Electric machine

Abstract

Electrical machine with a hollow drive shaft for supporting a rotor rotatable relative to a stator, the drive shaft being mounted in a housing so as to be rotatable about an axis of rotation, and with a hydraulic system for circulating a fluid which has a supply line leading to an axial bore of the drive shaft.

Description

The application relates to an electric machine having a hollow drive shaft for mounting a rotor which is rotatable with respect to a stator, wherein the drive shaft is mounted in a housing such that it can rotate about an axis of rotation, and having a hydraulic system for circulating a fluid within the housing, which hydraulic system has a feed line leading to an axial bore of the drive shaft.US 2019 / 0081537 A1 discloses a cooling system for a rotating electrical machine for driving a vehicle. The cooling system includes a first pump that is driven during running operation of the vehicle to supply lubricant to the electric rotary machine and a second pump that is driven by a second drive source to supply lubricant to the electric rotary machine. The first pump is configured to discharge the lubricant into the inside of a rotating shaft of a rotor core of the rotating electric machine through a first passage. The second pump is configured to direct the lubricant through a second passage to a coil of a stator of the rotating electrical machine.WO 2015 / 058788 A1 discloses a drive assembly for a motor vehicle having a first gear and a second gear, which are in drive connection with one another, and a lubricant filling, which defines a lubricant level in a static installed state of the drive assembly. Above the lubricant level, a first storage container is arranged, which can be filled with lubricant by the rotation of the first gearwheel. Above the lubricant level, a second storage container is arranged, which can be filled with lubricant by the rotation of the second transmission. The first storage container serves for lubricating a first bearing region, while the second storage container serves for lubricating a second bearing region of the drive unit.CN 111441926 A discloses an electric oil pump system with hybrid transmission and engine cooling and a control method. The system includes an intake filter, an oil pump, an oil pump motor, and an oil pump motor controller, wherein the intake filter is used to suck oil at the bottom of a hybrid transmission; the oil pump is used to pump the oil sucked from the intake filter; and the oil pump motor is used to provide rotational speed and torque to the oil pump, to power the oil pump, and to supply the oil as a cooling medium to the hybrid transmission.CN 107565756 A discloses an oil pump engine, a transmission, and a vehicle; the oil pump engine includes the following units: a housing having an oil inlet and an oil outlet; an engine and an oil pump disposed in the housing, the engine being used to drive the oil pump, the oil pump being provided with an oil inlet chamber and an oil outlet chamber that are connected to each other, and the oil outlet chamber being connected to the oil outlet; a cooling passage disposed in the housing and outside the engine and the oil pump, the tube wall of the cooling passage being in contact with the engine and the oil pump, the cooling passage having an inlet and an outlet, the inlet being connected to the oil inlet, and the outlet being connected to the oil inlet chamber. The transmission oil liquid circulates in the oil pump engine and flows into the cooling passage; the tube wall of the cooling passage comes in contact with the engine and the oil pump, so that the transmission oil liquid in the cooling passage can cool the engine and the oil pump, thereby achieving cooling and heat radiation effects without immersing the oil pump engine in the transmission oil liquid.The performance of an electric machine is thermally limited during operation. Inherent losses can occur in copper, iron, and magnets of electric motors, with material properties limiting the temperatures of the respective components and structures. To achieve adequate performance, effective cooling is required. However, if the cooling liquid is conveyed uniformly independently of a rotational speed or an operating point of the electric machine, the efficiency is adversely affected due to circulation losses of the electric machine and / or of a transmission. Direct oil cooling solutions for the active parts therefore require complex hydraulic circuits to ensure adequate pressure and flow of oil.An object may be to propose an electric machine with an efficient and less complex hydraulic system for cooling the electric machine.The object is achieved by an electric machine according to claim 1. Embodiments are described in the dependent claims.The electric machine has a hollow drive shaft for supporting a rotor that is rotatable relative to a stator, wherein the drive shaft is rotatably supported in a housing about an axis of rotation, and a hydraulic system for circulating a fluid having a feed line that leads to an axial bore of the drive shaft. A control valve is disposed in the axial bore to control the flow of fluid into the drive shaft, the control valve being centrifugal actuated.The centrifugal force acting on the control valve in the rotating drive shaft advantageously opens and closes the valve depending on the speed of the drive shaft. The control valve is a mechanical component of low complexity that allows effective control of fluid flow into the drive shaft. At low speed, the closed control valve reduces the flow rate and thus reduces the splashing losses of the electric machine. At high speed, the control valve opens and increases the flow rate, which in turn can result in a lower fluid level in the transmission, thereby reducing the churning losses of the transmission at high speeds. The drive shaft has radial bores which connect the axial bore to the rotor.According to one embodiment, the control valve has a plurality of cantilever arms which are arranged in the circumferential direction about the axis of rotation and are connected to a ring inserted into the axial bore, wherein the cantilever arms are prestressed axially inward. The centrifugal force urges the cantilever arms radially outward. The cantilever arms may form a nozzle having an opening through which the fluid may flow, an opening area depending on the respective position of the cantilever arms. The opening area increases as the speed of the drive shaft increases.According to a further embodiment, an oil flow rate through the control valve at a rotational speed of the drive shaft of zero revolutions per minute is between zero and 20 percent of a reference oil flow rate through the axial bore without the control valve. For example, at zero speed, the oil flow through the control valve is ten percent of the reference oil flow. The reference oil flow rate is the flow rate through the axial bore without the control valve, which results if all other parameters such as pressure, density or temperature are identical. The speed of the drive shaft can likewise be identical, but has no influence on the reference oil throughput. It is known to the skilled person that at low rotational speeds of the drive shaft the oil flow is greatly reduced. For example, at a driveshaft speed of 20 percent of the maximum speed, the oil flow through the control valve may be between 15 and 25 percent of the reference oil flow. At maximum input shaft speed, the oil flow through the control valve is greater than 75 percent of the reference oil flow through the axial bore (18) without the control valve, for example about 80 percent.According to a further embodiment, the opening surface is composed of a radial opening surface and a longitudinal opening surface. The opening area may be between zero and two percent of the cross-sectional area of the axial bore at a speed of rotation of zero revolutions per minute (U / min). The opening area at maximum rotational speed of the drive shaft can be more than five percent, in particular more than ten percent, of the cross-sectional area of the axial bore. The radial opening surface is a circular opening in a plane perpendicular to the axis of rotation, which is formed at a free end of the cantilever arms. The longitudinal opening surface is formed by tapering slots between the cantilevers. The diameter of the radial opening surface can increase from zero U / min up to the maximum rotational speed of the drive shaft by 15% to 25% of the axial length of the cantilever arms. Longer cantilever arms allow an increase in the overall opening area.According to a further embodiment, it is provided that each of the cantilever arms has a balancing weight at a head end. In particular, the cantilever arms can each have a resilient segment made of flat material, which is connected to the ring, and a head segment, which forms the balancing weight. The head segment can have a higher mass than the resilient segment, in particular at least 1.5 times the mass of the resilient segment.According to a further embodiment, the resilient segment has a neck portion, wherein the flat material of the neck portion is corrugated and has at least one S-shape. Wave peaks and wave valleys of the waveform or S-shape extend in the circumferential direction with respect to the axial direction. The flat material of the neck portion may have a plurality of S-shapes joined together. The higher the number of S-shapes, the lower the stress and the larger the resulting opening area.According to a further embodiment, the hydraulic system has a storage container for the fluid, wherein the feed line hydraulically connects the storage container and the axial bore. The reservoir may provide a constant fluid pressure that may be maintained by a pump. The reservoir may be located higher than the axial bore with respect to the direction of gravity, such that the fluid may be passively conveyed to the axial bore. In particular, the fluid can be conveyed into the storage container by rotating elements of the electric machine, in particular from an oil sump by gearwheels of a transmission connected to the drive shaft.Embodiments of the electric machine are explained with reference to the drawings. FIG. 1 shows an embodiment of the electric machine in longitudinal section with a control valve in the closed position; FIG. 2 shows a detail B from FIG. 1 ; FIG. 3 shows the detail B from FIG. 1 in another perspective; FIG. 4 shows the embodiment of FIG. 1 with the control valve in the open position. FIG. 5 shows a detail C from FIG. 4 ; FIG. 6 shows the detail C from FIG. 4 in another perspective; FIG. 7 shows a further embodiment of the electric machine in a longitudinal section; FIG. 8 shows a detail D from FIG. 7 ; FIG. 9 shows a further embodiment of the electric machine in a longitudinal section; FIG. 10 shows a further embodiment of the electric machine in a longitudinal section; FIG. 11 shows a perspective sectional illustration of a further embodiment of the electric machine; Figure 12 shows the control valve in three different positions.FIG. 1 shows an embodiment of the electric machine in longitudinal section. The electric machine comprises a hollow drive shaft 11 for supporting a rotor 10 which is rotatable relative to a stator 17, wherein the drive shaft 11 is rotatably supported in a housing 1 about an axis of rotation A. The rotor 10 is fixed on the drive shaft 11 and rotates inside the stator 17 connected to the housing 1. A hydraulic system for circulating a fluid has a feed line 14 which leads to an axial bore 18 of the drive shaft 11. In the axial bore 18 a control valve 12 is arranged, which controls a flow of the fluid into the drive shaft 11. From the axial bore 18 the fluid flows through radial bores 16 to the rotor 10.The control valve 12 is in a closed position. The detail B with the control valve 12 in the closed position is schematically illustrated in various views in FIGS. 2 and 3. The control valve 12 has a plurality of cantilevers 2 arranged circumferentially about the rotational axis A and connected to a ring 8 inserted into the axial bore 18. The cantilever arms 2 are biased axially inward toward a closed position shown in FIGS. 2 and 3.FIG. 4 shows the embodiment of FIG. 1 with the control valve 12 in the open position. The detail C with the control valve 12 in the open position is schematically illustrated in various views in FIGS. 5 and 6. The centrifugal force urges the cantilevers 2 radially outward and increasingly opens the control valve 12. The opening surface is composed of a radial opening surface 3 and a longitudinal opening surface 4. The radial opening surface 3 is a circular opening in a plane perpendicular to the rotational axis A formed at a free end of the cantilever arms 2. The longitudinal opening surface 4 is formed by tapering slots between the cantilever arms 2. The opening area increases continuously from the closed position of FIGS. 2 and 3 to the open position of the cantilever arms 2 as the rotational speed of the drive shaft 11 increases, as shown in FIGS. 5 and 6. The figures of the control valve 12 are schematic. The opening area in the closed position of the cantilever arms 2, i.e. at a rotational speed of the drive shaft of zero U / min, can be between zero and two percent of the cross-sectional area of the axial bore 18. In a maximum open position of the cantilever arms 2, i.e. at maximum rotational speed of the drive shaft, the opening area can be more than five percent, in particular more than ten percent, of the cross-sectional area of the axial bore 18. Depending on the design of the control valve, an increase in the cross-section of the axial bore 18 of up to 20 percent is possible.FIG. 7 shows a further embodiment of the electric machine in a longitudinal section. The electric machine is shown in part, with a part of the housing 1 and the hollow drive shaft 11 and the rotor and the stator have been omitted. FIG. 8 shows a detail D showing the closed control valve 12 within the axial bore 18 that controls fluid flow from the supply line 14. Each of the cantilevers 2 has a balance weight 5 at a tip end 6. A head segment 9 forms the balancing weight 5. the head segment 9 can have a higher mass than the resilient segment 7, in particular at least 1.5 times the mass of the resilient segment 7. the resilient segment 7 has a neck portion 19, wherein the flat material of the neck portion 19 has a corrugated shape or S-shape which facilitates the opening of the control valve 12.FIG. 9 shows a further embodiment of the electric machine in a longitudinal section. The electric machine is partially shown with the hollow drive shaft 11 and the control valve 12 in the axial bore 18 controls the fluid flow from the supply line 14, and the hydraulic system has a reservoir 15 which is hydraulically connected to the axial bore 18 via the supply line 14.FIG. 10 shows a further embodiment of the electric machine in a longitudinal section. The electric machine is partially shown, with a part of the housing 1 and the hollow drive shaft 11. the control valve 12 in the axial bore 18 controls the fluid flow from the supply line 14. the reservoir 15 is located outside the housing 1 in a higher position than the axial bore 18 with respect to a direction of gravity in order to passively convey the fluid.FIG. 11 shows a perspective sectional view of a further embodiment of the electric machine. The electric machine is partially shown, with a part of the housing 1 and the hollow drive shaft 11. the control valve 12 in the axial bore 18 controls the fluid flow from the supply line 14. the reservoir 15 is integrated into the housing 1 for passive conveyance of the fluid with respect to a direction of gravity higher than the axial bore 18. The fluid can be conveyed into the storage container 15 by rotating elements of the electric machine, in particular from an oil sump by gears of a transmission connected to the drive shaft 11.In FIG. 12, an exemplary embodiment of the control valve 12 is shown in three different positions with regard to its opening in two side views each. Position I is a maximum closed position in which the control valve 12 has the smallest possible opening formed by the radial opening surface 3 and the longitudinal opening surface 4. The centrifugal operated control valve 12 is in position I when the electric machine is at a standstill. The radius at the head end 6 is 8.3 mm. The radial opening surface 3 has a diameter of 2.2 mm, which corresponds to an area of 3.8 mm 2. The longitudinal opening surface 4 is composed of eight slots and has a comparable surface area to the radial opening surface 3. At a drive shaft speed of zero U / min, a flow rate of oil through the control valve 12 may be ten percent of a reference flow rate of oil through the axial bore 18 without the control valve 12 with otherwise the same parameters as pressure, density, or temperature.Position II is a position that is slightly more open, in which the centrifugal force acting on the cantilever arms 2 balances at approximately 3,000 U / min with the prestressing force that acts on the cantilever arms 2 inward in the direction of position I. The radius at the tip end 6 is larger by 0.65 mm than the 8.3 mm of the position I. The radial opening surface 3 has a diameter of 3.4 mm, which corresponds to an area of 9.1 mm 2. At a drive shaft speed of 3,000 rpm, which may be 20 percent of a maximum speed, the oil flow through the control valve 12 may be 20 percent of the reference oil flow rate that is unaffected by the speed.The position III is a significantly more open position, in which the centrifugal force acting on the cantilever arms 2 balances at approximately 15,000 U / min with the prestressing force which acts on the cantilever arms 2 inward in the direction of the position I. The radius at the head end 6 is larger than the 8.3 mm of the position I by 3.4 mm. The radius at the head end 6 increases linearly with the rotational speed of the drive shaft 11. The radial opening surface 3 has a diameter of 8.4 mm, which corresponds to an area of 55.4 mm 2. The diameter of the radial opening surface 3 has increased from position I at zero revolutions per minute to position III at the maximum rotational speed of 15,000 revolutions per minute by 6.2 mm, which in this embodiment corresponds to 20% of an axial length of the cantilever arms 2 of 30 mm. The longitudinal opening surface 4 is composed of the eight tapering slots and has a surface area comparable to the radial opening surface 3. At maximum speed, the oil flow through the control valve is about 80 percent of the reference oil flow.Reference numerals denote reference numerals1 Housing 2 Cantilever arms 3 Radial opening surface 4 Longitudinal opening surface 5 Balancing weight 6 Head end 7 Resilient segment 8 Ring 9 Head segment 10 Rotor 11 Drive shaft 12 Control valve 14 Feed line 15 Storage container 16 Radial bores 17 Stator 18 Axial bore 19 Neck portion A Axis of rotationReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedUS 2019 / 0081537 A1

[0002] WO 2015 / 058788 A1

[0003] CN 111441926 A

[0004] CN 107565756 A

[0005]

Claims

Electric machine, having a hollow drive shaft (11) for mounting a rotor (10) which can be rotated relative to a stator (17), wherein the drive shaft (11) is mounted in a housing (1) such that it can be rotated about an axis of rotation (A), a hydraulic system for circulating a fluid, having a feed line (14) which leads to an axial bore (18) of the drive shaft (11), and a control valve (12) which is arranged in the axial bore (18) and is intended to control a flow of the fluid into the drive shaft (11), wherein the control valve (12) is operated by centrifugal force.Electric machine according to Claim 1, characterized in that the control valve (12) has a plurality of cantilever arms (2) which are arranged in the circumferential direction about the axis of rotation (A) and are connected to a ring (8) which is inserted into the axial bore (18), the cantilever arms (2) being prestressed axially inward.Electric machine according to Claim 2, characterized in that centrifugal force urges the cantilever arms (2) radially outwards.Electric machine according to one of the preceding claims 2 or 3, characterized in that the cantilever arms (2) form a nozzle with an opening through which the fluid flows, wherein an opening area depends on the respective position of the cantilever arms (2), and wherein the opening area increases with increasing rotational speed of the drive shaft (11).Electric machine according to Claim 4, characterized in that the opening surface is composed of a radial opening surface (3) and a longitudinal opening surface (4).Electric machine according to one of the preceding claims, characterized in that, at a rotational speed of the drive shaft (11) of zero revolutions per minute, an oil throughput through the control valve (12) is between zero and 20 percent of a reference oil throughput through the axial bore (18) without the control valve.Electric machine according to one of the preceding claims, characterized in that, at a maximum rotational speed of the drive shaft (11), an oil flow through the control valve (12) is more than 75 percent of a reference oil flow through the axial bore (18) without the control valve.Electric machine according to one of the preceding claims 2 to 7, characterized in that each of the cantilever arms (2) has a balancing weight (5) at a head end (6).Electric machine according to Claim 8, characterized in that each of the cantilever arms (2) has a resilient segment (7) made of a flat material which is connected to the ring (8), and a head segment (9) which forms the balancing weight (5).Electric machine according to one of the preceding claims 8 or 9, characterized in that the head segment (9) has a higher mass than the resilient segment (7), in particular at least 1.5 times the mass of the resilient segment (7).Electric machine according to any of the preceding claims 8 to 10, characterized in that the resilient segment (7) has a neck portion (19), the flat material of the neck portion being corrugated and having at least one S-shape.Electric machine according to one of the preceding claims 8 to 11, characterized in that the head segment (9) and the resilient segment (7) consist of one or more of the following materials: a metallic material, a metal matrix composite material, a plastic material and a plastic matrix composite material.Electric machine according to one of the preceding claims, characterized in that the hydraulic system has a storage container (15), wherein the feed line (14) hydraulically connects the storage container and the axial bore (18).Electric machine according to Claim 13, characterized in that the storage container (15) is arranged higher than the axial bore (18) with respect to a direction of gravity.Electric machine according to one of the preceding claims 13 or 14, characterized in that the fluid is conveyed by rotating elements of the electric machine into the storage container (15), in particular from an oil sump by gearwheels of a transmission connected to the drive shaft.

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