Electric motor test bench

Abstract

The invention relates to a test bench for testing an electric motor (3) with internal rotor cooling, wherein the test bench (1) has a drive unit with a drive shaft (17) designed as a hollow shaft, which is connected in a torque-transmitting and coaxial manner to a rotor shaft (9) designed as a hollow shaft of the electric motor (3), namely via a coupling assembly (19) which has at least one elastically or flexibly yielding shaft connector (27) which is connected in a torque path between the drive shaft (17) and the rotor shaft (9) in order to compensate for coaxial errors between the two shafts (9, 17), wherein the test bench (1) has a coolant circuit (K) for internal rotor cooling, in which a coolant lance (29) is integrated, via which coolant can be guided into the rotor interior (11) in the axial direction.According to the invention, a coolant return line (41) is integrated in the coupling assembly (19), via which a part of the coolant can be returned from the rotor interior (11) in the coaxial direction and in the opposite direction to the coolant supply to the test bench (1).

Description

[0001] The invention relates to a test bench for testing an electric motor with internal rotor cooling according to the preamble of claim 1.

[0002] Using such a test bench, performance and functional tests can be conducted on an electric motor serving as the electric drive in an electric vehicle. A test bench of this type comprises a drive unit with a drive shaft that is connected to a rotor shaft of the electric motor in a torque-transmitting and coaxial manner. The two shafts are designed as hollow shafts and are connected to each other via a coupling assembly. The coupling assembly comprises at least one elastic or flexibly compliant shaft connector that is connected in a torque path between the drive shaft and the rotor shaft to compensate for coaxial errors between the two shafts.

[0003] Powerful electric motors for electromobility are equipped with internal rotor cooling. This is usually achieved on the transmission side via a coolant lance that is guided into the rotor. To ensure that performance and functional tests on the standard test bench are carried out under realistic operational conditions, the test bench also features an oil circuit for internal rotor cooling, which incorporates an integrated oil lance. The oil lance directs coolant axially into the interior of the electric motor's rotor.

[0004] The test bench drive must be designed for many times the number of operating hours (for example, 100 to 500 times) compared to the electric motor being tested. For this reason, the test bench drive is significantly larger than the electric motor being tested. As the test bench drive increases in size, the oil guide path between the test bench and the electric motor becomes longer than for the electric motor installed in the vehicle. Furthermore, perfect coaxial positioning of the test bench drive and the electric motor is not possible in practice for the following reason: Different operating temperatures can occur in the electric motor and the test bench drive during a performance test, which leads to different shaft expansions and thus to coaxial errors between the rotor shaft and the drive shaft. To compensate for such coaxial errors, the coupling assembly has an elastic or flexibly compliant shaft connector.This is connected in the torque path between the drive shaft and the rotor shaft to compensate for coaxial errors between the two shafts.

[0005] The elastic shaft connector is, for example, an elastomer coupling with a hollow shaft design or a metal bellows coupling. Due to its design, such an elastomer coupling is permeable to coolant in the radial direction. Therefore, to prevent oil leakage in the shaft connector, the state of the art does not include an axial oil return from the interior of the rotor toward the test bench drive, which is routed coaxially through the electrical shaft connector. A metal bellows coupling, which is also suitable, would, however, be tight in the radial direction for the coolant. However, the large diameters required for the high torques would create a large volume that would be flooded with coolant. This would negatively impact the weight and dynamic behavior (inertia of the fluid).

[0006] Instead of an elastomer coupling, a multi-disk coupling is also suitable. Similar to the elastomer coupling, this type of coupling is leaky in the radial direction and can therefore be considered equivalent to the elastomer coupling.

[0007] Instead of a coaxial oil return, the current technology uses a radial oil return, in which the coolant is diverted radially from the inside of the rotor via a coolant line to the outside and from there returned to the test bench. However, such a radial oil return is associated with high processing complexity.

[0008] DE 10 2004 025 828 B3 discloses a roller test bench for motor vehicles. This comprises a roller for directly driving or decelerating at least one wheel of the motor vehicle. An external rotor electric motor is also provided, the outer rotor of which is connected to the roller and the internal stator of which is supported against rotation. Furthermore, devices for measuring the support torque are provided. CN 111504531 A discloses a torque sensor which

[0009] The object of the invention is to provide a test bench for testing an electric motor which is technically simpler in construction than the prior art.

[0010] The object is solved by the features of claim 1. Preferred developments of the invention are disclosed in the subclaims.

[0011] The invention relates to a test bench for testing an electric motor with internal rotor cooling. The test bench has a test bench drive with a drive shaft. This drive shaft transmits torque and is coaxially connected to a rotor shaft of the electric motor. Both the test bench drive shaft and the electric motor rotor shaft are designed as hollow shafts and are connected to one another via a coupling assembly. The coupling assembly has at least one elastic or flexibly yielding shaft connector, which is connected in a torque path between the drive shaft and rotor shaft to compensate for a coaxial error between the two shafts. The test bench also has a coolant circuit for internal rotor cooling. Integrated into the coolant circuit is a coolant lance, through which coolant is guided axially into the interior of the rotor.According to the characterizing part of claim 1, a coolant return line is integrated into the coupling assembly. Via the coolant return line, a portion of the coolant can be returned from the interior of the rotor to the test bench in the axial direction as well as in the opposite direction to the coolant supply. By providing the coolant return line, a coaxial coolant return from the interior of the rotor to the test bench can be achieved, which is significantly easier to implement in terms of process technology than a radial coolant return.

[0012] In a technical implementation, the coupling assembly, in particular the elastically or flexibly yielding shaft connector, can be designed like a hollow shaft through which the coolant return line and the coolant lance extend. In a specific embodiment, the coolant return line can be formed as an annular gap between the radially inner coolant lance and the radially outer coupling assembly.

[0013] The flexible or elastically yielding shaft connector installed in the coupling assembly is preferably an elastomer coupling, which consists of a multi-part elastomer body and metallic coupling parts. Due to its design, the elastomer coupling can be permeable to coolant radially outward. A metal bellows coupling would be sealed to the outside. However, due to the large outer diameter of the metal bellows, it would be flooded with a large amount of oil. This increases the weight and inertia to such an extent that the coupling would be unusable.

[0014] In order to ensure a radially outward-tight coolant flow through the coupling assembly (or to prevent the complete flooding of a metal bellows coupling), a connecting pipe is provided. The connecting pipe divides the annular gap between the radially inner coolant lance and the radially outer coupling assembly into a radially inner, coolant-flowing partial annular gap between the coolant lance and the connecting pipe, and into a radially outer, coolant-free partial annular gap between the coupling assembly and the connecting pipe.

[0015] The connecting tube is preferably not rigid, but rather flexible, to compensate for coaxial errors between the rotor shaft and the drive shaft. It is particularly preferred if the connecting tube is implemented as a metal bellows element with at least one flexible bellows section. Alternatively, the connecting tube can also be rigid. In this case, the compensating movements resulting from coaxiality problems must be ensured by means of additional elastic elements, such as an O-ring.

[0016] The coupling assembly, which is preferably constructed in several parts, has an adapter at each of its two axial ends, i.e., an adapter on the drive shaft side and an adapter on the rotor shaft side. The coupling assembly can be connected to the drive shaft and the rotor shaft in a rotationally fixed manner via the two adapters, particularly via a flange connection or spline connection.

[0017] With regard to reliable positioning, it is preferred if the connecting pipe is connected to the coupling assembly in a rotationally fixed and coolant-tight manner. The connecting pipe can preferably be connected in a rotationally fixed manner only on one side, while the other connecting pipe side can slip slightly. During test operation, the connecting pipe is therefore essentially rotationally coupled to the coupling assembly. The connection to the coupling assembly can be realized as a fitting connection between the outer circumference of the respective connecting pipe end and an inner circumferential centering surface of the adapter. In addition, a sealing zone with a circumferential sealing element can be provided between the connecting pipe end and the adapter in order to completely seal the coolant-free, radially outer partial annular gap against coolant.

[0018] An alternative solution to the above-described fitting between the outer circumference of the connecting pipe end and the inner circumference centering surface of the adapter is presented below: Accordingly, a rolling bearing can be interposed between the outer circumference of the connecting pipe end and the inner circumference centering surface of the adapter, via which the connecting pipe end is supported on the inner circumference centering surface of the adapter. A sealing zone with a circumferential sealing element can also be arranged in front of the rolling bearing.

[0019] It is preferred if the connecting pipe extends axially between the two adapters without contact with the coupling assembly and the coolant lance. This prevents frictional contact between the connecting pipe and the stationary coolant lance during testing. Such frictional contact would adversely affect torque measurement.

[0020] In a technical implementation, the coupling assembly can include a torque sensor, in particular a torque measuring flange. This can be arranged in the axial direction between one of the two adapters and the elastically flexible shaft connector.

[0021] The coolant lance, unlike the coupling assembly, is mounted in the test bench in a rotationally fixed manner. Such a rotationally fixed mount can be implemented as follows: The coolant lance can be routed with its lance end out of a drive shaft end facing away from the electric motor. The thus exposed lance end can be mounted in a rotationally fixed manner at a test bench bearing point.

[0022] In a first option, the coolant lance can be elastically mounted on the test bench bearing to compensate for a coaxial misalignment between the test bench drive shaft and the rotor shaft of the electric motor. On the other hand, the coolant lance can be rigidly mounted on a rotor bearing. In a second option, the coolant lance can be rigidly mounted on the test bench bearing on only one side, while the coolant lance extends continuously toward the electric motor without bearings.

[0023] The test bench drive shaft is a component of a test bench drivetrain. This can be, for example, a chain drive, belt drive, electric motor, or even a transmission structure. The test bench drivetrain essentially corresponds to a vehicle drivetrain in which the electric motor is installed. It should be emphasized that – similar to the test bench drivetrain – the coolant lance in the vehicle drivetrain can also be mounted flexibly or resiliently on a bearing point.

[0024] Exemplary embodiments of the invention are described below with reference to the accompanying figures. They show: Fig. 1 shows a test bench with an electric motor installed therein according to a first embodiment; Fig. 2 the electric motor in a unique position; and Fig. 3 a test bench with an electric motor installed therein according to a second embodiment.

[0025] In the Fig. Figure 1 shows a rough schematic of a test bench 1 with an electric motor 3 installed therein, in which a motor performance test can be carried out. The test bench 1 and the electric motor 3 are only indicated in the figures to the extent necessary for understanding the invention. Accordingly, Fig. 2 shows a roughly sketched electric motor 3 in isolation. This has a stator housing 5 and a rotor shaft 9 which is rotatably mounted therein via pivot bearings 7. The other electric motor components (stator, rotor, windings, etc.) have been omitted for reasons of clarity. The rotor shaft 9, designed as a hollow shaft, extends out of the left-hand end face of the electric motor. When installed in the vehicle, a transmission input shaft 10 is inserted into the rotor interior 11 of the rotor shaft 9 with splines. An oil lance 13 is guided through the transmission input shaft 10, which is also designed as a hollow shaft and projects into the rotor interior 11 for internal rotor cooling. The oil lance 13 and the rotor interior 11 are components of an electric motor oil circuit in which a portion of the oil is drained axially from the rotor interior 11 to the outside via the splines. The oil lance 13 is furthermore mounted with its lance tip in a bearing point 15 in the rotor interior 11.

[0026] In the Fig. 1, the electric motor 3 is used for testing purposes in the test bench 1. The test bench 1 has a test bench drive (not shown) with a drive shaft 17. This is connected to the rotor shaft 9 via a coupling assembly 19, transmitting torque, and in a coaxial alignment. The coupling assembly 19 has a drive shaft-side adapter 21 and a rotor shaft-side adapter 23 at each of its two axial ends. The drive shaft-side adapter 21 is connected in a rotationally fixed manner to the drive shaft 17 via an indicated flange connection, while the rotor shaft-side adapter 23 is rotationally fixedly inserted into the rotor interior 11 of the rotor shaft 9 via a spline. Between the two adapters 21, 23 are a torque measuring flange 25 and an elastically (or flexibly) resilient shaft connector 27.The coupling assembly 19, consisting of the two adapters 21, 23, the torque measuring flange 25 and the elastically flexible connector 27, is designed in the manner of a hollow shaft.

[0027] As from the Fig. As can be seen from Figure 1, the test bench has an oil circuit K with internal rotor cooling, in which an oil lance 29 is integrated, via which oil is fed coaxially to the two shafts 9, 17 into the rotor interior 11. The oil lance 29 extends through the drive shaft 17 and through the coupling assembly 19 into the rotor interior 11 and is mounted therein with its lance tip in the bearing point 15. In the Fig. 1, the oil lance 29, with its axially opposite end, extends from a shaft end of the drive shaft 17 facing away from the electric motor 3. The lance end is mounted on a test bench bearing point 31 in a rotationally fixed but elastic or flexible manner to compensate for coaxial errors between the two shafts 9, 17.

[0028] The test bench drive shaft 17 is a component of a test bench drive train not shown in the figures. This can be, for example, a transmission structure. The test bench drive train essentially corresponds to a vehicle drive train in which the electric motor 3 can be installed. The vehicle drive train can—analogous to the test bench drive train—have a bearing point in which the oil lance 13 is mounted flexibly or resiliently.

[0029] A core of the invention is that the oil return from the rotor interior 11 to the test bench 1 is carried out in a simple process-technically coaxial manner with the oil lance 29. For this purpose, an oil return line 41 is formed in an annular gap 33 between the radially inner oil lance 29 and the radially outer coupling assembly 19, via which oil return line a portion of the oil is returned from the rotor interior 11 in the axial direction and counter to the oil supply to the test bench 1. The returned oil is collected in an oil sump 35 and from there circulated in the oil circuit via a pressure pump (not shown).

[0030] Due to its design, the elastically flexible shaft connector 27, which is designed as an elastomer coupling (or multi-disk coupling), is oil-permeable in the radial direction outwards. To ensure a tight oil flow through the elastic shaft connector 27 in the radial direction outwards, Fig. 1 a connecting pipe 37 is provided. The connecting pipe 37 is in the Fig. 1 a metal bellows element with two flexible bellows sections 39. The connecting tube 37 divides the annular gap 33 into a radially inner, coolant-flowing partial annular gap 41, which forms the oil return line, and a radially outer coolant-free partial annular gap 43. With the help of the bellows sections 39, the connecting tube 37 is designed to be sufficiently flexible to compensate for coaxial errors between the two shafts 9, 17.

[0031] The connecting pipe 37 is connected to the respective adapter 21, 23 in a rotationally fixed and coolant-tight manner. For this purpose, a fitting connection is realized between the outer circumference of the respective connecting pipe end and an inner circumferential centering surface 45 of the adapter 21, 23. Furthermore, a sealing zone with a circumferential sealing element 47 is provided between the connecting pipe end and the adapter 21, 23, which protects the radially outer partial annular gap 43 from oil. The connecting pipe connection to the two adapters 21, 23 is designed such that the connecting pipe 37 is connected in a rotationally fixed manner only on one side, while the other connecting pipe side can slip slightly.

[0032] By means of a labyrinth seal 49, Fig. 1, the electric motor 3 and the test bench oil circuit K are sealed from the outside environment, and oil is collected. The labyrinth seal 49 operates without contact, meaning it does not affect the torque measurement. Other types of seals, such as lip seals and radial shaft seals, are also conceivable; however, these can negatively affect the torque measurement.

[0033] With the help of the Fig. The compressed air supply 51 indicated in Figure 1 keeps the oil inside and the contamination outside. This function is particularly important during rotational standstill with an active oil circuit to prevent oil leakage.

[0034] The rotor shaft side adapter 23 is in the Fig. 1 is assigned an adapter plate 48. This seals the electric motor 3 and adapts it with respect to the coupling assembly 19. The adapter plate 48 is connected to the front face of the electric motor via positioning contours (i.e., positioning pins) 55.

[0035] With the help of the positioning aids 53, an exact, rigid and reproducible positioning of the test bench drive and the electric motor 3 (as well as its adapter plate 48) is made possible in order to avoid coaxiality problems as far as possible.

[0036] In the embodiment of the Fig. 1, the shaft connector 27 is designed as an elastomer coupling that is oil-permeable radially outward. However, the invention is not limited to such a shaft connector 27 designed as an elastomer coupling. Instead, the shaft connector 27 can also be designed as a metal bellows coupling. The metal bellows coupling is oil-tight radially outward, so that oil could in principle be returned through the metal bellows coupling. However, due to its large outer diameter, the metal bellows coupling has a correspondingly large internal volume or a correspondingly large passage cross-section, which would be flooded with a large return oil quantity. In this case, the weight and inertia would increase to such an extent that the metal bellows coupling would be unusable.In order to prevent a complete flooding of the inner volume of the metal bellows coupling with the oil return quantity, the oil-flowing connecting pipe 37 according to the invention is used, which prevents a complete oil flooding of the inner volume of the metal bellows coupling.

[0037] In the embodiment of the Fig. 1, the shaft connector is implemented as an elastomer coupling. This can allow an angular misalignment of approximately 0.8° to 2°. The metal bellows connecting tube 37, on the other hand, allows almost no angular misalignment. This discrepancy is shown in the Fig. 1 is compensated by the fitting connection between the pipe ends of the connecting pipe 37 and the centering surface 45 of the adapters 21, 23, which allows movements.

[0038] For a more controlled compensation of the discrepancy between the angular offsets described above, reference is made to the example of the Fig. 3. In the Fig. 3 is in a view corresponding to the Fig. 1 a test bench 1 is shown. Its structure and function essentially corresponds to the structure and function of the Fig. 1 shown test bench 1. Therefore, reference is made to the previous description.

[0039] In contrast to Fig. 1 is in the Fig. 3 an alternative solution to the one in the Fig. 1 shown fitting connection between the outer circumference of the connecting pipe end and the inner circumferential centering surface 45 of the adapter 21. Accordingly, in the Fig. 3 between the outer circumference of the connecting pipe end and the inner circumferential centering surface 45 of the adapter 21, a rolling bearing 57 is interposed. The connecting pipe end is supported via the rolling bearing 57 on the inner circumferential centering surface 45 of the adapter 21. The rolling bearing 57 is - as in the Fig. 1 - a sealing zone with a circumferential sealing element 47 is arranged in front. LIST OF REFERENCE SYMBOLS: 1 test bench 3 electric motor 5 Stator housing 7 pivot bearings 9 Rotor shaft 10 Gearbox input shaft 11 Rotor interior 13 Oil lance 15 Oil lance storage location 17 Drive shaft 19 Coupling module 21 drive shaft side adapter 23 rotor shaft side adapter 25 Torque measuring flange 27 elastic / flexible shaft connector 29 Oil lance 31 Test bench bearing point 33 Annular gap 35 Oil sump 37 Connecting pipe 39 Bellows section 41 inner partial annular gap 43 outer partial annular gap 45 Centering surface 47 Sealing element 48 adapter plate, 49 Labyrinth seal 51 Compressed air supply 53 positioning aids 55 positioning contours or positioning pins 57 rolling bearings K Oil circuit QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2004 025 828 B3

[0008] CN 111504531 A

[0008]

Claims

[1] Test bench for testing an electric motor (3) with internal rotor cooling, wherein the test bench (1) has a drive unit with a drive shaft (17) designed as a hollow shaft, which is connected in a torque-transmitting and coaxial manner to a rotor shaft (9) designed as a hollow shaft of the electric motor (3), namely via a coupling assembly (19) which has at least one elastically or flexibly yielding shaft connector (27) which is connected in a torque path between the drive shaft (17) and the rotor shaft (9) in order to compensate for coaxial errors between the two shafts (9, 17), wherein the test bench (1) has a coolant circuit (K) for internal rotor cooling, in which a coolant lance (29) is integrated, via which coolant can be supplied into the rotor interior (11) in the axial direction, characterized bythat a coolant return line (41) is integrated in the coupling assembly (19), via which a part of the coolant can be returned from the rotor interior (11) in the coaxial direction and in the opposite direction to the coolant supply to the test bench (1). [2] Test bench according to claim 1, characterized by that the coupling assembly (19), in particular the elastically or flexibly yielding shaft connector (27), is designed as a hollow shaft through which the coolant return line (41) and the coolant lance (29) extend, and that in particular the coolant return line (41) is formed by an annular gap (33) between the radially inner coolant lance (29) and the radially outer coupling assembly (19). [3] Test bench according to claim 2, characterized bythat the coupling assembly (19), in particular the elastically or flexibly yielding shaft connector (27), is permeable to coolant radially outwards due to its design or has an excessively large internal volume or passage cross-section, and / or that in particular for a coolant flow that is tight radially outwards, the coupling assembly (19) has a connecting pipe (37) which divides the annular gap (39) into a radially inner, coolant-flowing, in particular small-cross-sectional, partial annular gap (41) between the coolant lance (29) and the connecting pipe (37), and into a radially outer, coolant-free partial annular gap (43) between the coupling assembly (19) and the connecting pipe (37), and that the coolant-flowing partial annular gap (41) forms the coolant return line. [4] Test bench according to claim 3, characterized bythat the connecting tube (37) is designed to be flexible in order to compensate for coaxial errors between the rotor shaft (9) and the drive shaft (17), and that in particular the connecting tube (37) is a metal bellows element with at least one flexible bellows section (39). [5] Test bench according to one of the preceding claims, characterized by that the coupling assembly (19) has an adapter (21, 23) at each of its two axial ends, that is to say a drive-side adapter (21) and a rotor-side adapter (23), via which the coupling assembly (19) is connected to the drive shaft (17) and to the rotor shaft (9) in a rotationally fixed manner, in particular via a flange connection or a spline connection. [6] Test bench according to one of claims 3 to 5, characterized bythat the connecting pipe (37) is connected to the coupling assembly (19) in a rotationally fixed and coolant-tight manner, in particular in such a way that the connecting pipe (37) is connected in a rotationally fixed manner only on one side, while the other connecting pipe side can slip through somewhat, and that the connection is realized as a fitting connection or as a rolling bearing connection between the outer circumference of the respective connecting pipe end and an inner circumferential centering surface (45) of the adapter (21, 23), and that in particular between the connecting pipe end and the adapter a sealing zone with a circumferential sealing element (47) is provided. [7] Test bench according to claim 6, characterized by that the connecting pipe (37) extends in the annular gap (33) between the two adapter parts (21, 23) without contact with respect to the coupling assembly (19) and to the coolant lance (29). [8] Test bench according to one of the preceding claims, characterized bythat the coupling assembly (19) has a torque transducer (25), in particular a torque measuring flange, which is arranged in the axial direction between one of the adapters (21, 23) and the elastically flexible shaft connector (27), and that in particular the arrangement of the torque measuring flange and the shaft connector are interchangeable when viewed in the axial direction. [9] Test bench according to one of the preceding claims, characterized by that the coolant lance (29) is led out with its lance end from a shaft end of the drive shaft (17) facing away from the electric motor (3), and that the lance end is mounted in a rotationally fixed manner on a test bench bearing point (31). [10] Test bench according to claim 9, characterized bythat in a first option the coolant lance (29) is elastically supported on the one hand at the test bench bearing point (31) and on the other hand is rigidly supported on a rotor-side lance bearing point (15), or that in a second option the coolant lance (29) is rigidly supported on one side at the test bench bearing point (15) and extends continuously without bearings in the direction of the electric motor (3).

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