Vehicular air heater using PTC heater tablets associated with funnel heat exchanges

An air heater mounted in an elongated ventilation slot located beneath a window of a land, sea or air vehicle has a plurality of self-regulating ceramic heater tablets having a positive temperature coefficient (PTC) positioned between two metal strips and fastened thereto in thermally and electrically conductive relation. Heat exchangers comprising sheet metal fins with baffles are secured in electrically and thermally conductive relation to the opposite sides of the strips so that the baffles introduce turbulence into the air flowing over the strips. Other metal strips having electrical terminals are thermally and electrically connected to the fins opposite the first named strips for energizing the heater tablets. The PTC tablets are spaced to define flow passages therebetween so that the air flowing through the ventilation slot passes over the heat exchangers, plates and tablets for rapidly withdrawing heat from the tablets. At least one of the plates can be divided into segments with gaps therebetween to accomodate thermal expansion of the plates.

BACKGROUND OF THE INVENTION 
The invention relates to a land, sea or air vehicle provided with a cabin 
having windows or windscreens, under at least one of which a dashboard or 
panel provided with ventilation slots is disposed. 
In all motor vehicles a device is provided for heating the ventilation air 
which is to be directed onto the windscreen or to the passengers, making 
use of a heating radiator in which the ventilation air can be brought into 
a heat exchange relationship with the engine cooling water. Heated air is 
necessary in order to demist or defrost the windscreen. One problem is 
that when starting off with a cold engine the cooling water is still cold, 
so that the ventilation air cannot be heated, and therefore demisting or 
defrosting is impossible. This can lead to dangerous situations. In modern 
motor vehicles increasing use is made of glass, so that this problem 
becomes more urgent. Furthermore, engines are becoming more and more 
efficient, so that it takes longer for engine heat to become available for 
heating the interior of the vehicle. 
BRIEF SUMMARY OF THE INVENTION 
The invention seeks to avoid the disadvantage referred to, and to provide 
an arrangement whereby the cold ventilation air can be brought within a 
very short time to a temperature at which demisting and/or defrosting can 
be effected in an adequate manner. 
According to this invention, an air heater device for a passenger 
compartment of a motor vehicle has a plurality of self-regulating 
electrical resistance heater elements of a ceramic material of positive 
temperature coefficient of resistivity held between facing sides of two 
thermally and electrically conductive metal strips in thermally and 
electrically conductive relation to the strips, has sheet fins comprising 
sheet materials with a large number of louvers or baffles offset therefrom 
secured in electrically and thermally conductive relation to the opposite 
sides of the metal strips so that the baffles stand out from the metal 
strips and introduce turbulence into air flowing over the strips, has 
other metal strips held in thermally and electrically conductive relation 
to the sheet fins opposite the first named strips, has electrically 
conductive terminals connected to the other metal strips for connecting 
the heater elements in an electrical circuit in parallel relation to each 
other for energizing the heater elements, and has a housing for mounting 
the device and defining an air flow path directing air through the device 
in close heat-transfer relation to the sheet fins, whereby the device is 
adapted to be energized when the vehicle is started from promptly 
providing heat to the passenger compartment thereof. Preferably at least 
one side of each heater element is secured to close heat-transfer relation 
to one of the first named metal strips with an elastically and thermally 
conductive adhesive or solder and the strips are preferably segmented to 
permit close engagement of the strips with the heater elements without 
risk of damage to elements. According to a preferred invention, a heating 
device is for this purpose installed in one or more of the ventilation 
slots, this device having a relatively great length and slight width and 
being composed of a pair of plates between which are fastened tablets of a 
material having a positive temperature coefficient (PTC), while a heat 
exchanger is connected to the plate and means are provided for supplying 
electric energy to the tablets. 
The heating device has minimum heat capacity, so that the air can be heated 
quickly. Without sophisticated control mechanism it is ensured that the 
temperature cannot rise above a value determined by the properties of the 
PTC material. The heating device can be compact and light in weight, can 
be produced in modules, and can without great difficulty be adapted to the 
shape and dimensions of the ventilation slots. 
Good transfer of heat and a strong construction are achieved if the heating 
device is a sandwich, formed by at least two plates provided with a heat 
exchanger, with PTC tablets fastened between them. 
The pressure drop over the heat exchangers can be restricted to a minimum 
if they are of the plate type. This is necessary because the fans 
generally used have a high output and a low head. 
In order to distribute the air current in the direction of flow and thereby 
to improve heat-transfer without substantially increasing the pressure 
drop, the fins may have louver-like offsets which distribute the air 
current in the direction of flow. Another possibility is for the fins to 
consist of a plurality of crenellated bent strips, which can be formed 
from a length of material and which, viewed in the transverse direction of 
the heat exchanger, are disposed one behind the other, while the 
crenellations, viewed in the longitudinal direction of the heat exchanger, 
are staggered in relation to each other. 
The invention also relates to a heating device clearly intended for the 
above described land, sea or air vehicle.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 1 and 4 show in section the part of the cabin of a motor vehicle 
which is situated just under the windshield 1. As is customary, a 
plurality of ventilation slots 3 or the like are provided in the top edge 
of the dashboard 2 so that a stream of air furnished by fan means or the 
like (not shown) is directed from the duct 4 through the heater device 6 
as indicated by the arrow 20, the duct in a conventional vehicle typically 
leading to the slots 3 from a heating radiator and being connected to the 
slots. The slots have an air outlet baffle 5 directing the stream of air 
toward the inner surface of the windshield. Alternately, the air is 
utilized for heating the vehicle compartment as will be understood. For 
example, the duct 4 is cemented to the heater device 6 and the device is 
attached to the dashboard by screws indicated at 27. 
According to the invention, the heating device 6 is mounted to intercept 
and pass the stream of air 20 being directed through the slots 3.. This 
device consists in both embodiments of a sandwich composed of two metal 
strips 7 and 8 of a material of preferably high thermal and electrical 
conductivity, a plurality of self-regulating electrical resistance heater 
elements such as tablets 9 of an electrically resistive material of a 
ceramic material or the like having a positive temperature coefficient of 
resistivity (PTC) held or fastened between the strips 7 and 8, two heat 
exchanger strips or means 10 and 11, preferably two outer strips 14 and 
15, electrical conductor means which may include terminal spring means as 
diagrammatically indicated at 21 and 22 for connecting the resistance 
heater elements 9 in parallel relation to each other in an electrical 
circuit through strips 7, 8, 10, 11, 14 and 15, and housing means 23, 
preferably of an electrical and thermal insulating material, for mounting 
the heater device 6 to the dashboard 2 and/or to the duct 4. If desired, 
the spring means 21 and 22 are pressed between the housing and the strips 
14 and 15 for holding the assembly shown in FIG. 3 in the housing. The 
strips 7 and 8 can extend across the full width or length of the heater 
device 6 if desired but are (preferably) segmented or divided into 
separate sections as shown in FIG. 3. The tablets or resistance heater 
elements 9 preferably have metal electrical contact surfaces thereon at 
opposite sides of the elements disposed in thermally conductive, and 
electrically conductive relation to the respective strips 7 and 8. In a 
preferred embodiment, at least one of those sides of the tablets 9 is 
bonded fast to at least one of the strips 7 with the aid of an 
electrically and thermally conductive adhesive or solder or the like as 
indicated at 24 in FIG. 3. Preferably the opposite side of each element is 
secured in close thermally and electrically conductive relation to the 
other strip and if desired the same or similar bonding to the other strip 
is used as indicated at 25 in FIG. 3. 
In the embodiment shown in FIGS. 1-3, the heat exchangers 10 and 11 consist 
of sheet fins having sheet materials which are preferably bent 
approximately sinusoidally and in which louvers, baffles, or louver-like 
offsets 13, inclined or not relative to the axes of the bends in the sheet 
materials, are provided in order to introduce turbulence and dispose or 
distribute air or other fluid flowing over the sheet fins for improving 
heat-transfer between the sheet fins and the air. The sheet fins 10 and 11 
are disposed and preferably fastened between the strips 7 and 8 
respectively and the outer, preferably relatively thinner metal strips 14 
and 15 respectively by means of electrically conductive adhesive bonding 
or soldering or the like as indicated at 26 and 27 or by clamping in any 
conventional manner as by use of spring means 21 and 22 for improving 
heat-transfer between the resistance heater elements 9 and various 
portions of the heat exchanger means 10 and 11. The construction of some 
of these sheet fins is illustrated and described in the book "Compact Heat 
Exchangers" by Kays and London, 3rd Impression, 1984, page 178, FIGS. 9-5 
and it will be understood that various sheet/baffle configurations can be 
used. In accordance with the invention, the offsets 13 are bent out of 
sheet material of the sheet fins as shown in FIG. 2a, or are turned 
through a small angle in relation to the sheet material of the sheet fins 
as shown in FIG. 2b. 
The embodiment illustrated in FIGS. 4-6 differs from that shown in FIGS. 
1-3 in that the ventilation slots 3 have a rather different shape and in 
that the heat exchangers 10A and 11A are of different construction. The 
sheet fins between the sheets 7 and 8 respectively and the strips 14 and 
15 respectively consist of three strips 16, 17, and 18 staggered in 
relation to each other and bent into a crenellated shape. The air current 
is broken up by these strips in the passages a number of times. The 
construction of these fins is illustrated and described in the book 
"Compact Heat Exchangers" by Kays and London, 3rd Impression, 1984, page 
185, FIGS. 9-16. 
The heat exchangers shown produce excellent heat-transfer, while the 
pressure drop over the heat exchangers is slight. Because of their small 
dimensions in the direction of flow, they also fit into modern 
double-walled dashboards or elsewhere in the passenger compartment. Where 
one side of the heater tablets 9 is secured to a strip 7 or 8 with 
electrically and thermally conductive adhesive or solder to provide high 
heat-transfer, the division of the strip means 7 into plural segments as 
shown permits the strips to be in close engagement with the heater tablets 
and to be pressed into the housing with reduced risk of cracking of the 
tablets. The electrical connection to the heater elements 9 via the sheet 
fins also permits a compact structure to be utilized. 
When the heat exchangers are in operation, the temperature in the sheets 14 
and 15 will be lower than that in the sheets 7 and 8. The plastic casing 
in which the heating device is disposed will then also be thermally loaded 
to a lesser extent. 
When the engine is started, it can be ensured with the aid of a circuit 
arrangement that the electric current is fed automatically to the heating 
device, so that the air will be heated almost instantaneously, while after 
the ventilation air has been heated in the heating radiator to a 
sufficiently high temperature, the electric current supply to the heating 
device is switched off by means of a thermostat as indicated 
diagrammatically at 28 in FIG. 3. It is naturally also possible for the 
electric current supply to the heating device to be switched on and off by 
means of a manually operated switch. 
A heat exchanger of modular construction as shown in FIGS. 1-3 is, for 
example, 26 mm wide, 10 mm high, and 160 mm long, and comprises 4 PTC 
tablets. In tests with a heat exchanger of this kind, installed in 
ventilation slots in a motor vehicle, it was found that with a cabin 
temperature of 8.degree. C. the consumption of electricity increased from 
380 to 560 watts when the amount of air flowing through was increased from 
40 to 170 cubic meters per hour, while the pressure drop rose from 0.5 to 
only 3 mm water column. The tablets reached a temperature of 180.degree. 
C. It was also found that, by the application of the invention misted 
panes were demisted almost immediately after the electric current to the 
heating device was switched on. The heating device is disposed exactly 
under the pane, so that between its departure from the heat exchanger and 
its arrival at the pane the heated air scarcely loses any heat. 
It should be understood that although particular embodiments of the 
invention are shown by way of illustration. The invention includes all 
modifications and equivalents falling within the scope of the appended 
claims.