DE102007027185A1 - Fuel injector with linear drive - Google Patents

Abstract

The injector has a magnetic valve, and a valve ball and a valve slider that are moved from its seat or positioned in its seat for pressure discharge or pressurization of a control space, by the operation of the valve. The magnetic valve includes electromagnets (52) that contain coils (58), which operate the valve ball and the valve slider by a bobbin. The coils are arranged on a circumferential surface of a coil carrier (62). The coil carrier is connected with the valve ball and the valve slider.

Description

State of the art

According to DE 196 50 865 A1 and DE 197 08 104 A1 the armature of the solenoid valve is designed as a two-part armature, so as to reduce the moving mass of the unit of armature and valve member and thus the bouncing kinetic energy.

at The known solenoid valves, a valve element in the de-energized, this means in the inactive state of the solenoid valve over a biased compression spring pressed against a stop. This Stop is in most cases identical to the valve seat. In the idle state of the solenoid valve, d. H. with de-energized magnetic coil of the solenoid valve, the valve is closed, d. H. the anchor bolt with it recorded closure element is replaced by a Valve spring pressed into the seat of the closing element. If the magnetic coil of the solenoid valve, however, energized, it creates a Force the locking element against the force of the closing spring moved away from the seat. After the end of the current supply ensures the at the Upward movement of the anchor bolt preloaded closing spring making sure that the closing element is back in place Starting position is set. This is independent of whether by means of the closing element a pressure balanced or a pressure-dependent biased valve actuated becomes.

In high pressure accumulator injection systems, such as common rail accumulator injection systems, for autoignition internal combustion engines, electrically controlled fuel injectors are used for precise injection of the fuel into the combustion chamber of the internal combustion engine. These fuel injectors include various valves, each of which can be controlled by a magnet. Like all magnetic actuators, a magnet assembly comprises a magnetic coil, a magnetic core and an armature, be it one or more parts. A high pressure control unit for a solenoid valve according to DE 196 50 865 A1 includes a magnet group, an armature group and a valve group.

This typical for solenoid valves control takes place in the previous generations of fuel injectors on the flat armature principle. For generations to be used in the future, a principle which also operates according to the flat-armature principle is provided. The dynamics of an electromagnet are usually determined by the speed with which the magnetic field can be built up. Occurring eddy currents delay the field and the field degradation. The force generation is thus based on the magnetic flux through boundary layers with different permeability according to the following relationships: f = I 2 · Degree μ F = ∫∫fdA.

Disclosure of the invention

Of the present invention is based on the object, a fuel injector to provide an improved response with respect to on opening and closing movements of the injection valve member having.

According to the invention a fuel injector proposed that provides a linear drive which works on the basis of the Lorenz force.

The Lorenz force can be described by the following relationship: F → = I * (1 × B)

The According to the invention proposed linear drive operates as a plunger coil within a permanent magnet, comparable to a Loudspeaker drive, and may vary depending on the current direction work in two directions. Instead of a usable permanent magnet can also be used an electromagnet, to which an excitation coil located parallel to the solenoid coil in series or separated from this can be operated.

In a first embodiment, instead of the solenoid valves previously used for fuel injectors for their actuation, a permanent magnet can be used which generates a permanent magnetic flux in the air gap. Within this air gap moves a plunger coil, which also generates a magnetic field in the energized state. The generated magnetic field is oriented such that a force is generated which is directed against the force generated by a valve spring. The transmission of the force generated by the magnetic field via a valve spring receiving the spring. By the force generated by the magnetic force is a z. B. as a valve ball trained active element and thus relieves a control chamber of the fuel injector via the outlet throttle, so that the invention proposed fuel injector injects a defined amount of fuel into the combustion chamber of the self-igniting internal combustion engine. The injection process is then completed as soon as the energization of the solenoid is canceled and, consequently, the control chamber is closed again by the active element moved into its seat, here formed, for example, in a spherical shape, and in this one the Closing a needle-shaped injection valve member causing system pressure builds up.

In a first embodiment of the invention is based lying thought is on a bobbin a coil wound. This generates at the appropriate length of the coil wire and corresponding energizing a sufficient magnetic flux, such that a magnetic force sets in, which is larger is measured as the force applied by the valve spring. Of the Coil carrier is preferably fixed with a valve spring receptacle connected so that realize a power transmission leaves.

A Alignment of the mentioned valve spring receptacle relative to Electromagnet as well as relative to the solenoid valve is over reached a leadership. In this is the valve spring receptacle led with minimally trained game. The anchor stroke is adjusted by a shim that is between body and Guide is installed. The contacting of the magnetic coil takes place preferably via flexible lines, for example can be reinforced by a tissue. alternative the electrical connection can also be made via sliding contacts, as realized, for example, at the commutator of electric motors are to be realized. In a housing in which the at least one permanent magnet is received are lines integrated from the injector connector to the flexible cable. The connection of the integrated line with the flexible line can For example, via a plug contact.

Of the Magnetic head of the invention proposed Solenoid valve can by a magnetic clamping nut against the injector body the fuel injector are clamped and presses it at the same time the lead against the body of the fuel injector. The return occurs through the armature assembly of the solenoid valve and can be in different places. Optionally, you can Holes in the valve spring receptacle on the underside (valve spring support) be attached or in the coil carrier in the area inserted between the valve spring receptacle and magnetic coil cutouts.

The According to the invention proposed solution is characterized by the fact that compared to previously manufactured Solenoid valves a significantly lower number of items is required and the power loss, in particular the eddy currents, the entire system is reduced. By a smaller electrical Time constant and smaller moving masses can be realize a highly dynamic drive for a fuel injector, whereby multiple pre and post injections are realized can. Furthermore, by the invention proposed Solution realized a very lean-building fuel injector be in which a magnetic actuator instead of a piezoelectric actuator or a piezo-driven injector can be used. Furthermore can by the invention proposed Solution an inline solenoid valve can be displayed. Of the proposed solution according to the invention In addition, the advantage resides in that a residual air gap setting now can be omitted.

in the Contrary to previously used solenoid valves for actuation of fuel injectors is the force vector proposed by the invention Reversible solenoid valve.

Of the According to the invention proposed linear drive for Fuel injectors can on the one hand for the actuation of Fuel injectors are used, which have a z. B. have spherical shaped active element, On the other hand, it can also be expected in the future Applications can be used with a slide valve or pin valve variant.

Brief description of the drawings

Based In the drawings, the invention will be described below in more detail.

It shows:

1 FIG. 4 is an illustration of a prior art fuel injector actuated by a solenoid valve. FIG.

2 a schematic diagram of a proposed inventions immersion coil with electromagnet,

3 a variant of the in 2 illustrated schematic diagram, with permanent magnet instead of electromagnet,

4 A first embodiment of the inventively proposed linear drive in a fuel injector,

5 a further embodiment of the inventively proposed linear drive with a valve spool,

6 a linear actuator for an in-line solenoid valve with a long and slim magnetic actuator.

The representation according to 1 is to be taken from a known from the prior art solenoid valve for actuating a fuel injector.

As 1 shows includes a fuel injector 10 in the area of its injector head 12 a solenoid valve 14 , The solenoid valve 14 includes a magnetic group of an anchor group and a valve group. The magnet group includes a magnetic core 18 having a through hole in which a closing spring 16 located. In the magnetic core 18 is a magnetic coil 22 admitted. The anchor group includes an anchor bolt 32 , an anchor guide 30 and an armature plate movably guided on the anchor bolt 26 with a plan page 28 , The at the anchor bolt 32 slidably guided anchor plate 26 is over an anchor spring 50 biased.

The valve group includes one at the lower end of the anchor bolt 32 provided ball guide 34 as a valve ball 36 trained active element leads. The spherically formed active element 36 closes a drainage channel with outlet throttle 42 over which a control room 40 in a valve piece 38 is formed, can be depressurized.

For completeness, it should be mentioned that in the upper part of the anchor bolt 32 a safety sleeve 20 is attached, the one in a recess on the circumference of the anchor bolt 32 recessed circlip 24 encloses.

In the 1 illustrated closing spring 16 pushes in the de-energized state of the solenoid valve 14 over the anchor bolt 32 on the z. B. spherically formed active element 36 , This closes the outlet throttle 42 of the control room. Is the solenoid valve 14 as shown in 1 however energized, pulls the solenoid 22 of the solenoid valve 14 the anchor plate 26 on, the under high pressure (system pressure) fuel standing over the now opening flow restrictor 42 from the control room 40 in the valve piece 38 escape in a low-pressure return. By the pressure relief of Steuerrau mes 40 becomes an injection valve member 46 - in 1 only hinted at - by a pressure step, which in 1 is not shown, pressed in the opening direction. In the stroke movement of the preferably needle-shaped valve member 46 gives this injection openings at the combustion chamber end of the fuel injector 10 free so that fuel is injected into the combustion chamber, which lasts until the solenoid valve 14 goes back to the de-energized state. When de-energized, the outlet throttle becomes 42 by the spherically formed active element 36 closed again so that over the plan side of the injection valve member 46 in the control room 40 of the fuel injector 10 again pressure builds up and the injection valve member 46 is pushed back into his combustion chamber side seat. Is the preferred needle-shaped injection valve member 46 in the nozzle seat, no fuel reaches the at least one injection opening at the combustion chamber end of the fuel injector 10 and the injection of fuel into the combustion chamber is completed until the solenoid valve 14 energized again. The representation according to 1 is also removable that the anchor bolt 32 enclosing anchor guide 30 with a valve clamping nut 48 in the injector body of the fuel injector 10 is attached.

This in 1 shown high-pressure hydraulics of a solenoid valve 14 makes use of the flat anchor principle. This has proven itself because of its robustness and can also be in currently developing subsequent generations of fuel injectors 10 Find use.

embodiments

The dynamics of a solenoid valve 14 is determined, among other parameters, by the rate at which a magnetic field is built up in the iron. The resulting eddy currents delay the field and field degradation of the magnetic field in the iron. The force generation in a magnet is based on the magnetic flux through boundary layers with different permeability according to the following relationships: f = I 2 · Degree μ F = ∫∫fdA.

The proposed solution according to the invention, instead of the above-indicated principle for driving a high-pressure control, such as a magnet or an armature assembly of the fuel injector 10 , a linear drive based on the Lorenzkraft be used.

F →

Lorenzkraft,

I

Strom,

l

Länge der Spulenwicklung

B

magnetisches Feld.

This results according to the following relationship F → = I * (1 × B) With

F →

Lorentz force,

I

Electricity,

l

Length of the coil winding

B

magnetic field.

The inventively proposed drive operates as in the 2 and 3 , which contain only schematic diagrams of possible embodiments of the invention: In the in 2 illustrated embodiment, the magnetic group comprises an electromagnet 52 with an M-shaped yoke. The middle leg of the yoke of the electromagnet 52 is from an exciter coil 54 wrapped, their connections with reference numerals 56 Marked are. Between the two outer legs of the M-shaped yoke of the electromagnet 52 there is a coil carrier 62 , on the outer circumference of a coil 58 connected. The sink 58 has coil terminals indicated by reference numerals 60 Marked are. The sink 58 acts as a plunger coil. The electromagnet 52 creates a magnetic flux in the air gap. In this air gap, the coil moves 58 as a plunger coil, which also generates a magnetic field in the energized state, which acts in the direction against the valve spring (see position 16 in 1 ) acts. The transmission of the generated magnetic force via an in 4 illustrated valve spring receptacle 68 ,

3 shows an embodiment with a permanent magnet 66 , which is also designed M-shaped. At the coil carrier 62 is the coil 58 , which serves as a plunger coil, the direction of movement of the bobbin 62 is by reference numerals 64 indicated.

In the 2 and 3 are the directions of movement 64 , in which the coil carrier 62 with a coil attached to it 58 (Immersion coil) moves, by the reference numeral 64 designated double arrow marked. From the illustration according to 4 it turns out that in the injector head 12 of the fuel injector 10 the permanent magnet 66 is admitted. The permanent magnet 66 includes a part of one with reference numerals 74 designated drainage channel, by the opening of a seat 76 from the control room 40 controlled fuel in the low pressure region of the fuel injector 10 flows. The permanent magnet 66 as shown in 4 is rotationally symmetrical and comprises an inner yoke, which is enclosed by a yoke designed as an outer ring.

Between the pin-shaped inner yoke and the outer ring surrounding the inner yoke yoke is the coil 58 , The sink 58 has an annular shape and is at a in the illustration according to 4 sleeve-shaped coil carrier 62 added. At the lower end of the sleeve-shaped in this embodiment coil carrier 62 with coil connections 60 fitted to connecting cables 82 are connected. In the illustration according to 4 the coil acts 58 , Which is located between the inner pin-shaped yoke and the outer yoke formed as an outer yoke defined cavity, as a plunger coil and can be moved depending on the energization, either in the vertical direction upwards or in the vertical direction downwards.

The coil carrier 62 as shown in 4 is with a sleeve-shaped valve spring receptacle 68 connected. In the valve spring receptacle 68 is the closing spring 16 , By suitable energization of the coil 58 this can be the coil carrier 62 and the valve spring receptacle associated with this 68 Pull up in vertical direction, so that in the illustration 4 z. B. spherically formed active element 36 from his by reference 76 indicated seat is lifted.

From the in 4 illustrated embodiment also shows that the z. B. spherically formed active element 36 in a ball guide 34 at the bottom of the anchor bolt 62 is included. Below the seat 76 in the valve piece 38 there is a drainage channel for pressure relief of the control room 40 , Within the drain channel is the outlet throttle 42 educated; the control room 40 is a by reference numerals 44 indicated inlet throttle always acted on under standing at system pressure fuel. The valve piece 38 is through a sealing ring 78 sealed.

4 further shows that the valve piece 38 in the injector body of the fuel injector 10 through the valve clamping nut 48 is fixed. The valve spring receptacle 68 in which the closing spring 16 is received, in turn, by a guide 70 enclosed. The leadership 70 has at least one opening 72 on, about which diverted quantity from the control room 40 of the fuel injector 10 in the permanent magnets 66 passing through and to the low pressure area of the fuel injector 10 extending drain channel 74 can be canceled. The leadership 70 is on the one hand by the cover of the solenoid valve 14 and on the other hand, from the injector body of the fuel injector 10 enclosed and in the fuel injector 10 fixed.

On the coil carrier 62 is the coil 58 (Immersion coil) wound, which generates sufficient magnetic flux with appropriate wire length and energization, such that a force is generated which is greater than that by the valve spring 16 generated closing force. The coil carrier 62 is with the valve spring receptacle 68 firmly connected, so that a power transmission can take place at any time.

For alignment of the valve spring retainer 68 to the permanent magnet 66 as well as the solenoid valve 16 takes care of the leadership 70 , In this is the valve spring receptacle 68 guided with minimal radial play. The armature stroke is adjusted, for example via a shim that between the injector body and the guide 70 is installed. The contacting of the coil 58 takes place, for example, by flexible contacting 60 that, for example can be reinforced by a tissue. Alternatively, the electrical connection can also be replaced by sliding contacts, such as those used at the commutator of electric motors. In the enclosure of the permanent magnet 66 The lines from the injector connector to the flexible cables are integrated. The connection of the integrated connection cable 82 with the flexible coil terminals 60 can be done for example via a plug contact or the like.

The magnetic head is clamped by a magnetic clamping nut against the injector body and at the same time pushes the guide 70 against the injector body 102 , The return flow through the armature assembly can be done at various locations, such as through holes in the valve spring retainer 68 , at the bottom or through the coil carrier 62 be placed over cutouts. In 4 is an embodiment with permanent magnet 66 according to 3 indicated; instead of in 4 shown permanent magnet 66 but also the in 2 illustrated electromagnet 52 be used.

5 is a further embodiment of the present invention proposed linear actuator for actuating a fuel injector refer.

Also as shown in 5 includes the fuel injector 10 the injector head 12 inside which there is a solenoid valve 14 located. The solenoid valve 14 includes, on the other hand, the permanent magnet 66 comprising a substantially pin-shaped inner yoke, which from the drainage channel 74 is traversed. Under formation of a free space is on the permanent magnet 66 formed a the pin-shaped inner yoke enclosing outer yoke. In the space between the pin-shaped inner yoke and the outer yoke is the bobbin 62 , on the outer circumferential surface of the coil 58 is attached. The sink 58 or their coil terminals 60 are on a disc-shaped plug 80 contacted, in turn, over himself through the cover of the solenoid valve 14 extending connecting cables 82 electrically contacted.

By means of a union nut is the cover of the solenoid valve 14 with the injector body of the fuel injector 10 connected. Similar to the in 4 embodiment shown is the sleeve-shaped coil carrier 62 that's the coil 58 (Immersion coil) receives, with a valve spool 84 connected. The valve spool 84 is roughly equivalent to in 4 illustrated valve spring receptacle 68 and encloses the valve spring 16 , The valve spring 16 is in the valve spool 84 let in and supports with its upper end on the pin-shaped, inner yoke of the permanent magnet 66 , which from the drainage channel 74 is traversed, from.

Furthermore, the in 5 illustrated embodiment of erfindunsgemäß proposed fuel injector 10 the valve piece 38 which through control room 40 limited. In contrast to the embodiment of the valve piece 38 according to 4 located on the upper plan side of the valve piece 38 a bolt attachment 90 , which merges into a bolt on which the valve spool 84 is guided inside. On the outside of the valve spool 84 a collar is formed, which with one of the valve clamping nut 84 on a setting ring 88 fixed anchor stroke stop 86 interacts. The anchor stroke stop 86 is formed substantially annular and has an inner diameter which is smaller than the inner diameter of the adjusting ring 88 on which the armature stroke stop 86 supported. The inner diameter of the substantially disk-shaped Ankerhubanschlages 86 is in turn so dimensioned that on the outer circumferential surface of the valve spool 84 Trained covenant at Ankerhubanschlag 86 strikes. The valve spool 84 closes or opens a hydraulic space above the seat 76 , In this hydraulic space opens the outlet throttle 42 for pressure relief of the control room 40 , The control room 40 in turn, is always on the inlet throttle 44 pressurized with fuel at system pressure. Depending on the pressure relief or pressurization of the control room 40 moves the substantially needle-shaped - in 5 only partially shown - injection valve member 46 in the vertical direction upwards and opens the injection port at the combustion chamber end of the fuel finjektors 10 or down into the seat of the injection valve member 46 such that at least one at the combustion chamber end of the fuel injector 10 trained injection port is closed again.

As further from the presentation according to 5 results, the permanent magnet comprises 66 a peg-shaped inner yoke 56 which is from the drainage channel 74 is traversed in the vertical direction. The drainage channel 74 can also be arranged running outside of the magnetic core. In addition, the permanent magnet is on 66 analogous to the representation according to 4 an annular outer yoke 98 educated. Between the inner yoke 96 and the outer yoke 98 of the permanent magnet 66 there is a cavity 100 , The cavity 100 represents the space within which the on the outer peripheral surface of the bobbin 62 located coil 58 moved as a plunger in a vertical direction up or down. With reference number 102 is the injector body of the fuel injector 10 designated.

From the illustration according to 6 is a slimline design variant of the present invention proposed linear actuator for actuating a fuel injector.

As the representation according to 6 can be seen, is the shape of the coil 58 and the permanent magnet 66 so flexible that an inline solenoid valve - as in 6 represented - can be created. The trained in a large height H permanent magnet 66 has a diameter D, which is smaller by a multiple than the height. The in 6 shown linear drive can be in the injector body 102 of the fuel injector 10 accommodate and can serve as a substitution of the previously installed piezoelectric actuator, for example. Due to the slimline geometry of the in 6 shown permanent magnet 66 results in a long-building bobbin 62 , on the peripheral surface of which serving as a plunger coil 58 is wound. Also in the embodiment of the permanent magnet 66 according to the embodiment in 6 includes the permanent magnet 66 an inner yoke 96 and an outer yoke surrounding this ring 58 , Between the inner yoke 96 and the outer yoke 98 is the cavity 100 in which the coil 58 , recorded on the coil carrier 62 , is housed vertically movable. Also in the in 6 illustrated embodiment (inline solenoid valve) moves the bobbin 62 according to the double arrow 64 depending on the energization of the coil 58 in vertical direction of movement upwards or downwards. For completeness, it should be mentioned that the injector body 102 of in 6 illustrated fuel injector 10 from a high pressure line 92 is traversed and the outer yoke 98 of the permanent magnet 66 on a supporting edge 94 supported in the injector body 102 is trained.

The above with reference to in the 2 to 6 As shown embodiments shown linear drive is distinguished from known from the prior art solenoid valves in that it comprises a few items and the power loss of the solenoid valve is considerably lower than that of the solenoid valve 14 which is in the fuel injector 10 according to 1 Application finds. Furthermore, the inventively proposed linear drive according to the embodiments in the 2 to 6 a smaller electrical time constant and smaller moving masses of the parts, so that a highly dynamic drive can be realized. As in particular from the illustration according to 6 As can be seen, an extremely slim-fitting solenoid valve can be realized, so that it can replace the relatively expensive piezoelectric actuator used to date on fuel injectors, since the construction spaces of the slimline solenoid valve as shown in FIG 6 and the piezoelectric actuator are somewhat comparable so that an in-line solenoid valve implementation can be achieved. Furthermore, a complicated and time-consuming and, moreover, difficult to automate residual air gap adjustment is dispensable in the linear drive proposed according to the invention. In contrast to previously used magnets, the force vector can be reversed in the linear drive proposed according to the invention.

Furthermore, by the solution proposed according to the invention with a sufficient dimensioning of the coil used as a plunger coil 58 and the permanent magnet 66 a direct control of the needle-shaped injection valve member 46 possible. With this embodiment, the entire high-pressure hydraulics, ie the filling and pressure relieving the control room 40 according to the embodiments shown in the 4 and 5 are shown, eliminated and the power of the bobbin 62 directly on the needle-shaped injection valve member 46 be transmitted.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 19650865 A1 [0001, 0003]
• - DE 19708104 A1 [0001]

Claims (14)

Fuel injector ( 10 ) with a solenoid valve ( 14 ), via the actuation of which an active element ( 36 . 84 ) from his seat ( 76 ) is moved or placed in his seat, for pressure relief or pressurization of a control room ( 40 ), characterized in that the solenoid valve ( 14 ) a magnet ( 52 . 66 ) comprising a coil ( 58 ), which via a coil carrier ( 62 ) the valve element ( 36 . 84 ). Fuel injector ( 10 ) according to claim 1, characterized in that the coil ( 58 ) on the peripheral surface of the bobbin ( 62 ) is arranged. Fuel injector ( 10 ) according to claim 1, characterized in that the coil carrier ( 62 ) with the active element ( 36 . 84 ) connected is. Fuel injector ( 10 ) according to claim 1, characterized in that the active element ( 36 ) is spherical and is located on a valve spring receptacle ( 68 ) is located. Fuel injector ( 10 ) according to claim 1, characterized in that the active element ( 84 ) on a bolt of a valve piece ( 38 ) is guided. Fuel injector ( 10 ) according to claim 1, characterized in that the coil ( 58 ) as a plunger on the outer peripheral surface of a bobbin ( 62 ) and in a cavity ( 100 ) one as a permanent magnet ( 66 ) or as an electromagnet ( 52 ) immersed magnet dips. Fuel injector ( 10 ) according to claim 6, characterized in that the permanent magnet ( 66 ) or the electromagnet ( 52 ) at least one inner yoke ( 96 ) and a ring-shaped outer yoke ( 98 ), between which a cavity ( 100 ) is formed. Fuel injector ( 10 ) according to one or more of the preceding claims, characterized in that the valve spring receptacle ( 68 ) in a guided tour ( 70 ) with minimal play. Fuel injector ( 10 ) according to one or more of the preceding claims, characterized in that the coil ( 58 ) via flexible coil connections ( 60 ) with connecting cables ( 82 ) is electrically connected. Fuel injector ( 10 ) according to claim 1, characterized in that in the permanent magnet ( 66 ) a drainage channel ( 74 ) is formed to the low pressure side return. Fuel injector ( 10 ) according to claim 1, characterized in that serving as a plunger coil ( 58 ) with their coil terminals ( 60 ) on a disc-shaped plug element ( 80 ) is contacted. Fuel injector ( 10 ) according to claim 5, characterized in that the valve slide ( 84 ) a covenant ( 85 ) which is connected to one in the injector body ( 102 ) fixed disc-shaped Ankerhubanschlag ( 86 ) cooperates. Fuel injector ( 10 ) according to claim 5, characterized in that the valve slide ( 84 ) the closing spring ( 16 ) and to a bolt-shaped extension of the valve piece ( 38 ) is guided in the axial direction. Fuel injector ( 10 ) according to one or more of the preceding claims, characterized in that the magnet ( 52 . 66 ) has a height (H) which is many times higher than a diameter (D) of the magnet ( 52 . 66 ).