US20100319639A1

US20100319639A1 - Valve timing adjusting apparatus

Info

Publication number: US20100319639A1
Application number: US12/816,468
Authority: US
Inventors: Shingo Morishima
Original assignee: Denso Corp
Current assignee: Denso Corp
Priority date: 2009-06-19
Filing date: 2010-06-16
Publication date: 2010-12-23
Also published as: JP2011001914A

Abstract

A valve timing adjusting apparatus for an engine includes a casing, magnetorheological fluid, a control device, a brake rotor, a phase adjustment mechanism, and a sealing structure. The control device changes the degree of viscosity of magnetorheological fluid in the casing. The sealing structure seals a gap between the casing and the brake rotor. The sealing structure includes an annular permanent magnet and at least one annular magnetic flux guide. The at least one magnetic flux guide defines a guide gap between the at least one magnetic flux guide and the other one of the casing and the brake rotor. The direction of magnetic flux relative to an axial center of the brake rotor, which flux is generated by the control device is similar to a direction of magnetic flux relative to the axial center generated by the permanent magnet.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application is based on and incorporates herein by reference Japanese Patent Application No. 2009-146914 filed on Jun. 19, 2009.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a valve timing adjusting apparatus for adjusting valve timing of a valve that is opened and closed by a camshaft through torque transmission of a crankshaft in an internal combustion engine.
2. Description of Related Art
A conventional valve timing adjusting apparatus is known to adjust a relative phase (also referred to as “engine phase”) between a crankshaft and a camshaft, which phase determines valve timing, in accordance with brake torque generated by an actuator. For example, JP-A-2008-51093 describes a valve timing adjusting apparatus that adjusts the engine phase through brake torque generated by a fluid actuator.
In the apparatus described in JP-A-2008-51093, magnetorheological fluid is encapsulated in a fluid chamber of a casing and contacts a brake rotor. The apparatus of JP-A-2008-51093 has an actuator, which controls a degree of viscosity of the magnetorheological fluid by causing a magnetic flux to pass through the magnetorheological fluid. More specifically, although an “apparent degree of viscosity” of the magnetorheological fluid changes in accordance with generation of yield stress, in the present specification, the apparent degree of viscosity is referred to as the degree of viscosity in order to simplifying the description. In the above actuator, brake torque in accordance with the degree of viscosity of magnetorheological fluid is inputted to the brake rotor supported by the casing, and a phase adjustment mechanism, which is connected with the brake rotor, adjusts the engine phase based on the received brake torque.
Also, in the actuator of the apparatus of JP-A-2008-51093, the brake rotor extends through the casing such that the brake rotor is connected with the phase adjustment mechanism outside the casing. Thus, an oil seal or a magnetic sealing structure is provided between the casing and the brake rotor of the actuator in order to prevent the magnetorheological fluid in the fluid chamber inside the casing from leaking out of the casing. In the case of leakage, the input characteristic of the brake torque may change due to the leaked fluid disadvantageously. If the above sealing structure is capable of successfully preventing the leakage of the magnetorheological fluid, the input characteristic of the brake torque is prevented from being changed, and thereby an adjustment characteristic of the engine phase in accordance with the brake torque is prevented from being changed. As a result, it is possible to achieve reliability.

SUMMARY OF THE INVENTION

The present invention is made in view of the above disadvantages. Thus, it is an objective of the present invention to address at least one of the above disadvantages.
To achieve the objective of the present invention, there is provided a valve timing adjusting apparatus for an internal combustion engine having a camshaft and a crankshaft, the valve timing adjusting apparatus adjusting valve timing of a valve that is opened and closed by the camshaft through torque transmission from the crankshaft, the valve timing adjusting apparatus including a casing, magnetorheological fluid, control means, a brake rotor, a phase adjustment mechanism, and a sealing structure. The casing defines a fluid chamber therein. The magnetorheological fluid is received in the fluid chamber, and the magnetorheological fluid has a degree of viscosity changeable in accordance with magnetic flux that passes through the magnetorheological fluid. The control means changes the degree of viscosity of the magnetorheological fluid by causing magnetic flux to pass through the magnetorheological fluid in the fluid chamber. The brake rotor extends through the casing from an interior to an exterior of the casing. The brake rotor contacts the magnetorheological fluid in the fluid chamber. The brake rotor is rotatably supported by the casing, and the brake rotor generates brake torque in accordance with the degree of viscosity of the magnetorheological fluid. The phase adjustment mechanism is coupled with the brake rotor at the exterior of the casing, and the phase adjustment mechanism adjusts a relative phase between the crankshaft and the camshaft in accordance with the brake torque generated by the brake rotor. The sealing structure seals a gap between the casing and the brake rotor. The sealing structure includes an annular permanent magnet and at least one annular magnetic flux guide. The annular permanent magnet is placed at the interior of the casing to extend in a rotational direction of the brake rotor, and the permanent magnet generates magnetic flux. The permanent magnet is supported by one of the casing and the brake rotor. The at least one annular magnetic flux guide is placed at the interior of the casing to extend in the rotational direction, and the at least one magnetic flux guide is supported by the one of the casing and the brake rotor. The at least one magnetic flux guide defines a guide gap, through which magnetic flux generated by the permanent magnet travels, between the at least one magnetic flux guide and the other one of the casing and the brake rotor. The direction of magnetic flux relative to an axial center of the brake rotor, which flux is generated by the control means, and which flux passes through the magnetorheological fluid, is similar to a direction of magnetic flux relative to the axial center generated by the permanent magnet.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with additional objectives, features and advantages thereof, will be best understood from the following description, the appended claims and the accompanying drawings in which:

FIG. 1 is a cross-sectional view illustrating a valve timing adjusting apparatus according to the first embodiment of the present invention;

FIG. 2 is an enlarged schematic diagram for explaining a sealing structure shown in FIG. 1;

FIG. 3 is an enlarged sectional view illustrating an actuator of FIG. 1;

FIG. 4 is an enlarged sectional view illustrating an actuator according to the second embodiment of the present invention; and

FIG. 5 is an enlarged sectional view illustrating an actuator according to the third embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Multiple embodiments of the present invention will be described with reference to accompanying drawings. Similar components of one embodiment, which are similar to the components of the other preceding embodiment, will be designated by the same numerals, and the explanation thereof may be omitted. When only a part of the configuration in each of the embodiments is described, the other part of the configuration may use the description in the preceding other embodiments. Even if the possibility of the combination is not explicitly described, a part of one embodiment may be combined with a part of the other embodiment provided that the combination does not cause any harm.

First Embodiment

FIG. 1 illustrates a valve timing adjusting apparatus 1 of the first embodiment of the present invention. The valve timing adjusting apparatus 1 is mounted to a vehicle, and is installed to a transmission system that transmits engine torque to a camshaft 2 from a crankshaft (not shown) of an internal combustion engine. The camshaft 2 shown in FIG. 1 opens and closes an intake valve (not shown) that serves as a “valve” of the internal combustion engine. Thus, the valve timing adjusting apparatus 1 adjusts valve timing of the intake valve.

(Basic Structure)

Firstly, a basic structure of the first embodiment will be described. The valve timing adjusting apparatus 1 of the first embodiment includes an actuator 100, an energization control circuit 120, and a phase adjustment mechanism 110. The valve timing adjusting apparatus 1 realizes valve timing suitable to the internal combustion engine by adjusting an engine phase that is a relative phase of the camshaft 2 relative to the crankshaft.

(Actuator)

As shown in FIG. 1, the actuator 100 is an electric fluid brake mechanism, and includes a casing 70, a brake rotor 80, a solenoid coil 95, and a sealing structure 60.
The casing 70 has a generally hollow shape, and has a fixation member 71 and a fluid chamber defining member 72. The fixation member 71 is made of a magnetic material, such as carbon steel, and is formed into an annular plate, for example. The fixation member 71 is fixed to a chain case (not shown) that is a fixation part of the internal combustion engine. The fluid chamber defining member 72 is made of the magnetic material similar to the material of the fixation member 71 and is formed into a cylindrical cup. The fluid chamber defining member 72 is provided on one longitudinal side of the fixation member 71 opposite from the phase adjustment mechanism 110, and also the fluid chamber defining member 72 is provided coaxially with the fixation member 71. The fluid chamber defining member 72 is fixed to the fixation member 71 through a threaded member such that a fluid chamber 74 is defined within the casing 70 between the fluid chamber defining member 72 and the fixation member 71.
The brake rotor 80 includes a shaft member 81 and a magnetic rotation member 82, which are fixed to each other. The shaft member 81 is made of, for example, a metal, such as chromium molybdenum steel, into a shaft shape, and extends through the casing 70 between an interior and an exterior of the casing 70. The fixation member 71 has a hollow cylindrical housing part 71 a that projects from the fixation member 71 in a direction away from the fluid chamber defining member 72. In other words, the housing part 71 a projects from the fixation member 71 toward the exterior of the casing 70. The housing part 71 a has an inner peripheral wall, to which a bearing assembly 75 is provided, and the bearing assembly 75 rotatably supports the shaft member 81. In the above structure, the bearing assembly 75 of the first embodiment includes multiple radial bearings. Each of the radial bearings is made of inner and outer races and rolling elements, which are formed of a carbon steel, for example.
The shaft member 81 has one end portion 81 a that extends to the exterior of the casing 70, and the one end portion 81 a is connected with the phase adjustment mechanism 110 at the exterior of the casing 70. Thus, the brake rotor 80 rotates based on the engine torque outputted by the crankshaft and transmitted through the phase adjustment mechanism 110 during the operation of the internal combustion engine. More specifically, the brake rotor 80 rotates based on the engine torque during the operation of the internal combustion engine in a counterclockwise direction when observed in a direction from the phase adjustment mechanism 110 (when observed from a right side in FIG. 1).
As shown in FIG. 1, the magnetic rotation member 82 is formed of a magnetic material, such as carbon steel, and has a shaft portion 83 and a flange portion 84. The shaft portion 83 has a hollow cylindrical shape, and is coaxially fitted with the other end portion 81 b of the shaft member 81 in a fixed manner. In the above, the other end portion 81 b is located on the side of the shaft member 81 opposite from the one end portion 81 a connected to the phase adjustment mechanism 110. The shaft portion 83 is located adjacent to a first side of the bearing assembly 75. For example, the first side is located leftward and the second side is located rightward in FIGS. 1 and 2, for example, such that the first side of the bearing assembly 75 faces toward the interior of the casing 70 along the rotation axis. The sealing structure 60 is provided at a position radially outward of the shaft portion 83, and the sealing structure 60 seals a gap between the casing 70 and the brake rotor 80.
The flange portion 84 has an annular plate shape, and is coaxially provided at a portion radially outward of the shaft portion 83. Also, the flange portion 84 is received by the fluid chamber 74 within the casing 70 at a position on a longitudinal side of the sealing structure 60 away from the bearing assembly 75. Due to the above configuration, a magnetic gap 92 is defined at the fluid chamber 74 between the flange portion 84 and the fixation member 71. Also, a magnetic gap 91 is defined at the fluid chamber 74 between the flange portion 84 and a bottom wall part 72 a of the fluid chamber defining member 72. The magnetic gap 92 has an annular shape such that the magnetic gap 92 radially extends from an outer surface of the shaft portion 83 toward a radially outer segment of the flange portion 84. Also, the magnetic gap 92 circumferentially extends in a rotational direction of the flange portion 84. The magnetic gap 91 is formed on a side of the flange portion 84 opposite from the magnetic gap 92 and has an annular shape. More specifically, the magnetic gap 91 radially extends from a position around a radially inner end of a bottom wall part 72 a of the fluid chamber defining member 72 toward a position around the radially outer segment of the flange portion 84. Also, the magnetic gap 91 extends in the rotational direction of the flange portion 84. In other words, the magnetic gap 91 is defined between an axial surface of the radially outer segment of the flange portion 84 and an axially inner surface of the bottom wall part 72 a.
As above, the fluid chamber 74 defining the magnetic gaps 91, 92 is partially filled with magnetorheological fluid 90 and partially filled with air. The magnetorheological fluid 90 is one of smart fluid, and has liquid base material and magnetic particles suspended in the liquid base material. For example, the magnetorheological fluid 90 includes a liquid non-magnetic material, such as oil, as the base material, and more specifically, the magnetorheological fluid 90 employs a certain type of oil, which is similar to lubricating oil of the internal combustion engine. Also, for example, a powdered magnetic material, such as carbonyl iron powder, is employed as the magnetic particles of the magnetorheological fluid 90. The magnetorheological fluid 90 having the above components has an apparent degree of viscosity that changes with a magnetic flux density when magnetic flux passes through the magnetorheological fluid 90. Also, the magnetorheological fluid 90 has shearing stress that increases in proportion to the degree of viscosity and increases in inverse proportion to a size of space, in which the magnetorheological fluid 90 exists.
A peripheral wall part of the fluid chamber defining member 72 is fluid-tightly coupled with a radially outer portion of the fixation member 71. Thus, the peripheral wall part and the radially outer portion of the fixation member 71 provide connection between (a) the bottom wall part 72 a and the bottom wall part 72 b of the fluid chamber defining member 72 and (b) an inner wall part 71 b of the fixation member 71. An inner surface of the bottom wall part 72 a of the fluid chamber defining member 72, an inner surface of the inner wall part 71 b of the fixation member 71, and a radially inner surface of the peripheral wall part of the fluid chamber defining member 72 hold a bobbin 97 of the solenoid coil 95 at an outer peripheral side of the flange portion 84.
The bottom wall part 72 b of the fluid chamber defining member 72 has an inner surface, which is provided with a recess 72 c such that the recess 72 c is opposed to an radially inner segment of the flange portion 84. In the above, the radially inner segment of the flange portion 84 is located at a position radially inward of the radially outer segment toward the rotation axis. For example, the bottom wall part 72 b of the fluid chamber defining member 72 is thinner than the bottom wall part 72 a and is formed at a position radially inward of the bottom wall part 72 a. Also, the radially outer segment of the flange portion 84 is formed at a position such that the radially outer segment is opposed to the bottom wall part 72 a, which is thicker than the bottom wall part 72 b, and which is formed at a position radially outward of the bottom wall part 72 b. The recess 72 c has a circular cross section that is coaxial with the bottom wall part 72 b, and forms an enlarged gap 93 between the recess 72 c and the flange portion 84. For example, the enlarged gap 93 has a width greater than a width of the magnetic gap 91 in the longitudinal direction of the actuator 100. Also, the enlarged gap 93 has a radial end portion that is communicated with the magnetic gap 91.
The radially inner segment of the flange portion 84 defines the enlarged gap 93 as above, and the radially inner segment has multiple holes 85 that are arranged at equal intervals in the rotational direction. For example, there are three holes 85 arranged in the circumferential direction. Each of the holes 85 extends through the flange portion 84 in the rotation axis direction such that the hole 85 provides communication between the magnetic gap 91 and the magnetic gap 92, and thereby providing communication between the enlarged gap 93 and the magnetic gap 92. Each hole 85 is provided in the fluid chamber 74, which is defined within the casing 70, together with the enlarged gap 93 and the magnetic gaps 91, 92.
The fluid chamber 74 is partially filled with the magnetorheological fluid 90. Thus, when the brake rotor 80 is stopped, the magnetorheological fluid 90 flows into part of the magnetic gaps 91, 92, which parts are located vertically lower than the shaft portion 83. Also, the magnetorheological fluid 90 flows into a part of the enlarged gap 93, which part is vertically lower than the shaft portion 83. Also, the magnetorheological fluid 90 flows into the certain hole 85, which is located vertically lower than the shaft portion 83.
The solenoid coil 95 is provided coaxially with the flange portion 84 and is located at a position radially outward of the flange portion 84. The solenoid coil 95 is made by winding a metal wire rod around the bobbin 97, which has a hollow cylindrical shape. The solenoid coil 95 is supported by the fixation member 71 and the fluid chamber defining member 72 via the bobbin 97 and a spacer 96. When the solenoid coil 95 is energized, and thereby each part is magnetized, a magnetic flux is generated. In the present embodiment, by adjusting the direction and intensity (strength) of electric current given to the solenoid coil 95, the magnetic flux is generated as shown in FIG. 3 to pass through the fluid chamber defining member 72, the magnetic gap 91, the flange portion 84, the magnetic gap 92, and the fixation member 71. Thus, the direction of the magnetic flux (or the direction of the magnetic field) is generated. In other words, the magnetic flux extends in a gap direction of the magnetic gap 91 and 92. Also, the magnetic flux extends perpendicularly to the plane of the flange portion 84 or in parallel to the rotation axis.
Thus, when the solenoid coil 95 generates the magnetic flux during rotation of the brake rotor 80, the magnetorheological fluid 90 is attracted to each of the magnetic gaps 91, 92 and thereby flows thereinto. Thus, the generated magnetic flux passes through the magnetorheological fluid 90. As a result, braking torque is generated to the flange portion 84 in proportion to the degree of viscosity of the magnetorheological fluid 90, through which the magnetic flux passes. In other words, the braking torque is proportional to yield stress, which is generated by the magnetorheological fluid 90 based on the intensity of the magnetic field between the magnetic gaps 91, 92. More specifically, the braking torque is generated to the flange portion 84 between the elements 70, 80 that contact the magnetorheological fluid 90 at each of the magnetic gaps 91, 92. In the present embodiment, when the solenoid coil 95 generates the magnetic flux upon energization, the brake rotor 80 outputs the brake torque in accordance with the degree of viscosity of the magnetorheological fluid 90.

(Energization Control Circuit)

The energization control circuit 120 shown in FIG. 1 mainly includes a microcomputer, and is electrically connected with a battery 4, which is placed outside the actuator 100, and which is connected with both the solenoid coil 95 and the vehicle. During the stopping of the internal combustion engine, the energization control circuit 120 stops supplying electric power from the battery 4 to the solenoid coil 95 in order to deenergize the solenoid coil 95. Thus, in the above case, the solenoid coil 95 does not generate the magnetic flux, and thereby the brake torque does not exist or disappears.
In contrast, during the operation of the internal combustion engine, the energization control circuit 120 supplies electric power from the battery 4 to the solenoid coil 95 in order to control electric current for energization of the solenoid coil 95. Thus, the solenoid coil 95 generates the magnetic flux that passes through the magnetorheological fluid 90. As a result, in the above case, the degree of viscosity of the magnetorheological fluid 90 is changed, and thereby the brake torque generated by the brake rotor 80 is adjusted (increased and decreased) in accordance with the energization electric current for the solenoid coil 95.

(Phase Adjustment Mechanism)

As shown in FIG. 1, the phase adjustment mechanism 110 includes a driving-side rotor 10, a driven-side rotor 20, an assisting member 30, a planet gear carrier 40, and a planet gear 50.
The driving-side rotor 10 has a hollow cylindrical gear member 12 and a hollow cylindrical sprocket 13 that are coaxially engaged with each other in a threaded manner. An inner peripheral portion of the gear member 12 forms a driving-side internal gear portion 14. The sprocket 13 has multiple tooth 16 located at a radially outer portion of the sprocket 13, and the tooth 16 are connected with multiple tooth of the crankshaft through an annular timing chain. As above, the sprocket 13 is mechanically connected with the crankshaft. Thus, the engine torque outputted by the crankshaft during the operation of the internal combustion engine is transmitted to the sprocket 13 through the timing chain, and thereby the driving-side rotor 10 rotates synchronously with the crankshaft in a counter-clockwise direction when observed from a right side in FIG. 1.
As shown in FIG. 1, the driven-side rotor 20 has a hollow cylindrical shape, and is placed coaxially with the sprocket 13 within the sprocket 13. The driven-side rotor 20 has a driven-side internal gear portion 22 at a radially outer portion of the driven-side rotor 20. The driven-side rotor 20 has an inner peripheral portion that forms a connection portion 24. For example, the connection portion 24 is provided coaxially with the camshaft 2 and is fixed to the camshaft 2 through a bolt. Thus, the driven-side rotor 20 is rotatable synchronously with the camshaft 2 in the counter-clockwise direction when observed in the right side in FIG. 1. Also, the driven-side rotor 20 is rotatable relative to the driving-side rotor 10.
As shown in FIG. 1, the assisting member 30 is made of a helical torsion spring, and is provided coaxially within the sprocket 13. The assisting member 30 has one end portion 31 that is engaged with the sprocket 13, and the assisting member 30 has the other end portion 32 that is engaged with the connection portion 24. When twisted between the rotors 10, 20, the assisting member 30 generates assisting torque to urge the driven-side rotor 20 in a retard direction relative to the driving-side rotor 10.
The planet gear carrier 40 has a generally tubular shape. The planet gear carrier 40 has a transmitting part 41 formed at a radially inner portion of the planet gear carrier 40. The transmitting part 41 receives the brake torque from the brake rotor 80 of the actuator 100. Also, the transmitting part 41 is provided coaxially with the rotors 10, and the brake rotor 80 and has multiple fitting grooves 42. A coupling joint 43 is fitted with the fitting grooves 42. Thus, the planet gear carrier 40 is connected with the shaft member 81 of the brake rotor 80 through the coupling joint 43. Due to the above configuration, the planet gear carrier 40 is rotatable integrally with the brake rotor 80, and is rotatable relative to the driving-side rotor 10.
The planet gear carrier 40 forms an eccentric portion 44 at a portion radially outward of the planet gear carrier 40. For example, the eccentric portion 44 is provided eccentrically to the transmitting part 41. The eccentric portion 44 is fitted coaxially within the planet gear 50 through a planet bearing 45. Due to the above configuration, the planet gear carrier 40 supports the planet gear 50 such that the planet gear 50 is epicyclically movable in accordance with the rotation of the planet gear carrier 40 relative to the driving-side internal gear portion 14. For example, the epicyclic motion indicates that the planet gear 50 rotates about an eccentric axis of the eccentric portion 44, and simultaneously the planet gear 50 revolves in the rotational direction of the planet gear carrier 40.
The planet gear 50 has a hollow cylindrical shape, and is provided coaxially with the eccentric portion 44. In other words, the planet gear 50 is provided eccentrically to the gear portions 14, 22. The planet gear 50 has a driving-side external gear portion 52 and a driven-side external gear portion 54 at a portion radially outward of the planet gear 50. The driving-side external gear portion 52 and the driven-side external gear portion 54 are provided coaxial with each other. The driving-side external gear portion 52 meshes with the driving-side internal gear portion 14 at a position eccentric to the gear portions 14, 22, and the driven-side external gear portion 54 meshes with the driven-side internal gear portion 22 also at the eccentric position.
As above, the phase adjustment mechanism 110 adjusts the engine phase in accordance with the balance between the brake torque generated by the brake rotor 80, the assisting torque of the assisting member 30, and variable torque (torque reversal) applied to the camshaft 2.
Specifically, when the brake rotor 80 rotates at the same speed with the driving-side rotor 10 due to the holding of the brake torque at a center level, and thereby the planet gear carrier 40 does not rotate relative to the driving-side internal gear portion 14, the planet gear 50 does not epicyclically moves but rotates with the rotors 10, 20. As a result, the engine phase is maintained.
In contrast, when the brake rotor 80 rotates at a speed lower than the driving-side rotor 10 due to the increase in the brake torque, and thereby the planet gear carrier 40 rotates relative to the driving-side internal gear portion 14 in the retard direction, the planet gear 50 epicyclically moves such that the driven-side rotor 20 rotates relative to the driving-side rotor 10 in the advance direction. As a result, in the above case, the engine phase is shifted in the advance direction, or the engine phase is advanced.
In another case, when the brake rotor 80 rotates at a speed higher than the driving-side rotor 10 due to the decrease in the brake torque, and thereby the planet gear carrier 40 rotates relative to the driving-side internal gear portion 14 in the advance direction, the planet gear 50 epicyclically moves such that the driven-side rotor 20 rotates relative to the driving-side rotor 10 in the retard direction. As a result, in the above case, the engine phase is shifted in the retard direction, or the engine is retarded.

(Sealing Structure)

As shown in FIG. 2, in the actuator 100, the sealing structure 60 is covered by a non-magnetic shield 61 and is provided within the casing 70. Typically, the sealing structure 60 disconnects the fluid chamber 74, which encapsulates therein the magnetorheological fluid 90, from the exterior of the casing 70. The sealing structure 60 has a permanent magnet 62 and multiple magnetic flux guides 64, 65, which are provided on both longitudinal ends of the permanent magnet 62 such that the permanent magnet 62 is provided between the magnetic flux guides 64, 65 along the rotation axis of the rotor 80.
The non-magnetic shield 61 has a shield main body 61 a and a shield cover 61 b that covers an opening of the shield main body 61 a. The shield main body 61 a, for example, is made of a non-magnetic material, such as stainless steel, into a cylindrical cup shape. The shield main body 61 a is provided at a position radially outward of the shaft portion 83 of the brake rotor 80 and is provided between the flange portion 84 of the brake rotor 80 and the bearing assembly 75 of the casing 70 along the rotation axis of the rotor 80. The shield main body 61 a is fitted within the fixation member 71 of the casing 70 in a state, where the opening the shield main body 61 a is directed toward the bearing assembly 75. The shield main body 61 a has a bottom wall part, which has a circular ring shape, and which extends in a radial direction. In the above configuration, the bottom wall part of the shield main body 61 a is exposed to the fluid chamber 74 within the casing 70, and the bottom wall part faces with the flange portion 84. The shield cover 61 b is made of the magnetic material similar to the material of the shield main body 61 a, and is formed into a circular ring plate shape. The shield cover 61 b is provided at a position radially outward of the shaft portion 83 of the brake rotor 80 such that the shield cover 61 b is positioned adjacently to the first side (left side in FIG. 2) of the bearing assembly 75. The shield cover 61 b is fixedly fitted within the fixation member 71 such that the sealing structure 60 is held between the shield cover 61 b and the bottom wall part of the shield main body 61 a and is covered by the shield cover 61 b and the shield main body 61 a.
The permanent magnet 62 is made of, for example, a ferrite magnet into a circular ring shape. The permanent magnet 62 is provided coaxially with the shaft portion 83 at a position radially outward of the shaft portion 83. The permanent magnet 62 continuously extends in the rotational direction of the brake rotor 80. Due to the above configuration, the permanent magnet 62 has opposite magnetic poles at the longitudinal ends of the permanent magnet 62. In other words, the permanent magnet 62 has the opposite magnetic poles at the first side (left side in FIG. 2) and the second side (right side in FIG. 2) of the permanent magnet 62. The permanent magnet 62 always generates the magnetic flux between the magnetic poles. The permanent magnet 62 is fixedly fitted with the radially inner side of a peripheral wall part of the shield main body 61 a in a state, where the permanent magnet 62 is adjacent to the first side of the fixation member 71. Thus, the permanent magnet 62 is held by the casing 70 through the shield main body 61 a. It should be noted that the permanent magnet 62 has a thickness of, for example, 2.5 mm, which is measured in the longitudinal direction. The thickness of the permanent magnet 62 may be set at a value different from 2.5 mm, as required.
Specifically, the magnetic flux guide 64 is positioned adjacent to the second side of the bottom wall part of the shield main body 61 a, and the permanent magnet 62 is positioned adjacent to the second side of the magnetic flux guide 64. Also, the magnetic flux guide 65 is provided adjacent to the second side of the permanent magnet 62, and the shield cover 61 b is positioned adjacent to the second side of the magnetic flux guide 65. It should be noted that each of the magnetic flux guides 64, 65 may have a thickness of 0.5 mm measured along the rotation axis of the rotor 80, and the thickness of each of the magnetic flux guides 64, 65 is thinner than the thickness of the permanent magnet 62. For example, the magnetic flux guides 64, 65 may be formed by using a press work of a cold-rolled steel.
Each of the magnetic flux guides 64, 65 is made of a magnetic material and is formed into a circular ring plate shape. Also, each of the magnetic flux guides 64, 65 is positioned coaxially at a position radially outward of the shaft portion 83 and continuously extends in the rotational direction of the brake rotor 80. The magnetic flux guide 65 is fixedly fitted with the radially inner side of the peripheral wail part of the shield main body 61 a such that the magnetic flux guide 65 is supported by the casing 70 through the non-magnetic shield 61. An axial space 69 is formed on the second side of the magnetic flux guide 65. In other words, the axial space 69 is formed between the magnetic flux guide 65 and the bearing assembly 75, and the axial space 69 has an axial dimension measured along the rotation axis, which dimension is generally equivalent to that of the shield cover 61 b. The axial space 69 is formed at a position radially inward of the shield cover 61 b and has a circular ring shape.
The magnetic flux guides 64, 65 have inner diameters that are equivalent to each other. The inner diameter of each of the magnetic flux guides 64, 65 is smaller than the inner diameters of the elements 62, 61 b, which are arranged adjacent to the magnetic flux guides 64, 65 in the axial direction. Also, the inner diameter of each of the magnetic flux guides 64, 65 is greater than the outer diameter of the shaft portion 83, which extends through the radially inward part of the flux guides 64, 65. Due to the above configuration, there is formed a space between (a) the shaft portion 83 of the brake rotor 80 and (b) each of the magnetic flux guides 64, 65. More specifically, the space extends from the first side (interior of the casing 70) to the second side (exterior of the casing 70) along the rotation axis of the rotor 80, and a dimension of the space measured in the radial direction changes (increases and decreases) as a function of a longitudinal position of the space. There are multiple guide gaps 66 a, 66 b, 66 c, 66 d formed at positions, at which the gap dimension between the shaft portion 83 and (b) the magnetic flux guide 64 or 65 is relatively smaller than other positions. For example, in the present embodiment, there are two guide gaps for each of the magnetic flux guides 64, 65.
Because of the space having the above shape, each of the magnetic flux guides 64, 65 of the present embodiment has two guide-side projection portions 76 that extends toward the shaft portion 83. More specifically, the guide-side projection portions 76 are made by bifurcating the radially inward end of each of the magnetic flux guides 64, 65 such that the two guide-side projection portions 76 are arranged in the longitudinal direction of the shaft portion 83. The guide-side projection portion 76 extends in the circumferential direction to form a circular ring shape such that the guide-side projection portion 76 surrounds the outer periphery of the shaft portion 83 of the brake rotor 80.
It should be noted that the magnetic flux guides at both sides of the permanent magnet 62 may alternatively have mutually different shapes, and thereby only one of the magnetic flux guides, which is located on one side of the permanent magnet 62, may have the above multiple guide gaps alternatively. Also, in the sealing structure 60, at least one magnetic flux guide among the multiple magnetic flux guides may have the multiple guide gaps.
Also, in the present embodiment, there are shaft-side projection portions 86 that radially project from the shaft portion 83 of the brake rotor 80 toward the magnetic flux guides 64, 65 such that each of the shaft-side projection portions 86 are opposed to the guide-side projection portions 76 of the magnetic flux guides 64, 65, respectively. Each of the shaft-side projection portions 86 extends continuously in the circumferential direction at the outer periphery of the shaft portion 83 of the brake rotor 80, and is formed into a circular ring shape.
In other words, the guide gap has different gap dimension at different positions. The part of the guide gap having the relatively small gap dimension is formed between the guide-side projection portion 76 and the shaft-side projection portion 86, and the other part of the guide gap having the relatively large gap dimension is formed between (a) a recess defined by the adjacent guide-side projection portions 76 and (b) the outer surface of the shaft portion 83 positioned between the adjacent shaft-side projection portions 86, which outer surface being opposed to the guide-side recess. Also, each of the guide gaps 66 a, 66 b, 66 c, 66 d has the similar radial dimension with each other. More specifically, each of the guide gaps 66 a, 66 b, 66 c, 66 d has the dimension smaller than an axial dimension of a bottom wall part of the shield main body 61 a, which wall part is exposed to the fluid chamber 74. For example, the bottom wall part of the shield main body 61 a is located axially between the fluid chamber 74 and the magnetic flux guide 64 in FIG. 2.
It should be noted that in the present embodiment, in an example above, the multiple guide-side projection portions 76 and the multiple shaft-side projection portions 86 are formed in order to form the multiple guide gaps 66 a to 66 d. However, only the multiple guide-side projection portions 76 may be formed on the magnetic flux guides 64, 65 to form the multiple guide gaps without forming the projection portions 86. Alternatively, only the multiple shaft-side projection portions 86 may be formed on the shaft portion 83 to form the multiple guide gaps without forming the projection portions 76.
In the any of the above alternative case, the multiple guide gaps 66 a to 66 d having small dimension are formed between each of the magnetic flux guides 64, 65 and the shaft portion 83. For example, the multiple guide gaps 66 a to 66 d are formed between the multiple guide-side projection portions 76 and the opposing multiple shaft-side projection portions 86. The multiple guide gaps 66 a to 66 d are formed between the multiple guide-side projection portions 76 and the outer peripheral surface of the opposing shaft portion 83. The multiple guide gaps 66 a to 66 d are formed between the magnetic flux guides 64, 65 and the multiple shaft-side projection portions 86.
As a result, the magnetic flux by the permanent magnet 62 is highly effectively and reliably introduced to each of the guide gaps 66 a to 66 d and travels through the guide gaps 66 a to 66 d. Also, the magnetorheological fluid 90 flows into the guide gaps 66 a to 66 d from the fluid chamber 74 within the casing 70. Thus, the fluid 90 having the increased degree of viscosity is captured at the guide gaps 66 a to 66 d, and thereby the sealing film is formed. In other words, when the magnetorheological fluid 90 is captured at multiple positions along the shaft portion 83 that extends through the casing 70, the magnetorheological fluid 90 exerts self sealing function by forming sealing film. As a result, due to the above self sealing function, it is possible to reduce frictional resistance between the casing 70 and the brake rotor 80, and simultaneously it is still possible to limit the magnetorheological fluid 90 from leaking through the bearing assembly 75 to the exterior of the casing 70. Thus, wear of the elements 70, 80 due to the frictional resistance therebetween and the deterioration of the bearing assembly 75 due to the influent of the magnetorheological fluid 90 thereinto is avoided effectively. In addition to the above, it is also possible to avoid the input characteristic change of the brake torque due to the leakage of the magnetorheological fluid 90, and thereby to avoid the adjustment characteristic change of the engine phase.
Furthermore, the leaked magnetic flux from the solenoid coil 95 travels through the sealing films multiply formed at the guide gaps 66 a to 66 d, sealing capability of each sealing film is effectively improved, and thereby the brake output during the brake operation is effectively achievable.
Also, recesses are formed between the adjacent guide-side projection portions 76 and between the adjacent shaft-side projection portions 86 in order to enlarge the radial gap dimension. Then, the magnetorheological fluid is collected at the part having the relatively small radial gap dimension, and the sealing film is formed at the part. However, in some cases, the magnetorheological fluid 90 penetrates through the sealing film to flow into the adjacent downstream recess depending on the differential pressure across the adjacent recesses. In the above case, there is formed the enlarged recess that is positioned downstream in the travel direction of the fluid 90, and the enlarged recess has at least one radial dimension greater than the radial dimension of the guide gap. Thus, when the magnetorheological fluid 90 flows into the enlarged recess, the magnetorheological fluid 90 disperses in the enlarged space after penetrating through the restricted guide gap, and thereby the force or energy of the movement of the fluid 90 is reduced in the enlarged recess. As a result, the magnetorheological fluid 90 is effectively limited from penetrating through the further downstream sealing film.
The above advantages is more effective in the following case. For example, as shown in FIG. 2, in a case, where the recess, which is located downstream of the sealing film, has dimensions in the both radial directions greater than the radial dimensions of the guide gap, flow of the magnetorheological fluid 90 is equally dispersed, and thereby the above limitation effect is further effectively achievable.
In addition, in the sealing structure 60, because frictional resistance between the casing 70 and the brake rotor 80 is reduced as above, torque loss is effectively reduced for a case of the non-existing state of the brake torque of the brake rotor 80. More specifically, the torque loss is proportional to multiplication of the following first to third values. The first value is a square of a radius value of a common inner diameter of the guide gaps 66 a to 66 d. Alternatively, the first value may be a square of a radius value of an outer diameter of the shaft portion 83. The second value is sum of longitudinal lengths of the guide gaps 66 a to 66 d. In other words, the second value is total of the longitudinal thickness of each guide-side projection portion 76. The third value is sealing resistance generated at the guide gaps 66 a to 66 d. Alternatively, the third value may be yield stress of the magnetorheological fluid 90 generated between the gaps. Thus, if the sealing structure 60 is capable of relatively reducing the longitudinal thickness of the magnetic flux guides 64, 65, it is possible to enhance sealing capability, and it is also possible to substantially reduce the torque loss by the small longitudinal length of the guide gaps 66 a to 66 d. As a result, in the internal combustion engine, in which rotation loss corresponding to the torque loss is generated to the camshaft 2 caused by the connection to the brake rotor 80 through the phase adjustment mechanism 110, it is possible to effectively limit the decrease in the fuel efficiency caused by the rotation loss.
Also, the multiple guide gaps having the small gap dimension are formed between the single magnetic flux guide and the shaft portion 83 of the brake rotor. As above, the single magnetic flux guide is capable of providing the configuration having the multiple staged gaps for collecting or capturing the magnetorheological fluid 90.
In other words, even the single magnetic flux guide of the present embodiment is capable of achieving the similar advantage that is achievable by the multiple guide gaps formed between the multiple magnetic flux guides and the shaft portion 83 by the multiple magnetic flux guides. Thus, it is possible to increase the self sealing function of the magnetorheological fluid 90 in the present embodiment. Also, compared with the structure having multiple magnetic flux guides stacked on one another, the number of the magnetic flux guides is smaller in the present embodiment, and thereby the structure is made thinner accordingly. As a result, it is possible to reduce the size of the structure. Also, because the number of components is reduced, the assembly manpower is also reduced accordingly. As a result, it is possible to reduce the cost of the valve timing adjusting apparatus 1.
Also, in the sealing structure 60, at least two magnetic flux guides among the multiple magnetic flux guides have the same shape and structure. Due to the above, it is possible to reduce the types of the components, and thereby it is possible to reduce the manufacturing cost of the valve timing adjusting apparatus 1.
Furthermore, in the sealing structure 60, the permanent magnet 62 and each of the magnetic flux guides 64, 65 are held by the casing 70 that is fixed to the internal combustion engine. Thus, it is possible to limit the change of the magnetic flux that is introduced to each of the guide gaps 66 a to 66 d.
In the above, in the sealing structure 60, the axial space 69 is placed between the magnetic flux guide 65 and the bearing assembly 75. Thus, even in a case, where the magnetorheological fluid 90 penetrates through the guide gap 66 d, which is the closest to the bearing assembly 75, it is possible to capture the magnetorheological fluid 90 in the space 69. Due to the above configuration, it is possible to improve the limiting effect of limiting the magnetorheological fluid 90 from penetrating through the bearing assembly 75 to the exterior of the casing 70.
According to the present embodiment, it is possible to limit (a) wear caused by the frictional resistance between the elements 70, 80, (b) deterioration of the bearing assembly 75 caused by the influence of the magnetorheological fluid 90, and (c) the characteristic change caused by the leakage of the magnetorheological fluid 90. As a result, in addition to the improvement of the fuel efficiency, it is possible to achieve high durability and high reliability of the valve timing adjusting apparatus 1.
Because the solenoid coil 95 generates the brake torque, the magnetic flux, which is caused to pass through the magnetorheological fluid 90, may deviate from a predetermined magnetic circuit to leak toward a center axis of the brake rotor 80 in a comparison example. Because the above leaked magnetic flux leaks in the direction of the magnetic flux forming the magnetic circuit or the direction along the magnetic field, the above leaked magnetic flux in a certain leakage direction may cancel the magnetic flux (magnetic field) generated by the permanent magnet 62 at the guide gaps 66 a to 66 d. As a result, sealing capability of the sealing film may deteriorate in the comparison example.
In the sealing structure 60 of the present embodiment, the magnetic flux generated by the permanent magnet 62 is more limited from leaking through the bottom wall part of the shield main body 61 a toward the fluid chamber 74 due to the magnetic shield effect of the bottom wall part having the thickness greater than the radial dimension of the guide gaps 66 a, 66 b, 66 c, 66 d. In the present embodiment, the magnetic flux generated by the permanent magnet 62 travels through the permanent magnet 62, the magnetic flux guide 64, the guide gap 66 a and 66 b, the shaft portion 83, the guide gap 66 c and 66 d, the magnetic flux guide 65, the permanent magnet 62 in this order. Thus, the magnetic flux generated by the permanent magnet 62 causes the direction of the magnetic field that is schematically shown by an arrow in FIG. 3. In other words, the magnetic field caused by the generated magnetic flux is designed to have a direction from the interior of the casing 70 to the exterior of the casing 70 (from the first side to the second side in FIG. 1). Thus, the direction of the magnetic field relative to the axial center of the shaft portion 83 is identical with the direction of the magnetic field relative to the axial center, which field is caused by the energization of the solenoid coil 95. The direction of the magnetic field caused by the permanent magnet 62 is changeable by the appropriate arrangement of the north pole and the south pole of the magnet. Also, the direction of the magnetic field caused by the energization of the solenoid coil 95 is changeable by the appropriate setting of the electric current applied to the coil 95.
Due to the above configuration, the direction of the magnetic flux generated by the permanent magnet 62 and the direction of the magnetic flux generated by the solenoid coil 95 are the same with each other relative to the axial center of the shaft portion 83. In the above configuration, part of the magnetic flux generated by the solenoid coil 95 may leak toward the shaft member 81 of the brake rotor 80 (or toward the axial center of the casing 70) as shown in by a dashed line arrow in FIG. 3. In the above leakage case, when the leaked magnetic flux passes through each sealing film of the sealing structure 60, the leaked magnetic flux is overlappingly added to the effective magnetic flux caused by the permanent magnet 62 (shown by a solid line arrow in FIG. 3). As a result, the magnetic flux that passes through each of the guide gaps 66 a to 66 d is effectively increased. Thus, sealing capability achieved by each sealing film forming the self sealing portion is further enhanced, and thereby the brake output during the brake operation is effectively improved. It should be noted that the above improvement of the sealing capability may case the increase in the torque loss. However, because the improvement of the sealing capability occurs during the brake operation, the improvement of the sealing capability contributes to the brake output.
Furthermore, the multiple magnetic flux guides 64, 65 are arranged in a direction from the interior to the exterior of the casing 70 (from the first side to the second side in FIG. 2), and the multiple guide-side projection portions 76 are formed on each of the multiple magnetic flux guides 64, 65. Thus, the guide gaps 66 a to 66 d are also arranged along the rotation axis of the rotor 80 in the direction from the interior to the exterior of the casing 70 due to the multiple guide-side projection portions 76 of the multiple magnetic flux guides 64, 65. As a result, multiple sealing films having sealing capability are formed in multiple stages or side by side along the rotation axis, and thereby it is possible to further improve the brake output.
Further, each sealing film (self sealing portion) of the sealing structure 60 is realized by each guide gap 66 a to 66 d, which is formed between (a) at least one magnetic flux guide of the multiple magnetic flux guides 64, 65 and (b) the shaft portion 83 of the brake rotor 80, and which has a radial dimension that is increased and decreased depending on a position of the guide gap in a direction from the interior to the exterior of the casing 70. The above configuration of the self sealing portion and the configuration of the similar directions of the magnetic fluxes are capable of improving sealing capability for the self sealing portion of the magnetorheological fluid formed by the smaller number of the magnetic flux guide. Thus, it is possible to provide the valve timing adjusting apparatus 1 that has an improved sealing capability for a unit longitudinal length.
In the present embodiment, the casing 70 has the bearing assembly 75 that supports the brake rotor 80. For example, the sealing structure 60 is provided between the bearing assembly 75 and the fluid chamber 74 of the casing 70. In other words, the bearing assembly 75 is provided on an outer side of the sealing structure 60 away from the fluid chamber 74. Due to the above configuration, the magnetorheological fluid 90 within the casing 70 is effectively limited from reaching the bearing assembly 75, and thereby it is advantageously possible to avoid the case, in which the magnetorheological fluid 90 enters into the bearing assembly 75, and thereby deteriorating the durability of the bearing assembly 75.
In the present embodiment, the casing 70 is fixed to the internal combustion engine and each magnetic flux guide 64, 65 is supported together with the permanent magnet 62 by the above fixed casing 70. Also, the guide gap is defined between each magnetic flux guide 64, 65 and the brake rotor 80. Due to the above configuration, the magnetic flux guide 64, 65 is stably fixed at a position relative to the permanent magnet 62 despite of the rotation of the brake rotor 80, and thereby it is possible to guides the constant magnetic flux to the guide gap. As a result, it is advantageously possible to avoid the case, in which the self sealing function realized by the magnetorheological fluid 90 changes, and thereby deteriorating the reliability.
It should be noted that in the first embodiment, the energization control circuit 120 and the solenoid coil 95 correspond to “control means”.

Second Embodiment

As shown in FIG. 4, the second embodiment of the present invention is modification of the first embodiment. In contrast to the actuator 100 of the first embodiment, an actuator 100A of the second embodiment includes a leaked magnetic flux introducing part that is provided between (a) a route of the magnetic flux, which is generated by the solenoid coil 95, and which is caused to pass through the magnetorheological fluid 90, and (b) a route of the magnetic flux, which is generated by the permanent magnet 62. The leaked magnetic flux introducing part is made of a magnetic material.
More specifically, a configuration of a magnetic rotation member 82A of a brake rotor 80A in the second embodiment is different from the configuration of the magnetic rotation member 82 of the brake rotor 80 in the first embodiment. The magnetic rotation member 82A of the second embodiment has a circular ring shape projection portion 87 that projects from a longitudinal end surface of the shaft portion 83 toward the bottom wall part 72 b of the fluid chamber defining member 72. The circular ring shape projection portion 87 is provided such that the circular ring shape projection portion 87 is exposed to the enlarged gap 93 that is defined between (a) the magnetic rotation member 82A and (b) the recess 72 c defined by the bottom wall part 72 b. The circular ring shape projection portion 87 is made of a magnetic material as a part of the magnetic rotation member 82A, and thereby the circular ring shape projection portion 87 attracts the leaked magnetic flux leaked from the solenoid coil 95 to the enlarged gap 93 as shown by a dashed line arrow in FIG. 4. As above, a certain magnetic flux leaks to the enlarged gap 93, which flux is part of the magnetic flux that forms the magnetic flux route around the solenoid coil 95. The above leaked magnetic flux is attracted from the bottom wall part 72 a of the fluid chamber defining member 72 to the circular ring shape projection portion 87 such that the magnetic flux travels through the shaft portion 83 in the longitudinal direction toward the sealing structure 60. Then, the leaked magnetic flux is effectively introduced to each sealing film of the sealing structure 60. In other words, the circular ring shape projection portion 87 functions as the “leaked magnetic flux introducing part” that attracts the leaked magnetic flux from the solenoid coil 95.
In the second embodiment, the magnetic flux leaked from the magnetic flux formed by the solenoid coil 95 is attracted toward the shaft member 81 at the enlarged gap 93, and flows into the shaft portion 83 through the circular ring shape projection portion 87. Then, the leaked magnetic flux that passes through the shaft portion 83 is added to the effective magnetic flux (solid line arrow in FIG. 4) caused by the permanent magnet 62 when the leaked magnetic flux passes through each of the guide gaps 66 a to 66 d of the sealing structure 60. As above, it is effectively attracts the leaked magnetic flux toward the effective magnetic flux, and thereby the valve timing adjusting apparatus of the present embodiment is capable of highly effectively utilizing the leaked magnetic flux.
In the present embodiment, the leaked magnetic flux introducing part 87, which is made of the magnetic material, is provided between (a) a route of the magnetic flux, which is caused by the control means, and which is caused to pass through the magnetorheological fluid 90, and (b) a route of the magnetic flux generated by the permanent magnet 62. Due to the configuration, the leaked magnetic flux leaked from the (a) route of the magnetic flux that passes through the magnetorheological fluid 90 is more likely to be guided to the leaked magnetic flux introducing part 87. As a result, the leaked magnetic flux introducing part 87 facilitates the leaked magnetic flux to reach the (b) route of the magnetic flux that passes the guide gaps. Due to the above configuration, it is possible to increase the likelihood of the leaked magnetic flux to be attracted to the sealing structure 60, and thereby it is possible to increase the amount of the magnetic flux that is added to the effective magnetic flux generated by the permanent magnet 62.

Third Embodiment

As shown in FIG. 5, the third embodiment of the present invention is a modification of the first embodiment. In contrast to the actuator 100 of the first embodiment, in the actuator 100B of the third embodiment, a leaked magnetic flux introducing part is provided between (a) a route of the magnetic flux, which is generated by the solenoid coil 95, and which passes through the magnetorheological fluid 90, and (b) a route of the magnetic flux generated by the permanent magnet 62. The above leaked magnetic flux introducing part is made of a magnetic material.
More specifically, a configuration of the bottom wall part 72 a of the fluid chamber defining member 72A of the third embodiment is different from the configuration of the bottom wall part 72 a of the fluid chamber defining member 72 of the first embodiment. The fluid chamber defining member 72A of the third embodiment has a circular ring shape projection portion 72 d that projects from an inner surface of the bottom wall part 72 a toward the sealing structure 60. The circular ring shape projection portion 72 d is provided so as to be exposed to the enlarged gap 93 that is defined between (a) the magnetic rotation member 82 and (b) the recess 72 c formed at the bottom wall part 72 b. The circular ring shape projection portion 72 d is made of a magnetic material as a part of the casing 70A, and thereby the circular ring shape projection portion 72 d is capable of attracting the leaked magnetic flux that leaks to the enlarged gap 93 from the solenoid coil 95 as shown by a dashed line arrow in FIG. 5. Thus, a certain magnetic flux leaks toward the axial center of the shaft member 81 (toward the interior of the casing 70), which magnetic flux is a part of the magnetic flux that forms the magnetic flux route around the solenoid coil 95. The above leaked magnetic flux enters into the shaft portion 83 from the enlarged gap 93 through the circular ring shape projection portion 72 d, and passes through the shaft portion 83 toward the sealing structure 60 in the longitudinal direction. Then, the leaked magnetic flux is introduced to each sealing film of the sealing structure 60. In other words, the circular ring shape projection portion 72 d functions as “leaked magnetic flux introducing part” that attracts the leaked magnetic flux from the solenoid coil 95.
In the third embodiment, the magnetic flux leaked from the magnetic flux formed by the solenoid coil 95 is attracted toward the circular ring shape projection portion 72 d, travels through the enlarged gap 93, and then flows into the shaft portion 83. Thus, the leaked magnetic flux that passes through the shaft portion 83 is added to the effective magnetic flux (solid line arrow in FIG. 5) caused by the permanent magnet 62 when the leaked magnetic flux passes through each of the guide gaps 66 a to 66 d of the sealing structure 60. As a result, it is effectively attracts the leaked magnetic flux toward the effective magnetic flux, and thereby the valve timing adjusting apparatus of the present embodiment is capable of highly effectively utilizing the leaked magnetic flux. Furthermore, the above effect is realized by the leaked magnetic flux introducing part, which is provided to the casing 70 (stationary member) instead of, for example, the brake rotor 80 (movable member). As a result, it is possible to provide a valve timing adjusting apparatus that has an efficient structure without the rotation loss.
In the present embodiment, the leaked magnetic flux introducing part 72 d projects from the bottom wall part 72 b of the casing 70 toward the sealing structure 60. Due to the above configuration, the leaked magnetic flux introducing part 72 d projects from the inner surface of the bottom wall part 72 b of the casing 70 toward the route of the magnetic flux that passes through the guide gaps. Because the leaked magnetic flux introducing part 72 d is made of the magnetic material, the leaked magnetic flux is more likely to be guided to the guide gaps through the leaked magnetic flux introducing part 72 d. As a result, the leaked magnetic flux is more likely to be added to the sealing film advantageously. Also, for example, because the leaked magnetic flux introducing part 72 d is provided to the casing 70, which is the immovably fixed to the engine, it is possible to achieve the efficient structure without the substantial rotation loss.

Other Embodiment

Although multiple embodiments of the present invention are described as above, the present invention is not limited to the above embodiments. However, the present invention is applicable to various embodiments provided that the various embodiments do not deviate from the gist.
In each of the above embodiments, the direction of the magnetic flux relative to the axial center of the shaft portion 83 caused by the permanent magnet 62 is required to match with the direction of the magnetic flux relative to the axial center of the shaft portion 83 generated by the solenoid coil 95. Thus, the directions of the magnetic fluxes are not limited to the directions described in the above embodiments. For example, the directions of the magnetic fluxes at the magnetic gap and the shaft portion 83 may correspond to a direction from the exterior to the interior of the casing 70 (i.e., a direction from the right to the left in FIG. 1).
Also, in the first embodiment, the dimensions of the guide gaps 66 a to 66 d may be different from each other alternatively. For example, the radial dimensions of the guide gaps 66 a to 66 d may be increased toward the exterior of the casing 70 (or toward the second side in FIG. 2). Furthermore, the number of the magnetic flux guides in the first embodiment may be changed as required provided that there are multiple magnetic flux guides.
Also, in the first and second embodiments, the phase adjustment mechanism 110 may have a configuration, in which the rotor 10 rotates synchronously with the camshaft 2, and the rotor 20 rotates synchronously with the crankshaft. Furthermore, the phase adjustment mechanism 110 may employ other various mechanisms other than the planet gear mechanism (differential gear mechanism) as described above, provided that the engine phase is adjustable in accordance with a rotational state of the brake rotor 80 relative to the rotor 10.
Also, the present invention may be applicable to an apparatus that adjusts valve timing of an exhaust valve in addition to the apparatus that adjusts valve timing of the intake valve. Furthermore, the present invention may be applicable to an apparatus that adjusts valve timing of both the intake valve and the exhaust valve. Additional advantages and modifications will readily occur to those skilled in the art. The invention in its broader terms is therefore not limited to the specific details, representative apparatus, and illustrative examples shown and described.

Claims

1. A valve timing adjusting apparatus for an internal combustion engine having a camshaft and a crankshaft, the valve timing adjusting apparatus adjusting valve timing of a valve that is opened and closed by the camshaft through torque transmission from the crankshaft, the valve timing adjusting apparatus comprising:

a casing that defines a fluid chamber therein;

magnetorheological fluid received in the fluid chamber, the magnetorheological fluid having a degree of viscosity changeable in accordance with magnetic flux that passes through the magnetorheological fluid;

control means for changing the degree of viscosity of the magnetorheological fluid by causing magnetic flux to pass through the magnetorheological fluid in the fluid chamber;

a brake rotor that extends through the casing from an interior to an exterior of the casing, the brake rotor being rotatably supported by the casing, the brake rotor contacting the magnetorheological fluid in the fluid chamber, the brake rotor generating brake torque in accordance with the degree of viscosity of the magnetorheological fluid;

a phase adjustment mechanism that is coupled with the brake rotor at the exterior of the casing, the phase adjustment mechanism adjusting a relative phase between the crankshaft and the camshaft in accordance with the brake torque generated by the brake rotor; and

a sealing structure that seals a gap between the casing and the brake rotor, wherein:

the sealing structure includes:

an annular permanent magnet that is placed at the interior of the casing to extend in a rotational direction of the brake rotor, the permanent magnet generating magnetic flux, the permanent magnet being supported by one of the casing and the brake rotor; and

at least one annular magnetic flux guide that is placed at the interior of the casing to extend in the rotational direction, the at least one magnetic flux guide being supported by the one of the casing and the brake rotor, the at least one magnetic flux guide defining a guide gap, through which magnetic flux generated by the permanent magnet travels, between the at least one magnetic flux guide and the other one of the casing and the brake rotor; and

a direction of magnetic flux relative to an axial center of the brake rotor, which flux is generated by the control means, and which flux passes through the magnetorheological fluid, is similar to a direction of magnetic flux relative to the axial center generated by the permanent magnet.

2. The valve timing adjusting apparatus according to claim 1, wherein:

the at least one magnetic flux guide includes a plurality of magnetic flux guides that is arranged in a direction from the interior to the exterior of the casing.

3. The valve timing adjusting apparatus according to claim 2, wherein:

the guide gap is defined between (a) each of the plurality of magnetic flux guides and (b) a shaft portion of the brake rotor; and

the guide gap defined at each of the plurality of magnetic flux guides has a radial dimension that is increased and decreased in the direction from the interior to the exterior of the casing.

4. The valve timing adjusting apparatus according to claim 1, wherein:

the casing includes a bearing assembly that supports the brake rotor; and

the sealing structure is provided between the bearing assembly and the fluid chamber of the casing.

5. The valve timing adjusting apparatus according to claim 1, wherein:

the casing is fixed to the internal combustion engine;

the casing holds the at least one magnetic flux guide together with the permanent magnet; and

the guide gap is defined between each of the at least one magnetic flux guide and the brake rotor.

6. The valve timing adjusting apparatus according to claim 5, further comprising:

a leaked magnetic flux introducing part that is provided between (a) a route of magnetic flux, which is generated by the control means, and which passes through the magnetorheological fluid, and (b) a route of magnetic flux generated by the permanent magnet; and

the leaked magnetic flux introducing part is made of a magnetic material.

7. The valve timing adjusting apparatus according to claim 6, wherein:

the casing has a bottom wall part that defines the fluid chamber; and

the leaked magnetic flux introducing part projects from an inner surface of the bottom wall part toward the sealing structure.