electric motor with cooling

Abstract

An electric motor for a motor spindle or a rotary table or a multi-axis rotary head for a machine tool or the like, wherein a stator unit (3) having a coil-carrying stator lamination stack and a rotor unit (7) having at least one rotor shaft rotatable about an axis of rotation are provided, wherein a heat dissipation cooling device (4, 6) having at least one coolant channel (4) through which a coolant can flow is provided for cooling and dissipating the heat of the stator unit (3) and / or the rotor unit (7), wherein a housing (2) comprises an outer surface of the electric motor, characterized in that at least one thermal vacuum insulation unit (1) surrounding the stator unit (3) having the stator lamination stack is arranged outside the heat dissipation cooling device (4, 6) when viewed in the radial direction.

Description

[0001] The invention relates to an electric motor, preferably of a machine tool unit such as a multi-axis rotary head, a motor spindle, a rotary table or the like, comprising a stator unit and a rotor unit comprising at least one rotor shaft rotatable about an axis of rotation, according to the preamble of claim 1. State of the art

[0002] Electrically driven machine units, such as motor spindles, are used in machine tools. The task of machine tools is generally to produce component geometries, preferably using machining techniques, that are precisely defined in terms of shape, position, and dimensions. Accuracy requirements are constantly increasing, with not only hundredths of a millimeter but, at least in some cases, thousandths of a millimeter being required.

[0003] A major disruptive factor is thermal deformation of the machine tool, which, if not compensated for, leads to significant geometric errors in the component being manufactured. This deformation arises, among other things, from the heating of different areas of the machine tool during operation, and the cause of this heating is often a variety of heat loss sources within the machine.

[0004] A significant source of power loss is the motor spindle or the electric motor drive. The electric motor integrated into the motor spindle converts the supplied electrical energy into usable energy, but also always a certain amount into energy loss. Since modern motor spindles sometimes have considerable electrical power, the losses can also be substantial.

[0005] Up to now, commonly used motor spindles have been cooled, primarily to minimize thermal deformation and expansion within the spindle itself, and to prevent damage to the electrical insulation of the motor windings caused by excessively high temperatures. This is intended, for example, to prevent thermal stresses from affecting the rotor shaft bearings. With this type of cooling, especially when using a coolant, a large portion of the energy loss is dissipated from the machine tool via the cooling medium.

[0006] However, a significant portion of the heat loss is also transferred to the structure of the machine tool via conduction or radiation, leading to so-called "heat pockets" that can cause geometric deviations during workpiece machining. Consequently, these "heat pockets" result in inaccuracies in the machining process. Air-cooled electric motors or motor spindles generate thermal expansion and inaccuracies that are unacceptable for modern, high-precision workpiece machining. Only a coolant can dissipate these large amounts of waste heat sufficiently.

[0007] From DE 198 49 573 A1, an electric motor for a motor spindle is already known, which has a thermal insulation unit to dissipate the resulting heat loss as directly as possible at its source, so that thermal expansion in or on the stator has as little significant an impact as possible. For this purpose, at least two cooling layers with separate liquid cooling circuits are provided, between which the insulation layer is arranged. However, this electric motor with separate cooling circuits and an intermediate insulation layer is thus comparatively complex and bulky.

[0008] Accordingly, this electric motor not only represents a relatively large design and economic undertaking in its manufacture and operation, but the bulky cooling and insulation required in the confined spaces of modern machine tools also compromises the electric drive and motor performance. This latter point directly contradicts the ever-increasing demands for even greater motor output in the machine tool sector.

[0009] Furthermore, a motor spindle with vacuum insulation of the motor shaft has become known from JP 2001-71 202 A. Purpose and advantages of the invention

[0010] In contrast, the object of the invention is to propose an electric motor, in particular for a machine tool unit such as a multi-axis rotary head, a motor spindle, a rotary table or the like, which meets high requirements regarding the dimensional accuracy of the rotor shaft, but can be implemented with less effort and in particular in a space-saving manner or with a higher power density.

[0011] This problem is solved, starting from an electric motor of the type mentioned in the introduction, by the features of claim 1. Advantageous embodiments and further developments of the invention are possible by the measures mentioned in the dependent claims.

[0012] Accordingly, an electric motor according to the invention is characterized in that at least one thermal vacuum insulation unit surrounding the stator unit comprising the stator lamination stack is arranged radially outside the heat dissipation cooling device. Surprisingly, it has been found that this measure also makes it possible to significantly prevent heat conduction or radiation from the electric motor or the machine tool unit within the machine tool to / onto other components of the machine tool. This effectively prevents the formation of "hot spots" or thermal expansion or stress in components or the structure of the machine tool. Consequently, very high requirements regarding the geometry to be achieved on the component or workpiece to be manufactured can be met.

[0013] In contrast to the prior art according to DE 198 49 573 A1, it has surprisingly been shown that a single cooling layer is sufficient if, according to the invention, the vacuum insulation unit according to the invention is arranged around the cooling layer or cooling jacket of the stator unit. The elimination of a second, separate cooling layer with a separate second liquid cooling circuit significantly reduces the design and economic effort. Furthermore, operating the electric motor with only one liquid cooling circuit according to the invention is less complex than with the aforementioned prior art.

[0014] Furthermore, by avoiding a second cooling layer located outside the thermal insulation layer, a significantly more space-saving liquid cooling system with associated thermal insulation or shielding of the motor's waste heat from the environment of the electric motor is achieved.

[0015] On the other hand, the use of vacuum for insulation according to the invention, compared to the gas-filled insulation layer according to DE 198 49 573 A1, allows for a significant reduction in volume and a more space-saving design while maintaining the same or better thermal insulation performance. Consequently, according to the invention, with the same overall volume and external dimensions of the electric motor, considerably more installation space is available for the drive components and the electromagnetic drive system, i.e., for the magnet system of the rotor unit and for the coils and the laminated core of the stator unit.

[0016] Accordingly, the electric motor according to the invention not only exhibits high dimensional stability during operation, but also a significantly higher power density than this prior art, i.e., power per unit volume. The electric motor according to the invention thus combines very low thermal expansion during operation with drastically reduced effort and minimal space requirements, so that even future, particularly demanding requirements for machine tools can be met or realized.

[0017] Advantageously, the cooling device is arranged radially between the rotor unit and the insulation unit. This makes it possible for the heat loss generated within the electric motor or machine tool unit to be almost completely dissipated by the cooling device, which is preferably arranged at least partially radially outside or around the heat loss source, without any heat conduction or radiation being transferred to the outer surface of the casing or the outer surface of the motor. Thus, according to the invention, the thermal vacuum insulation unit effectively shields the heat source or heat-generating area, while the cooling device arranged between the heat source and the thermal vacuum insulation unit can dissipate the resulting heat loss essentially completely and without harm.

[0018] Preferably, a preferably polished, oriented towards the axis of rotation, and optionally advantageously coated surface is provided around the heat source and / or the cooling device in a jacket-like or hollow cylinder configuration, and / or a heat-reflective layer / surface or the like is arranged. This minimizes material loss into the vacuum and / or advantageously retains heat conduction or heat radiation within the stator or electric motor according to the invention.

[0019] Advantageously, the housing features at least a partial protective sleeve on the outside to protect the vacuum insulation unit. This protective sleeve can be, for example, a metallic covering such as a metal sheet, a metal sleeve, a plastic casing, a fiberglass casing, or the like. Experience has shown that, particularly for use in machine tools, a metal sheet protective sleeve, especially one made of steel, withstands the sometimes harsh operating conditions exceptionally well. For example, the protective sleeve or casing can effectively prevent mechanical damage to the thermal insulation unit.

[0020] In an advantageous embodiment of the invention, the protective sheath is essentially designed as a hollow cylinder. A hollow cylinder can be manufactured using established and proven methods and, for example, mounted as a stator protective sheath. Shrink-fitting processes can be used, for instance, whereby the hollow cylinder is advantageously shrunk onto at least one mounting flange and / or one or two spaced-apart, end-face stator components.

[0021] In principle, the thermal vacuum insulation unit can comprise, for example, walls and / or components made of plastic, mineral material, or various composite materials, etc., which advantageously exhibit low thermal conductivity. The use of porous materials or cavities is generally particularly advantageous, with the pores or cavities being advantageously vacuum-sealed. For example, fiberglass materials, polyurethane, especially open-cell polyurethane foam, or open-cell XPS, or similarly advantageous materials or material structures can be used. Support elements or the like can also penetrate the vacuum or vacuum space, thus preventing indentation or deformation of the vacuum insulation.

[0022] An advantageous embodiment of the invention is the use of an insulating powder for the vacuum insulation unit according to the invention. Preferably, the insulating powder is designed as a microporous insulating powder with a very low thermal conductivity. For example, silica powder or the like can be advantageously used.

[0023] Preferably, the insulating powder is arranged within an insulating shell. For example, an intermediate space can advantageously be generated by the protective jacket and an internal hollow cylinder, which can be designed as an insulating shell and into which insulating powder can advantageously be introduced. Preferably, however, the thermal insulation unit has an advantageous, separate insulating shell / film or the like, within which the insulating powder is arranged. This means that, for example, in a particular embodiment of the invention, the insulating shell is in direct contact with, or adjacent to, the stator housing or the protective jacket of the stator housing. It has been shown that a separately manageable thermal insulation unit as an insulating shell with powder filling is particularly advantageous in the manufacture of the electric motor according to the invention.

[0024] Advantageously, the vacuum according to the invention is present within the insulating shell. For example, a vacuum of approximately 0.1 to approximately 30 mbar is present. For this purpose, the insulating shell is advantageously designed to be as gas-tight as possible in order to maintain a long vacuum lifespan.

[0025] In a particular embodiment of the invention, a getter material is provided within the vacuum insulation unit or the cavity or the insulating shell in order to improve the vacuum of the insulation unit and / or to maintain it for as long as possible, if necessary by means of a (thermal) regeneration of the getter material.

[0026] Initial tests have shown that the use of suitably designed vacuum insulation components and / or vacuum cavities, preferably formed essentially as hollow cylinders oriented along the axis of rotation, is particularly advantageous. A hollow cylindrical vacuum insulation unit has no thermal bridges in the radial or circumferential direction. This is highly advantageous with regard to the thermal insulation effect, i.e., the most complete possible retention of heat within the stator and the most complete possible dissipation of heat from the machine tool unit by means of the cooling device according to the invention.

[0027] The design of the vacuum insulation unit as a hollow cylinder with a continuous circular cross-section means that this insulating jacket has no thermal bridges, unlike the prior art mentioned earlier. In the prior art, the existing thermal bridges parallel to the axis between the circular arc-shaped, gas-filled cavities make it essential to implement a second, outer cooling circuit or cooling layer to prevent heat transfer to the outer surface of the electric motor and the corresponding detrimental thermal expansion of the stator. However, as mentioned earlier, this results in considerable effort and space requirements.

[0028] In the inventive variants with filled vacuum insulation units, a microporous insulation powder can be used as the insulation material, which, for example, exhibits very low thermal conductivity values ​​of approximately 0.016 W / mK at normal pressure. The use of silica has proven particularly effective in this regard.

[0029] Advantageously, the waste heat cooling device comprises at least one coolant distribution unit arranged on a first end face of the stator unit and a coolant collection unit arranged on a second end face of the stator unit opposite the first end face for distributing and collecting the coolant in several separate cooling channels arranged around the axis of rotation. This enables advantageously uniform cooling around the axis of rotation. The uniform cooling or heat distribution around the axis of rotation prevents thermal expansion of the straight axis into a slightly curved line. Even a slightly curved rotor shaft leads to inaccuracies at the machining point, such as at the milling head or at the clamping point, in motor spindles or similar applications.However, such inaccuracies in the micrometer range, caused by thermally varying strains in the circumferential direction of the axis of rotation, are a disadvantage in the increasing demands of the machine tool sector.

[0030] A heat distribution or cooling of the drive system that is as uniform as possible around the axis of rotation (360°) prevents (slight) deflection of the rotor shaft or the electric motor. Consequently, the dimensional accuracy of the electric motor is significantly improved according to the invention. Preferably, the multiple cooling channels are designed as cooling coils extending along the axis of rotation.

[0031] Advantageously, at least one flange unit is provided for attaching the electric motor or the machine tool unit to a machine tool. This allows for a defined attachment of the electric motor or the machine tool unit to the machine tool. According to the invention, it is particularly advantageous to design the flange unit in such a way that heat conduction through the flange unit into the structure or other components of the machine tool is minimized. For this purpose, for example, an advantageous material selection for the flange unit can be provided. A comparatively small contact or mounting surface can also be implemented to minimize direct heat conduction.

[0032] Advantageously, to reduce heat conduction in the flange unit, at least one segmented mounting surface or several spaced-apart individual mounting surfaces are provided. Here, raised and recessed structures can be generated that create a comparatively small overall mounting surface with the structure or other components of the machine tool, yet can transmit relatively large fastening forces or moments. Accordingly, the direct heat conduction via the contact surfaces or the mounting surface of the flange unit is reduced.

[0033] Alternatively or in combination with this, the flange unit can be designed such that it includes at least one flange cooling channel for a flange cooling fluid. Advantageously, the flange cooling is operatively connected to the cooling device. For example, a flange channel can be provided that is fluidically connected to the cooling channel of the cooling device, so that the cooling fluid of the cooling device is identical to the flange cooling fluid of the flange cooling system. This reduces the need for a separate or special cooling system for the flange unit.

[0034] In a particular embodiment of the invention, the flange unit and / or the flange cooling channel, or the flange cooling system itself, is arranged on an end face of the vacuum insulation unit when viewed axially. This measure effectively prevents heat conduction and thermal bridging between the electric motor or the waste heat from the drive system and the machine tool. The advantageous thermal vacuum insulation unit according to the invention retains the waste heat from the drive system within the electric motor or its outer cylindrical surface and dissipates it via the liquid cooling system. The preferably hollow cylindrical vacuum insulation unit, whether as a cavity or as a hollow cylinder vacuum insulation element filled with insulating coils, etc., prevents the formation of thermal bridges over the entire 360° or the entire circumference of the axis of rotation or the stator unit.Only the end faces of the vacuum insulation unit may have metallic elements / components or thermal bridges.

[0035] Typically, a motor spindle or similar component is fixed or mounted / bolted to the machine tool at only one point or with a single flange (removable). This fixing, or the flange unit according to the invention, is also usually located in the (front) area of ​​the tool / workpiece holder. By arranging the flange unit at the end face of the vacuum insulation unit according to the invention, it is effectively prevented that the waste heat from the drive system is transferred via the flange unit or the mounting to the machine tool or its frame, or the like, and thus leads to detrimental thermal expansion and consequently to machining inaccuracies. Accordingly, the invention enables complete thermal encapsulation or shielding of the waste heat from the drive system from the machine tool or the environment.In this case, the advantageous cooling system of the electric motor advantageously removes all waste heat or loss heat from the electric motor.

[0036] Initial trials have shown that the inventive design allows, for example, the production of a motor spindle that no longer dissipates heat losses generated within the motor spindle to the machine tool structure via the housing's outer surface, since the entire spindle body or the stator's outer surface is advantageously thermally insulated. Furthermore, the advantageous cooling of the motor spindle's mounting flange effectively prevents or minimizes heat dissipation to the machine tool structure at this specific point in the inventive motor spindle design.

[0037] Accordingly, according to the invention, all electrical power generated in the motor spindle in the so-called steady state can be dissipated calorimetrically via cooling using the advantageous cooling fluid. Heat transfer to the machine tool no longer occurs in a machine tool unit according to the invention, or is optimally minimized. Example of implementation

[0038] An embodiment of the invention is shown in the drawing and is explained in more detail below with reference to the figures.

[0039] In detail: Fig. 1 schematically a motor spindle according to the invention with a vacuum insulation element, Fig. 2 schematically a motor spindle according to the invention with a vacuum-sealed cavity according to the invention and Fig. 3 schematically a motor spindle with a section of a motor mount of a machine tool with a vacuum-sealed cavity arranged in between according to the invention.

[0040] In Fig. Figure 1 schematically depicts a motor spindle according to the invention, wherein a thermal insulation layer 1 is arranged below a substantially cylindrical sheet steel casing 2 of a stator 3 of the motor spindle. Furthermore, the stator 3 has cooling channels 4 for a cooling fluid.

[0041] Furthermore, the stator 3 has a flange 5, which in turn includes a cooling channel 6. The cooling channel 6 of the flange 5 can, for example, be integrated into a separate liquid cooling circuit for the motor spindle. Alternatively, the cooling channel 6 of the flange 5 can also be fluidically connected to the cooling channels 4, so that one and the same cooling fluid can flow through both the cooling channels 4 and the cooling channel 6 of the flange 5 and dissipate the waste heat.

[0042] Basically, i.e., not only in the variant according to Fig. 1, but also in other variants, especially according to the Fig. 2 or Fig. 3. It is advantageous (without further description) to provide a distribution of the coolant as uniform as possible around the axis of rotation. For example, a waste heat cooling device according to the invention has a coolant distribution unit arranged on a first end face of the stator 3, which faces a tool / workpiece holder 10 or the flange 5, and a coolant collection unit arranged on a second end face of the stator 3, opposite the first end face or rear end face, for distributing and collecting the coolant in several separate, optionally helically shaped, cooling channels 4 arranged around the axis of rotation. This means that the motor spindle is preferably supplied with coolant from the front (from the tool holder 10) through the cooling channels 4 to the rear. This enables cooling that is advantageously uniform around the axis of rotation. The uniform cooling, orHeat distribution around the axis of rotation prevents thermal expansion of the straight axis into a slightly curved line.

[0043] The coolant distribution unit and the coolant collection unit comprise, for example, several supply and collection channels, respectively, oriented essentially along the axis of rotation, which originate from a common annular or polygonal distribution channel or are brought together again in such a channel. Accordingly, the motor spindle can have a single coolant supply opening and a single coolant outlet opening, but the hollow cylindrical shell surrounding the electromagnetic drive system can be uniformly cooled by means of several advantageously helical cooling channels 4.

[0044] Furthermore, the motor spindle comprises a rotor 7, which is rotatably mounted within the stator 3 via two bearing points 8 and 9 in a conventional manner. The motor spindle also features a tool or workpiece holder 10.

[0045] In Fig. Figure 1 clearly shows that the cooling channels 4, viewed radially, are arranged within the insulation 1, or between the insulation 1 and the rotor 7 or the rotor shaft. The heat source is the coils or stator windings 11. That is, possibly in conjunction with several permanent magnets (of the rotor 7), the windings 11 convert the electrical energy to drive the rotor 7, generating waste heat, which is dissipated via the cooling channels 4 and the flange channel 6, or via the cooling fluid flowing therein.

[0046] According to the invention, the insulating unit 1 effectively shields the heat conduction or heat radiation of the motor spindle from the structure or other components of a machine tool such as a motor mount 12 (cf. Fig. 3) effectively.

[0047] It also becomes clear that a comparatively thin-walled insulation 1 is provided, which according to the variant in Fig. 1 is filled with a microporous powder arranged within a highly gas-tight encapsulating film. Furthermore, an advantageous vacuum is maintained within this encapsulating film. This results in relatively high thermal insulation with a comparatively small insulation volume. This is particularly advantageous, for example, given the limited space available in a machine tool for the motor spindle.

[0048] In Fig. 2 and Fig. Figure 3 shows further variants of the invention in which no insulation 1 with a microporous powder is provided. Instead, a vacuum-sealed cavity 1 is used as insulation 1 in each case. The cavity 1 comprises an inner cylinder wall and an outer cylinder wall and is advantageously sealed by means of two end-face seals 13, 14. In the variant according to Fig. 2. The (somewhat reinforced or thicker) stator lamination 2 forms the outer cylinder wall. In contrast, in the variant according to Fig. 3 The stator lamination 2 of the motor spindle, in the installed / mounted state in the machine tool, forms the inner cylinder wall and the motor mount 12 of the machine tool, forming the outer cylinder wall of the cavity 1 or the insulation 1 according to the invention. The vacuuming can advantageously be carried out by means of a connection (not shown) of the hollow cylindrical cavity 1 according to the Fig. 2 or Fig. 3.

[0049] The motor spindle according to the invention can thus replace existing motor spindles according to the prior art without a thermal insulation layer, without requiring any special design modifications or alterations to the machine tool. Accordingly, motor spindles according to the invention, or similar devices, can advantageously replace or be exchanged for corresponding conventional motor spindles or similar devices in machine tools due to their nearly identical space requirements and external dimensions.

[0050] Compared to a motor spindle according to DE 198 49 573 A1, the motor spindle according to the invention is significantly more space-saving and less complex in design. The two cooling layers or cooling circuits and the gas-filled insulating layer according to DE 198 49 573 A1 must be several centimeters thicker in motor spindles with comparable performance data than in the invention. Thus, the overall diameter of such a motor spindle becomes considerably larger, with the same electrical drive power and comparable insulation effect or thermal expansion. Therefore, with the aid of the invention, a conventional non-insulated motor spindle with the same drive power can be replaced by a thermally decoupled motor spindle and fits, for example, into previously common (standardized) motor mounts 12. Reference symbol list 1 insulating layer 2 steel sheet casing 3 Stator 4 Cooling channel 5 flange 6 Cooling channel 7 Rotor 8 storage location 9 storage location 10 Workpiece holder 11 stator windings 12 Motor mount 13 Seal 14 Seal

Claims

[1] Electric motor for a motor spindle or a rotary table or a multi-axis rotary head for a machine tool or the like, wherein a stator unit (3) having a coil-carrying stator lamination stack and a rotor unit (7) having at least one rotor shaft rotatable about an axis of rotation are provided, wherein a heat dissipation cooling device (4, 6) having at least one coolant channel (4) through which a coolant can flow is provided for cooling and dissipating the heat of the stator unit (3) and / or the rotor unit (7), wherein a housing (2) comprises an outer surface of the electric motor, characterized by , that at least one thermal vacuum insulation unit (1) surrounding the stator unit (3) comprising the stator lamination stack is arranged outside the waste heat cooling device (4, 6) when viewed in the radial direction. [2] Electric motor according to claim 1, characterized by, that the housing (2) has a shell element (2) comprising the outer surface of the electric motor and essentially designed as a hollow cylinder. [3] Electric motor according to one of the aforementioned claims, characterized by , that the vacuum insulation unit (1) is arranged on the housing or on the jacket element (2). [4] Electric motor according to one of the preceding claims, characterized by , that the outer shell element (2) of the housing (2) is designed as the wall of the vacuum insulation unit (1). [5] Electric motor according to one of the preceding claims, characterized by , that the vacuum insulation unit (1) is essentially designed as a hollow cylinder (1) aligned along the axis of rotation. [6] Electric motor according to one of the preceding claims, characterized by, that the waste heat cooling device (4, 6) comprises at least one coolant distribution unit arranged on a first end face of the stator unit (3) and a coolant collector unit arranged on a second end face of the stator unit (3) opposite the first end face for distributing and collecting the coolant in several cooling channels arranged around the axis of rotation. [7] Electric motor according to one of the aforementioned claims, characterized by that the multiple cooling channels are designed as cooling coils extending along the axis of rotation. [8] Electric motor according to any of the preceding claims, characterized by , that at least one flange unit (5) is provided for attaching the electric motor to a machine tool. [9] Electric motor according to any of the preceding claims, characterized by, that the flange unit (5) comprises at least one flange cooling (6) having at least one flange channel (6) for a flange cooling fluid. [10] Electric motor according to any of the preceding claims, characterized by , that the flange unit (5) is arranged on an end face of the vacuum insulation unit (1) when viewed in the axial direction. [11] Machine tool with an electric motor according to one of the preceding claims. [12] Machine tool according to the preceding claim, characterized by , that the vacuum insulation unit (1) is arranged between the housing (2) and a motor mounting unit for receiving the electric motor. [13] Machine tool according to the preceding claim, characterized by , that the vacuum insulation unit (1) arranged between the housing (2) and the motor mounting unit is designed as a vacuum-sealed cavity.

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