Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TITLE OF THE INVENTION
COOLING SYSTEM FOR AN AUTOMOTIVE ENGINE
BACKGROUND OF THE INVENTION
The present invention relates to an automotive
engine cooling system having a thermostat, and more
particularly to a cooling system for controlling the
circulation of coolant when the automotive engine is
cold.
As shown in Fig. 7, a conventional cooling system
for an automotive engine comprises a first coolant
passage 6 disposed between an upper outlet 5 of water
jackets 4 and an upper inlet 12 of a radiator 11, and a
second coolant passage 14 provided between a lower
outlet 13 of the radiator 11 and a lower inlet 10 of the
water jackets 4, including a thermostat cap 16, a
thermostat housing 8 and a water pump 9. A bypass
passage 7 is provided between a junction J of the first
passage 6 and the housing 8 so as to communicate the
first passage 6 with the second passage 14 without
passing the radiator 11. A thermostat 1 is secured to
the housing 8 by the thermostat cap 16. The thermostat
1 has a main valve 3 and a bypass valve 2. In Fig. 7,
the reference A' designates a measuring point for
measuring the temperature of the coolant in the housing
8, and B' designates a measuring point provided in the
second passage 14 adjacent to the cap 16 and upstream of
the thermostat 1 for measuring the temperature of the
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coolant in the second passage 14. C designates a
measuring point for measuring the flow rate of the
coolant in the second passage 14.
During the engine is warmed up, the main valve 3 of
the thermostat 1 is closed, while the bypass valve 2
integrated with the main valve 3 is fully opened. Thus,
the coolant drawn from the outlet 5 of the water jackets
4 does not pass through the radiator 11. The coolant is
circulated by the water pump 9 through the junction J of
the first passage 6, bypass passage 7, housing 8, and
inlet 10 of the water jackets 4 as indicated by arrows.
Thus, the temperature of the coolant in the housing 8
quickly rises.
However, since the coolant in the radiator 11 and
the thermostat cap 16 is not circulated, the temperature
rising rate of the coolant therein is slow. Therefore,
as shown in a record of Fig. 8, even if temperature A at
the point A' becomes 85°C which is an opening
temperature of the main valve 3, temperature B at the
point B' is 56°C. There is a difference of 29°C between
the temperatures A and B.
When the main valve 3 of the thermostat 1 opens,
the coolant of a low temperature is drawn from the lower
outlet 13 of the radiator 11 and fed to the thermostat
housing 8 through the second passage 14. Consequently,
the temperature B of the coolant at the point B' is
further lowered by 20°C. As a result, the difference
between the temperature B of the coolant in the passage
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14 and the temperature A of the coolant in the housing 8
becomes 49°C.
Since the heat sensitivity of the thermostat 1 is
low, the response of the thermostat delays with respect
to the change of the coolant temperature. Therefore,
the main valve 3 opens after the temperature has become
higher than a predetermined opening temperature.
Similarly, the main valve 3 closes after the coolant
temperature has considerably decreased lower than a
Predetermined closing temperature. Namely, there is a
large heat overshoot in control of the coolant
temperature, which causes the main valve to be
repeatedly opened and closed. When the main valve 3
closes, a surge pressure occurs at the upstream of the
main valve. These variations of temperature and
pressure are repeated, and gradually reduced, and faded
away as the valve lift of the main valve 3 increases.
Such a variation of the temperature is definitely shown
in Fig . 8 .
Such a heat overshoot causes cracks of the cylinder
block and cylinder head, and the surge pressure causes
breakdown of the thermostat 1 and the radiator 11. The
fluctuation of the hydraulic pressure causes overload on
the water pump 9, which will shorten the life of the
pump. Furthermore, an abnormally low temperature of the
coolant at the opening of the main valve affects
combustion condition in cylinders, which causes
deteriorating the emission control and increasing fuel
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consumption of the engine.
These troubles are mainly caused by a large difference
between the coolant temperatures A and B. Therefore, it is
necessary to reduce the temperature difference for solving
the problems.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a
cooling system for an automotive engine which may eliminate
above described troubles at an early stage of the opening
of the main valve of the thermostat.
In a cooling system of the present invention, a second
coolant passage is connected to a first bypass passage by a
second bypass passage, so that a part of coolant flows
passing through a radiator and the second bypass passage,
when a bypass valve in the first bypass passage is opened.
Namely, a part of the coolant in a first coolant passage
drawn from water jackets circulates through the first
bypass passage as a first circulation, and the remainder of
the coolant passes through the radiator, second coolant
passage and second bypass passage as a second circulation.
The coolant from the second bypass passage is mixed with
the coolant in the first bypass passage.
These and other objects and features of the present
invention will become more apparent from the following
detailed description with reference to the accompanying
drawings.
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BRIEF DESCRIPTION OF DRAV~IINGS
Fig. 1 is a schematic diagram showing a cooling system
for an automotive engine according to the present
invention;
Fig. 2 shows a record of changes of temperature and
flow rate of the coolant with respect to the time;
Fig. 3 is a schematic diagram of a second embodiment
of the present invention;
Fig. 4 shows a record of the second embodiment;
Fig. 5 shows a record of a modification of the second
embodiment;
Fig. 6 shows a third embodiment of the present
invention;
Fig. 7 is a schematic diagram of a conventional engine
cooling system; and
Fig. 8 shows a record of the conventional system.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to Fig. 1 showing a cooling system of the
present invention, parts of the system which are the same
as the conventional cooling system of Fig. 7 are identified
with the same reference numerals as Fig. 7.
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A second bypass passage 15 is provided between a
first junction J-1 of the second passage 14 upstream of
the main valve 3 and a second junction J-2 of the first
bypass passage 7. The second bypass passage 15 is
connected to the second passage 14 at a position
adjacent to the inlet of the thermostat cap 16.
However, the second bypass passage 15 may be connected
to any place of the second passage 14 between the main
valve 3 and the outlet 13 of the radiator 11.
During the closing of the main valve 3, coolant
having a high temperature drawn from the water jackets 4
is divided at the junction J of the first passage 6. A
part of the coolant passes to the first bypass passage
7, and the remainder of the coolant is circulated
passing through the radiator 11, second passage 14,
second bypass passage 15, and first bypass passage 7.
The coolant in the second bypass passage 15 is mixed
with the coolant in the first bypass passage 7.
A pipe used for each of the first and second
coolant passages 6 and 14 is of 24 mm diameter, and a
pipe used for each of the first and second bypass
passages 7 and 15 is of 10 mm diameter. During the
closing of the main valve 3, the flow rate of the
coolant at the point C passing through the radiator 11
is 13 liters per minute. As shown in Fig. 2, the
difference between the temperatures A and B is 9°C.
When the temperature A of the coolant becomes 85°C,
the main valve 3 of the thermostat 1 begins to open, and
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inversely the bypass valve 2 begins to close a bypass port
18 with a delay. When the bypass valve 2 completely closes
the bypass port 18, the coolant flowing in the first and
second bypass passages 7 and 15 is stopped at the same
time. Thereafter, the coolant in the first passage 6 drawn
from the outlet 5 of the water jackets 4 circulates by the
water pump 9 passing through the radiator 11, second
passage 14, thermostat cap 16, housing 8, and inlet 10 of
the water jackets 4. Thus, the flow rate of coolant
quickly increases up to 60 liters per minute.
As shown in Fig. 2, a starting point of the
temperature A in the record is 75°C. The time until the
bypass valve 2 completely closes the bypass port 18 shown
in Fig. 2 is shorter by 2 minutes 12 seconds than that
shown in Fig. 8.
In the first embodiment, although the thermostat
housing 8 is disposed in the downward position, the housing
may be disposed in the upward position or the lateral
position. Since the coolant is forcibly circulated in the
radiator, the same effect is obtained in any position.
Fig. 3 shows the second embodiment. The same parts as
the first embodiment are identified with the same reference
numerals as Fig. 1.
The first junction J-1 is formed on the thermostat cap
16 in the form of an opening 16a. A second bypass passage
15a is provided between the bypass opening 16a and the
second junction J-2 of the first bypass passage 7.
Similar to the first embodiment, each of the pipes of
the coolant passages 6 and 14 is of 24 mm diameter, and
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each of the bypass passages 7 and 15a is of 10 mm diameter.
As shown in Fig. 4, during the closing of the main valve 3,
the difference between the temperatures A and B is 1°C.
In particular, the temperatures A and B increase at a
constant rate from about 75°C to a warmed up temperature
without changing at the opening of the main valve. In
other words, the time when the main valve opens is not
indicated on the record. The fact that the temperatures A
and B increase at a constant rate has a significant effect
on the cooling system. Namely, there is no heat overshoot
and pressure fluctuation. Thus, the devices of the system
are prevented from suffering.
In the system, the flow rate of the coolant passing
through the radiator 11 and the point C is 11.5 liters per
minute until the bypass valve closes.
When the bypass valve 2 closes the bypass port 18, the
coolant circulated passing through the first and second
bypass passages 7 and 15a is stopped at the same time.
Thereafter, the coolant in the first passage 6 circulates
by the water pump 9 passing through the radiator 11, second
passage 14, thermostat cap 16, housing 8, and inlet 10 of
the water jackets 4. Thus, the flow rate of the coolant
quickly increases up to 60 liters per minute.
The time until the bypass valve 2 closes the bypass
port 18 shown in the record of Fig. 4 is approximately the
same as that shown in the conventional record of Fig. 8.
The difference 1°C between the temperatures A and B in
the second embodiment can be easily reduced to zero.
Fig. 5 shows a record of the modification of the
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second embodiment. If the diameter of the pipe used for
the second bypass passage 15a is increased to 11 mm to
reduce the fluid resistance, the difference between the
temperatures A and B can be zero.
Fig. 6 shows the third embodiment of the present
invention. In the cooling system of the third embodiment,
the first passage 6 is provided to communicate the outlet 5
of the water jackets 4 with a lower inlet 12a of the
radiator 11. The second passage 14 is provided to
communicate an upper outlet 13a of the radiator 11 with the
thermostat cap 16. Namely, the cooling system has an X
crossing passage arrangement. The second bypass passage
15a is provided between the thermostat cap 16 and the first
bypass passage 7.
In the cooling system, although the coolant does not
flow in the radiator 11 during the warming up of the
engine, the high temperature coolant in the water jackets 4
is directly introduced in the lower inlet 12a. Therefore,
the heat of the coolant in the first passage 6 is
transmitted to the coolant in the radiator 11 by the
conduction and convection. Thus, the thermal efficiency is
more improved than the foregoing embodiments.
In accordance with the present invention, during the
warming up of the engine where the bypass valve is opened,
the difference between the temperatures (A and B) in the
thermostat housing and the second coolant passage is very
small. Thus, cracks of cylinder block and cylinder head
are prevented, and the lives of the thermostat, radiator
and water pump are extended. The cooling system of the
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present invention is effective to complete the combustion
in the engine, thereby reducing emission and fuel
consumption.
While the invention has been described in conjunction
with preferred specific embodiments thereof, it will be
understood that these descriptions are intended to
illustrate and not limit the scope of the invention, which
is defined by the following claims.
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