Vehicle heating system

In a vehicle heating system, heat exchange is made between a combustion gas generated by a burner of a heater and water by a heat exchanger of the heater and the hot water heated by the heat exchanger is sent into a cooling water heater unit of the vehicle for heating. The hot water for heating the vehicle can be obtained by change-over control of a change-over valve from the hot water of the heat exchanger or from the hot water of a radiator of an engine. Furthermore, the combustion gas generated by the burner is sent into an intake or exhaust pipe of the engine.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a vehicle heating system equipped with a heater 
which can operate independently of a car engine. 
2. Description of the Prior Art 
Vehicle heating systems are disclosed in Japanese Patent Laid-Open No. 
252018/1985 and Japanese Utility Model Laid-Open No. 59876/1986. 
First of all, the vehicle heating system described in Japanese Patent 
Laid-Open No. 252018/1985 will be explained with reference to FIG. 6 of 
the accompanying drawings. In this vehicle heating system, a burner 104 
for burning a fuel is disposed in an intake pipe 103 of an engine 101 and 
a heat exchanger 105 is disposed downstream of the burner 104 in order to 
provide heat exchange between the combustion gas generated by burning the 
fuel by the burner 104 and the air for heating, and the heating air thus 
heated is used for heating the car. 
Next, the warming-up means of the engine described in Japanese Utility 
Model Laid-Open No. 59876/1986 will be explained with reference to FIG. 7. 
In the warming-up means, an intake detour circuit 4 is disposed in 
parallel with an intake pipe 3 of an engine 1 at an intermediate part of 
the intake pipe 3, a burner 5 and a heat exchanger 8 communicating with a 
car heater unit 9 are disposed sequentially in this intake detour circuit 
4 and a pressure control valve 12 is disposed in the intake pipe 3 
bypassing the intake detour circuit 4. The burner 5 is connected via a 
fuel pipe 6 to a fuel injection pump 32' fitted to the engine 1 and fuel 
from a fuel tank 11 is burnt by the burner 5 disposed in the intake detour 
circuit 4. The air outlet side of the heat exchanger 8 is connected to the 
heater unit 9 of the car so that the hot air warmed up through heat 
exchange with the combustion gas of the burner having carbureter means 7 
flows into the heater unit 9. 
A check valve 15 such as a lead valve is disposed upstream of a confluence 
point of the intake detour circuit 4 with the intake pipe 3 to prevent 
suction air from the intake pipe 3 side from entering the intake detour 
circuit 4 at its downstream side. A pressure control valve 12 is disposed 
at the portion of the intake pipe 3 where it bypasses the intake detour 
circuit 4. This pressure control valve 12 is disposed in order to keep 
always constant a differential pressure of the intake pipe 3 between 
upstream and downstream of the safety valve 12. This valve 12 includes an 
arm 12b which is fitted to a rotary shaft 12a and connected to a rod 13c 
formed projectingly from a diaphragm 13a of a diaphragm type actuator 13. 
A spring chamber 13b of the actuator 13 is connected to a negative 
pressure sensor 14 disposed in the intake pipe 3 downstream of the 
pressure control valve 12 by a communication pipe 13d, so as to introduce 
the pressure downstream of the pressure control valve 12 into the spring 
chamber 13b. 
In the vehicle heating system shown in FIG. 6 and in the engine warming-up 
means shown in FIG. 7, the combustion gas is introduced into the intake 
pipe of the engine after passing through the heat exchanger of the heater, 
and the air for combustion which is sent in the burner of the heater is 
taken into from the air cleaner for the engine. As to the heat exchanger 
of the heater, heat exchange is made between the combustion gas and the 
heating air, that is, on the gas-to-gas basis. Accordingly, if the 
combustion gas mixes accidentally into the heating air during heat 
exchange between them, the combustion gas might enter the car. If unburnt 
gases such as CO, HC, and the like, are contained in this combustion gas, 
a critical problem that might prove fatal to the occupant may arise. 
Furthermore, the size of a piping arrangement must be increased or a blower 
having a higher capacity must be disposed to minimize resistance in the 
case of air, depending upon types or models of cars, but such means are 
difficult to employ because of a limited capacity of a power source. In 
the case of the combustion gas, or in the case of the gas-to-air heat 
exchange, an air conditioner unit of a carburetor must be changed or 
modified structurally and this results in a more complicated construction 
and a more troublesome fitting work. Moreover, the heating system itself 
becomes more expensive, and still another problem will develop in that the 
heating air will be overheated when the car stops abruptly. 
SUMMARY OF THE INVENTION 
To eliminate the problems of the prior art described above, the present 
invention is directed to provide a vehicle heating system which uses water 
for heat-exchanging the combustion gas generated in a burner of a heater 
at a heat exchanger to make heat exchange between the combustion gas 
generated by the burner and the heating water and which is highly safe 
because it does not employ direct heat exchange between the combustion gas 
and heating air, to prevent the combustion gas of the burner from entering 
the car. 
It is another object of the present invention to provide a vehicle heating 
system which stops the operation of the burner only after cooling water 
circulating through the radiator of an engine reaches the level of hot 
water suitable for warming the car, can selectively control this hot water 
and the hot water heated by the burner by means of a change-over valve, 
can rapidly heat the cabin at first by the burner and heat the cabin by 
the engine while the operation of the burner is stopped after the cooling 
water is heated, and thus provides an energy saving effect. 
It is still another object of the present invention to provide a vehicle 
heating system which can be constructed by merely arranging the cooling 
water circulating through the radiator of the engine and the hot water 
heated by the burner to be changeable-over by a change-over valve, has 
simple mountability to cars in terms of a piping arrangement and can be 
fitted to existing vehicles by changing slightly the design and can 
minimize the production cost. 
It is still another object of the present invention to provide a vehicle 
heating system which feeds the combustion gas generated in the burner into 
the intake pipe or exhaust pipe of the engine and processes the combustion 
gas of the burner by the engine and consequently, is extremely safe, and 
can operate the heater to heat the cabin while the engine stops. 
It is a further object of the present invention to provide a vehicle 
heating system which can utilize effectively the exhaust heat, that is, 
the heat of the combustion gas, can save energy, and is free from possible 
fire by use of water for heat exchange even if a blower or the like is out 
of order and from overheat even if a car stops abruptly, and hence is 
extremely safe. 
It is still another object of the present invention to provide a vehicle 
heating system which can use pipelines having a reduced diameter as the 
piping arrangement for heating and can apply easily to cars or vehicles 
having a cab-tiltable structure. 
It is still another object of the present invention to provide a vehicle 
heating system which can operate a heater, particularly only a heater of a 
quick heating system, independently of the engine, can pre-heat cooling 
water of the engine and can thus improve startability of the engine.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Hereinafter, one preferred embodiment of the present invention will be 
described with reference to the accompanying drawings. 
FIG. 1 illustrates the basic construction of a vehicle heating system as 
one embodiment of the present invention. This vehicle heating system 
applies to a car to which a quick heating system QHS is mounted. This 
quick heating system QHS includes primarily a blower 31, a burner 5 and a 
heat exchanger 8 that are disposed sequentially in order named and can 
attain quick heating by use of the burner 5 and the heat exchanger 8 as 
will be described later. 
Carbureter means 7 is disposed in the burner 5 and a first air cleaner 24 
for an engine is disposed at an upstream part of an intake pipe 3 of the 
engine 1. A silencing valve 42 is disposed in the intake pipe 3 upstream 
of a confluence point of a combustion gas passage 16 of the heater and the 
intake pipe 3. The intake pipe 3 downstream of the silencing valve 42 
communicates with an intake manifold 2. A change-over valve 25 for engine 
suction and a change-over valve 26 for atmospheric discharge (see FIG. 4) 
are disposed in order to selectively pass the combustion gas generated in 
the heater to a combustion gas passage 16 for discharging the gas to the 
intake pipe 3 of the engine 1 or another combustion gas passage 18 for 
discharging it to the atmosphere in response to the open/close operation 
of an exhaust brake valve 41. 
The exhaust brake valve 41 described above is disposed in the exhaust pipe 
6 upstream of the confluence point of the combustion gas passage 18 of the 
heater and the exhaust pipe 6 of the engine 1. A second air cleaner 23 is 
disposed upstream of the blower 31. In the heater described herein, the 
combustion gas generated in the burner 5 is subjected to heat exchange 
with water in the heat exchanger 8 and the hot water thus heated in then 
subjected to heat exchange with air in a cooling water heater unit 10 
disposed in the car so that the air is turned to hot air and used for 
heating the cabin 28 of the car. 
A flow path 80f for passing the water into the heat exchanger 8 and a flow 
path 80c for passing the heated water, that is, the hot water, from the 
heat exchanger 8 are disposed in the heat exchanger 8. A water pump 81 for 
the heat exchanger is disposed in the flow path 80f. This water pump 81 is 
driven by a motor 83 while the motor 83 is subjected to ON/OFF control by 
a switch 84 operated by a signal from a main control unit 50. The flow 
paths 80c and 80f are connected to a change-over valve assembly 80. The 
change-over valve assembly 80 communicates with the cooling water heater 
unit 10 through the flow paths 80a and 80b. The change-over valve assembly 
80 is also connected to the engine 1 through flow paths 80d and 80e to 
cool the engine 1. A water pump 82 for the engine is incorporated in the 
flow paths 80d and 80e. As to the circulation of the water for the heat 
exchanger 8, a water pump 81 which is smaller than the water pump 82 for 
circulating the cooling water of the engine 1 and driven separately is 
disposed for circulation. 
Furthermore, a thermostat housing consisting of electromagnetic valves or 
the like, that is, the change-over valve assembly, is disposed between the 
conventional cooling water heater unit 10 and the engine 1 in order to 
keep a balance with the temperature of the cooling water on the side of 
the engine 1, and to circulate the water directly to the cooling water 
heater unit 10 as desired by a user, or to circulate it partially mixed 
with the cooling water of the engine 1. Therefore, the cooling water 
heater unit 10 having the conventional structure can be used sufficiently 
and no design change or modification is necessary. Moreover, since the 
heater of the quick heating system QHS is employed, the time from ignition 
of the burner 5 till delivery of the hot wind to the seats such as a 
driver's seat can be made extremely short, such as about 3 minutes. In 
such a case, the water amount circulating between the heat exchanger 8 and 
the cooling water heater unit 10 is preferably up to about 5 l, for 
example. 
Incidentally, reference numeral 79 in the drawings represents a temperature 
sensor for sensing the temperature of the air for heating, 17 is a 
combustion gas passage, symbol A represents a flowing direction of the air 
for combustion, B is the flowing direction of the combustion gas, C is the 
flowing direction of the intake air of the engine and D is the flowing 
direction of water for heating. 
FIG. 2 shows the relationship between the flow path of the circulating 
water for the heat exchanger 8 and the flow path of the cooling water of 
the engine 1 as well as the detailed structure of the change-over valve 
assembly 80. Change-over valves 803, 804 which are electromagnetic valves 
are incorporated in the change-over valve assembly 80 and open and close 
the flow paths 80d and 80f, respectively. When the change-over valve 804 
closes the flow path 80f while the change-over valve 803 opens the flow 
path 80d, they open the path ranging from the water pump 82 for 
engine.fwdarw. flow path 80d.fwdarw. change-over valve assembly 80.fwdarw. 
flow path 80a.fwdarw. cooling water heater unit 10 in cab.fwdarw. flow 
path 80b.fwdarw. change-over valve assembly 80.fwdarw. flow path 
80e.fwdarw. engine 1.fwdarw. water pump 82, and cut off the path ranging 
from the water pump 81 for heat exchanger.fwdarw. heat exchanger 8.fwdarw. 
flow path 80c.fwdarw. change-over valve assembly 80.fwdarw. flow path 
80a.fwdarw. cooling water heater unit 10 in cab.fwdarw. flow path 
80b.fwdarw. change-over valve assembly 80.fwdarw. flow path 80f.fwdarw. 
water pump 81. 
When the change-over valve 804 opens the flow path 80f while the 
change-over valve 803 closes the flow path 80d, they open the flow path 
ranging from the water pump 81 for heat exchanger.fwdarw. heat exchanger 
8.fwdarw. flow path 80c.fwdarw. change-over valve assembly 80.fwdarw. flow 
path 80a.fwdarw. cooling water heater unit 10 in cab.fwdarw. flow path 
80b.fwdarw. change-over valve assembly 80.fwdarw. flow path 80f.fwdarw. 
water pump 81 and cut off the path ranging from the water pump 82 for 
engine.fwdarw. flow path 80d.fwdarw. change-over valve assembly 80.fwdarw. 
flow path 80a .fwdarw. cooling water heater unit 10 in cab.fwdarw. flow 
path 80b .fwdarw. change-over valve assembly 80.fwdarw. flow path 
80e.fwdarw. engine 1.fwdarw. water pump 82. 
FIG. 3 shows another example of the change-over valve assembly 80. Though 
the change-over valve shown in FIG. 2 is the electromagnetic valve, the 
change-over valve shown in FIG. 3 is of a fluid operation type using air 
48 but exhibits the same function as the electromagnetic valve shown in 
FIG. 2. Therefore, the explanation of the function will be omitted. 
FIG. 4 shows an example where the vehicle heating system of the invention 
shown in FIG. 1 applies to a car together with its control unit. In the 
components of the vehicle heating system shown in FIG. 4, like reference 
numerals are used to identify like components as in FIG. 1, and the 
explanation of such components will be omitted. 
In the burner 5, the liquid fuel is sent from the fuel tank 11 into the 
carbureter means 7 through the fuel pump 32, the fuel filter 49 and the 
return valve 46. The burner 5 is constructed in such a manner that the 
liquid fuel is vaporized by the carbureter means 7 to generate a gasified 
fuel, the resulting fuel is burnt and its combustion gas is sent into the 
heat exchanger 8. The intake pipe 3 of the engine 1 and the combustion air 
passage 17 for sucking the air for combustion are connected to separate 
air cleaners 23 and 24, respectively. The first air cleaner 24 for the 
engine is disposed at an upstream portion of the intake pipe 3 and has a 
function of relatively cleaning the air. The second air cleaner 23 having 
a different function from that of the first air cleaner 24 is disposed at 
an upstream portion of the combustion air passage 17. This air cleaner 23 
may be composed of a relatively rough, or coarse, filter and in such a 
case, the intake resistance of air is low and hence, suction capacity of 
the blower 31 may be small and its power comsumption may be small, too. 
In the vehicle heating system shown in FIG. 4, various functions can be 
attained by ON/OFF controlling the change-over valve 25 for engine intake, 
the change-over valve 7 for opening to the atmosphere, the change-over 
valve 26 for keeping the engine temperature and the change-over valve 40 
for the combustion gas passage 39. In other words, it is possible to 
auxiliarily start and warm up the engine by use of the combustion gas 
after heat exchange in accordance with a given condition by ON/OFF 
controlling the change-over valve 25 for the engine suction, the 
change-over valve 27 for opening to the atmosphere, the change-over valve 
26 for maintaining the engine temperature and the change-over valve 40 for 
the combustion gas passage 40. 
In the drawing, reference numeral 43 represents an operation switch of the 
quick heating system QHS; 44 is an operation switch for keeping the engine 
temperature which introduces the combustion gas to the outer surface of 
the engine 1, that is, to the outer surface of the cylinder block, the oil 
pan, and the like; 45, 47 and 79 are temperature sensors; 48 is an engine 
suction instruction switch which instructs whether or not the exhaust gas 
or the combustion gas is to be sucked manually into the intake pipe of the 
engine 1; 50 is a main control unit; 71 is an air tank for storing the air 
compressed by the engine 1 or the like; 72 is a timer as an optional item; 
73 is a clutch signal switch for inputting a ON/OFF signal of the clutch; 
74 is an accelerator step-in sensor generating a signal representing 
whether an accelerator pedal is free or somewhat stepped in; 75 is a 
starter for the engine 1; 76 is a key switch of the engine starter or the 
like disposed at the driver's seat; 77 is a silencer; 78 is an exhaust 
brake operation switch for cutting off the exhaust brake valve 41 to 
operate the exhaust brake; and 80 is a battery. 
It is preferred to use a burner having the following construction, for 
example, as the burner 5 described above, though its detail is not shown 
in the drawing. A preferred example will be described with reference to 
FIG. 4. 
This burner 5 consists of a ceramic combustion cylinder, which is divided 
into a carbureter chamber and a combustion chamber by a partition having 
communication holes. The carbureter means 7 with a built-in glow plug 30 
for gasification is disposed in such a manner as to penetrate through the 
combustion chamber and a jet port for jetting the gasified fuel gasified 
by the carbureter is open to the carbureter chamber, and a glow plug 29 
for ignition is disposed in the carbureter chamber. The liquid fuel is 
gasified by the gasification glow plug 30 into the gasified fuel and mixed 
with the air for combustion to form an air-fuel mixture. Oil droplets that 
exist in a very limited quantity or the air-fuel mixture is ignited by the 
ignition glow plug 29 to burn the air-fuel mixture in the combustion 
chamber. When the burner 5 described above is used, the liquid fuel can be 
gasified rapidly into the gasified fuel, which is ignited rapidly and can 
be burnt rapidly. As a result, the burner 5 can immediately feed the 
combustion gas into the heat exchanger 8 to let is rapidly exhibit its 
function. In this manner, the cabin 28 of the car can be heated rapidly. 
The vehicle heating system of the invention having the construction 
described above operates in the following way. First of all, the 
fundamental operating conditions of this vehicle heating system will be 
described. The vehicle heating system shown in FIG. 1 sets the change-over 
valve 25 so that even when the engine 1 is at halt, the heater consisting 
of the burner 5 and the heat exchanger 8 can be operated independently of 
the engine. The exothermic quantity obtained by the burner 5, that is, the 
combustion gas, is fed into the heat exchanger 8 and, after subjected it 
is to heat exchange, it is sent into the intake pipe 3 of the engine 1 
through the combustion gas passage 16 or into the combustion gas passage 
18 which opens to the atmosphere. 
When both the engine 1 and the heater operate simultaneously and moreover, 
when the combustion gas generated by the burner 5 of the heater is to be 
drawn into the engine 1, the change-over valve 25 is set to the open side 
with respect to the intake pipe 3. The combustion gas is sent into the 
engine 1 and completely burnt there. In this manner, high safety can be 
secured. In this case, the cooling water is not yet heated before and 
immediately after the start of the engine 1. Therefore, the change-over 
valve assembly 80 is operated so that the car can be heated by the heater 
of the quick heating system QHS which is disposed independently of the 
engine 1. Next, when the cooling water of the engine 1 is heated 
sufficiently and can be used for heating, the change-over valve assembly 
80 is operated so that the heating independent of the engine 1 is stopped, 
and only the cooling water of the engine 1 is used for heating the car. 
The controlling operations described above can be accomplished by 
operating the change-over valve assembly 80 as described above. 
When the heater operates while the engine 1 is at halt, control is provided 
so that the change-over valve 25 is closed with respect to the intake pipe 
3 but is open to the combustion gas passage 18 connected to the exhaust 
pipe 6 for opening to the atmosphere. Under this state, the combustion gas 
flows smoothly to the atmosphere due to the operation of the blower 31. In 
the heat exchanger 8, heat exchange is effected between the combustion gas 
from the burner 5 and water so that the water is heated and turned to hot 
water, which is then sent into the cooling water heater unit 10 and used 
for quickly heating the cabin 28. 
Next, the operation of the vehicle heating system having the quick heating 
system QHS shown in FIG. 4 will be explained. Furthermore, the operation 
processing state of the control unit for the vehicle heating system will 
be explained with reference to the change-over valve assembly 80 shown in 
FIGS. 2 and 3 and to the flow chart shown in FIG. 5. 
First, the vehicle heating system of this invention is started. . . . (51) 
Each valve is placed under the state where the air of the air cylinder is 
not operated, and only the quick heating system QHS can operate 
independently of the engine 1. Whether the operation switch 43 of the 
quick heating system QHS consisting of the burner 5 and the heat exchanger 
8 is ON or OFF is judged. If the operation switch 43 is not ON, the flow 
returns to the start. When the operation switch 43 is ON, the flow 
proceeds to the next processing (53). . . . (52) 
A current is applied to the gasification glow plug 30 and the ignition glow 
plug 29 in the quick heating system QHS. . . . (53) 
The liquid fuel pump 32 is operated to feed the liquid fuel from the liquid 
fuel tank 11 into the carbureter means 7. When this pump 32 is operated, 
the liquid fuel is supplied to the burner 5 and the liquid fuel is 
gasified and turned to the gasified fuel. . . . (54) 
The blower 31 is operated in order to feed the air for combustion into the 
burner 5. The burner 5 gasifies the liquid fuel into the gasified fuel and 
enters the combustion state. . . . (55) 
When various components of the quick heating system QHS associated with 
combustion are turned ON, the liquid fuel is gasified and turned to the 
gasified fuel, and whether or not it is ignited is judged by detecting the 
temperature of the combustion gas by the temperature sensor 34 disposed at 
the combustion gas outlet of the heat exchanger 8, that is, at the inlet 
of the combustion gas passage 16. For example, whether or not the 
combustion gas temperature is above about 200.degree. C. is judged. If the 
gas is not ignited, various controls are performed once again. If the gas 
is ignited, the flow proceeds to the next processing (57). . . . (56) 
If the temperature of the combustion gas is above a predetermined value, 
the change-over value 804 (or 801) is opened. . . . (57) 
The change-over valve 803 (or 802) is closed so that the hot water after 
heat exchange with the combustion gas of the quick heating system QHS 
becomes available. . . . (58) 
The motor 83 for driving the water pump 81 for the heat exchanger 8 is 
turned ON to operate the water pump 81 and the hot water heated by the 
heat exchanger 8 is circulated so that it flows through the heat exchanger 
8 and the cooling water heater unit 10. . . . (59) 
In the cooling water heater unit 10, heat exchange is made between the hot 
water and the air for heating and its warm air is delivered into the cabin 
28 of the car. The discharge temperature sensor 9 disposed at the outlet 
port to the cabin 28 judges whether the hot wind has reached a set 
temperature. If it has, the flow proceeds to the processing (62) and if 
not, the flow proceeds to the processing (61). . . . (60) 
If the warm air has not reached the set temperature, whether or not any 
input is given from an engine revolution sensor 35 for sensing, the number 
of revolution of the engine 1 is judged. If there is such an input signal, 
the flow proceeds to the processing (63) and if not, the flow returns to 
the entrance of the processing (60). . . . (61) 
When the warm air has reached the set temperature, the fuel pump 32 for 
supplying the fuel to the burner 5 is controlled and the processing (60) 
is repeated. . . . (62) 
When there is an input signal from the engine revolution sensor 35, whether 
or not the temperature of the engine cooling water is above the set 
temperature is detected and judged by the engine water temperature sensor 
45. If it is above the set temperature, the flow proceeds to the 
processing (64) and if not, the flow returns to the processing (60) to 
repeat the processing. . . . (63) 
When the temperature of the engine cooling water is above the set 
temperature, the change-over valve 803 (or 802) in the change-over valve 
assembly 80 is opened while the change-over valve 804 (or 801) is closed 
in order to feed the engine cooling water into the cooling water heater 
unit 10. . . . (64) 
The discharge temperature sensor 79 disposed at the outlet port to the 
cabin 28 judges whether or not the temperature reaches a set temperature. 
If it does, the flow proceeds to the processing (66) and if not, the flow 
returns to the processing (60) to repeat the processing. . . . (65) 
When the temperature reaches the set temperature, the fuel pump 32 for 
supplying the fuel to the burner 5 is stopped, the operation of the heater 
of the quick heating system QHS is stopped, too, and the combustion is 
discontinued. . . . (66) 
The suction return valve 46 is opened to instantaneously draw back the 
liquid fuel up to the carbureter means 7, in order to improve response to 
combustion extinguishment and the liquid fuel is recovered into the fuel 
tank 11. . . . (67) 
The motor 83 for driving the water pump 81 is turned OFF to stop the water 
pump 81 for heat exchange. 
The change-over valve 804 (or 801) in the change-over valve assembly 80 is 
closed. . . . (69) 
The control of the heating operation by the quick heating system QHS in the 
vehicle heating system is completed. . . . (70) 
Though the present invention has thus been described in detail with 
reference to one preferred embodiment thereof, the present invention is 
not particularly limited thereto. For example, various constructions can 
be employed for the burner and for the heat exchanger. As to the burner, 
for example, it may be of such a type that it turns the liquid fuel to the 
gasified fuel and the gasified fuel is ignited by the use of the heating 
plug, and the burner may be either a vertical type or a horizontal type. 
Various shapes and constructions can be employed for the heat exchanger, 
too, and various changes and modifications of the design can of course be 
made. Moreover, the control of water for circulation through the heat 
exchanger and the engine cooling water can of course be made by the use of 
a thermostat or the like.