FIELD OF THE INVENTION

The present invention relates to an electric motor having a rotor shaft and a first and a second bearing.

BACKGROUND INFORMATION

It is generally conventional for electric motors to have a rotor shaft.

German Patent Document No. 103 12 941 describes an assembly set for a type range of geared motors.

SUMMARY

Example embodiments of the present invention provide an electric motor in a manner that makes it insensitive to temperature.

According to example embodiments of the present invention, an electric motor includes a rotor shaft, a first bearing, and a second bearing. The rotor shaft includes a first rotor shaft part and a second rotor shaft part. The first rotor shaft part is rotatably mounted via the first bearing, and the second rotor shaft part is rotatably mounted via the second bearing. A bellows is connected at its first axial end region to the first rotor shaft part, e.g., by a welded connection, and the bellows is connected at its second axial end region to the second rotor shaft part, e.g., by a welded connection.

This has the advantage that the bellows is able to compensate for thermally induced, axially directed changes in length. Thus, both bearings may be arranged as fixed bearings, and devices, which are sensitive to axial expansions, may be placed axially outside the bearings on both sides. In particular, an angle sensor is able to be placed on the B-side and is protectable from interfering axial expansions with the aid of the fixed bearing. In the same manner, on the A-side, the second rotor shaft part may be provided with a helical gearing, which meshes with a tooth system, especially a helical gearing, of a toothing part of a gear unit driven by the motor. Position errors, in particular, angle position errors, on the output side of the gear unit are therefore avoidable.

According to example embodiments, a ring part is situated between the first and the second rotor shaft part. For example, the first or the second rotor shaft part has an annular groove circumferential in the circumferential direction in relation to the axis of rotation of the rotor shaft part, in which the ring part is at least partially accommodated and/or into which the ring part at least partially projects. This has the advantage that the two rotor shaft parts have a first point of support with the aid of the ring part, and the bellows specifies a second point of support which is axially set apart from the ring part. In addition, each one of the rotor shaft parts is fixed in place via a respective bearing so that further points of support are specified. Of importance in this context is that the bearings are axially set apart from the ring part and from the bellows, which is also set axially apart from the ring part. The bellows rigidly connects the two rotor shaft parts in the circumferential direction so that torque is transmitted. Using the mentioned elements, i.e., the first bearing, second bearing, ring part, and furthermore also the bellows, the entire rotor shaft is assembled in a stable manner and mounted as a whole via the two bearings.

According to example embodiments, the ring part is a sealing ring, in particular an O-ring, in particular made from rubber or a plastic material, especially polymer. This allows for an axial displacement of the two rotor shaft parts relative to each other while a point of support is defined nevertheless.

According to example embodiments, the axial region covered by the ring part is encompassed by the axial region covered by the second bearing. This has the advantage that greater stability of the rotor shaft is able to be achieved.

According to example embodiments, the bellows is situated axially between the first and the second bearing, the bellows in particular, being situated axially between the second rotor shaft part and the first bearing. This has the advantage that the bellows is able to compensate for a thermally induced axial change in length.

According to example embodiments, the bellows is supported on a step of the first rotor shaft part on the one side and on an end face of the second rotor shaft part on the other side. This offers the advantage that it is possible to center the shaft in that a displacement in the radial direction is provided prior to connecting the bellows by a welded connection.

According to example embodiments, the bellows touches the first rotor shaft part at a contact surface which has a single axial position and thus, in particular, extends in the circumferential direction and in the radial direction. This offers the advantage that a radial displacement of the first rotor shaft part is able to take place prior to producing the welded connection to the bellows, and the rotor shaft parts are therefore able to be centered relative to each other and be fixed in place by the subsequent welded connection.

According to example embodiments, the bellows touches the second rotor shaft part at a contact surface which has a single axial position and thus particularly extends in the circumferential direction and in the radial direction, in particular, such that during the production of the motor, the bellows is disposed so as to be radially displaceable before the bellows is connected to the second rotor shaft part by welding. This offers the advantage that a radial displacement of the second rotor shaft part is able to take place prior to producing the welded connection to the bellows and the rotor shaft parts are thus able to be centered relative to each other and be held in place by the subsequent welded connection.

According to example embodiments, the bellows is arranged as a ring element, and the ring opening has an inner diameter which is greater than the outer diameter of the first rotor shaft part in the axial region covered by the bellows, in particular, such that the bellows is situated in a radially displaceable manner during the production of the motor before the bellows is connected to the first rotor shaft part by welding. This offers the advantage that the first rotor shaft part is able to be passed through the bellows and introduced into a blind hole of the second rotor shaft part. In this manner, the bellows compensates in an axial relative displacement of the two rotor shaft parts and still allows for a torque transmission of the torque generated by the active part in an operative connection with the stator of the electric motor.

According to example embodiments, the first rotor shaft part is passed through the bellows, in particular, through the ring opening of the bellows. This has the advantage that the bellows rests against and is connected to a stepped wall of the first rotor shaft part, the first rotor shaft part projecting into the second rotor shaft part and thus resting against the second rotor shaft part via a ring part, with an axial clearance from the bellows.

According to example embodiments, the contact surface on the second rotor shaft part is an end face of the second rotor shaft part. This offers the advantage that the axially outermost end face is able to be used for the connection to the bellows. The axial clearance between the two connection regions, i.e., contact surfaces, of the bellows is thus able to be kept as small as possible so that the most rotationally stiff bellows can be used.

According to example embodiments, the contact surface on the first rotor shaft part is situated on a step of the first rotor shaft part. This has the advantage that the bellows is able to be welded to the stepped wall and the two rotor shaft parts are thus able to be coaxially aligned with each other prior to the welding.

According to example embodiments, an active part is accommodated by the first rotor shaft part, and the bellows is situated either axially between the active part disposed on the first rotor shaft part and the second bearing and/or the second rotor shaft part, or is situated axially between the active part disposed on the second rotor shaft part and the first bearing and/or the first rotor shaft part. For example, the active part is a short-circuit cage or a permanent magnet system. For example, the short-circuit cage is connected in a thermally conductive manner to the first rotor shaft part. The heat transfer resistance between the short-circuit cage and the first rotor shaft part may be smaller in its absolute amount than the heat transfer resistance between the first rotor shaft part and in the direction of the environment and/or the housing of the motor. This offers the advantage that the active part introduces torque generated by the operative connection to the stator into the first rotor shaft part.

According to example embodiments, the housing of the electric motor has a housing part which is connected to a first and a second flange part, the housing part being situated between the first and the second flange part. The first bearing is accommodated in the first housing part, and the second bearing is accommodated in the second housing part. This has the advantage that the two flange parts are able to be arranged as bearing flanges and therefore accommodate bearings, the two flange parts being axially set apart from each other with the aid of the housing part.

According to example embodiments, the electric motor has a gear unit, and the second rotor shaft part is provided with a helical gearing or is connected in a torsionally fixed manner to a helical geared toothing part. The helical gearing or the helical geared part meshes with a toothing part of the gear unit. This has the advantage that the helical geared parts are optimally aligned relative to each other with the aid of the second bearing arranged as a fixed bearing, and position errors on the output side of the gear unit are thus avoidable. This offers the advantage that position errors on the gear unit output side are able to be avoided.

According to example embodiments, the bellows is made from sheet metal. This is considered advantageous insofar as an uncomplicated production is possible.

According to example embodiments, a shaft sealing ring is situated on the side of the second bearing facing away from the first rotor shaft part. For example, the shaft sealing ring is accommodated in the first flange part and/or a sealing lip extends on the second rotor shaft part. This offers the advantage that no dirt enters the connection region between the two rotor shaft parts.

Further features and aspects of example embodiments of the present invention are described in greater detail below with reference to the appended Figures.

