WO1998036160A1

WO1998036160A1 - Internal combustion engine valve device

Info

Publication number: WO1998036160A1
Application number: PCT/DE1998/000376
Authority: WO
Inventors: Wolfgang Clemens; Klaus Ludwig; Richard Wimmer; Achim Koch
Original assignee: Siemens Aktiengesellschaft
Priority date: 1997-02-17
Filing date: 1998-02-11
Publication date: 1998-08-20
Also published as: DE19706106A1

Abstract

The invention relates to a valve device (2) comprising electromagnetic actuation means (8) for lifting (h) a valve (3). Also provided are measuring means (12) having a magnetic field-producing element (4) connected to a valve stem (3b') and a magnetic field-sensitive sensor (5). The sensor has a layer system with a magneto-resistive effect (GMR).

Description

description

Valve device of an internal combustion engine

The invention relates to a valve device of an internal combustion engine with actuating means for a stroke movement of a valve, which has a valve disk and a valve stem extending in the direction of movement of the valve. A corresponding valve device is e.g. from the book by H. Grohe: "Otto and Diesel engines", 9th edition,

1990, Vogel-Buchverlag Würzburg (DE), pages 124 to 131.

In known internal combustion engines, the actuating means for moving the individual valves, which are generally referred to as valve drives, are designed purely mechanically. The stroke movement of a valve is e.g. achieved in that a valve spring holding the valve plate of the valve in a filling position on a valve seat is compressed by means of a rocker arm engaging the valve stem, the rocker arm being actuated from a camshaft by means of a bumper with a tappet (cf. the aforementioned publication ).

The object of the present invention is to design the valve device with the features mentioned at the outset in such a way that controlled adjustment of the valve lift is made possible without the need for a camshaft.

This object is achieved in that the actuating means are designed electro-mechanically and that measuring means for contactless determination of the position of the valve are provided which have an element connected to the valve stem for generating a predetermined magnetic field and at least one magnetic field sensitive sensor contain, which has an increased magnetoresistive effect layer system with a measuring layer for detecting the magnetic field, the magnetic field generating element is to be guided relative to the magnetic field-sensitive sensor such that the components of the magnetic field impinging on the measuring layer with a reference axis in the measuring layer plane have a middle Include an angle that is clearly correlated with the respective position of the magnetic field sensitive sensor relative to the magnetic field generating element.

The invention is based on the consideration that the linear movement of the valve stem and thus of the magnetic field generating element rigidly connected to it can be measured in a contactless manner by means of the special, known magnetoresistive layer system despite critical measuring conditions. Because it is the intake and exhaust valves of an internal combustion engine, it is very hot at the sensor location, with typical ambient temperatures of around 150 ° C. In addition, the valve stem can rotate and also tilt slightly. Furthermore, the stroke, which is typically +/- 4 mm, must be measured to an accuracy of approximately 1/100 mm in order to enable effective valve control. It was recognized that sensors with a known magnet effect showing an increased magnetoresistive effect

Have the layer system used under the difficult conditions mentioned. The magnetoresistive effect of such layer systems is isotropic.

With such a magnetoresistive layer system, which in particular can also have a periodically repeating layer sequence, it is also advantageous to control the electromagnetic actuating means of the valve device according to the invention such that the valve strikes hard in its opening and / or closing position. tion is avoided. In addition, the control can be carried out in such a way that the consumption of electrical energy, in particular of the actuating means, remains limited to a relatively low level.

Furthermore, temperature compensation is advantageously possible using the special magnetoresistive layer system. In addition, essentially only the direction of a stray field is advantageously measured with the layer system, so that the characteristic curve of the sensor is not strongly dependent on the distance between the shaft and the sensor. Only the steepness of the characteristic curve is slightly influenced here. In addition, no additional flux guiding elements are required, which would have to be positioned precisely and which could cause magnetic hysteresis. The signal from the sensor is analog and frequency-independent, so that the resolution of the stroke essentially depends only on an evaluating electronics. The signal swing of the special sensors is typically 3% of the basic resistance and is therefore significantly higher than e.g. Hall sensors or anisotropic magnetoresistive sensors under comparable conditions. This also favors the signal / noise ratio when evaluating the sensor signal.

Advantageous refinements of the valve device according to the invention emerge from the dependent claims.

To further explain the invention, reference is made below to the schematic drawing, in which FIG. 1 illustrates a valve device according to the invention. FIG. 2 shows the measurement signal of a sensor of such a valve device in a diagram. FIGS. 3 to 5 show a special embodiment of actuating means of a valve device according to the invention in a representation corresponding to FIG. 1. In FIGS. 6 and 7, special designs of magnetic field generating elements are one such valve device indicated. Corresponding parts are each provided with the same reference numerals in the figures.

The valve device according to the invention, generally designated by 2 in FIG. 1 and shown in longitudinal section, has measuring means 12 for contactless determination of the position of a valve 3, with which an electrical signal dependent on the position is to be generated, which is further processed with downstream electronics . According to the invention, at least one special magnetic field-generating element 4 and at least one special magnetic field-sensitive sensor 5 are to be provided as signal-generating means. This sensor is assigned signal-evaluating electronics, not shown in the figure. It is said to have a thin-layer system which exhibits an increased magnetoresistive effect, which is often referred to as the "Giant Magneto Resistance" (GMR) effect. Corresponding thin-layer systems are known per se (cf., for example, WO 94/17426, WO 94/15223, EP 0 483 373 A or DE-A documents 42 32 244 or 42 43 357. Their magnetoresistive effect M _r should be at least 3%. In general, the agnetoresistive effect M _{r of} known GMR thin-layer systems is defined as follows: M _r = ΔR / R (0) = [R (0) - R (B)] / R (0).

Here R (B) is the electrical resistance in the magnetic field with an induction B and R (0) the resistance in the absence of a magnetic field. Corresponding thin-layer systems have a measuring layer with which the magnetic field H caused by the magnetic field-generating element is detected. This magnetic field should look such that the magnetic field components H) c detected by the layer system of the magnetic field sensitive sensor 5 are arranged in a stationary manner with a relative displacement of the magnetic field generating element 4 Magnetic field-sensitive sensor 5 are aligned at constantly changing angles with respect to the measuring layer of the layer system. A magnetic field H is therefore particularly suitable, which at least largely corresponds to a rod-shaped permanent magnet in a measuring layer plane. A suitable permanent magnet is therefore expediently used as the magnetic field-generating element. The magnetic field generating element is then movable relative to the magnetic field-sensitive sensor 5 so that the components H * of the magnetic field impinging on the measuring layer of the sensor with a reference direction or axis b form an average angle α in the measuring layer plane, which is clearly related to the respective position of the sensor Valve is correlated. It is assumed that the increased magnetoresistive effect (GMR) shows only a dependence on the angle of the measuring layer with respect to the magnetic field components and not on the magnetic field strength.

A magnetoresistive layer system is particularly advantageously provided for the valve device according to the invention, which has magnetic layers with different coercive field strengths that are magnetically decoupled from one another (cf. for example also EP 0 498 344 A). The directions of magnetization of the two layers are generally oriented antiparallel without the action of an external magnetic field. In such a layer system, the magnetically harder layer, often also referred to as the bias layer, or a corresponding layer subsystem, in particular, can be embodied as a so-called artificial antiferromagnet (cf. the aforementioned WO 94/15223). For the valve devices according to the invention described below, an embodiment of such a layer system with at least one artificial antiferromagnet is assumed. For corresponding layer systems, the magnetoresistive effect is also defined as follows:

R _p denotes the resistance of the layer system, which results when the direction of an external magnetic field is directed parallel to a predetermined reference direction. This reference direction of the layer system is determined by the direction of magnetization of the magnetically harder layer or a corresponding layer subsystem and is denoted by b in FIG. The resistance Rab is the resistance of the layer system, which results when the external magnetic field is aligned antiparallel to the aforementioned reference direction.

Of course, the layer system to be provided for a sensor 5 with an increased magnetoresistive effect can also have, in a manner known per se, a periodic repetition of the layer sequence of magnetic layers magnetically coupled or decoupled via at least one intermediate layer with the same or different coercive field strength.

A basic structure of a corresponding valve device of an internal combustion engine can be seen in FIG. 1. The internal combustion engine can be any internal combustion engine, for example an Otto or diesel engine, in which the valve device according to the invention enables access to a combustion chamber that can be controlled by the valve. Consequently, the magnetic field generating element 4 and the at least one magnetic field sensitive sensor 5 are generally at an elevated ambient temperature, for example at a temperature level of over 100 ° C. In Figure 1 are also designated a valve plate and a valve stem of the valve 3 movable along an axis A with 3a and 3b, a valve seat ring with 6, a valve stem guide with 7 and electromechanical actuating means for moving the valve 8. According to the exemplary embodiment shown, these actuating means, which are also referred to as valve actuators, have a valve spring 8a which is supported on one side on an engine block part 9, in which an inlet or outlet channel 10 for a gas mixture or for an exhaust gas. On the opposite side, the valve spring 8a is supported on a valve spring plate 8b. To compress the valve spring 8a and thus to open the valve, the actuating means 8 are also provided with a lifting magnet 8c enclosing the valve stem 3b. In the excited state, the lifting magnet then attracts a, for example, plate-shaped lifting element 8d rigidly connected to the valve stem. This lifting element therefore consists of a ferromagnetic material, while the valve stem is non-magnetic, at least in the area of the lifting magnet 8c. The valve 3 can thus be actuated electromechanically.

As can further be seen from FIG. 1, the GMR sensor 5 is used for contactless detection and control of the valve position during the stroke movement h of the valve illustrated by a double arrow. For this purpose, on the side of the valve stem 3b facing away from the valve plate 3a, the magnetic field generating element 4 is preferably attached or in the form of a permanent magnet to a section 3b 'of this stem outside the magnetic field region of the lifting magnet 8c

Part integrated. In the exemplary embodiment shown, the permanent magnet is arranged such that the magnetization of this magnet, illustrated by a north pole Np and a south pole Sp, points in the direction of the axis A or the stroke movement h of the valve. In particular, the permanent magnet should have an at least largely cylindrical or hollow cylindrical shape, so that rotation of the valve has practically no influence on the stray field generated by the magnet. From this stray field, a component striking the measuring layer of the GMR sensor 5 is shown in the figure. nente illustrated by an arrowed line marked H *.

During the stroke movement h of the permanent magnet, this stray field component H * strikes the measuring layer of the GMR sensor 5 at different angles oc. The angle α is defined by the direction of the magnetic field component H * with respect to a reference axis b in the measuring layer plane. According to the selected exemplary embodiment, this reference axis is perpendicular to axis A. Because of the known cosα dependency on GMR sensors (cf., for example, WO 94/17426), the structure shown shows an at least largely linear change in resistance of the sensor depending from the deflection of the permanent magnet from a predetermined zero position.

A characteristic curve of the sensor in an arrangement according to FIG. 1 is shown in a diagram in FIG. This characteristic curve shows the dependency of a sensor signal S plotted in the ordinate direction (in arbitrary units) on the valve lift or the stroke movement h. The deflection in the ordinate direction resulting from the stroke movement is plotted on the abscissa from a reference position (in arbitrary units). This takes advantage of the fact that a GMR sensor is essentially sensitive to the direction of the external magnetic field relative to an intrinsic reference axis, but not to the field strength of the external field (as long as the field strength is in a certain range). This dependency is shown in a cosine curve of the sensor resistance as a function of the angle of the external field to the reference axis. When the valve with the permanent magnet moves up and down, the direction of the stray field of the magnet rotates at the sensor position; thus the characteristic curve of the sensor also changes, as shown in FIG. 2. Over a certain range of This characteristic curve is linear. This linear range depends on the length of the magnet and the distance between the sensor and the axis of the valve stem. In order to obtain the most symmetrical possible characteristic, the sensor should preferably be arranged so that it is in the middle position of the valve (in the half-open position State) is located essentially at the level of the center M of the magnet. Such a case is the basis of the characteristic curve of FIG. 2.

Deviating from the arrangement option shown in Figure 1 of permanent magnet (magnetic field generating element) 4 and sensor 5, according to which the magnetic field-sensitive measuring layer of the sensor lies in a plane whose normal is perpendicular to the axis A of the magnet, the sensor can also be mounted so that the plane of its magnetic field sensitive measuring layer has a normal which runs parallel to the axis A. In addition, several corresponding sensors can also be provided, which can also be oriented differently with respect to the axis A. For example, it is possible to arrange several sensors on an imaginary surface of a fictitious cylinder concentrically surrounding axis A. In particular, two sensors arranged diametrically on such an imaginary lateral surface can be provided. In addition, a bridge circuit can advantageously be applied with several sensors. In this way, temperature compensation of the measurement signal can be achieved using additional electronic circuit means, since the sensor properties have an at least largely linear temperature profile.

In the embodiments with reference direction b and sensor plane of the sensor 5, preferably perpendicular to the valve axis A, slight deviations from the 90 ° orientation, ie slight tilting, may also be tolerated. According to the exemplary embodiment shown in FIG. 1, it was assumed that the valve spring 8a is a spring which is subjected to pressure and which is further compressed to open the valve 3 by means of the solenoid 8c. Of course, other actuating means for opening and closing the valve are also suitable. For example, tension springs can also be provided, which are pulled further apart by means of a lifting magnet. In other words, a lifting magnet and a lifting element of the valve device according to the invention are understood to mean any type of means by means of which the spring length can be changed in order to open or close the valve. If necessary, a valve spring can also be completely dispensed with in the actuating means 8 of the valve device according to the invention and its function can be performed by a further lifting magnet with a lifting element. It is then also possible to open and close the valve by performing its stroke movement h by means of a single stroke magnet with a corresponding stroke element.

FIGS. 3 to 5 show a special embodiment of actuating means 15 for opening and closing a valve 3 with the valve open (FIG. 3) or with the valve half open, in an equilibrium position (FIG. 4) or with the valve closed, as a longitudinal section - light. The actuating means here have two lifting magnets 16 and 17, the lower magnet 16 facing the valve plate 3a serving to open the valve and the upper magnet 17 serving to close the valve. By means of two valve springs 18 and 19 below the lower magnet 16 and above the upper magnet 17, an annular disk-shaped lifting element 8d connected to a valve stem 3b is expediently held in an equilibrium position in the absence of or equal excitation of the magnets 16 and 17, in which case the Valve 3 is in the half-open state (see FIG. 4). The excitation of the magnets is over in the figure Measuring means (12), not shown, are controlled with the special magnetoresistive layer system of their at least one sensor. In the figure there is also a hydraulic centering element 20 which surrounds the valve stem 3b and which serves for exact guidance of the valve during the lifting movement.

Of course, the measuring means 12 according to FIG. 1 can also be arranged elsewhere on the valve stem, particularly from the point of view of a compact structure and a limited expansion of the valve stem. An embodiment is indicated as a longitudinal section in FIG. 6, in which a hollow cylindrical permanent magnet serving as a magnetic field generating element 22 is arranged around a valve disk 19a of a valve spring 19, which is, for example, the upper valve spring shown in FIGS. 3 to 5 19 can act. The permanent magnet 22 in turn advantageously has a magnetization pointing in the axial direction and rotationally symmetrical with respect to the valve axis A. FIG. 6 also shows a holder 23 with a magnetic field-sensitive sensor 5, the reference direction b of which runs perpendicular to the direction of magnetization of the element generating the magnetic field.

In the embodiments of valve devices according to the invention on which FIGS. 1 and 6 are based, it was assumed that the magnet used as the magnetic field generating element 4 or 22 is axially magnetized. However, such an alignment of the magnetization is not absolutely necessary. A magnetic field generating element with radial magnetization can also be provided. It is again important that the reference axis b of the magnetic field-sensitive sensor is at least largely perpendicular to the direction of magnetization. A corresponding exemplary embodiment is indicated in FIG. 7. The measuring means 25 shown there of a valve device according to the invention The only difference from the embodiment 21 according to FIG. 6 is that the magnetic field generating element 26 is magnetized in the radial direction in the form of a hollow cylindrical permanent magnet. In this case too, the magnetization is rotationally symmetrical with respect to the valve axis A. The associated magnetic field-sensitive sensor 27 then has a reference direction or axis b which is at least approximately in the axial direction, that is to say perpendicular to the magnetization direction of the element 26. Such an embodiment of the measuring means 25 has the following advantages in particular:

While for an axially magnetized permanent magnet such as e.g. 1 results in a particularly homogeneous field strength distribution, however, this magnet has a relatively large axial length, which is generally greater than the stroke movement h. The material requirement for such a magnet is accordingly large. In contrast, permanent magnets with radial magnetization such as the magnet

26 according to FIG. 7 in the axial direction be significantly shorter than the stroke movement h. This results in a corresponding saving in material. In addition, the sensor 27 can then be integrated particularly well into a housing required for the measuring and actuating means.

If a rotation of the valve axis A can be prevented in a valve device according to the invention, embodiments of magnetic field generating elements can also be provided in which rotationally symmetrical magnetization is not provided. Then e.g. in an embodiment of the measuring means 25 according to FIG. 7, the hollow cylindrical permanent magnet 26 is replaced by a bar magnet with a radial bar axis, one magnetic pole of which is the sensor

27 is facing. If the magnetic field-sensitive sensor should be arranged in the area of magnetic interference fields, which are generated, for example, by a lifting magnet of the actuating means, in the valve devices according to the invention, in particular from the point of view of a compact design, magnetic shielding means can of course also be provided to reduce the interference field.

The valve devices according to the invention shown in FIGS. 1, 6 and 7 each have a permanent magnet as the magnetic field generating element 4 or 22 or 26. However, the magnetic fields generated by these magnets can also be produced by electromagnets.

Claims

claims

1. Valve device of an internal combustion engine with actuating means for a stroke movement of a valve, which has a valve disk and a valve stem extending in the direction of movement of the valve, characterized in that the actuating means (8, 15) are designed electromechanically and that measuring means (12, 21, 25) For a contactless determination of the position of the valve (3), there are an element (4, 22, 26) connected to the valve stem (3b ') for generating a predetermined magnetic field (H) and at least one magnetic field sensitive sensor (5, 27) contain a layer system showing an increased magnetoresistive effect with a measuring layer for detecting the magnetic field (H), the magnetic field generating element (4, 22, 26) being guided relative to the magnetic field sensitive sensor (5, 27) in this way, that the components (H _k ) of the magnetic field impinging on the measuring layer with a reference axis (b) in of the measuring layer plane include an average angle (α) which is clearly correlated with the respective position of the magnetic field sensitive sensor (5, 27) relative to the magnetic field generating element (4, 22, 26).

2. Valve device according to claim 1, d a d u r c h g e k e n n z e i c hn e t that the magnetic field generating element (4, 22) is preferably formed by a permanent magnet.

3. Valve device according to claim 2, characterized by a permanent magnet as a magnetic field-generating element (4, 22), the magnetization of which extends at least approximately in the direction of the axis (A) of the valve stem (3b, 3b ').

4. Valve device according to claim 2, g e k e n n z e i c h n e t by a permanent magnet as a magnetic field generating element (26), the magnetization of which is directed at least approximately perpendicular to the axis (A) of the valve stem (3b, 3b ').

5. Valve device according to one of claims 2 to 4, g e k e n e z e i c h n e t by a permanent magnet as a magnetic field-generating element (4, 22, 26) with an at least largely cylindrical or hollow cylindrical shape.

6. Valve device according to one of claims 1 to 5, characterized by an arrangement of the at least one magnetic field sensitive sensor (5, 27) such that the normal on the level of its measuring layer is at least approximately perpendicular to a magnetic axis (A) of the magnetic field generating element (4, 22, 26) is aligned.

7. Valve device according to one of claims 1 to 5, g e k e n n z e i c h n e t by an arrangement of the at least one magnetic field sensitive sensor such that the normal is aligned at least approximately parallel to a magnetic axis (A) of the magnetic field generating element on the level of its measuring layer.

8. Valve device according to one of claims 1 to 7, characterized by an arrangement of the at least one magnetic field-sensitive sensor (5) such that it is at a central position of the valve (3) between the open and closed state at least approximately at the level of the magnetic center ( M) of the magnetic field generating element (4, 22).

9. Valve device according to one of claims 1 to 8, characterized in that the actuating means (8) contain a valve spring (8a), the axial length of which by means of a magnet acting on a ferromagnetic lifting element (8d) of the valve stem (3b) lifting magnet (8c ) is to be changed.

10. Valve device according to one of claims 1 to 8, characterized in that the actuating means (15) contain two lifting magnets (16, 17) with associated valve springs (18 and 19), by means of which the valve (3) in the absence or same excitation of the magnets (16, 17) is in a semi-open state.

11. Valve device according to one of claims 1 to 10, g e k e n n z e i c h n e t by a plurality of sensors.

12. Valve device according to claim 11, d a d u r c h g e k e n n z e i c h n e t that several sensors are interconnected to form a bridge circuit.

13. Valve device according to one of claims 1 to 12, g e k e n n z e i c h n e t by at least one sensor (5, 27) with a layer system which has magnetic layers with different coercive field strength.