Thermostatic valve for compensating air fuel mixture for air temperature change

A thermostatic valve for compensating for the change in the intake air temperature of an internal combustion engine. The thermostatic valve has a temperature detector attached to a housing provided with a port in communication with atmosphere, a pipe in communication with a vacuum motor, a pipe in communication with the portion of the intake passage downstream from the throttle valve of carburetor and a pipe in communication with the float chamber of the carburetor and also with the air cleaner of the engine. A first valve element adapted to be operated by the temperature detector, and a second valve element adapted to be operated by the first valve element are disposed in the housing and are pressed against respective valve seats formed in the housing by means of springs. The introduction of vacuum in the intake passage into the vacuum motor for adjusting the intake air temperature is controlled in response to the change in the intake air temperature. At the same time, the shortage of intake air attributable to a rise of the intake air temperature is compensated by an additional supply of air which is made directly to the portion of the intake passage downstream from the throttle valve, upon detect of the rise of the intake air temperature.

BACKGROUND OF THE INVENTION 
The present invention relates to a thermostatic valve for compensating air 
fuel mixture for the change in the intake air temperature, so as to avoid 
disorder of internal combustion engine at specifically low and high 
ambient air temperature. 
Conventionally, there has been proposed such a thermostatic valve for use 
in combination with the carburetor of an internal combustion engine as 
having both of a cold air compensation valve and a hot air compensation 
valve. More specifically, the cold air compensation valve is adapted to 
detect a specifically low intake air temperature, as in the winter season, 
and to transmit the vacuum established at the downstream side of the 
throttle valve to a vacuum motor which is adapted to mix warm air with the 
cold intake air, so as to raise the temperature of the air supplied to the 
carburetor. On the other hand, the hot air compensation valve is adapted 
to supply a compensating air to the intake passage, when the ambient air 
temperature is specifically high as in the summer season, in order to 
prevent the air fuel mixture from becoming excessively rich, particularly 
during the idling of the engine. 
This type of thermostatic valve employs one or more bimetals. In order to 
effect a satisfactory control over a wide range of air temperature 
including specifically low and high temperatures, these bimetals must have 
an impractically large sizes. As a result, the weight and size of the 
thermostatic valve are inconventiently increased, resulting in a rise of 
the production cost. At the same time, the bimetals, which are subjected 
to the vibration caused by the engine, are likely to operate erroneously. 
Further, when the engine operates with a heavy load under a specifically 
low ambient air temperature, the vacuum in the intake air passage is 
lowered to such a level as can never actuate the vacuum motor for 
supplying warm air. Consequently, cold ambient air is induced into the 
carburetor to freeze the latter. At the same time, when the engine is 
stopped after a continuous running under a specifically hot ambient air 
temperature, as in the summer season, the temperature in the engine room 
is raised rapidly to cause an evaporation of the fuel in the float chamber 
of the carburetor. The fuel vapor is sucked into the carburetor to make 
the mixture excessively rich, so as to hinder the smooth running of the 
engine after restarting. 
SUMMARY OF THE INVENTION 
It is a major object of the invention to provide a thermostatic valve 
adapted to maintain a constant temperature of the intake air induced into 
the internal combustion engine, when the temperature of the ambient air is 
low, and to introduce the air from the float chamber of the carburetor and 
air cleaner of the engine into the intake passage, so as to maintain a 
constant air fuel ratio of mixture, when the temperature of the ambient 
air is high, thereby to prevent the disorder of the engine. 
To this end, according to the invention, there is provided a thermostatic 
valve comprising a temperature detector having an operation shaft adapted 
to be actuated by a thermally expandable body; a housing having a first 
port communicating with the atmosphere, a second port communicating with a 
vacuum motor, a third port communicating with the float chamber of a 
carburetor and a fourth port communicating with the intake passage at the 
downstream side of the throttle valve of the carburetor; a first valve 
element disposed in the housing and adapted to be actuated by the 
detector; a second valve element disposed in the housing and adapted to be 
actuated by the first valve element; and a check valve disposed between 
the second port and the fourth port and adapted to allow a fluid to pass 
therethrough only in one direction. Further, a first passage 
intercommunicating the first and the second ports, a second passage 
intercommunicating the second and the fourth ports and a third passage 
intercommunicating the third and fourth ports are formed in the housing. 
The first passage is adapted to be opened and closed by the first element, 
such that the communication between the atmosphere and the vacuum motor 
and the communication between the portion of the intake passage downstream 
from the throttle valve and the atmosphere are made and broken 
alternatingly. 
The check valve disposed in the second passage is opened when the intake 
vacuum in the intake passage transmitted through the fourth passage is 
high, and is closed when the vacuum acting on the check valve is lower 
than the vacuum at the second port, thereby to make and break the 
communication between the vacuum motor and the portion of the intake 
passage downstream from the throttle valve. 
The third passage is adapted to be opened and closed by the second valve 
element, so as to make and break the communication between the portion of 
the intake passage downstream from the throttle valve and the air supply 
source, i.e. the float chamber of the carburetor and the air cleaner.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring first to FIG. 1, an air cleaner and a filter element are 
designated, respectively, at reference numerals 1 and 2. A vacuum motor 3 
is constituted by housings 3a, 3b made of a metal or a plastic, spring 3c, 
diaphragm 3d, rod member 3e and a vacuum chamber 3g. This vacuum motor 3 
is adapted to effect the switching of the supply of warm air A and cold 
air B to the carburetor, as well as the adjustment of the mixing ratio of 
these airs, through an action of a change-over valve 5 disposed in the 
intake air passage 1a leading from the air cleaner 1. The vacuum motor 3 
is controlled by means of a vacuum which is established in the intake 
passage at the downstream side 6a of the throttle valve and applied to the 
vacuum chamber 3g. 
An intake pipe leading to the internal combustion engine E is designated at 
a numeral 6. The intake air A is heated by a heat collecting plate 52 
which overlies an exhaust pipe 51, and then introduced into the intake 
passage 1a through a hose 53. A thermostatic valve embodying the invention 
is generally denoted by the reference numeral 7. The thermostatic valve of 
the invention is connected between the vacuum motor 3 and the intake 
passage 6a. Rubber hoses 8, 9, 11a, 11b and 11c are used for the 
connection of the thermostatic valve 7. More specifically, rubber hoses 8 
and 9 are connected, respectively, to the vacuum motor 3 and the intake 
pipe 6. The rubber hose 11c is connected to a pipe 1b which is fixed to 
the portion of the air cleaner 1 inside of the filter element 2 by means 
of, for example, soldering. The rubber hoses 11a and 11b branches from a 
branch pipe 10 made of a metal or a plastic, and extends, respectively, to 
a float chamber 13 of the carburetor. 
The construction of the carburetor 4 is shown in more detail at FIG. 2 in 
which reference numerals 13 denotes, as mentioned above, the float chamber 
of the carburetor, while numerals 14 and 15 designate air bleeders. An 
economizer jet is denoted by numeral 16, while numeral 18 designates a 
solenoid valve which is energized and de-energized as the ignition switch 
of the engine is turned on and off, and is adapted to allow and cut off 
the supply of fuel. A low speed port 19 constitutes the outlet of a fuel 
passage 12 of a low speed fuel system, while an idle port is designated at 
a numeral 20. A pipe 21 opens in the upper space in the float chamber 13 
is in communication with the thermostatic valve 7, through the hose 11a. 
The space in the float chamber 13 is communicated with the upstream side 
of the throttle valve 4a, through an air vent 13a, so that the air at the 
upstream side of the throttle valve 4a may be introduced into the float 
chamber 13. 
The detail of construction of the thermostatic valve 7 will be understood 
from the following description. 
Referring to FIG. 3, a heat conductive temperature sensing member 22a is 
made of a copper or the like metal having a good heat conductivity. A 
thermally expandable member 22b is made of a material the volume of which 
expands and shrinks in response to the ambient temperature, e.g. wax. An 
operation shaft 22c is accommodated by a housing 22d and adapted to be 
actuated by the thermally expandable body 22b. These members and parts in 
combination constitutes a temperature detector 22 which is fixed by 
screwing to an upper housing 23 made of duranex (commercial name) or a 
metal such as aluminum, iron or the like. 
The upper housing 23 has in its side wall one or more ports 24 for 
communication with the ambient air, and a first valve seat surface 25 in 
its lower surface. A lower housing 26 is also made of a metal such as 
duranex, or a metal such as aluminum or iron. The upper and lower housings 
23 and 26 in combination form the major outer profile of the thermostatic 
valve 7. The lower housing 26 is provided at its side wall with pipes 28 
and 29. The pipe 28 is in communication with the vacuum chamber 3g of the 
vacuum motor 3 and has therein an orifice 27 of a small diameter of 0.7 
.phi. or so, while the pipe 29 leads to the portion of the intake pipe 6 
downstream from the throttle valve 4a of the carburetor 4. Further, a pipe 
33, which is in communication with the pipe 21 of the float chamber 13 and 
with the pipe 1b of the air cleaner 1 is attached to the lower housing 26. 
This pipe 33 is in communication at its inner end with a port 32 which is 
formed in the vicinity of a second valve seat surface 31 provided on a 
central partition wall 26b formed in the lower housing 26. 
A first valve element 34 made of duranex or a metal is covered at its 
peripheral portion of the upper surface with a gasket 35 made of, for 
example, silicone rubber and attached by baking. This first valve element 
34 is disposed in the lower housing 26. This first valve element 34 is 
pressed and seated on the first valve seat surface 25 of the upper housing 
23, through the gasket 35, by the force exerted by a spring 36. 
This first valve element 34 is adapted to open and close a first passage 
through which the port 24 of the upper housing is communicated with the 
pipe 28 of the lower housing 26. In other words, this valve element 34 
controls the introduction of atmospheric pressure into the vacuum chamber 
3g of the vacuum motor 3. 
The first valve element 34 is provided at its upper surface with a 
flattened portion 34a adapted to be contacted by the end of the operation 
shaft 22c of the temperature detector 22. Also, a hollow projection 34b, 
having an aperture 34c at its lower portion, extends downwardly from the 
lower surface of the first valve element 34. The periphery of the 
projection 34b of the first valve element 34 is sealed by means of an "O" 
ring 37 disposed in a central bore 26a of the lower housing 26. 
Consequently, the space 38 and the space 39 in the lower housing 26 are 
communicated with each other through the aperture 34c of the first valve 
element 34. 
A second valve element 41 is also made of duranex or a metal such as 
aluminum, and is coated at the peripheral portion of its upper surface 
with a gasket 42 made of rubber or the like material. This gasket 42 is 
attached by baking or by means of an adhesive. This second valve element 
41 has a tapered projection 41a and a through bore 41b which is large 
enough to receive the projection 34b of the first valve element 34. This 
second valve member 41 is disposed in the lower housing 26, in series 
relation to the first valve element 34, and is pressed against the second 
valve seat surface 31, through the gasket 42, by the force of a spring 44 
which acts between the second valve element 41 and a lower cover 43 made 
of a plastic or a metal such as aluminum. 
A partition 45 is made of duranex or a metal such as aluminum, and is 
provided with one or more bores 45a. An umbrella-shaped check valve 46 
made of rubber is fitted to the partition 45. This check valve is 
installed so as to allow the flow of air only in the direction of arrow A. 
This partition 45 is attached to the second valve element 41 such that the 
end of the projection 34b of the first valve element contacts a flat 
portion 45b of the partition 45. If the cross-sectional area of the 
annular gap formed between the through bore 26a of the lower housing 26 
and the outer periphery of the projection 34b of first valve element 34 is 
equal to that of the aperture 34c of the first valve element 34, the "O" 
ring 37 and the aperture 34 can be dispensed with. 
The thermostatic valve having the described construction operates in the 
manner explained hereinunder. When the ambient air temperature is low, as 
in the winter season, the temperature of the intake air is correspondingly 
low to incur a disorder of the internal combustion engine E. However, this 
problem is fairly avoided by the use of the thermostatic valve of the 
invention. Namely, when the ambient air temperature is low, the thermally 
expandable body 22b of the temperature detector 22 does not expand, so 
that the operation shaft 22c is not actuated. 
Consequently, the first valve element 34 is kept in pressure contact with 
the first valve seat surface 25 of the upper housing 23, through the 
gasket 35, by the force of the spring 36. Therefore, the first passage 
through which the port 24 is communicated with the pipe 18 is kept closed. 
If the engine operates with a light load under this condition, the large 
vacuum established at the portion 6a of the intake passage acts on the 
check valve 46 to open the latter, through the pipe 29. Consequently, the 
second passage which includes the aperture 34c of the first valve element 
34, bore 45a of the partition 45 and the pipe 29 is opened. As a result, 
the vacuum in the portion 6a of the intake passage is transmitted to the 
vacuum chamber 3g of the vacuum motor 3, so that the change-over valve 5 
is moved to the position as shown in FIG. 1. On the other hand, when the 
engine operates with a heavy load under a low ambient air temperature with 
the supply of warm air A, the vacuum is lowered at the portion 6a of the 
intake passage. Since this vacuum is smaller than the vacuum in the pipe 
28, the check valve 46, which has been opened, is closed, so that the 
vacuum which has been applied to the vacuum chamber 3g of the vacuum motor 
3 is maintained, and the change-over valve 5 is held at the position as 
shown in FIG. 1. Since in this state the warm air A which has been warmed 
by the exhaust pipe 51 and introduced through the heat collecting plate 52 
and the hose 53 is induced into the engine E, the temperature around the 
thermostatic valve 7 disposed in the air cleaner 1 is raised. 
As the temperature around the thermostatic valve 7 is raised above, for 
example, 25.degree. C., the thermally expandable body 22b of the 
temperature detector 22 is expanded to actuate the operation shaft 22c 
which in turn acts on the flattened portion 34a in the recess of upper 
surface of the first valve element 34, so as to depress the latter in the 
direction of arrow A. As a result, the first valve element 34 is moved 
downward away from the first valve seat surface 25, so that the first 
passage is opened. Consequently, the vacuum chamber 3g of the vacuum motor 
3 is opened to the atmosphere, to make the vacuum motor 3 inoperative. In 
this state, whole of the intake air induced into the engine E is 
constituted by the cold air B. This in turn causes the temperature around 
the thermostatic valve 7 to drop, so as to make the thermally expandable 
body 22b shrink, thereby to allow the first valve element 34 to be seated 
again on the first valve seat surface 25. The intake air temperature is 
maintained within a predetermined range, due to a repetition of the above 
explained opening and closing of the first valve element. When the ambient 
temperature is higher than, for example, 25.degree. C., the atmospheric 
air is introduced into the portion 6a of the intake passage through the 
aperture 34c of the first valve element 34, bore 45a of the check valve 45 
and the pipe 29. 
When the ambient air temperature is further raised up to 65.degree. C. or 
higher, for example, the thermally expandable body 22b is further expanded 
to increase the stroke of the operation shaft 22c to such an extent as to 
position the aperture 34c in the projection 34b of the first valve element 
34 below the "O" ring 37, and to depress the second valve element 41 in 
the direction of the arrow A. Consequently, the second valve element 41 is 
moved away from the second valve seat surface 31, so as to open the third 
through which the pipe 33 communicating with the float chamber 13 and the 
pipe 1b of the air cleaner 1 is communicated with the pipe 29 via the port 
32 and the space 40. Consequently, the air in the float chamber 13 and the 
air in the air cleaner 1 are introduced to the downstream side of the 
throttle valve 4a of the carburetor 4, so that the fuel vapor in the float 
chamber 13 under high temperature is diminished. At the same time, the 
shortage of the intake air induced into the engine E attributable to the 
rise of the ambient air temperature is compensated by the air which is 
induced from the air cleaner 1 through the pipe 33. In order that the 
compensation air may not rush into the engine, the projection 41a of the 
second valve element 41 is tapered as illustrated. 
As the temperature of the intake air is lowered due to a stop of engine 
operation or due to the reduction of the ambient air temperature, the 
thermally expandable body 22b of the temperature detector 22 is made to 
shrink to allow the second valve element 41 to be pushed back in the 
direction of arrow B by the force of the spring 44, into airtight contact 
with the second valve seat surface 31, thereby to cut the third passage. 
Consequently, the air supply from the float chamber 13 and the air cleaner 
1 into the downstream portion of the carburetor 4 is interrupted. As the 
ambient temperature further comes down, the first valve element 34 is 
pushed back by the force of the spring 36 in the direction of the arrow B, 
into airtight contact with the first valve seat surface 25, thereby to cut 
the first passage and close the second passage. Consequently, the 
thermostatic valve is reset to the starting condition. 
Characteristics of the thermostatic valve 7 of this embodiment are shown in 
FIGS. 4 to 6. Referring first to FIG. 4 in which the vacuum in the vacuum 
chamber 3g of the vacuum motor 3 and the vacuum in the portion 6a of the 
intake passage are shown in a full-line curve and a broken-line curve, 
respectively, the level of the vacuum in the vacuum chamber 3g is 
maintained substantially constant, irrespective of the time S, in spite of 
the change in the vacuum at the portion 6a of the intake passage. FIG. 5 
is a characteristic chart showing the relation between the temperature t 
of the intake air included into the engine E and the vacuum p applied to 
the vacuum motor 3, obtained when the vacuum at the portion 6a of the 
intake passage is maintained constant (450 mmHg), while FIG. 6 is a 
characteristic chart showing the relation between the temperature t of the 
intake air supplied to the engine and the amount of the air Q supplied to 
the portion 6a of the intake passage, obtained when the vacuum at that 
portion 6a of the intake passage is maintained constant (450 mmHg). The 
characteristics as shown in FIGS. 5 and 6 correspond to each other. 
In the described embodiment, the air in the air cleaner 1 is supplied to 
the portion 6a of the intake passage downstream from the throttle valve 4a 
of the carburetor 4, through the pipe 29, as the second valve element 41 
is opened. This arrangement, however, is not exclusive. For instance, the 
arrangement may be such that the projection 34b of the first valve element 
34 is tapered while the "O" ring 37 is eliminated. Then, an annular gap is 
preserved between the tapered projection 34b and the surface of the 
central through bore 26a in the central partition 26b of the lower flange 
26, so that the atmospheric air coming from the port 24 of the upper 
housing 23 is introduced to the pipe 29, through the above-mentioned 
annular gap, as the second valve element 41 is opened. 
In the described embodiment, the temperature of air in the air cleaner 1 is 
detected as the temperature of the intake air supplied to the engine E. 
However, it is possible to use the engine room temperature as the intake 
air temperature. 
As has been stated, according to the invention, there is provided a 
thermostatic valve having the following features. Namely, the thermostatic 
valve of the invention has a housing provided with a first port 
communicating with atmosphere, a second port communicating with the vacuum 
motor, a third port communicating with the float chamber of the carburetor 
and a fourth port communicating with the intake passage at a portion 
downstream from the throttle valve of the carburetor. A temperature 
detector having an operation shaft adapted to be actuated by a thermally 
expandable body which expands and shrinks depending on the temperature is 
attached to the housing. A first valve element adapted to be operated by 
the operation shaft and a second valve element disposed in series to the 
first valve element are mounted in the housing. Also, a check valve is 
disposed in the housing, so as to make and break the communication between 
the second and the fourth ports. This check valve is adapted to be opened 
when the intake vacuum acting on this check valve is high, thereby to 
complete the communication of a second passage through which the second 
and the fourth ports are communicated with each other. This check valve is 
closed, when the vacuum acting on this check valve comes down below the 
level of the vacuum at the second port, thereby to interrupt the 
communication of the second passage. The first valve element is adapted to 
open and close a first passage through which the first and the second 
ports are communicated with each other, while the second valve element is 
adapted to open and close a third passage through which the third and the 
fourth ports are communicated with each other. When the intake air 
temperature is low, the first and the second valve elements are seated on 
their valve seats, so as to close the first and the third passages. As the 
intake air temperature rises, the first valve element is opened to 
complete the communication of the first passage, so as to allow the supply 
of air which comes from atmosphere or other air source from the first port 
to the fourth port. Subsequently, the second valve element is opened to 
complete the communication of the third passage, and the air available at 
the first port, which has been supplied from atmosphere or other air 
source, is fed to the fourth port. 
It is remarkable that the complicated controls of the vacuum motor for 
adjusting the intake air temperature during running at a low ambient 
temperature, and of the compensation for the shortage of the intake air 
during running at high ambient air temperature through the supply of 
additional air are successfully performed by a thermostatic valve having a 
relatively simple construction constituted by small number of major parts 
such as the temperature detector, valve elements, housing, check valve and 
so forth. At the same time, the valve elements are actuated simply and 
directly by the operation shaft of the temperature detector. 
Thus, the present invention provides a small-sized thermostatic valve which 
can be produced at a low cost of production. 
In addition, in the thermostatic valve of the invention, the check valve is 
accommodated by the housing. This check valve offers the following 
advantage. If the load on the engine is increased during running at a low 
intake air temperature, the vacuum in the intake passage is lowered due to 
the opening of the throttle valve, down to such an extent as to make the 
vacuum motor inoperative. Consequently, intake air of the low temperature 
is inconveniently introduced into the carburetor to freeze the latter. 
However, this problem is avoided because the check valve of the invention 
conveniently closes the vacuum passage, so as to maintain the required 
level of vacuum acting on the vacuum motor. 
Further, according to the invention, the second valve element is opened 
when the intake air temperature is specifically high, so as to allow the 
float chamber of the carburetor to communicate with the downstream side of 
the throttle valve, through the third and the fourth ports. At the same 
time, the air coming from atmosphere or other air source is supplied to 
the intake passage through the first and the fourth ports. Consequently, 
the undesirable formation of excessively rich mixture, which may for 
otherwise take place when the engine is restarted after a continuous heavy 
load operation at high temperature, due to the fuel vapor filling the 
float chamber of carburetor and sucked into the carburetor, is fairly 
avoided. At the same time, excessive enriching of the mixture in the 
intake passage due to the material reduction of amount of intake air is 
also prevented. 
Thus, the thermostatic valve of the invention ensures smooth operation of 
the engine over a wide range of intake air temperature.