GB2033589A

GB2033589A - Mechanical-electrical pressure transducer

Info

Publication number: GB2033589A
Application number: GB7933458A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1978-09-28
Filing date: 1979-09-27
Publication date: 1980-05-21
Also published as: JPS5546199A; GB2033589B; FR2437614A1; FR2437614B1; DE2842140A1; DE2842140C2

Abstract

A Hall-effect component (10) is disposed on a diaphragm of an aneroid box and is located between two permanent magnets (7, 9) whose end faces of like polarity are located opposite one another, the distance between the Hall- effect component and one or both of the magnets being varied by means of the diaphragm (17) in dependence upon the pressure to be measured. The transducer is for measuring the vacuum in the intake manifold of an i.c. engine. The magnets may be of cobalt and samarium. Adjusting the compensating magnet 9 allows the Hall-effect component to be disposed at a region of zero magnetic induction. Subsequently a linear relation between pressure acting on the diaphragm and transducer output voltage may be achieved. <IMAGE>

Description

SPECIFICATION Mechanical-electrical pressure transducer The invention relates to a mechanical-electrical transducer for the measurement of pressures, particularly for measuring the vacuum in the intake manifold of an internal combustion engine.

In the known pressure transducers of this type, such as the pressure transducer described in German Offenlegungsschrift No. 16 73 938, there are provided a permanent magnet in an iron circuit in which is disposed the magnetic-field dependent semiconductor component (Hall generator) and an air gap into which extends a regulating member which influences the lines of force in the air gap.

However, transducers of this kind have to be manufactured and adjusted with very high precision and, moreover, have the disadvantage that it is a very expensive matterto protect them against soiling when they are operated in motor vehicles.

The object of the invention is to provide a pressure transducer which is especially suitable for measuring the pressure of the intake air in internal combustion engines and which, despite being of simple construction, has a high degree of accuracy and reproducibilty of the pressure values.

There is provided by the present invention a mechanical-electrical transducerforthe measurement of pressures, having a diaphragm to sense the pressure to be measured, a Hall effect component and a permanent magnet whose magnetic field supplies at the output of the component an electrical quantity varying in dependence upon the pressure wherein a second magnet is arranged at that side of the Hall-effect component which is remote from the first magnet, and like poles of the two magnets are located opposite one another.

Advantageously, the magnet can comprise, in a known manner, a compound of cobalt and rare earths, particularly cobalt and samarium (CoSm).

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which like parts are given the same reference numerals and in which: Figure 1 is a longitudinal section through a first embodiment of the present invention; Figure 2 is a like section of a second embodiment; Figure 3 is a like section of a fragment of a third embodiment; Figure 4 is a like section of a fragment of a fourth embodiment; Figure 5 is a like section of a fragment of a fifth embodiment, and Figure 6 is a like section through a sixth embodiment.

The pressure transducer of Figure 1 is intended for fitting into the intake manifold of a vehicle engine (not illustrated) and includes a metal housing 1 having a central longitudinal bore 2 and a screwthread 3 for screwing the pressure tranducer into the intake manifold. For this purpose, the bottom end portion of the housing 1 is provided with an external hexagonal portion 4.

A corrugated diaphragm 4 is clamped at its edge in the interior of the housing 1. The underside of the corrugated diaphragm remote from a central inlet bore 6 formed in the end face of the housing, carries a squat, cyclindrical permanent magnet 7 which is made from a compound of cobalt and samaricum and which is moved in the direction of the longitudinal axis 8 of the pressure transducer upon the occurrence of alternating pressures acting upon the diaphragm 5. This upper permanent magnet 7 is located opposite, and at a short axial distance from, a second permanent magnet 9 which is also arranged on the longitudinal axis 8 and which, like the magnet 7, is also made from CoSm. The two magnets 7 and 9 are magnetized longitudinally such that their mutually opposite end faces have the same polarity.

A Hall element 10 is provided substantially centrally between the two magnets and, in a preferred embodiment, forms part of a monolithic, integrated semiconductor switching circuit (IC) which, in addition to the Hall element, includes a source of constant current, an amplifier, and a temperature compensator. The integrated switching circuit supplies an output voltage which is proportional to the magnetic induction prevailing at the location of the Hall element and which is fed to an evaluation circuit 11. This evaluation circuit renders it possible to detect adjustment and enables the zero point and the operation to be set such that a specific linear range of the characteristic of the Hall element l.C. is covered upon the axial movement of the upper permanent magnet.The evaluation circuit 11 can be in the form of a hybrid circuit and, in the illustrated embodiment, is mounted in a rubber-elastic damping compound 12 for protection against the effects of vibration. The lower permanent magnet 9 serves for compensation and is mounted the free end of the set-screw 13 which renders it possible to adjust the magnet 9 axially and to set the zero induction. It is thereby readily possible, with a maximum deflection of approximately 0.5 mm of the upper permanent magnet 7, to obtain a substantially linear relationship between the pressure acting upon the diaphragm 5 and the output voltage. Three electrical connection contacts are provided on the underside of the housing, only the two connection contacts 14 and 15 being illustrated.

The special advantage of the illustrated pressure sensor resides in the following: 1. The position ofthe magnetic induction B = 0 lies centrally between the two magnets 7 and 9.

2. The induction B = 0 is readily mechanically adjustable by displacing the compensating magnet 9, particularly when the screw 13 is provided with a fine thread.

3. The operation can commence from B = 0, so that one finds oneself in the satisfactorily linear range of the Hall IC.

4. The detection of an over-pressure or a vacuum ensues in a simple manner from B > 0 or B < 0.

5. Very satisfactory linearity of the output volu tage in dependence upon the indcution ensues upon deflection in the range of zero induction.

6. Since no basic induction exists (offset), it is possible to obtain a high degree of amplification and consequently greater accuracy.

7. A mechanical guide is not required for the first magnet due to the fact that this magnet is secured to the diaphragm.

Figure 2 shows a different embodiment of a pressure transducer in accordance with the invention. In the present instance, in contrast to Figure 1, an aneroid box 17 is used instead of a diaphragm, the upper magnet 7 being secured to the underside of the aneroid box. The other components of the second embodiment are identical to those in Figure 1.

An aneroid box 17 is also used in the embodiment of Figure 3. There is secured to the underside of the aneroid box 17 a retaining pin 18 on which is mounted the Hall IC and which is moved upwardly or downwardly in the direction of the arrows 19 upon a change in the pressure P. Like the lower permanent magnet 9, the upper permanent magnet 7 is stationary and spatially fixed and includes a central through-bore 20 for the retaining pin 18.

Figure 4 shows a further embodiment having a diaphragm which, in contrast to Figure 1, carries the Hall IC 10 on its underside. The upper permanent magnet 7 is disposed above the diaphragm 5, and the lower magnet 9 is disposed below the diaphragm 5 at the same axial distance from the Hall IC 10 as the upper permanent magnet 7. In the same manner as in the embodiment described hitherto, this IC is connected to flexible leads 21 which lead to an evaluation circuit indicated at 11 in Figures 1 and 2.

In the embodiment of Figure 5, the two permanent magnets 7 and 9 and the Hall IC 10 are spatially fixed and arranged coaxially of one another on a transverse axis 23 extending transversely of the longitudinal axis 8. In order to influence, in dependence upon pressure, the magnetic induction acting at the location of the Hall IC 10, there is provided on the underside of the aneroid box 17 a soft-magnetic, wedge-shaped conducting member 24 which extends to a greater or lesser extent into the space between the left hand permanent magnet and the Hall IC 10 and moves in the direction of the arrows 25 parallel to the longitudinal axis of the pressure transducer when the pressure to be measured varies.

The advantages mentioned in connection with Figure 1 also apply to the embodiments of Figures 2 to5.

Owing to the fact that only the Hall element on a diaphragm or diaphragm box moves, the embodiments of Figure 3 and Figure 4 have a particularly satisfactory linearity of the output voltage as a function of the pressure.

The embodiment of Figure 6 constitutes a preferred embodiment of an arrangement in accordance with the invention. As in Figure 3 and Figure 5, an aneroid box 17 is provided and is mounted on a screw-threaded spigot 26 which is provided with a longitudinal bore 25 and which can be screwed to a greater or lesser extent into the bottom 27 of the housing 1 for the purpose of adjusting the aneroid box 17 and can be fixed in its adjusted position by means of a lock nut 28. The first CoSm magnet 7 is fixedly arranged on the inside of the diaphragm, connected to the screw-threaded spigot, of the aneroid box 17. The like pole at the end face of the second CoSm magnet 9 is located opposite the magnet 7, the magnet 9 being mounted on a screw-threaded spigot 29 which is adjustable in the direction of the axis 8 of the housing 1, and which is screwed into a transverse wall 30.The Hall element 10 is arranged between the two magnets 7 and 9 and is secured to the centre of that diaphragm of the aneroid box 17 which is remote from the magnet 7.

An integrated switching circuit 11 for evaluating the voltage supplied by the Hall element 10 is provided in line with the axis 8 and is secured by means of a damping compound 12.

The embodiment of Figure 6 offers the following advantages: 1. Very satisfactory linearity, since the Hall element 10 is moved and the two magnets 7 and 9 are spatially fixed, 2. the use of a diaphragm box is more advantageous than a single diaphragm with respect to linearity and accuracy; 3. it is very simple to manufacture.

It will be appreciated that the embodimetns of Figures 2,3,5 and 6 having a corrugated diaphragm box 17 can be used to measure absolute pressure instead of differential pressure when the box 17 is closed.

Claims

1. A mechanical-electrical transducer for the measurement of pressures, having a diaphragm to sense the pressure to be measured, a Hall effect component and a permanent magnet whose magnetic field supplies at the output of the component an electrical quantity varying in dependence upon the pressure wherein a second magnet is arranged at that side of the Hall effect component which is remote from the first magnet, and like poles of the two magnets are located opposite one another.

2. A transducer as claimed in claim 1, wherein the magnets are made from a compound of cobalt and a rare earth.

3. A transducer as claimed in claim 2, wherein the rare earth is Sm.

4. Atransducer as claimed in claim 1, 2 or 3, wherein the first permanent magnet is arranged on the diaphragm mounted between the said diaphragm and the Hall effect component.

5. A transducer as claimed in claim 1,2 or 3, wherein the two magnets are fixedly arranged.

6. A transducer as claimed in claim 1 or 2, wherein the component is connected to the diaphragm.

7. Atransducer as claimed in claim 5, wherein a soft-magnetic conducting member is connected to the diaphragm and projects between the component and one of the two fixed magnets.

8. A transducer as claimed in claim 5 or 6, wherein the first permanent magnet is fixedly mounted on the diaphragm box.

9. A mechanical electrical transducer substantially as hereinbefore described with reference to Figure 1, Figure 2, Figure 3, Figure 4, Figure 5 or Figure 6 of the accompanying drawings.