Sensor magnet device, gear mechanism and speed reducing electric motor

In a speed reducing electric motor, a speed reducing gear unit has a sensor magnet device, which is fixed to a worm wheel and includes an inner ring magnet, an outer ring magnet and connecting portions. The inner ring magnet is placed along a predetermined first imaginary circle. The outer ring magnet is placed along a predetermined second imaginary circle, which is coaxial with the first imaginary circle and has a diameter that is smaller or larger than that of the first imaginary circle. The connecting portions connect between the inner ring magnet and the outer ring magnet. The sensor magnet device is fixed to the worm wheel by a magnet fixing structure.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on and incorporates herein by reference Japanese Patent Application No. 2007-57621 filed on Mar. 7, 2007, Japanese Patent Application No. 2007-57622 filed on Mar. 7, 2007 and Japanese Patent Application No. 2007-182538 filed on Jul. 11, 2007.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sensor magnet device, a gear mechanism and a speed reducing electric motor.

2. Description of Related Art

The present invention relates to a sensor magnet device, a gear mechanism and a speed reducing electric motor.

A known speed reducing electric motor includes a speed reducing mechanism, which is formed as a unit that includes a worm speed reducing mechanism connected to a motor main body. An annular magnet, which serves as a sensing subject of a rotational position sensor (magnetic sensor), is coaxially fixed to a worm wheel of the worm speed reducing mechanism, which rotates together with an output shaft. Such a speed reducing electric motor is disclosed in, for example, Japanese Unexamined Patent Publication No. 2005-94821. According to the technique disclosed in this publication, the magnet is rotated together with the output shaft. A magnetic pole change, which is made by a characteristic magnetic pole pattern of the magnet, is sensed with a Hall IC to determine a rotational position of the output shaft.

However, the magnet of the above technique is merely configured into a simple annular body, so that there is still a need for improving the magnet to sense a greater amount of information about a rotational position (rotational state) of the output shaft to increase a sensing accuracy of the rotational position sensor.

Furthermore, the magnet of the above technique is fixed to the worm wheel by bonding the magnet to the worm wheel with a bonding agent, by snap-fitting claws of the worm wheel to a peripheral surface of the magnet or by welding a portion of the worm wheel upon installation of the magnet to the worm wheel to limit unintentional removal of the magnet. The first two methods, i.e., the bonding and the snap-fitting have the disadvantages discussed in Japanese Unexamined Patent Publication No. 2005-94821. Furthermore, heat generated at the time of welding of the portion of the worm wheel may possibly cause a deformation of the worm wheel and/or the magnet (particularly in a case of a bond magnet). The deformation of the gear and/or the magnet may possibly cause an error in a measurement of the rotational position sensor to deteriorate the sensing accuracy of the rotational position sensor.

SUMMARY OF THE INVENTION

The present invention addresses the above disadvantage. Thus, it is an objective of the present invention to provide a sensor magnet device, which enables a magnetic sensor to relatively accurately sense a greater amount of information about a rotational state of a sensing subject. It is another objective of the present invention to provide a gear mechanism having such a sensor magnet device. It is a further objective of the present invention to provide a speed reducing electric motor having such a gear mechanism.

To achieve the objectives of the present invention, there is provided a sensor magnet device, which includes at least one primary magnet portion, at least one secondary magnet portion and at least one connecting portion. The at least one primary magnet portion is placed along a predetermined first imaginary circle. The at least one secondary magnet portion is placed along a predetermined second imaginary circle, which is coaxial with the first imaginary circle and has a diameter that is smaller or larger than that of the first imaginary circle. The at least one connecting portion connects between the at least one primary magnet portion and the at least one secondary magnet portion.

To achieve the objectives of the present invention, there is also provided a gear mechanism, which includes a gear, the above-described sensor magnet device and a fixing means. The gear transmits rotation to an output shaft. The sensor magnet device is placed at one axial end side of the gear and is formed such that the sensor magnet device causes an external magnetic sensor to directly or indirectly sense a rotational state of the output shaft. The fixing means is for fixing the sensor magnet device to the gear. The fixing means includes at least one through hole, at least one fixing protrusion and at least one fixing element. The at least one through hole extends through one of the gear and the sensor magnet device in an axial direction of the output shaft. The at least one fixing protrusion protrudes from the other one of the gear and the sensor magnet device in the axial direction and is respectively received through the at least one through hole in the axial direction. The at least one fixing element is respectively securely installed to a protruding distal end portion of the at least one fixing protrusion, which respectively protrudes from the at least one through hole, in the axial direction, so that the sensor magnet device is coaxially and integrally rotatably fixed to the gear. The sensor magnet device of the gear mechanism may be replaced with another sensor magnet device that includes a magnetic material and is magnetized to have at least one predetermined magnetizing pattern. The sensor magnet device is placed at one axial end side of the gear and is formed such that the sensor magnet device causes an external magnetic sensor to directly or indirectly sense a rotational state of the output shaft.

To achieve the objectives of the present invention, there is also provided a speed reducing electric motor, which includes a motor unit and a speed reducing unit. The speed reducing unit includes the above described gear mechanism. The gear mechanism reduces a rotational speed of rotation transmitted from the motor unit and thereafter conducts the rotation to the output shaft to drive an external driven-side member connected to the output shaft.

DETAILED DESCRIPTION OF THE INVENTION

First Embodiment

A sensor magnet device100according to a first embodiment of the present invention will be described with reference toFIGS. 1 to 7. First, a structure of the sensor magnet device100alone will be described. Then, a speed reducing electric motor10having such a sensor magnet device100will be described. Thereafter, advantages of the sensor magnet device100will be described.

As shown inFIGS. 1A and 1B, the sensor magnet device100includes an inner ring magnet (serving as a primary magnet portion of the present invention)102, an outer ring magnet (serving as a secondary magnet portion of the present invention)104and connecting portions106. The connecting portions106connect between the inner ring magnet102and the outer ring magnet104. Here, it should be noted that the inner ring magnet102and the outer ring magnet104may alternately serve as the secondary magnet portion and the primary magnet portion, respectively, of the present invention in some cases.

As shown inFIG. 1A, the inner ring magnet102is configured into an annular body, which extends along generally a predetermined imaginary circle. The outer ring magnet104is configured as an annular body, which extends along generally another predetermined imaginary circle and has an inner diameter larger than an outer diameter of the inner ring magnet102. The outer ring magnet104and the inner ring magnet102are radially connected with each other by the connecting portions106such that the outer ring magnet104and the inner ring magnet102are concentric to each other. As shown inFIG. 1B, the inner ring magnet102and the outer ring magnet104have generally the same axial thickness t1and overlap with each other along generally the entire axial thickness thereof in the axial direction.

As shown inFIG. 1A, the connecting portions (three connecting portions in this embodiment)106are arranged at generally equal intervals in the circumferential direction of the outer ring magnet104. The connecting portions106connect between the inner ring magnet102and the outer ring magnet104within the axially overlapped extent, within which the inner ring magnet102and the outer ring magnet104axially overlap with each other. In other words, the connecting portions106are interposed between an outer peripheral surface102A of the inner ring magnet102and an inner peripheral surface104A of the outer ring magnet104and are placed within the extent of the thickness t1of the inner ring magnet102and of the outer ring magnet104.

As shown inFIG. 1B, each connecting portion106has an axial thickness t2, which is smaller than the thickness t1of each of the inner ring magnet102and the outer ring magnet104. In the present embodiment, each connecting portion106is configured such that an axial end surface106A of the connecting portion106in the axial direction of the sensor magnet device100is generally flush with an adjacent axial end surface102B of the inner ring magnet102and an adjacent axial end surface104B of the outer ring magnet104. Furthermore, each connecting portion106has a fitting hole108, which penetrates through the connecting portion106in the thickness direction. The fitting holes108of the connecting portions106are used to fix the sensor magnet device100to a worm wheel22(described latter) of the speed reducing electric motor10.

The sensor magnet device100, which is configured to have the above dimensions and the shape, is formed such that a center of mass of the sensor magnet device100alone coincides with the axis of the sensor magnet device100.

The inner ring magnet102and the outer ring magnet104of the sensor magnet device100are magnetized as follows. That is, inFIG. 1A, a shaded portion (dotted portion) of the inner ring magnet102forms an N-pole102N, and the rest of the inner ring magnet102forms an S-pole102S. Also, a shaded portion (dotted portion) of the outer ring magnet104forms an N-pole104N, and the rest of the outer ring magnet104forms an S-pole104S. An extent (at least one of a start point and an end point of the extent) of the N-pole102N of the inner ring magnet102in the rotational direction (circumferential direction) differs from an extent (at least one of a start point and an end point of the extent) of the N-pole104N of the outer ring magnet104in the rotational direction (circumferential direction). That is, in the present embodiment, the sensor magnet device100is constructed such that a magnetizing pattern of the inner ring magnet102in the rotational direction differs from a magnetizing pattern of the outer ring magnet104in the rotational direction.

The sensor magnet device100is made of plastic magnet (bond magnet), which is prepared by mixing magnetic powder into a resin material. Specifically, in the sensor magnet device100, the inner ring magnet102, the outer ring magnet104and the connecting portions106are integrally molded from the plastic magnet material. The magnetic powder may be selected from, for example, ferrite magnetic power, alnico magnetic powder, neodymium-iron-boron magnetic power and samarium-cobalt magnetic powder. Furthermore, the resin material may be selected from, for example, nylon, polypropylene and polyamide. In the present embodiment, the sensor magnet device100is made of the material, which is prepared by adding ferrite magnetic power into nylon.

The other end surface102C of the inner ring magnet102, which is opposite from the end surface102B, and the other end surface104C of the outer ring magnet104, which is opposite from the end surface104B, are opposed to a magnetic sensor150(described latter). A magnetic pole change, which is caused by the relative rotation of the sensor magnet device100with respect to the magnetic sensor150, is sensed with the magnetic sensor150.

Now, an example of applying the sensor magnet device100to the speed reducing electric motor10will be described. As shown inFIG. 2, the speed reducing electric motor10includes a motor unit12and a speed reducing gear unit14(worm speed reducing apparatus), which are assembled together. In the motor unit12, an armature (not shown) is provided, and a distal end side of a rotatable shaft16of the armature protrudes into a housing20of the speed reducing gear unit14. A worm18is provided in the housing20such that the worm18is coaxially and integrally rotated along with the rotatable shaft16.

In the housing20, the worm18is meshed with the worm wheel (serving as a gear of the present invention)22and cooperates with the worm wheel22to form a worm speed reducing mechanism24. As shown inFIGS. 3 and 5, the worm wheel22is configured into a circular disk body. A toothed portion23is provided in an outer peripheral part of the worm wheel22to mesh with the worm18, and an output shaft26is coaxially fixed to an axial center of the worm wheel22to rotate integrally with the worm wheel22. In this example, the worm wheel22is made of a resin material and is insert molded integrally with one axial end portion of the output shaft26, which is made of metal.

Although not depicted for the sake of simplicity, the output shaft26extends through a bottom plate20A of the housing20and is supported by a bearing in a rotatable manner relative to the housing20. A protruding distal end portion of the output shaft26, which protrudes outward from the housing20, is connected to a driven-side member (a load device) in a manner that enables transmission of a drive force therebetween. With the above construction, in the speed reducing electric motor10, when the motor unit12is driven, rotation (torque) of the motor unit12is transmitted to the output shaft26through the worm speed reducing mechanism24while a speed of the rotation is reduced to increase the torque through the worm speed reducing mechanism24.

Furthermore, as shown inFIG. 3, a position sensing device30, which senses a rotational position of the output shaft26in its rotating state, is provided to the speed reducing gear unit14. The position sensing device30includes the sensor magnet device100and the magnetic sensor150as its main components. The sensor magnet device100is coaxially fixed to the worm wheel22to rotate integrally with the worm wheel22. The magnetic sensor150outputs a signal, which corresponds to the magnetic pole change of the sensor magnet device100caused by the rotation of the worm wheel22.

As shown inFIGS. 3 and 5, the sensor magnet device100is fixed to an end portion22A of the worm wheel22, which is opposite from the side where the output shaft26protrudes. Furthermore, as shown inFIGS. 2 and 3, the magnetic sensor150is installed to a circuit board34, which is fixed to the housing20. An output signal of the magnetic sensor150is outputted to a controller (not shown), which is provided on the circuit board34.

Also, as shown inFIGS. 2 and 3, an inner cover36is interposed between the worm wheel22(thereby, the sensor magnet device100) and the circuit board34(thereby, the magnetic sensor150). The inner cover36covers the worm speed reducing mechanism24in the housing20. Furthermore, an outer cover38is connected to an opening end20B of the housing20. The housing20and the outer cover38cooperate together to cover (receive) the worm speed reducing mechanism24, the position sensing device30and the circuit board34(the controller).

Furthermore, as shown inFIGS. 3 and 4, the position sensing device30includes a plurality (two in this example) of Hall elements (or Hall ICs)44,46to correspond with the sensor magnet device100, which includes the multiple (two) magnetizing patterns, i.e., the inner ring magnet102and the outer ring magnet104. In this example, the Hall elements44,46are arranged one after another along a common imaginary straight line (radial line), which extends from a rotational center of the worm wheel22(the sensor magnet device100).

The Hall element44is placed to oppose the axial end surface102C of the inner ring magnet102and outputs the signal, which corresponds to the magnetic pole change caused by the rotation of the inner ring magnet102. In contrast, the Hall element46is placed to oppose the axial end surface104C of the outer ring magnet104and outputs the signal, which corresponds to the magnetic pole change caused by the rotation of the outer ring magnet104.

A reference position of the position sensing device30, which includes the inner ring magnet102, the outer ring magnet104and the Hall elements44,46, may be set as follows. That is, a position, at which the Hall elements44,46output signals, which respectively correspond to the magnetic pole changes with respect to the S-poles102S,104S, may be set as the reference position (e.g., a stop position). Additionally, a position, at which the Hall element44outputs a signal that corresponds to the magnetic pole change with respect to the N-pole102N, may be set as another reference position (e.g., a trigger position).

The above described speed reducing electric motor10may be used as a wiper motor, which serves as a drive source of a wiper system, particularly, a wiper motor, which is reciprocally rotated (rotated forward and backward) through a predetermined angular range. In such a case, in the position sensing device30, for example, the reference position may be set as a lower turning position of a wiper arm. Here, an armature pulse is counted up until the time of reversing the rotational direction of the motor unit12(i.e., until the wiper arm reaches an upper turning position thereof), and then the armature pulse is counted down during a downward movement of the wiper arm toward the lower turning position. Furthermore, the trigger position is set as a trigger for initiating forceful setting (forceful correcting) of the counted number of the armature pulse to a predetermined number, which corresponds to a predetermined position of the output shaft (a predetermined position of the wiper).

Next, a magnet fixing structure (serving as a fixing means)50, which fixes the sensor magnet device100to the worm wheel22of the speed reducing electric motor10, will be described.

The magnet fixing structure50is constructed to fix the sensor magnet device100to the worm wheel22in such a manner that the end surfaces102B,104B,106A of the sensor magnet device100contact seat surfaces22C of protruded seat portions22B, which are arranged one after another in the circumferential direction at the end portion22A of the worm wheel22. As shown inFIGS. 5 to 7, the magnet fixing structure50includes the fitting holes108of the connecting portions106of the sensor magnet device100, fixing pins (fixing protrusions)56of the worm wheel22and internal toothed rings58. Each fixing pin56protrudes from the seat surface22C of a corresponding one of the seat portions22B of the worm wheel22, and each toothed ring58is securely fitted to a corresponding one of the fixing pins56. The above structure of the magnet fixing structure50will be described in detail.

As shown inFIG. 7, a protruding height H of each fixing pin56, which is measured from the corresponding seat surface22C, is set to be smaller than the axial thickness t1of each of the inner ring magnet102and the outer ring magnet104and is larger than the axial thickness t2of each connecting portion106. A cross sectional area (a circular cross sectional area in this example) of each fitting hole108and a cross sectional area (a circular cross sectional area in this example) of the corresponding fixing pin56correspond with each other and are configured such that the fixing pin56is fitted (lightly press fitted) into the fitting hole108. In this way, the sensor magnet device100has the above described installation position relative to the worm wheel22. In this installation position, each fixing pin56, which has the above described protruding height, extends through the fitting hole108and thereby through the connecting portion106without protruding from the end surface102C of the inner ring magnet102and the end surface104C of the outer ring magnet104.

As shown inFIG. 7, in this example, a distal end portion56A of each fixing pin56, which protrudes from the corresponding connecting portion106, has a smaller outer diameter in comparison to an outer diameter of a fitting portion56B of the fixing pin56, which is fitted to the fitting hole108. In the above-described installation position, the distal end portion56A of the fixing pin56is placed between the outer peripheral surface102A of the inner ring magnet102and the inner peripheral surface104A of the outer ring magnet104.

Furthermore, as described above, the magnet fixing structure50includes the toothed rings58, each of which serves as a fixing element that is engaged (fitted) to the distal end portion56A of the fixing pin56. The toothed ring58is engaged with the distal end portion56A of the corresponding fixing pin56in a manner that limits unintentional removal of the fixing pin56from the connecting portion106(more specifically, from the fitting hole108).

The structure of each toothed ring58will now be described in more detail. As shown in.FIG. 6, the toothed ring58has a ring portion58A and a plurality (for example, four) of teeth58B. InFIG. 6, the teeth58B uprightly and inwardly extend in a radial direction of the ring portion58A from an inner peripheral edge of the ring portion58A and are arranged one after another at generally equal intervals in a circumferential direction of the ring portion58A. The teeth58B are formed by cutting a corresponding annular section, which is located radially inward of the ring portion58A, into corresponding pieces (serving as the teeth58B in the final product) and pulling these pieces upwardly, so that the teeth58B are tilted relative to an axis of the ring portion58A. The toothed ring58is made of a metal material (e.g., spring steel). For example, a well known internal toothed washer may be used as the toothed ring58, if desired.

The toothed ring58is installed to the fixing pin56made of the resin as follows. That is, the ring portion58A is pushed around the fixing pin56until the ring portion58A is seated against the connecting portion106, so that the distal end portion56A of the fixing pin56is received through an opening located radially inward of the teeth58B, and radially inner ends58C of the teeth58B engage with (bite into) an outer peripheral surface of the distal end portion56A of the fixing pin56. In this way, the teeth58B of the toothed ring58radially inwardly clamp the distal end portion56A of the fixing pin56to tightly engage with the distal end portion56A, so that the unintentional removal of the fixing pin56from the connecting portion106is advantageously limited by the toothed ring58. Thereby, the sensor magnet device100is fixed to the worm wheel22while each connecting portion106of the sensor magnet device100is clamped between the ring portion58A of the corresponding toothed ring58and the corresponding seat surface22C of the worm wheel22.

Furthermore, as described above, the sensor magnet device100of the speed reducing gear unit14is formed such that the center of mass of the sensor magnet device100alone coincides with the axis of the sensor magnet device100. Thus, when the sensor magnet device100is fixed to the worm wheel22, the center of mass of the sensor magnet device100coincides with the rotational axis of the worm wheel22, i.e., the rotational axis of the output shaft26. That is, the magnet fixing structure50, which uses the connecting portions106arranged one after another in the circumferential direction of the sensor magnet device100, maintains the center of mass of the sensor magnet device100and of the worm wheel22.

Next, the operation of the motor10of the present embodiment will be described.

In the speed reducing electric motor10, which has the sensor magnet device100, when the motor unit12is driven, the worm18of the speed reducing gear unit14is rotated about its axis, so that the worm wheel22, which is meshed with the worm18, is rotated about its axis. Since the worm wheel22is fixed to the output shaft26, the output shaft26is rotated integrally with the worm wheel22at the rotational speed (with the increased torque), which is reduced in comparison to the rotational speed of the worm18.

At this time, the sensor magnet device100is rotated integrally with the worm wheel22, so that the signal, which corresponds to the rotational position of the output shaft26, i.e., the rotational position of the inner ring magnet102and of the outer ring magnet104, is outputted from the Hall elements44,46(thereby enabling the sensing of the rotational state of the output shaft26). The controller, which is provided in the circuit board34, controls the actuation, stop and rotational direction of the motor unit12based on the signal, which corresponds to the rotational position of the output shaft26and is received from the Hall elements44,46.

As described above, the sensor magnet device100includes the inner ring magnet102and the outer ring magnet104, which are arranged coaxially along two coaxial circles, respectively. Thus, in comparison to the single ring magnet, the greater amount of information about the rotational state (rotational position) of the output shaft26can be sensed through the magnetic sensor150in the case of the sensor magnet device100. Furthermore, in the sensor magnet device100, the inner ring magnet102and the outer ring magnet104are connected together by the connecting portions106. Therefore, it is possible to limit the circumferential positional deviation between the inner ring magnet102and the outer ring magnet104. In this way, in the sensor magnet device100, the relative position between the inner magnetizing pattern of the inner ring magnet102and the outer magnetizing pattern of the outer ring magnet104are maintained by the connecting portions106. As a result, the information about the rotational state of the output shaft26can be more accurately sensed based on the relative position (difference) between the inner magnetizing pattern of the inner ring magnet102and the outer magnetizing pattern of the outer ring magnet104.

As described above, in the case of the sensor magnet device100of the present embodiment, the relatively large amount of information about the rotational state of the output shaft26can be relatively accurately sensed by, for example, the controller through use of the magnetic sensor150.

Furthermore, in the sensor magnet device100, the inner ring magnet102is configured into the annular form, so that it is possible to maintain the position of the sensor magnet device100along the predetermined circle by the inner ring magnet102alone. Thus, the structure of the sensor magnet device100is relatively simple. Similarly, in the sensor magnet device100, the outer ring magnet104is configured into the annular form, so that it is possible to maintain the position of the sensor magnet device100along the other predetermined circle by the outer ring magnet104alone. Thus, the structure of the sensor magnet device100is relatively simple. In the sensor magnet device100, the inner ring magnet102and the outer ring magnet104are connected together by the connecting portions106, which also serve as the components of the magnet fixing structure50. Therefore, the entire sensor magnet device100can be handled as the single component.

Furthermore, in the sensor magnet device100, the inner ring magnet102and the outer ring magnet104are overlapped with each other in the axial direction, so that the entire sensor magnet device100is relative thin in the axial direction. Furthermore, the connecting portions106are provided in this overlapped extent, so that the connecting portions106can be provided without axially protruding from the inner ring magnet102and the outer ring magnet104.

Furthermore, in the sensor magnet device, the magnet fixing structure50is formed by providing the fitting hole108in each connecting portion106. Thus, a non-magnetized portion (a non-continuous portion) is not formed by the fitting holes108in the inner ring magnet102and the outer ring magnet104. Thereby, it is possible to form the continuous magnetizing pattern all around the inner ring magnet102and the continuous magnetizing pattern all around the outer ring magnet104.

Furthermore, in the speed reducing electric motor10, the center of mass of the sensor magnet device100coincides with the center of mass of the worm wheel22. Thus, even when the sensor magnet device100and the worm wheel22are rotated together, the rotational balance of the worm wheel22and thereby of the output shaft26are not deteriorated. Therefore, the worm wheel22and the output shaft26can be rotated in the stable manner.

Furthermore, in the sensor magnet device100, the magnetizing pattern of the inner ring magnet102and the magnetizing pattern of the outer ring magnet104are different from each other in the circumferential direction (rotational direction). Therefore, various types of information about the rotational state of the output shaft26can be sensed based on the difference between the magnetizing pattern of the inner ring magnet102and the magnetizing pattern of the outer ring magnet104. Particularly, in the case of the speed reducing electric motor10where the Hall elements44,46of the magnetic sensor150are arranged one after another along the imaginary straight line, which radially extends from the rotational center of the output shaft26, i.e., where the Hall elements44,46of the magnetic sensor150are arranged at the same phase in the rotational direction of the worm wheel22, it is still possible to sense various types of information about the rotational state of the output shaft26due to the difference between the magnetizing pattern of the inner ring magnet102and the magnetizing pattern of the outer ring magnet104.

Now, a procedure of fixing the sensor magnet device100to the worm wheel22of the speed reducing gear unit14through use of the magnet fixing structure50will be described in detail. First, the sensor magnet device100is brought toward the worm wheel22in the axial direction while the sensor magnet device100is oriented such that the end surface102B of the inner ring magnet102, the end surface104B of the outer ring magnet104and the end surface106A of each connecting portion106are opposed to the end portion22A of the worm wheel22.

In this process, the fixing pins56of the worm wheel22are fitted into the fitting holes108of the connecting portions106of the sensor magnet device100until the end surface102B of the inner ring magnet102, the end surface104B of the outer ring magnet104and the end surfaces106A of the connecting portions106contact the seat surfaces22C of the seat portions22B of the worm wheel22. In this way, the fitting portions56B of the fixing pins56are lightly press fitted into the fitting holes108, respectively. Thereby, the sensor magnet device100is temporarily held by the worm wheel22. Then, the toothed rings58are fitted to the distal end portions56A of the fixing pins56by urging each toothed ring58against the distal end portion56A of the corresponding fixing pin56in the axial direction of the fixing pin56(the axial direction of the worm wheel22) until the ring portion58A of the toothed ring58, which receives the distal end portion56A of the fixing pin56therein, is seated against the corresponding connecting portion106.

In this way, at the magnet fixing structure50, the unintentional removal of each fixing pin56from the corresponding fitting hole108is limited. In other words, in the installed state of the toothed ring58where the corresponding connecting portion106is clamped between the seat portion22B of the worm wheel22and the toothed ring58, movement of the toothed ring58relative to the worm wheel22is limited, and thereby movement of the sensor magnet device100relative to the worm wheel22is limited. Thus, the sensor magnet device100is fixed to the worm wheel22by the magnet fixing structure50, so that the sensor magnet device100can rotate coaxially and integrally with the sensor magnet device100.

In the magnet fixing structure50of the speed reducing gear unit14, the sensor magnet device100is clamped between the worm wheel22and the toothed rings58to fix the sensor magnet device100to the worm wheel22. Therefore, a heat treatment is not required unlike the case where heat welding is required to fix the worm wheel22and the sensor magnet device100. Thus, in the magnet fixing structure50of the speed reducing gear unit14, thermal deformation of the worm wheel22and the sensor magnet device100, which would be caused by the heat treatment, will not occur.

In this way, in the speed reducing gear unit14, the required dimensional accuracy of the worm wheel22can be achieved. As a result, the rotation of the worm18(the motor unit12) can be smoothly transmitted to the output shaft26. Furthermore, in the speed reducing gear unit14, the required dimensional accuracy of the inner ring magnet102(and the magnetizing pattern thereof) and of the outer ring magnet104(and the magnetizing pattern thereof) of the sensor magnet device100is achieved. Thus, the required sensing accuracy of the rotational position of the output shaft26can be achieved.

Furthermore, in the speed reducing gear unit14, since the sensor magnet device100can be fixed to the worm wheel22by the magnet fixing structure50without requiring the heat treatment of the sensor magnet device100, it is possible to limit a decrease in the magnetization of the sensor magnet device100caused by the heat treatment. Therefore, a change in the magnetic characteristics of the sensor magnet device100, which would be caused by the decrease in the magnetization, can be advantageously limited. Even in this way, the sensing accuracy of the rotational position of the output shaft26can be enhanced.

As described above, in the speed reducing gear unit14, the rotational state of the output shaft26can be accurately sensed.

Furthermore, in the magnet fixing structure50of the speed reducing gear unit14, the sensor magnet device100can be accurately fixed to the worm wheel22without making an excessive play by simply fitting the fixing pins56of the worm wheel22into the fitting holes108of the sensor magnet device100and by simply fitting the toothed rings58to the distal end portions56A of the fixing pins56. Particularly, since the installation direction of these components coincide with the axial direction of the worm wheel22(the sensor magnet device100), the automatic assembling machine for assembling these components can be made relatively simple.

Furthermore, in the magnet fixing structure50of the speed reducing gear unit14, the fixing pins56(the fitting portions56B) of the worm wheel22are lightly press fitted into the fitting holes108of the sensor magnet device100. Thus, at the time of assembling, the sensor magnet device100can be accurately positioned relative to the worm wheel22and can be provisionally held to limit the unintentional removal of the sensor magnet device100from the worm wheel22. Also, since the fixing pins56(the fitting portions56B) of the worm wheel22are lightly press fitted into the fitting holes108of the sensor magnet device100, wobbling of the sensor magnet device100relative to the worm wheel22in the radial direction (direction perpendicular to the axial direction) can be limited. Furthermore, the press fitting direction of the fixing pins56of the worm wheel22against the fitting holes108of the sensor magnet device100is the same as the installation direction of each toothed ring58to the corresponding fixing pin56. Thus, the sensor magnet device100, which is in the provisionally held state, can be securely fixed to the fixing pins56at the time of installing the toothed rings58to the fixing pins56.

Furthermore, in the speed reducing electric motor10, which has the speed reducing gear unit14, the rotational state of the output shaft26can be accurately sensed. Thus, the operation of the driven-side member (e.g., the wiper arm), which is connected to the output shaft26, can be accurately controlled based on the sensed result, which indicates the rotational state of the output shaft26.

In the first embodiment, the inner ring magnet102and the outer ring magnet104are both configured into the annular form. However, the present invention is not limited to this. For example, as shown inFIGS. 8A to 8D, the inner ring magnet102and the outer ring magnet104may be modified as follows. In a first modification shown inFIG. 8A, a plurality (three in this modification) of arcuate magnets112(serving as secondary magnet portions) is provided in place of the outer ring magnet104and is connected to the inner ring magnet102(serving as the primary magnet portion) through the connecting portions106to form a sensor magnet device110.

In a second modification shown inFIG. 8B, a plurality (three in this modification) of arcuate magnets122(serving as primary magnet portions) is provided in place of the inner ring magnet102and is connected to the outer ring magnet104(serving as the secondary magnet portion) through the connecting portions106to form a sensor magnet device120.

In a third modification shown inFIG. 8C, the arcuate magnets122(serving as the primary magnet portions) are held together by a center connecting portion132to have a fixed relative position thereof along a predetermined circle and are connected to the arcuate magnets112(serving as the secondary magnet portions) through the connecting portions106to form a sensor magnet device130.

In a fourth modification shown inFIG. 8D, each adjacent two of the arcuate magnets122(serving as the primary magnet portions) are held together by a corresponding circumferential connecting portion142to have a fixed relative position thereof along a predetermined circle and are connected to the outer ring magnet104(serving as the secondary magnet portion) through the connecting portions106to form a sensor magnet device140. In the fourth modification, the three fitting holes108are formed in the three circumferential connecting portions142, respectively. In this example, the outer ring magnet104may be alternatively used as the primary magnet portion, and the arcuate magnets122may be alternatively used as the secondary magnet portions. Furthermore, in the structure ofFIG. 8D, in place of the outer ring magnet104, the arcuate magnets112may be provided as the secondary magnet portions.

Although not described in detail, it should be understood that besides the above exemplary modifications, any other combinations and modifications may be made within the spirit and scope of the present invention.

Furthermore, in the above embodiment and modifications, the magnets of the sensor magnet device100,110,120,130,140are arranged along two concentric circles. However, the present invention is not limited to such a configuration. For example, multiple magnets may be arranged along three or more concentric circles (including arcs) to form the sensor magnet device.

Furthermore, in the above embodiment and the modifications, the inner ring magnet102, the outer ring magnet104and the arcuate magnets112,122have generally the same axial thickness and are overlapped generally along the entire thickness. However, the present invention is not limited to this. For example, the inner ring magnet102(or the arcuate magnets122) and the outer ring magnet104(or the arcuate magnets112) may be axially offset from each other and may have different axial thicknesses, respectively, depending on the need. Furthermore, the connecting portions106are not necessarily placed in the overlapped extent, in which the inner ring magnet102and the outer ring magnet104are overlapped with each other, or in the axial thickness range of the inner ring magnet102or of the outer ring magnet104.

Furthermore, in the above embodiment, the magnetizing pattern of the inner ring magnet102and the magnetizing pattern of the outer ring magnet104are different from each other such that the angular extent or size (circumferential length) of the N-pole40N (or S-pole102S) differs from the angular extent or size (circumferential length) of the N-pole104N (or S-pole104S). However, the present invention is not limited to this. For example, while keeping the angular size of the N-pole102N generally equal to the angular size of the N-pole104N, the N-pole102N and the N-pole104N may be displaced from each other in the rotational direction, so that the magnetizing pattern of the inner ring magnet102and the magnetizing pattern of the outer ring magnet104are different from each other. Alternatively, the angular size of the N-pole102N and the angular size of the N-pole104N may coincide with each other, and at the same time, the angular location of the N-pole102N and the angular location of the N-pole104N may coincide with each other. In such a case, the circumferential position of the Hall element44and the circumferential position of the Hall element46may be different from each other. Specifically, the speed reducing electric motor10may be constructed to have different magnetizing patterns by using the magnetic sensor150that has the Hall elements44,46, which are circumferentially spaced from each other. Furthermore, for example, at least one of the inner ring magnet102and the outer ring magnet104may have more than one N-pole102N,104N and/or more than one S-pole102S,104S to implement the different magnetizing patterns.

Second Embodiment

Next, a speed reducing gear unit (worm speed reducing apparatus)70according to a second embodiment of the present invention will be described with reference toFIGS. 9 to 11. Components, which are similar to those of the first embodiment, will be indicated by the same reference numerals and will not be described further.

As shown inFIGS. 9 and 10, the speed reducing gear unit70is different from the speed reducing gear unit14of the first embodiment such that the speed reducing gear unit70includes a magnet fixing structure72in place of the magnet fixing structure50. The magnet fixing structure72is different from the magnet fixing structure50as follows. That is, in the magnet fixing structure72, each connecting portion106of the sensor magnet device100has a tapered opening74, which is coaxial with the corresponding fitting hole108and extends continuously from the fitting hole108.

Specifically, as shown inFIG. 9, the tapered opening74is configured to open on the side of the connecting portion106, which is opposite from the end surface106A of the connecting portion106located on the worm wheel22side. An inner diameter of the tapered opening74continuously changes such that the tapered opening74has a maximum inner diameter at an opening end (a maximum diameter portion)74A of the tapered opening74and a minimum inner diameter at an opposite fitting hole108side end of the tapered opening74. Also, as shown inFIG. 9, the maximum inner diameter Dmax of the tapered opening74is set to be larger than the outer diameter Dk of the toothed ring58, and the minimum inner diameter Dmin of the tapered opening74is set to be smaller than the outer diameter Dk of the toothed ring58. Furthermore, the maximum inner diameter Dmax of the tapered opening74is generally the same as a gap G between the inner ring magnet102and the outer ring magnet104.

Thus, the tapered opening74is tapered like a bowl between the outer peripheral surface102A of the inner ring magnet102and the inner peripheral surface104A of the outer ring magnet104to receive the toothed ring58.

Furthermore, as shown inFIG. 9, the protruding height (the height in the axial direction of the worm wheel22) H of the fixing pin56is larger than the thickness t3of the connecting portion106, which is a sum of the axial length of the fitting hole108and the axial length of the tapered opening74. The thickness t3of the connecting portion106may be set to be the same as the thickness t2of the first embodiment. Also, the thickness t3of the connecting portion106may be regarded as the sum of the thickness t2, which corresponds to the length of the fitting hole108, and the axial length of the tapered opening74. In other words, the fitting hole108and the tapered opening74may be considered as the through hole of the present invention. Alternatively, the fitting hole108alone may be considered as the through hole of the present invention.

In the second embodiment, a protruding height h of a portion of the fixing pin56, which protrudes from the opening end74A, is a difference between the protruding height H of the fixing pin56and the thickness t3of the connecting portion106. This protruding height h is set to be larger than an entire thickness tk of the toothed ring58, which includes a protruding height of the tooth58B of the toothed ring58. More specifically, as shown inFIG. 11, the above dimensions are set such that the teeth58B of the toothed ring58are engaged with the distal end portion56A of the fixing pin56before the ring portion58A of the toothed ring58enters into the tapered opening74.

In the magnet fixing structure72, as shown inFIGS. 9 and 10, an outer peripheral edge58D of the ring portion58A is urged (engaged) against an inner peripheral surface74B of the tapered opening74in the installed state of the toothed ring58to the fixing pin56. That is, in the case of the magnet fixing structure72, the toothed ring58is axially urged along the fixing pin56until the outer peripheral edge58D of the toothed ring58engages or slightly bits the inner peripheral surface74B of the tapered opening74. In this way, the sensor magnet device100is fixed to the worm wheel22.

The rest of the structure of the magnet fixing structure72is the same as that of the magnet fixing structure50of the first embodiment. Specifically, the rest of the structure of the speed reducing gear unit70is the same as that of the speed reducing gear unit14of the first embodiment.

Therefore, the speed reducing gear unit70(the magnet fixing structure72) of the second embodiment can achieve advantages similar to those of the speed reducing gear unit14(the magnet fixing structure50) of the first embodiment. Furthermore, in the magnet fixing structure72of the speed reducing gear unit70, the toothed ring58is urged against the inner peripheral surface74B of the tapered opening74. Therefore, wobbling of the sensor magnet device100relative to the worm wheel22in the circumferential direction (rotational direction) and also in the radial direction can be limited. Particularly, in the case where the speed reducing gear unit70is used in the speed reducing electric motor10, which is rotatable in both of the forward and reverse rotational directions, the influences of the circumferential wobbling on the accuracy may possibly be two times greater than that of the one-way motor, which rotates only in a single direction. However, the speed reducing gear unit70of the present embodiment can advantageously limit such wobbling.

Furthermore, in the magnet fixing structure72, the distal end portion56A of the fixing pin56protrudes from the opening end74A. Thus, as shown inFIG. 11, at the time of fixing the toothed ring58over the fixing pin56, the distal end portion56A of the fixing pin56can be first received into the toothed ring58, that is, the teeth58B of the toothed ring58can be engaged with the distal end portion56A. In this received state, when the toothed ring58is further pressed in the axial direction of the fixing pin56, the toothed ring58is securely installed to the fixing pin56. That is, the toothed ring58can be smoothly urged against the inner peripheral surface74B of the tapered opening74while the toothed ring58is guided by the fixing pin56at an appropriate orientation. Thus, in the magnet fixing structure72, the toothed ring58can be securely installed to the fixing pin56while the toothed ring58is urged against the inner peripheral surface74B of the tapered opening74at the appropriate orientation.

In the second embodiment, the maximum inner diameter Dmax of the tapered opening74generally coincides with the gap G between the inner ring magnet102and the outer ring magnet104. Alternatively, as shown inFIG. 12, the magnet fixing structure72may be construed such that the maximum inner diameter Dmax of the tapered opening74is set to be smaller than the gap G.

Furthermore, in the second embodiment, the outer peripheral edge58D of the toothed ring58directly engages or bites against the inner peripheral surface74B of the tapered opening74. However, the present invention is not limited to this. For example, an intermediate component (e.g., a rubber ring) may be interposed between the outer peripheral edge58D and the tapered opening74.

Furthermore, in the second embodiment, the fitting holes108(and the associated tapered openings74) are provided in the sensor magnet device100, and the fixing pins56are provided in the worm wheel22. However, the present invention is not limited to this. For example, at least one of the fitting holes108(and at least one of the associated tapered openings74) may be provided in the worm wheel22, and at least one of the fixing pins56may be provided to the sensor magnet device100to engage with the at least one of the fitting holes108(and the at least one of the associated tapered openings74) provided in the worm wheel22. Furthermore, in the above embodiment, the multiple fitting holes108(and the associated tapered openings74) and the multiple fixing pins56are provided. However, the present invention is not limited to this. For example, a single fitting hole108(and an associated tapered opening74) may be provided to a center of one of the worm wheel22and the sensor magnet device100, and a single fixing pin56may be provided in a center of the other one of the worm wheel22and the sensor magnet device100. In such a case, the fitting hole108and the fixing pin56may have a corresponding non-circular cross section, i.e., a relative rotation limiting cross section (such as a polygonal cross section or an oblong cross section) to reliably limit relative rotation of the sensor magnet device100relative to the worm wheel22.

Furthermore, in the second embodiment, the gear mechanism of the present invention is provided as the speed reducing gear unit14in the speed reducing electric motor10. However, the present invention is not limited to this. For example, any of various other speed reducing mechanisms (e.g., a spur gear train, a hypoid gear train or a sun-and-planet gear train) may be used in the speed reducing gear unit14of the speed reducing electric motor10. Also, the present invention may be applied to a drive force transmitting mechanism or a speed increasing device of any other apparatus other than the speed reducing electric motor10. Furthermore, the gear of the present invention is not limited to the final stage gear, to which the sensor magnet device100is fixed to directly sense the rotational state of the output shaft26by rotating integrally with the output shaft26. That is, for example, the present invention may be applied to fix the sensor magnet device100to a first stage gear or an intermediate stage gear. Even in such a case, the rotational state of the output shaft26may be indirectly sensed based on a speed ratio (a rotational speed ratio) between such a gear and the output shaft26.

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. For example, any one or more of the components of the first embodiment or modifications thereof may be combined with any one or more of the components of the second embodiment or modifications thereof, if desired.