Electric machine

Abstract

An electric machine comprising a rotor (4) with a hollow rotor shaft (5) and a stationary cooling device (8) received in the rotor shaft (5), which has a first supply device (9) for supplying a first coolant, with an inlet (24) and an outlet (26) for the first coolant, and a second supply device (10) for supplying a second coolant, with an inlet (32) and an outlet (34) for the second coolant, characterized in that the first supply device (9) is a supply tube (23) and the second supply device (10) has a cylindrical cooling section (27) comprising several radial openings (37),wherein the feed pipe (23) is radially encompassed section by section by the cylindrical cooling section (27) and the first coolant exiting from the outlet (26) of the feed pipe (23) is radially accelerated via an acceleration device (38) provided on the rotor shaft (5) and driven radially through the openings (37) of the cooling section (27).

Description

[0001] The invention relates to an electric machine comprising a rotor with a hollow rotor shaft and a stationary cooling device received in the rotor shaft, which has a first supply device for supplying a first coolant, with an inlet and an outlet for the first coolant, and a second supply device for supplying a second coolant, with an inlet and an outlet for the second coolant.

[0002] EP 3 696 424 A1 discloses a system, particularly for an electric machine, comprising a shaft body with a longitudinal axis, wherein two internal fluid channels, each having an inlet and an outlet opening, extend axially within the shaft body to guide external fluid into the channels and convey it from there to an area outside the shaft body. The first and second internal fluid channels are isolated from each other within the shaft body to ensure independent fluid communication.

[0003] An electric machine according to the preamble of claim 1 is described in US 2014 / 0333161 A1. The electric machine is used in a wide variety of applications, particularly as a drive system to generate torque that is transmitted to a downstream drive train. One example is the use of such an electric machine in the e-axle of a motor vehicle. As is known, the electric machine has a stator in which a rotor is mounted. The rotor has a rotor shaft, via which the rotor is rotatably mounted to a housing by means of suitable bearings. Since heat is generated on the rotor side during operation, cooling of the rotor is advantageous. This cooling can be achieved by means of a stationary cooling device integrated into the hollow rotor shaft, which is designed and operates like a heat exchanger.For this purpose, a first supply device for supplying a first coolant, for example oil, is integrated in the hollow rotor shaft, which is obtained, for example, from a cooling circuit of an operating component assigned to the electric machine, for example, a gearbox assigned to the electric machine, and which serves as the primary coolant.

[0004] To cool the primary coolant or oil so that it can absorb as much heat as possible as it flows through the rotor shaft, a second supply device for a second coolant, for example, water, is integrated into the hollow rotor shaft. This second coolant is drawn from another cooling circuit to which the electric machine is connected. The first and second supply devices are stationary inside the rotating hollow rotor shaft and form a heat exchanger. This allows the primary coolant to absorb heat generated by the rotor while simultaneously being cooled itself and having the absorbed heat transferred to the second coolant. Such a machine with a stationary cooling device integrated into a hollow rotor shaft is known from US 2014 / 0333161A1.A stationary lance, i.e., one that does not rotate, is inserted into the hollow rotor shaft. A first channel, running lengthwise along the lance, has an inlet and an outlet, forming the first supply device. A first coolant, namely oil, is introduced into the hollow rotor shaft via this channel. It exits the hollow rotor shaft and flows to an oil outlet on the rotor shaft, absorbing heat in the process. A second channel, also with an inlet and an outlet, is provided. A second coolant, namely water, is guided through the lance via this channel. The inlet and outlet are located on a common side of the lance, giving the channel a U-shape. The water flowing through this channel cools the lance, and the oil is cooled by the water flowing through it.

[0005] The invention is based on the problem of specifying an improved electric machine with integrated rotor shaft cooling.

[0006] To solve the problem, in a machine of the type mentioned at the outset, the invention provides that the first feeding device is a feeding tube and the second feeding device has a cylindrical cooling section comprising several radial openings, wherein the feeding tube is radially encompassed section by section by the cylindrical cooling section and the first coolant exiting the outlet of the feeding tube is radially accelerated via an acceleration device provided on the rotor shaft and driven radially through the openings of the cooling section.

[0007] The electric machine according to the invention is characterized by a second cooling device designed to enable particularly efficient cooling. This cooling device comprises a cylindrical cooling section with several radial openings. This cylindrical cooling section is thus designed in the manner of a cage. The cooling section is located inside the hollow rotor shaft. The second coolant, for example, cold water, is guided or passed through this cylindrical cooling section. The first supply device is a simple supply pipe that is guided into the hollow rotor shaft and positioned such that the end of the supply pipe, in the region where the outlet is provided from which the first coolant, for example, oil, exits, is located, is arranged inside the cage-like cooling section. That is, the cage-like cooling section accommodates the end of the supply pipe.The invention further provides an acceleration device designed such that the first coolant, for example oil, exiting the outlet of the feed pipe is accelerated radially outwards, thus imposing or amplifying a radial flow component. The second coolant is therefore driven radially outwards. Since, as described, the end of the feed pipe where the first coolant exits is radially enclosed by the cage-like, cylindrical cooling section, the first coolant is consequently driven radially through the openings of the cylindrical cooling section. It thus flows through the cylindrical cooling section.Due to its cage-like structure, achieved through perforations, this cooling element has a remarkably large contact surface. The first coolant, for example, oil, flows along this surface, passing through the second cooling element, through which the cold second coolant, i.e., cold water, flows. Thus, direct cooling contact is established. The acceleration device consequently creates forced convection through the acceleration-induced high velocity of the first coolant, allowing for very efficient heat exchange. The second coolant, flowing through the cooling section and thus being cooled, then continues into the volume of the hollow rotor shaft, where it can absorb further heat before being dissipated.For example, it can be ejected radially from the hollow rotor shaft at a suitable position to wet and cool adjacent winding heads of the stator, or it can be diverted into an associated gearbox.

[0008] The electric machine according to the invention, with the stationary cooling device integrated into the hollow rotor shaft as designed according to the invention, allows for extremely efficient cooling. The rotor shaft thus has a highly efficient, integrated heat exchanger.

[0009] According to a further development of the invention, the rotor shaft is formed from a first shaft component and a second shaft component attached thereto, the second shaft component engaging axially in sections within the first shaft component, forming an annular space between the two shaft components, and in which the feed pipe is received. The cylindrical cooling section engages axially within this annular space, and the second shaft component has one or more radial recesses to form the acceleration device, allowing radial flow of the first coolant exiting the outlet of the feed pipe to the cooling section. Accordingly, the rotor shaft is two-part. It consists of two shaft components inserted one inside the other, with the first shaft component radially encompassing the second shaft component in sections. An annular space is formed in the area of ​​this circumference, into which the cylindrical, cage-like cooling section engages.The feed tube, forming the first feed device, is inserted into the second shaft component and terminates, axially speaking, in the region of the annular space. The second shaft component, which is largely or completely axially closed at the inserted end, has several radial recesses that allow the first coolant exiting the feed tube to flow radially into the annular space. As described, the hollow rotor shaft, and therefore necessarily the second shaft component as well, rotates, while the cooling devices remain stationary. As a result of this rotation of the rotor shaft and the second shaft component, the first coolant exiting the feed tube is radially accelerated and forced radially into the annular space and subsequently through the cage-like cooling section.The second shaft component, with its radial recesses, which are preferably arranged equidistantly around the circumference and can be designed as individual, hole-like openings or as elongated slots, consequently forms the acceleration device. This device serves for radial acceleration and thus the forced flow of the first coolant radially through the cage-like cooling section, resulting in forced flow. Since the second shaft component is axially largely or completely closed, as described, the first coolant can only exit the second shaft component into the annular space via these radial recesses. Therefore, all or at least almost all of the first coolant is forced to flow through the cage-like cooling section and is efficiently cooled there, as this cooling section, as described, is traversed by the cooled second coolant.

[0010] As described, the or each recess can be designed as a hole-like recess or as a slot extending in the axial direction, with several recesses being provided around the circumference and / or axially distributed.

[0011] The second shaft component is rigidly connected to the first shaft component to form the hollow rotor shaft. This connection can be made via a weld, meaning the second shaft component is welded to the first. Alternatively, a connection using fasteners, such as a bolted connection, is also possible.

[0012] In a more specific embodiment of the hollow rotor shaft, the first shaft component can have a cylindrical first section with a first diameter, to which a cylindrical second section with a larger second diameter is attached, and the second shaft component has a cylindrical third section with a third diameter, preferably corresponding to the first diameter, and a cylindrical fourth section with a fourth diameter smaller than the second diameter, with the annular space formed between the second and fourth sections. Accordingly, both shaft components have specific geometries that allow them to be nested together, forming the annular space.The cylindrical first section with the first diameter and the cylindrical third section with the third diameter, preferably corresponding to the first diameter, serve to accommodate corresponding bearing elements by which the rotor shaft is supported in the housing of the electric machine. The two interlocking second and fourth sections necessarily have different diameters, since the annular space is formed between them, into which the cooling section engages or in which it is located.

[0013] Furthermore, the fourth section of the second shaft component can have a subsection that widens in diameter and rests against the second section, axially limiting the annular space. This provides direct support for the elongated fourth, hollow cylindrical section within the second section. Additionally, the axial length of the annular space can be limited accordingly, with the cage-like cooling section generally filling the annular space as much as possible, preferably almost completely, thus extending over its essential axial length.

[0014] A further advantageous embodiment of the invention provides that the outlet of the supply pipe is formed by several openings distributed around the circumference and / or axially, or by slots extending in the axial direction. The coolant thus exits at several positions, resulting in a correspondingly distributed discharge into the surrounding space of the second shaft component, combined with a radial flow component already present due to the radial outlet.

[0015] A key element is the cylindrical, cage-like cooling section through which the second coolant flows. One embodiment of such a cooling section comprises several axially extending pipe sections arranged cylindrically, connected at both ends by distribution rings. Each distribution ring is connected to an inlet pipe and an outlet pipe. The cooling section is thus a cage-like, radially open structure, with the radial openings formed by the spaces between the axially extending pipe sections. The pipe sections are connected at both ends to corresponding distribution rings, each of which is in turn connected to two pipes: an inlet pipe and an outlet pipe, through which the second coolant flows.The supplied coolant flows into the first distribution ring and from there into the corresponding elongated pipe sections, through which it flows into the second distribution ring. From there, it flows into further pipe sections for return flow and returns to the first distribution ring, where it is discharged via the drain pipe. This ensures efficient flow through the cooling section and the pipe sections.

[0016] As described, one part of the pipe sections, in particular half of the pipe sections, serves for flow in the direction of the inlet, while the other part of the cooling section, i.e., the other half of the pipe sections, serves for flow in the opposite direction, in the outlet. The distribution or supply of the first coolant to the respective pipe section is effected via the first and second distribution rings. Preferably, the two distribution rings are designed, or the cooling section is designed, such that the second coolant is guided through the pipe sections in a meandering pattern.The supplied first coolant flows through all pipe sections, or defined groups of pipe sections, in a meandering pattern. For example, half of the pipe sections form a first group, thus being connected accordingly for flow efficiency, and the other half of the pipe sections form a second group, also being connected accordingly via the distribution rings for flow efficiency. Alternatively, it is also conceivable that the second coolant is guided through the pipe sections in a U-shape via the two distribution rings. That is, the coolant flows through a first pipe section from the first to the second distribution ring and through an adjacent pipe section from the second to the first distribution ring, and from there to the discharge pipe. Thus, various flow scenarios are conceivable with regard to the design of the distribution rings and the connection of the pipe sections.

[0017] The invention is explained below with reference to exemplary embodiments and the drawings. The drawings are schematic representations and show: Fig. 1 a schematic representation of an electrical machine according to the invention, Fig. 2 an exploded view of the components of the hollow rotor shaft, Fig. 3 a schematic representation of the components according to Fig. 2 formed rotor shaft, Fig. 4 the rotor shaft out Fig. 3 with flow arrows of the first and second coolant shown, and Fig. 5 a perspective view of the second feed device showing the flow of the second coolant through the cage-like cooling section.

[0018] Fig. Figure 1 shows an exemplary electric machine 1 according to the invention, comprising a housing 2 in which a stator 3 and a rotor 4 are accommodated. The stator 3 is fixed in position, while the rotor 4 is rotatably mounted on the housing 2 by means of suitable bearing means not shown in detail. The rotor 4 has a hollow rotor shaft 5 which carries an output gear 6 that transmits a generated torque to a downstream gearbox 7. The basic design of such an electric machine is known.

[0019] In the machine 1 according to the invention, a stationary cooling device 8 is provided inside the hollow rotor shaft 5. This cooling device is designed and operates like a heat exchanger and serves to cool the rotor 4. The cooling device 8 is stationary, i.e., its position is fixed and it does not rotate with the rotor shaft 5 during operation. The cooling device 8 has a first supply device 9 for supplying a first coolant, for example, oil, and a second supply device 10 through which a second coolant, for example, water, can be supplied to cool the first coolant. Further details on the construction of the rotor shaft 5 and the cooling device 8 are described in the following. Fig. 2 - 4 shown.

[0020] Fig. Figure 2 shows an exploded view of the components of the hollow rotor shaft 5 and the first and second cooling devices 9, 10. The hollow rotor shaft 5 consists of a first shaft component 11 and a second shaft component 12, which, see Fig. 1 or Fig. The three shaft components are axially inserted one inside the other. The first shaft component has a first cylindrical section 13 with a first diameter, to which, separated by a radial annular flange 14, a second cylindrical section 15 with a larger second diameter is attached. The second shaft component 12 has a cylindrical third section 16 with a third diameter that is approximately or exactly the same as the first diameter. A fourth cylindrical section 18, whose diameter is smaller than the inner diameter of the second section 15, is attached via another radial annular flange 17. In the assembly position, when the shaft component 12 with the fourth section 18 is inserted into the first shaft component 11 or the second section 15, the radial flange 17 rests against the second section 15. A welded connection can be provided in this area to fix the shaft components 11 and 12 to one another.In the assembled position, a section 19 of the fourth section, which widens in diameter, rests against the inner circumference of the second section 15, thus providing support and guidance, and simultaneously defining the annular space that forms, which will be discussed later. Furthermore, the fourth section 18 is axially closed by an end wall 20. This end wall may optionally include a recess 21 that allows for the axial outlet of a small quantity of the first coolant. In any case, the fourth section 18 is provided with several radial recesses 22 that allow the first coolant to flow radially outwards.

[0021] The first supply device 9 is designed as a simple supply tube 23, with an inlet 24 and an outlet 26 formed by several radial openings 25, which can be configured as circumferentially or axially distributed holes or as elongated slots, allowing the first coolant to exit radially. In the assembly position, the area with the outlet 26 is located inside the fourth section 18, so that the supplied first coolant can exit directly into this section 18, which is perforated via the recesses 22.

[0022] The second supply device 10 has a cylindrical, cage-like cooling section 27, formed from several axially extending pipe sections 28, which are connected to a first distribution ring 29 and a second distribution ring 30 and between which slot-like openings 37 are formed. A supply pipe 31 with an inlet 32 ​​and a discharge pipe 33 with an outlet 34 are also provided, through which the second coolant, for example water, can be supplied and discharged. The supply and discharge pipes 31 and 33 are connected to a corresponding coolant supply for the second coolant. The same applies, of course, to the inlet 24 of the supply pipe 23, which is connected to a separate coolant supply for the first coolant. The second coolant supplied via the supply pipe 31 flows into the first distribution ring 29, from where it flows into one or more pipe sections 28.From there, the second coolant flows into the second distribution ring 30, where it is redirected and flows again into one or more pipe sections 28. From there, it returns to the first distribution ring 29, from where it then flows to the discharge pipe 33 and is discharged. The corresponding distribution and flow direction is achieved through a suitable design of the distribution rings 29 and 30 in conjunction with a corresponding connection of the individual pipe sections 28. In the assembly position, the second feed device 10 is housed in the first shaft component 11, with the cooling section 27 being housed in the second section 11, and the feed pipe 31 and the discharge pipe 33 extending into the first section 13. The fourth section 18 extends into the cooling section 31, meaning that the first coolant exiting from the recesses 22 flows directly into the area of ​​the cooling section 27.

[0023] An assembly drawing of the rotor shaft 5 with integrated cooling device 8 is shown in Fig. Figure 3 shows that the two shaft components 11 and 12 are nested and firmly connected. The second section 15 rests against the flange section 17, and the subsection 19 against the inner wall of the second section 15. An annular space 35 forms between the fourth section 18 and the second section 15, into which the cylindrical, cage-like cooling section 27 engages. The inlet pipe 31 and the outlet pipe 33 extend into the first section 13, where they are connected to the inlet 32 ​​and outlet 34 via corresponding pipe connections of the associated coolant supply.

[0024] The first feed device 9, i.e., the feed tube 23, extends into the fourth section 18, i.e., the openings 25 forming the outlet 26 are located, viewed radially, adjacent to the recesses 22 of the fourth section 18. The inlet 24 is appropriately connected to a coolant supply for the first coolant.

[0025] During operation, the rotor shaft 5 rotates, while the cooling device 8, i.e., the two feed devices 9, 10, are stationary and therefore do not rotate. In particular, this means that the second shaft component 12 and with it the fourth section 18, on which the recesses 22 are provided, also rotate.

[0026] Within the company, a situation arises in Fig. Figure 4 shows the flow situation. The first coolant is supplied via the feed pipe 23, as indicated by arrow P1. It exits radially from the openings 25, as indicated by arrows P2, and already has a radial flow component due to the direction of the openings 25. It enters an annular space 36 formed by the fourth section 18, which is bounded by the fourth section 18. This fourth section 18 rotates at a correspondingly high speed. The first coolant flows towards the recesses 22 and is radially accelerated by the rotational speed of the fourth section 18 and driven through the recesses 22, as shown by arrows P3. Radially outside this fourth section 18 is the cooling section 27, which, as described, is cage-like and has a plurality of slot-like openings 37. Fig. 5, which are formed between the pipe sections 28. Due to its acceleration and flow direction, the first coolant flows through this cage-like cooling section 27, which in turn, as will be discussed later, is traversed by the cooled second coolant. After passing through the cooling section 27, the first coolant distributes itself in the remaining volume of the rotor shaft 5, from where it is discharged, as indicated by arrows P4.

[0027] Arrow P5 shows the supply line of the second coolant to the second cooling unit 10. It flows into the first distribution ring 29 and is distributed via this ring into the pipe sections 28 connected in this flow direction (arrow P6), from where it flows into the second distribution ring 30. From there, it flows back into the connected pipe sections 28 (arrow P7) and from there into the discharge pipe 33, as shown by arrow P8.

[0028] The first coolant, for example the oil, is therefore necessarily accelerated by the rotation of the fourth section 18 with its recesses 22, which together form an acceleration device 38 that radially accelerates the first coolant. The coolant is then driven through the cooling section 27, inevitably resulting in wetting and flow around the cooled cooling section 27 and thus heat transfer. Consequently, the first coolant can be actively and very efficiently cooled and subsequently absorb heat from the rotor via its further flow path.

[0029] Fig.Figure 5 shows a schematic diagram of the flow of the second coolant through the second supply device 10. The coolant flows in via the supply pipe 31 and, in the example shown, is guided in a meandering pattern through the individual pipe sections 28 via the distribution rings 29, 30, as indicated by the meandering flow arrows P9. It finally reaches the discharge pipe 33, where it is drawn off. Instead of this meandering flow through all pipe sections 28, it would also be possible to connect the pipe sections 28 in such a way that two, three, or four individual blocks are formed, through which the coolant flows separately in a meandering pattern. Reference symbol list 1 machine 2 cases 3 Stator 4 Rotor 5 Rotor shaft 6 Output gear 7 gearboxes 8 Cooling unit 9 Feeding device 10 Feeding device 11 Shaft component 12 shaft component Section 13 14 ring flange Section 15 Section 16 17 Ring flange Section 18 19 Subsection 20 Front wall 21 Exclusion 22 Exclusion 23 Feed pipe 24 Admission 25 Opening 26 Outlet 27 Cooling section 28 Pipe section 29 distribution ring 30 distribution ring 31 Inlet pipe 32 Admission 33 Drain pipe 34 Outlet 35 annular space Room 36 37 Breakthrough 38 Acceleration device P1-P9 Arrow

Claims

Electric machine comprising a rotor (4) with a hollow rotor shaft (5) and a stationary cooling device (8) received in the rotor shaft (5), which has a first supply device (9) for supplying a first coolant, with an inlet (24) and an outlet (26) for the first coolant, and which has a second supply device (10) for supplying a second coolant, with an inlet (32) and an outlet (34) for the second coolant, characterized in that the first supply device (9) is a supply tube (23) and the second supply device (10) has a cylindrical cooling section (27) comprising several radial openings (37),wherein the feed pipe (23) is radially encompassed section by section by the cylindrical cooling section (27) and the first coolant exiting from the outlet (26) of the feed pipe (23) is radially accelerated via an acceleration device (38) provided on the rotor shaft (5) and driven radially through the openings (37) of the cooling section (27). Electric machine according to claim 1, characterized in that the rotor shaft (5) is formed from a first shaft component (11) and a second shaft component (12) attached thereto, which engages axially in the first shaft component (11) section by section, forming an annular space (35) between the two shaft components (11, 12) and in which the feed tube (23) is received, wherein the cylindrical cooling section (27) engages axially in the annular space (35), and wherein the second shaft component (12) has one or more radial recesses (22) for forming the acceleration device (38), which allow a radial flow of the first coolant exiting from the outlet (26) of the feed tube (23) to the cooling section (27). Electric machine according to claim 2, characterized in that the or each recess (22) is designed as a hole-like recess or as a slot extending in the axial direction, wherein several recesses (22) are provided distributed around the circumference and / or axially. Electric machine according to claim 2 or 3, characterized in that the second shaft component (12) is welded to the first shaft component (11) or fastened via connecting elements. An electric machine according to one of claims 2 to 4, characterized in that the first shaft component (11) has a cylindrical first section (13) with a first diameter, to which a cylindrical second section (15) with a larger second diameter is attached, and the second shaft component (12) has a cylindrical third section (16) with a third diameter, preferably corresponding to the first diameter, and a cylindrical fourth section (18) with a fourth diameter smaller than the second diameter, wherein the annular space (35) is formed between the second and the fourth section (15, 18). Electrical machine according to claim 5, characterized in that the fourth section (18) has a subsection (19) that widens in diameter and abuts the second section (15) under axial limitation of the annular space (35). Electric machine according to one of the preceding claims, characterized in that the outlet (26) of the feed tube (23) is formed by several openings (25) distributed around the circumference and / or axially or by slots extending in the axial direction. An electric machine according to one of the preceding claims, characterized in that the cooling section (27) has several axially extending pipe sections (28) arranged in a cylindrical arrangement, which are connected at both ends to distribution rings (29, 30), wherein a supply pipe (31) having the inlet (32) and a discharge pipe (33) having the outlet (34) are connected to a distribution ring. Electric machine according to claim 8, characterized in that the first coolant is guided through the pipe sections (28) in a meandering manner via the two distribution rings (29, 30), or that the first coolant is guided through the pipe sections in a U-shape via the distribution rings (29, 30).

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