WO1983000225A1

WO1983000225A1 - Sensor

Info

Publication number: WO1983000225A1
Application number: PCT/DE1982/000025
Authority: WO
Inventors: Bosch Gmbh Robert
Original assignee: Dobler, Klaus; Gruner, Heiko; Grünwald, Werner; Heinz, Rudolf; Schoor, Ulrich
Priority date: 1981-06-30
Filing date: 1982-02-18
Publication date: 1983-01-20
Also published as: IT1151655B; IT8222023A0; DE3125640A1; EP0082151A1

Abstract

The sensor, intended to detect de pressure of a medium, employs at least one element modifying its resistance value under the effect of a pressure. Said element is an ordinary resistive element, preferably a coal layered resistance, a thin layered resistance or a thick layered resistance. The elements (21) are preferably arranged in a bridge circuit wherein, in order to compensate for the temperature influences and to increase the pressure-dependent signal, resistive elements are used which have different temperature and pressure coefficients. The resistive elements are further arranged in a support (32) which may be resiliently deformed under the effect of the pressure, so as to obtain an increase of the signal by the conjugated effect of the pressure and an expansion, respectively of a deformation of the resistive element.

Description

sensor

State of the art

The invention relates to a sensor according to the preamble of the main claim.

There are already numerous sensor arrangements for. Measuring a pressure in a medium has become known, in particular for measuring high pressures, for example the oil pressure in hydraulic systems or in fuel injection pumps.

However, these known pressure sensors are generally based on piezoelectric effects and are therefore complicated and expensive to set up and are temperature-sensitive. Advantages of the invention

The sensor according to the invention with the characterizing features of the main claim has the advantage that an amazingly simple and thus inexpensive to manufacture arrangement is possible by using conventional resistance components.

Advantageous further developments of the sensor specified in the main claim are possible through the measures listed in the subclaims.

For example, use can be made of the fact known per se that the manufacture of resistance components with different temperature coefficients is possible with simple means, for example in the case of thin-film resistors in a TaNi system. If such resistor components with different temperature coefficients are interconnected in a bridge to form an overall arrangement, a sensor with low temperature dependence of the output signal can be constructed in this way with particularly little effort.

Furthermore, temperature compensation can be brought about by exposing only part of the elements of the bridge to pressure and the other part being pressure-shielded. Such an arrangement can be implemented in a particularly simple manner in thick-film technology in that the part of the bridge to be shielded in a pressure-tight manner is provided with a ring and a cover plate.

In a further embodiment of the invention, for those cases in which the sensor is in a flowing medium, the occurrence of temperature-related Error signals due to the inflow of the medium are reduced in that elements of the bridge are provided with an elastic covering layer which, however, does not distort the detection of the static or dynamic pressure. The lower usable cut-off frequency of the sensor can be significantly reduced in dynamic measurements without temperature compensation.

In a further preferred embodiment of the invention, the output signal is increased by using elements in the bridge which have a different pressure coefficient. In an analogous manner, it is possible, by using elements with different temperature and pressure coefficients, to produce an overall adjustment of the bridge, in which extensive elimination of the total temperature coefficient is combined with a particularly high pressure sensitivity of the arrangement.

Finally, in a further preferred embodiment of the invention, a further increase in the output signal is brought about in that the elements are arranged on a support which can be deformed elastically under the action of pressure, whereby the elements are simultaneously exposed to the action of pressure and an expansion or compression. It is particularly advantageous, when using a laterally clamped membrane, to arrange the elements of a bridge in a defined manner on the membrane so that they are each in the range of positive or negative expansion of the membrane, with resistance materials such as those with positive or negative pressure coefficients Use come so that the above-mentioned high output signal is produced by the superimposition of the signals by pressure and deformation. drawing

Embodiments of the invention are shown in the drawing and explained in more detail in the following description. FIG. 1 shows the circuit diagram of a bridge arrangement as can be used in the sensor according to the invention; Figure 2 is a sectional view through a first embodiment of a sensor according to the invention; Figure 3 is a sectional view through a second embodiment of a sensor according to the invention; FIG. 4 shows a sectional view through a third embodiment of a sensor according to the invention; FIG. 5 shows a sectional view through a fourth embodiment of a sensor according to the invention using thick-film technology; FIG. 6 shows a further circuit diagram of a bridge arrangement as can be used in the sensors according to the invention.

Description of the embodiments

The sensor according to the invention is intended to measure pressures in a medium using at least one element which changes its resistance under the action of pressure. The sensor is particularly suitable for measuring high pressures, such as those that occur in hydraulic systems or injection pumps of internal combustion engines. In the latter case, the sensors are part of a control system in which various operating parameters are used to control an internal combustion engine, including the injection quantity, which is determined indirectly via the pressure in the injection pump.

While complex sensors are usually used for such measurement purposes, it is possible with the sensors according to the present invention to produce such pressures easily and inexpensively Elements. These elements are commercially available resistance components, the manufacture of which is known and is easy to carry out.

For example, according to the invention it is possible to use carbon film resistors, thin film resistors or thick film resistors. These resistance elements are directly exposed to the pressure to be measured, it having been shown that these elements have a considerable pressure coefficient, so that measurements of the static and dynamic pressure are possible without special circuitry measures.

In these components, which are only mentioned as examples, different materials or material combinations can be used, with which different pressure and temperature coefficients can be set, so that - as will be shown in more detail below - circuits are possible which produce particularly high useful signals with low temperature dependence, provided that bridge circuits can be used with suitable dimensioning of the individual components.

When using thin film resistors, these different properties can be represented from a thin film system TaNi. In this system, temperature-dependent resistors (overall TaNi) and practically temperature-independent resistors (selectively etched-out Ta layer) can be produced in a very simple manner.

Pressure measurements with such resistors gave the surprising result that the Ta resistors produced with the addition of air to the discharge gas by sputtering, in contrast to the literature value for Have tantalum negative pressure coefficients; the TaNi resistors formed from the entire layer, on the other hand, have a positive pressure coefficient. The absolute pressure of the pressure coefficient for Ta resistors is of the order of magnitude of manganine, from which resistors for direct pressure measurement can advantageously be produced, as described in the earlier application F 30 28 188.0. In contrast, the pressure coefficient of TaNi resistors is about two to three times larger.

In Figure 1, a bridge circuit 10 is shown, which consists of four resistors 11, 12, 13, 4. A bridge voltage U _{B is} applied to one bridge diagonal, the measuring voltage U _M is taken from the other bridge diagonal, which voltages can of course also be interchanged.

According to the invention, the diagonally opposite resistors are now made of the same material, namely resistors 11, 13 made of Ta, resistors 12, 11 made of TaNi. Due to the different pressure coefficients specified above, the bridge circuit 10 shown in FIG. 1 accordingly has six to eight times the pressure sensitivity to a bridge made up of ganine resistors.

If the bridge arrangement according to FIG. 1 is used to measure dynamic pressures, in which absolute amounts are not important, the temperature dependence of the bridge signal does not interfere. The lower limit frequency for such dynamic measurements is also determined by the reaction speed of the bridge to temperature changes in the pressure medium. Is the bridge arrangement shown in Figure 1 in a flowing medium, can Falsifications of the measurement result occur in that the medium flows against the resistors 11 to 14 and thereby causes temperature-related false signals. In a further embodiment of the invention it is therefore provided that the resistors 11 to 1 4 are covered with an elastic organic protective layer, for example silicone, so that the sensitivity during pressure measurements is not impaired. A predetermined inertia of the measuring system against temperature influences can thereby be brought about.

A first practical embodiment of a sensor according to the invention is shown in FIG. Carrier of the sensor is a screw 15 which, provided with a seal 16, can be screwed into a pressure housing 17. The pressure housing is, for example, the wall of a hydraulic element or an injection pump in a motor vehicle. The screw 15 is provided with an axial bore 18 into which a multi-core feed line 19 extends pressure-tight from the outside. The feed line 19 is fastened in the bore 18 to a plate 20 on which the resistor arrangement 21, for example a bridge circuit 10 according to FIG. 1, is arranged. The flat rather. 20 with the resistor arrangement 21 is surrounded by an elastic covering layer 22, as described above. The elastic covering layer 22 is in turn protected with a protective grid 23 against mechanical damage.

Another practical exemplary embodiment of a sensor according to the invention is shown in FIG. Here, too, a screw 15 is screwed into a pressure housing 17 as a support for the sensor via a seal 16. In contrast to the exemplary embodiment according to FIG. 2, however 3, the axial bore 30 is formed continuously by the screw 15. The bore 30 is filled with an elastic potting compound 31, a base 32 being seated on the screw head and the potting compound 31 at the end of the screw facing the pressure. The base 32 again carries a resistance arrangement 21 covered with an elastic cover layer 22. Feedthroughs 33 lead from the base 32 into the sealing compound 31. An electronic circuit 35, for example a preamplifier, can be connected to the feedthroughs 33. The electronic circuit 35 with its leads 34 is also poured into the potting compound 31. In this way, a highly sensitive pressure sensor can be constructed, in which the base 32 is preferably designed in the form of an elastically deformable membrane, which, as will be described further below, results in a further increase in the useful signal.

A third practical embodiment of a sensor according to the invention is shown in FIG. 4a and b in section. shown in top view. In turn, an axial bore 30 ′ runs in the screw 15, but in this exemplary embodiment is conically stepped outward. The bore 30 'is in turn filled with the elastic casting compound 31 and the base 32', which in a preferred embodiment is designed to be elastically deformable, rests on the pressure-facing end of the screw thread 15. The resistance arrangement 21 covered by the elastic covering layer 22 is in turn arranged on the base 32 '. The leads 34 of the resistor arrangement 21 lead through the casting compound 31 to the outside. In this way it is possible to construct a particularly simple and inexpensive sensor. According to the invention it is further provided to reduce the temperature coefficient of the entire sensor arrangement part of the resistance elements used pressure-tight, so that by comparing these pressure-tightly shielded resistance elements with the unshielded resistance elements an elimination of temperature influences is possible.

Such an arrangement can preferably be constructed using thick-film technology, as illustrated in FIG. 5. It goes without saying, however, that this production technology is only given as an example and that the sensor arrangements described here in detail can be constructed with all of the resistor elements mentioned, provided that nothing else arises from the specially used elements and their special properties.

In the embodiment according to FIGS. 5a, b and c, an Ealbbrückenancrdnung 39 is used, which consists of the resistors 4 1 and 42 and is arranged on a substrate 40 serving as a base. Resistors 41, 42 are particularly suitable for use in thick-film technology, for example cermet, conductive plastic, fiatin, etc. As has been shown, these resistors show an enormously high change in resistance depending on the pressure. It is possible according to the invention to vary the pressure-dependent resistance coefficient within wide limits by selecting the resistance pastes and by adding admixtures of conductive and non-conductive Steffen, as well as their grain size and shape. When using thick-film technology, the ring 43 is printed around the resistor 41 from a suitable material, for example glass, ceramic or the like, and the cover plate 44 is placed pressure-tight in a further operation.

In addition to the pressure-tight shielding, an additional measuring effect can be achieved by specifically designing the cover.

As shown in FIGS. 5b and c, it is possible to set the thickness of the base 40 or the cover plate 44 within wide limits. If, as shown in FIG. 5b, the base 40 is made substantially thinner than the cover plate 44, a concave deflection of the base 40 results when pressure is applied, as is indicated in FIG. 5b by the line 15 of the positive deflection. In the opposite case, a thick base 40 results in a convex deflection, as is shown by the line 46 of the negative deflection in FIG. 5c. The deflection of the base 40 results in an expansion or compression of the resistor 41, which opens up the possibility of utilizing this in addition to the pressure load to increase the mechanical load to increase the signal. In the same way, this is possible with the arrangements according to FIGS. 3 and 4 if - as already indicated above - the base 32 or 32 'is designed in the form of an elastically deformable membrane. Since these membranes are clamped on the sides, there are deflections in different directions on the edge and in the middle. By suitable geometric attachment of the resistance elements of the arrangements 21, it is then possible to subject a part of the resistance elements to compression and another part to an expansion when subjected to pressure. Will these items Now, as already shown in FIG. 1 for the case of the different pressure coefficient, arranged diagonally or adjacent to one another in a bridge arrangement, an additional signal increase can be achieved by compressing or stretching, and thus changing the resistance, causing an additional detuning of the bridge when pressure is applied becomes.

Finally, a bridge circuit 50 is shown in FIG. 6, in which temperature compensation is possible by suitable selection of the bridge elements. The bridge circuit 50 consists in two opposite branches of resistors 51a, 51b and 53a, 53b and in the other two branches of individual resistors 52 and 54. The resistors 51a, 53a are as TaNi resistors and the resistors 51b, 53b Ta resistors formed. The resistors 52, 54 consist of a material with a positive pressure coefficient and a temperature coefficient which is in the range of + 200 ppm / К. These conditions are fulfilled e.g. Silver-manganese alloy layers.

By appropriately dimensioning all bridge resistances, it can be achieved that only a specific bridge branch, for example 51a, b, must be used to zero the bridge 50. For this purpose, the bridge branch 51a, b is designed to have a low resistance during manufacture by means of targeted path widening. Due to the usual manufacturing variation of + 5%, the resistance of branch 51a, b can now be increased and the temperature coefficient reduced by laser adjustment, with which a range of + 20% can be adjusted. By appropriately dividing the resistors 51a, 51b, it is possible to to set the resistance value and the temperature coefficient of this branch independently of one another, as is described, for example, in DE-OS 29 06 813. Since the TaNi resistor 51a has a smaller value than the resistor 52 but a larger temperature coefficient, this setting can have the effect that the overall temperature coefficient of the bridge circuit 50 is minimized.

Claims

Expectations

1. Sensor for detecting the pressure of a medium using at least one element changing its resistance value under the action of pressure, characterized in that the element is a conventional resistance component

(11 to 14, 21, 4 1, 42, 51 to 54), preferably a carbon film resistor, a thin film resistor or a thick film resistor.

2. Sensor according to claim 1, characterized in that the at least one element (11 to 14, 21, 41, 42, 51 to 54) is a thin film resistor (11 to 14, 21, 51, 53) of a TaNi system.

3. Sensor according to claim 1, characterized in that the at least one element (11 to 14, 21, 41, 42, 51 to 54) is a thick-film resistor (21, 41, 42), for example cermet, conductive, plastic, platinum, etc. is.

4th Sensor according to one of claims 1 to 3, characterized in that the elements (11 to 14, 21, 41, 42, 51 to 54) are components of a bridge arrangement (10, 39, 50).

5. Sensor according to any one of the preceding claims, characterized in that at least one element (11 to 14, 21, 42, 51 to 54) for reducing the thermal load in the case of direct flow through the medium with an elastic cover layer (22), preferably silicone, is provided.

6. Sensor according to claim 5, characterized in that to reduce the response speed of the element (11 to 14, 21, 42, 51 to 54) on temperature changes, the mass of the cover layer (22) is adjustable.

7. Sensor according to claim 5 or 6, characterized in that the elements (11 to 14, 21, 51 to 54) are arranged on a plate (20) at the foot of a pressure-tight screw into a pressure housing (17) screwable (15th ) attached and surrounded by the elastic cover layer (22) and a protective grille (23).

8. Sensor according to one of claims 4 to 7, characterized in that part of the bridge (10, 39, 50) is covered pressure-tight.

9. Sensor according to claim 8, characterized in that when using thick-film elements around the at least one, on a substrate (40) located thick film resistor (41) to be covered, a ring (43), preferably made of glass, ceramic or the like which is closed with a cover plate (44).

10. Sensor according to one of claims 4 to 7, characterized in that the elements (11 to 14, 21, 51 to 54) have a different pressure coefficient.

11. Sensor according to claim 10, characterized in that a full bridge with four elements (11 to 1 4) is used, with two Ta resistors (1 2, 1 4) and two TaNi resistors (11, 13) each diagonally opposite.

12. Sensor according to claim 10, characterized in that a full bridge with at least six elements (51 to 54) is used, two diagonally opposite bridge branches from the series connection A TaNi resistor (51a, 53a) and a Ta resistor (51b, 53b) and the other two bridge branches are each made up of a resistor (52, 54) that has a positive pressure coefficient and a temperature coefficient in the range of - 200 ppm / k.

13. Sensor according to claim 10, characterized in that the resistors (52, 54) forming the remaining bridge branches are sputtered silver-manganese alloy layers with a positive pressure coefficient and a temperature coefficient of at least approximately + 10 ppm / K.

14. Sensor according to one of the preceding claims, characterized in that at least one element (11 to 14, 21, 4 1, 42, 51 to 54) is arranged on a support (32, 32 ', 40) which is elastically deformable by the action of pressure is.

15. Sensor according to claim 9 and 14, characterized in that the thickness of the substrate (40) and / or the cover plate (44) is adjustable so that a convex or concave deformation of the substrate (40) results when subjected to pressure.

16. Sensor according to claim 14, characterized in that diε elastically deformable base (32, 32 ') on the Head of an axially drilled screw (15) serving as the sensor body is arranged.

17. Sensor according to claim 16, characterized in that the bore (30, 30 ') for receiving leads (34), electronic circuits (35) or the like. Serves and is preferably cast pressure-resistant.

18. Sensor according to one of claims 14 to 17, characterized in that when using a bridge circuit for the elements (11 to 14, 21, 41, 42, 51 to 54) at least one element in the area of convex deflection (45) of the base ( 32, 32 ') and at least one further element in the area of concave deflection (46) of the base (32, 32') is arranged.