Intercooler for supercharged internal combustion engine

An intercooler includes a first heat exchanger into which liquid coolant is sprayed and subsequently converted to vapor via the absorption of its latent heat of vaporization. The vapor is condensed in a radiator under the influence of a fan. The condensate is pumped back to the first heat heat exchanger via an thermostatically controlled expansion valve. When the intercooler is not in use it is filled with liquid coolant to prevent the intrusion of contaminating air. Excess coolant may be forced into the system when cold to purge out any non-condensible matter.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to an intercooler for a 
supercharged internal combustion engine and more specifically to a 
self-contained intercooler wherein coolant is evaporated under reduced 
pressure in a manner to utilize the latent heat of vaporization thereof 
and the vapor used as a vehicle for removing heat from the intercooler. 
2. Description of the Prior Art 
In order to improve engine performance superchargers especially exhaust gas 
driven turbo-chargers are often fitted to internal combustion engines. 
However, these devices, while improving engine performance, have 
encountered drawbacks in that the temperature of the air charged into the 
cylinders increases due to compression (often as high as 
150.degree.-170.degree. C.) which reduces the density of the air thus 
reducing charging efficiency, and tends to induce knocking (in Otto cycle 
engines). To solve the latter mentioned problem it is usual to retard the 
ignition timing and/or lower the compression ratio. This of course also 
tends to reduce engine power output. Accordingly, it has been proposed to 
interpose an intercooler between the supercharging compressor and the 
engine cylinders in order to reduce the temperature of the incoming 
charge. 
FIG. 1 shows an example of a previously proposed intercooler arrangement. 
This arrangement is integrated with the engine cooling system. In this 
arrangement coolant from a reservoir 1 is fed to a heat exchanger 2 which 
forms a vital part of the intercooler 3 and to a pressure pump or 
compressor 4. The pressurized fluid discharged by the pump 4 is circulated 
through the engine coolant jacket 5 to absorb the heat produced by the 
engine. The resulting high pressure-temperature mixture of boiling coolant 
and vapor is ejected toward a condenser through a variable nozzle jet pump 
7. Simultaneously, the liquid coolant fed into the intercooler heat 
exchanger 2 absorbs heat from the supercharged air passing through the 
intercooler 3 and vaporizes. This vapor is extracted from the heat 
exchanger and directed to the condenser 6 under the influence of the 
venturi action produced by the ejection of the high temperature-pressure 
liquid/vapor mixture ejected from the variable nozzle jet pump 7. The 
vaporized coolant is condensed in the condenser 6 and returned to the 
reservoir 1. 
However, this arrangement has encountered several drawbacks in that the 
compressor 4 consumes valuable engine output, in that it is very difficult 
to control the temperatures in the system to desired levels with any 
degree of reliability and in that the liquid coolant fed to the 
intercooler heat exchanger sometimes becomes excessively heated forming a 
superheated vapor which lowers the heat exchange efficiency of the 
intercooler. Further, upon stopping the engine the condensation of the 
vaporized coolant in the system induces a sub-atmospheric pressure therein 
which tends to induct air into the system. The system once contaminated 
with air tends to lose its efficiency due to the pockets and bubbles of 
air which can absorb little or no heat and which inevitably find their way 
into the condenser of the system. For further disclosure relating to this 
device, reference may be had to "MOTOR TREND" published in the U.S. in 
June 1983 and/or to Japanese Patent Application First Provisional 
Publication No. Sho 56-146417 (1981). 
FIG. 2 shows a second example of a previously proposed intercooler 
disclosed in Japanese Patent Application First Provisional Publication No. 
Sho 57-46016 laid open to public inspection on Mar. 16, 1982. In this 
arrangement liquid coolant from the engine radiator is admitted to a heat 
exchanging device 9 via a valve 10. This valve is controlled by a level 
sensor 11 in a manner to maintain an essentially constant level of liquid 
coolant within the device. The hot supercharged air from the turbo-charger 
compressor C, passes over and around a plurality of essentially vertically 
arranged pipes or conduits 12 containing liquid coolant. A vacuum pump or 
the like 13 driven by an electric motor 14 (or alternatively by way of a 
mechanical connection with the engine crankshaft) is used to reduce the 
pressure within the liquid filled portion of the heat exchanger 9 to a 
level whereat the coolant boils at a suitably low temperature. The coolant 
vapor extracted from the heat exchanger by the pump 13 is discharged into 
the conduit 15 leading from the engine coolant jacket 16 to the engine 
radiator 8 and permitted to mix with the liquid coolant and condense at 
essentially atmospheric pressure. 
However, this arrangement has suffered from the drawbacks that the vacuum 
pump 13 is relatively large and bulky consuming valuable engine room space 
as well as engine power and in that temperature control with respect to 
change in the temperature of the air discharged by the turbocharger tends 
to be undesirably sluggish. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an intercooler 
arrangement which consumes very little engine power, which is efficient 
and which prevents the intrusion of contaminating air during non-use. 
It is a further object of the present invention to provide an intercooler 
arrangement which can maintain the temperature of the air delivered to the 
combustion chambers of the engine essentially constant irrespective of 
sudden fluctuations in the temperature of the air discharged by the 
compressor of the turbocharger. 
In brief, the above objects are fulfilled by an intercooler which includes 
a first heat exchanger into which liquid coolant is sprayed and 
subsequently converted to vapor via the absorption of its latent heat of 
vaporization and wherein the vapor thus produced is condensed in a 
radiator under the influence of a fan and the condensate pumped back to 
the first heat heat exchanger via an thermostatically controlled 
exapansion valve. When the intercooler is not in use it is filled with 
liquid coolant to prevent the intrusion of contaminating air. Excess 
coolant may be forced into the system when cold to purge out any 
non-condensible matter. 
More specifically, the present invention takes the form of a device having 
a passage through which heated fluid flows and a device for cooling the 
heated fluid comprising: a first heat exchanger exposed to the heated 
fluid and in which liquid coolant is converted to its gasesous form via 
absorbing its latent heat of evaporation, a second heat exchanger in fluid 
communication with the first heat exchanger and in which the vapor 
generated in the first heat exchanger is condensed back to its liquid 
form, a device responsive to a parameter which varies with the temperature 
of the fluid in the passage downstream of the first heat exchanger, for 
varying the rate of condensation in the second heat exchanger, and a first 
pump for returning the liquid coolant from the second heat exchanger to 
the first heat exchanger.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 3 shows an engine system in which the present invention is 
incorporated. As shown, this system includes (merely by way of example) a 
turbo-charged fuel injected spark ignition Otto cycle engine 100. In this 
arrangement an induction passage or conduit 101 leads from an air cleaner 
102 via an air flow meter 103 to the compressor 104 of the turbo-charger. 
The output of the compressor 104 is fed through a self-contained 
intercooler 105 according to the present invention, to an induction 
manifold 106. The impeller 107 of the turbo-charger is supplied hot 
exhaust gases form the combustion chamber or chambers of the engine via an 
exhaust manifold 108. Located downstream of the impeller 107 are catalytic 
converter 109 and muffler 110. An EGR conduit 111 leads from upstream of 
the catalytic converter 109 to an EGR valve 112 operatively mounted on the 
induction manifold 106. A wastegate 113 controlled by the supercharging 
pressure provided by the compressor 104, by-passes exhaust gases around 
the impeller 107 in the event of excessive supercharging. The wastegate 
can be replaced with a capacity varying device if desired. 
FIG. 4 shows the intercooler 105 in detail. This device includes a heat 
exchanger 120 comprised of a housing 122 through which the air under 
pressure discharged from the compressor 104 passes enroute to the 
combustion chambers of the engine 100. Disposed within the housing 122 is 
an evaporator 124. In this embodiment the evaporator 124 takes the form of 
a plurality of relatively small diameter finned tubes 126 through which 
coolant is passed. Located at the upstream end of the tubes 126 is a 
distribution chamber 128 into which coolant is sprayed by an expansion 
valve 130 in manner to assume an essentially mist-like form. The amount of 
coolant discharged by the expansion valve 130 is controlled in response to 
the pressure developed in a bulb 131 filled with a volatile fluid. This 
bulb is, as shown, attached to the exterior of a collection chamber 132 
arranged at the downstream ends of the tubes 126 so as to be sensitive to 
the temperature of the effluent discharged from the latter. 
A temperature sensor 134 is disposed in this chamber for sensing the 
temperature of the effluent. The outlet of the collection chamber 132 is 
connected via a suitable conduit 136 with a condenser or radiator 138. In 
this embodiment the radiator may take the form of upper and lower tanks 
140, 142 interconnected by relatively small diameter conduits 144 over 
which a draft of cooling air is forced by a fan 146. To maintain the 
maximum effeciency of the radiator, it is preferred to maintain the 
conduits 144 essentially free of liquid coolant under the normal 
operation. This maximizes the surface area via which the vapor may release 
its latent heat to the atmosphere. 
The lower tank 142 is provided with a level sensor 148. This sensor may be 
of the float and reed switch type and which is arranged to close upon the 
level of coolant having risen above a predetermined level. The lower tank 
142 is connected via conduit 150 with a pressure pump 152. This pump 
communicates with the thermostatically controlled expansion valve 130 via 
a so called three-way valve 154. This valve 154 is arranged to connect the 
pump 152 with the expansion valve 130 when de-energized and establish 
communication between the pump 152 and a return conduit 156 when 
energized. A relief valve 158 is arranged to establish communication 
between the return conduit 156 and conduit 150 upon a predetermined 
pressure differential existing therebetween. The return conduit 156, as 
shown, leads to a reservoir 160. The interior of this reservoir is 
constantly maintained at atmospheric pressure via the provision of an air 
permeable cap 162. 
A second relief valve 164 is disposed in a bypass conduit 166 which leads 
around the pump 152. This valve opens to relieve excess pressure in the 
event that the pump supplies more coolant than that is required to be 
injected into the evaporator. 
A second pump 168 is disposed in a supply conduit 170 and arranged to pump 
coolant from the reservoir 160 into the lower tank 142 upon demand. An 
electromagnetic valve 172 which assumes a closed position when energized 
is disposed in a conduit 174 which by-passes the second pump 168. 
The intercooler further includes a control circuit 176 which controls the 
operation of the pumps and valves in response to inputs from the level 
sensor 148 and temperature sensor 134 disposed in the collection chamber 
134. 
An overflow conduit 178 fluidly connects the highest point of the cooling 
circuit, which in this embodiment is the distribution chamber 128, with 
the reservoir 160. Disposed in conduit 178 is an electromagnetic valve 180 
which is opened only when energized. 
With the present invention it is very important to ensure that all 
non-condensible matter such as air is excluded from the system. In order 
to achieve this the present invention provides for the system to be 
completely filled when not in use and for any non-condensible matter which 
may have found its way into the system to be purged during the initial 
stages of the intercooler being put into use. To this end the system is 
completely filled with coolant such as shown in FIG. 5. 
When the engine with which the invention is associated, is started and the 
control circuit supplied with electrical power, electromagnetic valve 172 
closes and if the temperature sensor 134 senses the temperature of the 
coolant in the system as being below a predetermined level (45.degree. C. 
for example) then valve 180 is energized and pump 168 operated for a 
predetermined period of time. This inducts coolant from reservoir 160 via 
conduit 170 and forces same into the system. As valve 180 is open, the 
excess coolant pumped into the system overflows through the overflow 
conduit 178 back to the reservoir 160 displacing any air or the like that 
may have found its way into the system. The period of time for which the 
pump is operated may be 3 to 5 seconds for example. Upon stoppage of the 
pump 168 after this purging operation, valve 180 is again de-energized, 
while valve 154 and pump 152 are subsequently energized. This inducts 
coolant out of the cooling circuit and pumps same via conduit 156 to the 
reservoir 160. Due to the reduction in coolant volume, the pressure within 
the system lowers. Simultanously, the hot air which is passing through the 
evaporator 124 due to the operation of the turbocharger, warms the coolant 
which begins to generate vapor pressure. When the coolant is water the 
saturation temperature is approximately 60.degree. C. at 0.2 atmos 
absolute pressure. This, in combination with the operation of the pump 152 
drains the liquid coolant out of the system and pumps same into the 
reservoir 160. During this operation, if an excessively low pressure (for 
example less than 0.2 atmos.) develops within the system, relief valve 158 
opens until sufficient vapor pressure develops and obviates any tendancy 
for the conduiting and the like constituting the intercooler to be crushed 
by the external atmospheric pressure. In this embodiment the rate at which 
coolant may flow into the system through the relief valve 158 is greater 
than the rate at which coolant can be pumped out of the system by pump 
152. 
When the coolant level falls to that of level sensor 148, valve 154 is 
de-energized to establish communication between the pump 152 and the 
expansion valve 130. Simultaneously, fan 146 is energized to induce 
condensation of the vapor which fills the radiator 138. As the 
condensation proceeds the pressure within the radiator 138 drops inducing 
vapor from the evaporator 124 to flow theretoward. 
The conversion of liquid coolant to its gaseous form via the absorption of 
its latent heat of vaporization removes the heat from the air flowing 
through the evaporator 124. The temperature of the air discharged from the 
intercooler is regulated via the pressure generated in the bulb 131 and 
the output of the temperature sensor 134. Viz., if the temperature of the 
effluent from the evaporator tubes 126 is above a predetermined level, the 
expansion valve 130 is opened to increase the amount of liquid coolant 
sprayed into the distribution chamber 128 and thus increase the amount 
coolant which may be converted into vapor. Simultaneously the operation of 
the fan 146 is controlled in response to the output of the temperature 
sensor 134 in a manner that upon the temperature sensed thereby increasing 
above a predetermined level the fan 146 is energized to increase the rate 
of condensation in the radiator 138. This, in combination with the coolant 
flow control provided by of the expansion valve 130 functions to maintain 
the temperature of the evaporator effluent essentially constant and 
therefore the temperature of the air discharged from the intercooler 
essentially constant. 
During normal operation, should the rate of condensation within the 
radiator increase beyond control due to external influences, such as very 
low atmospheric temperature or the like, and the pressure within the 
cooling circuit drops below the previously mentioned low limit, then 
coolant will flow into the system from the reservoir 160 via relief valve 
158. This will tend to partially fill the radiator 138 with coolant and 
thus reduce the heat exchange efficiency thereof by reducing the surface 
area available for the vapor introduced thereinto to release its latent 
heat to the atmosphere. Upon the level of coolant rising above the level 
sensor 148, the control circuit 176 energizes valve 154 to direct the 
output of pump 152 back to the reservoir 160. However, as the rate at 
which coolant may enter through the relief valve 158 is greater than the 
rate of discharge of the pump 152, the level of coolant within the 
radiator 138 rises. Accordingly, as the supply of coolant to the expansion 
valve 130 is momentarily terminated while the amount of heat which may be 
released by the radiator 138 is decreased by the partial filling of the 
radiator with liquid coolant, the vapor pressure within the system very 
quicky returns to a safe level and permits the relief valve 158 to close. 
Any excess coolant in the radiator 138 is directed back to the reservoir 
through the valve 154 under the influence of the pump 152. Upon the level 
of coolant falling to that of the level sensor 148, valve 154 is 
de-energized and the system re-enters normal operation. 
Should any excess coolant tend to enter the system by leaking in past the 
pump 168 or via relief valve 158, for example, in sufficient quantity to 
immerse the level sensor, pump 152 is again temporarily energized to 
permit this excess to be directed back to the reservoir 160. However, as 
this operation is very brief no noticeable effect on the temperature 
control by the intercooler occurs. 
When the engine 100 is stopped the control circuit can be simultaneously 
de-energized or it can be maintained operative for a short period. Upon 
deenergization of the control circuit, valve 172 is deenergized and opens. 
Accordingly, the coolant in the reservoir 160 flows into the system via 
conduit 170 and valve 172. As there is essentially no non-condensible 
matter in the system the latter is completely filled with liquid coolant 
upon all of the vapor therein condensing to liquid form. Accordingly, no 
negative pressure prevails within the system when the engine is not used 
whereby the tendency for any contaminating air to find its way in is 
eliminated. However, in the event that some air is inducted during running 
of the vehicle, under the influence of the sub-atmospheric pressure which 
is maintained throughout the operation of the intercooler, this air will 
be purged out upon a cold (below 45.degree. C.) restart of the engine. 
The reason that all air and the like non-condensible matter should be 
excluded from the system is that it tends to block and badly impair the 
heat exchange capacity of the radiator. Viz., any air which finds its way 
into the radiator tends to rise countercurrent to the coolant vapor which 
in the process of condensing decends. This produces a kind of "embolism" 
in the radiator which drastically impairs its utility. 
FIG. 6 shows a second embodiment of the present invention. In this 
embodiment the expansion valve control bulb 131 is disposed within the 
housing 122 so as to be directly exposed to the air which is flowing 
through the intercooler and thus responsive to the temperature of the air 
actually being charged into the cylinders. In this embodiment the 
temperature sensor 134 may also be disposed in the housing proximate the 
bulb (as shown in phantom) if desired. 
FIG. 7 shows an example of a circuit arrangement which can be used in the 
control circuit. As shown this circuit includes a switch 200 which 
advantageously is operated synchronously with the ignition switch of the 
engine to which the present invention is applied. A timer circuit 202 is 
arranged to be responsive to the closure of the switch in a manner to 
output a signal to the base of transistor 204 which renders same 
conductive. A second transistor 206 is circuited with transistor 204 in a 
manner that while transistor 204 is conductive, if transistor 206 is 
rendered conductive by an output of a comparator 208, pump 168 and valve 
180 are energized. The comparator 208 is arranged to receive on its 
non-inverting terminal (+) an input from a first voltage divider comprised 
of resistor R1 and thermistor T.sub.M (which forms the heart of 
temperature sensor 134). The inverting terminal (-) of the comparator 208 
receives a reference signal from a second voltage divider comprised of R2 
and R3. The reference voltage produced by the second voltage divider (R2, 
R3) is selected so that as long as the temperature of the coolant within 
the cooling circuit of the intercooler is below 45.degree. C. (for 
example) the comparator 208 outputs a high level signal. This arrangement 
of course controls the purging operation which ensures that the system of 
the invention remains free from non-condensible matter throughout its 
working life. However, during the purging it is necessary that neither 
pump 152 nor valve 154 be energized. Accordingly, the output of the 
comparator 208 is also applied to the base of transistor 210 which when 
rendered conductive permits current to flow through the series connected 
(alternatively parallel connection is also acceptable) coils of normally 
closed relays 212, 214. Accordingly, during the purging operation, the 
valve and motor are securely prevented from being energized. 
A second comparator 216 receives an input from the first voltage divider on 
its inverting terminal (-) and a reference voltage tapped off from a third 
voltage divider arrangement comprised of resistors R4 and R5, is applied 
to the non-inverting terminal thereof. The resistances of resistors R4, R5 
are selected so that upon the temperature of the coolant rising above a 
predetermined level (e.g. 60.degree. C.) the comparator 216 outputs a high 
level signal which energizes fan 146 via rendering a transistor 218 
conductive and inducing a relay 220 to close under the influence of 
current passing through the coil thereof. Accordingly, each time the 
temperature of the coolant is sensed by the temperature sensor as being 
above 60.degree. C., the fan 146 will be energized to increase the rate of 
condensation within the radiator 138. 
Level sensor 148 is circuited with a transistor 222 so that upon the level 
of coolant rising thereabove, the transistor 222 is rendered conductive 
and valve 154 energized so that the output of the pump 152 is directed to 
the reservoir 160. Valve 172 remains energized as long as switch 200 is 
closed. 
It will be appreciated that the above is merely an example of a control 
circuit for use with the present invention. Alternatively, the control may 
be provided by a microprocessor which is suitably programmed to provide 
the desired control. This microprocessor may also be used to control the 
engine as well as the intercooler. 
The coolant used in the embodiments disclosed hereinbefore is preferably 
water. The water of course may contain additives such as anti-freeze etc. 
However, the use of other coolants is within the perview of the present 
invention. 
In the embodiments disclosed hereinbefore, it is possible to eliminate pump 
168 by disposing valve 172 in its place, eliminating the branch conduit 
174 and disposing reservoir 160 at a level which is higher than valve 180. 
Thus upon opening of valve 180, gravity will force additional coolant into 
the system in sufficient quantity to displace any non-condensible matter 
out to the atmospheric side of valve 180. 
The various possible variations which may made to the above disclosed 
arrangements will be obvious to those skilled in the art to which this 
invention pertains.