DE2938205A1 - CAPACITIVE PRESSURE SENSOR AND EVALUATION DEVICE HERE - Google Patents

Description

R. 5 73 2

29.8.1979 Lr / Hm

ROBERT BOSCH GMBH, 7OOO Stuttgart Capacitive pressure transmitter and evaluation device therefor

The invention relates to a capacitive pressure transducer, in particular for determining the intake air pressure of a Internal combustion engine, with a metallically conductive, pressure-dependent deforming membrane, the one opposite the membrane is isolated, metallic surface opposite, which together with the membrane, the two Form electrodes of an electrical capacitor.

In electronic control and regulation systems for internal combustion engines Absolute pressure transducers are required to measure the intake manifold pressure. Such pressure transducers should in addition to the usual requirements such as a high operating temperature range, etc., above all the requirement smaller The size and insensitivity to acceleration are sufficient for the pressure transducer to be inserted directly into the intake manifold of the internal combustion engine can be installed.

To solve this problem, in the case of a capacitive pressure transmitter of the type described at the outset, those in the label of the main claim mentioned features provided.

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Using a profile etched membrane instead of a The otherwise common corrugated membrane has the advantage that profile-etched membranes are made from almost any spring material can be manufactured with great accuracy, the material used to the thermal Expansion coefficient of the carrier can be adjusted. In addition, the characteristics of the pressure transducer, such as, for example, the dependence of the capacitance C on the pressure ρ by appropriate choice of the etching profile can be easily adapted to the respective requirements.

Advantageous refinements of the pressure transmitter are mentioned in the subclaims. It is particularly advantageous if, in a further embodiment of the invention, the insulating material plate on its second, remote from the membrane Side carries an evaluation circuit, in particular in the form of a thin-film circuit. This can useful as an RC oscillator, especially as a multivibrator be designed with an operational amplifier.

Embodiments of the invention are described below and shown in the drawing. Show it:

Figure 1 shows a first embodiment of a capacitive pressure transducer according to the invention in section,

FIG. 2 shows another pressure transducer in section at an external pressure ρ = 0 and

FIG. 3 shows the same pressure transducer in section, but with an external pressure that is higher than its internal pressure p,

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Figure 4 shows an evaluation circuit that an output frequency ^ returns and

FIG. 5 shows another evaluation circuit with an operational amplifier .

The pressure transducer according to FIG. 1 has a thin insulating carrier plate 1, which is made of ceramic AlpO, - and in the middle of one of its two upper sides a thin-film metallization 2 carries. The thin layer has a one that extends through the plate 1 Contact 3 with that arranged on the opposite rear side of the plate 1, also as a thin layer formed conductor track 4 connected.

On the upper side of the plate 1 carrying the thin layer 2 there is also a thin layer Conductor track 5 is provided which, as a closed ring, surrounds the central thin layer 2 at a distance in a ring shape. With the ring-shaped conductor track 5 is the edge

6 a membrane which is profile-etched from a metal plate

7 connected pressure-tight by soldering. The membrane encloses a cavity 8 which is evacuated. The bottom 9 of the membrane 7 that remained during the etching process forms together with the opposite thin film 2, an electrical capacitor whose capacitance C is the same becomes greater, the higher the external pressure ρ acting on the bottom 9 of the membrane 7 rises, and thereby the bottom 9 bends against the thin layer 2.

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The membrane 7 acting as the second electrode of the capacitor is by means of a plated through connection 11 connected to a contact rail 12, also applied using thin-film technology, which is part of a this back of the plate 1 arranged evaluation circuit 13 is. Belong to this evaluation circuit several components, two of which are indicated at 14 and 15 are.

The illustrated design of the pressure transmitter has the advantage that the pressure transmitter is only a small one Has space requirements, is largely insensitive to temperature and easily into the intake manifold of an internal combustion engine can be installed, where there is an electrical Size, preferably a pressure-dependent frequency f supplies.

In the exemplary embodiment according to FIGS. 2 and 3, as in the exemplary embodiment according to FIG. 1, a Ceramic plate 1 serving as a carrier and a thin-film electrode 2 applied to this is provided. In contrast to the first embodiment, however, here has a profile-etched metal plate produced membrane 20 along its edge zone 21, on which the membrane is annular in plan view Conductor 22 is soldered pressure-tight, a circumferential annular groove 23 which is etched so deep that there is a thin wall part 24 at the bottom of the groove 23, which can easily be deformed in the manner shown in FIG. 3 and has only low restoring forces having. In the center 25 enclosed by the groove 23

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the membrane 20 faces the thin-film electrode 2 with only a small distance e when the external pressure p = 0 and the interior space 26 enclosed by the membrane 20 is evacuated. As a result of the small distance e there is already a relatively large capacitance value for the case p = 0 shown in FIG of the capacitor formed by the central region 25 and the opposite thin-film electrode 2.

When a pressure ρ acts on the membrane 20 in the manner shown in FIG. 3, the central area becomes 25 closely approximates the thin-film electrode 2 and consequently the one between these two electrodes Capacity increased significantly.

The capacitance C between the two electrodes 2 and 25 and its course as a function of the external pressure ρ can easily be determined by the respective etching depth of the groove 23 and the free end face in the central area 25 can be influenced.

To evaluate the pressure-dependent capacity C, the RC oscillator shown schematically in FIG. 4 is provided at which a voltage occurs at output terminal A, the frequency of which is £ v. «? Τ arises. A feedback resistor R leads from output A to the input of the oscillator, which can be permanently set can and together with the variable capacitance C of the printer according to Figure 1 or Figure 2 the Oscillation frequency f is determined.

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In Figure 5, another evaluation circuit is shown, which is referred to as a multivibrator with operational amplifier can be. There, at the output A of an operational amplifier O, an alternating voltage Ua can be tapped Frequency f = 1/2 RC In (1 + 2 R1 / R2).

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Claims (6)

«· 5732 8/29/1979 Lr / Hm ROBERT BOSCH GMBH3 7000 Stuttgart Claims 1. Capacitive pressure transducer, in particular for determining the intake air pressure of an internal combustion engine, with a metallically conductive, pressure-dependent deforming membrane, which insulates a membrane from opposite metallic surface, which together with the membrane the two electrodes of an electrical Forms capacitor, characterized in that the metallic surface (2) in the form of a thin, conductive Layer on one side of an insulating plate (1) is attached and that the membrane (7) consists of a profile-etched metal plate, the edge zone (6) of which remained during the etching process with the Insulating plate (1) is connected airtight and pressure-tight. 2. Pressure transmitter according to claim 1, characterized in that the metal plate (7) has a central zone (9) less Has strength which is produced by 'etching 130015/0184 ORIGINAL INSPECTED 5732 3. Pressure transmitter according to claim 1 or 2, characterized in that the membrane (20) has a central zone (25) which is delimited from this edge zone by an etched groove (23) running along the edge zone (21) is. 4. Pressure transmitter according to one of claims 1 to 3, characterized characterized in that the insulating plate (1) made of ceramic, in particular of AlpO-. consists. 5. Pressure transducer according to one of claims 1 to 4, characterized in that the insulating material plate (1) _{carries an evaluation circuit (13) s,} in particular in the form of a thin-film circuit, on its second side facing away from the membrane (7, 20). 6. Pressure transmitter according to claim 5, characterized in that the evaluation circuit as an RC oscillator, in particular is designed as a multivibrator with operational amplifier. 130015/0184