Inlet air temperature control for an I.C. engine

The ratio of preheated inlet air to ambient inlet air supplied to an internal combustion engine is controlled by a proportioning valve operated by a vacuum motor. Operating pressure for the motor is controlled by valve means responsive to the inlet air temperature for normally preventing changes in the motor operating pressure, but which selectively connects the motor via a predetermined restriction with essentially atmospheric pressure, or with sub-atmospheric pressure in the engine inlet air induction passage downstream of the throttle valve, when said inlet temperature is correspondingly above or below a predetermined operating range, whereby the operating pressure for the vacuum motor and actuation of the proportioning valve are functions of an algebraic integration of the time intervals that the inlet air temperature varies from the predetermined operating range.

BACKGROUND AND OBJECTS OF THE INVENTION 
This invention relates to the control of the inlet air temperature for an 
internal combustion engine. In a conventional means for controlling such 
temperature, as illustrated in the King U.S. Pat. No. 3,444,847, a vacuum 
motor responsive to the low pressure of the engine inlet induction passage 
downstream of the throttle operates an inlet air proportioning valve to 
increase the ratio of preheated air to ambient air in the inlet flow to 
the engine when the inlet air temperature is less than a predetermined 
minimum. 
An air bleed valve responsive to the inlet air temperature opens at a 
predetermined maximum temperature to bleed atmospheric air into the vacuum 
motor and thus into the induction passage to reduce the vacuum actuation 
of the motor and decrease the ratio to preheated to ambient inlet air. 
Such a system achieves an approximation of the desired inlet air 
temperature, but is sensitive to the pressure of the inlet induction 
passage and to the ambient temperature. 
When a rise in the inlet air temperature calls for more ambient air, the 
air bleed opens to atmosphere, increases the operating pressure for the 
vacuum motor, and thereby causes the latter to open the proportioning 
valve to ambient air. Unless the air bleed valve has precise metering 
characteristics and opens gradually with increasing pressure, the 
proportioning valve will over react and admit too much ambient air. In any 
event, after the operating pressure for the vacuum motor and the 
temperature of the inlet air are stabilized by the position of the bleed 
valve, the induction vacuum operating the motor will change in consequence 
of changing engine operating conditions and call for more or less heated 
air as the case might be, even though the ambient air temperature remains 
constant. 
The bleeding of atmospheric air into the inlet induction passage, as 
required by prior devices of the type described, may also impair 
drivability, especially for very small automobile engines where various 
vacuum operated devices already in use have preempted the vacuum capacity 
of the inlet induction passage. On the other hand, a convenient aspect of 
the above described prior devices arises from the fact that at wide open 
throttle operation when a maximum inlet flow of unheated air is desired, 
the pressure in the induction inlet passage is a maximum and automatically 
causes the proportioning valve to open fully to the ambient air and block 
the inlet of preheated air completely. 
Important objects of the present invention are to provide an improved 
temperature sensor for controlling a vacuum motor to actuate a 
proportioning valve, whereby a more precise control of the inlet air 
temperature within a predetermined operating range is achieved then 
heretofore by comparable devices, wherein actuation of the vacuum motor is 
not directly susceptible to changes in the inlet induction passage 
pressure, and whereby the bleeding of atmospheric air into the inlet 
induction passage during operation of the vacuum motor is virtually 
eliminated except for negligible bleeding during transient situations. 
Another object is to provide such a device that is responsive to operation 
at wide open throttle for actuating a proportioning valve to shut off the 
flow of preheated inlet air completely and to admit the maximum inlet flow 
of ambient air; or in the alternative, that is responsive to the ambient 
inlet air flow at wide open throttle to close the proportioning valve to 
preheated air and simultaneously to open the latter to admit the maximum 
of ambient air. 
Another object is to provide such a device that is comparatively simple in 
structure and operation, economical to manufacture, and highly efficient 
in operation.

It is to be understood that the invention is not limited in its application 
to the details of construction and arrangement of parts illustrated in the 
accompanying drawings, since the invention is capable of other embodiments 
and of being practiced or carried out in various ways. Also it is to be 
understood that the phraseology or terminology employed herein is for the 
purpose of description and not of limitation. 
Referring to the drawings, an embodiment of my invention is illustrated by 
way of example with an automobile internal combustion engine 10 having an 
inlet air and filter housing 11 mounted on a carburetor 12 for supplying 
inlet air to the engine via a central inlet air induction passage 13. A 
throttle valve 14 is pivotally mounted at 15 within the passage 13 to 
control the inlet air flow. An air inlet or snorkel 16 opens into the 
housing 11 to supply air thereto at essentially ambient atmospheric 
temperature and pressure, which air passes through the annular filter 17, 
then axially into the central induction passage 13, past the throttle 14, 
and finally to the engine for combustion therein. The hot combustion 
exhaust products are discharged to the atmosphere via an exhaust header or 
pipe 18 having a stove 19 associated therewith for preheating a second 
source of inlet air. Preheated air from the stove 19 is carried by an 
inlet air duct 20 into the housing 11 adjacent and immediately downstream 
of the snorkel 16 for mixing with the ambient air. 
A proportioning gate or valve 21 normally closes the passage 20 into the 
housing 11 when the inlet air temperature is above a predetermined maximum 
as explained below, and is pivoted on the housing 11 at 22 for swinging 
counter-clockwise in FIG. 2 to admit heated air and to close or partially 
close the opening of snorkel 16 into the housing 11 when the inlet air 
temperature falls below a predetermined minimum. By suitably varying the 
ratio of heated inlet air to the ambient inlet air, the resulting inlet 
air temperature may be controlled for optimum engine operation. 
The position of the valve or gate 21 is determined by the position of a 
plunger 23 pivotally connected at one end 23a to the gate 21 and connected 
at its opposite end to a flexible diaphragm 24 comprising a movable wall 
of a vacuum motor 25. A conduit 26 comprises the only communication with 
the interior of the motor 25. It is thus apparent that upon the 
application of a sub-atmospheric pressure within motor 25 via conduit 26, 
the diaphragm 24 and plunger 23 are moved leftward in FIG. 2 to open valve 
21 for admitting preheated air from the stove 19 via conduit 20. A biasing 
spring 27 seated within the motor housing 25 urges the diaphragm 24 
rightward in FIG. 2 to close the heated air passage 20 from the housing 11 
and to open the latter for receiving ambient air via snorkel 16. 
The conduit 26 extends from the motor 25 and communicates with the interior 
of a temperature sensor housing 28 having a port 29 opening via duct 30 
into the filter housing 11 downstream of the filter 17 to essentially 
atmospheric pressure, and also having a second port 31 in communication 
via duct 32 with the induction passage 13 at a location downstream of the 
throttle 14. A pair of reed valves 33 and 34 normally close the ports 29 
and 31 respectively to seal the interior of housing 28 from external 
pressure variations. 
As illustrated in FIG. 4, the housing 28 in the present instance is 
cylindrical and the reed valves 33 and 34 extend radially from peripheral 
attachments 35 and 36 respectively with the interior cylindrical wall of 
the housing 28. The reed valve 34 normally overlies the upwardly directed 
port 31 to close the same and is yieldably upwardly to open the port 31 to 
communicate the sub-atmospheric pressure of the induction passage 13 to 
the interior of the housing 28. The reed valve 33 normally underlies the 
downwardly directed port 29 to close the same and is yieldably downwardly 
to open the latter port to admit substantially atmospheric pressure into 
the housing 28. 
The reed valves 33 and 34 are controlled by a temperature responsive 
bimetal 37 secured at 38 to the cylindrical wall of the housing 28 and 
extending radially inwardly at a location intermediate the reed valves 33 
and 34, FIGS. 3 and 4. Also as illustrated in FIGS. 1 and 2, the location 
of housing 28 within the filter housing 11 downstream of the filter 17 
renders the bimetal 17 responsive to the temperature of the filtered inlet 
air entering passage 13 downstream of the proportioning valve 21. The 
bimetal 37 is calibrated so that when the latter temperature is within a 
predetermined operating range, both ports 29 and 31 are closed. Thus, 
whatever pressure is within the housing 28, that pressure will be sensed 
by the motor 25 and the latter with plunger 23 and proportioning valve 21 
will be locked in their adjusted positions regardless of pressure changes 
in the induction passage 13 resulting from engine operation. 
In the event that the filtered inlet air temperature is colder than desired 
for proper engine operation, the bimetal 37 will move upwardly to unseat 
reed valve 34 from port 31 and connect the interior of housing 28 via 32 
with the sub-atmospheric pressure of the induction passage 13 downstream 
of throttle 14. Any pressure change in housing 28 is then communicated via 
a restriction 39 in conduit 26 to the vacuum motor 25 to actuate the 
diaphragm 24. If the pressure in housing 28 as a result of opening port 31 
becomes less than the pre-existing pressure in the vacuum motor 25, the 
latter pressure will be gradually reduced in consequence of the restricted 
fluid flow through restriction 39, causing gate 21 to move 
counter-clockwise gradually to increase the ratio of heated air from 
passage 20 with respect to the ambient air via snorkel 16. As the inlet 
air temperature to which the bimetal 37 is responsive gradually increases 
to the normal or desired operating temperature, the bimetal 37 gradually 
moves to the centered position illustrated to enable closing of port 31 by 
reed valve 34. As long as the temperature thereafter remains in the 
desired operating range, the gate 21 will remain fixed in its adjusted 
position regardless of changes in engine operating conditions that affect 
the sub-atmospheric pressure in the induction passage 13. In the event of 
a subsequent increase in the ambient temperature, such that the resulting 
inlet air temperature rises above the desired operating range, the bimetal 
37 will move downwardly against reed valve 33 and open port 29 to the 
essentially atmospheric pressure within housing 11, thereby to increase 
the pressure applied to motor 25 gradually via restriction 39 until the 
gate 21 is adjusted to admit more ambient air and less heated air in the 
proportion required to achieve the desired inlet air temperature. 
During the time that port 31 is open, a limited amount of air will bleed 
into the inlet induction passage 13 via restriction 39 and conduit 32, but 
the total of such bleeding cannot exceed the combined volumes of housing 
25 and 28 which will be nominal. The volume of housing 28 especially will 
be as small as feasible. 
In the event that the pressure within housings 28 and 25 is less than the 
sub-atmospheric pressure within the induction passage 13 as a result of 
previous operation of the reed valve 34 and opening of port 31, a one-way 
check valve 40 in conduit 32 prevents communication between the induction 
passage 13 and the interior of housing 28 regardless of the position of 
reed valve 34. Such a situation might result temporarily during 
acceleration from a cruising condition, for example. The pressure in 
induction passage 13 will rise in consequence of the acceleration and 
might exceed the pressure in chamber 28. If during the acceleration, the 
inlet air temperature to which bimetal 37 is responsive should fall below 
the predetermined operating range and cause bimetal 37 to lift reed valve 
34 and open port 31, the check valve 40 will prevent the higher induction 
passage pressure from entering chamber 28 and motor 25 and moving gate 21 
clockwise to decrease the proportion of heated inlet air from conduit 20. 
As soon as the temporary acceleration ceases, the induction passage 
pressure will return to the cruise condition and to a pressure less than 
the pressure in sensor housing 28, thereby to operate motor 25 to open 
gate 21 to admit more heated inlet air from conduit 20 and decrease the 
ambient inlet air from snorkel 16 until the resultant inlet air 
temperature sensed by bimetal 37 rises to the desired operating range. 
It is conceivable in the situation described immediately above that the 
final cruise speed following the acceleration will be so great that the 
induction passage pressure communicated to conduit 32 will still be higher 
than the pressure in the sensor housing 28. In such an event, a demand for 
warmer inlet air by upward movement of bimetal 37 to open port 31 will 
have no effect upon motor 25. However, the area of diaphragm 24 and the 
size of spring 27 are determined with respect to the size of the engine 10 
so that the latter event will occur only at velocities near wide open 
throttle that will not normally be sustained for extended time intervals. 
During such temporary unusual high velocities, the engine will be working 
so hard and the inlet air flow will be so great that adequate mixing and 
evaporation of the liquid fuel will take place before entering the engine 
combustion chamber. Thus driveability will not be seriously impaired even 
though the inlet air temperature might be somewhat below the desired 
operating range. 
By virtue of the inevitable time lag required for the bimetal 37 to adapt 
itself to changing inlet air temperatures, an initial demand for warmer 
inlet air might result in an opening of the gate 21 to more heated inlet 
air than is desired before the bimetal 37 enables closing or port 31 via 
reed valve 34 for example. The overheated inlet air will then move the 
bimetal 37 downwardly and move reed valve 33 to open port 29 and enable a 
more precise adjustment of the positiion of gate 21. The resulting 
pressure in housing 28 after closure of port 29 will be a function of a 
summation of the time intervals that port 29 has been opened, minus a 
summation of the time intervals that port 21 has been opened or, in other 
words, the algebraic summation of the time intervals that ports 29 and 31 
have been open. The time intervals that port 29 is open for increasing the 
pressure within housing 28 may be considered positive and the time 
intervals that port 31 is open to reduce the pressure may then be 
considered negative. 
It is also to be noted that the effect of hunting by the thermostat or 
bimetal 37 to establish the proper opening of gate 21 is minimized by the 
restriction 39 and the volume of housing 28. The volume of housing 28 is 
preferably negligible with respect to the volume of the housing 25, so 
that the position of the diaphragm 24 and proportioning gate 21 resulting 
from the algebraic integration of the time intervals that the ports 29 and 
31 have been open will be determined by the volume of housing 25 and the 
size of the restriction 39. Obviously, the greater the resistance to fluid 
flow effected by restriction 39, and the greater the volume of motor 25, 
the more slowly will be the movement of diaphragm 24 and gate 21 in 
response to opening of either of the ports 29 or 31, and as a colollary 
the more closely to the desired operating temperature will be the 
temperature of the inlet air when the bimetal 37 moves to the intermediate 
neutral position illustrated whereat both ports 29 and 31 are closed. 
In order to enable rapid movement of gate 21 to the wide open position for 
ambient air, whereat the heated inlet air duct 20 is completely closed, a 
second air bleed port 42 opens from the atmosphere into the vacuum motor 
25 on the vacuum motor side of restriction 39. Port 42 is normally closed 
by a valve 43 operatively connected as indicated by 44 with the throttle 
valve 14 for opening port 42 to the pressure within housing 11 downstream 
of the filter when throttle valve 14 moves to the wide open position. Thus 
regardless of the temperature of the inlet air and the position of bimetal 
37, atmospheric pressure will be applied to the diaphragm 24 to move the 
gate 21 clockwise in FIG. 2 to the position for admitting the maximum 
ambient air as desired for wide open throttle operation. During such wide 
open throttle operation, the temperature of the inlet air will drop to the 
ambient temperature, tending to cool the thermostat 37 and open port 31 to 
call for warmer air. By virtue of restriction 39, only a small bleed to 
the sub-atmospheric pressure in the induction passage 13 will result 
during the wide open throttle operation and such bleeding will be nominal 
because at wide open throttle the pressure in the induction passage 13 
will also be neaarly atmospheric. The nominal air bleed into passage 13 
will be unobjectionable in comparison to the comparatively large air flow 
at wide open throttle and will have negligible effect upon the engine 
operation. 
When the wide open throttle operation terminates, the closing or partial 
closing of the throttle 14 will actuate valve 43 to close port 42 from 
motor 25 and return the temperature control system to its customary mode 
of operation.