Electric machine and method for assembling an electric machine

Abstract

Electric machine (1) with a drive shaft (2) on which a rotor (3) and a connecting element (4) are arranged and in which an at least partially friction-fit torque transmission connection is formed between the rotor (3) and the connecting element (4) by means of a locking element (18) being pressed in the direction of the rotor (3), characterized in that the locking element (18) is designed as a screw and has an external screw thread (25) which is screwed into an internal shaft thread (26) of the drive shaft (2).

Description

[0001] The invention relates to an electric machine with a drive shaft on which a rotor and a connecting element are arranged, and in which an at least partially friction-fit torque transmission connection is formed between the rotor and the connecting element by means of a locking element pressing the connecting element towards the rotor. The invention further relates to a method for assembling an electric machine. State of the art

[0002] Electrical machines of the type mentioned above are known from the prior art. The electrical machine can be configured in any way and can, in particular, be a motor, generator, or motor-generator of a motor vehicle. The electrical machine has a drive shaft through which it delivers or, alternatively, receives torque. The rotor and the connecting element are at least partially arranged on the drive shaft.

[0003] The rotor is mounted in the electric machine by means of the drive shaft. Next to the rotor, a connecting element is provided on the drive shaft. This element supplies torque from the drive shaft or the rotor to another device, or transmits torque from the other device to the rotor. The connecting element is, for example, a pulley, which is operatively connected to the other device via a flexible circulating element, in particular a belt, thus transmitting torque. The torque transmission connection is located between the rotor and the connecting element. This means that the rotor and the connecting element are connected in such a way that torque, preferably without slippage, can be transmitted between them. The torque transmission connection is at least partially friction-fit, and in particular, completely friction-fit.

[0004] This means that the torque between the rotor and the connecting element is not transmitted, or at least only to a subordinate extent, via a positive-locking or material-locking torque transmission connection. For example, the rotor and the connecting element may be rotatably mounted on the drive shaft, and torque transmission between the two elements is enabled solely by frictional engagement. This means, in particular, that the connecting element is pressed towards the rotor in such a way that torque can be transmitted by frictional engagement, thus establishing the torque transmission connection. For this purpose, a locking element is provided, which presses the connecting element axially, i.e., along the longitudinal axis of the drive shaft, towards the rotor.

[0005] The locking element is preferably attached to the drive shaft. This attachment exerts an axial force on the connecting element and any torque transmission element that may be present, which forces them towards the rotor. In such an embodiment, the maximum torque that can be transmitted between the rotor and the connecting element depends on the (maximum) axial force. However, this force cannot be increased arbitrarily because it is introduced into the drive shaft, and excessive stress can damage the drive shaft. In typical designs of the electric machine, the maximum transmissible torque is approximately 50 to 60 Nm. Further increasing the axial force can lead to cracking and failure of the drive shaft, particularly during assembly of the electric machine.

[0006] For example, DE 10 2007 036 313 A1 is known from the prior art, which describes a method for manufacturing a winding for the stator of an electric machine. In this method, a nut is screwed onto the drive shaft to force the connecting element towards the rotor and thus create a friction-fit torque transmission connection.

[0007] US 2005 O 119 077 A1 describes a combination of a pulley and a rotor of a rotating electric machine for a motor vehicle, comprising a rotor shaft carrying a rotor and a front ball bearing, and a pulley with a peripheral working area. The peripheral working area engages with a drive belt. The pulley has a central hub with an axial bore for the passage of the rotor shaft. The pulley has an internal splined section so that it can be mounted onto a complementary external splined section of the rotor shaft. Disclosure of the invention

[0008] The electric machine with the features mentioned in claim 1 has the advantage that the maximum torque transmissible between the rotor and the connecting element is increased, in particular by exerting a greater axial force on the connecting element in the direction of the rotor. According to the invention, this is achieved by designing the locking element as a screw with an external screw thread that is screwed into an internal shaft thread of the drive shaft. The locking element forces the connecting element directly or indirectly in the direction of the rotor. In the former case, the locking element is in direct contact with the connecting element. For this purpose, the locking element and the connecting element have dimensions that enable them to interact to apply an axial force to the connecting element via the locking element.If only indirect pressure is intended, a further element can be provided between the connecting element and the locking element, which at least partially transmits the axial force of the locking element to the connecting element. This further element is, for example, a fastening element for the connecting element.

[0009] According to the invention, the locking element or screw has an external thread that is screwed into an internal thread of the drive shaft. The drive shaft is thus designed, at least partially, as a hollow shaft, with the screw extending into the drive shaft, at least with its external thread, up to the internal thread. This reduces the weight of the electric machine because the hollow shaft is significantly lighter than the solid drive shaft known from the prior art. The rotor is fixed to the drive shaft in such a way that it counteracts this axial force and cannot move axially. The rotor is thus fixed to the drive shaft, at least in the direction away from the connecting element, in the axial direction.This can be achieved, for example, analogously to the connection element, by providing a locking element that presses the rotor towards the connection element. Alternatively or additionally, the rotor can also be provided with a rotationally fixed connection to the drive shaft, for example via a crimp connection.

[0010] The rotor can have at least one permanent magnet element or be an electromagnetically excited rotor. In the latter case, the rotor is, for example, designed as a claw-pole rotor and thus consists in particular of two claw pole plates, on the outer circumference of which claw pole fingers extending axially are arranged. Ultimately, the rotor is any element that is arranged on the drive shaft and can be set in rotation. It is therefore not necessary that the rotor actually has all the elements of a rotor, armature, inductor, or pole wheel of the electric machine. Rather, the term "rotor" can also refer only to a portion of such an element, in particular a rotor core.The claw pole plates are arranged such that their claw pole fingers, extending axially along the circumference of the electric machine, alternate as north and south poles. For this reason, gaps typically exist between the oppositely magnetized claw pole fingers. The claw pole fingers preferably taper towards their free ends and thus run slightly obliquely with respect to a longitudinal axis of the electric machine.

[0011] A further development of the invention provides an additional fastening element that pushes the connecting element towards the rotor and, in particular, is arranged – viewed axially – between the connecting element and the locking element. Thus, the locking element is provided, which pushes the connecting element towards the rotor. Additionally, the fastening element is present, which also exerts an axial force on the connecting element in the direction of the rotor. In this way, an additional axial force is provided for the torque transmission connection, thereby increasing the maximum transmissible torque. Furthermore, the drive shaft, and in particular any freewheel groove provided on it, is further relieved of stress. In such an embodiment, the locking element preferably communicates with the connecting element only indirectly.It can be designed such that the locking element acts on the fastening element and pushes it towards the rotor. The fastening element alone thus pushes the connecting element directly towards the rotor. In particular, the fastening element is located axially between the connecting element and the locking element, so that the locking element is operatively connected to the fastening element and the fastening element to the connecting element.

[0012] As already explained above, the rotor is fixed axially on the drive shaft, at least in the direction away from the connecting element. In particular, it can also be fixed to the drive shaft in a rotationally fixed manner, so that a functional connection exists between the rotor and the drive shaft. For example, a fastening element and a locking element are also present on the rotor side, with the fastening element pressing the rotor and the locking element pressing the fastening element towards the connecting element. Additionally, it can be provided that the fastening element and / or the locking element of the connecting element and / or the rotor are connected to the drive shaft or to each other by a material bond, in particular a welded joint.In this way, in addition to increasing the axial force, the elements are fixed against each other in the circumferential direction, so that torque can be transmitted between them not only via friction but also via material contact. This also increases the maximum transmissible torque between the rotor and the connecting element.

[0013] A further development of the invention provides that the fastening element is a nut, in particular a flanged nut, which is screwed onto an external thread of the drive shaft, and that the locking element is a screw whose head is positively engaged with the nut. The nut has an internal thread which is operatively connected to the external thread of the drive shaft. The fastening element in the form of the nut is screwed onto the drive shaft to such an extent that it interacts with a counter-surface of the connecting element, at least via a clamping surface, in a torque-transmitting manner. A clamping connection exists between the clamping surface and the counter-surface, which transmits torque essentially purely by friction.The locking element, on the other hand, is designed as a screw with a head and a shank, the head of which rests against the fastening element or nut in such a way that a force-fit connection is also established. The fastening element or nut thus has an additional clamping surface which interacts clampingly with a counter-clamping surface of the screw head. The screw is fastened on the side of the fastening element facing away from the rotor or connecting element, in particular on the drive shaft.

[0014] A further development of the invention provides that the internal shaft thread and the external screw thread are located at the same axial position as the rotor. The same axial position is understood to mean a position in which the internal shaft thread, the external screw thread, and the rotor have at least one common axial position in the sense of a section perpendicular to the longitudinal axis of the electrical machine. Preferably, however, the internal shaft thread and / or the external screw thread, or in particular only the internal shaft thread or only the external screw thread, lie completely within an axial extent of the rotor, so that the rotor prevents any expansion of the drive shaft that might be caused by the interaction of the internal shaft thread and the external screw thread.

[0015] A further development of the invention provides that the internal shaft thread and the external shaft thread are designed with opposite directions. The locking element thus forms a counter-element for the fastening element and prevents the simultaneous loosening of both. Instead, it is necessary that the fastening element be unscrewed from the drive shaft in a different direction of rotation than the locking element. In this way, unintentional loosening of the fastening element is prevented simply and effectively, without, for example, the need for a material-bonded connection between the fastening element and the drive shaft.

[0016] A further development of the invention provides that the drive shaft has a free-running groove adjacent to the fastening element. The free-running groove is located on the drive shaft as a relief groove and serves in particular as a run-off zone for the external shaft thread onto which the fastening element or nut is screwed. The free-running groove is usually arranged directly adjacent to the fastening element or the external shaft thread. It can also be provided that it is at least partially overlapped by the connecting element and / or the fastening element. The free-running groove is typically located in an extremely highly stressed area of ​​the drive shaft. It is relieved of stress by the provision of the locking element, thus enabling an increase in the transmissible torque.

[0017] A further development of the invention provides that at least one torque transmission element is arranged on the drive shaft between the rotor and the connecting element – ​​viewed in the axial direction – which is designed for the frictional transmission of torque between the rotor and the connecting element. The rotor and the connecting element therefore do not need to be directly adjacent to each other to form the torque transmission connection. Rather, it can be provided that the at least one torque transmission element is located axially between them, i.e., the rotor and the connecting element are spaced apart from each other in the axial direction. Specifically, there is a torque transmission connection between the rotor and the torque transmission element, and another between the torque transmission element and the connecting element.Accordingly, a torque transmission chain is established between the rotor and the connecting element via the at least one torque transmission element. The torque transmission element allows the axial distance between the rotor and the connecting element to be increased.

[0018] A further development of the invention provides that the connecting element and / or the torque transmission element are rotatably arranged on the drive shaft. This means that the two elements do not have a torque transmission connection to the drive shaft and are therefore rotatable in the circumferential direction. In particular, no toothing is provided between the connecting element and the drive shaft or between the torque transmission element and the drive shaft.

[0019] A further development of the invention provides that the torque transmission element is a spacer ring, a ball bearing, or a fan wheel. Instead of the spacer ring, a spacer sleeve with a larger axial extension can also be provided. The ball bearing serves to support the drive shaft and thus also the elements arranged on it, such as the rotor and the connecting element. Of course, any bearing, in particular any rolling bearing, can also be provided instead of the ball bearing. The fan wheel is a component of a fan, which serves to cool the electric machine. The fan wheel typically has several blades which, when the drive shaft rotates, create an airflow towards the rotor or in the opposite direction, in particular over or through the rotor.

[0020] The invention further relates to a method for assembling an electric machine, particularly according to the foregoing embodiments, wherein the electric machine has a drive shaft on which a rotor and a connecting element are arranged, and in which an at least partially friction-fit torque transmission connection is formed between the rotor and the connecting element by means of a locking element pressing the connecting element towards the rotor. It is provided that the locking element is designed as a screw and is attached to the drive shaft by screwing an external thread of the locking element into an internal thread of the drive shaft. The electric machine can be further developed according to the foregoing embodiments.

[0021] During the assembly of the electric machine, the drive shaft is provided, and then the rotor, the connection element, and, if necessary, at least one torque transmission element are mounted on the drive shaft. The rotor may be connected to the drive shaft, for example, by crimping. The connection element and the torque transmission element are usually rotatably mounted on the drive shaft. Finally, the locking element, which is in the form of a screw, is attached to the drive shaft.

[0022] Additionally, a fastening element in the form of a nut can be provided, which is screwed onto an external thread of the drive shaft. Only subsequently is the locking element attached, which exerts an axial force on the fastening element in the direction of the rotor. For example, the drive shaft is designed as a hollow shaft and has an internal thread at the level of the rotor, i.e., at least partially concurrent axial positions. In this case, the locking element can be a screw with an external thread, which is screwed into the drive shaft in such a way that the external thread engages with the internal thread. In this way, the locking element, or rather one of its heads, is displaced towards the rotor and thus also forces the fastening element in this direction.

[0023] The invention is explained in more detail below with reference to the exemplary embodiments shown in the drawing, without limiting the invention. The drawing shows: Fig. 1 a section of an electric machine with a drive shaft on which a connecting element is attached in a conventional manner by means of a fastening element, and Fig. 2 a longitudinal section through a region of an electrical machine according to the invention.

[0024] The Fig. Figure 1 shows a section of an electrical machine 1 known from the prior art. The electrical machine 1 can be, for example, a motor, generator, or motor-generator. It has a drive shaft 2 through which it can deliver or receive torque. A rotor 3 (not shown) and, preferably spaced axially from the rotor 3, a connecting element 4 are arranged on the drive shaft 2. The connecting element 4 is, for example, a pulley and thus has a running surface 5 for a flexible wrapping element, such as a belt. The connecting element 4 is attached to the drive shaft 2 by means of a fastening element 6 and is forced by it in the direction of the rotor 3, i.e., in the direction of arrow 7. Arrow 7 is parallel to a longitudinal axis 8 of the drive shaft 2 and also of the electrical machine 1.

[0025] The fastening element 6 is designed as a nut, which is screwed onto an external shaft thread 9 of the drive shaft 2 (only partially shown here). To enable this screwing, the drive shaft 2 has internal teeth 10 extending from the end face of the drive shaft 2 into the interior of the drive shaft 2 in the direction of the rotor 3. However, viewed axially, the internal teeth 10 terminate at the latest at the connecting element 4. Thus, the internal teeth 10 do not extend beyond the rotor 3. This prevents the drive shaft 2 from being weakened by the internal teeth 10.

[0026] The fastening element 6 forces the connecting element 4 in the direction of arrow 7, i.e., towards the rotor 3. In this way, a torque transmission connection is established between the connecting element 4 and the rotor 3, although this is not visible here. This torque transmission connection is at least partially friction-fit, preferably completely friction-fit. This means that the torque between the rotor 3 and the connecting element 4 is preferably transmitted entirely by friction.

[0027] The Fig. Figure 2 shows a section of an electric machine 1 according to the invention. The drive shaft 2, the rotor 3, and the connection element 4 are again shown, at least by way of example. Because the electric machine 1 according to the invention can be based on a prior art design, reference is made to the preceding explanations regarding Fig. 1 referred to. In the axial direction, i.e., along the longitudinal axis 8, several torque transmission elements 11 are located between the rotor 3 and the connecting element 4. One of the torque transmission elements 11 is designed as a bearing shell 12' of a bearing 12. The bearing is preferably a ball bearing, as in the Fig. 2 can be seen. In principle, however, any type of bearing can be provided. The bearing shell 12 is enclosed on both sides – viewed in the axial direction – by torque transmission elements 11 designed as spacer rings 13. A final torque transmission element 11 is provided as a fan wheel 14 or as an intermediate disk.

[0028] The torque transmission elements 11 and the connecting element 4 are rotatably mounted on the drive shaft 2. This means that there is no positive or material connection directly between these elements and the drive shaft 2. The torque transmission between the rotor 3 and the connecting element 4 occurs solely through the frictional torque transmission connection established via the torque transmission elements 11. For this purpose, the fastening element 6 forces not only the connecting element 4 but also the torque transmission elements 11 towards the rotor 3. The drive shaft 2 counteracts the resulting force.

[0029] By pushing the connecting element 4 towards the rotor 3, frictional torque transmission connections are created between the connecting element 4 and the nearest torque transmission element 11, between the adjacent torque transmission elements 11, and between the rotor 3 and the adjacent torque transmission element 11, thus forming a frictional torque transmission chain between the rotor 3 and the connecting element 4. The drive shaft 2 therefore transmits no or only a small portion of the torque between the rotor 3 and the connecting element 4. Rather, it primarily serves to axially clamp the connecting element 4, the torque transmission elements 11, and the rotor 3.

[0030] The connecting element 4 is pressed towards the rotor 2 by means of the fastening element 6. For this purpose, during assembly of the electric machine 1, the fastening element 6 is screwed onto the external shaft thread 9 until a sufficiently large frictional connection exists between the connecting element 4, the torque transmission elements 11, and the rotor 3 to transmit the desired maximum torque between the rotor 3 and the connecting element 4. The fastening element 6 has a clamping surface 15 which interacts with a counter-clamping surface 16 of the connecting element 4 to establish a frictional connection between the fastening element 6 and the connecting element 4. The clamping connection 17 formed by the clamping surface 15 and the counter-clamping surface creates a frictional torque transmission connection between the connecting element 4 and the fastening element 6, and consequently also between the drive shaft 2 and the motor shaft 2.

[0031] To further increase the maximum torque that can be transmitted between rotor 3 and connecting element 4, an additional locking element 18 is provided, which is in the form of a screw. Of course, an embodiment can also be implemented in which only the locking element 18, but not the fastening element 6, is provided. The advantages of the invention can also be realized with such an embodiment. The locking element 18, designed as a screw, has a head 19 and a shank 20. The head 19 extends radially over the drive shaft 2 and at least partially over the fastening element 6, so that a further clamping connection 21 exists between the fastening element 6 and the locking element 18. This connection consists of a clamping surface 22 on the fastening element 6 and a counter-clamping surface 23 on the locking element 18.

[0032] The shaft 20 of the locking element 18 engages, at least partially, in a central recess 24 of the hollow drive shaft 2. The internal toothing 10, described earlier, is located on the end of the drive shaft 2 facing the connecting element 4. However, this toothing extends only partially into the recess 24. In particular, the axial extent of the internal toothing 10 is less than that of the fastening element 6. The internal toothing 10 serves to secure the drive shaft 2 circumferentially during the assembly of the fastening element 6 onto the drive shaft 2, i.e., during the screwing process. For this purpose, a rotationally fixed counter element (not shown), matched to the internal toothing, is inserted into it, the fastening element 6 is installed, and the counter element is then removed.The internal toothing 10 is designed in such a way that it can transmit a maximum assembly torque occurring during assembly, for example 100 Nm.

[0033] The shaft 20 of the locking element 18 has an external screw thread 25, which interacts with an internal shaft thread 26 of the drive shaft 2 to hold the locking element 18. The locking element 18 is screwed into the recess 24 of the drive shaft 2. The internal shaft thread 26 is configured opposite to the external shaft thread 9, so that the locking element 18 serves as a counter-element for the fastening element 6. The locking element 18 applies an additional axial force in the direction of the rotor 3, resulting in greater axial clamping between the connecting element 4 and the rotor 3. This allows a higher maximum torque to be transmitted via the frictional torque transmission connection. Furthermore, the locking element 18 relieves the load on a free-running groove 27, or undercut, for the external shaft thread 9 in the drive shaft 2.

[0034] Overall, the electric machine 1 according to the invention enables the force-fit transmission of a larger maximum torque between the rotor 3 and the connecting element 4. At the same time, the load on the drive shaft 2 is reduced and loosening of the fastening element 6 is effectively prevented. This is the case both when the fastening element 6 and the locking element 18 are provided, and when only the locking element 18, but not the fastening element 6, is present.

Claims

[1] Electric machine (1) with a drive shaft (2) on which a rotor (3) and a connecting element (4) are arranged and in which at least a partially frictional torque transmission connection is formed between the rotor (3) and the connecting element (4) by means of a locking element (18) pressing the connecting element (4) towards the rotor (3), characterized by , that the locking element (18) is designed as a screw and has an external screw thread (25) which is screwed into an internal shaft thread (26) of the drive shaft (2). [2] Electric machine according to claim 1, characterized by , that an additional fastening element (6) is provided which pushes the connecting element (4) towards the rotor (3). [3] Electric machine according to any one of the preceding claims, characterized by, that the fastening element (6) is in the form of a nut which is screwed onto an external shaft thread (9) of the drive shaft (2), and that a head (19) of the locking element (18) is positively connected to the nut (6). [4] Electric machine according to any one of the preceding claims, characterized by , that the internal shaft thread (26) and the external screw thread (25) are located in the same axial position as the rotor (3). [5] Electric machine according to any one of the preceding claims, characterized by , that the internal shaft thread (26) and the external shaft thread (9) are designed in opposite directions. [6] Electric machine according to any one of the preceding claims, characterized by , that the drive shaft (2) has a freewheel notch (27) adjacent to the fastening element (6). [7] Electric machine according to any one of the preceding claims, characterized by, that on the drive shaft (2) between the rotor (3) and the connecting element (4) - viewed in the axial direction - at least one torque transmission element (11) is arranged, which is provided for the force-fit torque transmission between the rotor (3) and the connecting element (4). [8] Electric machine according to any one of the preceding claims, characterized by , that the connecting element (4) and / or the torque transmission element (11) are rotatably arranged on the drive shaft (2). [9] Electric machine according to any one of the preceding claims, characterized by that the torque transmission element (11) is a spacer ring (13), a ball bearing (12) or a fan wheel (14). [10] Method for assembling an electric machine (1), wherein the electric machine (1) has a drive shaft (2) on which a rotor (3) and a connecting element (4) are arranged and in which at least a partially friction-fit torque transmission connection is formed between the rotor (3) and the connecting element (4) by means of a locking element (18) pushing the connecting element (4) towards the rotor (3), characterized by , that the locking element (18) is designed as a screw and is attached to the drive shaft (2) by screwing an external screw thread (25) of the locking element (18) into an internal shaft thread (26) of the drive shaft (2).

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