Patent Description:
<CIT> discloses to valves and, more particularly to valves of the pneumatic type.

<CIT> describes electroactive polymer transducers. They are biased in a manner that provides for increased force and/or stroke output, thereby offering improved work potential and power capacity.

<CIT> discloses valve that controls the movement of fluids such as liquid or gas.

<CIT> discloses an electromagnetic valve consisting substantially of an electromagnet in the form of a hollow cylinder through which the fluid passes, the movable core of the said valve playing the role of valve stem and of valve per se. It relates to a fully open or fully closed electromagnetic valve.

<CIT> discloses a valve device for fluids in which the valve or control member is normally resiliently retained in a valve-closed position and moved to a valve-open position by electromagnetic means aided by permanent magnets. <CIT> discloses an electromechanical control valve in which a poppet is biased against a seat therefor within an enclosing chamber having inlet and outlet ports and which is balanced against fluid pressure forces.

<CIT> discloses another known valve positioner system.

A valve positioner, respectively a system including valve positioners with pneumatic output, faces two contrary business demands. On the one hand, there is a demand for high pneumatic pressure to operate the pneumatic actuator; on the other hand, there are stringent requirements for a low power consumption of the overall system. For this, a conventional positioner includes several submodules. These submodules can be seen as force amplifiers. However, this state-of-the-art arrangement leads to a complex and bulky setup. In order to operate high pneumatic pressure with low, particularly electrical, power, a close to equilibrium topology is applied, in which the forces by the pneumatic pressure are balanced by e.g. compensation springs. Thus, only a small force, and correspondingly energy, is sufficient to control a position of the process valve.

This small amount of "controlled force" is conventionally also based on pneumatic pressure. Therefore, a "pressure reducer" is used, which reduces the total pneumatic pressure partly to provide low-pressure to a subsystem, which is configured to be controlled with low electrical power. This "low-pressure-subsystem", is the "pilot stage". Using other words, the pilot stage acts as a force amplifier, controlling a larger force of a pneumatic pressure by a smaller controlled force. The usage of pilot stages in general is inefficient and cost intensive. Former power requirements have led to the design of a balanced main stage and a controllable sub-unit (pilot stage) that is to control a fraction of the pneumatic pressure.

State of the art systems of valve positioners with pneumatic output s are operated using such a pilot stage, which can be configured in different ways and are based on different technologies, as e.g. based on a piezo-nozzle or a flapper-nozzle.

The usage of pilot stages in general leads to a bulky design and is cost intensive. A further problem using a pilot stage designs for valve positioners is a constant blow-off of the pneumatic medium, which results in inefficiency.

This problem can be overcome by using a positioner drive for controlling a valve positioner with pneumatic output, wherein the positioner drive is configured to be mechanically coupled to a valve of the valve positioner with pneumatic output for controlling the valve positioner with pneumatic output.

Using other words, by using such a positioner drive the valve positioner with pneumatic output, or units of a main stage of a valve positioner with pneumatic output system, is driven and/or operate directly by the positioner drive to make a pilot stage and/or a pressure reducer obsolete to save energy and/or to have a less bulky system of valve positioners with pneumatic output. That means the valve positioner with pneumatic output driven by a positioner drive can result in a reduced design space, as compared to a system of valve positioners with pneumatic output as is state-of-the-art.

This direct actuation, not using pneumatic pressure, of units of the main stage by a positioner drive can be controlled by electrical signals and/or electrical power provided to the positioner drive.

The positioner drive can be configured to be mechanically coupled directly to a plunger of the valve of the valve positioner with pneumatic output to set up a simple system using such valve positioners with pneumatic output including positioner drives, which can be electrically driven directly.

The concept of direct driving the valve positioned using a positioner drive removes a pilot stage as is state of the art, and thereby reduces the system complexity and increases robustness.

Moreover, the system becomes more controllable, since each main stage component can be controlled individually, as opposed to one pilot stage controlling a multitude of main stage elements in the state of the art.

Such a positioner drive can be based on an electromagnetic actuator, in which an input electrical power is converted to an output mechanical power, in respect to force and speed, are a suitable candidate actuator technology.

A positioner drive driving the valve positioner directly means that the actuator can be directly mechanically coupled to a moving part of the main stage without any mechanical transmission.

For a typical valve positioner the valve is mechanically coupled with a plunger of the valve, which is movable arranged within the valve positioner and there results a stem force to be applied to hold the plunger of the valve at a given position, to maintain a certain valve gap opening. Using a system of positioner drives directly driving the valve positioner, this force must be provided by the positioner drive, e.g. by an actuator of the positioner drive.

The stem force can be dominated by a stiffness of flexible sealings of the valve positioner, if a gap of a valve of the valve positioner is in a fairly open position. When the valve gap is small, just before the valve is closed, the stem force typically increases steeply with the remaining valve gap to drive a valve seat of the valve positioner into a sealed position. Consequently, the actuator must provide a high force at this stage.

The present invention is related to a valve positioner system, comprising a valve positioner and a positioner drive system, the positioner drive system comprising an electromagnetic actuator and a magnetic force compensator and a use of a valve positioner system with subject matter as described in the independent claims.

Advantageous modifications of the invention are stated in the dependent claims. All combinations of at least two of the features disclosed in the description, the claims, and the figures fall within the scope of the invention. In order to avoid repetition, features disclosed in accordance with the method shall also apply and be claimable in accordance with mentioned systems.

In this entire description of the invention, some features are provided with counting words to improve readability or to make the assignment more clear, but this does not imply the presence of certain features.

To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, there is provided a valve positioner system according to claim <NUM>. The magnetic force compensator for at least partially compensating a closing force required to shift a valve of a pneumatic positioner into a closed position, comprises a magnetic means, including a permanent magnet, and a magnetic counterpart for the magnetic means, wherein the magnetic means and the magnetic counterpart are configured to interact to create an attracting force for the at least partially compensation of the closing force; and the magnetic force compensator is mechanically coupled to the valve of the pneumatic positioner.

The attracting force is created by a magnetic coupling between the magnetic means and the magnetic counterpart.

Advantageously the magnetic force compensator can be used instead of a mechanical spring to provide the force required to compensate the mentioned closing force, respectively a stem force, wherein the magnetic force compensator is configured to provide the closing force, which can be just strong enough to drive the valve into sealed position, but can be configured to not be any larger, such that the force required from the actuator can be minimized.

By compensation of the closing force, respectively stem force, by using the magnetic force compensator with a valve positioner and an electromagnetic actuator a system can be provided and configured, e.g. by additional springs, wherein the valve of the valve positioner is open or closed in case of a fail operation of the positioner drive and/or in case there is no electrical power provided to the positioner drive.

Advantageously, the magnetic force compensator can be configured by the magnetic coupling between the magnetic means and the magnetic counterpart, separated by magnetic gap, to provide a force characteristic, that is similar to a relationship between the stem force and a valve gap. To compensate the stem force, the magnetic force compensator is arranged in parallel to a positioner drive in the form of an electromagnetic actuator, which is configured to operate the valve positioner. The magnetic means or the magnetic counterpart can be directly mechanically coupled to the valve positioner for at least partially compensating of the stem force.

The magnetic counterpart comprises a ferromagnetic material, configured to interact with the magnetic means.

Advantageously, by configuring the magnetic counterpart as described above the magnetic coupling can be adapted to the stem force versus valve relationship required to shift the valve of the valve positioner.

The magnetic means comprises a yoke arranged and configured to increase the attracting force and to adapt an attracting force versus valve-shift relationship to a closing force versus valve-shift relationship.

Advantageously by configuring and/or shaping and/or arranging the yoke of the magnetic means the magnetic coupling relationship between the magnetic means and the magnetic counterpart can be adapted to the stem force versus valve gap relationship.

According to an aspect, the magnetic means is shaped as a circular ring.

The magnetic field of the magnetic means can be oriented vertical to the shift direction of the plunger of the valve.

According to another aspect, the yoke of the magnetic means is shaped as a circular ring and/or a circular disc.

Adapting the form of the yoke of the magnetic means helps to adapt the magnetic force compensator to the specific needs to compensate the stem force.

According to an aspect, the magnetic means comprises a pole face adjacent to the permanent magnet to adapt the attracting force versus valve-shift relationship to the closing force versus valve-shift relationship.

Combining the magnetic means with a specific formed and arranged pole face enables to adapt the magnetic force compensator to the stem force versus valve gap relationship.

According to an aspect, the magnetic means includes a plurality of permanent magnet units magnetically coupled to the yoke.

Using other words, the yoke can embed a plurality of permanent magnets, which can be distributed within the yoke evenly, particularly in respect to a rotational symmetry.

According to the invention, the magnetic force compensator includes an adjustment means, which is configured for adjusting the magnetic coupling between the magnetic means and the magnetic counterpart to adapt the attracting force versus valve-shift relationship to the closing force versus valve-shift relationship.

Advantageously, such an adjustment means can be used to compensate for assembly and material property tolerances that occur in practice. The adjustment means can be used to modify the characteristics of the magnetic force versus magnetic relationship. A simple example of an adjustment means can be a means to adjust the magnetic gap between the magnetic means and the magnetic counterpart, by modification of the distance between the magnetic means and/or the magnetic counterpart. This can be used to adjust the valve gap to the magnetic gap and/or the magnetic force versus magnetic gap relationship to the stem force versus valve gap relationship.

According to an aspect, the magnetic force compensator is configured, and arranged in respect to the valve of the pneumatic positioner, to lock the valve in case of fail operation of the electromagnetic actuator for controlling the pneumatic positioner; or to open the valve in case of fail operation of the electromagnetic actuator for controlling the pneumatic positioner.

The magnetic force compensator can be provided by a spring accordingly, to keep the valve open or closed, i.e. "Fail to close", in case of fail operation of the positioner drive and/or to provide a power off status of the positioner drive.

By this there is provided a defined state at non-power to force the valve of the valve positioner to a closed and sealed position.

There is provided a positioner drive system for controlling a valve positioner, including an electromagnetic actuator and a magnetic force compensator, as described above, wherein the electromagnetic actuator is based on an electromagnetic Lorentz effect and/or an electromagnetic reluctance effect.

There is provided a valve positioner system, including a valve positioner and a positioner drive system, as described above, wherein the positioner drive system is mechanically coupled to a valve of the valve positioner for controlling the valve positioner.

There is proposed a use of a magnetic force compensator, which includes a magnetic means and a magnetic counterpart, as described above, for at least partially compensating a closing force, wherein the closing force is required to shift a valve of a valve positioner into a closed position.

This direct actuation by a positioner drive, not using pneumatic pressure to operate units of the main stage, can be controlled by electrical signals and/or electrical power provided to the positioner drive.

Advantageously the valve positioner, which is mechanically coupled to a positioner drive can provide a robust system, because it can be built by a less complex mechanical construction. In addition, such a valve positioner with pneumatic output can be configured to be more robust towards temperature changes and external vibrations than a pneumatic pilot stage and by this it can be adapted to a plurality of production environments. To drive the valve positioner with pneumatic output directly reduces the requirements in respect to a quality of the air of the overall pneumatic system, because it is less sensitive to particles distributed by the air, which may get stuck within, e.g., a pneumatic pilot stage. A separate operation of the individual valves of the system of valve positioners with pneumatic output by the corresponding positioner drives can improve the performance of the system of valve positioners with pneumatic output. Because there is no steady state air flow necessary for a pilot stage this steady-state air consumption is eliminated.

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiments of the invention and together with the description serve to explain the principle of the invention. The drawings display:.

<FIG> sketches schematically a state-of-the-art valve positioner <NUM> with pneumatic output mechanically coupled to a positioner drive <NUM>, which is directly mechanically coupled to a valve <NUM> of the valve positioner <NUM>, wherein the valve positioner is provided with a reset spring <NUM> to closed the valve <NUM> in case the positioner drive <NUM> is off and/or in a fail mode.

The state-of-the-art valve positioner with pneumatic output <NUM> includes a valve <NUM> and a plunger <NUM> of the valve mechanically coupled to the valve <NUM>, a first valve compartment <NUM> and a second valve compartment <NUM>, which can be pneumatically coupled by the valve <NUM> and a first sealing diaphragm <NUM>, which seals the first compartment <NUM> in respect to an outside of the valve positioner <NUM> with pneumatic output as well as a second sealing diaphragm <NUM>, configured to seal the second compartment <NUM> of the valve positioner <NUM> to the outside of the valve positioner <NUM> with pneumatic output. The first and the second sealing diaphragms <NUM>, <NUM> are mounted in a housing of the valve positioner <NUM> and are coupled to the plunger <NUM> of the valve.

A "Fail to close" functionality of the valve positioner <NUM> can be required by applications of the valve positioner <NUM> to ensure that the valve <NUM> of the valve positioner <NUM> is closed in case of a failure. The requirement can include a functionality of the valve positioner <NUM> with an actuator coupled to the valve positioner <NUM> that a defined state is achieved for a non-electrical power status; meaning that the valve positioner <NUM> is closed and sealed, e.g. if the electrical power of the actuator is cut off.

This can be achieved by the reset spring <NUM> as shown in <FIG>. For operation of the valve positioner <NUM> a positioner drive <NUM> has to work against that spring <NUM> to operate the valve <NUM>.

<FIG> shows a diagram, where a force F required to shift the valve <NUM> of the valve positioner <NUM> into a closed position is plotted against a valve gap of the valve <NUM> of the valve positioner <NUM> according to a state-of-the-art valve positioner <NUM> as shown.

A force <NUM> of the reset spring <NUM> is also plotted against the valve gap within the diagram. It is shown by the gradient of the force <NUM> of the reset spring <NUM> that the reset spring <NUM>, if mechanically coupled to the valve <NUM> of the valve positioner <NUM>, is configured to make sure that the force F of the reset spring <NUM> is high enough to force the valve <NUM> into the closed and sealed position, if e.g. the positioner drive <NUM> fails.

A stem force <NUM>, required to shift the valve <NUM> of the valve positioner <NUM>, which results from a closing of the valve <NUM>, versus valve gap curve starts with a flatter slope section 130a, when the valve gap is shifted to a closed position starting with an open position. This is because the stem force in the first section 130a is primary caused by a stiffness of the flexible sealings of the valve positioner <NUM>.

When the valve gap starts to close, the force F to drive the valve seat into a sealing position increases steeply, as shown in a steeper second segment 130b of the curve <NUM>. Consequently, the positioner drive <NUM> must provide a high force in this steeper segment 130b.

As becomes clear from the diagram, the spring force, caused by the reset spring <NUM>, is higher than the stem force <NUM> such that the reset spring <NUM> can drive the valve <NUM> into a sealed position. To open and/or keep a position of the valve <NUM> of the valve positioner <NUM> the positioner drive <NUM> can be configured to provide a force, which corresponds to the difference between the force of the reset spring <NUM> and the stem force <NUM>. It has to be noted that the diagram does not take into account the direction of the forces, but plots the absolute values of the forces. Note that the force of the reset spring decreases towards the sealed position of the valve <NUM>, which is the end of the spring-driven motion.

The stem force must be applied to hold the moving shaft at a given position, to maintain a certain valve gap opening. This force must be provided by the positioner drive <NUM>.

<FIG> sketches schematically a valve positioner <NUM> with pneumatic output, which is controlled by a positioner drive <NUM> and mechanically coupled to a force compensator <NUM>. The positioner drive system of <FIG> is not according the claimed invention.

The force compensator <NUM> is sketched as an ideal force compensator <NUM>, whose force would be just high enough to drive the valve <NUM> into the sealed position and/or for compensation the stem force, corresponding to the stem force valve gap relationship <NUM>, such that the force required of the positioner drive <NUM> to control the valve positioner <NUM> can be minimized.

<FIG> shows a diagram, where a required stem force F curve <NUM> to shift a valve <NUM> of the valve positioner <NUM> into a closed position is plotted against a valve gap of the valve <NUM> of the valve positioner <NUM> according to a state-of-the-art valve positioner <NUM> as shown corresponding to the diagram of <FIG>.

A force curve <NUM> of an ideal force compensator <NUM> is also plotted against the valve gap within the diagram. The force of the force compensator <NUM> related to the valve gap <NUM> corresponds to the stem force valve gap relationship <NUM>, such that the force provided by the positioner drive <NUM> to control the valve positioner <NUM> can be minimized.

<FIG>sketches schematically variations of valve positioner <NUM> with a directly mechanically coupled positioner drive <NUM> as well as a direct mechanically coupled force compensator <NUM> configured parallel and mechanically coupled to a plunger <NUM>, which is coupled to a valve of the valve positioner <NUM>. The positioner drive system of <FIG>and <FIG> is not according the claimed invention.

In <FIG> the force compensator <NUM> comprises a magnetic means <NUM>, including a permanent magnet, which is mechanically coupled to the valve <NUM> of the valve positioner <NUM> for at least partially compensation of the stem force needed to shift the valve <NUM> of the valve positioner <NUM>. The magnetic means <NUM> is magnetically coupled to a magnetic counterpart <NUM> with a small magnetic coupling gap to provide a magnetic force versus coupling relationship to approximate the stem force valve gap relationship <NUM> of the valve positioner <NUM>. Therefore, the force compensator <NUM> is arranged mechanically parallel to the positioner drive <NUM>.

<FIG> corresponds to <FIG>, but here the magnetic means <NUM>, including a permanent magnet, is fixed and the magnetic counterpart <NUM> is mechanically coupled to the valve <NUM> of the valve positioner <NUM> for at least partially compensation of the stem force needed to move the valve <NUM> of the valve positioner <NUM>. As described above, the magnetic means <NUM> is magnetically coupled to a magnetic counterpart <NUM> with a small magnetic coupling gap to provide a magnetic force versus magnetic gap relationship <NUM> to approximate the stem force versus valve gap relationship <NUM> of the valve positioner <NUM>. Choosing between the embodiments as described with <FIG> can take into account the weight of the magnetic means <NUM> and/or the magnetic counterpart <NUM>, in case there is a significant weight difference between the magnet means <NUM> and the magnetic counterpart <NUM>.

<FIG> corresponds to <FIG>, but the force compensator <NUM> is configured to form an integral part of the positioner drive system <NUM>, <NUM>. This can result in a compact assembly of a positioner drive system.

<FIG> sketches schematically half a part of a cross section of a magnetic force compensator <NUM> comprising a magnetic means <NUM> and a magnetic counterpart <NUM>. The structure of the magnetic means <NUM> and the magnetic counterpart <NUM> is rotationally symmetric in respect to a z-axis drawn as a dot dash line. A permanent magnet <NUM> of the magnetic means <NUM> is magnetized parallel to that z-axis and surrounded partially at two sites, not including the site of the permanent magnet <NUM> facing the magnetic counterpart <NUM>, by a yoke <NUM>. The magnetic counterpart <NUM> is arranged separated by a magnetic gap adjacent to the magnetic means <NUM>, such that the magnetic means <NUM> and the magnetic counterpart <NUM> create a magnetic coupling resulting in an attracting magnetic force between the magnetic means <NUM> and the magnetic counterpart <NUM>.

Such a magnetic force compensator <NUM> can be directly mechanically coupled to a valve of the valve positioner <NUM> with the magnetic means <NUM> or the magnetic counterpart <NUM>, e.g. by mechanical coupling the magnetic force compensator <NUM> to the plunger <NUM> of the valve of the valve positioner <NUM>. Either the magnetic means <NUM> or the magnetic counterpart <NUM> can be coupled to the plunger <NUM> of the valve.

<FIG> shows a diagram, which relates to the magnetic force compensator <NUM> of <FIG>, where a force F, created by the attracting magnetic force of the magnetic means <NUM> and the magnetic counterpart <NUM>, is plotted against a magnetic gap distance between the magnetic means <NUM> and the magnetic counterpart <NUM>.

The resulting curves <NUM> a, b, c correspond to different diameters, a) <NUM>; b) <NUM>; c) <NUM>, of the permanent magnet <NUM>, where the larger diameter corresponds to the steeper form of the curve respectively. For comparison a required force F to shift a valve <NUM> of the valve positioner <NUM> into an open position relationship <NUM> is plotted against a valve gap x of the valve <NUM> of the valve positioner <NUM>.

As shown by adapting the diameter of the permanent magnet <NUM> as well as by adapting other configurations of the magnetic force compensator <NUM>, as e.g. a height of the permanent magnet, the relationship of the attracting force F of the magnetic force compensator <NUM> can be adapted to the required stem force to shift the valve <NUM> of the valve positioner <NUM>.

<FIG>and <FIG> schematically sketches further half cross sections of rotational symmetric variations, in respect to a configuration of the magnetic means <NUM>, of the magnetic force compensator <NUM> with indicated magnetic flux lines within the yoke <NUM> and the magnetic counterpart <NUM> as computed by finite-element simulations.

In <FIG> a yoke <NUM>, as an "inner yoke", of the magnetic means <NUM> is formed L-shaped as a ring rotational symmetric in respect to the z-axis with the yoke <NUM> adjacent to the rotational symmetric permanent magnet <NUM> at an inner site and opposite to the magnetic counterpart <NUM> of the permanent magnet <NUM>, wherein the permanent magnet <NUM> is also formed as a ring in respect to z-axis.

In <FIG> a yoke <NUM> of the magnetic means <NUM> is shown, formed as an "outer yoke", partially as a disc rotational symmetric in respect to the z-axis covering the permanent magnet <NUM>-shaped at a site opposite to the magnetic counterpart <NUM> and wherein another part of the yoke <NUM> is adjacent at an outside of the permanent magnet <NUM>, which is formed as a ring in respect to the z-axis.

In <FIG> a yoke <NUM> of the magnetic means <NUM> is shown, formed as an "inner and outer yoke", incorporating the permanent magnet <NUM> at three sites leaving the site adjacent to the magnetic counterpart <NUM> open, wherein the permanent magnet <NUM> is formed as a ring in respect to the z-axis.

By adapting the magnetic force compensator corresponding to the shown variations enables an adaption of the attracting force versus magnetic gap distance relationship 450a, b, c to be adapted to the required stem force versus valve gap relationship <NUM> to shift the valve <NUM> of the valve positioner <NUM> into a closed position.

<FIG> schematically sketches further modifications of the magnetic force compensator <NUM> additionally incorporating and configuring magnetic pole faces <NUM> for adaptation of the attracting force created by a magnetic means <NUM> and the magnetic counterpart <NUM> to the required force to shift the valve <NUM> of the valve positioner <NUM> into a closed position.

All four <NUM>-D cross sections of the magnetic force compensators <NUM> are rotationally symmetric around the z-axis, and comprise axially magnetized permanent magnets <NUM> and provide specially shaped ferromagnetic material, as e.g. iron, parts called magnetic pole faces <NUM>. The ferromagnetic pole faces <NUM> are directly adjacent to the permanent magnet <NUM> and they may be utilized to influence the magnetic force vs magnetic gap relationship of the magnetic force compensator <NUM> according to a required stem force versus valve relationship <NUM>.

<FIG> schematically sketches a segment of a rotational symmetric magnetic force compensator <NUM> in respect to a z-axis, where several permanent disc magnets <NUM> are inserted into the holes within the transparent drawn yoke <NUM> of the magnetic means <NUM>. The drawn magnetic counterpart <NUM> is formed as a disc shaped ferromagnetic part <NUM>.

Claim 1:
A valve positioner system, comprising:
a valve positioner (<NUM>); and
a positioner drive system;
wherein the positioner drive system is mechanically coupled to a valve (<NUM>) of the valve positioner (<NUM>) for controlling the valve positioner (<NUM>),
wherein the positioner drive system for controlling the valve positioner (<NUM>), comprises:
an electromagnetic actuator (<NUM>);
wherein the electromagnetic actuator is based on an electromagnetic Lorentz effect or an electromagnetic reluctance effect,
a magnetic force compensator (<NUM>) for at least partially compensating a closing force required to shift the valve (<NUM>) of the valve positioner (<NUM>) into a closed position, wherein the magnetic force compensator (<NUM>) comprises:
a magnetic means (<NUM>), comprising a permanent magnet (<NUM>); and a magnetic counterpart (<NUM>);
wherein the magnetic means (<NUM>) and the magnetic counterpart (<NUM>) are configured to interact to create an attracting force for the at least partially compensation of the closing force;
wherein the magnetic counterpart (<NUM>) comprises a ferromagnetic material, configured to interact with the magnetic means (<NUM>),
wherein the magnetic force compensator (<NUM>) is mechanically coupled to the valve (<NUM>) of the valve positioner (<NUM>);
wherein the electromagnetic actuator (<NUM>) and the magnetic force compensator (<NUM>) are arranged parallel to each other and are directly mechanically coupled to a plunger (<NUM>), which is coupled to the valve (<NUM>) of the valve positioner (<NUM>),
and characterised in that the magnetic means (<NUM>) comprises a yoke (<NUM>) arranged and configured to increase the attracting force and to adapt an attracting force versus valve-shift relationship to a closing force versus valve-shift relationship and in that the magnetic force compensator comprises:
an adjustment means (<NUM>), which is configured for adjusting the magnetic coupling between the magnetic means (<NUM>) and the magnetic counterpart (<NUM>) to adapt the attracting force versus valve-shift relationship to the closing force versus valve-shift relationship.