DYNAMIC DAMPER DEVICE

Abstract

A dynamic damper device for inhibiting torque fluctuations in a rotor to which a torque is inputted includes a mass body and a magnetic damper mechanism. The mass body is disposed to be rotatable with the rotor and be rotatable relatively to the rotor. The magnetic damper mechanism includes at least a pair of magnets disposed in the rotor and the mass body. The magnetic damper mechanism couples the rotor and the mass body in a rotational direction by a magnetism of the pair of magnets.

Claims

1. A dynamic damper device for inhibiting torque fluctuations in a rotor to which a torque is inputted, the dynamic damper device comprising: a mass body disposed to be rotatable with the rotor and be rotatable relatively to the rotor; and a magnetic damper mechanism including at least a pair of magnets disposed in the rotor and the mass body, the magnetic damper mechanism for coupling the rotor and the mass body in a rotational direction by a magnetism of the pair of magnets.

2. The dynamic damper device according to claim 1, wherein the magnetic damper mechanism includes a plurality of first magnets attached to the rotor, and a plurality of second magnets attached to the mass body, the plurality of second magnets opposed to the plurality of first magnets.

3. The dynamic damper device according to claim 2, wherein the mass body has an annular shape, the mass body disposed on an outer peripheral side of the rotor, the mass body opposed at an inner peripheral surface thereof to an outer peripheral surface of the rotor, the plurality of first magnets are disposed in an outer peripheral part of the rotor, and the plurality of second magnets are disposed in an inner peripheral part of the mass body.

4. The dynamic damper device according to claim 2, wherein the plurality of first magnets are disposed in an outer peripheral part of the rotor in a circular alignment, the plurality of second magnets are disposed in an inner peripheral part of the mass body in a circular alignment, and the magnetic damper mechanism further includes flux barriers provided circumferentially between two adjacent magnets of the plurality of first magnets and circumferentially between two adjacent magnets of the plurality of second magnets respectively.

5. The dynamic damper device according to claim 2, wherein the plurality of first magnets are disposed such that polarities thereof are aligned circumferentially and alternately, the plurality of second magnets disposed such that polarities thereof are aligned circumferentially and alternately.

6. The dynamic damper device according to claim 1, wherein at least one of the rotor and the mass body is axially divided into at least two parts.

7. The dynamic damper device according to claim 6, wherein the magnetic damper mechanism further includes insulators provided on a boundary surface between divided parts of the rotor and a boundary surface between divided parts of the mass body.

8. The dynamic damper device according to claim 2, wherein at least one of the first and second magnets is divided into at least two parts, the at least two parts opposed to each of the plurality of the other of the second or first magnets.

9. The dynamic damper device according to claim 1, further comprising: a moving mechanism for axially moving either the rotor or the mass body.

10. The dynamic damper device according to claim 9, wherein the torque inputted to the rotor is from an engine, the dynamic damper device further comprising: a drive mechanism for driving the moving mechanism; and a moving control part for controlling the drive mechanism in accordance with at least a rotational speed of the engine.

11. The dynamic damper device according to claim 10, wherein the moving mechanism includes a piston, the piston axially movable together with either the rotor or the mass body, the drive mechanism is a hydraulic control valve for driving the piston by a hydraulic pressure from a hydraulic source, and the moving control part outputs a hydraulic control signal to the hydraulic control valve.

12. The dynamic damper device according to claim 1, wherein the magnetic damper mechanism couples the rotor and the mass body in a rotational direction by the pull force of the pair of magnets.

13. A power transmission device comprising: a rotor to which a torque is inputted; a mass body disposed to be rotatable with the rotor and be rotatable relatively to the rotor; and a magnetic damper mechanism including at least a pair of magnets disposed in the rotor and the mass body, the magnetic damper mechanism for coupling the rotor and the mass body in a rotational direction by the magnetism of the pair of magnets.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] FIG. 1 is a cross-sectional configuration view of a power transmission device including a dynamic damper device according to a first preferred embodiment of the present disclosure.

[0037] FIG. 2 is a front view of a hub, an inertia member and a magnetic damper mechanism in the power transmission device shown in FIG. 1.

[0038] FIG. 3 is a diagram showing a magnetic field when a torsion angle of the magnetic damper mechanism is 0 degrees.

[0039] FIG. 4 is a diagram showing a magnetic field when the torsion angle of the magnetic damper mechanism is 10 degrees.

[0040] FIG. 5 is a torsional characteristic diagram of the first preferred embodiment and modifications 1 and 2.

[0041] FIG. 6 is a diagram according to the modification 1 and corresponds to FIG. 2.

[0042] FIG. 7 is a diagram according to the modification 2 and corresponds to FIG. 2.

[0043] FIG. 8 is a diagram according to the modification 3 and corresponds to FIG. 2.

[0044] FIG. 9A is a diagram according to a second preferred embodiment of the present disclosure and corresponds to FIG. 1.

[0045] FIG. 9B is a diagram of a condition made after actuation of a moving mechanism according to the second preferred embodiment of the present disclosure.

[0046] FIG. 10 is a control block diagram according to the second preferred embodiment.

[0047] FIG. 11 is a control flow chart according to the second preferred embodiment.

[0048] FIG. 12 is a diagram showing an application example of the dynamic damper device of the present disclosure.

[0049] FIG. 13 is a view of a hub and an inertia member according to another preferred embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Preferred Embodiment

[0050] FIG. 1 is a cross-sectional view of a power transmission device including a dynamic damper device according to a first preferred embodiment of the present disclosure. In FIG. 1, line O-O indicates a rotational axis.

[0051] [Entire Configuration]

[0052] A power transmission device 1 includes a rotor 10, to which a torque is inputted, and a dynamic damper device 20 for inhibiting fluctuations in torque inputted to the rotor 10. The rotor 10 is, for instance, an output-side rotor of a lock-up device of a torque converter. In this case, the torque is inputted to the rotor 10 from a front cover through a clutch part and a damper mechanism. The torque, inputted to the rotor 10, is then transmitted to a transmission-side input shaft. Additionally, the torque is inputted to the rotor 10 from a turbine of the torque converter as well.

[0053] [Rotor 10]

[0054] The rotor 10 includes a body 11, a hub 12 and a pair of inner peripheral side plates 13 and 14.

[0055] The body 11 includes an inner peripheral cylindrical portion 110 and a disc portion 111. The inner peripheral cylindrical portion 110 has an axially extending shape and the center axis thereof is matched with the rotational axis. When used as the output-side rotor of the lock-up device, the rotor 10 is provided with a spline hole in the interior thereof. Additionally, the input shaft of the transmission is engaged with the spline hole. The disc portion 111 includes a radial support portion 111a in the outer peripheral part thereof. The radial support portion 111a is made in the shape of a tube extending in the axial direction. Additionally, the distal end of the radial support portion 111a is bent to extend radially outward, and is provided as an axial support portion 111b. The axial support portion 111b is provided with screw holes 111c axially penetrating therethrough.

[0056] The hub 12 has an annular shape, and is supported by the outer peripheral surface of the radial support portion 111a of the disc portion 111. The hub 12 is made of soft magnetic material such as iron. The hub 12 is provided with holes 12a axially penetrating the inner peripheral part thereof.

[0057] Additionally, as shown in FIG. 2, the hub 12 is provided with a plurality of first accommodation portions 12b and a plurality of first flux barriers 12c on the outer peripheral side of the holes 12a. It should be noted that FIG. 2 only shows the hub 12, an inertia member 21 (to be described) and magnets 31 and 32 accommodated in the hub 12 and the inertia member 21, while the other members are removed therefrom.

[0058] Each first accommodation portion 12b is an opening that has a rectangular shape as seen in a front view and has a predetermined thickness in the radial direction. Additionally, each first accommodation portion 12b axially penetrates the hub 12. Also, the first accommodation portions 12b are disposed in circular alignment. One pair of first flux barriers 12c is provided on both circumferential ends of each first accommodation portion 12b. It should be noted that each first accommodation portion 12b and each pair of first flux barriers 12c are continuously provided, and compose a single opening axially penetrating the hub 12. In other words, the first flux barriers 12c are herein gaps. It should be noted that non-magnetic material such as resin can be attached, as the first flux barriers 12c, to the first accommodation portions 12b.

[0059] The pair of inner peripheral side plates 13 and 14 is made of non-magnetic material such as aluminum, and is disposed axially on both sides of the hub 12. In other words, the pair of inner peripheral side plates 13 and 14 is disposed to interpose the hub 12 axially therebetween. Each of the pair of inner peripheral side plates 13 and 14 is provided with holes 13a, 14a axially penetrating the inner peripheral part thereof. Both the holes 13a and the holes 14a are disposed in corresponding positions to the holes 12a of the hub 12.

[0060] Additionally, the hub 12 and the pair of inner peripheral side plates 13 and 14 are fixed by bolts 16 penetrating triads of holes 12a, 13a and 14a, respectively. In more detail, the bolts 16 are screwed into the screw holes 111c of the axial support portion 111b, whereby the hub 12 and the pair of inner peripheral side plates 13 and 14 are fixed to the axial support portion 111b.

[0061] With the configuration described above, a unit, composed of the hub 12 and the pair of inner peripheral side plates 13 and 14, is radially positioned by the radial support portion 111a of the body 11, while being axially positioned by the axial support portion 111b.

[0062] [Dynamic Damper Device 20]

[0063] The dynamic damper device 20 is a device for inhibiting fluctuations in torque inputted to the rotor 10. The dynamic damper device 20 includes the inertia member 21 provided as a mass body, a pair of outer peripheral side plates 22 and 23, a support member 24 and a magnetic damper mechanism 25.

[0064] <Inertia Member 21 and Pair of Outer Peripheral Side Plates 22 and 23>

[0065] The inertia member 21 has an annular shape and is disposed radially outside the hub 12 so as to be radially opposed to the hub 12. In other words, the inner peripheral surface of the inertia member 21 and the outer peripheral surface of the hub 12 are radially opposed at a predetermined gap. Similarly to the hub 12, the inertia member 21 is made of soft magnetic material such as iron. The inertia member 21 is provided with holes 21a axially penetrating the outer peripheral part thereof.

[0066] Additionally, as shown in FIG. 2, the inertia member 21 is provided with a plurality of second accommodation portions 21b and a plurality of second flux barriers 21c on the inner peripheral side of the holes 21a.

[0067] Each second accommodation portion 21b is an opening that has a rectangular shape as seen in a front view and has a predetermined thickness in the radial direction. Additionally, each second accommodation portion 21b axially penetrates the inertia member 21. Also, the second accommodation portions 21b are disposed in circular alignment, while being radially opposed to the first accommodation portions 12b, respectively. One pair of second flux barriers 21c is provided on both circumferential ends of each second accommodation portion 21b. The second flux barriers 21c are openings axially penetrating the inertia member 21. In other words, the second flux barriers 21c are herein gaps. It should be noted that non-magnetic material such as resin can be attached, as the second flux barriers 21c, to the second accommodation portions 21b. One pair of second flux barriers 21c is provided to continue to each second accommodation portion 21b, and each is shaped to slant radially inward with separation from the boundary thereof against each second accommodation portion 21b.

[0068] The pair of outer peripheral side plates 22 and 23 is made of non-magnetic material such as aluminum, and is disposed axially on both sides of the inertia member 21. In other words, the pair of outer peripheral side plates 22 and 23 is disposed to interpose the inertia member 21 axially therebetween. Each of the pair of outer peripheral side plates 22 and 23 is provided with holes 22a, 23a axially penetrating the outer peripheral part thereof. Both the holes 22a and the holes 23a are disposed in corresponding positions to the holes 21a of the inertia member 21.

[0069] <Support Member 24>

[0070] The support member 24 is rotatably supported by the rotor 10 through a bearing 27. In more detail, the support member 24 is rotatably supported by the inner peripheral cylindrical portion 110 of the rotor 10 through the bearing 27. The support member 24 includes an inner peripheral support portion 24a, a disc portion 24b and an outer peripheral support portion 24c.

[0071] The inner peripheral support portion 24a is made in the shape of a tube that the bearing 27 is attached to the inner peripheral part thereof. The disc portion 24b extends radially outward from one end of the inner peripheral support portion 24a. The outer peripheral support portion 24c is made in the shape of a tube that axially extends from the outer peripheral part of the disc portion 24b. Additionally, the inertia member 21 and the pair of outer peripheral side plates 22 and 23 are fixed to the inner peripheral surface of the outer peripheral support portion 24c. In more detail, the disc portion 24b is provided with screw holes 24d in the outer peripheral part thereof. Bolts 28 are screwed into the screw holes 24d, respectively, while penetrating triads of holes 21a, 22a and 23a, respectively. Accordingly, the inertia member 21 and the pair of outer peripheral side plates 22 and 23 are fixed to the support member 24.

[0072] With the configuration described above, a unit, composed of the hub 21 and the pair of outer peripheral side plates 22 and 23, is radially positioned by the outer peripheral support portion 24c of the support member 24, while being axially positioned by the disc portion 24b of the support member 24.

[0073] <Magnetic Damper Mechanism 25>

[0074] The magnetic damper mechanism 25 is a mechanism that magnetically couples the inertia member 21 and the rotor 10 (the member of which the magnetic damper mechanism 25 acts on is the hub 12, directly speaking, and will be hereinafter simply referred to as the hub 12) and generates a resilience force when relative displacement is produced between the hub 12 and the inertia member 21 in a rotational direction in order to reduce the relative displacement. It should be noted that magnetically coupling means coupling the hub 12 and the inertia member 21 in the rotational direction by the magnetism.

[0075] The magnetic damper mechanism 25 includes a plurality of first magnets 31 and a plurality of second magnets 32. The plural first magnets 31 are disposed in the first accommodation portions 12b of the hub 12, respectively. Additionally, the plural second magnets 32 are disposed in the second accommodation portions 21b of the inertia member 21, respectively. Therefore, the first magnets 31 and the second magnets 32 are disposed in radial opposition to each other.

[0076] The first and second magnets 31 and 32 are permanent magnets formed by neodymium sintered magnets or so forth. As shown in FIG. 2, each opposed pair of first and second magnets 31 and 32 is disposed to have opposite polarities N and S so as to generate a pull force therebetween. Additionally, both the plural first magnets 31 and the plural second magnets 32 are disposed such that the polarities N and S are aligned circumferentially and alternately.

[0077] [Actuation of Magnetic Damper Mechanism 25]

[0078] In the present preferred embodiment, a torque is inputted to the rotor 10 from a drive source such as an engine (not shown in the drawings). For example, when the power transmission device 1 is used for a lock-up device of a torque converter, in a lock-up on state, a torque transmitted to a front cover is transmitted to the rotor 10 through an input-side rotor and a damper including torsion springs.

[0079] FIGS. 3 and 4 are magnetic field diagrams showing lines of magnetic force between the first magnets 31 and the second magnets 32. It should be noted that in FIGS. 3 and 4, radially extending straight lines are depicted between circumferentially adjacent pairs of first and second magnets 31 and 32 for convenience and easy understanding of the rotational phase difference between the hub 12 and the inertia member 21 and a condition of lines of magnetic force. Hence, the radially extending straight lines are not depicted as lines of magnetic force. Additionally, circumferential division between the hub 12 and the inertia member 21 is not indicated by the radially extending straight lines.

[0080] When torque fluctuations do not exist in torque transmission, the hub 12 and the inertia member 21 are rotated in the condition shown in FIG. 3. In other words, the hub 12 and the inertia member 21 are rotated without relative displacement in the rotational direction (i.e., in a condition that the rotational phase difference is 0), because the hub 12 and the inertia member 21 are magnetically coupled by the pull forces of the first and second magnets 31 and 32 provided in both members 12 and 21.

[0081] In such a condition that the polarity N of the first magnet 31 and the polarity S of the second magnet 32 are opposed in each pair of first and second magnets 31 and 32 without being displaced in the rotational direction, lines of magnetic force generated by the first and second magnets 31 and 32 are in the most stable condition. This condition corresponds to the origin (where torsion angle is 0 degrees) in the torsional characteristic diagram of FIG. 5.

[0082] On the other hand, when torque fluctuations exist in torque transmission, a rotational phase difference 0 (of 10 degrees in this example) is produced between the hub 12 and the inertia member 21 as shown in FIG. 4. In this condition, lines of magnetic force generated by the first and second magnets 31 and 32 are distorted, and are in an unstable condition. The lines of magnetic force in the unstable condition are going to restore to the stable condition as shown in FIG. 3, whereby a resilient force is generated. In other words, the resilient force is generated to make the rotational phase difference between the hub 12 and the inertia member 21 0. The resilient force corresponds to an elastic force in a heretofore known damper mechanism using torsion springs.

[0083] As described above, when the rotational phase difference is produced between the hub 12 and the inertia member 21 by torque fluctuations, the hub 12 receives the resilient force that is attributed to the first and second magnets 31 and 32 and is directed to reduce the rotational phase difference between both members 12 and 21. Torque fluctuations are inhibited by this force.

[0084] The aforementioned force for inhibiting torque fluctuations varies in accordance with the rotational phase difference between the hub 12 and the inertia member 21, whereby torsional characteristic C0 can be obtained as shown in FIG. 5.

[0085] [Modifications 1, 2 and 3]

[0086] In the example of FIG. 2, the second magnets 32 are disposed in opposition to the first magnets 31 on a one-to-one basis. However, one of each pair of first and second magnets 31 and 32 can be divided.

[0087] For example, in modification 1 shown in FIG. 6, two second magnets 32a and 32b are disposed in opposition to one first magnet 31. On the other hand, in modification 2 shown in FIG. 7, one second magnet 32 is disposed in opposition to two first magnets 31a and 31b.

[0088] According to these examples shown in FIGS. 6 and 7, in the stable condition as shown in FIG. 3, in other words, in the condition without rotational phase difference between the hub 12 and the inertia member 21, initial distortion is supposed to be caused in lines of magnetic force. A preliminary resilient force (a resilient force generated in the stable condition) is generated by this initial distortion. Therefore, torsional stiffness can be enhanced. For example, as shown in FIG. 5, the value of torque to torsion angle can be enhanced from characteristic C0 to characteristic C1 in a low torsion angular range of 0 to 4 degrees. It should be noted that in the torsional characteristics of modifications 1 and 2, the value of torque is 0 at a torsion angle of 0 degrees. This is because initial distortions (preliminary resilience forces) of the divided magnets are directed oppositely, and are thereby canceled out.

[0089] FIG. 5 shows torsional characteristics of the examples shown in FIGS. 2, 6 and 7. Characteristic C0 indicates the characteristic of the example shown in FIG. 2; characteristic C1 indicates the characteristic of modification 1 shown in FIG. 6; and characteristic C2 indicates the characteristic of modification 2 shown in FIG. 7.

[0090] Furthermore, as shown in FIG. 8, both of the first magnets 31 and the second magnets 32 can be divided and disposed in opposition to on a one-to-one basis. In the example of FIG. 8, two first magnets 31a and 31b with the polarities S are opposed in each pair of two second magnets 32a and 32b with the polarities N. Additionally, in the hub 12 and the inertia member 21, a set of two magnets with the same polarities are disposed to be aligned alternately in the circumferential direction, such as two magnets 31a and 31b with the polarities S (32a, 32b).fwdarw.two magnets 31a and 31b with the polarities N (32a, 32b).fwdarw.two magnets 31a and 31b with the polarities S (32a, 32b).

Second Preferred Embodiment

[0091] FIGS. 9A and 9B show a power transmission device 1 including a dynamic damper device 40 according to a second preferred embodiment. The second preferred embodiment will be hereinafter explained. In the second preferred embodiment, when a given constituent element is similar to or corresponds to a comparative one in the first preferred embodiment, a reference sign assigned to the comparative one will be similarly assigned to the given constituent element, and explanation of the given constituent element will be omitted.

[0092] The dynamic damper device 40 according to the second preferred embodiment includes an effective thickness variable mechanism (moving mechanism) 42 that axially moves the inertia member 21 with respect to the hub 12. The effective thickness variable mechanism 42 includes an oil chamber forming member 43 and a piston 44.

[0093] The oil chamber forming member 43 is disposed in axial opposition to the inner peripheral part of the body 11 of the rotor 10. The oil chamber forming member 43 includes a disc portion 43a and a tubular portion 43b.

[0094] The disc portion 43a is fixed at the inner peripheral part thereof to the outer peripheral surface of the inner peripheral cylindrical portion 110 of the rotor 10. In more detail, the inner peripheral cylindrical portion 110 is provided with a step portion and includes a snap ring 46 attached to the outer peripheral surface thereof. The oil chamber forming member 43 is fixed by this step portion and the snap ring 46, while being axially immovable. It should be noted that a seal member 47 is disposed between the inner peripheral surface of the disc portion 43a and the outer peripheral surface of the inner peripheral cylindrical portion 110.

[0095] The tubular portion 43b axially extends from the outer peripheral part of the disc portion 43a. A cylinder part 43c, which is an annular space, is formed between the tubular portion 43b and the radial support portion 111a of the rotor 10. It should be noted that the inner peripheral cylindrical portion 110 of the rotor 10 is provided with an oil pathway 48 for introducing the hydraulic oil to the cylinder part 43c.

[0096] The piston 44 is disposed axially between the rotor 10 and the support member 24, while being axially movable. The piston 44 includes a body 44a and a support portion 44b.

[0097] The body 44a has an annular shape and includes a space in the interior thereof. The body 44a is attached to the cylinder part 43c, while being axially slidable. Seal members 49 and 50 are disposed on the outer and inner peripheral surfaces of the body 44a, respectively, so as to be disposed between the body 44a and the cylinder part 43c.

[0098] The support portion 44b is provided further radially inside the body 44a. The support portion 44b is made in the shape of a tube extending in the axial direction, and a bearing 41 is attached to the inner peripheral surface of the support portion 44b and the outer peripheral surface of the inner peripheral support portion 24a of the support member 24. In other words, the support member 24 is rotatably supported by the support portion 44b of the piston 44 through the bearing 41.

[0099] In the second preferred embodiment described above, when the hydraulic oil is introduced to the cylinder part 43c through the oil pathway 48, the inertia member 21 supported by the support member 24 can be axially moved. For example, as shown in FIG. 9B, when the inertia member 21 is moved to the right side of FIG. 9B with respect to the hub 12, the magnetic damper mechanism 25 can be reduced in effective thickness (that refers to, as described above, the axial length of a region in which the hub 12 and the inertia member 21 axially overlap as seen in a direction arranged orthogonally to the axis). With reduction in effective thickness, it is possible to reduce the magnetic coupling force between the hub 12 and the inertia member 21, i.e. the elastic force (the resilient force). Therefore, the dynamic damper device can be reduced in torsional stiffness. Specifically, the slope of the characteristic shown in FIG. 5 can be made as gentle as possible.

[0100] As described above, with the effective thickness variable mechanism 42 being provided, the effective thickness of the magnetic damper mechanism 25 can be changed, and the torsional stiffness of the dynamic damper device can be set to an arbitrary characteristic.

[0101] FIG. 10 shows a control block diagram of the effective thickness variable mechanism 42. A hydraulic control valve 51, provided as a drive mechanism, is connected to the effective thickness variable mechanism 42. Hydraulic pressure is supplied to the hydraulic control valve 51 from a hydraulic source such as an oil pump. Additionally, the hydraulic control valve 51 is controlled by a hydraulic control signal from a controller 52, whereby the hydraulic pressure controlled by the hydraulic control valve 51 is supplied to the oil pathway 48 of the effective thickness variable mechanism 42.

[0102] The controller 52 receives, as control parameters, the engine rotational speed inputted from an engine rotational speed sensor 53 and the number of active cylinders inputted from an engine controller 54. Then, by following a flowchart shown in FIG. 11, the controller 52 computes a hydraulic control signal based on the aforementioned control parameters, and outputs the hydraulic control signal to the hydraulic control valve 51. It should be noted that the number of active cylinders refer to the number of cylinders actually activated in all the cylinders of the engine.

[0103] First, in steps S1 and S2, engine combustion order frequency and dynamic damper torsional stiffness are computed based on the engine rotational speed and the number of active cylinders. As shown in FIG. 11, the following formulas (1) and (2) are herein given:

Engine combustion order frequency f=N.Math.n/120(1)

Dynamic damper resonance frequency f=().Math.(k/I).sup.1/2(2) [0104] where I: the amount of inertia of the inertia member 21 [0105] N: the engine rotational speed [0106] n: the number of active cylinders
Therefore, based on the formulas (1) and (2), torsional stiffness k of the dynamic damper is computed with the following formula:

Dynamic damper torsional stiffness k=I.Math.(.Math.N.Math.n/60).sup.2

[0107] Next in step S3, as shown in FIG. 11, with reference to table T1, effective thickness is computed based on the dynamic damper torsional stiffness k obtained in step S2. The table T1 has been preliminarily obtained and shows a relation between effective thickness and torsional stiffness.

[0108] Furthermore in step S4, with reference to table T2, hydraulic pressure is computed based on the effective thickness obtained in step S3. The table T2 has been preliminarily obtained and shows a relation between hydraulic pressure and effective thickness. Then in step S5, a hydraulic control signal is computed. The hydraulic control valve 51 is controlled by the hydraulic control signal.

[0109] It should be noted that as shown with dashed two-dotted line in FIG. 10, the effective thickness or displacement in movement attributed to the effective thickness variable mechanism 42 can be configured to be detected and inputted to the controller 52, and the controller 52 can be configured to perform feedback control based on the detection result.

Application Examples

[0110] FIG. 12 shows an example that the power transmission device 1 according to the aforementioned preferred embodiments is applied to a torque converter. The torque converter includes a front cover 2, a torque converter body 3, a lock-up device 4 and an output hub 5. A torque is inputted to the front cover 2 from the engine. The torque converter body 3 includes an impeller 7 coupled to the front cover 2, a turbine 8 and a stator (not shown in the drawings). The turbine 8 is coupled to the output hub 5, and the input shaft of the transmission (not shown in the drawings) is capable of being spline-coupled to the inner peripheral part of the output hub 5.

[0111] [Lock-Up Device 4]

[0112] The lock-up device 4 includes a clutch part, a piston to be actuated by hydraulic pressure, and so forth, and is settable to a lock-up on state and a lock-up off state. In the lock-up on state, the torque inputted to the front cover 2 is transmitted to the output hub 5 through the lock-up device 4 without through the torque converter body 3. On the other hand, in the lock-up off state, the torque inputted to the front cover 2 is transmitted to the output hub 5 through the torque converter body 3.

[0113] The lock-up device 4 includes an input-side rotor 61, a hub flange 62, a damper 63 and a dynamic damper device 64.

[0114] The input-side rotor 61 includes an axially movable piston, and is provided with a friction member 66 fixed to the front cover 2-side lateral surface thereof. When the friction member 66 is pressed onto the front cover 2, the torque is transmitted from the front cover 2 to the input-side rotor 61.

[0115] The hub flange 62 is disposed in axial opposition to the input-side rotor 61 and is rotatable relatively to the input-side rotor 61. The hub flange 62 is coupled to the output hub 5.

[0116] The damper 63 is disposed between the input-side rotor 61 and the hub flange 62. The damper 63 includes a plurality of torsion springs and elastically couples the input-side rotor 61 and the hub flange 62 in a rotational direction. The damper 63 transmits the torque from the input-side rotor 61 to the hub flange 62, and also, absorbs and attenuates torque fluctuations.

[0117] In the lock-up device 4 configured as described above, the hub flange 62 corresponds to the rotor 10 in the preferred embodiment shown in FIG. 1, whereas the dynamic damper device 64 corresponds to the dynamic damper device 20 in the preferred embodiment shown in FIG. 1.

Other Preferred Embodiments

[0118] The present disclosure is not limited to the preferred embodiments described above, and a variety of changes or modifications can be made without departing from the scope of the present advancement.

[0119] (a) As shown in FIG. 13, at least one of the hub and the inertia member can be axially divided, and the divided parts can be insulated from each other. In the example shown in FIG. 13, the hub 12 is composed of a first divided hub 121 and a second divided hub 122. On the other hand, the inertia member 21 is composed of a first divided inertia member 211 and a second divided inertia member 212. Then, an insulator 55 is provided axially between the first divided hub 121 and the second divided hub 122, whereas an insulator 56 is provided axially between the first divided inertia member 211 and the second divided inertia member 212.

[0120] In the example described above, it is possible to reduce eddy current generated in the hub 12 and the inertia member 21. Therefore, it is possible to inhibit heat generation caused by generation of eddy current and inhibit a hysteresis torque appearing in the torsional characteristics.

[0121] (b) In the example shown in FIG. 13, the insulators are provided on the boundary surface between the divided parts of the hub and that between the divided parts of the inertia member, respectively. However, the insulators might not be provided. When the insulators are not provided, the hysteresis torque, attributed to the eddy current generated in the hub and the inertia member, can be made relatively large in magnitude. In other words, the dynamic damper device, although requiring a hysteresis torque with a predetermined magnitude in some engine specification or so forth, can be realized with such desired performance when not provided with insulators between the divided parts of the hub and between the divided parts of the inertia member, respectively.

[0122] (c) In the modifications shown in from FIG. 6 to FIG. 8, one or both of the magnets can be divided into two magnets. However, examples of the number of the divided magnets and the like are not limited to the aforementioned modifications. For example, one magnet can be divided into two (or three) magnets and the other magnet can be divided into three (or two) magnets.