Device to press the shaft of a rotor into a stator housing

A device to press a rotatably supported shaft of a rotor of a spindle motor for a hard disk drive into a shaft receiving portion of an associated stator housing by means of a first pressing tool acting on the rotor and a second pressing tool acting on the stator housing. A first aligning apparatus for the rotor and a second aligning apparatus for the stator housing are provided. The first and second aligning apparatuses are formed in such a way that they guide the rotor by means of a rotor carrier and the stator housing by means of a stator carrier. The rotor carrier and the stator carrier are exactly aligned with respect to each other during the pressfitting process. The first pressing tool has a first pressing element acting on the shaft of the rotor that is independent of the first aligning apparatus and the second pressing tool has a second pressing element acting on the stator housing that is independent of the second aligning apparatus. The first and second pressing elements abut against the shaft or the stator housing respectively, at the latest at the start of the pressfitting process.

The present disclosure relates to the subject matter disclosed in German applications No. 103 43 317.1 of Sep. 10, 2003 and No. 103 47 477.3 of Sep. 30, 2003, which are incorporated herein by reference in their entirety and for all purposes.

BACKGROUND OF THE INVENTION

The invention relates to a device to press a rotatably supported shaft of a rotor of a spindle motor for a hard disk drive into a shaft receiving portion of an associated stator housing by means of a first pressing tool acting on the rotor and a second pressing tool acting on the stator housing.

In the devices known to date, the force to press the shaft into the shaft receiving portion via the rotor and the stator housing is introduced in such a way that process tolerances are created on the one hand, and damage to the bearing system can also not be excluded on the other hand.

The object of the invention is therefore to improve a device to press the shaft of the rotor into the shaft receiving portion inasmuch as high manufacturing precision, with low process tolerances in particular, can be achieved.

SUMMARY OF THE INVENTION

This object has been achieved in accordance with the invention by a device of the type described in the opening paragraphs in that a first aligning apparatus for the rotor and a second aligning apparatus for the stator housing are provided, that the first and second aligning apparatuses are formed in such a way that they guide the rotor by means of a rotor carrier and the stator housing by means of a stator carrier exactly aligned with respect to each other at least during the pressfitting process, and that the first pressing tool has a first pressing element acting on the shaft of the rotor that is independent of the first aligning apparatus and the second pressing tool has a second pressing element acting on the stator housing that is independent of the second aligning apparatus, the first and second pressing elements fitting snugly against the shaft or the stator housing respectively, at the latest at the start of the pressfitting process.

The advantage of the solution according to the invention is to be seen in the fact that the aligning apparatuses acting independently of the pressing elements make it possible for the rotor and the stator housing to be precisely aligned to each other during the pressfitting process and to be then held in a precisely aligned state, allowing the pressfitting process to be carried out with high precision in respect of the alignment of the two parts to each other.

The exact alignment of the rotor can be achieved in a particularly advantageous manner if the rotor, at least from the start of the pressfitting process, is held in a precisely aligned state in that a precision-related surface of the rotor engages against a first support surface of the rotor carrier of the first aligning apparatus with a defined first holding force.

In that a defined holding force holds down the precision-related surface, the disk supporting surface of the rotor for example, onto the first support surface of the rotor carrier, the exact alignment of the rotor determined by the first support surface of the rotor carrier can be maintained throughout the pressfitting process from the very beginning.

Within the scope of the solution according to the invention, the first aligning apparatus can either be associated with one of the pressing tools or arranged entirely independently of the pressing tools.

A particularly favorable solution provides that the first aligning apparatus is associated with the first pressing tool.

In order to achieve and maintain the exact alignment of the rotor, it is particularly favorable if the first support surface of the rotor carrier can be movably guided with respect to the first pressing element, so that, independent of the pressing force exerted with the first pressing element, the first holding force between the precision-related surface of the rotor and the support surface of the rotor carrier can be maintained.

A particularly favorable realization provides that the rotor carrier is movably guided by means of at least one first linear guide of the first aligning apparatus.

To maintain high guiding precision in the aligning apparatus, it is preferable if the first linear guide is supported by rolling element bearings, preferably having no free play.

The first linear guide preferably comprises a guide column and a first guide sleeve that is movable with respect to the guide column.

In respect of the association of the rotor carrier with the guide column and the guide sleeve, such association can basically take a large variety of conceivable forms. A particularly favorable association provides for the rotor carrier to be mounted on the first guide sleeve.

In principle, the linear guide can be independent of the arrangement of the pressing element. A particularly compact design can be realized, however, if the first pressing element is mounted on the guide column.

To advantageously generate the holding force with which the precision-related surface of the rotor is to engage against the first support surface of the rotor carrier, it is preferably provided that the rotor carrier can be moved in the direction of the pressing tool located opposite the rotor carrier until it reaches a starting position, that a first holding force acting in the direction of the starting position is exerted on the rotor carrier, that the rotor supported by the rotor carrier, in the starting position with the shaft, is spaced from the first pressing element and that a movement of the rotor with the shaft in the direction of the first pressing element works against the first holding force.

In order to prevent any damage whatsoever to the pair of bearings used to support the rotor on the shaft, it is preferable if the holding force is less than 1.5 times the preload force of a pair of bearings provided between the shaft and the rotor, and even more preferable if it is less than this preload force.

The holding force can basically be generated in a large variety of different ways. It is particularly favorable if the first holding force can be generated by an energy or force storage unit acting between the rotor carrier and a base of the first pressing tool, preferably an elastic force storage unit.

In relation to the embodiments of the solution according to the invention mentioned up to this point, only the first holding force to achieve the exact alignment of the rotor has been dealt with.

To prevent the rotor from being attracted to the stator due to magnetic interaction before the pressfitting process has begun and thus possibly becoming partially disengaged from the rotor receiving portion and consequently losing its alignment, it is preferable if, before the pressfitting process begins, the precision-related surface of the rotor can be butted against the first support surface of the rotor carrier by means of a first applying force.

The applying force goes to prevent the rotor from disengaging from the rotor receiving portion in the manner described above.

The first applying force is preferably dimensioned in such a way that it is less than the first holding force but greater than the effective force produced by the magnetic interaction between the rotor and the stator.

The first applying force can be preferably generated by a force transmission element which becomes effective as the first pressing tool and the second pressing tool approach each other before the start of the pressfitting process.

It is particularly favorable if the first force transmission element is disposed on the second pressing tool and can thus be easily put into effect.

So far, no precise details have been given in relation to the above explanation of the device according to the invention concerning the alignment of the stator housing. A further beneficial embodiment of the invention provides for the stator housing, at the latest at the start of the pressfitting process, to be held in a precisely aligned state in that one or more precision-related surfaces of the stator housing, reference or mounting surfaces for example, abut a second support surface of the stator carrier of the second aligning apparatus. This also goes to ensure that during the pressfitting process the stator housing is always held precisely aligned in the required manner.

The second aligning apparatus can be associated with the second pressing tool.

It is, however, conceivable that in another solution, the second aligning apparatus is associated with the first pressing tool.

In order to maintain the second holding force throughout the pressfitting process, it is preferable if the second support surface of the stator carrier can be movably guided with respect to the second pressing element.

Such guided movement can be achieved, for example, in that the stator carrier is movably guided by at least one second linear guide of the second aligning apparatus.

The second linear guide is preferably supported by rolling element bearings.

In the simplest case, provision is made for such a second linear guide to comprise a second guide column and a second guide sleeve which can be moved with respect to the second guide column.

The way in which the guide sleeve and the guide column are associated with the stator carrier can basically be chosen arbitrarily.

A beneficial solution provides for the guide sleeve to carry the stator carrier. However, it is also conceivable to arrange the guide column in such a way that it carries the stator carrier.

Moreover, the guide sleeve and guide column can be arranged entirely independently of the second pressing element.

A particularly compact design provides for the second guide column to carry the second pressing element.

Another beneficial solution provides that, as a stator carrier, the second aligning apparatus has a carrying member guided by a plurality of linear guides.

Such a carrying member can be particularly advantageously employed if it were to have a plurality of second support surfaces for the precision-related surfaces of the stator housing.

So far, no precise details have been given concerning the generation of the second holding force. A particularly beneficial embodiment thus provides that the stator carrier can be moved in the direction of the pressing tool located opposite the stator carrier until it reaches a starting position, that a second holding force acting in the direction of the starting position is exerted on the stator carrier, that the stator housing held by the stator carrier is spaced at a distance from the second pressing element and that the second holding force works against a movement of the stator housing with the stator carrier in the direction of the second pressing element.

The second holding force is also preferably selected in such a way that no deformation of the stator housing can occur.

The second holding force can be generated in a particularly favorable way when it is generated by a force storage unit acting between the stator carrier and a base of the associated pressing tool, preferably an elastic spring force storage unit.

To prevent the stator housing from becoming at least partially disengaged from the stator receiving portion due to the magnetic attraction of the rotor and the stator as the rotor and the stator approach each other before the actual pressfitting process, it is preferably if, before the start of the pressfitting process, the precision-related surfaces of the stator housing can be supported on the second support surface by means of a second applying force. Here, the second applying force, for example, can be less than the first holding force but always strong enough so as not to be overcome by the magnetic attraction between the rotor and the stator.

Such an applying force can preferably be generated by at least one force transmission element which becomes effective when the first pressing tool is conveyed in the direction of the second pressing tool, that is when the two pressing tools are brought together.

The second force transmission element is preferably disposed on the first pressing tool.

To ensure a centric alignment of the stator housing and rotor shaft at the start of the pressfitting process, a centering element is also preferably provided.

The centering capability of this element is particularly effective if it acts on the shaft receiving portion of the stator housing.

In order to pressfit the rotor up to a defined spacing of the precision-related surface of the rotor and stator housing, one of the two interacting elements of a measuring device is preferably associated with the first support surface and the second support surface respectively to measure a precise spacing between these two surfaces.

It is preferable if the measuring device generates a signal for the control of a drive motor when a defined, predetermined spacing between the first support surface and the second support surface is reached.

The first and second support surfaces can be particularly precisely positioned with respect to each other when the measuring device is part of a closed-loop circuit of the control of the drive motor.

In particular, the spacing between the first support surface and the second support surface can be achieved with great repeat accuracy when the control operates the drive motor in a section before an expected pressfit end as a stepping motor operating in start-stop mode, providing the possibility of ending the movement of the second pressing tool with respect to the first pressing tool with stepped precision.

Furthermore, to prevent damage to the pressing tools, or also to the rotor or stator housing, from occurring, it is preferable if a force sensor is provided between a press drive and the associated pressing element, making it possible to detect whether atypically high force peaks occur during the course of the pressing process.

Such a force sensor is preferably disposed in an open control loop of the press control, allowing the press control to detect the occurrence of unexpected, large forces and to switch off the press drive.

In order to achieve the greatest possible accuracy, it is preferable if the press drive is a spindle drive.

Further characteristics and advantages of the invention form the subject matter of the description below as well as the illustration in drawings of several embodiments.

DETAILED DESCRIPTION OF THE INVENTION

A first embodiment of a device according to the invention illustrated inFIG. 1 to 4to pressfit a shaft10, to which a rotor12of a spindle motor is mounted by means of a pair of bearings11, into the shaft receiving portion14of a stator housing16of a stator15(FIG. 2) of the spindle motor comprises a pressing device18(FIG. 1), described in more detail below, having a first pressing tool20acting on the rotor12and a second pressing tool22acting on the stator housing16, which can be moved towards each other in a pressing direction24, the first pressing tool20being connected to the pressing device18via a first base26and the second pressing tool22being connected to the pressing device18via a second base28.

For its part, the first pressing tool20comprises a first pressing element30provided with a first pressing surface32with which a force can be exerted on an end face38of the shaft10located opposite an end face36disposed at a pressfit end34of the shaft10for the purpose of pressfitting the pressfit end34into the shaft receiving portion14.

To align the rotor12when the shaft10is pressed into the shaft receiving portion14, a first aligning apparatus, indicated in its entirety by40and associated with the first pressing tool20is provided which has a rotor carrier42provided with a rotor receiving portion44. The rotor receiving portion44is preferably formed as a negative pressure receiving portion and provided with a suction connection45so that the rotor12can be held with its hub47in the rotor receiving portion44through negative pressure.

The rotor12with its hub47can be inserted into the rotor receiving portion44in such a way that it can be butted with a disk supporting surface46formed as a precision-related surface against a first support surface48of the rotor carrier42, enabling the rotor12to be precisely aligned by means of the rotor carrier42.

The rotor carrier42is guided by a first guide50in the pressing direction24linearly movable with respect to the first pressing element30, the first guide50comprising a first guide column52held on the first base26and a first guide sleeve56precisely guided with respect to the first guide column52by means of rolling elements54, the first guide sleeve56being provided with the rotor carrier42on the side facing the second pressing tool22.

By means of first spring elements58acting on the rotor carrier42, the rotor hub47is held, without additional outside force being exerted, by the rotor carrier42with respect to the first pressing element30, in a first starting position in which the first pressing element30does not act on the end face38of the shaft10, but is rather spaced at a distance from it.

The first spring elements58are supported on the one hand by the base26and on the other hand they exert a force on the first guide sleeve56in a direction heading away from the base26in order to hold the rotor carrier42with respect to the base26in the starting position defined by stops.

The overall first holding force exerted by the first spring elements58is less than 1.5 times the bearing preload force of the pair of roller bearings11so that overcoming the holding force H1with effect on the shaft10, its end face36for example, avoids damaging the pair of bearings11.

For its part, the first guide column52is firmly seated via the baseplate26on a plunger60of the pressing device18and can be moved in the pressing direction24by a movement of the plunger60. Moreover, the first guide column52carries the first pressing element30at the end62facing the second pressing tool22, the first pressing element30being firmly connected to the first guide column52.

The first guide50is preferably formed in such a way that the first guide column52is a cylindrical column, the rolling elements54fitting snugly against its sleeve surface64and preferably being held in a conventional rolling element cage65, the first guide sleeve56supporting itself against the rolling elements54with its inner surface66, and in this way being guided along the first guide column52via the rolling elements54. The inner surface66is likewise preferably formed as a cylindrical surface, the sleeve surface64and the inner surface66extending coaxial to a cylindrical axis68that is aligned parallel to the pressing direction24.

To align the stator housing16, formed for example as a flange in the spindle motor of the first embodiment, a second aligning apparatus70, associated with the second pressing tool22, is provided, the second aligning apparatus70comprising a stator carrier72having a stator receiving portion74in which the stator housing16can be placed in such a way that the stator housing16with a mounting surface76as a precision-related surface of the stator housing16engages against a second support surface78of the stator carrier72, in this case the stator housing16penetrating with its hub member77into the stator receiving portion74.

To exert a force on the stator housing16in the region of the shaft receiving portion14, a second pressing element, indicated in its entirety by80, is provided which, with a second pressing surface82, can act on a contact surface86of the stator housing16located opposite a pressfit opening84in the shaft receiving portion14, disposed on the stator housing16and preferably enclosing the shaft receiving portion14.

Here, for example, the second pressing element80is supported on a counter support90to the plunger60of the pressing device18via a second base28, with respect to which the plunger60can be moved.

To guide the second aligning apparatus70with respect to the second pressing element80a second guide, indicated in its entirety by 100, is provided which comprises a second guide column102and a second guide sleeve106journalled on this guide column102via rolling elements104, the second guide sleeve106being provided with the stator carrier72and a second spring element108exerting a second holding force H2on the second guide sleeve in such a way that the second guide sleeve106, and thus the second aligning apparatus70, are in a starting position in which the stator housing16, accommodated in the stator receiving portion74, abuts the second support surface78with the mounting surface76, no force being exerted, however, on the stator housing16in the region of its contact surface86by the second pressing surface82.

The second spring element108is preferably supported on the base28of the second pressing tool22mounted on the counter support90.

The second guide column102is preferably seated on the base28and carries. the second pressing element80on the end located opposite the counter support90.

Furthermore, the second pressing element80is allocated a centering pin110which is held by a guide bolt112reaching through the second guide column102, a force being exerted on the guide bolt112via a pressure cylinder114in a direction of pressure116running opposite to the pressing direction24.

The centering pin110projects beyond the pressing element80in such a way that, in a starting position of the pressing tools20,22, the centering pin110engages into the shaft receiving portion14and uses this to center the stator housing16with respect to the second pressing tool22so that the shaft receiving portion14is aligned coaxial to the shaft10of the rotor12held by the first pressing tool20.

The center pin110further engages through the shaft receiving portion14and, as an applying element, exerts a force with its end face118on the end face36of the shaft10disposed at the pressfit end34before this end face36enters into the shaft receiving portion14when the pressing tools20,22are brought together, in order to support the rotor12in a stable way, despite incipient magnetic attraction between the rotor12and the stator15, with its disk supporting surface46on the first support surface48using an applying force A1and to thus precisely align the rotor12, together with the shaft10, before the pressfitting process.

The first applying force A1acting on the shaft10is to be preferably dimensioned in such a way that it is less than a preload force of the pair of bearings11in order to prevent the pair of bearings11from being damaged due to applying force A1.

In order to further ensure that the stator housing16abuts the second support surfaces78with its mounting surfaces76by means of a second applying force A2before the shaft10is pressfitted and, despite incipient magnetic attraction between the rotor12and the stator15, continues to be held in close contact, a holding-down apparatus120is provided having holding-down devices122on which a force is exerted by means of pressure springs124.

The holding-down apparatus120is integrated, for example, in the first aligning apparatus40, the holding-down devices122being formed as pins lodged in bores126in the rotor carrier42, on which a force is exerted by pressure springs124disposed in bores128in the first guide sleeve56in such a way that the holding-down devices122project beyond the first aligning apparatus40in the direction of the second pressing tool22and thus, when the first pressing tool20is moved in the pressing direction24towards the second pressing tool22, exert a force on the stator housing16on an end located opposite the mounting surface76and thus support the mounting surface76with this exerted force on the second support surface78.

In order to form the second applying force A2exerted by the holding-down devices122independently of the force acting on the first guide sleeve56generated by the spring elements58, the pressure springs124are supported directly on the base26of the first pressing tool20.

In order to achieve a defined spacing between the mounting surface76of the stator housing16and the disk supporting surface46of the rotor hub47when the shaft10is pressed into the shaft receiving portion14, and to ensure that it is reproducible, a measuring device130, illustrated inFIG. 1 and 3, is provided comprising a measuring probe132, firmly positioned in the pressing direction24with respect to the first support surface48, and a sensor contact surface134, firmly positioned in the pressing direction24with respect to the second support surface78, the measuring probe132being held by a probe holder136disposed on the rotor carrier42in which the measuring probe132can be fixed in a defined alignment so that a probe needle138is in a defined position to the first support surface48in the pressing direction24, while the sensor contact surface134is likewise disposed in a defined alignment to the second support surface78by means of an appendage140formed on the stator receiving portion74.

The measuring probe132can now be aligned with respect to the first support surface48in the pressing direction24in such a way that, with the probe needle138engaging on the sensor contact surface138, the measuring probe132releases a signal exactly when the disk supporting surface46is at the desired predetermined distance from the mounting surface76.

A measuring probe is any device which is capable of registering the desired position and emitting a signal with a sufficient degree of precision.

The pressing device18mentioned earlier comprises two guide columns142,144rising from the counter support90that are connected by a cross bar146. on which a drive motor148, having a rotor with a hollow shaft150, is arranged.

The hollow shaft150drives a spindle nut154via a coupling152, the spindle nut154being seated on a sliding spindle156which can be pushed into the hollow shaft150.

The sliding spindle156is fixedly connected to the plunger60via a flange158, the plunger60in turn being precisely aligned and movably guided on the two guide columns142and144in the pressing direction24in order to thus also guide the first pressing tool20to the second pressing tool22in a perfectly aligned manner.

To register the force acting on the plunger60, a force sensor160is provided between the flange158and the plunger60, the force sensor160being connected to a pressing control162which not only registers the values of the force sensor160but also the switching signals of the measuring probe132.

The device according to the invention now works such that the first pressing tool20and the second pressing tool22are pushed by the control162, by moving the plunger60in the opposite direction to the pressing direction24, so far apart from each other that the rotor12with its rotor hub47can be placed in the rotor receiving portion44of the rotor carrier42, the rotor hub47initially being held in the rotor receiving portion44by negative pressure so that the rotor12cannot fall out of the rotor receiving portion44due to the force of gravity.

Moreover, the stator15with the stator housing16is inserted into the stator receiving portion74, the centering pin110jutting through the shaft receiving portion14and thus centering the stator housing16via the shaft receiving portion14.

Then, by activating the control162, the plunger60with the first pressing tool20is moved by means of the drive motor148in the direction of the second pressing tool22, the hollow shaft150driving the spindle nut154via the coupling152which moves the sliding spindle156that is fixedly connected to the plunger60in the direction of the counter support90of the pressing device18.

Before the actual process of pressing the pressfit ends34of the shaft10into the shaft receiving portion14begins, as can be seen inFIG. 2, the holding-down devices122of the holding-down apparatus120touch the stator housing16on the surface facing away from the mounting surface76and press the stator housing16with the mounting surface76against the second support surface78of the stator carrier72with applying force A2.

Here, applying force A2is less than holding force H2with which the stator carrier72is held in the starting position described above in which the stator housing16does not yet touch the second pressing surface82.

This force is sufficient, when the first pressing tool20and the second pressing tool22are brought closer together, to move the holding-down devices122in the direction opposite to the direction in which the pressure springs124work.

When the first pressing tool20and the second pressing tool22are brought even closer together, the centering pin110comes into contact with the end face36of the shaft10and thus exerts applying force A1on the entire rotor12by means of which the disk supporting surface46is held in close contact with the first support surface48by means of this applying force A1.

Applying forces A1and A2, acting in opposite directions to each other, are further so great that they counteract a magnetic attraction of the rotor12and the stator15so that, despite this magnetic attraction, the mounting surface76and the second support surface78as well as the disk supporting surface46and the first support surface48respectively remain in close contact with each other.

As the pressing tools20and22move even closer together, the pressfit end34of the shaft10then touches the pressfit opening84of the shaft receiving portion14and great forces now act not only on the shaft10, and thus on the rotor,12but also on the stator housing16.

These forces are so great that holding force H1is overcome and the rotor12together with the rotor carrier42moves in the direction of the base26against the force of the first spring elements58, and continues until the end face38of the shaft10abuts the first pressing surface32.

Since this force acting on the rotor carrier42is transferred from the shaft10via the pair of bearings11to the rotor hub47, holding force H1should preferably be dimensioned in such a way that it is less than 1.5 times the preload force of the pair of bearings11, so that the pair of bearings11cannot be damaged. Thus at the start of the pressfitting process, the disk supporting surface46and the first support surface48are pressed against each other with the first holding force H1, which goes to ensure that the rotor hub47, and thus the rotor12, is aligned in a stable and precise manner with respect to the stator housing16, in particular that the shaft10with the pressfit end34is aligned coaxial with respect to the shaft receiving portion14.

Likewise, at the start of the pressfitting process, the stator housing16, together with the stator receiving portion74, is also pushed in the direction of the base28, overcoming the second holding force H2, until the contact surface86abuts the second pressing surface82.

Holding force H2is also dimensioned in such a way that it is at any event less than any resulting bending forces that can deform the stator housing16, so that any changes in measurement resulting from distortion and/or deflection of the stator housing16can be prevented or excluded.

On the other hand, at the start of the pressfitting process the mounting surface76and the second support surface78are thereby pressed together with holding force H2thus ensuring that the stator housing16is precisely aligned with respect to the rotor12.

As the pressfitting process continues, the first pressing surface32and the end face38of the shaft10as well as the second pressing surface82and the contact surface86interact directly with each other so that the pressfit end34can be pressed into the shaft receiving portion14with as large a force as necessary.

To avoid damaging the pressing tools20and22, the movement of the first pressing tool20in the direction of the second pressing tool22is monitored by the pressing control162coupled to the force sensor160in an open control loop and, if any large, atypical forces appear, the drive motor148is switched off.

Using a stepping motor as the drive motor148also creates the possibility of comparing the forces measured at the force sensor160with allowable and/or at least necessary forces associated with individual forward feed positions and to interrupt the pressing process should deviations occur.

In the spindle motors manufactured according to the invention, it is moreover necessary to carry out the process of pressing the shaft10into the shaft receiving portion14in such a way that the disk supporting surface46is disposed with an exact spacing from the mounting surface76.

It is for this reason that the control162is coupled to the measuring device130and is thus able to maintain with stepped precision the forward feed of the drive motor, taking the form of a stepping motor in a closed control loop operating in start-stop mode, in the pressing direction24only until the first support surface48and the second support surface78have the predetermined spacing from each other, it being possible to preset the spacing by adjusting the measuring probe132.

If the measuring probe132is precise enough, the process of pressing the shaft10into the shaft receiving portion14can be precisely repeated in the micrometer range.

In a second embodiment illustrated inFIG. 5, the elements that are identical to the elements of the first embodiment are given the same reference numbers so that with regard to their description, full reference can be made to the details provided for the first embodiment.

In the second embodiment, the arrangement of the first pressing tool20in respect of the second pressing tool22with respect to the plunger60and to the counter support90is inverted. This means that the first pressing tool20′ is held on the counter support90by its base26while the second pressing tool22′ is held by its base28at the plunger60.

As to the construction of the rotor carrier42and the first pressing element30, the first pressing tool20′ is formed in an identical way to the first embodiment, with the difference, however, that the rotor receiving portion44no longer needs negative pressure to hold the rotor12but rather the rotor12remains in the rotor receiving portion44due to the force of gravity.

In contrast to the first embodiment, however, the second aligning apparatus70′ is not associated with the second pressing tool22′ but rather with the first pressing tool20′, since the stator housing16′ has reference surfaces76′ that are located on the side of the stator housing16′ from which the shaft10is pressed into the shaft receiving portion14.

The second aligning apparatus70′ thus has a carrying member170as stator carrier72′ which encloses the first guide sleeve56from the outside, the first guide sleeve56engaging through a central opening172in the carrying member170.

This carrying member170is then movably guided on a plurality of second guides100′, three by way of example, with respect to the base26, the guides likewise comprising second guide columns102and second guide sleeves106. The guide sleeve106is connected firmly to the base26whereas the guide column102is connected firmly to the carrying member170of the stator carrier72′.

In the second embodiment, the stator receiving portion74′ is formed by means of alignment pins174which project beyond the carrying member170in the direction of the second pressing tool22′ and fit snugly against corresponding alignment surfaces of the stator housing16′.

In addition, the reference surfaces76′ of the stator housing16′ abut second support surfaces78′ that can be adjusted with respect to the carrying member170by means of adjusting elements176in order to preset the exact alignment of the stator housing16′.

In the second aligning apparatus70′ as well, a force is exerted on the stator receiving portion72′ in the direction of the starting position by means of an elastic force storage unit, not illustrated in the drawings, with the generation of holding force H2which acts in the same direction as holding force H1of the first aligning apparatus40.

In contrast to the first embodiment, in the second embodiment the second pressing tool22′ only comprises the pressing element80with the pressing surface82, and the centering pin110′ is further disposed in a column member180carrying the second pressing element80and has a force exerted on it by a force storage unit114′ so that, on the one hand, the centering pin110′ also centers the stator housing16′ by engaging into the shaft receiving portion14and, on the other hand, can still act on the end face36of the pressfit end34to ensure that the disk supporting surface46of the rotor12abuts the first support surface48when the stator housing16′ is lowered, despite the incipient magnetic interaction between the rotor12and then stator15, and does not thus disengage from the rotor receiving portion44.

The second embodiment of the device according to the invention now functions such that initially the first pressing tool20′ and the second pressing tool22′ are again pushed apart from each other in order to first place the rotor12in the rotor carrier42and then to put the stator housing16′ on the stator carrier72′.

Due to the force of gravity, the disk supporting surface46and the first support surface48lie against each other as do the reference surfaces76′ and the second support surfaces78′.

The starting position of the rotor carrier42corresponds to the starting position of the first aligning apparatus40described in the first embodiment and the starting position of the second aligning apparatus70′ holds the stator housing16′ such that there is a space between the end face36and the pressfit opening84. Moreover, the second pressing element80with the second pressing surface82is already spaced at a distance from the contact surface86of the stator housing16′.

By conveying the second pressing tool22′ in the direction of the first pressing tool20′ the centering pin110′ initially penetrates the shaft receiving portion14and thus centers the stator housing16′ in the manner described above. The centering pin110′ furthermore penetrates the shaft receiving portion14and then, with its front end118, exerts a force on the end face36of the shaft10, generating the first applying force A1, which results in the fact that at the start of the pressfitting process, the disk supporting surface46cannot lift away from the first support surface48due to the magnetic interaction between the rotor12and the stator15.

Owing to the changes in the arrangement of the second aligning apparatus70′ brought about by the relocation of the reference surfaces76′ to the front of the stator housing16′, the magnetic interaction between the rotor12and the stator15does not cause the mounting surfaces76′ to lift away from the second support surfaces78′, but rather presses them together so that there is no longer need to generate a second applying force to prevent the mounting surfaces76′ from lifting away from the second support surfaces78′.

When the second pressing tool22′ is conveyed in the direction of the first pressing tool20′, the second pressing surface82comes to rest against the contact surface86and, with a continued movement of the second pressing tool22′ in the direction of the first pressing tool20′, causes the stator housing16′ to be pushed, against holding force H2of the second aligning apparatus70′, in the direction of the rotor12and continuing until the pressfit end34of the shaft10comes to rest against the pressfit opening84.

As the second pressing tools22′ continues to be conveyed in the direction of the first pressing tool20′, the rotor12together with the rotor carrier42is moved, overcoming the first holding force H1, until the end face38of the shaft10also abuts the first pressing surface32. This means that at the start of the pressfitting process in which the pressfit end34of the shaft10is pressed into the shaft receiving portion14, a precise alignment of the rotor12and the stator housing16′ with respect to each other is achieved since, similarly to the first embodiment, the disk supporting surface46is pressed against the first support surface48with first holding force H1and, in addition, the mounting surfaces76′ are pressed against the second support surfaces78′ with second holding force H2. When the second pressing tool22′ is conveyed further in the direction of the first pressing tool20′, with the precise alignment of the rotor12to the stator housing16′, the pressfit end34is pressed into the shaft receiving portion14in the same way as described in detail in relation to the first embodiment.

Concerning the parts that are identical to those in the first embodiment and the processes of pressing the pressfit end34into the shaft receiving portion14that have not been expressly described in relation to the second embodiment, reference is made in full to the embodiments relating to the first embodiment.

IDENTIFICATION REFERENCE LIST