System for heating interior spaces of engine-driven vehicles

A heat pipe provided with a vaporizable working fluid is utilized to transfer heat from exhaust gas flowing through the exhaust pipe of an engine driving a vehicle to air flowing through an air duct to an interior space to be heated in the vehicle. The heat pipe has a loop return pipe for returning condensed fluid to a heat absorption part of the heat pipe and a control valve in the return pipe for controlling the flow of returning fluid, the control valve being controllable manually or automatically by a temperature control system including a sensor in the air duct, a control circuit, and a solenoid valve actuator.

BACKGROUND OF THE INVENTION 
This invention relates generally to heating of spaces in the interior of 
engine-driven vehicles and more particularly to a system for such heating 
in which a heat pipe is used to utilize the heat in the exhaust gas of the 
engine. 
While the heating system of this invention is applicable principally to the 
heating of the interiors of motor vehicles or automobiles, it is not 
necessarily so limited, being applicable to other engine-driven vehicles 
such as small to medium size sea craft such as ferry boats, fishing boats, 
and recreational sea craft and certain aircraft. 
Among such heating systems known heretofore which are adapted to heat 
interior spaces of vehicles by utilizing the heat in the engine exhaust 
gas of the vehicles, there is a system in which the heat absorption part 
of the heat pipe is installed within the exhaust pipe of the engine, and 
the heat discharge part of the heat pipe is installed within a heating air 
duct for conducting heating air to the space to be heated, the heat of the 
exhaust gas being transmitted to the heating air in the air duct by way of 
the heat pipe (as disclosed in Japanese Patent Laid-Open Publication 
(Kokai) No. 24617/1977). 
In a known heating system of this character, however, since a control means 
is not provided, control of the degree of space heating and ON-OFF control 
cannot be carried out. 
SUMMARY OF THE INVENTION 
In view of the above described circumstances in the prior art, this 
invention contemplates the provision of a system for heating vechicle 
interior spaces which is capable of efficiently heating with the use of a 
heat pipe and, moreover, is capable of readily carrying out control of the 
temperature of vehicle interiors such as control of the degree or rate of 
heating or "ON-OFF" control. 
According to this invention, briefly summarized, there is provided a system 
for heating the interior space of an engine-driven vehicle having an 
engine exhaust gas pipe, said system comprising: an air duct connected at 
a downstream end thereof to said interior space; an air-propelling means 
for propelling air through the air duct into the interior space; and a 
heat pipe comprising a heat absorption part adapted to absorb heat from 
engine exhaust gas flowing through said exhaust gas pipe, a heat discharge 
part disposed within the air duct and functioning to transfer heat to said 
air in the air duct, a vapor passage pipe connected at one end thereof to 
the heat absorption part and at the other end thereof to the heat 
discharge part, a working liquid sump disposed below, and communicating 
with the heat discharge part, a working liquid return pipe connected at 
one end thereof to said sump and at the other end thereof to a part of the 
vapor passage pipe near the heat absorption part, and control valve means 
installed in an intermediate part of said return pipe, a working fluid 
being enclosed in sealed state within the heat pipe and performing the 
operation of absorbing heat in the heat absorption part to vaporize, 
flowing as a vapor through the vapor passage pipe to the heat discharge 
part, discharging heat to the air in the air duct to condense into liquid 
form and flowing into the sump, and returning through the working liquid 
return pipe to the heat absorption part, the control valve means being 
operable to control the return flow of the working fluid. 
The nature and utility of this invention will be more clearly apparent from 
the following detailed description when read in conjunction with the 
accompanying drawings, briefly described below.

DETAILED DESCRIPTION OF THE INVENTION 
As mentioned briefly in the foregoing summary, and as illustrated 
schematically in FIG. 1, the principal component of the space heating 
system according to this invention is a heat pipe 2 comprising a heat 
intake or absorption part 2a installed within an exhaust pipe 1 for 
exhausting the combustion gas from the engine E of a vehicle, a heat 
discharge part 2b installed within a heating air duct 4 and having a 
working liquid sump 8 at its bottom, a vapor passage pipe 7 connecting the 
heat absorption part 2a and the heat discharge part 2b, a working liquid 
return pipe 9 connecting the bottom of the sump 8 and a part of the vapor 
passage pipe 7 near the outer part of the exhaust pipe 1, a control valve 
mechanism 10, which is a solenoid valve in the illustrated embodiment and 
is installed in an intermediate part of the working liquid return pipe 9, 
and a working fluid contained in sealed-in state within the heat pipe. 2. 
The working fluid is a liquid such as water. When the working fluid is 
water, an agent for preventing freezing thereof may be added thereto. Any 
of the alcohols including glycols can be used as such an agent depending 
upon the atmospheric temperature. 
At its part where the vapor passage pipe 7 enters the exhaust pipe 1, it is 
connected to the wall of the exhaust pipe 1 by way of a flexible bellows 
member 11 for absorbing vibrations of the exhaust pipe 1 and thereby 
preventing their being transmitted to the vapor passage pipe 7 and the 
working liquid return pipe 9. A pipe coupling 5 may be provided adjacent 
to the bellow member 11 as illustrated in FIG. 2 to enable easy and quick 
attachment and detachment of the pipe 7 to and from the pipe portion of 
the heat absorption part 2a. The heat absorption part 2a is provided on 
its outer surface with fins 3 for increasing its outer surface area 
thereby to improve its heat absorption efficiency. The heat discharge part 
2b is also provided with a large number of cooling fins 6. The downstream 
end 4a of the heating air duct 4 communicates with the vehicle interior 
space S to supply heated air thereinto. The flow rate of the heated air 
thus supplied may be controlled by means such as damper means 19. 
In the operation of space heating system having the above described 
essential construction and arrangement, the working fluid in the heat 
absorption part 2a undergoes heat exchange with the hot exhaust gas 
flowing through the exhaust pipe 1. That is, the working fluid is heated 
by heat absorbed from the exhaust gas and is vaporized. The resulting 
vapor rises through the vapor passage pipe 7 and enters the heat discharge 
part 2b, where the vapor gives up heat to the heating air flowing in the 
air duct 4 and condenses. The condensed working fluid flows downward and 
is collected in the working liquid sump 8. This fluid further flows 
downward through the working liquid return pipe 9 to return to the 
peripheral part of the heat absorption part 2a. The operation of the heat 
pipe 2 is a continuous repetition of the above described cyclic process 
except when the flow of the working liquid through the return pipe 9 is 
stopped by the control valve mechanism 10 as described hereinafter. 
The heating air thus heated in the air duct 4 by the heat discharged by the 
working fluid in the heat discharge part 2b flows into the vehicle 
interior space S and heats the same. At least one portion of the air in 
the space S thus warmed may be circulated via a return duct (not shown) 
back to the upstream end of the heating air duct 4. 
One example of the control valve mechanism 10, which is operable to control 
the flow rate of the condensed working liquid returning through the 
working liquid return pipe 9 to the heat absorption part 2a of the heat 
pipe 2, will now be described in greater detail. As shown in FIGS. 3 and 
4, the control valve mechanism 10 in the illustrated embodiment has a 
gating member 12 which can be thrust directly into and retracted from the 
interior of the working liquid return pipe 9, in a direction substantially 
perpendicular to the axis thereof, through a cutout part 9a in the wall 
thereof. 
The gating member 12 is actuated to undergo the above described movement by 
the armature or plunger 14a of a solenoid 14 by way of a stem 13 fixed at 
one end thereof to the outer end of the plunger 14a and at the other end 
to the gating member 12. The solenoid 14 is supported by support means 
(not shown) in a fixed state relative to the return pipe 9 and operates in 
response to control signals from a temperature control circuit 17 (FIG. 1) 
activated by the temperature within the downstream exit end 4a of the 
heating air duct 4 as measured by a temperature sensor 18. 
Referring again to FIGS. 3 and 4, the stem 13 of the control valve 
mechanism 10 and a portion of the gating member 12 are enclosed and 
airtightly sealed within a bellows envelope 15, which is secured at its 
two ends by brazing 16 respectively to the joint between the plunger 14a 
and the stem 13 and to the outer surface of the return pipe 9 around the 
cutout part 9a This bellows envelope 15 is compressed and expanded in 
unison with the thrusting and retracting action of the plunger 14a, that 
is, with the closing and opening action of the gating member 12, thereby 
continually sealing the interior of the return pipe 9 from the outside 
atmosphere irrespective of the operation of the control valve mechanism 
10. 
In the foregoing embodiment, the heat absorption part 2a of the heat pipe 2 
is a tube of a certain length extending coaxially within the exhaust pipe 
1 and provided on its external surface with fins 3 for increasing its heat 
absorbing area. The heat absorption part 2a, however, may take a number of 
other forms, examples of which will now be described with references to 
FIGS. 5A through FIG. 9. In all cases, the heat absorption part 2a is 
essentially a heat exchanger in which heat in the exhaust gas EG is 
transferred to the working fluid WF without direct contact therebetween. 
In the example illustrated in FIGS. 5A and 5B, the heat absorption part 2a 
is in the form of a cylinder enclosing a number of exhaust gas conducting 
tubes 1a which are spaced apart from each other and from the enclosing 
cylinder and extend parallelly to the longitudinal axis of the cylinder. 
These tubes 1a are communicatively connected to an intermediate part of 
the engine exhaust pipe 1 and conduct therewithin the exhaust gas EG. The 
space mutually between the tubes 1a and between the tubes 1a and the 
cylinder contains the working fluid WF. 
In the example shown in FIGS. 6A and 6B, a part of the engine exhaust pipe 
1 is enclosed coaxially in a cylinder. The inner diameter of this cylinder 
is greater than the outer diameter of the exhaust pipe 1, whereby an 
annular space 20 is formed therebetween to contain the working fluid WF. 
The interior of the exhaust pipe 1, at its part thus encompassed by the 
cylinder, is filled with fins 23 for increasing the heat transmission 
area. The hot exhaust gas EG is thus caused to flow between these fins 23. 
In one example of this construction, the fins 23 are twisted as indicated 
in FIG. 7. 
In still another example as shown in FIGS. 8A and 8B, the structural 
configuration of the engine exhaust pipe 1 and the cylinder is the same as 
that in the example shown in FIG. 6, but the interior of the exhaust pipe 
1, at its part encompassed by the cylinder, is provided with perforated 
transverse baffle plates 24, which are fixed around their peripheries to 
the inner wall surface of the exhaust pipe 1 and are spaced apart in the 
axial direction of the exhaust pipe 1. The positions of the perforations 
or passage holes 22 in adjacent baffle plates are staggered, whereby the 
exhaust gas EG is caused to flow turbulently through these holes in 
undulating paths. Examples of the patterns of the holes in the baffle 
plates 24 are shown in FIG. 8B. The heat exchange rate is thereby 
increased by the increased heat absorption area and by the turbulent flow 
of the hot exhaust gas EG. 
The heat absorption part 2a of the heat pipe 2 of the constitution shown in 
FIG. 1 can be additionally provided at its upstream end with a flow guide 
member 25 made of shape memory alloy or bimetal as shown in FIG. 9. This 
guide member 25 is normally in a state wherein it is closely hugging the 
end of the tube of heat absorption part 2a as indicated by solid line, and 
wherein it has little influence on the exhaust gas flow. Then, as the 
exhaust gas temperature rises, the guide member 25 automatically opens 
outwardly as indicated by intermittent line and thereby guides the exhaust 
gas away from the tubular part of the heat absorption part 2a and its fins 
3. As a result, the heat absorption rate, and therefore the heat exchange 
rate, are lowered. Thus a temperature control means, in addition to the 
control means comprising the temperature sensor 18, the temperature 
controller 17, the solenoid 14, and the control valve mechanism 10, is 
provided to compensate for excessively high temperature of the exhaust 
gas. 
When, in the operation of the space heating system of this invention in one 
embodiment thereof, the temperature within the downstream exit end 4a of 
the air duct 4, as sensed by the temperature sensor 18, reaches or 
slightly exceeds the upper limit of a temperature range which has been 
preset in the temperature controller 7, the controller 17 operates 
responsively to transmit a control signal to the solenoid 14. The solenoid 
thereupon operates as described hereinbefore to close the gating member 12 
to its fully closed state as shown in FIG. 4. 
When the control valve mechanism 10 is thus fully closed, the working fluid 
which has condensed in the heat discharge part 2b no longer returns to the 
heat absorption part 2a of the heat pipe 2, which thereby assumes a 
so-called "dry-out" state. Thus heat exchange by the heat pipe 2 stops. 
When this heat exchange thus stops, the temperature within the vehicle 
interior space S and the air duct 4 progressively become lower. When the 
temperature within the duct 4 as sensed by the sensor 18 drops below the 
lower limit of the above mentioned preset range, the controller 17 
operates to activate the solenoid 14, which thereupon opens the gating 
member 12. The working fluid is thereby released, whereby heat exchange by 
the heat pipe 2 is resumed. 
Thus, by the use of a heat pipe 2, the heat possessed by the exhaust gas 
flowing through the exhaust pipe 1 can be transferred with high efficiency 
to the air flowing through the air duct 4. 
Furthermore, since a control valve mechanism is provided in the working 
liquid return pipe 9 of the heat pipe 2 to control the return flow rate of 
the condensed fluid to the heat absorption part 2a, control of the heating 
temperature in the vehicle interior S, which could not be easily 
accomplished heretofore, is made readily possible. 
As mentioned hereinbefore, another feature of this invention is the 
provision of the vibration absorbing bellows 11, by which vibrations on 
the engine exhaust pipe 1 are absorbed and prevented from being 
transmitted via the heat pipe 2 to the air duct 4. This bellows 11 further 
serves to absorb strains and deformations due to differential thermal 
expansions. 
Still another advantageous feature of this invention is the provision of 
the bellows envelope 15 to cover and seal the moving parts of the control 
valve mechanism 10, which is thereby made positively gas tight. 
Accordingly, there is no possibility of a noncondensing gas infiltrating 
into the interior of the heat pipe 2, the serviceable life of which and 
the entire space heating system can thereby be prolonged. 
The control of the control valve mechanism 10 thereby to control the 
temperature in the vehicle interior space S through the temperature 
control system comprising the temperature sensor 18, the control circuit 
17, and the solenoid 14 can be accomplished in an "ON-OFF" manner between 
upper and lower limits preset in the temperature controller 17 as 
described hereinbefore. Alternatively, this temperature control can be 
carried in a more finely graduated manner or in a freely variable manner. 
Furthermore, the control valve mechanism 10 need not be driven by a 
solenoid 14 as in the illustrated embodiment, it being possible to 
utilized other actuating means, such as a pneumatic or hydraulic 
cylinder-piston actuator or a motor, to actuate the gating member 12. It 
will be obvious that the control valve mechanism 10 can be manually 
actuated. 
By the use of a heat pipe in the space heating system in accordance with 
this invention, the heat exchange between the engine exhaust gas EG in the 
exhaust pipe 1 and the heating air in the air duct 4 by way of the working 
fluid WF can be accomplished efficiently, whereby the vehicle interior 
space S can be heated rapidly, even at the time of starting of the engine.