Electromagnetic Damper

An electromagnetic damper 100 according to an embodiment of the present invention includes a first tubular member 111, a second tubular member 121, a rod 123, a plurality of electromagnetic coils 113, permanent magnets 125, and a short circuit 130. The second tubular member 121 is mounted on the first tubular member 111 and is configured to be capable of being relatively displaced in one axis direction with respect to the first tubular member 111. The rod 123 extends in the one axis direction and is, at one end, fixed to the second tubular member 121. The plurality of electromagnetic coils 113 are disposed in either one of an inside of the first tubular member 111 or the rod 123. The permanent magnet generates induced electromotive force in the plurality of electromagnetic coils 113 by relative displacement with respect to the plurality of electromagnetic coils 113 and are disposed in the other of the inside of the first tubular member 111 or the rod 123. The short circuit 130 is connected to the plurality of electromagnetic coils 113 and shorts the terminals of the plurality of electromagnetic coils 113 to each other.

TECHNICAL FIELD

The present invention relates to an electromagnetic damper utilizing a cylindrical linear motor.

BACKGROUND ART

In recent years, electromagnetic dampers are being developed for improving damping properties for automobiles, vehicles of railroads and the like, architectural structures, and the like.

For example, Patent Literature 1 has described a power generation type damper including: a first direct-current motor that functions as an electric generator; a ball screw mechanism that translates vibration of a vibration system into rotational motion and transmits it to the first direct-current motor; and a second direct-current motor that functions as a vibration exciter, in which direct current of the first direct-current motor is amplified by a current amplifier and the second direct-current motor is driven. With this configuration, it is said that the amplified current can flow through the second direct-current motor (vibration exciter), which can provide large exciting force.

CITATION LIST

Patent Literature

DISCLOSURE OF INVENTION

Technical Problem

However, the power generation type damper described in Patent Literature 1 has a problem that the apparatus configuration is complicated due to the provision of the ball screw mechanism that translates vibration in the one axis direction into rotational motion. Further, it is impossible to sufficiently damp minute vibration due to backlash of the ball screw mechanism. In addition, it is difficult to provide a sufficient damping characteristic for vibration of a high frequency band.

In view of the above-mentioned circumstances, it is an object of the present invention to provide an electromagnetic damper capable of enhancing a damping characteristic for minute vibration and high-frequency vibration.

Solution to Problem

In order to accomplish the above-mentioned object, an electromagnetic damper according to an embodiment of the present invention includes a first tubular member, a second tubular member, a rod, a plurality of electromagnetic coils, a permanent magnet, and a short circuit.

The second tubular member is mounted on the first tubular member and is configured to be capable of being relatively displaced in one axis direction with respect to the first tubular member.

The rod extends in the one axis direction and is, at one end, fixed to the second tubular member.

The plurality of electromagnetic coils are disposed in either one of an inside of the first tubular member or the rod.

The permanent magnet generates induced electromotive force in the plurality of electromagnetic coils by relative displacement with respect to the plurality of electromagnetic coils and is disposed in the other of the inside of the first tubular member or the rod.

The short circuit is connected to the plurality of electromagnetic coils and shorts terminals of the plurality of electromagnetic coils to each other.

The electromagnetic damper includes the short circuit that shorts the terminals of the electromagnetic coils to each other. Thus, during relative displacement of the permanent magnet with respect to the electromagnetic coils, the induced electromotive force is generated in the electromagnetic coils due to electromagnetic induction, and predetermined electromagnetic force that impedes movement of the second tubular member is generated. In this manner, with the electromagnetic damper, reaction force can be directly generated to the vibration in the one axis direction, and thus the damping characteristic for minute vibration and high-frequency vibration can be improved.

The short circuit may include a passive element capable of adjusting current flowing through the plurality of electromagnetic coils.

With this configuration, magnetic force (magnetic field) generated in the electromagnetic coils can be adjusted, and thus a damping coefficient of the electromagnetic damper can be arbitrarily adjusted.

The passive element may be a variable resistor.

The electromagnetic damper may further include an adjuster that is installed in an outside of the first and second tubular members and is capable of adjusting an electrical resistance value of the variable resistor.

With this configuration, the damping function can be arbitrarily adjusted also after the electromagnetic damper is mounted on a device.

The plurality of electromagnetic coils may include a plurality of ring wires including air core portions which are arranged in the one axis direction and which the rod penetrates. In this case, the short circuit shorts the plurality of ring wires to each other.

With this configuration, a desired vibration damping characteristic can be efficiently provided.

The electromagnetic damper may further include a supporting portion that supports the first tubular member, in which the short circuit may include a wire that passes an inside of the supporting portion and connects to the plurality of electromagnetic coils.

With this configuration, the configuration of the electromagnetic damper can be downsized while protecting the wire.

The electromagnetic damper may further include a detector and a driving coil.

The detector is configured to be capable of detecting a position of the rod in the one axis direction.

The driving coil is disposed in the inside of the first tubular member and is configured to be capable of generating thrust in the one axis direction with respect to the rod when the driving coil is supplied with driving current generated on the basis of an output of the detector.

With this configuration, the electromagnetic damper having both of a passive damping action and an active damping action can be configured.

MODE(S) FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. It should be noted that in the figures shown below, X-, Y-, and Z-axis directions are three axis directions orthogonal to one another.

First Embodiment

FIGS. 1 and 2are cross-sectional views each showing a configuration of an electromagnetic damper100according to this embodiment.FIG. 1shows a maximum compression position of the electromagnetic damper100.FIG. 2shows a maximum extension position of the electromagnetic damper100. It should be noted that the configuration of the electromagnetic damper100is not limited to the configuration described in the drawings of this application.

As shown inFIGS. 1 and 2, the electromagnetic damper100according to this embodiment includes a fixed portion110, a movable portion120, and a short circuit130. The electromagnetic damper100is configured as a damper for a vehicle which is mounted between each wheel and a vehicle body of an automobile. For example, the fixed portion110is connected to a vehicle body side and the movable portion120is connected to a wheel side. It should be noted that the present technology is not limited thereto, and the fixed portion110may be connected to the wheel side and the movable portion120may be connected to the vehicle body side.

The fixed portion110includes a first tubular member111and an electromagnetic coils113disposed inside the first tubular member111. The first tubular member111has an axial center parallel to the Z-axis direction, and retains the plurality of electromagnetic coils113via a coil holder112made of a magnetic material in an inner circumferential surface thereof. The first tubular member111is opened at one end portion (upper end portion inFIGS. 1 and 2). The first tubular member111is fixed to a base portion115via an adaptor114at the other end portion (lower end portion inFIGS. 1 and 2). The electromagnetic coils113include a plurality of ring wires arranged in the Z-axis direction and are connected to the short circuit130via wires W1.

The movable portion120includes a second tubular member121and a rod123that supports permanent magnets125. The second tubular member121has an axial center parallel to the Z-axis direction and is mounted on an outer circumferential surface of the first tubular member111so as to be capable of being relatively displaced in the Z-axis direction with respect to the first tubular member111. The second tubular member121is opened at one end portion (lower end portion inFIGS. 1 and 2). A cover portion122is mounted at the other end portion (upper end portion inFIGS. 1 and 2) of the second tubular member121. The rod123extends inside the first tubular member111in the Z-axis direction and is fixed to the second tubular member121via the cover portion122. The rod123is connected to a vibration receiving portion124at one end portion (upper end portion inFIGS. 1 and 2).

The short circuit130shorts the terminals of the plurality of electromagnetic coils113to each other and induced electromotive force is generated in the plurality of electromagnetic coils113due to the relative displacement of the rod123(permanent magnets125) with respect to the plurality of electromagnetic coils113. With this configuration, as will be described later, a vibration damping effect of the movable portion120to the fixed portion110can be provided.

Hereinafter, detailed configurations of the respective portions of the electromagnetic damper100will be described.

The fixed portion110includes the first tubular member111, the coil holder112, the adaptor114, the base portion115, supporting portions116, and a bottom guide portion117.

The first tubular member111is formed in a cylindrical shape including a hollow portion111ainside and is supported on the base portion115via the adaptor114. It should be noted that the shape of the first tubular member111is not limited to a cylindrical shape, and may be a square tubular shape or the like having a rectangular cross-section, for example.

The first tubular member111is inserted into the second tubular member121of the movable portion120and is brought into contact with the inner circumferential surface of the second tubular member121. The first tubular member111has a function of guiding sliding of the movable portion120with respect to the fixed portion110in the Z-axis direction.

Further, a first slide ring R1is provided in the outer circumferential surface on a side of the one end portion of the first tubular member111. The first slide ring R1has an annular shape, and is configured such that the outer circumferential surface thereof is brought into contact with the inner circumferential surface of the second tubular member121.

The coil holder112is formed in a cylindrical shape concentric with the first tubular member111, and is fixed to the inner circumferential surface of the first tubular member111. The coil holder112retains the electromagnetic coils113including the plurality of ring wires on an inner circumferential side thereof. The respective ring wires are arranged with a predetermined space therebetween in the Z-axis direction and include air core portions that communicate with the hollow portion111a.

The respective ring wires constituting the electromagnetic coils113are connected to the short circuit130via the wires W1. In this embodiment, the respective ring wires are classified in three phases of a U-phase, a V-phase, and a W-phase. The ring wires of the respective phases are respectively shorted due to the short circuit130.

The configuration of each of the ring wires constituting the electromagnetic coils113is not particularly limited. The ring wire includes, for example, a polyurethane copper wire, a polyester copper wire, a polyesterimide copper wire, a polyamidimide copper wire, a polyimide copper wire, and the like.

The adaptor114has an annular shape and is mounted on one end (upper end inFIGS. 1 and 2) of the base portion115. The base portion115and the first tubular member111are coupled to each other. The adaptor114is configured to be capable of being brought into contact with a flange portion121aprovided at the one end portion of the second tubular member121to be projected radially outward. That is, the adaptor114functions as a locking portion that defines a closest position of the movable portion120to the base portion115and a position at which the second tubular member121is brought into contact with the adaptor114corresponds to the maximum compression position of the electromagnetic damper100(seeFIG. 1).

As shown inFIGS. 1 and 2, the base portion115supports the adaptor114and the bottom guide portion117. The base portion115is supported by a support S on the vehicle body side via the supporting portions116. The base portion115has a cylindrical shape. The adaptor114is fixed to one end portion of the base portion115. The bottom guide portion117is fixed to the other opposite end portion of the base portion115.

The supporting portions116are mounted at two positions on the outer circumferential surface of the base portion115, the two positions being opposed to each other in the X-axis direction. The base portion115and the support S are coupled to each other via the supporting portions116. In this embodiment, the supporting portions116include trunnions that support the base portion115to be rotatable about the X-axis. With this configuration, the electromagnetic damper100is coupled to the support S to be movable about a single axis in a tilted state. It should be noted that the supporting portions116may include a universal joint such as a ball joint and a clevis.

The support S according to this embodiment is a member for fixing the electromagnetic damper100to a predetermined vibration damping system, for example. The support S corresponds to, for example, a frame portion of a vehicle body in a case where the electromagnetic damper100is used to be mounted on a vehicle. The support S corresponds to a foundation of a building, for example, in a case where the electromagnetic damper100is used for damping for an architectural structure.

The electromagnetic damper100according to this embodiment is provided with a through-hole H1penetrating one supporting portion116of the two supporting portions116supported by the support S and through the base portion115supported by that supporting portion116in the X-axis direction as shown inFIG. 1.

The bottom guide portion117is a member having a cylindrical shape concentric with the first tubular member111. The bottom guide portion117has a function of guiding movement of a stopper126in the Z-axis direction, which is mounted at the other end of the rod123of the movable portion120. At the one end portion of the bottom guide portion117which is on a side of the base portion115, there is provided an annular projection117aprojected radially inward to be capable of being brought into contact with the stopper126. That is, the bottom guide portion117functions as a locking portion that defines a furthest position of the movable portion120from the base portion115and a position at which the stopper126is brought into contact with the projection117aof the bottom guide portion117corresponds to a maximum extension/compression position of the electromagnetic damper100(seeFIG. 2).

The material of each of the members constituting the fixed portion110is not particularly limited. For example, a synthetic resin, a metal material, and the like can be employed. The metal material is favorable for ensuring rigidity and durability of the electromagnetic damper100.

The movable portion120includes the second tubular member121, the cover portion122, the rod123, and the stopper126.

The second tubular member121includes a member having a cylindrical shape concentric with the first tubular member111. It should be noted that the shape of the second tubular member121is not limited to the cylindrical shape and may be a square tubular shape or the like having a rectangular cross-section, for example.

A second slide ring R2is provided at an end portion of the second tubular member121which is closer to the flange portion121a. The second slide ring R2has an annular shape and is configured such that an inner circumferential surface thereof is brought into contact with the outer circumferential surface of the first tubular member111. In this embodiment, the first slide ring R1that is brought into contact with the inner circumferential surface of the second tubular member121and the second slide ring R2that is brought into contact with the outer circumferential surface of the first tubular member111are provided. With this configuration, relative movement (relative displacement) of the movable portion120with respect to the fixed portion110in the Z-axis direction can be stably guided.

The cover portion122closes the one end portion of the second tubular member121and prevents foreign substances and the like from entering the electromagnetic damper100(hollow portion111a). A retaining portion122ais provided at a center portion of the cover portion122. The retaining portion122ahas a cylindrical shape and retains the one end portion of the rod123. The rod123is fixed to the second tubular member121via this retaining portion122a.

The stopper126is connected to the other end portion of the rod123and is formed in a disk-like shape having a circumferential portion to be slidable on the inner circumferential surface of the bottom guide portion117. The circumferential portion of the stopper126is provided with an annular projection126aextending toward the cover portion122in the Z-axis direction and is configured to be capable of being brought into contact with the projection117aof the bottom guide portion117at the maximum extension position of the electromagnetic damper100. Therefore, the maximum extension position of the electromagnetic damper100can be arbitrarily adjusted on the basis of a dimension of the projection126ain the Z-axis direction.

As shown inFIGS. 1 and 2, the rod123is a cylindrical bar-like member having a longitudinal direction in the Z-axis direction, is inserted into the hollow portion111a, and penetrates the air core portions of the plurality of ring wires constituting the electromagnetic coils113. The rod123is positioned on the axial center of the first tubular member111in such a manner that both ends thereof are retained by the cover portion122and the stopper126. With this configuration, the rod123can be moved in the Z-axis direction without causing axial runout. In addition, durability against offset load in a direction crossing the Z-axis is ensured.

The rod123includes a shaft body123a, the plurality of tubular permanent magnets125inserted in the shaft body123a, and annular yokes F each provided between the plurality of permanent magnets125. The shaft body123apenetrates the retaining portion122aof the cover portion122and is connected to the vibration receiving portion124. The vibration receiving portion124is configured to have an arbitrary structure that transmits vibration of a vibration system such as a wheel to the electromagnetic damper100.

The plurality of permanent magnets125are arranged in the Z-axis direction and are retained by the rod123such that the same poles are opposed to each other in the Z-axis direction. The types of permanent magnets125are not particularly limited and, for example, an Al—Ni—Co magnet, a ferrite magnet, a neodymium magnet, or the like may be employed. It should be noted that the yokes F may be omitted if unnecessary.

The size of the permanent magnets125and the number of permanent magnets125are not particularly limited and can be set as appropriate in a manner that depends on the number of ring wires and the arrangement pitch and the like of the ring wires constituting the electromagnetic coils113. Further, in this embodiment, the permanent magnets125are arranged over a range of an approximately entire axial length of the rod123. However, the permanent magnets125only need to be arranged over an axially long range such that those can pass at least the air core portions of the electromagnetic coils113.

The material of the second tubular member121, the cover portion122, the stopper126, and the like is not particularly limited. For example, a synthetic resin, a metal material, and the like can be employed. The metal material is favorable for ensuring rigidity and durability of the electromagnetic damper100.

As shown inFIGS. 1 and 2, the short circuit130includes a plurality of electrical wires W1and variable resistors130a. The plurality of electrical wires W1are, at one ends, connected to respective terminals of the plurality of ring wires (electromagnetic coils113) and are, at the other ends, commonly connected to form a neutral point N. That is, the short circuit130according to this embodiment includes an electrical circuit that shorts the terminals the plurality of ring wires constituting the electromagnetic coils113to each other.

As shown inFIGS. 1 and 2, the plurality of electrical wires W1are bundled as a tube T and are inserted in the through-hole H1. That is, the short circuit130has a configuration including the electrical wires W1that pass the inside of the supporting portion116and the base portion115and are electrically connected to the electromagnetic coils113.

With this configuration, the plurality of electrical wires W1bundled as the tube T are housed in the electromagnetic damper100. Thus, it is possible not only to suppress deterioration of the electrical wires W1and but also to downsize the apparatus configuration of the electromagnetic damper100. Therefore, the electromagnetic damper100according to this embodiment is favorably applicable to the suspension of the automobile and the like.

In this embodiment, as shown inFIGS. 1 and 2, a part of the short circuit130is provided outside the electromagnetic damper100, but not limited thereto. The entire short circuit130may be housed inside the electromagnetic damper100. A power distribution method for the short circuit130is also not particularly limited. The power distribution method for the short circuit130is typically a 3-phase, 3-wire method. However, a single-phase, 2-wire method, a single-phase, 3-wire method, or the like may be employed.

The number of variable resistors130ais not particularly limited and may be singular or plural. In this embodiment, the variable resistors are provided for the respective electrical wires W1(electromagnetic coils113of the respective phases), but not limited thereto. A variable resistor may be commonly provided for the respective electrical wires W1. The types of variable resistors are also not particularly limited and any types of variable resistors such as a volume type and a rheostat type can be employed.

Instead of or in addition to the variable resistors130a, other passive elements capable of limiting current flowing through the short circuit130, such as a fixed resistance, a coil, and a capacitor, may be used or those may be combined and used. A connection form of those passive elements is not limited and may be a series circuit or may be a parallel circuit.

The electromagnetic damper100of this embodiment further includes an adjuster140capable of externally adjusting electrical resistance values of the variable resistors130a. With this configuration, the vibration damping characteristic of the electromagnetic damper100can be arbitrarily adjusted. The adjuster140is typically disposed outside the fixed portion110and the movable portion120. With this configuration, also after the electromagnetic damper100can be mounted on the vehicle body, the damper characteristics can be arbitrarily and individually adjusted. The adjuster140may typically include a dial type or slide type operation element and may include any number of press buttons and the like.

Next, a typical operation of the electromagnetic damper100configured in the above-mentioned manner will be described.

In this embodiment, the electromagnetic damper100is installed between the vehicle body and the wheel, and has a function of damping vibration transmitted from the wheel side to the vehicle body side and suppressing change in the attitude of the vehicle body. That is, when vibration from the wheel side is input into the vibration receiving portion124, the electromagnetic damper100is extended and compressed. During relative displacement of the rod123(permanent magnets125) with respect to the electromagnetic coils113, induced electromotive force is generated in each electromagnetic coil113due to electromagnetic induction. In the short circuit130, the respective terminals of the electromagnetic coils113is shorted to each other. Therefore, induced current flows in the respective ring wires, such that predetermined electromagnetic force that impedes movement of the rod123acts on the rod123. In this manner, a vibration damping action due to the electromagnetic damper100can be provided.

As described above, the electromagnetic damper100of this embodiment includes a cylindrical linear motor in which linear vibration of the vibration system is directly input. Thus, backlash is not present as compared to a conventional electromagnetic damper including a ball screw mechanism that translates linear vibration into rotational motion. Therefore, a stable damping action can be provided also for minute vibration having a small amplitude. Further, it can sufficiently follow high-speed vibration, and thus a stable vibration damping characteristic can also be provided for a relatively high frequency band.

In addition, the electromagnetic damper100can be configured without needing an external power supply, an amplification circuit, and the like. Thus, simplification of the apparatus configuration, downsizing, and cost reduction can be achieved.

Then, with the electromagnetic damper100of this embodiment, due to the provision of the variable resistors130a(adjuster140) capable of adjusting characteristics of current flowing through the electromagnetic coils113, a damping coefficient of the electromagnetic damper100can be arbitrarily adjusted. In addition, the adjuster140is installed outside the electromagnetic damper100, and thus the electromagnetic damper100can be easily adjusted also after it is mounted on the vehicle body.

Moreover, with the electromagnetic damper100of this embodiment, the trunnion structures are employed for the supporting portions116. Therefore, rotational motion about the X-axis of the electromagnetic damper100is allowed. With this configuration, a predetermined vibration damping action can be provided while the electromagnetic damper100is moved about the X-axis in a tilted state, and thus the electromagnetic damper100favorable to be used in a suspension system for a vehicle can be provided.

Second Embodiment

FIG. 3is a cross-sectional view showing a configuration of an electromagnetic damper200according to a second embodiment of the present invention. Hereinafter, configurations similar to those of the first embodiment will be denoted by similar reference signs and detailed descriptions will be omitted.

As shown inFIG. 3, the second embodiment is the same as the first embodiment in that an electromagnetic damper200according to this embodiment includes the fixed portion110, the movable portion120, and the short circuit130while the second embodiment is different from the first embodiment in that the electromagnetic damper200according to this embodiment further includes a detector210and driving coils220.

The detector210is configured to be capable of detecting a position of the rod123in the Z-axis direction. As shown inFIG. 3, the detector210is electrically connected to a driving circuit D wirelessly or via a wire. The detector210is provided at any position within the fixed portion110(e.g., the projection117aof the bottom guide portion117) and is opposed to the permanent magnets125retained by the rod123in a direction orthogonal to the Z-axis direction. The mounting position of the detector210is not limited to the mounting position shown inFIG. 3and any mounting position can be employed as long as it is a position at which the detector210can detect the magnetic poles of the permanent magnets125.

The detector210according to this embodiment detects a magnetic flux density of a magnetic flux extending from the S-poles (N-poles) to the N-poles (S-poles) of the permanent magnets125and outputs a detection signal including relative-position information of the movable portion120(rod123) with respect to the fixed portion110to the driving circuit D.

The detector210is typically a magnetic sensor (pole sensor), but not particularly limited thereto. Further, a Hall element, a magneto-resistive element, a magnetic-impedance element, a bistable magnetic element, a fluxgate sensor, a proton precession magnetometer, a Faraday element, an electrodynamic magnetic sensor, a superconducting quantum interference device, or the like may be employed as the magnetic sensor, and any types can be employed therefor.

The driving coils220include a plurality of ring wires. As in the electromagnetic coils113, the respective ring wires are arranged with a predetermined space therebetween in the Z-axis direction and include air core portions that communicate with the hollow portion111a.

The driving coils220are retained in the coil holder112common to the electromagnetic coils113. The coil holder112includes a region for retaining the driving coils220and a region for retaining the electromagnetic coils113. In this embodiment, inFIG. 3, an upper half region of the coil holder112is set as the region for retaining the driving coils220and a lower half region of the coil holder112is set as the region for retaining the electromagnetic coils113. The present technology is not limited thereto, and the respective ring wires constituting the driving coils220and the respective ring wires constituting the electromagnetic coils113may be respectively alternately arranged by using the three U, V and W phases as a single unit.

That is, the respective ring wires constituting the driving coils220are classified in three phases of a U-phase, a V-phase, and a W-phase. The ring wires of the respective phases are individually connected to the driving circuit D via wires W2.

The configuration of each of the ring wires constituting the driving coils220is not particularly limited. The ring wire includes, for example, a polyurethane copper wire, a polyester copper wire, a polyesterimide copper wire, a polyamidimide copper wire, a polyimide copper wire, and the like.

The driving circuit D is typically configured as a suspension control unit installed on the vehicle body side. As shown inFIG. 3, the driving circuit D is connected to the respective terminals of the driving coils220via the plurality of electrical wires W2. The plurality of electrical wires W2are bundled as a tube T as in the electrical wires W1and provide electrical connection between the driving coils220and the driving circuit D via a through-hole H2penetrating the base portion115and the supporting portions116in the X-axis direction.

The driving circuit D supplies driving current generated on the basis of the output of the detector210to the driving coils220. Specifically, the driving circuit D receives a detection signal from the detector210, generates driving current of each phase in a manner that depends on a positional relationship between the driving coils220and the rod123(each magnetic pole of the permanent magnets125), and supplies it to the driving coils220. With this configuration, the driving coils220are excited, and an electromagnetic damper having a function as an electromagnetic actuator that generates thrust (electromagnetic force) that moves the rod123in the Z-axis direction is configured.

As described above, in accordance with this embodiment, the electromagnetic damper200having both of a passive damping action and an active damping action can be configured. With this configuration, it is possible to control the attitude of the vehicle body with higher expandability.

Further, in accordance with this embodiment, it is unnecessary to additionally provide a control circuit in order to provide such a passive damping action. Therefore, the configuration of the driving circuit D and control can be simplified. In addition, even if a failure occurs in the driving circuit D, a predetermined vibration damping action of the electromagnetic coils113due to the short circuit130is ensured. Therefore, a minimum damper function can be stably ensured.

Modified Example

Although the embodiments of the present invention have been described above, the present invention is not limited only to the above-mentioned embodiments of the present invention and can be variously modified as a matter of course.

For example, in the electromagnetic dampers100and200according to the above-mentioned embodiments, the electromagnetic coils113are disposed on the side of the fixed portion110and the permanent magnets125are disposed on the side of the movable portion120, but not limited thereto. The permanent magnets125may be disposed on the side of the fixed portion (e.g., inside of the first tubular member111) and the electromagnetic coils113may be disposed on the side of the movable portion (e.g., the rod123).

In addition, in each of the above-mentioned embodiments, the cases where the electromagnetic dampers100and200are applied to the damper for the automobile have been exemplified and described, but not limited thereto. The present invention is applicable also to dampers for railroads and architectural structures.

REFERENCE SIGNS LIST