Rapid acting gas temperature sensor

A meander-shaped layer of nickel is deposited by evaporation on a ceramic wafer over an intermediate layer of tantalum serving to improve adhesion, and covered by a protective coating of silicon or epoxy resin is used as a temperature sensor in the intake pipe of a supercharged internal combustion engine. The low mass of the sensor element thus provided enables the resistance of the nickel path to follow rapidly, by its variation, the variations of temperature of the intake air. The sensor has a casing made up of two parts, the lower one of which has two connection prongs molded into it, the ends of which are flattened into tabs that are soldered to contact areas of the ceramic wafer. The upper casing portion has a cavity for the ceramic wafer, the lower part of which is filled with a potting compound to protect the solder joints. The width of the nickel paths that provide the temperature sensitive resistance is about 50 .mu.m and the thickness is from 0.2 to 1 .mu.m and the resistance may be typically 1000 ohms.

This invention concerns a temperature sensor for a gas flow, capable of 
sufficiently rapid response for service in the air intake system of an 
internal combustion engine, particularly a supercharged engine. 
When it is necessary to control the rate of supply of fuel to an internal 
combustion engine in accordance with the intake air temperature, it is 
necessary that the temperature sensor serving to measure the air 
temperature be capable of following all temperature changes very rapidly, 
and therefore that the sensor should possess only a slight heat capacity. 
THE INVENTION 
It is an object of the present invention to provide a temperature sensor of 
very small heat capacity that can be mounted to the air intake duct of an 
internal combustion engine and exposed to the flow of air therein. It has 
been found that such a low heat capacity can be provided in a practical 
way by a resistance path of nickel provided by thin film technology in 
meander shape on a thin small plate or wafer of insulating material, 
protected from corrosion by a covering of silicone or epoxy resin 
material. It is preferred for the resistance path to be provided by a 
conducting nickel layer about 50 .mu.m wide and having a thickness in the 
range from 0.2 to 0.6 .mu.m, most preferably about 0.3 .mu.m. The 
substrate for the thin film resistance path is preferably a ceramic wafer 
of a thickness of about 0.25 mm. The ends of the resistance path 
preferably have widened contact portions running along the longer sides of 
the substrate wafer, which is preferably of rectangular contour. 
Means for supporting the substrate in an air duct where air can pass over 
it are of course necessary, and such means preferably comprise a casing 
composed of two pieces of insulation material, of which one holds the 
wafer and makes air accessible to it and the other contains connection 
strips molded into the casing part when the latter is injection molded, 
the strips being soldered to the contact portions of the nickel film 
structure on the ceramic substrate wafer. Preferably, the solder joint is 
located in a cavity filled with an epoxy resin containing up to 70% of a 
titanium dioxide filler 75 and also an amine hardener.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The temperature sensor illustrated in the drawing is designed for building 
into an intake pipe, not shown in the drawing, of an internal combustion 
engine, for operation in the temperature range extending from -40.degree. 
C. to 180.degree. C. It has an injection molded casing of thermosetting 
plastic that is composed of a lower part 1 and an upper part 2. Both parts 
have a wide flange (3,4) at which they are connected by two hollow rivets 
5. 
The lower part 1 contains two prong strips 6, the lower end sections of 
which project into a cavity 7 serving for insertion of a connection 
bushing (socket connector) not shown in the drawings. At their upper ends 
each of the prongs 6 is pressed flat into a tab or lug 8. 
The upper part 2 of the casing has two support pillars 9 spaced from each 
other, above which a protective cap 10 of sheet metal is held in 
engagement. Windows 11, stamped out of the protective cap 10, allow the 
intake air of the engine to have access to a small wafer 12 of insulating 
material shown in more detail in FIG. 4. The wafer 12 is about 0.25 mm 
thick and is made of a ceramic, preferably aluminum oxide. Directly on the 
surface of the wafer 12, a tantalum layer is applied that serves to 
improve the adhesion of a meander-shaped resistance path 13 made out of 
nickel that is vapor deposited on top of the tantalum layer. 
The nickel resistance path 13 contains a number of conducting segments, 
each about 10 mm long and about 50 .mu.m wide, with a layer thickness of 
from 0.2 to 1 .mu.m. The thickness of 0.3 .mu.m is preferred for the 
illustrated embodiment and results in a resistance value of about 1 K ohms 
between the two connection conductors 15 and 16 that are wider extensions 
of the resistance path running along the long sides of the substrate wafer 
12, likewise applied in thin film technique. These conducting films 15 and 
16 are soldered to the connection tabs 8 of the prongs 6. In the region of 
these conducting paths 15 and 16 and their zone of connection with the 
tabs 8, the cavity 17 of the upper part 2 is filled with a "potting" mass 
18 composed of epoxy resin having a filler of up to 70% titanium dioxide 
(preferably at least 75%) and also an amine hardener (preferably from 7% 
to 8% by weight). The solder joints of the tabs 8 with the conducting 
paths 15 and 16 are mechanically and chemically protected by the potting 
mass. The portion of the ceramic wafer 12 that extends out of the potting 
mass 18 and carries the meander-shaped nickel layer is protected against 
deterioration by the intake air by a firmly adhering protective layer of 
silicone resin or epoxy resin. 
The particular advantage of the temperature sensor according to the 
invention is that it has only a very slight mass and accordingly can 
follow quickly the temperature changes that occur in he intake air. 
Although the invention has been described with reference to a particular 
illustrative example, it will be understood that modifications and 
variations are possible within the inventive concept.