Automotive climate control with infra-red sensing

An air temperature sensor and an infrared sensor are used along with an outside temperature sensor to control an HVAC system. During vehicle operation the IR sensor views an occupant seating area and realistically determines the thermal comfort level and the air temperature adds stability to that determination to control the air output. For dual zone systems two IR sensors separately monitor the two zones for accurate control of each zone air output. When the vehicle is not operating, the internal temperature is monitored and compared to a threshold and to outside temperature to turn on ventilation for limiting the internal temperature, subject to sufficient battery voltage.

FIELD OF THE INVENTION 
This invention relates to heating, ventilating and air conditioning (HVAC) 
systems for motor vehicles and particularly to a control for such a system 
utilizing infra-red sensing as well as air temperature sensing. 
BACKGROUND OF THE INVENTION 
It is common practice in automotive climate control to determine the 
thermal comfort level of a passenger compartment by drawing a stream of 
air from the compartment across a sensor to measure the air temperature 
and to estimate the effect of sun load on the occupants by a solar sensor 
mounted on top of the instrument panel for exposure to the sun. These 
measurements are combined with measurements of outside air temperature and 
engine coolant temperature to supply a control algorithm with the data 
needed to determine the optimum settings for HVAC mode, blower speed, and 
mixer door settings which together determine outlet air temperature and 
air speed needed to achieve a target temperature or comfort setting which 
is chosen by operator input. 
The degree of success in achieving the desired comfort level varies 
according to specific design parameters including the placement of the 
solar sensor which for aesthetic reasons may be positioned where it is not 
the most effective. In any event, the measurement of sun load can be 
misleading in its computed effect on comfort since the sun direction, 
passenger clothing and other variables are not readily taken into account. 
To avoid the drawbacks of solar load control as well as some objections to 
the conventional method of obtaining the air temperature, it has been 
proposed to replace both solar sensing and air temperature measurement 
with infrared (IR) sensing which directly detects the temperature of the 
occupant seating area and the occupants themselves. Thus irradiation from 
seat surfaces, occupant skin and occupant clothing, as well as any object 
in view of an IR sensor becomes the prime control parameter, and the air 
temperature in the passenger compartment is not considered at all. While 
this system affords an improvement over the prior systems by providing 
better correction for solar load and other sources of radiant energy 
within a vehicle, under many circumstances this correction can be too 
much, causing the system to overreact to introduction of hot sources. The 
air temperature has an effect on comfort and the system performance can be 
improved by including that measurement in the control algorithm. 
Dual zone or multiple zone HVAC systems are already known to supply outlet 
air at different temperatures to different locations in the vehicle in 
accordance with individual temperature settings at each location. For 
example, the driver and passenger may have separate controls and 
separately managed air outlets. In the prior multiple zone systems the 
same temperature parameters, except for the selected target temperatures, 
are used to determine each air outlet temperature. The use of IR sensors, 
however, make it possible to improve those systems by separately measuring 
the irradiation from each zone. 
It has been recognized that a major cause of discomfort during hot sunny 
days is that when a vehicle is idle, the interior can become extremely 
hot, so that upon first entering the vehicle the heat seems to be 
intolerable. The use of IR sensors make it practical to realistically 
monitor in-car temperatures even when the vehicle is not in operation and 
to prevent excessive temperatures by turning on ventilation. 
SUMMARY OF THE INVENTION 
It is therefore an object of the invention to incorporate the advantages of 
IR sensing in a climate control system while avoiding overreaction to 
changes in radiant energy in the vehicle. Another object is to enhance 
multiple zone HVAC systems by detecting and responding to the thermal 
condition of each zone. A further object is to control vehicle ventilation 
to prevent very hot conditions in an idle vehicle. 
The climate control of an HVAC system uses a microcomputer to receive 
inputs from sensors and to control the system mode, blower speed and mixer 
door positions, thereby regulating the air output to the passenger 
compartment. The sensors comprise an IR sensor, an internal air 
temperature sensor, an outside air temperature sensor, and an engine 
coolant sensor. The latter only affects the mixer door position since the 
coolant temperature determines the hot air temperature in the system. 
The IR sensor monitors the radiation level of the front seat and its 
occupants and includes a thermopile having a sensing junction affected by 
the radiation level of the scene and a reference junction. The reference 
junction may be warmer or cooler or the same as the sensing junction, and 
the thermopile output voltage is dependent on the difference in junction 
temperatures. A thermistor packaged with the thermopile is responsive to 
the reference junction temperature. A sensor circuit combines the 
thermistor and the thermopile outputs to generate a signal which in effect 
is the combined outputs of those sensors. The signal represents the 
absolute temperature of the scene and is linear at least in the target 
temperature range of the climate control. 
The internal air sensor is an aspirated thermistor; i.e., a stream of the 
vehicle compartment air flows across the thermistor so that its output 
signal represents the internal air temperature. Conventionally, the air 
flow is produced by a suction arrangement attached to the ventilation 
blower assembly, but instead it can be produced by a separate motor driven 
fan. 
In the microcomputer an algorithm combines the selected target temperature, 
IR sensor circuit output information, the internal air temperature 
information, and outside temperature information to select the HVAC mode 
(heating, cooling or ventilation) and the blower speed, and further 
includes engine coolant temperature to select mixer door positions. This 
combination of information yield an improved comfort level by responding 
to air temperature and sun load to achieve the selected target temperature 
without overreacting to the sun load or other radiation source affecting 
the IR sensor output. 
Dual zone control is accomplished by two IR sensors or two thermopiles in 
the same sensor, each viewing the radiation from one zone, and separate 
temperature selectors for each zone. The microcomputer separately controls 
the air outlet to each zone using the same algorithm for each zone. Where 
the two thermopiles are close together or even in the same package, a 
single reference junction thermistor and sensor circuit can be used, 
either one of the two thermopiles being switched into the circuit as 
needed for each zone control computation. 
Automatic ventilation of a vehicle while not in operation is carried out by 
sensing the in-car temperature by the IR sensor, sensing the outside 
temperature, and sensing the battery voltage, and turning on the 
ventilation if the sensed temperature is above a threshold and above 
outside temperature by a certain increment, and the voltage is above a 
given value. The ventilation is turned off in dependence on the same 
variables. Thus when inside temperature reaches a high value and the 
outside air is cool enough to effectively temper the inside temperature, 
the HVAC unit will blow in outside air. At all times, the ventilation is 
subject to available battery voltage since it is not desirable to run down 
the battery. An additional control may be to actuate the automatic 
ventilation only just prior to the time the operator expects to return to 
the vehicle thereby preventing excessive temperatures upon vehicle entry. 
This may be accomplished by a timer set by the operator according to a 
known schedule. Still another variable would be opening a sun roof for 
ventilation instead of or in addition to turning on a blower. In this case 
it would be desirable to also have a rain sensor to prevent opening the 
sun roof when it is raining.

DESCRIPTION OF THE INVENTION 
Referring first to FIG. 1, a vehicle climate control 10 is shown comprising 
a heating, ventilation and air conditioning (HVAC) control 20 comprising a 
conventionally known microcomputer (not illustrated) having a central 
processing unit, ROM, RAM, I/O ports and A/D converters which receive 
various analog input signals from discrete sensors 30-36 and digitize the 
same for use in automated control of passenger compartment thermal level. 
Interior air temperature (IAT) sensor 30 and infrared (IR) sensor 32 
provide the primary inputs to HVAC control 20 with outside air temperature 
(OAT) sensor 34 providing further data to HVAC control 20 for climate 
control. OAT sensor 34 provides in conjunction with IAT sensor 30 a 
differential measurement between the passenger compartment and the 
exterior environment which effects the rate of heat transfer therebetween, 
while the IR sensor 32 provides a measure of the radiation from the 
vehicle interior and occupants which provides radiant heat resulting from 
sun load, occupant's skin and clothing and other sources within the 
passenger compartment. Coolant temperature (COOLANT) sensor 36 provides a 
signal to HVAC control 20 which is indicative of the heat capacity of the 
heater core. Another input to the control includes an operator selected 
temperature setting signal (SET TEMP) 38 corresponding to the desired 
thermal level. The various inputs are monitored and processed for 
controlling temperature maintenance functions of the heater, evaporator 
and blower assembly (HEBA) 40 which, as the name suggests, includes; a 
heater core for circulating engine coolant for warming air, an evaporator 
core for circulating refrigerant for cooling air, a blower or fan for 
circulating air through the heater and evaporator cores in proportion to 
the position of an air mix door as determined by solenoid operated vacuum 
switches or electrical motors responsive to the HVAC controller outputs 
25. The position of the air mix door determines the temperature of the air 
circulated by HEBA 40. The HEBA often times further includes control of 
exiting air to passenger determined modes such as lower, upper, bi-level, 
defog and defrost and entering air between fresh and recirculated modes. 
Solenoid controlled vacuum switches responsive to HVAC outputs 25 are the 
most prevalent actuators used for motive control of air delivery doors 
effective to establish the modes as described above. Electrical motor 
control of air delivery doors is also practiced in the art and is equally 
applicable to the present invention. 
FIG. 1 further illustrates the means by which passenger compartment air 
temperature is measured. In addition to IAT sensor 30 which is normally 
positioned behind the instrument panel (not illustrated), aspirator tube 
50 (functionally illustrated) is utilized to draw passenger compartment 
air in the vicinity of the front of the instrument panel across IAT sensor 
30 for example by connecting the remote end of the tube to a high air flow 
portion of HEBA 40 through a venturi arrangement to generate a small air 
flow. A measure of the interior air temperature is thereby obtained. 
Turning to FIG. 2, a vehicle seat is designated by the numeral 42 and an 
occupant by the numeral 44. An infra-red (IR) sensor assembly 32 is 
positioned within the passenger compartment of the vehicle such that the 
viewing field, indicated by the ellipse 48 is representative of 
predetermined portions of the seat 42 and occupant 44. Appropriate 
locations for the IR sensor assembly 32 include the vehicle instrument 
panel such that the viewing field is rear facing with respect thereto. 
This way, a good portion of passenger compartment is within the viewing 
field of the sensor. In a first embodiment, the IR sensor 32 has a 
relatively wide field of view as illustrated in two dimensions by the seat 
and passenger area delimited by the elliptical line 48. 
The viewing angle of an IR sensor is determined by design of the sensor 
and, if inadequate for the desired viewing field, may be modified by 
lensing. A particularly attractive option for widening the viewing angle 
and minimizing dimensional penalty is to use a fresnel lens comprised of 
low loss material such as polyethylene. 
Response of the sensor to different wavelengths of electromagnetic 
radiation can be controlled by the window material. Most of the energy of 
concern is in the ten micron wavelength range and an electromagnetic 
radiation sensor designed with windows providing admissibility in that 
range has been shown to perform adequately for providing a measure of 
passenger compartment thermal level. Silicon window material has been 
shown to provide approximately 60 percent admissibility in this range, 
with polyethylene window material improving this figure to approximately 
90 percent. The various window materials therefore provide the means by 
which selective wavelengths of thermal energy are filtered for inclusion 
or exclusion depending upon the desired measurement. 
FIG. 3 depicts an IR sensor assembly 32 which comprises a can 50 having a 
window 52 and a target region 54 which receives or transmits IR through 
the window 50 to approach the temperature of the viewed scene. A 
thermocouple or thermopile 56 has a sensing junction 58 at the target 54 
and a reference junction 60 thermally coupled to the wall of the can 50. 
The thermopile 56 leads extend to an IR circuit 62. A thermistor 64 on the 
can senses the temperature of the reference junction and has leads 
extending to the circuit 62. 
In the present embodiment, an IR sensor part number PL-82 available from 
Armtec/Ragen Incorporated, 10 Ammon Drive, Manchester, NH is utilized. 
This sensor is a twenty junction thermocouple device with a silicon window 
52 and produces a voltage output on the order of 45 microvolts per degree 
fahrenheit. It is apparent that a change in passenger compartment thermal 
level of several degrees therefore will only result in voltage changes on 
the order of tens or perhaps hundreds of microvolts, which small signals 
pose unique amplification challenges. A cost effective and widely 
available means for signal amplification meeting the needs of this 
embodiment is a chopper stabilized amplifier in differential mode which is 
innately characterized by extremely low input offset voltage thereby being 
responsive to the small voltage changes provided by the IR sensor chosen. 
An exemplary circuit 62 is set forth in FIG. 4 for accomplishing a chopper 
stabilized amplification of the IR sensor signal wherein chopper 
stabilized amplifier 66 is designated a TL2654 available from Texas 
Instruments, Dallas, Tex. Exemplary component values are shown but are 
subject to modification according to required operation. 
The present embodiment is configured for non-inverting operation having the 
non-inverting terminal connected to the positive terminal of the IR 
sensor. The negative terminal of the thermopile 56 is coupled to one end 
of a resistor R1 to establish offset node 68, the other end thereof 
coupled to the inverting input of the amplifier. The output of the 
amplifier is coupled through resistor R2 to the inverting input in 
feedback to establish the gain (G) of the circuit in accordance with a 
ratiometric relationship between R2 and R1[G=(R1+R2)/R1]. Integrating 
capacitor C1 is preferably coupled across the inverting terminal and the 
output in order to stabilize the output signal. Each of the capacitors 
C2,C3 shown coupled to ground provides storage of a potential for nulling 
the amplifier offset voltage during a respective one of amplifying or 
nulling phases of the chopper amplifier's operation. The output of 
amplifier 66 comprises a conditioned IR sensor signal for input into an 
HVAC control. An offset voltage substantially equal to one-half the 
operating voltage V of the amplifier is provided at offset node 68 
established between thermopile 56 negative terminal and resistor R1 to 
allow operation through the entire operating voltage range. Output voltage 
is therefore represented by the equation: 
EQU Vo=Voff+G*Vir, 
where Vo is the output voltage, Voff is the offset voltage, G is the gain 
and Vir is the IR sensor voltage. 
As with any thermopile device, the voltage produced between two output 
terminals thereof is a function of the temperature differential between a 
set of measuring junctions and reference junctions; and, in the present 
embodiment, the chosen IR sensor produces a voltage signal substantially 
proportional to the difference in temperature. In the present embodiment 
using the above exemplary IR sensor, the measuring junctions are exposed 
through a silicon window to the passenger compartment infra-red radiation 
content, and the reference junctions are shielded therefrom so as to 
remain immune to thermal influences attributed thereto. The reference 
junction temperature will naturally tend toward a temperature in 
accordance with thermal influences apart from the infra-red radiation 
content of the passenger compartment from which they are shielded. These 
influences include convection from passenger compartment and instrument 
panel air and conduction from mounting means for the IR sensor and 
resistive heating of the junctions due to current flow therethrough. The 
sensor output will: 1) approach zero in the case where the reference 
junctions tend toward the passenger compartment thermal level as "seen" by 
the measuring junctions, or; 2) approach an offset in the case where the 
reference junctions tend toward some dominant local thermal influence such 
as a proximate incandescent light source. 
The present embodiment therefore provides a compensation to the offset 
voltage applied at the offset node by using the thermistor 64 having 
variable resistance RT connected in series with a resistor R between a 
supply voltage V and ground, the junction being connected to the node 68 
to supply the offset voltage Voff. The thermistor measures the temperature 
at the reference junctions, its negative coefficient of resistance causing 
adjustment to offset voltage Voff in proportion to the temperature change 
at the reference junction to null the effects of varying reference 
junction temperature from whatever influence. Therefore, the gain G as 
determined by the resistor pair R2 and R1 is chosen to produce this 
desired relationship whereby each unit of temperature change at the 
reference junctions produces a change to the term Voff which is balanced 
by the change in the term Vir multiplied by the gain G. 
Elements of the illustrated preferred climate control architecture of FIG. 
1 are further expanded in FIG. 5. IR sensor assembly 32 is shown as an 
input to an HVAC control. The internal air temperature sensor IAT 30 and 
outside air temperature sensor OAT 34 are illustrated. Coolant temperature 
COOLANT 36 is also shown with a signal therefrom as an input to the HVAC 
control. Operator selected temperature setting signal SET TEMP 38 is 
similarly shown as an input thereto. Sensors 30-36 and 32 are assumed to 
produce analog signals, which signals are passed to A/D converter 70 for 
digitization. The OAT output is converted to OAT.sub.-- COR by a look up 
table 72. SET TEMP signal 38 is assumed a digital input signal commonly 
obtained from an instrument panel climate control operator interface at 
the instrument panel. Where SET TEMP signal is analog, A/D conversion can 
be employed to digitize the signal. 
Control processing is advantageously described in terms of establishing a 
program number PGMno and air mix door number MIXno though other 
alternatives will be readily apparent to those possessing ordinary skill 
in the art. PGMno is established according to the following function: 
EQU PGMno=IAT+5*(SET TEMP)+IR+OAT.sub.-- COR+K) 
where IAT is the internal air temperature signal from sensor 30, SET TEMP 
is the operator temperature setting, IR is the passenger compartment 
thermal level as established by the IR sensor assembly 32, OAT.sub.-- COR 
is the outside air temperature correction factor from calibration table 
72, and K represents a calibration constant to scale PGMno into a number 
range compatible with the microcomputer architecture (0&lt;PGMno&lt;255 for 8 
bit architecture). PGMno is then utilized to reference blower speed and 
mode for HEBA 40 operation such as through calibration tables 74 and 76, 
respectively. The mode is also used for the look-up from calibration table 
78 of a corrective value MOD.sub.-- COR associated therewith and summed 
with PGMno at node 80 to establish a mode corrected program number MPGMno. 
For control of mixer door position, MIXno is established according to the 
following general function: 
EQU MIXno=f(COOL, .DELTA.T(COOL, Te), MPGMno, K1, K2) 
where COOL is the coolant temperature as established by coolant sensor 36, 
Te is a predetermined evaporator temperature equivalent to a fixed 
calibrated value when the compressor is cycling and to the ambient 
temperature as measured by OAT sensor 34 when the compressor is not 
cycling, MPGMno is the mode adjusted program number, and K1 and K2 
represent calibration constants used to scale the function into a number 
range compatible with the microcomputer architecture (0&lt;MIXno&lt;255 for an 
8-bit architecture). MIXno is then utilized to select a temperature door 
position from the mix door position look-up table 82. This selected door 
position is used in positioning the air mix door in HEBA 40. 
It has been found that this arrangement using the IR signal in conjunction 
with IAT and the other inputs gives superior control of temperature 
without the need for solar sensors and in particular improves the 
correction for radiant energy sources such as sun load. 
The same control advantages apply to dual zone or multiple zone systems. As 
shown in FIG. 6, by using two IR sensors 32 and 33, called IRa and IRb, 
and separate user controls 38 and 39 to set temperature A and temperature 
B, two zones, A and B can be individually controlled. Typically the two 
zones have common mode and common blower speed, and separate mixer doors 
are set according to individual needs. The HVAC 20 readily calculates the 
MIXno for each zone using the same algorithm for both zones with the 
appropriate IR and Set Temp inputs for each zone. 
FIG. 7 illustrates the application of two IR sensors 32 and 33 which view 
local zones 46 and 47 respectively, so that the thermal level of each zone 
is sensed. It often occurs that sun load affects one side more than the 
other so that the thermal levels as detected by the IR sensors may differ 
considerably. If the sensors 32, 33 are physically close to each other, 
they may use the same IR circuit to generate both IR output signals on a 
time sharing basis. Referring to FIG. 8, the thermopile 56 of sensor 32 
and the thermopile 57 of sensor 33 are connected together at the node 68 
at one end and are coupled through a switch 86 to the amplifier 66. The 
switch is controlled in concert with the HVAC control for employing each 
IR sensor according to which zone control settings are being calculated. 
When a vehicle is left unattended under conditions of high sun load, the 
interior becomes very hot. To precool the vehicle the blower may be turned 
on as needed to circulate cooler outside air into the vehicle. The 
interior temperature as sensed by the IR sensor is used as the primary 
parameter and is compared to a threshold and the outside temperature for 
controlling the blower. A program run by the HVAC controller 20 is given 
in FIG. 9 for a precool control, using particular parameter values which 
are not necessarily the optimum values for a given application but which 
illustrate the control method. Using this algorithm the IR temperature is 
checked every four minutes when the vehicle is off and compared to a 
115.degree. F. degree threshold and to outside temperature. When preset 
conditions are met the system blower is turned on and then every four 
minutes the temperature is checked to determine when to turn the blower 
off. In any event the program is interrupted if the vehicle is started. 
Referring to FIG. 9, the description of the flow chart contains numerals in 
angle brackets &lt;nnn&gt; which refer to functions in blocks with corresponding 
reference numerals. The programmed is entered if the vehicle is off &lt;100&gt; 
and then a four minute timer is started &lt;102&gt;. If the timer reaches four 
minutes &lt;104&gt; the IR temperature is compared to a 115.degree. F. threshold 
&lt;106&gt;. If the IR temperature does exceed the threshold it is determined 
whether the temperature is at least 10.degree. higher than the outside 
temperature OAT &lt;108&gt;. If it is, the system voltage is checked to assure 
that it is above 11.5 volts &lt;110&gt;. Then the precool system is activated to 
operate the blower &lt;112&gt;. If any condition in blocks 106, 108 and 110 is 
not met, the timer is restarted &lt;102&gt;. Once the precool system is 
activated, another four minute timer is started &lt;114&gt; and when it times 
out &lt;116&gt;, the system voltage is tested &lt;118&gt; and the system is 
deactivated &lt;120&gt; if the voltage falls below 11.5 volts. If the voltage 
is above that limit, two temperature conditions are tested &lt;122&gt;: if the 
IR temperature is below 85.degree. or the IR temperature is within 
5.degree. of the outside temperature OAT, the precool system is 
deactivated &lt;120&gt;; otherwise the timer is restarted &lt;114&gt;. 
Since the operation of the precool system is limited by vehicle battery 
limitations, it is desirable to further enhance it by selectively 
determining when it may be operative, thereby permitting the ventilating 
function only when vehicle usage is imminent. For example, a scheduling 
timer may be set by the operator to indicate the next expected vehicle use 
or may be programmed with a daily schedule of use which is stored for use 
each day or on predetermined days. Then the algorithm of FIG. 9 would be 
entered. Still another scheduling system would employ an adaptive 
algorithm to learn an operator's schedule by monitoring the vehicle usage 
over some time period.