defines a fuel well 54 and an orifice 56 at the head

of the main nozzle 48, and an orifice 56 communicates

quer the nozzle 48 with the chamber 26. The nozzles of mar-

vacuum che 50 and 52 communicate with a fuel chamber

5.

idling rant 51 through channels 53 and 55, res-

pectively, these three elements being defined by the body 12. The chamber 51 communicates with the chamber 26 by a channel 57 defined in the body 12. An adjustable needle valve 58 is positioned in the orifice 56 so as to control the

fuel flow rate leaving chamber 26; the punch valve

sheet 58 is controlled by a threaded shaft 60. A plate 62 forming a butterfly is pivotally mounted in the introduction channel 14 between the main nozzle 48 and a

îO explosion (not shown).

  The body 12 of the carburetor 10 also defines an assembly comprising an exhaust valve 64, having a vapor chamber 66 and an air flow control chamber 68. A pneumatic actuator 70 is mounted between the chambers 66 and 68. wall 72 defines the upper surface of chamber 66. Wall 72 also defines a recess 74 and an orifice 76 for a discharge valve inside the recess 74 so as to receive a valve element 78 fixed to a rod 80. Fixed to the pneumatic actuator 70 in the chamber 66 is a mounting element 82 to which the rod 80 is fixed. On the surface of the actuator 70 opposite to that on which the rod 80 is fixed is a mounting plate 84 , which is located in the chamber 68. A wall 86 of the chamber 68. is defined by the wall 16 of the introduction channel 14, a wall which has a protruding button 88

towards the interior of chamber 68. A spring for biasing

tion 90, fixed to the button 88, extends into the chamber 68 and is fixed to the mounting plate 84. A hole for pneumatic signal 92, a channel 93 and a hole 94, all defined in the body 12, pass the current passing through the channel 14 in the air flow control chamber 68. A vapor exhaust orifice 95, a channel 96 and an orifice of the vapor chamber 97, all defined in the body 12, make the chamber communicate 66 of the valve assembly 64 and the fuel chamber 26. A channel 98 of the assembly 64 and a

opening 99 defined in the wall 16 of the channel 14 makes common

insert the recess 74 and the insertion channel 14 downstream 248137i 6.

of butterfly 62.

  The carburetor 10 is a membrane carburetor of a type known in the prior art. The fuel comes from a source (not shown) through the main line 18 and enters the pump 20, and from there goes to the channel 24 communicating with the fuel chamber 26. The fuel is pumped

to be introduced into chamber 26 depending on the de-

mande, which depends on a differential pressure between the chamber 26 and the atmospheric pressure, so as to implement the actuator 32 of the membrane. This in turn moves the lever 38 despite the biasing spring 42

and the lever 38 pivots around the axis 40 to open the

pet 44, which allows the filling of the chamber 26 in car-

burant. The fuel then passes through the orifice 56 at the top

needle valve 58, then in the main nozzle

48. At idling speeds, the fuel is

seen downstream of the butterfly 62 actually closed, via

nozzles 50 and 52 after leaving room 51, in response to a reduced request. Fuel demand is the demand caused by the rapid introduction of air into

channel 14 after nozzle 48. Fuel is dosed from

shot from nozzle 48, causing the circulation of a mixture

air-fuel in the channel 14, at the throttle 62,

and therefore to the internal combustion engine.

During normal operation of the engine and the crankcase, the engine temperature rises well above ambient temperature. However, largely because of the continuity of the flow of liquid fuel to and through carburetor 10, the temperature of

the fuel chamber 26 is maintained at a temperature

  lower than that of the engine. When the engine is off, the car-

burant stops running and the carburetor 10 is now

subject to an increase in temperature due to the temperature

high engine erasure. This non-operating period

causes the carburetor temperature to rise.

We found that the most volatile fraction of most

gasolines had a fractional distillation temperature

7.

Mayor of 650C. In this case, we found that the car-

  burant located in room 26 was completely evaporated after about 10 minutes of shutdown. The fuel chamber volume of the test carburetor, as well as that of most small engine carburetors, is approximately a few cubic centimeters. The carburetor 10 can thus be at a high temperature for a considerable period of time, which has

empty the room. Restarting the ne-

  stops fuel. However, during its pumping into the hot chamber 26, the fuel is almost immediately transformed into vapors and cannot be dosed in

nozzle 48, which results in the problem of restarting

hot rage.

In the present invention, the valve assembly 64 includes the valve member 78 which is normally open.

during engine shutdown. Therefore, during the introduction

tion of the fuel in chamber 26 while the engine is

  restarted, it vaporizes and can escape by the

intermediate of assembly 64. This assembly constitutes a class

pet-normally open whose chamber 66 communicates with the fuel chamber 26 through the channel 96 and the orifices 95

and 97. Room 66 also communicates with the information channel.

troduction 14 located downstream of the butterfly 62 through the orifice 76, the recess 744 the channel 98 and the orifice 99 when the element

valve 78 is in its open position. The the-

valve 78 is stressed in this open position--

ture or evacuation by the biasing spring 90 which acts on the pneumatic actuator 70 via the mounting plate 84. During the periods of operation of the engine, there is a rapid circulation of air in the channel 14. This circulation creates a vacuum or reduced pressure in the chamber 68 of the valve assembly 640 The chamber 68 communicates with the introduction channel 14 through the channel 93

and ports 92 and 94. While the air or air-mixture

fuel rushes to the orifice 94 of channel 14, a pressure below atmospheric pressure is

established in chamber 68. When the pressure in the chamber

248137 i 8. bre 68 is about 75 millimeters of water below the

chamber pressure 66, the pneumatic actuator 70

comes back despite the tension of the spring 90, which has

the effect of causing the valve element 78 to close the orifice

ce 76 despite the evacuation of fuel vapors and,

identically, to prevent the entry of air into the room

fuel 26 while the engine is running.

Therefore, as noted, the element of

  valve 78 is closed during air circulation in the case

nal introduction 14 at a level sufficient to create a differential pressure reduced by at least 75 millimeters of water between the chambers 66 and 68. The valve member 78 is open at all times. After a "vapor lock", the carburetor and the fuel chamber 26 are both at a temperature above 650C. While fresh fuel

is introduced by pumping into chamber 26 so as to redefine

start the engine, it is vaporized almost immediately and

this vapor must be removed before more fuel

rant is not pumped into chamber 26. Steam in chamber 26 prevents proper operation

actuator 32 and therefore the introduction of more

fuel level for restarting the engine. This evapo-

liquid fuel ration in chamber 26 causes a

cooling action. Unfortunately the volume of car-

burant is not adequate to cool the car completely

burator 10 or more particularly chamber 26 and, by

therefore, the introduction of fresh fuel must be repeated.

  This requires rapid evacuation of the fuel vapors.

rant out of room 26 by the assembly 64. When the mo-

  re-started, air circulates through the inlet channel

troduction 14, which causes closure by the valve member 78 of the orifice 76 and the carburetor 10 operates in its normal mode. Similarly, the recess 74 could be connected to the atmosphere, but for convenience and in order to maintain a relatively clean and

closed, we prefer that it opens into the introductory canal

tion 14.

9. Figure 2 shows another embodiment of the present invention where the carburetor 10 and an exhaust valve assembly 120 are shown as separate units. In FIG. 2, the assembly 120 comprises a body 122 which encloses a vapor chamber 66 and a chamber 68 for controlling the air flow. Body 122 defines channels

124 and 125 in which fittings 126 and 127, respectively-

are inserted to act as a connection means. Similarly, in channels 93 and 96 of the carburetor 10 are inserted

fittings 128 and 130, respectively. A pipe 132 re-

connecting fittings 126 and 128 connects room 68

to the introduction channel 14. A line 134 connecting the connections

cords 127 and 130 communicates the chamber 66 of the valve 120 with the fuel chamber 26 of the carburetor 10. In the case

present, chamber 26 opens into the atmosphere through the

medial of the orifice 76 and one recess 74 of the assembly when the valve element 78 is in its open position. The assembly 120 of FIG. 2 operates so as to evacuate the vapors formed in the chamber 16, then to evacuate them through the orifice 76 and the recess 74 of the assembly 120 when the valve element 78 is in its open position. In the same way as for the valve assembly 64 of FIG. 1. In the embodiment of FIG. 2, the vapors are evacuated into the atmosphere instead of being in the introduction channel 14, as this is represented in

figure 1.

The appreciation of some of the measurement values

above must take into account that they come from

result from the conversion of Anglo-Saxon units into metric units

ques.

The present invention is not limited to the examples

ples of realization which have just been described, it is on the contrary susceptible of variants and modifications which

will appear to those skilled in the art.

10.

Claims (6)

1 - Diaphragm carburetor (10) for an explosion engine sion comprising a body (12) which defines an introduction channel tion (14) in which is pivotally mounted a plate mant butterfly and having a fuel chamber (26), in combination with an exhaust valve assembly (64) taking a body (12 or 122) with a cavity, characterized in that the body defines an orifice (76) of the discharge valve tion, a normally open valve member (78) being po- lo sitioned in the discharge orifice and movable between posi- opening and closing, the body also defining if a vapor chamber (66) communicating with the fuel chamber (26) and an air flow control chamber (68), a biasing spring (90) being positioned so as to keep the valve element in the normal position Lately open, a pneumatic actuator (70) being connected to the valve member, and in that the body further defines a pneumatic signal orifice (92) in communication with the introduction channel, the pneumatic actuator being arranged managed and arranged so as to move the valve element between the normally open position and the closed position in re-   response to a current flowing in the introduction channel. 2 - Carburetor according to claim 1, character- rised in that the pneumatic actuator can operate so as to close the normally open valve member for a predetermined differential pressure between the chambers of the valve assembly. 3 - Carburetor according to claim 2, character- laughed at in that the differential pressure is substantially 75 mm of water vapor or less. 4 - Carburetor (10) according to claim 1, ca-   characterized in that the signal orifice (92) communicates with the introduction channel downstream of the papillary plate lon (62). 5 - Combination of a membrane carburetor for internal combustion engine, carburetor which includes a defined body an inlet channel, a mounted butterfly plate 2 481371 11. in pivoting in this introduction channel, a fuel chamber, a signal orifice providing a signal control in response to the air flow in the inlet channel tion, and an exhaust port (95) for discharging the fuel vapors, characterized in that it comprises a hot restart exhaust valve assembly, having a body with a cavity, a pneumatic actuator position- born in the cavity so as to define a discharge chamber steam and an air flow control chamber, an ori 10. drain valve function defined in the body of the assembly ble in communication with the vapor discharge chamber, a biasing spring positioned in one of the chambers so as to apply a biasing force allowing to hold a discharge valve element in the orifice this exhaust valve in the open state when the action- pneumatic neur is in a reference position, means (126, 127) coupling the vapor discharge chamber fears at the carburetor exhaust port so that   allow the evacuation of fuel vapors by the vapor discharge and the exhaust valve orifice when the pneumatic actuator is in the po- reference position and a means coupling the com- position chamber at the carburetor signal port, to perform moving the pneumatic actuator out of position reference tion in a direction to overcome the biasing force in response to the presence of the control signal, which has the effect of closing the valve member evacuation and avoid the evacuation of any vapor from   burant, when air circulates in the introduction channel carburetor. 6 - Combination according to claim 5, character- ensured that the hot restart valve assembly evacuates cue the vapors in the inlet channel of the carburetor.