Low profile gaseous fuel carburetor

A low profile gaseous fuel carburetor provided with deflector valves to improve mixing of gas and air in a mixture stream of short length. It also shows improved idling and starter valves, and a link for a parallelogram throttle linkage that maintains a correct lever relationship despite operational wear.

FIELD OF THE INVENTION 
This invention relates to carburetors for engines powered by gaseous fuels, 
and especially to an efficient gaseous fuel carburetor with a low profile. 
BACKGROUND OF THE INVENTION 
Carburetors for supplying mixtures of air and gaseous fuels are known. 
Their function is to provide throttling means and a responsive metering 
valve to supply a mixture of suitable richness and quantity to operate the 
engine at required loads and engine speeds. 
This is an old art whose fortunes vary with the relative cost of gasoline 
and of gaseous fuels such as liquefied petroleum gas or natural gas. They 
also vary with environmental concerns. For example, even when gaseous 
fuels cost considerably more than gasoline, their use is still compelled 
for indoor engine operations. One example is the indoor warehouse forklift 
where the pollutants from gasoline engines are not tolerated, and the 
alternatives are battery power or gaseous fuels. 
Because of the continuing demand for gaseous fuel carburetors, however 
variable the demand may be, the art has been crowded with efforts to make 
a carburetor which is alertly responsive to wide ranges of operating 
demands and ambient conditions such as atmospheric pressure. Generally the 
developments have utilized increasingly complicated regulators and 
metering valves. Their complexity has resulted in higher prices, 
marginally acceptable exhaust pollution emission, and mechanical 
performance which degrades with long-continued usage. They also have 
tended to be quite bulky. 
Newer vehicles, especially forklifts, allow very little headroom for the 
carburetor. Conventional systems inherently have had to be bulky, with a 
relatively high profile. The carburetor of this invention can supply the 
demands of a 45 HP engine with a head height of only about three inches. 
Its other dimensions are similarly minimized. Such small dimensions for 
its envelope are an important improvement. 
Especially for indoor operation, the generation of carbon monoxide is not 
tolerable. A nearly stoichiometric mixture must be burned efficiently. 
Slowly degrading performance and frequent adjustments are not considered 
to be too objectionable in many installations, such as in trucks and 
automobiles. However, in others they render a carburetor unacceptable. For 
example, forklift trucks are operated for months at a time without much 
engine maintenance. This tendency is so pronounced that when forklift 
carburetors are tested by air quality districts for qualification they 
must be operated for as long as six months without adjustment, and still 
perform acceptably. In the course of this extended testing, there is ample 
opportunity for valves and linkages to wear, and for any latent design 
defects which would result in improper mixtures to become apparent. 
It is another object of this invention to provide valves and linkages which 
are self-compensating for wear so as to function efficiently without 
external adjustments for an extended period of time. 
Although one might theorize that uniform mixing of a gaseous fuel in an 
airstream in inherently simple, and is greatly simpler than mixing 
gasoline into an airstream, this is not the case. Mixing gaseous fuel and 
vaporizing gasoline involve many of the same problems. One problem arises 
from the fact that the velocity of the airstream through the carburetor 
venturi is much faster in the center of the stream than nearer to the 
wall, where it may be nearly stagnant. Getting the fuel into the total 
airstream--through the slower and into the faster regions, and mixing well 
with both, is a considerable problem. The injection of the gaseous fuel 
into the airstream to produce a uniform mixture has often been attained 
only at the cost of a longer passage in which to mix the gas and air, 
resulting in a taller carburetor. 
Good mixing is required not only for proper combustion, but also for proper 
distribution of the charge among the cylinders. When the stream of mixture 
enters the manifold, it divides to the various cylinders, and if the 
dividing gases are not uniformly mixed relative to one another, imbalance 
among the cylinders will result. 
It is another object of this invention to provide means for improving the 
uniformity of mixture in a relatively short path length, thereby enabling 
a carburetor of lower profile to be made. 
BRIEF DESCRIPTION OF THE INVENTION 
A carburetor according to this invention comprises a body with a passage 
having an air intake port and a mixture outlet port. Between the intake 
and outlet ports there is a venturi. A throttle valve such as a butterfly 
is fitted in the passage. 
A plurality of gas injector ports enters the passage through the passage 
wall immediately downstream from the throttle valve. These ports are at 
least partially overhung by an equal number of deflector vanes that 
project from the wall immediately upstream from the injector ports, and 
extend toward the center of the passage. The deflector vanes have a face 
that faces upstream, each of which extends inwardly as its extends from 
the wall, and downstream. The deflector vanes are angularly spaced apart 
to leave spacings for linear air flow between them, and their free ends 
are spaced from one another so as to leave a central region of unimpeded 
air flow. 
The downstream-facing faces of the deflector vanes slope inwardly from the 
wall, and downstream, so as to provide regions inwardly from the injector 
ports that are sheltered from the linear air flow so as to direct at least 
some of the gas, undiluted by air, toward the center of the passage. 
A metering valve is mounted to the body. It has an inlet port, a valving 
chamber, and an outlet port in that order. The outlet port discharges to 
conduitry that connects to the injector ports. The valving chamber is 
cylindrical, and houses a valve rotor. The rotor has a central axis of 
rotation and a peripheral wall which makes a valving contact with the 
chamber wall at a valving port in the chamber wall. The valving port is 
contoured--usually a circular section entering a circular cylinder. A 
single valving notch is formed in the rotor wall. The notch is a modified 
V shape with a contoured edge that narrows toward the central axis. It is 
aligned with the valving port when fully open, and except for a small 
region for idling operations closes the valving port when in its closed 
position. 
A starter by-pass groove extends axially in the rotor wall, communicating 
with the inlet port when the rotor is in its idling (and starting) 
position. The groove is fluidly connected to a by-pass passage in the 
rotor leading to the valving port when the rotor is in its idling 
position. A spring-loaded poppet closes the by-pass passage when the 
manifold vacuum is of such value as to indicate that the engine has 
started. 
The valve rotor and the throttle valve each have centers of rotation, and a 
respective operating lever. Those levers are joined by a compensating 
linkage that maintains the spacing of centers on the operating levers 
constant regardless of linkage wear so as to constitute a parallelogram 
movement despite wear in the linkage. 
The above and other features of this invention will be fully understood 
from the following detailed description and the accompanying drawings, in 
which:

DETAILED DESCRIPTION OF THE INVENTION 
A carburetor 10 according to this invention is shown in FIG. 1. It includes 
a body 11 having a base 12 with a flange 13 adapted to fit on an intake 
manifold (not shown). Mounting holes 14 pass bolts (not shown) to hold the 
carburetor to the manifold. 
As best shown in FIGS. 1 and 3, a passage 15 extends from an air intake 
port 16 to a mixture outlet port 17. A venturi 18, comprising a region of 
reduced diameter, is disposed between these ports. An axis of downstream 
flow 19 is shown. 
A closure plate 19a closes a portion of the lower end of the body and when 
installed fits against the manifold. 
A vacuum port 20 provides access to the pressure in the throat of the 
venturi. A throttle valve 25 in the form of a conventional butterfly is 
disposed in the passage. It includes a throttle shaft 26 and a disc-like 
butterfly plate 27. Rotating throttle shaft 26 varies the flow conditions 
in the passage, and is controllable to cause the carburetor to respond to 
the demands of the operator, all in accordance with known techniques. 
A rim 28 on the body receives an air filter, air conduit, or other 
connections to atmospheric air. 
As best shown in FIG. 1, throttle lever 30 is fixed to throttle shaft 26, 
so that turning lever 30 will turn the throttle valve. 
Four identical fixed deflector vanes 31, 32, 33 and 34 are shown projecting 
from passage wall 35. They are all identical, so that only vane 31 will be 
described in detail. It projects inwardly from wall 35 and slopes in a 
downstream direction. It has an upstream facing face 36 and a downstream 
facing face 37, both of which faces project inwardly and slope downstream. 
Four gas inlet ports 40, 41, 42 and 43 enter the passage through wall 35. 
They are directed radially inward, and are about as wide as the vanes. 
Thus, the vanes perform two functions relative to the airstream and to the 
incoming gaseous fuel. 
First, by overhanding the gas ports, the vanes protect at least part of the 
gas stream from direct impingement by the airstream. Accordingly, the gas 
streams impinge on the downstream facing faces, and are directed toward 
the middle portion of the airstream between the free tip ends of the 
vanes. They are also given a downstream component, so as to enter and be 
more readily entrained in the central part of the airstream. 
Second, those portions of the air stream which impinge on the 
upstream-facing faces of the vanes are directed inwardly and with a 
downstream component. These features result in a good mixing, especially 
near the central axis. 
However, these vanes not only provide access for the gas to the central 
regions, but they pass a relatively slowly moving part of the stream in 
regions 45 between them. This air will readily mix with gas from the sides 
of the gas ports. Because of the turbulence at the center gas injected 
there will be incorporated as a part of a well-mixed stream in a short 
path length. A thoroughly mixed gas-air mixture is produced by this 
carburetor in less than one-half inch of axial travel in a throat of about 
11/4 inches diameter. 
A gas passage 50 enters the side of the body from a mounting pad 51. It 
branches to two conduits that in turn branch to a pair of plenums 52, 53 
from which the gas ports exit. Closure plate 19a closes the bottom ends of 
plenums 52 and 53. 
A metering valve 60 is mounted to mounting pad 51. It includes a body 60a 
having a gas inlet port 61 to be connected to a conduit from a regulator 
valve (not shown). It has a rotor passage 62 with a cylindrical wall 63 
through which a valving port 64 exits to gas passage 50. Valving port 64 
has a generally circular edge intersecting the wall of rotor passage 62. 
If desired, port 64 can be formed in a washer that can be removed and 
replaced, so that valving ports of different size and shape can be 
provided without modifying the body itself. 
A cylindrical valve rotor 65 is rotatably fitted in the rotor passage. It 
includes a V-shaped transverse notch with shape sides 66, 67 and a flat 
bottom 68. The bottom is so disposed and arranged that when the metering 
valve is in its most-closed position (FIG. 4), there will still remain a 
small opening 69 at the bottom to gas passage 50. This provides limited 
gas flow for idling operation. Thus, the metering valve does not function 
as a shut-off valve. In its most-closed position it passes gas for idling 
operation and for starting operation. 
The rotor provides for maximum output when the notch is placed for 
straight-across flow of gas (FIG. 5). Intermediate flow conditions will be 
determined by the shape of the notch and by the rotational position of the 
rotor in the rotor passage. The shapes of the notch edges will be 
empirically designed. 
The rotor tends to be pressed toward valve port 64 by gas pressure. This 
provides an improved valving action, especially in the event of valve 
wear. 
A rotor lever 70 is pinned to the rotor shaft. Turning lever 70 will turn 
the rotor. Pins 71, 72 are fixed to levers 30 and 70, respectively. There 
is a reference spacing 73 between the centers of the two shafts. A link 75 
is provided to hold the centers of pins 71, 72 apart by this same spacing. 
The levers and link therefore move as a parallelogram system, so that the 
relationship between the setting of the throttle valve and of the metering 
valve are always precisely known. One or the other of the two shafts will 
ordinarily be turned by an external throttle linkage of no special 
importance to the invention. It will be adjustable relative to the 
carburetor by known connection means. 
The rotor is provided with means to supply additional gas during starting 
operations when the metering valve is in its most-closed (idling) 
position. In the idling position, insufficient gas will be supplied for a 
starting operation, although enough will be supplied for a continuing 
idling operation. 
It is possible, but not best practice, to start engines of this type with 
the throttle in an operating position. A better technique is to provide 
supplementary gas with the throttle closed and the metering valve in the 
idling position to get the engine started, and then open the throttle. For 
this purpose there is provided a starting by-pass system which is 
effective only in the throttle-closed (idling) setting, and with the 
manifold at pressures respective to starting efforts for supplementing the 
gas flow which gas flow passes through opening 69. 
In this invention, a by-pass groove 80 extends along the rotor from a 
position that overlaps the inlet port, to the end of the rotor. The groove 
80 has a central passage 81 in the rotor that terminates at a by-pass port 
82 which is positioned where it discharges into the valving port, but only 
when the rotor is in its starting-idling position. Significant rotation of 
the rotor causes by-pass port to leave the valving port and thereby close 
the by-pass system. 
Also in the passage 81 is a poppet 85, spring-loaded open by bias spring 
86. Poppet 85 permits by-pass flow under starting conditions. However, 
when the engine starts, the resulting manifold vacuum will close the 
poppet to by-pass flow and closes the by-pass system. 
The features of positioning the by-pass port, and of the poppet assure that 
the by-pass system will be closed except during staring operations with 
the throttle in its most-closed position. This conserves fuel that would 
otherwise be wasted in other conditions of operation. 
The setting and construction of the metering valve and of the throttle 
valve are uniquely related to one another. Each of the levers can be set 
to adjust the lever position relative to its respective valve. Then these 
are locked so they move in unison. The parallelogram relationship places 
them in a true slave relationship. 
However, there is a serious tendency for wear to occur in the linkages, 
such as in ball-type rod ends, and this is one of the reasons why frequent 
adjustments such as turnbuckles are required to keep carburetors of this 
type in proper operation. Especially for installations where such 
adjustments are rarely made, and where agency qualification requires long 
service without adjustments, linkage wear can render even an otherwise 
suitable carburetor unacceptable. 
Existing linkages have not provided means to compensate for this wear in 
such a way as to maintain a constant and precise spacing between the 
centers of the linkage pins. This is not surprising because previous 
efforts have generally been to provide bearings which have minimum wear, 
at the ends of rigid links whose length is adjustable, perhaps by 
turnbuckles. As a consequence, eventually the linkage wears at its joints 
and becomes sloppy. The adjustment is lost. 
This invention utilizes a linkage which is related not to the worn working 
surface, but to the centers of the pins. The pins are identical, and are 
presumed to undergo identical wear. The linkage comprises a pair of plates 
both of which embrace the two pins, and are diametrically opposed across 
both pins. Accordingly the links follow up any pin wear by moving 
diametrically to continue to embrace both pins, with the established 
spacing between centers maintained. That spacing is not adjustable. It is 
established when the metal is cut to form the links as will now be seen 
with reference to FIGS. 7-11. 
Link 75, is shown merely as a simple plate in FIG. 1, because an improved 
linkage is not necessary for the enjoyment of the other features of this 
invention. However, in combination with the other features of this 
invention. However, in combination with the other feature it provides a 
greatly improved total carburetor whose advantages will be retained 
despite linkage wear. 
Linkage 100, which is the presently-prefered embodiment, is shown in FIGS. 
7 to 11. Its assembly is shown in FIG. 7 functioning to interconnect pins 
71 and 72. Two identical link plates 101, 102 are arranged in flat sliding 
adjacency. It is important that certain of their dimensions be identical, 
and that their wear properties be identical. For that reason it is best to 
punch them from the same die and from the same run of material, usually a 
low carbon steel. Also, because the system is to adjust itself for wear, 
it is important that the pins themselves be of the same material and of 
the same dimensions. The equal wear of both pins and equal wear of both 
plates can logically be assumed. This is an assumption of this invention. 
In practice it has held true, and tests of significant duration have 
proved the effectiveness of this linkage. 
As shown in FIGS. 8-11, plates 101, 102 are arranged head-to-toe. A 
tension-type bias spring 103 draws identical regions toward one another. 
Because both plates are identical, only plate 101 will be described in 
detail. 
In FIGS. 8 and 9, it is assumed that link plate 101 as shown is overlaid 
flat on link 102 as shown. The same relationship is assumed in FIGS. 10 
and 11. 
Reverting to FIG. 8, link plate 101 has a keyhole slot 105 with an enlarged 
portion 106 sufficient to pass head 107 of pin 71, and a neck portion 108 
of reduced width to receive the shank 109 of pin 71, but to retain the 
head 107 from out-of-plane separation. Its width is about equal to the 
diameter of the pin shank before wear occurs. A contact portion 110 at the 
end of the neck section has a radius about equal to the radius of shank 
109 before it wears. 
A slot 111 extends into the other end of the link plate. Its width is about 
equal to the diameter of shank 112 of pin 72 before the pin wears. A 
contact portion 113 has a radius about equal to the radius of the shank 
before the plate or the pin wears. 
Reference spacing 114 is equal to reference spacing 73. It is the intended 
spacing to be maintained between the centers of the pins. Notice in FIG. 8 
that the farthest to the right extremes of the contact portions 110 and 
113 are spaced by the same dimension as reference spacing 73. 
An aperture 120 extends along the plate to receive the convolutions of a 
tension-type coil spring 103. The coil spring has retention hooks 122, 123 
which respectively hook over the edges of portions 106 of plates 101 and 
102, thereby pulling all four contact portions against the pins so as 
identically to embrace both of the pins. The pins are thereby trapped at 
the reference spacing. 
Now assume that wear occurs. FIGS. 10 and 11 show equally worn pin shanks, 
and unworn link plates. Notice that link 101 will be pulled to the left to 
bear against the right sides of both pins as shown in FIG. 10. Link 102 
will be pulled to the right as shown in FIG. 11 to bear against both left 
sides. It is important to observe that both links moved equally, in 
opposite directions, and continue to embrace the pin shanks to hold them 
at the reference spacing. 
Wear on the link plates is presumed to be equal at all contact surfaces. 
Accordingly, the "wear" extends in the same direction and to the same 
extent at both contact portions, so that they maintain the reference 
spacing. Thus, any combination of pin wear and link plate wear still 
results in maintenance of the reference spacing. Again, it is presumed 
that both pins wear equally, and that both link plates wear equally, 
although the rate of wear of the pins and of the plates may be and 
probably will be different. Slight difference between the pins or between 
the plates can result in some deviation from constant spacing, but it will 
still be better than the results attained when conventional rod ends and 
turnbuckles are used. They are very small, if they occur at all. 
It is also presumed that the spring force is sufficient to overcome any 
drag of the shafts which might cause plate 101 to move to the right in 
FIG. 8 relative to plate 102 as shown in FIG. 9. The linkage can of course 
be overcome, but not by forces than can reasonably be anticipated in this 
device. 
This linkage thereby requires no adjustment. The valves and their levers 
are identically adjusted with the linkage in place, and the levers are 
tightened in place. Thereafter adjustment is unnecessary. 
The carburetor and linkage provide the advantages described with parts 
which can be die cast, machined or stamped to best advantage. The 
carburetor can function at very close to stoichiometric ratios, with 
negligible carbon monoxide emission. It can fit inside very restricted 
enclosures. 
This invention is not to be limited to the embodiments shown in the 
drawings and described in the description, which are given by way of 
example and not of limitation, but only in accordance with the scope of 
the appended claims.