Air quantity metering apparatus

An apparatus is proposed for metering air quantity, particularly for metering induction air quantity in internal combustion engines, which has a temperature-dependent resistor disposed within an air stream, the temperature and/or resistance value of which is regulated in accordance with the air quantity, and with the control value providing a standard for induction air quantity. The temperature-dependent resistor is embodied as a heating wire and is stretched in a V-shape on a carrier member, whereby the temperature coefficient of the carrier member and that of the heating wire are compatible with each other. The stretching of the wire is accomplished with the aid of support elements which are fixed within the carrier member. The heating wire has each end affixed at a support point, while it is guided only loosely over an intermediate support element.

CROSS-REFERENCE TO RELATED INFORMATION 
This application in so far as it relates to platinum-glass material 
identifies a prior use of platinum-glass as found in a German publication 
entitled Feinmechanik u. Prazision (Precision Engineering), No. 62, Glas 
als Werkstoff der Vakuumtechnik, A V 10 DK 666.03, page 117 (1958). 
BACKGROUND OF THE INVENTION 
The invention relates to an apparatus for air quantity metering, 
particularly for metering the induction air quantity in internal 
combustion engines, having a temperature-dependent resistor element 
disposed within the air stream the temperature and/or resistance of which 
is regulated in accordance with the air quantity, and with the control 
value providing a standard for the air quantity. Such apparatuses are 
already known, in which a heating wire is utilized as a 
temperature-dependent resistor, which is stretched tautly between two 
points. Because of strong variations in temperature both in the vehicle 
and caused by the particular mode of operation of the wire, breakage of 
the wire occurs relatively quickly. 
OBJECT AND SUMMARY OF THE INVENTION 
The arrangement in accordance with the invention has the advantage over the 
prior art that temperature variations in the vehicle and those occasioned 
by the mode of operation of the heating wire have no influence on the life 
of the apparatus, and furthermore that tensile or compressive strains are 
not conducted to the wire, so that damage to the wire resulting from 
temperature changes is eliminated. 
It is considered a further advantage that the wire can be stretched 
relatively simply, so that the air quantity metering apparatus can be 
produced simply and at a favorable cost. 
The invention will be better understood as well as further objects and 
advantages thereof become more apparent from the ensuing detailed 
description of a preferred embodiment taken in conjunction with the 
drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
In FIG. 1, a sensor ring or carrier member 10 is shown. This sensor ring is 
provided with three support elements 11, 12 and 13. With the aid of the 
sensor support elements 11, 12, 13, a heating wire 14 is stretched in a 
V-shape. The heating wire 14 has its ends fixed only at two support points 
12 and 13, while it is guided only loosely over the third support point 
11, this latter support point being embodied in the form of a hook. 
The heating coil is suitably produced of platinum. The sensor ring 10, 
which serves as the carrier member for the heating wire 14, has its 
heat-expansion coefficient adapted to the heat-expansion coefficient of 
the heating wire 14, so that changes in length of the wire or of that of 
the sensor ring caused by heat expansion do not cause any tensile or 
compressive strains in the wire 14, but instead are compensated for by 
variations in distance between the points of support of the wire as 
indicated by numerals 11, 12, 13. 
Stretching the wire in such a way that it is free of tensile and 
compressive strains is extraordinarily important if the heating coil is to 
be utilized as an air quantity meter in the intake manifold of a motor 
vehicle, for example. The temperature range which then must be considered 
is generally from -30.degree. C. to +120.degree. C. Furthermore, still 
another temperature variation is occasioned by the mode of operation of 
the heating wire 14. Frequently, the heating wire is heated further to a 
high temperature and made to glow, so that residues firmly deposited on 
its surface can be burned off. This brief elevation in temperature also 
causes changes in the length of the wire, which could cause tensile and 
compressive strains when the wire is rigidly stretched. 
By means of stretching the wire in a V-shape and adapting the 
heat-expansion coefficients of the sensor ring 10 and of the heating wire 
14 to each other, the possibility of conducting tensile or compressive 
strains into the heating wire 14 is eliminated. When the heating wire 14 
is made of platinum, it is effective to embody the sensor ring 10 in a 
nickel-iron alloy, the heat-expansion coefficient of which corresponds 
approximately to that of platinum. It is also possible to make the sensor 
ring of glass, particularly of so-called platinum-glass. The 
heat-expansion coefficient of this glass also corresponds substantially to 
that of platinum, so that no tensile or compressive strains caused by 
temperature changes can be conducted into the heating wire 14, but rather 
that changes in length of the heating wire 14 can be compensated for by 
changes in distance between the support points 11, 12, 13, each of which 
is attached to the sensor ring 10. 
In FIG. 3, the mounting of the heating wire 14 is clearly illustrated once 
more. If the sensor ring 10 is made, for example, of a nickel-iron alloy, 
then at least two of the support points 11, 12 and 13 must be electrically 
insulated from the sensor ring. As may best be seen in the upper fixation 
point in FIG. 3, the support 13 is soldered into the sensor ring 10 via an 
insulation insert 15. A solder layer is marked with the reference numeral 
16. At the lower fixation point in which the support point 11 is shown, it 
may be seen that a support point can be directly attached to the sensor 
ring 10, that is, directly fixed within the sensor ring 10. The support 
elements 11, 12, 13 may be so disposed that the heating wire 14 is 
stretched within the sensor ring 10. However, it is suitable to have the 
support points 11, 12, 13 bent and projecting outwardly away from the 
front face of the sensor ring 10 in such a manner that the heating wire 14 
can be stretched outside the sensor ring 10, all of which is clearly shown 
in FIG. 2. This has advantages relating to fabrication techniques. 
In FIG. 4, a different embodiment of the central support point for the 
heating wire 14 is illustrated. The central support point, over which the 
heating wire 14 is guided only loosely, has an insulation layer 17, which 
may be, for example, of glass. Within the glass layer there is a depressed 
or constricted area 18 for the purpose of better guiding the heating wire 
14. The particular guidance of the heating wire 14 is therefore 
particularly suitable, because in this manner the metering accuracy of the 
air quantity metering apparatus can be increased. The wrap angle which the 
heating wire 14 forms at the support point 11 can change as a result of 
pulses in the air flowing past it. If no insulation were employed in the 
guidance of the heating wire, then depending on the wrap angle a resistor 
of indeterminate value could be switched in parallel to the heating wire 
14, which could lead to an undesirable alteration of the metering product. 
By employing the insulation layer 17 on the central support point, no 
parallel resistors appear, so that the desired metering product is 
extraordinarily precise. 
As a result of the suspension of the heating wire as described, it is 
possible to compensate for changes in the length of the heating wire 14 to 
such an extent that no tensile or compressive strains at all are conducted 
into the heating wire, so that a long operational life of the air quantity 
metering apparatus is achieved. 
The foregoing relates to a preferred embodiment of the invention, it being 
understood that other embodiments and variants thereof are possible within 
the spirit and scope of the invention, the latter being defined by the 
appended claims.