Measuring and testing – Volume or rate of flow – Thermal type
Patent
1991-02-27
1993-02-16
Goldstein, Herbert
Measuring and testing
Volume or rate of flow
Thermal type
G01F 168
Patent
active
051860511
DESCRIPTION:
BRIEF SUMMARY
PRIOR ART
The invention relates to a device for measuring a flowing air quantity.
A device for measuring a flowing air quantity according to the generic category of the main claim is already known from SAE Technical Paper Series 880,560, pages 105-109, in which device the heating film resistor is arranged on one side of the insulating substrate and the sensor film resistor serving to sense the temperature of the heating film resistor is arranged on the other side of the insulating substrate, opposite the heating film resistor, these two resistors being applied in a planar form to the flat surface of the insulating substrate. However, since the insulating substrate, for reasons of stability, must not fall below a certain minimum thickness, a construction of this type means that the thermal coupling between the two abovementioned resistors via the insulating substrate lying in between cannot be sufficient. On the one hand, the thermal transfer through the insulating substrate does not take place quickly enough; on the other hand, a portion of the dissipated heat developing in the heating film resistor is dissipated laterally in the insulating substrate parallel to the substrate surface so that the temperature sensing by means of the sensor film resistor is inaccurate and sluggish.
Furthermore, U.S. Pat. No. 4,382,247, Stecher et al./Bosch, discloses a pressure cell which contains a pressure-sensitive diaphragm which consists of a bubble which is made of glass ceramic and is produced on an insulating substrate in thick-film technology.
ADVANTAGES OF THE INVENTION
Compared with the known device described at the beginning for measuring a flowing air quantity, the device according to the invention for measuring a flowing air quantity, has the advantage that the sensor film resistor and the heating film resistor are uncoupled thermally in a very effective manner from the insulating substrate and from the further components applied to the latter if need be, and that the mutual thermal coupling between the sensor film resistor and the heating film resistor is considerably improved. Short response times are thereby achieved. Another advantage is very effective thermal uncoupling of the further sensor film resistor from the insulating substrate and a very effective thermal coupling of this resistor to the air flowing past, whose temperature is to be measured by this resistor. Further advantages will be apparent from the description.
BRIEF FIGURE DESCRIPTION
The invention is described in greater detail with reference to the drawing, in which:
FIG. 1 shows the electrical circuit diagram of a known air-mass flow meter and the air-mass flow meter according to the invention,
FIG. 2 shows an air-mass flow meter according to the invention, partly in circuit diagram, partly in the schematically represented plan view of a sensor element constructed in thick-film technology,
FIG. 3 shows a section along the line III--III in FIG. 2,
FIG. 4 shows a section along the line IV--IV in FIG. 2,
FIG. 5 schematically shows an air-mass flow meter according to the invention for measuring the air quantity drawn in the suction pipe of a motor vehicle.
DETAILED DESCRIPTION
The air-mass flow meter shown in FIG. 1 in its electrical circuit diagram contains a bridge circuit which interacts in a manner known per se with an externally arranged heating film resistor R.sub.H, thermally coupled to one of the bridge resistors, in such a way that the heating current flowing through the heating film resistor is a measure of the air quantity flowing past.
Connected to the voltage U.sub.BAT of a motor-vehicle battery is a voltage divider consisting of a resistor R.sub.o and a zener diode Z, the negative pole of the battery and the anode of the zener diode at the same time being connected to earth. A largely constant voltage U.sub.K is provided between the tap T of the voltage divider R.sub.o, Z and earth. A first bridge branch of a bridge circuit consisting of the resistors R.sub.2, R.sub.T and R.sub.1 is connected to the voltage U.sub.K, with
REFERENCES:
patent: 4382247 (1983-05-01), Stecher et al.
patent: 4777820 (1988-10-01), Hecht et al.
patent: 4831876 (1989-05-01), Porth et al.
Bergfried Dietrich
Hecht Hans
Muehlheim Richard
Stecher Gunther
Ziegenbein Botho
Goldstein Herbert
Robert & Bosch GmbH
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