Abstract:
The moving parts of an electric motor are intended to be cooled more effectively and in a simple manner. For this purpose, the invention proposes an electric motor with a first motor part ( 1 ) and a second motor part, which interacts magnetically with the first motor part ( 1 ) and with respect to which the first motor part is capable of moving in two opposite movement directions (A, B). The electric motor is also equipped with a cooling system, which is fitted to the first motor part ( 1 ) and which has a cooling medium for cooling at least the first motor part. The cooling medium is moved, exclusively by means of acceleration of the first motor part ( 1 ), in one of the two opposite movement directions (A, B) in the cooling system. The movement can be triggered, for example, by the dead weight in an open cooling cycle system or else by means of a piston ( 23 ) in a closed cooling cycle system. The movement of the motor is therefore also used for pumping the coolant and additional electrical components such as fans can be dispensed with.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an electric motor with a first motor part, a second motor part, which interacts magnetically with the first motor part and with respect to which the first motor part is capable of being moved in two opposite movement directions, and a cooling system, which is fitted to the first motor part and which has a cooling medium for cooling at least the first motor part. Furthermore, the present invention relates to a corresponding method for cooling an electric motor. 
     Electric motors are provided with cooling systems in order to increase utilization. In this case, not only the stationary part of the motor but also the moving part is intended to be cooled. In the case of a rotary motor this is the rotor, and in the case of a linear motor this is generally the primary part. 
     Cooling with liquids is significantly more efficient than cooling with air or other gases. The cooling medium respectively used is delivered, for example, with the aid of a fan or a feed wheel through cooling pipes of the cooling system. In this case, a choice is also made between internal or external ventilation. In the latter case, the power of the motor is not used for ventilation purposes. 
     Other possibilities for heat removal consist in the utilization of pure convection or radiation. Furthermore, so-called heat pipes and thermopipes are also used for heat removal. 
     Precisely in the case of the moving parts of the motor, however, it is difficult to attach or connect the respective cooling equipment. Cooling of the moving part of the motor is therefore often dispensed with, which means losses in terms of power, however. 
     SUMMARY OF THE INVENTION 
     The object of the present invention therefore consists in providing a simple and easily manageable cooling system in particular for the moving part of a motor. 
     This object is achieved according to the invention by an electric motor with a first motor part, a second motor part, which interacts magnetically with the first motor part and with respect to which the first motor part is capable of being moved in two opposite movement directions, and a cooling system, which is fitted to the first motor part and which has a cooling medium for cooling at least the first motor part, being the cooling medium is capable of being moved, exclusively by acceleration of the first motor part, in one of the two opposite movement directions in the cooling system. 
     In addition, the invention provides a method for cooling an electric motor with a first motor part and a second motor part, which interacts magnetically with the first motor part and with respect to which the first motor part is capable of being moved in two opposite movement directions, and with a cooling system, which is fitted to the first motor part and which has a cooling medium for cooling at least the first motor part, by acceleration of the first motor part with respect to the second motor part in one of the two opposite movement directions, and movement of the cooling medium in the cooling system exclusively by the acceleration of the first motor part. 
     Advantageously, the heat removal from a moving motor part is possible in a very simple manner since the acceleration of the motor part is also used for moving the cooling medium. There is therefore no need for a special drive for the movement of the cooling medium. 
     Preferably, the electric motor is in the form of a linear motor, the movable, first motor part preferably being the primary part, in/on which a cooling pipe of the cooling system is arranged. In this case, the to-and-fro movement of the linear motor primary part is used to cool said primary part. 
     Furthermore, the cooling system can have a cooling pipe with at least one nonreturn or check valve, through which the cooling medium can only pass in one direction. As a result, the efficiency of a cooling system can be increased. 
     It is also particularly advantageous if the cooling system is in itself closed. This makes it possible to avoid the need for connections to be provided externally, for example in the case of cooling of a moving part of the motor, if the cooling system overall is arranged on the moving part of the motor. 
     In addition, the cooling system can have a piston in a cooling pipe or vessel, the density of said piston deviating from that of the cooling medium. The piston is then moved in the case of the acceleration of the first motor part in the cooling medium. As a result, in particular also symmetrical cooling systems can be constructed. In addition, the piston can be used for increasing the throughput of cooling medium. 
     Furthermore, the cooling system can have at least one compensating vessel, in which a gaseous compensating medium is located in addition to the liquid cooling medium. In this case, gravitation can also be used to deliver the cooling medium, in addition to the acceleration of the first motor part. 
     In a specific embodiment, the cooling system has two pipe sections, which run parallel to one another and open out into one another and which each have a check valve, of which both valves are directed either towards the opening or away from the opening, with the result that the cooling medium only flows in one pipe section in the case of one movement direction of the first motor part and only flows in the other pipe section in the case of the opposite movement direction of the first motor part. In this way, the acceleration of the first motor part can be used not only in one direction but in both directions. 
     Instead of a freely movable piston, it is also possible for a body whose density deviates from that of the cooling medium to be fixed in a section of the cooling system with the aid of a diaphragm which at least largely covers the inner cross section of the section. In the case of acceleration, the diaphragm is then deflected by the body, as a result of which the cooling medium is delivered through the cooling system. 
     Furthermore, the cooling system can have a pressure vessel and an expansion section connected thereto, and in this case a section of the first motor part which is to be cooled is cooled by the expansion section. If cooling medium from the pressure vessel then expands in the expansion section, thermodynamic cooling effects are also utilized. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The present invention will now be explained in more detail with reference to the attached drawings, in which: 
         FIG. 1  shows a linear motor according to the invention in accordance with a simple, first embodiment, in cross section; 
         FIG. 2  shows a linear motor with a closed cooling system on the primary part; 
         FIG. 3  shows a basic diagram of a water-cooled linear motor with cooling pipeline which are provided with check valves in accordance with a third embodiment of the present invention; 
         FIG. 4  shows a basic diagram of a water-cooled linear motor with a piston in the cooling system in accordance with a fourth embodiment of the present invention, and 
         FIG. 5  shows a basic diagram of a water-cooled linear motor with additional thermodynamic cooling in accordance with a fifth embodiment. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The exemplary embodiments outlined in more detail below represent preferred embodiments of the present invention. 
       FIG. 1  illustrates a very simple example of a water-cooled primary part  1  of a linear motor. The primary part  1  is moved, according to the arrow A, over the secondary part  2  of the linear motor towards the right in the drawing or, according to the arrow B, towards the left. A cooling pipe  3  is located parallel to the movement directions A, B in the primary part  1  for cooling the coils. A coolant vessel  4  is located on the left-hand side of the primary part  1 , and a coolant vessels is located on the right-hand side. The cooling pipe  3  is connected to the two coolant vessels  4 ,  5  so as to enable the flow of liquid. The level of the coolant  6  is above the cooling pipe  3  in both coolant vessels  4 ,  5 . Not only the coolant vessels  4 ,  5  but also the cooling pipe  3  are therefore filled with the cooling medium  6 . 
     The cooling pipe  3  is thermally coupled as best as possible to the coils of the primary part  1 . This takes place, for example, by means of it being pressed into the housing of the primary part. 
     If the primary part  1  is now accelerated in the direction A, the cooling liquid  6  flows through the cooling pipe  3  in the direction B as a result of the acceleration, with the result that the coolant vessel  4  is filled to an ever greater extent and the coolant vessel  5  is emptied to an ever greater extent. 
     In the other case in which the primary part  1  is accelerated in the direction B towards the left, the cooling liquid flows towards the right in the cooling pipe  3 , with the result that the right-hand coolant vessel  5  is filled and the left-hand coolant vessel  4  is emptied. As a result of the flow of cooling liquid  6  in the cooling pipe  3 , heat is removed more effectively from the primary part  1 . The coolant flow is interrupted if there is no longer any acceleration of the primary part  1 . If there is no longer any acceleration, the linear motor now also consumes correspondingly less electrical energy, or none at all, however. For heat removal of the cooling liquid  6 , heat sinks or heat exchangers  7 ,  8  are fitted to the coolant vessels  4  and  5 , which heat sinks or heat exchangers emit the heat to the surrounding environment. 
       FIG. 2  shows a further-developed second embodiment of a linear motor with an autonomous cooling system, likewise in a longitudinal section. The design of the electric motor is substantially similar to that in  FIG. 1 . In this second embodiment, the coolant system is closed, however. Specifically, the individual coolant vessels  4  and  5  are covered and connected to one another via an air bridge  9 . In the example in  FIG. 2 , the primary part  1  is accelerated towards the right in the direction A. The cooling liquid  6 , for example water, therefore flows in the cooling pipe  3  in accordance with the arrow illustrated towards the left. In the air bridge  9 , however, the air flows for compensation purposes towards the right from the left-hand coolant vessel  4  into the right-hand coolant vessel  5 . In the case of acceleration in the opposite direction in the direction B, the flow directions in the cooling pipe  3  and in the air bridge  9  are correspondingly reversed. Furthermore, gravitation ensures compensation of the levels in the two coolant vessels  4 ,  5 . 
     In order to improve the cooling power, the cooling principle in  FIG. 2  (closed cooling system) can be developed further corresponding to  FIG. 3 . This drawing again shows a primary part  1 , which is accelerated in the directions A and B. A secondary part is not illustrated here. Coils  10 , which have a certain power loss, are arranged in the primary part  1 . The resultant heat is conducted to a cooling pipe  11  arranged perpendicular to the movement directions A, B. The cooling liquid  6  originates from a liquid vessel  12 , which is arranged at the upper end of the cooling pipe  11  and is connected thereto. 
     The cooling liquid  6  flows downwards in the cooling pipe  11  and flows through an air-cooled heat exchanger  13  below the primary part  1 . Below the heat exchanger  13 , the cooling pipe  11  branches into a first cooling pipe section  14  in direction A and into a second cooling pipe section  15  in direction B. The two cooling pipe sections  14 ,  15  open out into a lower liquid vessel  16  at points P 2  and P 4 , respectively. Furthermore, the two cooling pipe sections  14 ,  15  are provided with nonreturn or check valves  17 ,  18 , which only allow the cooling liquid to flow into the lower liquid vessel  16  from the respective cooling pipe section  14 ,  15 . 
     In each case rising pipes  19 ,  20  are arranged at the outermost left-hand end (point P 1 ) and at the outermost right-hand end (point P 3 ) of the liquid vessel  16 . The two rising pipes are provided with check valves  21 ,  22 , with the result that the cooling liquid  6  can only flow from the lower liquid vessel  16  into the rising pipes  19 ,  20 . The two rising pipes  19 ,  20  open out into the upper liquid vessel  12 . The upper liquid vessel  12  is not completely filled with cooling liquid  6 , but is partially filled with air or another gas. 
     In the case of an acceleration of the primary part  1  together with the two-way cooling system in the direction A, the pressure rises at point P 1 , where the left-hand rising pipe  20  is fitted to the lower liquid vessel  16 . Correspondingly, the cooling liquid  6  in the rising pipe  20  rises upwards and is conducted into the upper liquid vessel  12 . At the same time, a considerable reduced pressure is produced at point P 2  in the lower liquid vessel  16  in comparison with point P 1 , with the result that cooling liquid then flows from the upper liquid vessel  6  through the cooling pipe  11  and the cooling pipe section  14  into the lower liquid vessel  16 . The corresponding cooling liquid flow is denoted by WA. 
     In the other case in which the primary part  1  together with the cooling system is accelerated in the direction B, the pressure rises at point P 3 , where the right-hand rising pipe  19  is coupled to the lower liquid vessel  16 . At the same time, the pressure lowers at point P 4 , where the left-hand cooling pipe section  15  opens out into the lower liquid vessel  16 . This results in the coolant flow WB illustrated through the left-hand cooling pipe section  15  and the right-hand rising pipe  19 . In the case of a to-and-fro movement of the linear motor, liquid is therefore continuously pumped into the upper liquid vessel  12  and flows from there downwards through the primary part  1 , with the result that heat can be removed from said primary part  1 . 
     A third embodiment of a water-cooled linear motor primary part is illustrated in  FIG. 4 . The design is similar to that in  FIG. 3 . The primary part  1  with its coil  10  emits heat to a vertically arranged cooling pipe  11 . The heat exchanger  13  therebeneath removes the heat from the cooling pipe  11 . Then, the cooling pipe is again split into the cooling pipe sections  14  and  15  with the check valves  17  and  18 . The cooling pipe sections  14 ,  15  open out into the lower water vessel  16 , at whose outer ends the rising pipes  19 ,  20  rise upwards, with said rising pipes  19 ,  20  likewise being provided with check valves  21  and  22 . The two rising pipes  19 ,  20  together open out into the cooling pipe  11 , without a liquid vessel being interposed here. This results in a closed cycle system with a single vessel, which is filled completely with cooling liquid or water. 
     A piston  23  is located in the liquid vessel  16 , which is in the form of a pipe, for example. This piston  23  has a density ρ k , while the density of the cooling liquid or the water is ρ w . 
     It is assumed for the functional example below that ρ k &gt;ρ w . If the primary part  1  including the cooling cycle is now accelerated in the direction A, the piston  23 , whose density is greater than that of the cooling liquid, is moved towards the left (towards the right for ρ k &lt;ρ w ), with the result that the cooling liquid is pushed into the rising pipe  20  since it cannot enter the cooling pipe section  15  owing to the check valve  18 . At the same time, a reduced pressure is produced in the vessel space to the right of the piston, with the result that the cooling liquid flows through the cooling pipe  11  and the right-hand cooling pipe section  14  corresponding to the liquid flow WA. 
     If the primary part  1  is accelerated towards the left in the direction B, on the other hand, the piston  23  is moved towards the right and pushes the liquid into the right-hand rising pipe  19 , through the cooling pipe  11  and the left-hand cooling pipe section  15  back into the left-hand part of the cooling liquid vessel  16 . 
     In the case of this closed cooling cycle system as well, either the coolant cycle WA or the coolant cycle WB is therefore set in motion, depending on the acceleration direction. The two cycles ensure a flow through the primary part and therefore removal of heat therefrom. 
     The cooling system in the example in  FIG. 4  has until now been considered as a vertical system with rising pipes corresponding to the example in  FIG. 3 . The closed cycle system of the fourth exemplary embodiment also functions, however, if the pipes illustrated in  FIG. 4  are arranged horizontally. In this case, too, the piston  23  is moved in the event of an acceleration in one of the directions A, B and therefore delivers the coolant. 
     A fifth exemplary embodiment of a water-cooled linear motor with a closed cooling cycle is illustrated schematically in  FIG. 5 . The design substantially corresponds to that in  FIG. 4 , for which reason no description is given of the individual components which remain unchanged. A first substantial change in comparison with the fourth exemplary embodiment consists in the fact that a diaphragm  24 , to which a mass or a body  25  is fixed, is arranged in the liquid vessel  16  instead of the piston  23 . The movement principle of the body  25  is the same as that of the piston  23  in  FIG. 4 . The body  25  has a density ρ M  which differs from the density ρ W  of the water or the liquid. If the density ρ M  of the body  25  is greater than the density ρ W  of the cooling liquid, in the case of an acceleration in the direction A said body  25  is moved in the opposite direction B. If the density ρ M  of the body  25  is less than the density ρ W  of the cooling liquid, however, it likewise moves in the direction A in the case of an acceleration of the primary part  1  in the direction A. In the case of an acceleration of the primary part  1  in the direction B, the opposite movements of the body  25  take place. 
     The diaphragm  24  is deflected corresponding to the movement of the body  25 . Since it separates the liquid vessel  16  into a left-hand and a right-hand half, which are not connected to one another in such a way that liquid can flow, again one of the two cooling cycles WA or WB corresponding to the example in  FIG. 4  is triggered in the case of an acceleration of the primary part  1 , depending on the direction. 
     A further substantial change in the fifth exemplary embodiment in comparison with the fourth exemplary embodiment consists in the fact that the central cooling pipe  11  is in this case replaced by a pressure vessel  26 , a constriction  27  in the pipe and an expansion section  28 . The thermodynamic principle that a medium is cooled in the case of a drop in pressure, for example as a result of evaporation of the cooling liquid, is utilized for cooling purposes by this pressure vessel  26  with the adjoining expansion section  28 . 
     The operation of the closed cooling cycle system illustrated in  FIG. 5  can be outlined as follows. As a result of the acceleration of the primary part  1  for example in the case of a to-and-fro movement, the diaphragm  24  to which the body  25  is fitted acts as a pump and pumps cooling liquid into the pressure vessel  26 . There, the temperature rises to a value T 1  and the pressure rises to a value p 1 . The heat exchanger  13  is thermally coupled to the pressure vessel  26  owing to the increased temperature. As a result, the degree of efficiency in the removal of heat of the cooling liquid is increased. The cooling liquid passes through the constriction  27  into the expansion section  28 , where it can expand corresponding to a polytropic change of state and preferably evaporates. In this case, the pressure is reduced to the value p 2 . Likewise, the temperature is reduced to a temperature T 2 . The primary part  1  or a coil  10  is thermally coupled to this expansion section  28 . Since the expansion section  28  has a lower temperature T 2 , the removal of heat thereof is correspondingly more effective. 
     In order to improve the removal of heat, under certain circumstances it may be advantageous not to position the valves  21 ,  22  directly at the pressure vessel  26  but in the vicinity of the liquid vessel  16 , as in the example in  FIG. 3 . In this case, the liquid in the outer pipes or rising pipelines  20 ,  21  also has the high temperature T 1 , with the result that additional removal of heat towards the surrounding environment can be carried out there. 
     The abovementioned exemplary embodiments are in part represented as two-way systems, which demonstrate pumping action in the case of accelerations in both directions. However, the cooling systems can also be in the form of one-way systems, with the coolant only being pumped in one direction in the case of acceleration. Furthermore, the systems can also be equipped with a plurality of pipes which run parallel to one another and possibly have flows in opposite directions, in order to improve the cooling effect. In general, all of the individual elements of the cooling systems such as the piston, diaphragm, thermodynamic elements etc. can be combined with one another as desired in order to obtain a corresponding cooling cycle. 
     The closed cooling systems proposed have advantages in particular in the case of so-called pick-and-place machines, where conventional water cooling systems are undesirable since these machines are permanently in motion and therefore constantly pump the coolant. As a result, additional electrical component parts such as air fans or the like can be saved. Nevertheless, the heat can be transported away from the motor effectively. 
     Illustrated examples apply for acceleration in the case of linear movement. The same principle can be applied to rotary motors by the angular acceleration of the rotor being utilized.