Note: Descriptions are shown in the official language in which they were submitted.
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SUNLOAD SENSOR FOR AUTOMOTIVE VEHICLES
FIELD OF THE INVENTION
The present invention relates to an apparatus to measure the solar radiative
power
that penetrates inside the cabin of a car through the windshield, and the
predominant direction from which this radiative power load is coming, for the
purpose of controlling the air conditioning of the car in a manner that
maximizes
1o the comfort of the passengers.
BACKGROUND OF THE INVENTION
Currently sunload sensors, either single- or dual-channel, are commercially
available. Most are optoelectronic devices and use a silicon photodiode as a
sensing element. A number of vehicle manufacturers have integrated into their
products dual-channel sunload sensors in an attempt to provide improved
temperature stability in the cabin, and comfort to the passengers. Dual-
channel
sunload sensors must provide not only a measurement of the total solar heat
load
entering the car through the windshield, but also an indication of which side
of the
car, the driver side or the passenger side, is subjected to more or less heat,
so
that cool air from the air conditioning system be preferentially distributed
on the
side that requires more.
Present dual-channel sensors do not however fully respond to the need that
they
at once provide a measurement of the total heat load entering the cabin, and
of
the relative distribution of this radiative heat load on the driver and on the
passenger, especially when the sun is at an angular position that is low with
respect to the horizontal plane of the vehicle. Typically, when the sun is
low, the
total heat load is under-estimated, and the comparative signal of the two
channels
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becomes an unreliable indicator of the relative fractions of the heat load
that are
affecting the two sides of the cabin.
In addition, some present dual-channel sensors require the presence of sensing
elements that are mounted at some angle from one another, a feature that
renders
their fabrication more complex and costly.
SUMMARY OF THE INVENTION
It is a primary object of this invention to provide a dual-channel sunload
sensor
capable of generating output signals that are reliable indicators of the total
solar heat
load entering a vehicle through the windshield, and of the relative fractions
of the
radiative heat loads that are perceived by the driver and by the passenger,
for almost
all angular positions of the sun.
In accordance with the invention, this object is achieved with a dual sunload
sensor to
sense the intensity and directionality of solar radiative power entering the
cabin of a
vehicle through a windshield, said sensor comprising:
a housing;
a substrate bearing only two light sensitive semiconductor elements thereon
housed in said housing;
two optical lenses, one lens being located above one of said only two light
sensitive semiconductor elements, the other lens being located over the other
one of
said only two light sensitive semiconductor elements, each of said optical
lenses
refracting light towards the respective corresponding light sensitive
semiconductor
element; and
an optically opaque wall holding and separating said two optical lenses lying
in
a vertical plane along a longitudinal axis of the vehicle;
wherein said sensor further comprises a layer of light diffusive material
added to a
base of each said optical lens and having its edges at least partially exposed
directly
to incoming solar light for light to reach said light sensitive element either
by the lens,
through the diffusive layer and to the light sensitive element or directly by
the edge of
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the diffusive layer, through the diffusive layer and to the light element.
The geometry of the sensor is such that it can be constructed economically, as
the
sensing elements of the two channels rest in the same plane. The output
signals from
the sensor can be used to control the temperature and distribution of cool air
in cars
equipped with an air conditioning unit.
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DESCRIPTION OF THE DRAWINGS
This and other advantages of the invention will become apparent from a reading
of
the following detailed description made with reference to the following
drawings in
which:
Figure 1 is an exploded view of a sunload sensor according to a preferred
embodiment of the invention.
Figure 2 is a cutout view showing the internal opaque wall between the clear
areas
of the housing of the sensor of Fig. 1.
Figure 3 is an external view of the sunload sensor of Fig. 1.
Figure 4 is a top view of the sunload sensor of Fig. 1.
Figure 5 is a diagonal cutout view of the sensor of Fig. 1 showing the
internal
shapes of the transparent, diffusive and opaque sections of the plastic
housing, in
a plane whose position is shown in figure 4.
Figure 6 is the same diagonal cutout view of Fig. 5 showing an alternative
embodiment where the diffusive part of the optics has its outer edges exposed
directly to light coming from the outside of the sensor.
Figure 7 is a circuit diagram of a preferred embodiment of the invention,
where the
signal conditioning electronics is entirely passive.
Figure 8 is a circuit diagram of an alternative embodiment of the invention,
where
the signal conditioning electronic circuit is an active circuit comprising
amplifiers.
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Figure 9 is a block diagram that illustrates how the sensor related to the
data
processing and the HVAC system of the vehicle. The dashed line indicates the
boundary of the sensor itself.
Figures 10a, 10b and 10c are schematic representations of the paths the light
travels towards a photodiode according to a preferred embodiment of the
invention, when no diffuser is present, and when the sun is high above horizon
(Fig. 10a), moderately high above the horizon (Fig. 10b) and low on the
horizon
(Fig. 10c).
Figures 11 a and 11 b are schematic representations of the paths the light
travels
towards a photodiode according to another preferred embodiment of the
invention,
when a diffuser is present at the base of the lens, when the sun is high above
horizon (Fig. 11 a) and low on the horizon (Fig. 11 b).
Figure 12 illustrates a typical angular response for the driver-side channel,
when a
thin diffuser is present at the base of the lens, its edges not exposed to
external
sunlight (dashed line); and when a thicker diffuser is present, its edges
directly
exposed to external sunlight (solid line).
Figure 13 illustrates that the optical axes of the lenses are aligned along
the
diagonals of virtual cubes resting on the sensing elements, according to a
preferred embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to the following Figures, the present invention concerns a
sunload
sensor 10. The sensor 10 consists of the following basic components. A flat
substrate 1 commonly used for the manufacture of electronic circuits, either a
printed circuit board made of composite material, or a ceramic material, bears
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circuit metallization (not shown) printed on the substrate by typical methods
known
in the art. Two silicon photodiode chips 2 are mounted on this substrate
circuit, to
serve as sensing elements for solar radiation.
5 It should be understood that, optionally, other electronic components can be
mounted on the same substrate, to tailor the signal of the photodiodes 2 to
the
specific requirements of the electrical circuitry used in a particular vehicle
model;
such electronic components may particularly include capacitors, amplifiers and
resistors, including the printed thick film version of the latter. Circuit
diagrams for
two alternative' versions of such conditioning electronics are shown in
Figures 7
and 8. Figure 7 shows a circuit that is entirely passive, where each of the
photodiodes 2 is accompanied by appropriate resistors both in parallel and in
series. The output of the circuit is at the top of the Figure. The passive
components can be thick film resistors that can be laser trimmed to precisely
balance the output from the two channels of the sensor 10.
Alternatively, Figure 8 shows an active circuit including op-amps for
conditioning
the signal. It will however be appreciated that any appropriate circuit will
meet the
objects of the present invention.
An electrical interface links the sensor 10 internal circuitry to the external
circuitry
of the vehicle, so that electrical signals provided by the two photodiode
sensing
elements 2, and suitably conditioned by the electronics comprised in the
sensor
10, are made separately available to the external circuitry of the vehicle
(Figure 9
illustrates how these signals relate to the data processing and the heating,
ventilation and air conditioning systems of the vehicle). It will be
appreciated that
each vehicle manufacturer, and indeed each different type of vehicle, will
have
proprietary external circuitry to control the heating, ventilating and air
conditioning
system of the vehicle, and that appropriate interface circuitry is required to
properly interface with the external circuitry. However, such a design is
within the
skill of a person versed in this field, and beyond the scope of the present
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invention. The present invention deals with a solution for properly
discriminating
between driver side and passenger side reception of solar radiation by
optically
isolating the respective photodiodes, and advantageously, with being able to
measure radiation although the sun is low on the horizon.
The circuit and photodiodes are mounted in a housing 20. The housing comprises
two distinct transparent areas 3 on its top part, held and separated by an
opaque
section 4. The transparent areas have external convex shapes (better seen in
Fig.
1) that collect solar radiative power by refracting light coming from one side
of a
plane bisecting the sensor 10 to a respective sensing photodiode 2. An aspect
of
the shape of the transparent areas is that the light received is guided and
collected to the appropriate photodiode notwithstanding the angular position
of the
sun on the horizon. Stated differently, the transparent areas act as a beam
deflector, so that even if the sun is a few degrees above horizon, the near
totality
of the light will reach the photodiode. This requires optics that are within
the skill
of a person expert in this field, and schematic representations of the path
followed
by the light are shown in Figs. 10a, 10b and 10c. In Fig. 10a, the sun is high
above horizon, whereas in Fig. 10b, the sun is moderately high above the
horizon
and in Fig. 1 Oc, the sun is low on the horizon.
In a preferred embodiment of the invention, the driver-side transparent area 3
guides light to the driver-side photodiode 2, and the passenger side
transparent
area 3 guides light to the passenger side photodiode 2. Optionally the
transfer of
light from the convex shaped transparent areas 3 to the photodiodes 2 can be
improved by the introduction between them of a piece of clear plastic having
the
shape of a truncated cylinder 5, better shown in Figs.1 and 2.
In a preferred embodiment of the invention, the optical axes of the
transparent
areas 3 are inclined in a direction corresponding substantially to the
diagonals of
virtual cubes resting in the plane of the sensing elements. This is better
shown in
Figs. 13a, 13b and 13c.
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The exact shape of the transparent and opaque parts can be adjusted to obtain
an output-signal versus sun-angular-position relationship adapted to the
particular
requirements of a given application. Figures 1 through 5 illustrate the shapes
of
these parts in one embodiment.
Optionally, a layer of diffusive plastic material 7, shown on Figure 5, can be
added
at the base of the transparent plastic parts with external convex shapes, such
that
light collected by the convex parts is diffused towards the sensing element.
This
can serve to broaden and smooth out the angular dependency of the sensor
output. Figures 11a and 11b illustrate schematically the paths of light for
two
different angular positions of the sun, when such a diffuser is present.
Figure 12
illustrates the resulting relative output signal of the driver-side channel,
as function
of the angular position of the sun. The layer of light diffusive material
preferably
consists of clear polymer in which grains of titanium dioxide are dispersed,
the
density and dimensional distribution of grains being selected so as to
optimize the
Rayleigh scattering of light. The dashed curve on Figure 12 illustrates how
the
output of the driver-side channel of the sensor varies with the angular
azimuthal
position of the sun, for one value of the elevation angle, for this particular
embodiment of the invention.
Also optionally, this layer of diffusive material can be shaped and located so
that
its outer edges are directly exposed to incoming solar radiation, as
illustrated on
Figure 6. This provides a second path for light to reach the sensing elements:
either by the convex optical part, through the diffusive part and eventually
to the
sensing element, or directly by the edge of the diffusive part, through the
diffusive
part and to the sensing element. This alters the angular dependency of the
output
signal of the apparatus in a manner that may be advantageous for some
applications, such as cases where it is desired that the output of a channel
remain
at some low, but non-zero, value even when the angular position of the sun is
far
on the side of the sensor opposite that corresponding to said channel. The
solid
curve on Figure 12 illustrates how the output of the driver-side channel of
the
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sensor varies with the angular azimuthal position of the sun, for one value of
the
elevation angle, for this alternative embodiment of the invention.
In its automotive application, the sensor 10 is mounted in a vehicle,
generally on
the dash board and under the windshield, so that the line joining the centers
of the
two photodiode sensing elements is approximately perpendicular to the
longitudinal axis of the vehicle, and so that the surfaces of the sensing
elements
are approximately parallel to the surface over which the vehicle rests.
In operation, the sensor 10 is exposed to sunlight that penetrates the vehicle
through the windshield. If the sun is located very close to the projection of
the
median plane of the car into the sky, the light strikes the two transparent
convex
areas at the same relative angle, and the same amount of light is brought to
the
two sensing elements. The two electrical outputs are then equal. If the sun
moves
to one side of the longitudinal plane, the shape of the transparent optical
areas,
and of the opaque wall that separates them, is such that the signal from the
sensing element corresponding to the side where the sun is located remains
approximately constant, while the signal of the opposite sensing element drops
to
near zero. In this manner the amplitude of the higher of the two output
signals
provides a measurement of the solar radiative power, while the ratio of, or
the
difference between, the two output signals provides information as to whether
the
sun is located on the left side or on the right side of the median plane of
the
vehicle.
In the optional implementation where light is allowed to enter the apparatus
also
through the edge of a diffusive plastic piece located at the base of the
transparent
convex plastic parts, the signal does not drop all the way to zero when the
sun
moves to the opposite side of the longitudinal plane, but to some low value.
The invention presents many advantages over prior art. It provides signals
that are
better suited to the control of the air conditioning of a car so as to provide
optimum
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comfort to both the driver and the front-seat passenger. It can be
manufactured
economically thanks to the simplicity of its geometry.
Its output signals provide direct and separate information on the level of
solar
power entering the car, irrespective of the direction of the sky from which it
is
coming, and of the part of the sky in which the sun is located, either on the
left or
on the right of the longitudinal plane of the car. This is the information
needed to
properly control the air conditioning in a vehicle, the total sunload value
indicating
the overall degree of air conditioning needed, and the general angular
position of
the sun indicating whether the cold air should be preferentially directed at
the
driver side or at the passenger side.
Whereas other such apparatus provide this type of angular discrimination of
the
sun position by using two photodiode sensing elements mounted at an angle with
one another, the sensor of the present invention does so by inclining the
optical
axes of the clear convex plastic parts of the housing instead. This allows for
more
economical fabrication of the sensing circuit, since all the elements,
including the
two photodiodes, can be mounted on a single flat substrate.
Whereas still other apparatus provide some angular discrimination of the sun
position, and make use of two photodiode sensing elements mounted in the same
plane, by the method of diffusing light through an appropriately shaped
opalescent
piece of plastic material, the apparatus described herein maintains a near
constant
signal output when the sun comes down very close to the horizon, in contrast
with
those other apparatus whose output signal typically drops significantly when
the
sun approaches the horizon by less than 20 degrees.
The concept of the present invention is such that the geometrical parameters
of
the clear optical regions, and of the optional diffusive areas, and of the
opaque
region that separates them, can be modified to adjust the manner in which the
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output per channel varies with the angular position of the sun, enabling the
sensor
to meet specific application requirements.
In one preferred embodiment of the invention, the circuit is mounted on a
ceramic
5 substrate and incorporates thick film resistors that can be trimmed by a
laser beam
so as to insure that the level of signal is equal from the two sensing
elements
when the sun is located in the longitudinal plane of the vehicle, and is also
the
same from one sensor to another for the same level of solar power, in spite of
the
variation in the intrinsic sensitivity of the photodiodes from chip to chip.
