Cooling system for automotive engine

In order to detect cooling system malfunction, the operation of a pump which recycles the liquid coolant from a radiator (or condensor) to the coolant jacket of a vapor cooled type engine, is monitored. In the event that the pump operation period and frequency (viz., the time between changes in pump operation) fail to fall within a predetermined time schedule, a malfunction indicating signal is issued. The schedule can be varied in accordance with a signal indicative of the amount of fuel being combusted in the engine (viz., the amount of heat being produced by the engine) so as to take into the account the increased amount of coolant circulation which occurs under high engine load operation and the accompanying changes in pump operation characteristics.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to a cooling system for an internal 
combustion engine wherein liquid coolant is boiled to make use of the 
latent heat of vaporization thereof and the vapor used as a vehicle for 
removing heat from the engine, and more specifically to such a system 
which includes circuitry which monitors the operation of an arrangement 
which recycles condensed coolant back to the coolant jacket of the system 
for re-evaporation and which issues an alarm when the recycling 
characteristics indicate that a malfunction has occured in the system. 
2. Description of the Prior Art 
In currently used "water cooled" internal combustion engines such as shown 
in FIG. 1 of the drawings, the engine coolant (liquid) is forcefully 
circulated by a water pump, through a circuit including the engine coolant 
jacket and an air cooled radiator. This type of system encounters the 
drawback that a large volume of water is required to be circulated between 
the radiator and the coolant jacket in order to remove the required amount 
of heat. Further, due to the large mass of water inherently required, the 
warm-up characteristics of the engine are undesirably sluggish. For 
example, if the temperature difference between the inlet and discharge 
ports of the coolant jacket is 4 degrees, the amount of heat which 1 Kg of 
water may effectively remove from the engine under such conditions is 4 
Kcal. Accordingly, in the case of an engine having 1800 cc displacement 
(by way of example) is operated at full throttle, the cooling system is 
required to remove approximately 4000 Kcal/h. In order to achieve this a 
flow rate of 167 Liter/min (viz., 4000-60.times.1/4) must be produced by 
the water pump. This of course undesirably consumes a number of otherwise 
useful horsepower. 
FIG. 2 shows an arrangement disclosed in Japanese Patent Application Second 
Provisional Publication No. Sho 57-57608. This arrangement has attempted 
to vaporize a liquid coolant and use the gaseous form thereof as a vehicle 
for removing heat from the engine. In this system the radiator 1 and the 
coolant jacket 2 are in constant and free communication via conduits 3, 4 
whereby the coolant which condenses in the radiator 1 is returned to the 
coolant jacket 2 little by little under the influence of gravity. 
This arrangement has suffered from the drawbacks that the radiator, 
depending on its position with respect to the engine proper tends to be at 
least partially filled with liquid coolant. This greatly reduces the 
surface area via which the gaseous coolant (for example steam) can 
effectively release its latent heat of vaporization and accordingly 
condense and thus has lacked any notable improvement in cooling 
efficiency. 
Further, with this system in order to maintain the pressure within the 
coolant jacket and radiator at atmospheric level, a gas permeable water 
shedding filter 5 is arranged as shown, to permit the entry of air into 
and out of the system. However, this filter permits gaseous coolant to 
gradually escape from the system, inducing the need for frequency topping 
up of the coolant level. 
A further problem with this arrangement has come in that some of the air, 
which is sucked into the cooling system as the engine cools, tends to 
dissolve in the water, whereby upon start up of the engine, the dissolved 
air tends to form small bubbles in the radiator which adhere to the walls 
thereof forming an insulating layer. The undisolved air tends to collect 
in the upper section of the radiator and inhibit the convection-like 
circulation of the vapor from the cylinder block to the radiator. This of 
course further deteriorates the performance of the device. 
European Patent Application Provisional Publication No. 0 059 423 published 
on Sept. 8, 1982 discloses another arrangement wherein, liquid coolant in 
the coolant jacket of the engine, is not circulated therein and permitted 
to absorb heat to the point of boiling. The gaseous coolant thus generated 
is adiabatically compressed in a compressor so as to raise the temperature 
and pressure thereof and introduced into a heat exchanger. After 
condensing, the coolant is temporarily stored in a reservoir and recycled 
back into the coolant jacket via a flow control valve. 
This arrangement has suffered from the drawback in that air tends to leak 
into the system upon cooling thereof. This air tends to be forced by the 
compressor along with the gaseous coolant into the radiator. Due to the 
difference in specific gravity, the air tends to rise in the hot 
environment while the coolant which has condensed moves downwardly. The 
air, due to this inherent tendency to rise, forms large bubbles of air 
which cause a kind of "embolism" in the radiator and badly impair the heat 
exchange ability thereof. 
U.S. Pat. No. 4,367,699 issued on Jan. 11, 1983 in the name of Evans (see 
FIG. 3 of the drawings) discloses an engine system wherein the coolant is 
boiled and the vapor used to remove heat from the engine. This arrangement 
features a separation tank 6 wherein gaseous and liquid coolant are 
initially separated. The liquid coolant is fed back to the cylinder block 
7 under the influence of gravity while the "dry" gaseous coolant (steam 
for example) is condensed in a fan cooled radiator 8. The temperature of 
the radiator is controlled by selective energizations of the fan 9 to 
maintain a rate of condensation therein sufficient to maintain a liquid 
seal at the bottom of the device. Condensate discharged from the radiator 
via the above mentioned liquid seal is collected in a small reservoir-like 
arrangement 10 and pumped back up to the separation tank via a small pump 
11. 
This arrangement, while providing an arrangement via which air can be 
initially purged from the system tends to, due to the nature of the 
arrangement which permits said initial non-condensible matter to be forced 
out of the system, suffers from rapid loss of coolant when operated at 
relatively high altitudes. Further, once the engine cools air is 
relatively freely admitted back into the system. The provision of the 
separation tank 6 also renders engine layout difficult. 
Japanese Patent Application First Provisional Publication No. Sho. 56-32026 
(see FIG. 4 of the drawings) discloses an arrangement wherein the 
structure defining the cylinder head and cylinder liners are covered in a 
porous layer of ceramic material 12 and coolant sprayed into the cylinder 
block from shower-like arrangements 13 located above the cylinder heads 
14. The interior of the coolant jacket defined within the engine proper is 
essentially filled with gaseous coolant during engine operation during 
which liquid coolant sprayed onto the ceramic layers 12. However, this 
arrangement has proved totally unsatisfactory in that upon boiling of the 
liquid coolant absorbed into the ceramic layers the vapor thus produced 
escaping into the coolant jacket inhibits the penetration of liquid 
coolant into the layers whereby rapid overheat and thermal damage of the 
ceramic layers 12 and/or engine soon results. Further, this arrangement is 
plagued with air contamination and blockages in the radiator similar to 
the compressor equipped arrangement discussed above. 
U.S. Pat. No. 1,787,562 issued on Jan. 6, 1931 in the name of Barlow, 
discloses a vapor cooled engine wherein a level sensor is disposed in the 
coolant jacket and arranged to control a pump which recycles condensed 
coolant from a small reservoir located at the base of the radiator in 
which coolant vapor is condensed, back to the coolant jacket. However, in 
this system the interior of the system is vented to the atmosphere via a 
small valve disposed atop of the reservoir. Accordingly, with this system 
although some provision is made for displacing the air which inevitably 
enters the cooling circuit of this arrangement, this very provision 
prevents control of the boiling point of the coolant via varying the 
pressure within the system. Further, the low level location of the valve 
inhibits complete purging of the air which exters the system during 
non-use. 
Moreover, with the above arrangement, should the system develop a leak or 
otherwise lose coolant in a manner that insufficient liquid is available 
for providing adequate cooling of the system, no warning device or the 
like is provided to bring attention to this fact. Thus, the engine is 
likely to undergo severe thermal damage. 
In summary, although the basic concepts of open and closed "vapor cooling" 
systems wherein the coolant is boiled to make use of the latent heat of 
evaporation thereof and condensed in a suitable heat exchanger, is known, 
the lack of a control system which is both sufficiently simple as to allow 
practical use and which overcomes the various problems plauging the prior 
art is wanting. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a "vapor" type cooling 
system for an internal combustion engine or like device which apart from 
preventing the intrusion of non-condensible matter such as air and the 
like into the system also, includes a monitoring circuit which does not 
require special sensors of its own and which issues a signal indicative of 
cooling system malfunction. 
In brief, in order to achieve the above object, the operation of a pump 
which recycles the liquid coolant from a radiator (or condenser) to the 
coolant jacket of a vapor cooled type engine, is monitored. In the event 
that the pump operation period and frequency (viz., the time between 
changes in pump operation) fail to fall within a predetermined time 
schedule, a malfunction indicating signal is issued. The schedule can be 
varied in accordance with a signal indicative of the amount of fuel being 
combusted in the engine (viz., the amount of heat being produced by the 
engine) so as to take into the account the increased amount of coolant 
circulation which occurs under high engine load operation and the 
accompanying changes in pump operation characteristics. 
This arrangement of course provides a very simple and reliable method of 
detecting low coolant levels and/or similar malfunctions and eliminates 
the need for a number of complex and expensive sensors to be disposed in 
various locations in the cooling circuit. 
In more specific terms a first embodiment of the present invention is 
deemed to take the form of a cooling system for an internal combustion 
engine comprising: a coolant jacket formed about structure of the engine 
subject to high heat flux; a radiator in which coolant vapor is condensed 
to liquid form; a vapor transfer conduit leading from the coolant jacket 
to the radiator; means for returning liquid coolant from the radiator to 
the coolant jacket in a manner to maintain the level of liquid coolant in 
the coolant jacket above the structure subject to high heat flux and lower 
than the uppermost section of the coolant jacket so as to provide a vapor 
collection space above the surface of the liquid coolant; and a circuit 
which monitors the operation of the liquid coolant returning means and 
which issues a signal upon the operational characteristics of the liquid 
coolant returning means indicating a malfunction in the cooling system. 
A second aspect of the present invention is deemed to come in a method of 
cooling an internal combustion engine comprising the steps of: introducing 
liquid coolant into a coolant jacket formed about structure of the engine 
subject to high heat flux in a manner to immerse the structure in a 
predetermined depth of liquid coolant; allowing the liquid coolant in the 
coolant jacket to boil; transferring the coolant vapor produced by the 
boiling in the coolant jacket from the coolant jacket to a radiator using 
a vapor transfer conduit; condensing the vapor to its liquid form in the 
radiator; returning liquid coolant from the radiator to the first coolant 
jacket using a coolant return arrangement in a manner to maintain the 
structure subject to high heat flux immersed in the predetermined depth of 
liquid coolant and define a vapor collection space within the coolant 
jacket; monitoring the operation of the liquid coolant returning means; 
and issuing a signal upon the step of monitoring indicating that the 
operation characteristics of the coolant returning means deviates from a 
predetermined schedule.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Before proceeding with the description of the actual embodiment of the 
present invention, it is deemed advantageous to firstly discuss the 
concepts on which the present invention is based. 
FIG. 5 graphically shows, in terms of engine torque and engine speed, the 
various load "zones" which are encountered by an automotive vehicle 
engine. In this graph, the curve F denotes full throttle torque 
characteristics, trace L denotes the resistance encountered when a vehicle 
is running on a level surface, and zones I, II and III denote respectively 
what shall be referred to as "urban cruising", "high speed cruising" and 
"high load operation" (such as hillclimbing, towing etc.). 
A suitable coolant temperature for zone I is in the order of 120.degree. C. 
(for example) while as low as 90.degree. C. (for example) for zones II and 
III. If desired it is possible to induce the coolant to boil at 
approximately 100.degree. C. in zone II if so desired. 
The high temperature during "urban cruising" promotes improved thermal 
efficiency and fuel economy while the lower temperatures promote improved 
charging efficiency while simultaneously removing sufficient heat from the 
engine and associated structure to obviate engine knocking and/or 
possibility of engine damage in the other zones. 
With the present invention, in order to control the temperature of the 
engine, advantage is taken of the fact that with a cooling system wherein 
the coolant is boiled and the vapor used a heat transfer medium, boiling 
is most vigorous in zones of high heat flux, whereby the temperature of 
engine structure subject to high heat flux is maintained essentially equal 
to that of structure subject to less intensive heating whereat boiling is 
less vigorous and less heat removed; the amount of coolant actually 
circulated between the coolant jacket and the radiator is very small; the 
amount of heat removed from the engine per unit volume of coolant is very 
high; and upon boiling, the pressure prevailing within the coolant jacket 
and consequently the boiling point of the coolant rises if the system 
employed is closed. Thus, by circulating a controlled amount of cooling 
air over the radiator, it is possible reduce the rate of condensation 
therein and cause the pressure within the cooling system to rise above 
atmospheric and thus induce the situation, as shown in FIG. 6, wherein the 
engine coolant boils at temperatures above 100.degree. C.--for example at 
approximately 110.degree. C. 
On the other hand, during high speed cruising, it is further possible by 
increasing the flow of cooling air passing over the radiator (for example 
by energizing a cooling fan as required to supplement the natural draft of 
air which occurs under such conditions) to increase the rate of 
condensation within the radiator to a level which reduces the pressure 
prevailing in the cooling system below atmospheric and thus induce the 
situation wherein the coolant boils at temperatures below 100.degree. 
C.--for example at approximately 90.degree. C. 
FIG. 7 shows an engine system incorporating a first embodiment of the 
present invention. In this arrangement, an internal combustion engine 100 
includes a cylinder block 106 on which a cylinder head 104 is detachably 
secured. The cylinder head 104 and cylinder block 106 include suitable 
cavities which define a coolant jacket 120 about the heated portions of 
the cylinder head and block. 
Fluidly communicating with a vapor discharge port of the cylinder head 104 
via a vapor manifold 122 and vapor transfer conduit 123, is a radiator or 
heat exchanger 126. It should be noted that the interior of this radiator 
126 is maintained essentially empty of liquid coolant during normal engine 
operation so as to maximize the surface area available for condensing 
coolant vapor (via heat exchange with the ambient atmosphere) and that the 
cooling system as a whole (viz., the cooling circuit encompassed by the 
coolant jacket, radiator and conduiting interconnecting same) is 
hermetically closed when the engine is warmed-up and running. These 
features will become clearer as the description proceeds. 
If deemed advantageous a mesh screen or like separator (not shown) can be 
disposed in the vapor discharge port 121 of the cylinder head so as to 
minimize the transfer of liquid coolant which tends to froth during 
boiling, to the radiator 126. Alternatively, cylinder head/manifold 
arrangements such as disclosed in U.S. Pat. No. 4,499,866 issued on Feb. 
19, 1985 in the name of Hirano and U.S. patent application Ser. No. 
642,369 filed June 25, 1984 in the name of Hirano et al, can be employed 
if desired. 
Located suitably adjacent the radiator 126 is a electrically driven fan 
127. Defined at the bottom of the radiator 126 is a small collection 
reservoir or lower tank 128 as it will be referred to hereinafter. 
Disposed in the lower tank 128 is a level sensor 130 which is adapted to 
output a signal indicative of the level of liquid coolant in the lower 
tank 128 falling therebelow. Viz., being lower than a level which is 
beneath the lower ends of the relatively small diameter tubing which 
constitute heat exchanging portion the radiator. 
Leading from the lower tank 128 to the cylinder block 120 is a return 
conduit 132. As shown, a "three-way" type electromagnetic valve 134 and a 
relatively small capacity return pump 136 are disposed in this conduit. 
The valve 134 is located upstream of the pump 136. The return conduit 132 
is arranged to communicate with the lowermost portion of the coolant 
jacket 120. 
In order to sense the level of coolant in the coolant jacket and 
appropriately control the operation of the pump 136, a level sensor 140 is 
disposed as shown. It will be noted that this sensor is arranged at a 
level higher than that of the combustion chambers, exhaust ports and 
valves (i.e. structure subject to high heat flux) so as to enable same to 
be securely immersed in coolant and thus attenuate any engine knocking and 
the like which might otherwise occur due to the formation of localized 
zones of abnormally high temperature or "hot spots". It will also be noted 
that the level sensor 140 is located at a level lower than the upper 
section or roof of the structure of the cylinder head which defines the 
coolant jacket therein, so as to define a coolant vapor collection space 
above the liquid coolant. 
Located below the level sensor 140 so as to be immersed in the liquid 
coolant is a temperature sensor 144. 
A coolant reservoir 146 is located beside the engine proper as shown. An 
air permeable cap 148 is used to close the reservoir 146 in a manner that 
atmospheric pressure continuously prevails therein. 
The reservoir 146 fluidly communicates with the "three-way" valve 134 via a 
supply conduit 149 and with the engine coolant jacket 120 via a 
fill/discharge conduit 150 and an ON/OFF type electromagnetic valve 152. 
The three-way valve 134 is arranged to establish fluid communication 
between the lower tank 128 and the coolant jacket 120 when de-energized 
while establish fluid communication between the coolant jacket 120 and the 
reservoir 146 when energized. Valve 152 is arranged to be closed when 
energized. 
The vapor manifold 122 is formed with a "purge" port 166 and a riser like 
portion 167 which is hermetically closed by a cap 168. The purge port 166, 
as shown, communicates with the reservoir 164 via a overflow conduit 169. 
A normally closed electromagnetic valve 170 is disposed in the overflow 
conduit 169. This valve is arranged to be open only when energized. 
The above mentioned level sensors 130 & 140 may be of any suitable type 
such as float/reed switch types. 
As shown, the outputs of the level sensors 130 & 140 and temperature sensor 
144 are fed to a control circuit 180. In this embodiment the control 
circuit 180 includes therein a microprocessor including input and output 
interfaces I/O a CPU, a RAM and a ROM. Suitable control programs are set 
in the ROM and are used to control the operation of the valves 134, 152 & 
170, pump 136 and fan 127 in response to the various data supplied 
thereto. 
In order that the temperature of the coolant be appropriately controlled in 
response to changes in engine load and speed, a load sensor 182 and an 
engine speed sensor 184 are arranged to supply data signals to control 
circuit 180. The load sensor may take the form of a throttle position 
switch which is tiggered upon the engine throttle valve being opened 
beyond a predetermined degree. Alternatively the output of an air flow 
meter or an induction vacuum sensor may be used. The engine speed signal 
may be derived from the engine distributor, a crankshaft rotational speed 
sensor or the like. 
It is within the scope of the present invention to arrange for a look-up 
table of the nature of that shown in FIG. 5 to be provided in the ROM of 
the microprocessor, or alternatively programs may be suitably devised to 
achieve the desired load/engine speed responsive temperature control in 
response to the inputted data signals. For further disclosure relating to 
this particular control reference should be had to the documents 
incorporated by reference hereinlater. 
Prior to initial use the cooling system (including the heat exchanger 
housing passages 804) is completely filled with coolant (for example water 
or a mixture of water and antifreeze or the like) and the cap 168 securely 
set in place to seal the system. A suitable quantity of additional coolant 
is also introduced into the reservoir 146. Although at this time by using 
de-aerated water when initially filling the system and reservoir, the 
system is essentially free of contaminating air etc., over a period of 
time non-condensible matter will find its way into the system. For, 
example the water (coolant) in the reservoir 146 will tend to absorb 
atmospheric air and each time the system is filled with coolant 
(explanation given in detail later) a little non-condensible matter will 
tend to find its way into the system. Further, during given modes of 
engine operation, negative pressures develop and although the system is 
operating in a sealed or closed mode at the time, air, little by little, 
tends to leak into the system via the gasketing and the like defined 
between the cylinder head and cylinder block and between the seals defined 
between conduiting and associated elements of the system. 
Accordingly, upon start-up of the engine, given that the engine temperature 
is below a predetermined value (45.degree. C. for example) a 
non-condensible matter purge operation is carried out. In this embodiment 
the purge operation is effected by pumping excess coolant into the system 
for a predetermined period of time. As the system should be essentially 
full before the initiation of this operation, the excess coolant thus 
introduced, positively displaces any air or the like the might have 
collected. In this embodiment the purge operation is carried out by 
energizing valves 152, 134 and 170 and energizing the pump for several 
tens of seconds. More specifically, valve 152 is conditioned to assume a 
closed condition, valve 170 an open one and valve 136 conditioned to 
establish communication between the reservoir 146 and the coolant jacket 
120. Thus, pump inducts coolant from the reservoir 146 via conduit 149 and 
forces same into the coolant jacket through conduit 132. The excess 
coolant thus introduced accordingly escapes from the top of the system via 
overflow conduit 169 and is returned to the reservoir. Any air or like 
non-condensible matter is carried out of the system along with the 
overflowing coolant. 
Upon termination of this mode of operation the system enters a so called 
"excess coolant displacement mode" wherein the coolant is permitted to 
heat, produce vapor pressure and displace itself out of the system back to 
the reservoir via conduit 150. In order to achieve this, only valve 152 is 
energized to assume an open state while valves 170 and 134 are deenergized 
to respectively assume a closed position and one in which the coolant 
jacket 120 is placed in fluid communication with the reservoir 146. 
As the coolant is displaced out of the system, the level of liquid coolant 
falls below that of level sensor 140. Accordingly, pump 136 is energized 
and coolant is pumped from the radiator 126 into the coolant jacket so as 
to maintain the level of coolant therein at that of level sensor 140. 
Accordingly, as coolant is simultaneously being displaced from the system 
via conduit 150, the radiator and second vapor conduit are emptied of 
coolant until the situation show in FIG. 1 occurs. 
It will be noted that as the system is initially filled with coolant, as 
the coolant is not circulated as in conventional type circulation systems, 
very little heat can be removed from the engine whereby the coolant and 
the engine rapidly warm-up and quickly produces the necessary vapor 
pressure to carry out the above discussed "displacement" mode of 
operation. 
During normal operation the vapor produced in the coolant jacket 120 is 
condensed in the radiator. The rate at which the vapor is condensed is 
controlled in accordance with the engine load and rotational speed as 
mentioned earlier. During this mode pump 136 is operated as shown in FIG. 
10. Viz, level sensor 140 is arranged to output a signal indicative of the 
coolant having fallen below a first predetermined level and maintain said 
output until the coolant has risen to a second level which is higher than 
the first. This hysteresis action of course obviates rapid ON/OFF cycling 
of the pump. 
When the engine is stopped, due to "thermal inertia" phenomenon, caused by 
the heat capacity of the cylinder head, cylinder block etc., the coolant 
will inevitably continue to boil for a short period. This tends to 
generate a slightly superatmospheric pressure within the system. 
Accordingly, it is deemed necessary to allow the coolant temperature to 
drop to a level whereat a slightly sub-atmospheric pressure prevails 
before permitting the system to assume an open state. This obviates the 
tendency of large quantities of coolant be displaced out of the system and 
ensures that upon the system being placed in an open condition that the 
coolant stored in the reservoir will be smoothly inducted to fill the 
system. That is to say, as the vapor condenses the coolant from the 
reservoir will inducted in a manner to replace same and hence completely 
fill the system. This eliminates the tendency for any atmospheric air to 
seek its way into the system due to the presence of a sub-atmospheric 
pressure. 
If the engine is restarted before the temperature of the coolant has 
lowered to any notable degree (for example 45.degree. C.), the system 
immediately undergoes a "warm start" wherein the purge operation is 
by-passed and the coolant displaced mode directly entered. 
However, with the above described system it will be noted that: 
(i) if the pump 136 per se were to fail, then irrespective of energization 
signals fed thereto from the control circuit 180, coolant would not be 
recirculated from the collection tank 128 to the coolant jacket 120. 
Accordingly, the coolant in the coolant jacket 120 would be gradually 
boiled off leading to (a) too much coolant in the radiator (viz. the 
radiator would become partially flooded and the surface area via which 
latent heat of vaporization which can be released to the ambient 
atmosphere, reduced) and (b) too little in the coolant jacket. 
Accordingly, as the cylinder head would not be immersed in sufficient 
coolant to remove the heat emitted therefrom the engine would undergo 
rapid overheating and thermal damage; 
(ii) if level sensor 140 were to malfunction in a manner as to not output 
an indication of the coolant having fallen below same, then the above 
situation would occur even though the pump were fully operative; 
(iii) conversely, if the level sensor were to malfunction in a manner to 
continuously output a signal indicative of the coolant level having fallen 
below same, irespective of the actual liquid level, then pump would be 
continuously energized. This apart from being unnecessary could lead to 
overfilling of the coolant jacket whereby coolant would be apt to 
constantly overflow to the radiator. This of course would tend to wet at 
least part of the radiator conduiting and lead to a reduction in heat 
exchange efficiency; 
(iv) if the conduiting interconnecting the radiator and coolant jacket 
fails and allows liquid coolant to leak out of the system, as the level of 
coolant in the coolant jacket falls, level sensor 140 would induce 
energization of pump 136. However, due to the chronic lack of coolant, 
pump 136 would be continuously energized in a effort to replace the lost 
coolant; 
(v) if insufficient coolant were to be contained in the cooling circuit 
upon the system being switched from open to closed circuit operation, the 
lack of same would tend to induce prolonged pump operation similar to the 
case of (iv). 
Accordingly, by simply monitoring the time between changes in pump 
operation, viz., the time for which the pump 136 is on or off, it is 
possible to detect a malfunction in the system without the need for a 
plurality of additional sensors which add both cost and weight to the 
system. 
A first embodiment of a malfunction detection circuit 200 according to the 
present invention is incorporated with the engine system shown in FIG. 7. 
This arrangement includes a differential circuit 210 which is connected to 
the "live" terminal of the pump 136 so as to be responsive to the 
energization signals fed thereto. Connected in series between the 
differential circuit 210 and a comparator 212 is a circuit 214 which 
detects the period for which the pump 136 operates and is non-operative. 
Following the comparator 212 is a driver or amplifier circuit 216 which 
upon receiving an output from the comparator generates a suitable voltage 
signal via which an alarm indicator 218--such as a lamp or buzzer (or 
alternatively a voice warning system) is energized. 
FIG. 9 shows in timing chart form, the signals which characterize the 
operation of the above disclosed circuit. The left-hand section of this 
chart shows normal or malfunction free operation while the right-hand side 
section shows the operation which occurs in the event of a malfunction. 
As shown, the differential circuit 210 produces a pulse (see chart "A") 
each time the pump 136 is started or stopped. The period responsive 
circuit 214 responds to each of the pulses in a manner to be "reset" by 
same and thereafter develop a voltage which develops essentially 
proportionally with respect to time (see chart "B"). Accordingly, the 
greater the lapse of time between any two pulses the higher the voltage 
becomes. By setting the reference voltage (REF V) of the comparator at a 
suitable level, it is possible to render the warning device active (see 
chart "D") only after the pump has been running or alternatively has not 
been energized for a period of time in excess of that experienced under 
normal (malfunction free) operation. 
FIG. 8 shows a second embodiment of the present invention. This arrangement 
takes into account the changes in pump operation characteristics which 
occur with changes in engine load. Viz., under high load the amount of 
power that must be produced by the engine is high and accordingly a 
relatively large amount of fuel is combusted to produce the necessary 
power output. The more fuel that is combusted, the more heat that is 
produced by the engine. Under these circumstances the amount of coolant 
that must be circulated by the pump increases whereby the time for which 
the pump operates increases while the time for which it is non-operative 
decreases. FIG. 11 demonstrates this point graphically. As shown, during 
idling the time for which the pump is active is relatively short while the 
intervals between pump energization relatively large. On the other hand, 
during high load operation such as hill climbing, towing, or high speed 
cruising, the pump is required to pump more coolant more often. 
Accordingly, in order to render the monitoring circuit more responsive to 
the mode of engine operation it is preferred in the second embodiment to 
render said circuit responsive to a signal indicative of the amount of 
fuel being fed to the engine. In the case of fuel injected engines, the 
fuel injector control pulse can be used. On the other hand, in the case of 
carbureted engines the opening degree of the throttle valve may be used. 
The second embodiment includes a timer 310 circuit which determines the 
time or period for which the pump is active/non-active. In response to a 
signal indicative of low fuel consumption it is possible to render the 
timer 310 responsive to the pump 136 being "on" so as to count up to a 
level at which a warning device (312) energization signal is produced 
faster than in the case that the pump 136 is not energized. Conversely, 
when the amount of fuel fed to the engine increases (high load) it is 
possible by using the signal indicative thereof to increase the rate at 
which the counter 310 counts up to a value at which the alarm signal is 
issued or conversely lower the count at which said signal is generated. 
The particular circuits which may be used in the above mentioned 
arrangements will be only too clear to those skilled in the art of 
electronics. Accordingly, no further description will be given for 
brevity. 
It should be noted that the engine system to which the malfunction 
detection arrangement of the present invention can be applied is not 
limited to that illustrated in FIGS. 7 and 8 and may, by way of example 
take the form of the arrangements disclosed in: 
1. copending U.S. patent application Ser. No. 602,451 filed on Apr. 20, 
1984 in the name of Hayashi now U.s. Pat. No. 4,545,335; 
2. copending U.S. patent application Ser. No. 676,937 filed on Nov. 30, 
1984 now U.S. Pat. No. 4,574,747 in the name of Hirano or (alternatively) 
the corresponding Eurpean patent application No. 84114579.0 filed on Nov. 
30, 1984 in the name of Nissan Motor Co. Ltd.; 
3. European Patent Application No. 84112777.2 filed on Oct. 23, 1984 in the 
name of Nissan Motor Co. Ltd.; and 
4. European Patent Application No. 84114579.0 filed in Nov. 30, 1984 in the 
name of Nissan Motor Co. Ltd. 
The disclosure contained in these documents is hereby incorporated by 
reference thereto.