Motor with gap sleeve

Abstract

The invention relates to an electric motor with a gap sleeve. By the invention, an improved heat removal of the rotor is for the first time possible by overpressure in the inner rotor region of a canned electric motor. By the overpressure, the wall thickness of the gap sleeve can be reduced by more than 50%, whereby the heat transfer can also be increased and a gas with a high heat capacity can be used.

Description

[0001] The invention relates to an electric motor with a gap tube.

[0002] An increase in the power density of electric motors is becoming increasingly important in the field of electrified mobility, for example in electrically driven motor vehicles, such as buses, passenger cars, commercial vehicles, trains, ships and aircraft, since through more powerful electric motors weight can be saved.

[0003] For this reason, liquid-cooled electric motors are increasingly being used.

[0004] The resulting waste heat and the problems that go with it have a decisive influence on the electrical power density of electric motors. Problems are, for example, the failure of the polymer insulation of the winding coils in the laminated core of the stator of each electric motor. Therefore, the maximum temperature in the stator winding is often a particularly critical point when developing higher power densities in electric motors.

[0005] The trend towards liquid cooling is based on the fact that through liquid cooling a higher waste heat flow can be achieved compared to gas-air cooling. Here, the stator with the laminated core and the winding coils present in the polymer casting is usually cooled, not the rotor. Due to the lack of polymer insulation, the rotor is less sensitive to heat than the laminated core of the stator, which has a polymer casting. Usually, the liquid cooling of the electric motor is preferably carried out outside the stator, because otherwise the boundary surface to the rotor must be sealed inside the stator.

[0006] For this reason, the channels for the liquid cooling are usually located outside the stator. The problem is that the cooling ring of the liquid cooling is located outside the laminated core, so that this is necessarily first completely traversed by the heat flow in the radial direction. For this reason, electric motors with liquid cooling inside and outside the stator have also been on the market for some time. These contain so-called gap tubes.

[0007] The gap tube separates the cooling liquid in the stator region from the rotating rotor. Otherwise, the cooling liquid would severely impede the rotation of the rotor.

[0008] In the development of the gap tube, the goal is to achieve the smallest possible wall thickness, since this reduces the electrical losses of the electric motor.

[0009] In the component development of the gap tube, different boundary conditions must be observed:

[0010] The task of the gap tube is to separate the liquid cooling from the rotor, since otherwise high friction losses would brake the electric motor.

[0011] The use of a gap tube only makes sense when the electrical losses are relatively offset by the increased power that is achieved due to the improved cooling in the stator region.

[0012] The gap sleeve is located between the rotor and the stator and should therefore be as thin as possible.

[0013] Alternating magnetic fields occurring, for example, in the air gap of electric motors of extreme size induce eddy currents in electrically conductive materials. The eddy currents in turn generate magnetic fields, which are oriented in the opposite direction to their initiating magnetic fields. In addition, induced eddy currents cause rapid heating of the components. It is therefore undesirable in many respects for the gap sleeve to consist of electrically conductive materials. For this reason, reinforced composite materials are used, including ceramic and / or glass-ceramic composite materials.

[0014] The gap sleeve has a certain minimum thickness, since loads, in particular dimensional loads, which have a decisive influence on the thickness of the gap sleeve, are external pressures caused by the acceleration of the cooling medium in the moving use of the electric motor, which occur, for example, on motor vehicles, trains, aircraft and ships.

[0015] A gap sleeve that is too thin collapses under the above-mentioned pressures, wherein, in the initial phase, a buckling mechanical phenomenon can be seen. A gap sleeve that has already aged as a result of the load can therefore be identified by a radial buckling.

[0016] A pipe-tight electric motor is known, for example, from DE 10 2010 011 316. There, a gap sleeve for use in a hermetically sealed pump is proposed, which can be designed very thin, since it is supported in the radial direction by support wedges fixed in recesses of the stator lamination core.

[0017] The intermediate slot wedge support technology of the gap sleeve described therein was investigated by means of simulation, see Figure 1 However, it was found there that the disadvantage of this technology is that the gap sleeve and the lamination core of the stator have significantly different coefficients of expansion, so that in operation extreme stresses occur on the gap sleeve, which there lead to material stresses.

[0018] The technical problem to be solved is to realize an electric motor with a gap sleeve, with liquid cooling of the stator, in which the gap sleeve is designed to be as thin as possible.

[0019] The above-mentioned technical problem is solved by the subject matter disclosed, for example, in the description, the drawings and the claims of the present invention.

[0020] The content of the present invention is therefore an electric motor with a gap sleeve, with liquid cooling on the inside of the stator and sealing of the interior region of the rotor by the gap sleeve, wherein an overpressure, i.e. a pressure of more than 1 bar, is provided in the rotor region delimited by the gap sleeve, i.e. the pressure provided in the rotor region delimited by the gap sleeve is at least 1 bar greater than the pressure exerted on the gap sleeve by the cooling liquid.

[0021] The overall finding of the present invention is that a gap sleeve designed extremely thin can be stabilized by applying pressure from the inside, so that it withstands the external pressure caused by the liquid cooling of the stator, i.e. the load caused by the movement of the liquid cooled in the stator in mobile applications, better than under standard conditions, i.e. with an internal pressure of 1 bar.

[0022] In an electric motor with liquid cooling, i.e. a liquid cooling device or system, inside the stator, the gap sleeve defines a rotor interior region which is hermetically closed with respect to the stator region through which the coolant flows. In this electric motor, the rotor interior region is hermetically closed in any case, so that an overpressure can be maintained even without additional means for sealing the gap sleeve in the rotor interior region in terms of construction.

[0023] In this electric motor, the overpressure in the rotor interior region can even be used to seal an undesired leak of the gap sleeve by overpressure, through which liquid could undesirably enter into the rotor interior region in the absence of overpressure, so that the overpressure in the rotor interior region can correct the leak. Such a leak can occur temporarily in a pipe-enclosed electric motor due to different coefficients of thermal expansion.

[0024] At the same time, the efficiency reduction which accompanies the increase in the internal pressure in the rotor interior region can be compensated by the efficiency increase caused by the thin wall thickness of the gap sleeve.

[0025] According to the invention, the gap sleeve with a small wall thickness is stabilized with respect to the resulting external pressure of the coolant of the stator region by an internal pressure. The entire portion located behind the gap sleeve is under an increased gas pressure as a rotor interior region of the electric motor. The pressure formation can be coupled to the operation of the electric motor, but a constant overpressure can also be provided in the rotor interior region of the electric motor.

[0026] Here, the gas pressure is chosen, for example and preferably, but not necessarily, so high that the maximum external pressure load situation leaves the gap sleeve unstressed.

[0027] In the rotor region, a grading of the sought internal pressure is provided, which is adapted to the application and cannot be determined absolutely here. In general, the gas pressure is chosen so high that the frequently occurring high external pressure load situation leaves the gap sleeve unstressed. The gas pressure in the rotor interior region is particularly preferably chosen so that the maximum external pressure load situation is compensated in the force balance.

[0028] In order to set a suitable internal pressure, the gap sleeve thickness and the internal pressure are determined in such a way that, on the one hand, a bulging of the gap sleeve due to the internal pressure at a low load caused by the coolant liquid, for example when the electric motor is moving uniformly or not at all, can be avoided, but on the other hand, a sufficient internal pressure can occur when the electric motor is moving, which prevents the gap sleeve from sinking inward into the stator region like a beverage bottle for a carbonated beverage such as Coca-Cola.

[0029] According to an advantageous embodiment of the application, the gas in the rotor interior region is air.

[0030] According to another advantageous embodiment of the application, the gas in the rotor interior region is another gas or gas mixture, for example an inert gas, for example nitrogen. It is particularly advantageous here that the inert gas is a gas with a high heat capacity or other physical properties that promote the heat removal from the rotor.

[0031] According to an advantageous embodiment of the application, a first sensor is provided, by means of which the pressure in the rotor interior region can be measured.

[0032] According to an advantageous embodiment of the application, a second sensor is provided, by means of which the pressure in the liquid-cooled stator can be measured.

[0033] The cooling liquid for liquid cooling of the stator is located inside the stator housing, which is closed at the end side by an end cap that exactly matches the stator housing and guides the drive shaft that emerges from the rotor.

[0034] According to an advantageous embodiment, one or more valves are provided, for example in the end cap and / or the housing of the electric motor. The one or more valves are preferably used for pressure regulation in the rotor interior region.

[0035] According to another advantageous embodiment, the first and / or second sensor is connected to a regulating and control device. It is provided here in particular that the valves that generate and / or maintain the internal pressure in the rotor interior region can be regulated by means of the control and regulating device.

[0036] The regulating and control device can be arranged at different locations of the electric motor. For example, the regulating and control device is located at the end cap or the housing of the electric motor.

[0037] According to an advantageous embodiment of the application, an air pump is provided, which can be operated by means of the regulating and control electronics.

[0038] According to an advantageous embodiment in this regard, the air pump is mounted on the outside of the end cap.

[0039] According to another advantageous embodiment, a line is provided which guides air into the rotor interior region by means of an air pump.

[0040] According to another advantageous embodiment, it is provided that the internal pressure in the rotor interior region can be adjusted by means of an adjusting and control device.

[0041] By actively controlling the internal pressure in the rotor interior region as a function of the rotor and / or stator temperature of the electric motor, an advantageous embodiment of the application seeks to actively correct the different thermal expansion coefficients of the laminated core on the one hand and the gap sleeve on the other hand by adjusting the internal pressure in the rotor interior region accordingly.

[0042] For example, as soon as the rotor is in danger of colliding with the gap sleeve due to thermal expansion, the internal pressure acting on the gap sleeve, which limits and restricts the rotor interior region, is increased, so that the gap sleeve expands. Conversely, as soon as the stator is in danger of colliding with the gap sleeve due to thermal expansion, the internal pressure acting on the gap sleeve is reduced, so that the gap sleeve contracts.

[0043] In Figure 2 the simulation results of the gap sleeve according to the application in operation are shown. It is shown here, for example, that in the case of an internal pressure in the rotor interior region of more than 3 bar, sufficient stability can be produced in the case of a small wall thickness of less than 1 mm to resist bulging or other, in particular mechanical, damage to the gap sleeve.

[0044] According to the application, electric motors of any size with a gap sleeve can be operated under internal pressure in the rotor interior region.

[0045] Exemplary embodiments in which the wall thickness of the gap sleeve is less than 3 mm, in particular less than 2 mm, preferably less than 1 mm and particularly preferably less than 0.7 mm have been tested very successfully, see Figure 2 .

[0046] Here, internal pressures in the rotor interior region of 3 bar, more than 4 bar and more than 5 bar were realized and tested.

[0047] Figure 2 Exemplary embodiments of the simulation of the gap sleeve with a wall thickness of 0.5 mm to 0.7 mm and a rotor internal pressure of 4.5 to 5 bar are shown. In a comparison of the same load, a significantly thicker gap sleeve with a wall thickness of approximately 2 mm performs significantly worse in terms of bulging, see Figure 1 .

[0048] By the present invention, improved heat removal of the rotor is for the first time possible by overpressure in the inner region of the rotor of a canned motor. By overpressure, the wall thickness of the gap sleeve can be reduced by more than 50 %, in particular by more than 70 %, heat transfer can be increased, and a gas with a high heat capacity can be used.

Claims

1. An electric motor with a clearance sleeve, having liquid cooling on the inner side of the stator, and sealing an internal region of the rotor relative to the cooling liquid through the clearance sleeve, wherein, An overpressure is provided in the rotor region defined by the clearance sleeve, that is, the pressure provided in the rotor region defined by the clearance sleeve is at least 1 bar greater than the pressure applied to the clearance sleeve by the cooling liquid, wherein the gas in the rotor interior region is air, or the gas in the rotor interior region is an inert gas.

2. The electric motor according to claim 1, wherein, A pump is provided, which can generate increased gas pressure in the internal region of the rotor.

3. The electric motor according to claim 1, wherein, Liquid cooling is provided on the inner and outer sides of the stator.

4. The electric motor according to claim 1, wherein, A first sensor is provided, which can measure the pressure in the internal region of the rotor.

5. The electric motor according to claim 1, wherein, A second sensor is installed, which can measure the pressure in the stator region through which the coolant flows.

6. The electric motor according to claim 4, wherein, A pipeline is provided that connects the first sensor to the regulating and control equipment.

7. The electric motor according to claim 5, wherein, A pipeline is provided that connects the second sensor to the regulating and control equipment.

8. The electric motor according to claim 6 or 7, wherein, At least one valve is provided for pressure regulation in the internal region of the rotor.

9. The electric motor according to claim 8, wherein, The at least one valve is disposed in the end cover and / or housing of the motor.

10. The electric motor according to claim 6 or 7, wherein, The adjustment and control equipment is arranged at the end cover or housing of the motor.

11. The electric motor according to claim 1, wherein, A pump is provided to generate overpressure in the region inside the rotor.

12. The electric motor according to claim 11, wherein, The pump is located at the end cap.

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