Abstract:
A liquid-air cooling system ( 1 ) has at least one fan device ( 2 ) including at least one variable-speed fan motor ( 3 ) driving a fan impeller ( 4 ) to create a cooling power for a fluid ( 5 ) in a fluid cycle ( 6 ). To regulate the speed of the fan motor ( 3 ) by a control and/or regulation device ( 24 ), at least one actual value (Ta) downstream of a segmented heat exchanger ( 19 ) is compared to a predefined desired value (Tb). The control and/or regulation device ( 24 ) adjusts the cooling power according to the current power values of the respective machine unit ( 9 ).

Description:
FIELD OF THE INVENTION 
     The invention relates to a liquid-air cooling system that includes at least one fan device comprising at least one variable-speed fan motor that powers a fan impeller to generate cooling capacity for a fluid of a cooling cycle. To control the speed of the fan motor by an automatic control system, at least one actual default value that originates from a machine unit connected to the liquid-air cooling system, is compared to a desired default value. The cooling capacity of the liquid-air cooling system is then adjusted as a function of the current output temperature values of the respective machine unit. 
     BACKGROUND OF THE INVENTION 
     EP 0 968 371 81 discloses and describes a fluid cooling device comprising a motor that powers a fan impeller and a fluid pump. The fluid pump takes fluid from an oil reservoir and conveys it into a hydraulic operating cycle. In the hydraulic operating cycle, the fluid (hydraulic medium) is heated and routed to a heat exchanger. From the heat exchanger, the cooled fluid is recirculated to the oil reservoir. The oil reservoir of the fluid cooling system is configured in the shape of a basin with particularly high-reaching basin edges that are suitable to form a housing part for receiving the fan impeller and an air-routing chute for a heat exchanger of the fluid cooling device. With the fluid cooling device, an oil reservoir can be provided in an especially compact assembly for storing and circulating large fluid volumes. 
     A control system and a method for controlling the speed of a plurality of fans for cooling a plurality of flow media of a machine unit are disclosed in DE 100 62 534 A1. The speed of each of the plurality of fans is controlled specifically according to an individual heat dissipation requirement of heat transfer cores. For one temperature sensor, respectively, of each of the plurality of flow media, current temperatures are monitored. Each sensor can be operated to generate a signal that displays the temperature of the respective flow medium, while transferring the signal to an electronic control device to control the respectively singular speed of each of the fans. 
     Using the previously described solution, temperature-control, especially cooling, tasks for a fluid of a hydraulic circuit can be basically implemented. However, particularly the temperature of the fluid that has passed through the fan device is, seen in absolute terms, dependent on the respective and varying ambient temperature of the hydraulic power pack. The output temperature of the fluid therefore fluctuates in the known hydraulic power packs and fluid cooling devices after it passes through the fan device. 
     SUMMARY OF THE INVENTION 
     An object of the present invention to provide an improved liquid-air cooling system having a fan device with a cooling capacity that takes into account the ambient temperature of the liquid-air cooling system and that is able to permanently implement an exact desired temperature of the fluid. 
     This object is basically achieved by a liquid-air cooling system that includes a fan device with a fan impeller powered by a variable-speed fan motor. The system basically allows for the implementation of cooling capacity for a fluid in a cooling cycle taking into account an actual default value—such as a temperature value—that originates from a machine unit that can be connected via the fluid cycle to a liquid-air cooling system. According to the invention, the liquid-air cooling system also includes the possibility of taking into account a desired default value, The desired default value is then compared to the actual default value such that the cooling capacity of the fan device is adjusted as a function of the actual output values of the machine unit that is supplied with fluid. 
     An automatic control system handles a corresponding desired/actual comparison and speed control of the fan motor. The actual default value and the desired default values therein can be represented by a temperature value. The actual default value and the desired default value can also be described by suitable other characteristic values that relate to a current operating point of the machine unit and a current actual temperature value that reflects the current operating conditions with regard to the liquid-air cooling system. 
     In an especially preferred embodiment of the liquid-air cooling system, and particularly using a memory and as a processor of the automatic control system that adjust the speed of the fan impeller, an air temperature is provided, for example as a desired default value, on the air supply side of the fan device. A desired default value is either a temperature of the ambient air of the hydraulic power pack or a temperature of the machine unit or of a component of the machine unit that receives a fluid flow-through for the purpose of temperature control. 
     Ambient air is provided as a cooling medium to increase the energy efficiency of the liquid-air cooling system. Advantageously, the speed of the fan motor is controlled in such a manner that the fluid temperature of the coolant is maintained at a value that is lowered, for example, by 5° Kelvin or more in comparison to a desired temperature that represents the desired default temperature. To be able to implement a cost-effective liquid-air cooling system, advantageously, a variable-speed motor is selected as the fan motor. For a fan motor control, a corresponding automatic control system is advantageously used in connection with a machine unit or, when bus systems are used, for the transmission of the desired default value as well as the actual default value, or, in the sense of a field bus system, for networking a plurality of machine units. A PID controller therein controls the speed of the fan motor. PID control systems are known to the person skilled in the art and are commonly used for controlling the operation of mechanical drives or other mechanical equipment accessories of machine units. The invention comprises using any type of PID control. The output quantity of the PID control is limited to the maximum allowable speed of the fan motor and/or the fan impeller. 
     In an especially preferred embodiment, the liquid-air cooling system is combined onto a compact unit with a minimized required assembly space comprising a fluid tank, a motor for powering a fluid pump, the fluid pump itself and the fan motor plus the fan impeller and any associated cooling apparatus as well as a cooler housing. Especially preferably, the motor for powering the fluid pump is mounted directly on the fluid tank. 
     For expediency, the geometric dimensions of the aforementioned components of the liquid-air cooling system are selected in such a manner that the fan device and the motor for powering the fluid pump essentially do not extend beyond a base area of the fluid tank. 
     The fluid can be, for example, transmission oil or hydraulic oil, or also a mixture of water and glycol. 
     With the liquid-air cooling system, very exact temperature-control tasks can be carried out on a machine tool, transmission, extruder, motor, frequency converter or on other types of machine units. Using a minimum of energy, a permanent, relative to temperature fluctuations or a temperature-controlled machine unit, exact operation of a corresponding machine unit can be achieved. Using the liquid-air cooling system, a bed of a machine unit or a singular machine component, such as a spindle of the machine unit, can be supplied with fluid, particularly a temperature-control fluid. 
     Other objects, advantages and salient features of the present invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring to the drawings that form a part of this disclosure and that are not drawn to scale: 
         FIG. 1  is a perspective view of a liquid-air cooling system according to an exemplary embodiment of the invention; 
         FIG. 2  is a top plan view of the liquid-air cooling system of  FIG. 1 ; 
         FIG. 3  is a schematic circuit diagram of the liquid-air cooling system of  FIG. 1 ; 
         FIG. 4   a  is a graph of an example of the heat output from a machine unit that is supplied to the liquid-air cooling system; 
         FIG. 4   b  is a superimposed curve diagram showing the developments over time of the temperature of the fluid before entering in the machine unit, the temperature of the fluid downstream of the pump outlet, the fluid volume flow V, and the air ambient temperature of the hydraulic power pack; 
         FIG. 4   c  is a superimposed curve diagram showing the developments over time of the motor current of the fan motor, measured in Amperes, and the provided motor power of the fan motor, measured in kilowatts; and 
         FIG. 4   d  is a graph showing the development over time of the speed of the fan motor. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a perspective view and partially exploded diagram of a liquid-air cooling system  1  that supplies a machine unit  9  and/or a component  11  of a machine unit  9 , shown schematically, with a fluid  5 , which fluid is envisioned as a temperature-control fluid. Associated with the liquid-air cooling system  1  is a fan device  2  that includes a variable-speed fan motor  3 , embodied as an electric motor  12 , that powers a fan impeller  4  with individual fan vanes in the manner of an axial fan. The fan impeller  4  is partially received by a fan impeller housing  22  and protective grate  17 . The fan impeller housing  22  can be made of plastic or sheet metal parts. As also seen in  FIG. 2  in a top view of the liquid-air cooling system of  FIG. 1 , a protective grate  18  is provided in the rear section of the fan impeller  4  for safety reasons. On the opposite side of the fan impeller  4 , a heat exchanger  19  in the form of a cellular radiator is disposed in relation to the protective grate  18 . The heat exchanger  19  extends across the totality of the projection area swept by the fan impeller  4 . 
     As shown in  FIG. 1 , the fan impeller  4  sucks ambient air from right to left through the ribs of the cellular radiator and toward the fan motor  3 . In principle, the presently shown fan device  2  can also be designed and operated with the cooling air in the opposite direction of flow. The fan impeller housing  22  is designed as a box mounted vertically on a fluid tank  13 . The fluid tank  13  is essentially formed as a block-shaped component. The cross-section of the fluid tank  13  has an L-shape, as shown in  FIG. 1 , such that an assembly base  20  for a motor  15  is elevated above the remainder of the cross-section of the fluid tank  13  and is formed for a motor  15  of a fluid pump  14  located inside the fluid tank  13 . The distributor rail  7  is disposed on the fan impeller housing  22 . A sensor  28  for detecting the actual temperature Ta is disposed in the fluid connection of the heat exchanger  19  between the cellular radiator  19  and the fluid tank  13 . The control system  24  is disposed on the motor  3 . The sensor for detecting the desired temperature  10  is disposed in the direction of flow upstream of the cellular radiator  19  and protected against direct air flow. The total fan device  2  and the motor  15  for powering the fluid pump  14  extend only negligibly beyond a base area  16  of the fluid tank  13 . The desired temperature can additionally or alternately also be measured directly on the machine unit that is in operation by a corresponding sensor. 
     A motor control unit  24  is mounted directly on the top side of the fan motor  3 , or the outside area thereof provided with cooling ribs, respectively. Resulting is an integrated cable connection between the motor control unit  24  and the fan motor  3 . This structural measure avoids electromagnetic interference fields during the operation of the fan motor  3  and increases the EMV tolerance of the hydraulic power pack  1 . The motor control unit  24  includes, in particular, a frequency converter that is parameterized individually in the presently shown embodiment by a separate operating unit and can be connected by a cable plug-in connection that is adjustable for the respective application of the fan motor  3 . 
     The fluid pump  14  conveys a temperature-control fluid in the presently shown embodiment, preferably a water-glycol mixture, and is embodied as an immersion pump. The fluid pump  14  therein can basically be designed, in terms of the construction type, more for a large volume flow or more for a correspondingly high pressure level of fluid  5  in a liquid-air cooling system circuit  6  for the machine unit  9 . The construction type of the fluid pump  14  can be, for example, a rotary pump or a pump with displacement elements like, for example, a roller pump or a rotary vane-type pump or a gear-type pump. Pump parts of the fluid pump  14  extend from and into the fluid tank  13  for the removal of fluid, not shown in further detail. In particular, the fluid pump  14  has a pump opening  25  for removing the fluid  5  from the fluid tank  13 . After the fluid  5  has run through the machine unit  9  or also a component  11  of the machine unit  9 , it is routed into the cellular radiator  19  via connection K. Cooled fluid  5  leaves the heat exchanger  19  directly via the actual value sensor and pipes  26  in the fluid tank  13 . 
     The temperature difference that is adjusted in the present embodiment is &gt;5° Kelvin. A PID controller  27  in the motor control unit  24  serves particularly as a speed controller for the fan motor  3 . The distributor rail  7 , the motor control unit  24  as well as the PID controller  27  can also be combined into an automatic control system (not shown). 
       FIGS. 4   a  to  4   d  show logs of relevant operational parameters during the operation of the liquid-air cooling system  1  and of the machine unit  9  that is cooled by the same. For example,  FIG. 4   a  shows the heat output that is supplied by the machine unit  9  to the liquid-air cooling system  1  via the fluid  5  heated inside the machine unit  9  over a time interval from 0 to 6000 seconds. The supplied heat output fluctuates during this time interval between approximately 0.8 to 6.3 kW. During normal operation (time interval between 1000 seconds and 4,500 seconds), the supplied heat output fluctuates in the presently shown embodiment between 2.5 and 6.3 kW. 
       FIG. 4   b  shows relevant temperature developments on the liquid-air cooling system plotted over the same time interval. The top curve in  FIG. 4   b  shows an embodiment of the temperature development of the temperature of fluid  5  at the inlet of the liquid-air cooling system  1 , meaning after it has left the machine unit  9  and prior to flowing into the heat exchanger  19 . The desired default value as depicted in the embodiment by the mentioned temperature fluctuates between approximately 28 and 32° C. 
     Below the top curve in  FIG. 4   b  is a curve of the fluid temperature of the fluid  5  after leaving the liquid-air cooling system  1  and after the cooling operation. This curve shows that the output temperature of the fluid  5  almost does not fluctuate at all after an adjustment process during a time interval of approximately 250 to 600 seconds, after which the temperature adjusts itself to approximately 27.8° C. 
     Below these mentioned temperature courses,  FIG. 4   b  depicts a volume flow V of the fluid  5  in the liquid-air cooling system  1  during the same time interval. The volume flow V is almost exactly 25 l/min. Below this curve,  FIG. 4   b  shows a typical course of a desired default value; presently a temperature Tb of the ambient air of the liquid-air cooling system  1  is shown. During the depicted time interval, the ambient air temperature fluctuates between 21 and 23° C. Correspondingly, with the liquid-air cooling system  1 , very exact temperature management of the components  11  of a machine unit  9 , for example in form of a machine tool spindle drive or a total machine unit  9 , such as a processing center or a machine tool, has become possible. The liquid-air cooling system  1  according to the invention is therefore able to provide for a marked improvement of the machine&#39;s accuracy during processing. 
       FIG. 4   c  depicts, in the top curve, the course that the motor current of the fan motor  3  takes, while the bottom curve represents the course of the motor output of the liquid-air system of the fan motor  3 . In the depicted embodiment, the motor current fluctuates between approximately 1.2 and 2.2 Ampere, while the recorded motor output is between approximately 0 and 400 Watt. 
       FIG. 4   d  is a representation of the speed fluctuation of the fan impeller  4  that is necessary to be able to depict the exact output temperature of fluid  5 , as shown in  FIG. 4   b , after exiting the heat exchanger  19 . The speed of the fan impeller  4  therein fluctuates in a relatively wide range between approximately 200 and almost 1000 revolutions/min. The selected speed and/or speed range is also documented, such that the hydraulic power pack  1  is quite able to ensure, owing to comparatively minimal blade tip speeds of the fan blades, a minimal noise level during operation. 
     While one embodiment has been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in the appended claims.