Bearing holding structure for motor

A metallic member 22 is integrated with a molded rotor 12, and a bearing 16 is held to the rotor 12 through this metallic member 22. At that time, a washer 24 is secured to the metallic member, and the rotating portion of the bearing is held by this washer, thereby improving holding property and durability of the bearing. A stopper plate 21 for limiting the displacement of the output shaft of a motor is used as the metallic member, thereby enabling holding property and durability of the bearing to increase without increasing the number of components. The base-end side of the metallic member 22 is integrally in-mold molded with the rotor 12, which enables the metallic member 22 to be firmly held.

TECHNICAL FIELD

The present invention relates to a bearing holding structure for a motor driving an electric control valve.

BACKGROUND ART

Conventional motor-bearing holding structures that rotatably hold, on the bearing, the rotor of a motor driving an electric control valve include an example in which “The rotor portion of a motor driving the EGR (exhaust gas recirculation) valve of an internal combustion engine is integrally molded with a magnet, a ball bearing, and a resin-made magnet holder supporting these parts by means of insert-molding” (For example, see JP-A-10-082349).

To be more specific, the bearing holding structure is a structure in which part of the magnet holder constituting the rotor protrudes in a sword-guard shape to support the inner ring of the bearing holding the rotor.

However, such a bearing holding structure can have only holding strength obtained with the resin for the bearing holding strength, and is unsatisfactory in terms of reliability and durability. Particularly, in a high-power motor driving an electric control valve, the output power of the motor is transmitted from the output shaft thereof to the bearing inner-ring holding part through the rotor to damage the resin securing the bearing inner-ring, thereby causing the maloperation of the motor.

In the conventional motor-bearing holding structure, there is a problem that the structure can have only holding-strength obtained with the resin for the bearing holding strength, and the structure, therefore, has low reliability and durability.

The present invention has been accomplished to solve the above-mentioned problem. An object of the present invention is to provide a motor-bearing holding structure with improved reliability and durability.

DISCLOSURE OF THE INVENTION

The motor-bearing holding structure according to the present invention is a structure in which the bearing is held to a rotor through a metallic member that is integrally molded with the rotor.

Further, the motor-bearing holding structure according to the present invention is a structure in which the bearing is held to a rotor through a metallic member that is integrally molded with the rotor such that the travel of a motor shaft which reciprocates in an axial direction is limited.

In such a way, because it is arranged that the bearing be held by the metallic member thereby having holding force that is greater than the holding strength obtained by the resin, reliability and durability of the rotor bearing portion can be improved.

Furthermore, it is arranged that the bearing be held by using the metallic member limiting the travel of the motor shaft, thereby enabling the bearing to be firmly held without increasing the number of components.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will now be described by reference to the drawings in order to make description in further detail of the present invention.

FIG. 1is a sectional view of an EGR valve device, showing an electric control valve equipped with a motor-bearing holding structure according to Embodiment 1 of the present invention.FIG. 2is an enlarged view showing the bearing portion thereof. The embodiment will be described referring to these drawings.

The EGR valve device1shown inFIG. 1has a valve housing2that forms a fluid channel (exhaust gas recirculating passage)3through which the exhaust gas from an engine is circulated. This valve housing2is axially movably equipped with a valve rod4. The valve rod4has a valve5that can make contact with and separate from a valve sheet6installed within the valve housing2. The valve rod4is upwardly energized (in a valve-closing direction) by a spring8interposed between a spring holder7, which is integrally fitted around the rod, and the bottom wall of the external concavity of the valve housing2. Further, the valve rod4integrally has a head4a.

In addition, the valve housing2is externally equipped with an electric control motor10used for axially driving the valve rod4. This electric control motor10is arranged to include: a coil11serving as a stator; a rotor12placed within this coil11; and a motor shaft14serving as a motor output shaft, which has, on the one-end side, a screw rod13screwed into the central bore of this rotor12and can axially travel. The electric control motor can be applied by the one of the type capable of housing the screw rod13. Examples of the electric control motor include a DC motor and a step motor. The valve used in this example requires high power, and therefore, a DC motor is mainly used. The rotor12is rotatably and axially movably over a defined range held by upper and lower bearings15and16.

In this case, the external wheel16bof the lower bearing16of the rotor12is pressurized and axially elastically movably held by a washer18interposed between the wheel and a boss (suppressing member)17fitted around the bottom opening of the motor housing10aof the electric control motor10. The boss17is sandwiched between the top end of the valve housing2and the motor housing10a, and these motor housing10a, boss17, and valve housing2are integrally fastened and secured by a fastening bolt19.

It is arranged that the inner wheel16aof the bearing16integrate a portion of a metallic member22, which is the holding means according to the present invention, to the rotor12, and the bearing be held through this metallic member22. The metallic member22in the example shown in the drawing is formed of a bent piece, which is bent in an L shape; the base-end side of the member is integrated within the rotor12; and the end of the other-end side is caulked and caused to abut the inner wheel16a. Thus, because the inner wheel16aof the bearing16is held by using the metallic member22having holding force that is greater than the holding strength obtained by the resin, reliability and durability of the rotor-bearing portion can be improved.

The metallic member22is arranged to hold the rotating portion of the bearing, that is, the inner wheel16a, at two or more places at equally spaced intervals around the rotary central axis O-O of the rotor12. Thus, the stable bearing holding can be performed, resulting in improving reliability of the bearing holding.FIG. 1andFIG. 2are sectional views, and therefore, the two metallic members22are shown at the right and left two places, respectively, therein; however, the inner wheel16ais held at four places at 90 degree intervals about the rotary central axis O-O. Of course, the inner wheel can be held at two, three, or six places. The number of the holding places can be optionally determined as the need arises.

The base-end side of the metallic member22is integrated within the rotor12. Any one of bonding, screwing, or engaging is applicable to such an integration means; however, in this embodiment, the base-end side thereof is integrally molded within the rotor12. The molding thereof enables the base-end side to be easily and firmly integrated within the rotor12.

In the conventional art, when performing the insert-molding of the bearing into the rotor12, a process by which no small performance-deterioration is caused is employed. For example, when the bearing is held in the insert-molding process, it is necessary that the bearing should be set in a high-temperature metal mold in the working process. Therefore, there may be an apprehension of viscosity reduction of the grease within the bearing. However, according to Embodiment 1 of the invention, the bearing (inner wheel16a) is held to the rotor by the metallic member22, thereby eliminating the necessity of insert-molding the bearing to the rotor12. Therefore, there is no lowered viscosity of the grease within the bearing.

Moreover, in the conventional art, when the bearing is insert-molded to the rotor, contrivance and consideration to hold the bearing without wobbles are required, which makes the assembly process (manufacturing method) complex and difficult. For example, holding of the bearing by means of insert-molding needs to fix the bearing within the mold when performing the molding. When the fixing load is large, the bearing is deformed to deteriorate its performance. The prevention measures for this were necessary. However, according to Embodiment 1 of the invention, the bearing (inner wheel16a) is held to the rotor by the metallic member22. This eliminates the necessity of such consideration and makes easy the assembly work.

The bottom of the motor shaft14(portion jointed with the valve rod4) is integrally provided with a protrusion14afor caulking. This protrusion14ais connected with the valve rod4through a plate20. The screw rod13is a male screw, and the rod is screwed into the female screw provided around the central bore of the rotor12. The lower part of the screw rod13is the motor shaft14having a diameter that is larger than that of the screw rod13, and such a difference in diameter forms a step portion14b.

Around the bottom portion of the central bore of the rotor12, a stopper plate21formed of metal in a ring shape is integrally molded with the rotor12. The stopper plate21forms a circular exposed abutting face21awithin a large diameter hole communicating to the central bore of the rotor12. The step portion14bcan make contact with and separate from this circular exposed abutting face21a(see enlarged view ofFIG. 2).FIG. 1andFIG. 2show the state where the step portion14babuts the exposed abutting face21a. The motor shaft14penetrates the boss17; however, the shaft is supported by using a supporting means, which can axially travel or displace through this penetrating portion but cannot rotate therethrough, for example, a D-type fit, a key, or a suitable means.

The basic operation of the EGR valve device1shown inFIG. 1will be described as below.

InFIG. 1, when the step portion14babuts the circular exposed abutting face21a, the valve5is seated on the valve seat by the elasticity of the expanding spring8, and the head4aand the to-be-caulked protrusion14aare separated from each other within the plate20to ensure seating of the valve5. The electric control motor10is driven, and then the rotor12is rotated in a predetermined direction. Thus, the rotational motion of the rotor12is transformed to the downward motion of the motor shaft14, so that the motor shaft14can be downwardly traveled. In connection with this, when the step portion14bgot detached from the circular exposed abutting face21a, and simultaneously, the protrusion14afor caulking approaches the head4ato finally abut against the head. Thereafter, the elastic force of the spring8acts on the motor shaft14, and the elastic force is transferred to the rotor12through the screw rod13, thereby the rotor receiving the upward elastic force. The rotation of the rotor12downwardly pushes the valve rod4against the elastic force of the spring8to open the valve5. The opening of the valve5is controlled by the amount of rotation of the electric control motor10.

When the valve5is closed, the rotor12is reversely rotated, then the motor shaft14is upwardly traveled or displaced, and the valve rod4is upwardly traveled according to the amount of travel of the motor shaft. Before long, when the valve5is seated on the valve seat6, thereafter the elastic force of the spring8is received by the valve5having seated thereon, thereby the valve rod4ceases its upward travel, the to-be-caulked protrusion14agets upwardly detached from the head4a, and after the step portion14babuts against the circular exposed abutting face21a, the rotation of the rotor12is stopped. Thus, when the step portion14babuts against the exposed circular abutting face21aafter the valve5is seated thereon, the maximum pulling-in position of the motor shaft14is restricted to secure the seating of the valve.

As is understood from the basic operation of the aforementioned EGR valve device1, because the rotor12repeatedly receives the upward elastic force F from the spring8, the portion of the metallic member22according to the invention which engages against the inner wheel16ais also acted upon by the repeated stress by this elastic force, and the portion thereof is under severe conditions. However, as compared with the arrangement in which the bearing is held by the molding resin integrated with the rotor as in the conventional structure, the present invention can improve reliability of the bearing holding structure by holding the bearing by use of the metallic member with high strength.

In the metallic member22shown inFIG. 2, described in Embodiment 1, the base-end side thereof, inserted within the rotor12, is straight. Therefore, depending on the conditions where the invention is carried into effect, the holding of the inner wheel16amay become unstable by the elastic force F in the direction pulled out from the rotor12. For this reason, in Embodiment 2, the base-end side of the metallic member22is bent to form a convexity22ain an L-shape as shown inFIG. 3, or the same side of the metallic member22is bent to form a convexity22bin a T-shape as shown inFIG. 4. Thereby, the integration function of the metallic member22to the rotor12improves, enhancing durability and reliability of the bearing. Embodiment 2 has all the structural advantages in Embodiment 1 in addition to this improvement.

The top of the metallic member22explained in Embodiments 1 and 2 described above is directly caulked to be abutted on the inner wheel16a, thereby holding the metallic member. However, such a caulking process may damage the bearing if the work is not considerably carefully performed. Further, it is also considered difficult for the plurality of metallic members22to hold the inner wheel16awith a uniform abutting force. Hence, in Embodiment 3, it is arranged that a washer be fixed to the metallic members, and the rotating portion (the inner wheel16a) of the bearing be held with this washer.

InFIG. 5, in accordance with the invention of Embodiment 3, just like the metallic member22in Embodiments 1 and 2 described above, the metallic member23is integrally in-mold molded with the rotor12with the base-end side thereof (upper top end in the drawing) placed within the rotor. The base-end side thereof is formed into an L-shaped convexity23a, as described by reference toFIG. 3in Embodiment 2, thereby strengthening the integration with the rotor12, and enabling the metallic member to endure the elastic force F. Moreover, in consideration of the installation of the washer in terms of shape, the bottom side of the metallic member23is arranged to be protruded below the rotor12.

The metallic members23are provided at two or more places at equally spaced intervals around the rotary central axis O-O of the rotor12. The washer24is provided in such a size that its external diameter is superimposed on the inner wheel16a, and also is provided in the central portion with a hole made of such a size that the motor shaft14can be penetrated. Furthermore, the washer is provided with holes that allow the metallic members23to be penetrated at a position corresponding to each of the metallic members23provided at the plurality of places, respectively.

As shown inFIG. 5, the holes formed through the washer24are penetrated by the motor shaft14and the metallic members23, respectively, and the washer24is pressed to be abutted against the inner wheel16awith a uniform force. At that time, the bottom portion of each of the metallic members23penetrates the washer24, and downwardly protrudes therefrom. The metallic members23downwardly protruding therefrom and the washer24are secured to each other by welding or caulking.

Thus, in the structure holding the inner wheel16awith the washer24, placing a uniform load on the inner wheel16ato hold the wheel is easy, thereby not damaging the reliability of the bearing. As compared with the structures of Embodiments 1 and 2 in which the inner wheel is directly held by caulking the metallic member22, the structure of Embodiment 3 has less influence on the inner wheel16a. Further, the application of material and size having required holding strength to the structure thereof can eliminate the damage to the bearing, and enhance the reliability and durability of the bearing. If the number of the metallic members23is two, this Embodiment employing the washer24is unstable. The number thereof is preferably three or more.

When compared to the structure in which the inner wheel16ais directly held by each of the plurality of metallic members, as in Embodiments 1 and 2, the structure in which the washer24is used has the property of stably holding the inner wheel16aalso in the mass production process. In other words, interposing the washer24therebetween substantially prevents the influence caused by the holding of the washer24to the metallic members23by caulking or welding from extending to the bearing, thereby reducing the influence exerted upon the accuracy of the bearing.

The example shown inFIG. 6is a modification of this Embodiment 3 described by reference toFIG. 5. The difference between this example and the example shown inFIG. 5is only that the base-end side of the metallic member23(top portion in the drawing) has a convexity23bin a T-shape, and they have substantially equal property except that. Embodiment 3 also has all the advantages described in Embodiment 1.

Known rotors for a motor driving an electric control valve include a rotor that is equipped with a stopper plate21that abuts on a motor output shaft reciprocating according to the rotation of this rotor to open and close the valve, thereby limits the travel of the motor output shaft, and restricts the maximum pulling-in position of the motor output shaft. This Embodiment 4 can be applied to this type of electric control valve provided with such a stopper plate21. Embodiment 4 will be described below as compared with Embodiment 3 described above. Embodiment 3 is provided with the metallic members23separately from the stopper plate21as shown inFIG. 5andFIG. 6. As contrasted to this, as shown inFIG. 7, in this Embodiment 4, is provided an integrated member25obtained by integrating the stopper plate21and the metallic member23, in place of the stopper plate21and the metallic members23employed in the examples described above.

This integrated metallic member25has a bottom26forming the exposed abutting face21a, a retaining portion27, which functions to prevent the member from falling out, and a holding plate28holding the washer30, and the integrated metallic member is formed in a ring shape. In the center of the member, is provided a hole29. This hole29is larger than the diameter of the screw rod13, and is smaller than the diameter of the motor shaft14. The exposed abutting face21ais provided on the circumference or edge of the hole29.

As seen from the above, front and below, the shapes of this integrated metallic member25are shown inFIG. 8,FIG. 9, andFIG. 10, respectively. In these drawings, the retaining portion27, which is molded and integrated within the rotor12and projects in a direction parallel to the elastic force F, has a top portion formed in inverted triangular shape; and the holding plate28is provided with a convex and concave portion28a, thereby enabling firm integration by resin wrap-around in the molding integration. The bottom of the holding plate28is provided with a U-shaped groove28b, thereby bifurcating the bottom.

As shown inFIG. 7, the integrated metallic member25is provided as follows: the central axis thereof is aligned with that of the rotor12; the exposed abutting face21a, which is an internally contacting face of the bottom26and which is in the vicinity of the edge of the hole29is exposed from the rotor12; and the retaining portion27and the base-end side of the holding plate28are positioned within the rotor12and integrated by molding.

A washer30having a structure basically similar to the washer24shown inFIG. 5andFIG. 6in Embodiment 3 is held and secured to the holding plates28in a condition where the washer is penetrated by the holding plates28through holes formed at equally spaced intervals concentrically with the hole29and further where the outer peripheral edge of this washer30comes in contact with the inner wheel16a. The fastening procedure of this washer30is as follows: the optional opposed holding plates28are temporarily welded to the washer30at the portions bifurcated by the grooves28bat the places penetrating the washer30, and further, the bottoms of the remaining holding plates28are caulked to secure the washer. As the state after caulking is shown inFIG. 7in which the indicated portion31indicated by circling inFIG. 11is enlarged, each of the two legs bifurcated by the groove28bis transformed in an opening direction and thereby caulked to secure the washer.

As compared with the securing methods by caulking and by welding, the method by welding may gives a higher strength. However, if the washer30is not fixed while being pressed against the inner wheel16aat the time of fixing the washer, there may be a possibility that wobbles take place due to the contact failure. In order to prevent this trouble, the holding plates are not welded at all point, but the plates are fixed by welding at several points. By using the welded places as the supporting points, the remaining places are caulked to thereby be pressed against the inner wheel16a, thereby holding the inner wheel16aat the equally spaced positions in the inner wheel16athrough the washer30. After that, when the caulked portions are also welded, the strength is secured.

Thus, the welding method and the caulking method are used to fix the holding plates at the plurality of places. The washer30is held by using the caulked portion directed toward preventing the bearing from wobbling and the welded portion directed toward improving the holding strength. Thereby, the occurrence of the wobble at the time of assembling the bearing is prevented, and the holding strength is improved, enabling reliability and durability of the electric control valve to improve.

The arrangement in which the washer30is held by the holding plates28, that was shown inFIG. 7, is also shown inFIG. 12, the arrangement being seen from under. InFIG. 7, the four caulked portions in the holding plates28can been seen in the vicinity of the hole29. The bearing16is shown with the circular outline along the external edge of the washer30. The area shown with the double dashed line corresponds to the inner wheel16a.

Conventionally, the stopper plate21has been only insert-molded into the rotor12, and the plate has not had the function of increasing its holding strength, accordingly causing the problem of dropping off and being damaged. However, as described in Embodiment 4, the stopper plate21is integrated with the metallic member (the metallic members22and23in Embodiments 1-3) used for holding the inner wheel16a, to form the integrated metallic member25, thereby enabling also the accuracy of the plurality of holding plates28to increase without increasing the number of components. Moreover, the sections inserted in the rotor12increase to strengthen the integration with the rotor12, thereby enhancing the integration of each of the members of the functioning portion serving as the stopper plate and of the functioning portion serving as the metallic member, with the rotors12. Embodiment 4 also has all the advantages described in Embodiment 1 in addition to the advantages described here. As a result, the performance of the electric control valve can be stably secured for a long term.

INDUSTRIAL APPLICABILITY

The present invention is suitable for use in the motor-bearing holding structure that drives the EGR (exhaust gas recirculation) valve of an internal combustion engine.