Torsion damper

A craft damper (torsion damper) includes a crankshaft (shaft member) to be input with a torsion vibration, a disc member coaxially attached to the crankshaft, a ring-shaped inertia mass body connected to an outer peripheral side of the disc member via a magneto-rheological elastomer member so as to be coaxial with the crankshaft, and an electromagnetic coil for applying a magnetic field to the magneto-rheological elastomer member.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the foreign priority benefit under Title 35, U.S. Code, § 119 (a)-(d) of Japanese Patent Application No. 2016-119097, filed on Jun. 15, 2016, the disclosure of which is herein incorporated by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a torsion damper.

BACKGROUND ART

Conventionally, there has been known a torsion damper including a disc-shaped inertia body connected to a crankshaft of an engine and rotating around an axis of the crankshaft, and a damper spring interposed between the crankshaft and the inertia body (for example, see Patent Documents 1, 2). Such a torsion damper shows dynamic damping effect by vibrating in opposite phase with respect to torsional vibration to be input (hereinafter, also simply referred to as input vibration) at a resonance frequency (natural frequency) f0indicated by the following equation.
f0=½π√(k/m)

where k is a spring constant of a damper spring, and m is a mass of the inertia body

CITATION LIST

Patent Literature

Japanese Patent Application Publication No. 2012-210937

SUMMARY OF INVENTION

Technical Problem

As described above, a conventional torsion damper (for example, see Patent Documents 1, 2) has a natural resonance frequency f0determined by a spring constant k of the damper spring and a mass m of the inertia body. However, since a revolution speed (vibration frequency) of the engine fluctuates, a frequency of the input vibration may vary. When the frequency of the input vibration varies in this manner, the torsion damper cannot sufficiently reduce the input vibration.

Therefore, an object of the present invention is to provide a torsion damper excellent in dynamic damping effect even when a vibration frequency fluctuates.

Solution to Problem

In order to solve the above problems, a torsion damper of the present invention includes a shaft member to be input with a torsion vibration, a disc member attached to the shaft member so as to be coaxial with the shaft member, a ring-shaped inertia mass body connected to an outer peripheral side of the disc member via a magneto-rheological elastomer member so as to be coaxial with the shaft member, and an electromagnetic coil for applying a magnetic field to the magneto-rheological elastomer member. In this torsion damper, a spring constant of the magneto-rheological elastomer member is changed by adjusting a magnitude of current flowing through the electromagnetic coil, and thus the resonance frequency (natural frequency) can be adjusted.

Advantageous Effects of Invention

According to the present invention, it is possible to provide a torsion damper excellent in dynamic damping effect even when the vibration frequency fluctuates.

DESCRIPTION OF EMBODIMENTS

Next, embodiments of the present invention will be described. A torsion damper (torsional damper) of the present invention is a variable stiffness dynamic damper for reducing torsional vibration input to a shaft member, and can be applied to various mechanisms for generating torsional vibration. In the present embodiment, the torsion damper of the present invention will be described in detail with reference to a crank damper disposed between an output shaft and a crankshaft of a vehicle engine as an example.

FIG. 1is a view showing a configuration of a crank damper1according to the present embodiment, and is a view showing the configuration in which an electromagnetic coil30is partially cut away. As shown inFIG. 1, the crank damper1includes a damper body10and a pair of electromagnetic coils30composed of a first electromagnetic coil30aand a second electromagnetic coil30b, which will be described in detail below. Further, the crank damper1includes a spring constant control mechanism20for controlling a spring constant of a magneto-rheological elastomer member14constituting the damper body10. In the following description, when it is not necessary to distinguish between the first electromagnetic coil30aand the second electromagnetic coil30b, they are simply referred to as the electromagnetic coils30.

InFIG. 1, reference numeral51is a bracket for attaching the electromagnetic coils30to a predetermined base50(basic structure). Reference numeral11is a crankshaft (shaft member) to be input with torsional vibration, and reference numerals C are arrows indicating directions of currents flowing through winding wires31constituting the electromagnetic coils30. An engine speed sensor21, an ECU (Electronic Control Unit)22, a PDU (Power Drive Unit)23and a battery24constituting the spring constant control mechanism20will be also described in detail below.

FIG. 2is a cross-sectional view of the crank damper1in an axial direction of the crank shaft11(shaft member).FIG. 3is a perspective view of the damper body10constituting the crank damper1. As shown inFIGS. 2 and 3, the damper body10includes the crank shaft11(shaft member), a disc member12, an inertia mass body13and the magneto-rheological elastomer member14.

Although not shown, the crank shaft11is connected to a piston slidably disposed in a cylinder bore of the engine via a connecting rod. Further, the crankshaft11is rotatably supported by a crankcase connected to a lower surface of a cylinder block formed with the cylinder bore. The crankshaft11extending from the crankcase is shown inFIG. 1. An end portion of the crankshaft11on a side opposite to the crankcase is connected to an output shaft of a power transmission system.

The disc member12is formed of a thick plate having a circular planar shape. The disc member12is coaxially attached to the crankshaft11(shaft member). The disc member12is fixed to the crankshaft11and rotates synchronously with rotation of the crankshaft11.

The disc member12of the present embodiment is assumed to be made of a metal. As this metal, for example, a known metal material for a pulley can be used, but a nonmagnetic metal such as an aluminum alloy or a stainless steel is preferably used. Although a method of fixing the disc member12to the crankshaft11is not particularly limited, for example, shrink fitting or welding can be used. When the disc member12is made of a cutting machinable metal, the disc member12can be fixed to the crankshaft11also by, for example, serration processing.

The inertia mass body13has a ring shape, and is disposed coaxially with the crankshaft11(shaft member). The inertia mass body13is connected to an outer peripheral side of the disc member12via the magneto-rheological elastomer member14. The inertia mass body13forms a mass body on the outer peripheral side of the disc member12rotating synchronously with the rotation of the crankshaft11, to show inertia. That is, the inertia mass body13applies inertial force in an opposite direction (in opposite phase) to the disc member12to be rotated, via the magneto-rheological elastomer member14described below.

As a material of such an inertia mass body13, for example, the same material as the material of the disc member12can be used, but a nonmagnetic material capable of forming the mass body on the outer peripheral side of the disc member12is preferably used.

The magneto-rheological elastomer member14connects the disc member12and the inertia mass body13so that the inertia mass body13can be disposed on the outer peripheral side of the disc member12and coaxially with the crankshaft11(shaft member). The magneto-rheological elastomer member14is composed of a matrix elastomer having viscoelasticity as a matrix, and magnetic particles contained in the matrix elastomer. As the matrix elastomer, for example, ethylene-propylene rubber, butadiene rubber, isoprene rubber or silicone rubber can be used, however, it is not limited thereto, and known rubbery polymer materials having viscoelasticity at room temperature can be used.

As the magnetic particles, for example, metals such as pure iron, electromagnetic soft iron, directional silicon steel, Mn—Zn ferrite, Ni—Zn ferrite, magnetite, cobalt and nickel, organic compounds such as 4-methoxybenzylidene-4-acetoxyaniline and triaminobenzene polymer, and organic-inorganic composites such as ferrite-dispersed anisotropic plastic can be used, however, they are not limited thereto, and particles made of a known material which is magnetically polarized by action of a magnetic field can be used.

Shape of the magnetic particles is not particularly limited, and it may be, for example, a spherical shape, a needle shape or a flat plate shape. Although particle diameter of the magnetic particles is not particularly limited, an average particle diameter thereof is preferably about 0.01 μm to 500 μm, for example, by particle size distribution measurement by laser diffraction/scattering method.

Although rate of the magnetic particles in the magneto-rheological elastomer member14can be arbitrarily set, it is preferably about 5% to 70% by volume fraction. Although rate of the matrix elastomer in the magneto-rheological elastomer member14can be arbitrarily set, it is preferably about 30% to 95% by volume fraction.

In the magneto-rheological elastomer member14, when the magnetic field is not applied by the electromagnetic coils30described below, an interaction between the magnetic particles contained in the matrix elastomer is small. When the magnetic field is applied by the electromagnetic coils30, the magnetic particles contained in the matrix elastomer tend to be oriented along magnetic field lines. Thus, shear stress in a plane perpendicular to the magnetic field line changes. In particular, as magnetic field strength H (A/m) increases, the shear stress increases by the interaction between the magnetic particles. A change in the spring constant of the magneto-rheological elastomer member14due to the shear stress will be described in detail below.

FIGS. 4A, 4Bare schematic cross-sectional views showing aspects of the magneto-rheological elastomer member14,FIG. 4Ais a cross-sectional view of a magnetic particle dispersed type magneto-rheological elastomer member14, andFIG. 4Bis a cross-sectional view of a magnetic particle oriented type magneto-rheological elastomer member14. As shown inFIG. 4A, the magneto-rheological elastomer member14of the present embodiment is assumed to be a magnetic particle dispersed type in which magnetic particles16are randomly dispersed in a matrix elastomer15.

Instead of the magnetic particle dispersed type magneto-rheological elastomer member14, the magnetic particle oriented type can also be used. As shown inFIG. 4B, in the magnetic particle oriented type magneto-rheological elastomer member14, the magnetic particles16are oriented in a predetermined direction. In particular, the magnetic particles16are distributed in advance in the matrix elastomer15so as to follow magnetic field lines L when the magnetic field is applied by the electromagnetic coils30described below. Incidentally, the magneto-rheological elastomer member14shown inFIG. 4Bhas a ring shape in which the magnetic particles16are oriented in a radial direction thereof.FIG. 4Bschematically shows how the magnetic particles16are oriented, for convenience of drawing, and is different from an actual one.

In this magnetic particle oriented type magneto-rheological elastomer member14, when the magnetic field is applied thereto, the interaction between the magnetic particles is stronger than that in the magnetic particle dispersed type magneto-rheological elastomer member14(seeFIG. 4A), and the shear stress in the plane perpendicular to the magnetic field line L is larger than that in the magnetic particle dispersed type magneto-rheological elastomer member14. That is, change rate of the spring constant of the magneto-rheological elastomer member14to the current (current value) applied to the electromagnetic coils30described below increases.

The magneto-rheological elastomer member14connects the disc member12and the inertia mass body13by vulcanization bonding. Incidentally, the vulcanization bonding between the disc member12and the inertia mass body13is performed by injecting a raw material of the magneto-rheological elastomer member14containing a crosslinking agent (vulcanizing agent) into a predetermined mold in which the disc member12and the inertia mass body13are arranged, and by allowing crosslinking reaction of the raw material to proceed.

The crosslinking agent (vulcanizing agent), heating temperature and the like for allowing the crosslinking reaction to proceed can be selected from known conditions depending on a type of the matrix elastomer to be selected. The magnetic particle oriented type magneto-rheological elastomer member14shown inFIG. 4Bcan be obtained by allowing the crosslinking reaction to proceed while the magnetic particles16contained in the raw material are oriented in a direction in a predetermined magnetic field.

Next, the electromagnetic coil30will be described. As shown inFIGS. 1 and 2, the electromagnetic coil30of the present embodiment is composed of the first electromagnetic coil30aand the second electromagnetic coil30b. The first electromagnetic coil30aand the second electromagnetic coil30bare arranged so as to sandwich the magneto-rheological elastomer member14in the axial direction of the crankshaft11(shaft member). The first electromagnetic coil30aand the second electromagnetic coil30bare configured to apply the magnetic field to the magneto-rheological elastomer member14(seeFIG. 1).

As shown inFIG. 2, each of the first electromagnetic coil30aand the second electromagnetic coil30bforms a ring body R. These ring bodies R are formed by winding wires31(seeFIG. 1) around the crankshaft11(shaft member). The ring bodies R have the same outer diameter, the same inner diameter and the same thickness in the axial direction with each other. In other words, the number of turns and wire diameter of the first electromagnetic coil30aare substantially the same as those of the second electromagnetic coil30b.

The currents (numeral references C, C inFIG. 1) opposite to each other in a circumferential direction flow respectively through the winding wires31of the first electromagnetic coil30aand the second electromagnetic coil30b.

As shown inFIG. 2, each of the ring bodies R is disposed at a predetermined distance S in the axial direction of the crankshaft11(shaft member) with respect to the magneto-rheological elastomer member14. That is, each of the first electromagnetic coil30aand the second electromagnetic coil30bis attached to the bracket51(seeFIG. 1) and positioned to be disposed at the predetermined distance S as described above.

The base50(seeFIG. 1) provided with the bracket51(seeFIG. 1) is not particularly limited as long as it is a vehicle structural member formed independently from and close to the damper body10. The distance S is preferably set so that the first electromagnetic coil30aand the second electromagnetic coil30bdo not contact the damper body10but come closest thereto.

Each of the ring bodies R is disposed side by side in the axial direction of the crankshaft11(shaft member) with respect to the magneto-rheological elastomer member14. Since a central axis of the ring body R and a central axis of the magneto-rheological elastomer member14are arranged coaxially, it is preferred that the following equation (1) is satisfied for an inner diameter D1and an outer diameter D2of the magneto-rheological elastomer member14and an inner diameter D3and an outer diameter D4of the ring body R.
D1+D2=D3+D4  Equation (1)

With the ring body R and the magneto-rheological elastomer member14satisfying the equation (1), a distance P from an axial center of the crankshaft11to a thickness center of the ring body R and a distance P from the axial center of the crankshaft11to a thickness center of the magneto-rheological elastomer member14are equal to each other.

The following equation (2) is preferably satisfied for a thickness T1in the radial direction of the magneto-rheological elastomer member14and a thickness T2in the radial direction of the ring body R.
T2>T1  Equation (2)
That is, the following equation (3) is satisfied.
D4−D3>D2−D1  Equation (3)
In the equation (3), D1, D2, D3and D4have the same meanings as described above, and T2=D4−D3, T1=D2−D1.

Next, the spring constant control mechanism20shown inFIG. 1will be described. The spring constant control mechanism20changes the spring constant of the magneto-rheological elastomer member14in the damper body10depending on a change in frequency of torsional vibration (input vibration) input to the crankshaft11. As shown inFIG. 1, the spring constant control mechanism20of the present embodiment includes the engine speed sensor21, the ECU22, the PDU23and the battery24.

The engine speed sensor21of the present embodiment is assumed to detect a rotational speed of the crankshaft11magnetically or optically, however, it is not particularly limited thereto as long as it can detect a revolution speed of the engine.

The ECU22is an electronic unit including a CPU (Central Processing Unit), a memory and the like. The ECU22executes a control program stored in a storage unit such as a memory by the CPU.

The ECU22detects an engine revolution speed by the engine speed sensor21. Further, the ECU22identifies the frequency of the input vibration to the crankshaft11based on the detected engine revolution speed. The frequency is identified by the CPU referring a memory stored with a map showing a relationship, which is obtained in advance, between an engine revolution speed Rx(variable) and a frequency fy(variable) of the input vibration to the crankshaft11.

The ECU22defines specifications (a mass m of the inertia mass body13and a spring constant k of the magneto-rheological elastomer member14) of the damper body10based on the identified frequency. That is, the spring constant k of the magneto-rheological elastomer member14for dynamically damping torsional vibration is calculated from an equation “f0=½π√(k/m)” based on the identified frequency f0of the input vibration and the mass m (constant value) of the inertia mass body13.

The ECU22calculates the current value, which is required to set the spring constant k to the calculated value and is applied to the first electromagnetic coil30aand the second electromagnetic coil30b. The current value is calculated by the CPU referring a memory stored with a map showing a relationship, which is obtained in advance, between a spring constant kx(variable) of the magneto-rheological elastomer member14and a current value Iy(variable) to be applied to the first electromagnetic coil30aand the second electromagnetic coil30b.

The map referred by the ECU22is not limited thereto as long as it can calculate the current value to be applied to the first electromagnetic coil30aand the second electromagnetic coil30bbased on the engine revolution speed.

FIG. 5is a graph showing an example of the map stored in the memory of the control unit (ECU22) constituting the crank damper1according to the present embodiment. As shown inFIG. 5, the map shows the relationship, which is obtained in advance, between the engine revolution speed Rx(variable) and the current value Iy(variable) to be applied to the first electromagnetic coil30aand the second electromagnetic coil30b, without showing the relationship between the current value Iyand the spring constant kxof the magneto-rheological elastomer member14. An input response speed of the spring constant control mechanism20is increased by using this map.

When the ECU22controls an ignition timing of the engine, the ECU22can also calculate the frequency of the input vibration to the crankshaft11based on the ignition timing without using the engine speed sensor21.

The PDU23is composed of an electric circuit including an inverter and the like. The PDU23supplies power from the battery24to the first electromagnetic coil30aand the second electromagnetic coil30bat the predetermined current value in response to a command from the ECU22.

Next, operation and effect of the craft damper1of the present embodiment will be described.FIG. 6is a flowchart illustrating the operation of the crank damper1. In the crank damper1(seeFIG. 1) of the present embodiment, the ECU22(seeFIG. 1) detects the engine revolution speed based on a detection signal from the engine speed sensor21(seeFIG. 1) as the engine is started (Step S1inFIG. 6).

The crank damper1identifies the frequency of the input vibration to the crankshaft11(seeFIG. 1) based on a detected value of the engine revolution speed (see Step S2inFIG. 6). The ECU22calculates the spring constant k of the magneto-rheological elastomer member14for dynamically damping the input vibration as described above.

Next, the ECU22calculates the current value (see Step S3inFIG. 6), which is required to set the spring constant k of the magneto-rheological elastomer member14to the calculated value and is applied to the electromagnetic coils30(seeFIG. 1). Then, the ECU22commands the PDU23to apply this current value to the first electromagnetic coil30aand the second electromagnetic coil30b.

The PDU23applies the current value to the electromagnetic coils30using the battery24as a power source to form the magnetic field based on the command from the ECU22. Thus, the spring constant k of the magneto-rheological elastomer member14is set (see Step S4in FIG.6).

FIG. 7is a view illustrating the operation of the crank damper1and showing how the magnetic field is formed when the predetermined current value is applied to the electromagnetic coil30. Reference numerals L indicate the magnetic field lines.

The currents are applied to the first electromagnetic coil30aand the second electromagnetic coil30brespectively in arrow directions ofFIG. 1. InFIG. 7, Marks “·” attached to the winding wires31indicate that the current flows from a back side of a paper ofFIG. 7to a front side thereof, and marks “×” indicate that the current flows from the front side of the paper ofFIG. 7to the back side thereof.

As shown inFIG. 7, when the currents are respectively applied to the first electromagnetic coil30aand the second electromagnetic coil30bas described above, the magnetic field is formed, so that the magnetic field lines L are formed in a direction from a radially inner side to a radially outer side of the ring-shaped magneto-rheological elastomer member14. Incidentally, when the currents are respectively applied to the first electromagnetic coil30aand the second electromagnetic coil30bin opposite directions to the arrow directions ofFIG. 1, the magnetic field lines L are formed in a direction from the radially outer side to the radially inner side of the ring-shaped magneto-rheological elastomer member14.

When the vibration is input to the crankshaft11and the shear stress is generated in the plane perpendicular to the magnetic field lines in the magneto-rheological elastomer member14, the spring constant k of the magneto-rheological elastomer member14is set to a value corresponding to the frequency of the input vibration as described above. Further, the inertia mass body13(seeFIG. 2) dynamically damps the input vibration by vibrating around the crankshaft11in opposite phase to the input vibration via the magneto-rheological elastomer member14.

According to the crank damper1of the present embodiment described above, it is possible to adjust the spring constant k of the magneto-rheological elastomer member14in the damper body10based on the frequency of the input vibration to the crankshaft11. Therefore, according to this crank damper1, it is possible to obtain excellent dynamic damping effect for the input vibration to the crankshaft11, even when the engine revolution speed (vibration frequency) fluctuates.

Further, unlike the crank damper1of the present embodiment, it is also possible to provide plural crank dampers1having spring constants different from each other on the crankshaft11in order to obtain dynamic damping effect depending on fluctuating frequency of the input vibration. However, when the plural crank dampers1are provided on the crankshaft11in this manner, new problems such as an interference with peripheral members of the crank damper1and increased fuel consumption due to an increase in moment of inertia around the crankshaft11occur. In contrast, in the crank damper1of the present embodiment, since the spring constant k of the magneto-rheological elastomer member14is variable, it is possible to obtain dynamic damping effect depending on fluctuating frequency of the input vibration by a single crank damper1provided on the crankshaft11. Therefore, according to the crank damper1of the present embodiment, it is possible to avoid the interference with the peripheral members and the increase in moment of inertia around the crankshaft11.

In the crank damper1of the present embodiment, the electromagnetic coils30are the ring bodies R formed by winding the winding wires31around the crankshaft11. The ring bodies R are arranged side by side at the predetermined distance S in the axial direction of the crankshaft11with respect to the magneto-rheological elastomer member14. Thus, the electromagnetic coil30forms the magnetic field so as to generate the magnetic field lines L in the radial direction of the magneto-rheological elastomer member14as described above. The spring constant k of the magneto-rheological elastomer member14appropriately changes depending on the input vibration by this magnetic field, and thus it is possible to dynamically damping the input vibration in an efficient way by the inertia mass body13disposed outside the magneto-rheological elastomer member14.

In the crank damper1of the present embodiment, the first electromagnetic coil30aand the second electromagnetic coil30bare arranged so as to sandwich the magneto-rheological elastomer member14in the axial direction of the crankshaft11. Thus, the crank damper1can apply stronger magnetic field to the magneto-rheological elastomer member14.

In the crank damper1of the present embodiment, the winding wire31of the first electromagnetic coil30aand the winding wire31of the second electromagnetic coil30bare configured such that the currents opposite to each other in the circumferential direction flow respectively therethrough (seeFIG. 7). Thus, as shown inFIG. 7, the first electromagnetic coil30aand the second electromagnetic coil30bform the magnetic field lines L in a radially outward direction in the magneto-rheological elastomer member14. According to this craft damper1, it is possible to avoid mutual cancellation between the magnetic fields formed by the first electromagnetic coil30aand the second electromagnetic coil30b, thereby forming stronger magnetic field in the magneto-rheological elastomer member14.

In the crank damper1of the present embodiment, it is preferred that the inner diameter D1and the outer diameter D2of the magneto-rheological elastomer member14and the inner diameter D3and the outer diameter D4of the ring body R are set to satisfy the following equation (1).
D1+D2=D3+D4  Equation (1)

In this craft damper1, the magneto-rheological elastomer member14and the electromagnetic coil30, which are arranged side by side, face each other. Thus, craft damper1can form stronger magnetic field in the magneto-rheological elastomer member14.

In the crank damper1of the present embodiment, the following equation (2) is preferably satisfied for the thickness T1in the radial direction of the magneto-rheological elastomer member14and the thickness T2in the radial direction of the ring body R.
T2>T1  Equation (2)
That is, the following equation (3) is satisfied.
D4−D3>D2−D1  Equation (3)
In the equation (3), D1, D2, D3and D4have the same meanings as described above. This craft damper1can form the magnetic field lines L more linearly in the radial direction of the magneto-rheological elastomer member14as compared with a craft damper in which the thickness T2in the radial direction of the ring body R is less than or equal to the thickness T1in the radial direction of the magneto-rheological elastomer member14.

In the crank damper1of the present embodiment, the central axis of the ring body R and the central axis of the magneto-rheological elastomer member14are arranged coaxially. According to this crank damper1, even when the magneto-rheological elastomer member14rotates around the crankshaft11with respect to the stationary electromagnetic coils30, the electromagnetic coils30can accurately apply the magnetic field.

As a result, according to the present embodiment, even when the vibration frequency fluctuates, it is possible to provide the craft damper1(torsion damper) excellent in dynamic damping effect.

Hereinabove, the embodiment of the present invention has been described, however, the present invention is not limited to the above-described embodiment, but can be variously modified without departing the spirit and scope of the present invention.FIG. 8is a cross-sectional view of a crank damper1aaccording to a first modification of the embodiment,FIG. 9is a cross-sectional view of a crank damper1baccording to a second modification of the embodiment, andFIG. 10is a cross-sectional view of a crank damper1caccording to a third modification of the embodiment. In the crank dampers1a,1b,1caccording to the first to third modifications, the same components as those of the embodiment are denoted by the same reference numerals, and a detailed description thereof will be omitted.

As shown inFIG. 8, the crank damper1aaccording to the first modification includes only one electromagnetic coil30. According to this crank damper1a, it is possible to achieve compactness of a dynamic damper by reducing the number of parts.

As shown inFIG. 9, the crank damper1baccording to the second modification is configured with the electromagnetic coil30in which the winding wire31is wound around a bobbin32. According to this crank damper1b, the electromagnetic coil30is excellent in shape stability, and thus it is possible to precisely and easily position the electromagnetic coil30with respect to the magneto-rheological elastomer member14.

As shown inFIG. 10, in the crank damper1caccording to the third modification, the electromagnetic coil30is supported in a casing52and the crankshaft11is supported by the casing52via a bearing53. According to this crank damper1c, it is possible to precisely and easily position the electromagnetic coil30with respect to the magneto-rheological elastomer member14, and to prevent foreign matter from contacting the magneto-rheological elastomer member14and the electromagnetic coil30. As a material of the casing52, a non-magnetic material is preferably used.

In the above-described embodiments, although the crank dampers1,1a,1b,1chave been described, the torsion damper of the present invention can be applied to various mechanisms to be input with torsional vibration. Further, in the above-described embodiments, although the crankshaft11as the shaft member of the crank dampers1,1a,1b,1crotates synchronously with rotation of the engine, the torsion damper of the present invention can also be used to reduce torsional vibration input to the shaft member that does not rotate.

REFERENCE SIGNS LIST