Detector device for evaluating the thermal comfort conditions in an environment, for example, in the interior of a motor vehicle

The device comprises a heat-sensitive element which is heated to a controllable extent so as to keep it at a predetermined temperature, for example, average body temperature. Detector means measure the power or energy required to keep the heat-sensitive element at this predetermined temperature, thus providing a signal indicative of the thermal comfort conditions of the environment. The heat-sensitive element has a general elongated shape so that it can be inserted, for example, into a motor vehicle safety belt, ensuring that the indication obtained indicates the general thermal comfort conditions throughout the entire region of the environment in which the heat-sensitive element extends.

This invention relates to a detector device for evaluating the thermal 
comfort conditions in an environment. The invention has been developed 
paying particular attention to the possible use of a detector device of 
this kind for evaluating the thermal comfort conditions in the interior of 
a motor vehicle, for example, for generating a signal adapted to be used 
to control the air-conditioning system of the motor vehicle interior. 
It is known that the degree of thermal comfort in an environment does not 
depend exclusively on the air temperature of this environment. It is in 
fact possible for there still to be a feeling of discomfort, even if the 
air temperature is satisfactory. On the other hand, in other situations it 
is possible to experience a feeling of thermal comfort even when the air 
temperature is relatively low. The feeling of thermal comfort perceived by 
the human body is in fact determined not only by the air temperature, but 
also by other factors, such as humidity, air turbulence, thermal radiation 
conditions, etc. 
Prior Italian Patent No. 1 183 980 proposes a device for providing a 
reliable measurement of the degree of thermal comfort of an environment, 
taking account of a plurality of factors which may condition the feeling 
of thermal comfort. In particular, the solution described in this prior 
patent provides for the use of a heat-sensitive element supplied with heat 
to a controllable extent by control means which, in this manner, keep the 
heat-sensitive element at a predetermined temperature, for example, a 
temperature substantially equal to average body temperature. Detector 
means therefore make it possible to detect the power or energy required at 
the said heater means to keep the heat-sensitive element at this 
predetermined temperature, thereby obtaining an indication of the degree 
of thermal comfort which takes account of a plurality of factors capable 
of influencing it, such as temperature, air speed and turbulence and 
thermal radiation conditions. 
In particular, the Applicant has obtained a method of detecting, in a 
solution such as the one described in the prior patent, that there is a 
very precise correlation between the electrical power required to keep the 
heat-sensitive element at the predetermined temperature and the degree of 
thermal comfort of the environment. 
This applies above all in the case of environments subjected to heating or 
to loss of heat by radiation (for example, heating environments with 
infrared rays) or in environments in which the rate of humidity has 
anomalous values, and in specially ventilated environments, as even in 
this case the feeling of thermal comfort cannot be correlated with the air 
temperature alone, these all being situations of use encountered in the 
interior of a motor vehicle, above all taking account of the fact that it 
is surrounded to a considerable extent by glass surfaces. 
This prior patent therefore suggests the use of a certain number of sensor 
devices arranged at the points at which some of the parts of the body of a 
motorist (or of a dummy simulating the said motorist ), for example, the 
feet, the head, the hands, etc., will be situated, in order to detect with 
accuracy whether uniform thermal comfort conditions exist in the interior 
of the motor vehicle.. 
In fact, the thermal and thermodynamic conditions that tend to be 
established in the interior of a motor vehicle (above all during running ) 
are quite different, so that, using the F solution according to prior 
patent No. 1 183 980, it is in fact necessary to provide a certain number 
of thermal comfort sensors, this being disadvantageous in terms of 
simplicity of the system for detecting and processing the relative signals 
and, consequently, in terms of cost. 
Therefore, the object of this invention is to improve the solution 
described in the above prior patent by providing means capable of 
effecting overall detection of the thermal comfort conditions in an 
environment, even in an environment, precisely like the interior of a 
motor vehicle, in which completely non-uniform conditions often tend to be 
established.

With reference to the embodiment of FIG. 1, the device according to the 
invention comprises two resistors 1 and 2, the first of which has variable 
resistance as a function of the temperature, while the other has constant 
resistance. These resistors are thermally coupled to one another, a result 
which can be achieved, for example, by winding the heat-sensitive resistor 
1 on to the heating resistor ("heat exchange means") 2 or vice versa. 
Both of the resistors 1 and 2 are of a generally elongated shape and 
therefore have a general ribbon-like structure, preferably flexible, and 
have a length, for example, of approximately one meter or more, so that 
they can be arranged within an environment, typically the interior of a 
motor vehicle, so that the heat-sensitive resistor 1 extends for a certain 
distance within the said motor vehicle interior. 
For example, with reference to the embodiment of FIG. 3, the resistor 1 
forms a type of arch or overturned U extending along a first side, the top 
and the Second side of the back B of a seat S of a motor vehicle. 
On the other hand, in the embodiment referred to by FIG. 4, the resistor 1 
is in fact incorporated into one of the straps (for example, the oblique 
strap G) of the safety belt which encloses the body of a motorist C 
occupying the seat S. 
In both of the solutions illustrated in FIGS. 3 and 4, it would appear to 
be preferable for the resistor 1 to be sensitive primarily to the ambient 
conditions, while still being screened from the emission of heat by the 
body of the person occupying the seat S. This result can be obtained in a 
simple manner by associating a ribbon-like screening element W with the 
resistor 1, capable of adapting to the orientation and general flexibility 
of the resistor 1, made of material having good thermal insulation 
properties (above all with respect to infrared radiation) and arranged so 
as to be interposed between the body of the person C occupying the seat S 
and the said resistive element 1. 
With regard to the production of the latter, it is possible to adopt 
various solutions, both with respect to the selection of the constituent 
material and with respect to the general arrangement of the said resistor. 
The constituent material of the resistor 1 may be, for example, a metal, 
such as copper or nickel. The selection of a material of this kind is 
certainly advantageous both for the general characteristics of ductility 
(allowing the resistor 1 to be produced in the form of a ribbon-like coil 
having good flexibility characteristics and, possibly, restrained 
longitudinal extensibility characteristics) and with respect to the 
strictly intended electrical properties. Nickel would appear to be 
preferable to copper from this point of view, both for its higher 
intrinsic resistivity and for its higher coefficient of variation of 
resistivity with temperature. 
As a further alternative, one may consider the use of, for example, 
conductive plastics materials. 
Examining the structure of the resistor illustrated in FIG. 1 in more 
detail, it will be noted that it consists essentially of two elongated 
rheophores 10 between which there extends a mass of ribbon-like resistive 
material 12 (formed, for example, of a ribbon of conductive plastics). 
Assuming that the length of the resistor 1 (length L) can be expressed by a 
standard parameter X included between O and L, the conductance G (that is, 
the reciprocal of the resistance R) demonstrated completely by the 
resistor 1 between the two rheophores 10 can be expressed in general 
according to a relation of the type 
##EQU1## 
where the factor g(x, T(x)) indicates the conductivity of the 
infinitesimal element of resistive material 12 which is situated at the 
length x of the resistor and T expresses in general the dependency of this 
elementary conductivity on the local temperature of this infinitesimal 
element, a temperature which, in turn, also depends on the parameter x, 
since, as can be seen, the thermal and thermodynamic conditions of the 
environment are generally different from point to point. 
Therefore, it follows that the relation 1 expresses a principle on the 
basis of which the conductance of the resistor 1 incorporates an 
integration effect (of the conductance value) over the length of the 
resistive element. 
This ensures that the resistor 1 is not sensitive exclusively to a local 
thermal or thermodynamic condition (as is the case with the sensor of 
prior U.S. Pat. No. 1,183,980, in practice, punctiform), but, on the other 
hand, expresses a detecting action of the comfort throughout the entire 
zone of the environment in which the said resistive element 1 extends. 
Returning to the diagram of FIG. 1, it will be noted that the 
heat-sensitive resistor 1 is connected to a processing circuit 100, which 
is then inserted accurately in a bridge circuit 4 connected in a power 
source (for example, a battery of a motor vehicle) which supplies a 
voltage VB and earth M. 
Two sides of the bridge circuit 4 comprise the two portions 5a and 5b of 
the resistive element of a potentiometer 5, the sliding contact of which 
is designated by 5c. The other two sides comprise a resistor 6 and the 
heat-sensitive resistor 1. 
A differential amplifier 7 has its inputs connected respectively to the 
sliding contact 5c of the potentiometer 5 and to the junction of the 
resistors 1 and 6. The output of the amplifier 7 is connected to the 
driver input of a driven current generator circuit 8. The heating resistor 
2 is interposed between this current generator and earth M. A voltmeter 
9..is connected to the ends of this resistor, the scale of which may 
advantageously be calibrated in watts. 
In use, the current generator 8 supplies a current I to the heating 
resistor 2 which, following thermal dissipation, tends to keep the 
heat-sensitive resistor 1 at a temperature as close as possible to an 
identified reference temperature regulating the potentiometer 5. In 
general, the regulation can be effected by selecting a temperature as 
close as possible to the average body temperature, since this selection is 
preferred in many ways in order to detect a condition which is closer to 
the normal feeling of comfort. If, in the environment in question, the 
humidity or the air speed in the zone completely occupied by the sensor 1 
(thus, with reference to the solutions for assembly illustrated in FIGS. 3 
and 4, throughout the entire zone surrounding a seat S or the person 
occupying a seat within the interior of a motor vehicle) are such that 
they cause a reduction in temperature of the resistor 1, the consequent 
variation in the resistance of the said heat-sensitive resistor 1 causes a 
corresponding variation in the voltage between the inputs of the amplifier 
7. The latter supplies a signal to the current generator 8, so as to cause 
an increase in the current I supplied by the heating resistor 2, so as to 
oppose the temperature reduction of the heat-sensitive resistor 1, in 
order to keep it substantially at the temperature defined hereinabove. The 
voltmeter 9 calibrated in watts supplies in a corresponding manner an 
indication of the electrical power required to keep the resistor 1 at the 
predetermined temperature. Instead of the voltmeter 9, it is of course 
also possible to use a wattmeter or any other device capable of indicating 
the electrical power absorbed by the resistor 2 in order to effect the 
thermostatic action described hereinbefore. It is also possible to 
envisage the association of an integrator device with the voltmeter 9 (or 
with any equivalent element), capable of providing an indication not only 
of the electrical power, but also of the electrical energy absorbed over a 
certain period of time by the resistor 2. 
In both cases, the indication of the power or energy absorbed in order to 
effect the thermostatic action of the resistor forms a good indication of 
heat "dispersion" phenomena experienced by a person situated in the zone 
of the environment in which the heat-sensitive resistor 1 extends (for 
example, along the paths illustrated in FIGS. 3 and 4). 
Of course, for use in environments with an air temperature in excess of 
36.degree.-37.degree. C., the resistor may advantageously consist of a 
Peltier effect element. 
FIG. 2 relates to a variant embodiment of the detector device according to 
the invention. In this drawing, the elements already described 
hereinbefore with reference to the embodiment according to FIG. 1 are 
designated by the same reference numerals. 
In essence, the embodiment of FIG. 2 differs from the embodiment of FIG. 1 
in two aspects: 
the absence of the heating resistor 2 associated with the heat-sensitive 
resistor 1, and 
the fact that the said resistor 1 is produced in the form of a resistor 
comprising two end rheophores 14 between which there extends in the 
direction of the length of the said resistor 1 a strip or ribbon of 
resistive material 16. 
With reference specifically to the first aspect, it will be noted that the 
bridge circuit 4 is supplied with the current emitted by the current 
generator 8. In this case, therefore, instead of being heated by an 
auxiliary resistor, the heat-sensitive resistor 1 is brought to the 
temperature by the electric current by which it is traversed, this current 
being supplied by the current generator 8 in an amount controlled by the 
amplifier 7 as a function of the voltage detected thereby. The voltmeter 
9, again in this case preferably calibrated in watts (or any other device 
for measuring the power or electrical heating energy absorbed by the 
resistor 1) is connected to the ends of the said heat-sensitive resistor 
1. 
In other words, in this case, the resistor 1 acts at the same time as a 
heat-sensitive element and as a heating element ("heat exchange means") 
adapted to effect the thermostatic action of the said heat-sensitive 
element. 
However, with respect to the general structure of the resistor 1 of FIG. 2, 
it will be noted that in this case the resistance R present at the ends 
thereof may generally be expressed by a relation of the type 
##EQU2## 
where r(x, T(x))indicates the resistance of an infinitesimal element of 
the resistive mass 16 disposed at a distance x from one of the rheophores 
14 taken as a point of origin O of the resistor. Here once again, the 
local resistance varies as a function of the temperature T, which, as a 
result of the presence of non-uniform thermal and thermodynamic conditions 
within the environment, also varies with the parameter x. 
Consequently, while with reference to the resistor 1 of FIG. 1, mention was 
made of integrating behaviour with respect to conductance, in the case of 
the resistor 1 of FIG. 2, it is a question of integrating behaviour with 
respect to resistance. 
In one specific embodiment, the resistor 1 (FIG. 2) is associated with a 
safety belt in the manner shown in FIG. 4. 
In particular, the resistor 1 is produced using copper wire having a 
diameter of 1/10 mm. The wire is applied by means of stitching to a ribbon 
support 1a in the form of a coil with loops having an amplitude equal to 
approximately one centimeter in the region of approximately five loops per 
centimeter. The coil resistor 1 is produced with a length equal to 
approximately one meter so that it can be applied by means of stitching of 
the ribbon support to the oblique strap of a safety belt. 
The nominal resistance value of the resistor (at 20.degree. C.) is of the 
order of a few ohms (typically 3 ohms). 
A strip of thermally insulating material consisting of foamed polymethane 
adapted to form the screening element W is applied to the side of the 
resistor 1 directed towards the belt (thus towards the body of the 
motorist) below the ribbon support. 
Of course, while adhering to the principle of the invention, the 
embodiments and the features may be varied considerably with respect to 
those described and illustrated by way of a non-limiting example, without 
thereby going beyond the scope of this invention.