Combined carburetor and impulse fuel pump

A combined float bowl carburetor and fuel pump for small engines has a lateral extension on its carburetor body that terminates at a flat exterior surface to which open certain cavities and a passageway leading to the float valve inlet. A block-like pump body having flat inner and outer surfaces overlies said exterior surface and has cavities opening to its inner surface that cooperate with those in the carburetor body. A resilient pump membrane, providing a pump diaphragm and valves, is confined between the pump body and said exterior surface. Two cavities open to the outer face of the pump body, which is overlain by an imperforate resilient membrane to define inlet and outlet surge chambers that are respectively communicated with the pump by way of the inlet and outlet valves. All cavities, inlets and outlets are arranged to ensure maintenance of a consistent head of fuel at every inlet.

This invention relates to internal combustion engine fuel systems that 
comprise a fuel pump for transferring liquid fuel from a fuel tank to a 
carburetor float bowl; and the invention is more particularly concerned 
with a combined carburetor and fuel pump for such a fuel system, wherein 
the carburetor body constitutes a portion of the fuel pump and wherein the 
fuel pump is actuated by pressure pulsations imposed upon one side of a 
pump diaphragm from a source of pulsating pressure such as the interior of 
the engine crankcase. 
In fuel systems of the type with which the present invention is concerned, 
a supply of fuel is maintained in a float bowl that is more or less 
integral with the carburetor body, and venturi suction in the carburetor 
mixing passage draws fuel up out of the float bowl and into the mixing 
passage through a jet nozzle. To ensure that the flow of fuel through the 
jet will change only in accordance with changes in venturi suction, fuel 
in the float bowl is kept at a constant level by means of a float actuated 
valve that controls the admission of fuel to the bowl. 
The pump by which fuel is transferred from the fuel tank to the float bowl 
inlet must be capable of drawing fuel out of the tank at a rate sufficient 
to satisfy the maximum fuel flow requirement of the engine even when the 
tank is nearly empty. Hence such a pump must have a capacity which is 
substantially excessive for the condition in which the tank is nearly full 
and the engine requires a low rate of fuel flow. Nevertheless, the excess 
capacity of the pump cannot be allowed to bring about a condition of 
excess pressure at the float bowl inlet whereby the float controlled valve 
will be forced off its seat or prevented from closing. Furthermore, even 
during suction strokes of the pump, fuel should be present at the float 
bowl inlet and should be under a small head of pressure that will move it 
into the float bowl if the float valve is open. 
U.S. Pat. No. 3,556,687, to A. J. O'Connor, discloses a fuel pump for small 
engines which is operated by crankcase pressure impulses from the engine 
that it serves. The pump of that patent has so-called booster 
chambers--actually surge cushioning chambers--whereby the pressure and 
suction impulses of the pump are smoothed to produce a fairly steady 
pressure on fuel at the float bowl inlet, rather than a pulsating one. 
Each of the so-called booster chambers has one wall that is defined by a 
flatwise flexible resilient membrane so that the volume of the chamber can 
expand with increasing fuel pressure and contract with decreasing fuel 
pressure. The pumped fuel passes through one such chamber immediately 
before entering the pump itself and another such chamber immediately after 
leaving the pump. 
The mechanism of the O'Connor patent is described in that patent as "a pump 
and booster unit formed in a housing independent of a carburetor and 
engine." It will be apparent that there are advantages to be gained by 
integrating the fuel pump mechanism with the carburetor body; and in fact 
Marvel-Schebler Division of Borg-Warner Corporation has manufactured and 
sold such a combined float bowl carburetor and fuel pump. 
The general object of the present invention is to provide a device of the 
type that comprises a float bowl carburetor combined with a fuel pump, 
wherein there are improvements that cause fuel in the float bowl to be 
very steadily and consistently maintained at a constant level 
notwithstanding widely varying conditions of engine operation and through 
the full range of levels of fuel in the tank. 
More specifically, it is an object of this invention to provide a combined 
fuel pump and float bowl carburetor comprising a fuel pump of the 
diaphragm type, actuated by pressure pulsations, wherein a head of fuel 
tends to be maintained at the pump inlet at all times, to prevent the pump 
from losing its prime, and wherein a small head of fuel is also steadily 
maintained at the float bowl inlet, so that fuel can always flow into the 
float bowl whenever the float valve is open, even during suction strokes 
of the pump, to provide for very reliable maintenance of the desired level 
of fuel in the float bowl. 
Any reciprocating engine tends to produce a certain amount of vibration 
when it is in operation, but in the case of a small engine installed on a 
riding tractor or similar machine, engine vibration is compounded with 
other possibly severe vibrations, as from the operation of an implement 
hitched to the machine and from bumps in terrain over which the machine 
moves. All such vibration tends to cause somewhat erratic opening and 
closing of the float valve as fuel sloshes in the float bowl and the float 
actuator bobs and joggles. If a relatively constant head of fuel is 
maintained at the float valve seat, the various erratic movements of the 
float valve have a cancelling effect upon one another, so that a 
satisfactorily uniform level of fuel is maintained in the foat bowl; but 
if pressure at the float bowl inlet is permitted to pulse in step with 
pulsations of the fuel pump, the float bowl fuel level tends to vary 
markedly so that the engine receives too rich a mixture at some times and 
too lean a mixture at other times. It is likewise desirable that there be 
a constant, steady flow of fuel from the fuel tank towards the fuel pump, 
rather than an intermittent flow that surges in step with pump pulsations, 
since pulsing motion requires repeated acceleration and deceleration of 
the stream of fuel moving towards the pump, and vibration can aggravate 
the unsteadiness of such fuel flow to the point where the pump is starved 
from time to time, further contributing to variations in float bowl fuel 
level. With these considerations in mind, it is another object of this 
invention to provide a combined carburetor and fuel pump of the character 
described which is so arranged that an even, steady pressure in the 
direction of flow tends to be maintained on fuel flowing both to and from 
the pump, notwithstanding that the pump is actuated by rather abrupt 
pressure pulsations. 
Another object of the present invention is to provide a combined carburetor 
and fuel pump of the character described wherein the fuel pump component 
incorporates surge cushioning chambers and comprises relatively few and 
simple parts that cooperate with the carburetor body and can be readily 
assembled to it. 
A further object of this invention is to provide a combined carburetor and 
fuel pump whereby all of the above stated objectives are obtained and 
wherein the carburetor body provides portions of the chambers and 
passageways of the pump mechanism, which chamber and passageway portions 
can be formed in the carburetor body without the need for difficult or 
unusual manufacturing operations. 
Still another object of the invention is to provide a combined carburetor 
and diaphragm-type fuel pump of the above described character whereby all 
of the above stated objects are achieved and wherein the fuel pump 
component comprises a very compact subassembly that is mounted on the 
exterior of the carburetor body and consists, in the main, of a unitary 
body part that can be readily molded in plastic, a simple cover member 
that can be inexpensively made as a metal stamping, and a pair of 
resilient flat membranes that overlie opposite flat surfaces of the body 
part. 
With these observations and objectives in mind, the manner in which the 
invention achieves its purpose will be appreciated from the following 
description and the accompanying drawing, which exemplify the invention, 
it being understood that changes may be made in the specific apparatus 
disclosed herein without departing from the essentials of the invention 
set forth in the appended claims.

Referring now to the accompanying drawings, the numeral 5 designates 
generally the body of the carburetor component of a combined carburetor 
and fuel pump embodying the principles of this invention. The fuel pump 
component comprises a fuel pump body 6 which is mounted on one side of the 
carburetor body 5. 
The particular carburetor body 5 that is here illustrated is more or less 
annular to define a vertical mixing passage 7 that has its inlet at the 
top of the carburetor. As the description proceeds, it will be apparent 
that the principles of this invention are equally applicable to other 
carburetor arrangements than the downdraft carburetor here specifically 
illustrated; and in fact the invention has also been successfully embodied 
in a carburetor having a horizontally extending mixing passage, with its 
float bowl located wholly beneath that mixing passage. The illustrated 
carburetor body is formed at its top for connection with a conventional 
air cleaner (not shown) and has its bottom formed for connection to a 
conventional engine intake manifold duct (not shown). A choke butterfly 8 
is located near the upper inlet end of the mixing passage 7, and a 
throttle butterfly 9 is swingable in a lower portion of that passage. 
In this case the lower portion of the carburetor body comprises an annular 
float bowl 10 that surrounds the mixing passage and normally contains a 
supply of fuel that is maintained at a constant level. Entry of fuel into 
the float bowl is controlled by means of a valve 13 that is actuated by a 
float 14 in the float bowl. 
The carburetor body includes means defining at least one jet passage (not 
shown) that leads from the float bowl 10, at a level below the normal 
level of fuel therein, to a nozzle outlet 12 in a venturi portion of the 
mixing passage 7. In this case the carburetor body 5 comprises an upper 
body part 105 and a complementary lower body part 205, the latter defining 
the float bowl 10 and the upper body part having a portion of the jet 
passage therein. 
The carburetor elements that have been mentioned to this point will be 
recognized as generally conventional in float bowl carburetors and 
therefore need not be described in further detail. 
The fuel pump body 6 is mounted on a portion 15 of the carburetor body that 
projects to one side thereof and can be cast or molded in one piece with 
the lower part 205 of the carburetor body. The extension portion 15 
terminates at a flat vertical surface 16 which is parallel to, and faces 
radially outwardly from, the vertical float bowl axis and is overlain by 
the pump body 6. Certain cavities in the carburetor body that are 
described below open to the vertical exterior surface 16, and from that 
surface a passageway 17 in the carburetor body leads inward to the float 
bowl inlet, which comprises the seat for the float valve 13. 
The pump body 6 can comprise a block-like part that can be molded of 
plastic. It has an inner flat surface 18 that opposes the flat exterior 
surface 16 on the carburetor body and a flat outer surface 19 that is 
opposite and parallel to its inner surface 18. The inner and outer 
surfaces of the pump body are rectangular in outline and correspond in 
shape and size to the carburetor body exterior surface 16 that the pump 
body overlies. The pump body is relatively shallow, in that its opposite 
surfaces 18 and 19 are spaced apart by a relatively small distance, and 
therefore its top, bottom and side surfaces--respectively designated 20, 
21, 22 and extending from one to the other of its flat surfaces 18 and 
19--can be regarded as edge surfaces. 
Confined between the flat inner surface 18 on the pump body and the 
exterior flat surface 16 on the carburetor body is a resilient pump 
membrane 24 which provides the diaphragm and valves of the fuel pump, as 
explained hereinafter. Overlying the outer flat surface 19 of the pump 
body is an imperforate resilient membrane 25 which cooperates with certain 
cavities in the pump body, as explained hereinafter, to provide expansible 
and contractable inlet and outlet surge cushioning chambers. A cover 
member 26 overlies the imperforate membrane 25 to flatwise clamp it in 
sealing relationship to the flat outer surface 19 of the pump body. The 
several members of the pump assembly are held in flatwise overlying 
relationship to one another and to the exterior flat surface 16 on the 
carburetor body by means of screws 27 that extend through registering 
holes in the cover member 26, the imperforate membrane 25, the pump body 6 
and the pump membrane 24, and are received in threaded holes 28 in the 
carburetor body that open to its exterior surface 16. Each of the flat 
surfaces 18 and 19 on the pump body has a narrow raised bead 31 thereon 
that cooperates with the overlying resilient membrane 24, 25 to form a 
seal around the cavities which open to that flat surface. 
Of the several cavities that open to the exterior flat surface 16 of the 
carburetor body, the largest, designated by 29, defines one of the pumping 
chambers of the fuel pump. The diaphragm 30 of the fuel pump, which 
comprises an imperforate area of the pump membrane 24, extends across the 
mouth of the cavity 29 to close it and to separate the pumping chamber 
that it defines from an opposite pumping chamber defined by a cavity 32 in 
the pump body that opens to its inner flat surface 18. In this case, the 
pumping chamber defined by the carburetor body cavity 29 is the liquid 
chamber, and the opposite pumping chamber, defined by the pump body cavity 
32, is an actuating chamber which is subjected to pulsating pressure for 
actuation of the pump diaphragm 30. The two pumping chamber cavities 29 
and 32 have circular mouths, both being of such diameter that the 
diaphragm 30 extends across a substantial portion of the height of the 
membrane 24. A coiled expansion spring 33 is confined in the pumping 
chamber cavity and reacts against the diaphragm 30 through a grommet-like 
reinforcing washer 34 to urge the diaphragm flatwise inwardly relative to 
the carburetor body. 
For delivery of pulsing pressure to the actuating chamber, a nipple 35 
projects from the bottom edge portion 21 of the pump body 6 and is 
communicated with the interior of the actuating chamber by way of a 
passage 36 in the pump body. The nipple 35 is connectable with a hose (not 
shown) or the like that is in turn communicated with the interior of the 
crankcase of the engine served by the fuel system, to subject the 
actuating chamber to the rapid alternations of suction and pressure that 
are developed in the crankcase by engine piston motion. 
For control of fuel flow to and from the liquid chamber defined by the 
carburetor body cavity 29, the pump membrane 24 is formed with a pair of 
tongue-shaped flapper-type check valves 37 and 37' both of which are 
spaced to one side of the diaphragm portion 30 of that membrane. The check 
valve 37, which serves as an inlet valve for the pump, is defined by a 
narrow, slot-like, U-shaped cutout in the pump membrane and is located 
near the bottom edge thereof. The outlet check valve 37' is defined by a 
larger and somewhat irregularly shaped cutout 38 in the pump membrane and 
is near its top edge. 
Attention is now directed to the outer side of the block-like pump body 6, 
which is overlain by the imperforate membrane 25. Two cavities 39 and 40 
in the pump body open to its flat outer surface 19 and cooperate with the 
membrane 25 to define inlet and outlet surge chambers, repectively. The 
cavity 39 that defines the inlet surge chamber occupies the lower portion 
of the pump body but is L-shaped to have a portion which extends 
substantially to the top of that body. The outlet surge chamber cavity 40 
is smaller and occupies an upper portion of the body 6. 
For delivery of fuel from a tank (not shown) to the inlet surge chamber, 
the pump body has a second nipple 41 projecting from its bottom edge 
surface 21, which nipple is connectable to a hose or the like that leads 
from the fuel tank. Fuel enters the inlet surge chamber from the fuel line 
nipple 41 by way of an inlet 42 that is at a level some distance above the 
bottom of the cavity 39. The outlet 43 from the inlet surge chamber is at 
a lower level than the inlet 42. Hence, if any return flow of fuel to the 
tank tends to occur when the pump is not operating or is in an expulsion 
stroke, due to siphoning action or the like, fuel will nevertheless remain 
in the inlet surge chamber to a level high enough to cover the outlet 43, 
so that the pump will not lose its prime. Further assurance of positive 
pumping action is afforded by the L-shaped configuration of the cavity 39, 
whereby fuel which fills the inlet surge chamber to its top maintains a 
small head of pressure upon fuel at the outlet 43. 
The outlet 43 from the inlet surge chamber is defined by a short bore that 
extends inwardly through the pump body and opens to its flat inner surface 
18. When the inlet flapper valve 37 is closed, during the expulsion stroke 
of the pump, it overlies the inner end of the bore 43 to seal off the 
inlet surge chamber from the liquid chamber of the pump. In opening, the 
flapper valve 37 swings into a cavity 44 in the carburetor body that opens 
to its flat exterior surface 16. The carburetor body has a bored passage 
45, located inwardly of its flat exterior surface 16, which extends from 
near the bottom of the cavity 44 to the cavity 29 that defines the liquid 
chamber of the pump itself. Because the cavity 44 is a relatively large 
one, it holds a sufficient supply of fuel to ensure that under all normal 
conditions fuel will be present at the inlet end of the passage 45 to be 
drawn into the liquid chamber of the pump. 
A stud-like boss 46 is formed in the cavity 44, projecting partway out to 
the flat exterior surface 16 on the carburetor body, supports a light 
coiled expansion spring 47 which bears against the inlet flapper valve 37 
to bias the same to its closed position. 
It will be seen that the bore 43 in the pump body cooperates with the 
cavity 44 and the bore 45 in the carburetor body to provide a pump inlet 
passageway that leads from the inlet surge chamber past the inlet check 
valve 37 to the liquid chamber of the pump. 
A passage that conducts fuel out of the liquid chamber has one portion 48 
in the carburetor body that extends radially from the cavity 29, inwardly 
of the flat exterior surface 16, and has another portion 49 in the 
carburetor body that opens out to its surface 16. When the outlet flapper 
valve 37' is closed, it blocks the outlet of the last mentioned passage. 
When open, the flapper valve 37' is received in a cavity 50 in the pump 
body that opens to its inner flat surface 18 laterally adjacent to the 
pumping chamber cavity 32 and near the top of the pump body. A stud-like 
boss in the cavity 50, extending partway to the level of the inner surface 
18 on the pump body, supports a coiled expansion spring 52 that bears 
against the flapper valve 37' to bias it to its closed position. 
Through the cutout 38 in the pump membrane the cavity 50 in the pump body 
is communicated with the mouth of the delivery passage 17 that extends 
from the exterior flat surface 16 on the carburetor body to the float bowl 
inlet; and through that same cutout the cavity 50 is also communicated 
with a third cavity 53 in the carburetor body that opens to its flat 
exterior surface. Through a pair of bores 54 and 55 in the pump body the 
pump body cavity 50 is also communicated with the pump body cavity 40 that 
comprises the outlet surge chamber. Hence the cavity 50 in the pump body 
and the cavity 53 in the carburetor body are at all times communicated 
with one another and with the outlet surge chamber that comprises the 
cavity 40, and the cavities 50 and 53 thus serve as extensions or 
enlargements of the outlet surge chamber. Note that the bore 54 in the 
pump body is in line with the mouth of the pump outlet passage portion 49 
in the carburetor body, and the bore 55 is in line with the inlet to the 
delivery passage 17, to facilitate flow of fuel directly to and from the 
outlet surge chamber. 
The delivery passage 17, by which fuel is conducted from the cavity 50 in 
the pump body to the float bowl inlet, is defined by a horizontal bore 
extending into the carburetor body from its exterior surface 16, in 
cooperation with communicating bores (not shown) that are drilled into the 
carburetor body from other surfaces thereof. 
The steadiness of the pressure in the flow direction that is exerted upon 
fuel flowing to and from the liquid chamber of the fuel pump has been 
found to depend not only upon the change in volume that can take place in 
the inlet and outlet surge chambers by virtue of resilient flatwise 
flexing of the imperforate membrane 25 but also upon the effective volume 
of those surge chambers. Over a rather broad range of values, it has been 
found that smoothness of fuel flow and reliability of fuel level 
maintenance in the float bowl increases with increasing volume of the 
surge chambers. It is for this reason that the cavity 53 that opens to the 
inner flat surface of the pump body is effectively made a part of the 
outlet surge chamber by means of the bores 54 and 55, and said surge 
chamber is further effectively enlarged by its communication, through the 
cutout 38 in the pump membrane 24, with the blind cavity 53 in the 
carburetor body. In the same way, the relatively large cavity 44 in the 
carburetor body that receives fuel just before it enters the liquid 
chamber of the pump cooperates with the inlet surge chamber (with which it 
is communicated by way of the inlet valve 37) to maintain a steady 
pressure on fuel that is on its way to the pump. 
Another feature of the structure of the present invention that promotes 
reliably accurate maintenance of a constant level of fuel in the float 
bowl is the arrangement of the passages in the pump body and carburetor 
body in such a manner that the force of gravity maintains a head of fuel 
at the inlet to the pump and at the inlet to the float bowl. It has 
already been pointed out that in the inlet surge chamber defined by the 
cavity 39 in the pump body the outlet 43 is at a lower level than the 
inlet 42 to prevent back-siphoning of fuel towards the tank during the 
intake stroke of the pump, and that the inlet surge chamber is L-shaped to 
normally maintain fuel therein to a level substantially above its outlet. 
The short bored passage 45 in the carburetor body that communicates the 
cavity 44 in the carburetor body with the liquid chamber of the pump 
likewise has its inlet end at a low level in the cavity 44, and that 
cavity has a relatively large volume to ensure that fuel will always be 
present and under a pressure head at the inlet to the passage 45. 
The passage 48, 49 that conducts fuel from the liquid chamber of the pump 
to the outlet flapper valve 37' has its outlet end at a relatively high 
level in the carburetor body, whereas the inlet portion of the delivery 
passageway 17 in the carburetor body opens to the flat exterior surface 16 
at a level below the outlet flapper valve 37', again serving to maintain a 
head of pressure on fuel moving to the float valve inlet from the pump. 
To provide for adequate expansion of the surge chambers comprising the 
outwardly opening cavities 39 and 40 in the pump body, the cover member 26 
that overlies the imperforate membrane 25 is outwardly embossed to define 
shallow, inwardly opening recesses 60, 61 into which that membrane can 
flatwise flex. The cover member can suitably comprise a stamped metal 
plate. Preferably a gasket 62 is interposed between the imperforate 
membrane and the cover member, having a shape substantially identical with 
that of the flat outer surface 19 on the pump body, to cooperate with the 
recesses in the cover plate in providing room for outward flexing of the 
membrane. Small vent holes 63 in the cover plate provide for displacement 
of air at the outer side of the imperforate membrane so that its flatwise 
flexing will not be impeded by suction or pressure in the recesses 60 and 
61. 
To facilitate assembly of the several parts of the pump, the pump body is 
preferably formed with an integral locating pin 65 that projects from its 
inner flat surface 18. That pin extends through a hole 66 in the pump 
membrane 24 and is received in a well 67 in the carburetor body that opens 
to its flat surface 16. 
From the foregoing description taken with the accompanying drawings it will 
be apparent that this invention provides a combination fuel pump and float 
bowl carburetor that is well suited for small engines in being compact, 
simple and inexpensive, and whereby fuel is subjected to a substantially 
steady and constant pressure by which it is moved from a fuel tank towards 
the float bowl inlet. 
Those skilled in the art will appreciate that the invention can be embodied 
in forms other than as herein disclosed for purposes of illustration. 
The invention is defined by the following claims.