Patent Publication Number: US-2010122673-A1

Title: Drive unit for a fan and arrangement with  a drive unit

Description:
This application claims the benefit under 35 USC §119(a)-(d) of German Application Nos. 10 2008 058 377.4 filed Nov. 20, 2008 and 10 2009 011 347.9 filed Mar. 5, 2009, the entireties of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The invention relates to a drive unit for a fan and an arrangement with a drive unit. 
     BACKGROUND OF THE INVENTION 
     Fan systems or cooling systems and arrangements with such systems are known in vehicles, in particular in motor vehicles with internal combustion engines. In contemporary systems, in particular, multi-stage electromagnetic clutches or what are referred to as viscous clutches are installed. In such cases, a considerable loss of power may occur in a low rotational speed range of a fan of the cooling system via a system which is continuously subject to slip. Viscous clutches can ensure, in particular, free setting of the rotational speed of the fan drive as long as a power loss does not exceed certain operating limits. In this context, power losses of several kilowatts which depend on the parameters of the fan torque and differential rotational speed of the coupled rotating elements can be produced. Disadvantages are found to occur with viscous clutches in particular in a cold start phase or in the case of deactivation. 
     If multi-stage electromagnetic clutches are used for operating a fan, said fan can be deactivated completely. There is no permanent slip in the switched-on state. However, control can be carried out only to a limited degree with electromagnetic clutches. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to make available a drive of a cooling system for a vehicle having an internal combustion engine, which drive can advantageously be adapted to the operating states which are relevant in practice, in particular while avoiding the disadvantages which have occurred hitherto with drive systems of the generic type. 
     The invention is based firstly on a drive unit for a fan of an internal combustion engine of a vehicle, having a friction clutch which can be shifted in order to drive the fan via the internal combustion engine. The core of the drive unit according to the invention is that an electric motor is also provided for driving the fan, and that a torque-transmission path is formed between the friction clutch and the fan by means of a rotatably mounted part of the electric motor. The electric motor has, in particular, a stator and a rotor which can rotate in relation to one another. 
     The invention permits a drive unit to be obtained which is advantageous in terms of improved control and comfortable adaptation of the fan power in the low power range by means of a desired or settable fan rotational speed. In addition, relatively high or maximum fan power levels can be implemented for selected operating states, for example. 
     The drive unit according to the invention combines, in particular, the advantages of a viscous clutch and the advantages of a multi-stage friction clutch, for example of an electromagnetically actuable frictionally engaging clutch. With the proposed drive unit it is possible to implement a free rotational speed setting as long as the power loss does not exceed its operating limits. Furthermore, the drive effect on the impeller wheel can be completely deactivated or switched on without permanent slip. A direct drive by a drive shaft to the impeller wheel or an impeller wheel hub is possible 1:1. Overall, the drive according to the invention is advantageous, in particular, for utility vehicles. 
     In particular, in the case of hybrid vehicles which generally have, for example, an on-board electrical voltage range to above 400 volts, an electric motor with an electrical power level of approximately 5 kW can be made available without problems. With the electric motor which can be switched on and off it is possible to implement a first operating state according to which the impeller wheel is not driven, and also a second operating state with control as far as approximately 5 kW. 
     In practice, power peaks which occur cannot, however, be appropriately covered in terms of the radiator power or fan power with an electric motor which can reasonably be used in the vehicle, since the sizes of electric motor which are necessary for this purpose are uneconomical or the installation situation is impractical due to complex cabling. 
     Power peaks can therefore be covered according to the invention by means of a simple friction clutch, in particular, for example, an electromagnetic clutch. 
     The invention therefore allows, in particular, for the fact that, for example, for utility vehicles, in practice cooling of the cooling system generally occurs as a result of the relative wind for 80% of the time of use. The fan power of a maximum of approximately 5 kW is required for approximately 18% of the operating time. Only in 2% of the operating time is a relatively high to maximum fan power level required. These operating states can be advantageously covered with the drive unit according to the invention. It is also advantageous that, even when the internal combustion engine is stationary, a cooling power level of a maximum of 5 kW is possible by means of the electric motor. 
     It is also advantageous that the friction clutch is designed to permit direct drive of the fan by the internal combustion engine. 
     The friction clutch can advantageously be embodied as an electromagnetically actuable friction face clutch, for example, as a friction disk clutch. A slip-free connection of a motor-side drive shaft and of a fan-side fan shaft can therefore be made possible in a non-positively or frictionally locking fashion. 
     Furthermore, it is advantageous that a rotationally flexible clutch is provided for driving the fan by the internal combustion engine. The fan can be driven, for example, at a rotational speed which is relatively low with respect to the rotational speed of the internal combustion engine by means of the rotationally flexible clutch. It is thus basically possible to provide a drive of the impeller wheel which is subject to slip in addition to or instead of the direct drive. A torque-dependent overload protection can be implemented by means of the rotationally flexible clutch, and this can be advantageous in certain applications. For example, an eddy current clutch is possible as a rotationally flexible clutch. 
     In addition, it is possible that, in the installed state, the friction clutch and the electric motor do not extend, or only extend insignificantly, over a diameter of an impeller wheel hub of the fan in a radial direction. It is therefore possible to implement a particularly compact design of the drive unit. In particular, installation space which is necessary in any case in the radial direction, in particular with respect to an axis about which the fan or an impeller wheel can rotate during operation, can be used, which easily permits integration or retrofitting of the drive unit according to the invention for existing assemblies. 
     It is also advantageous that the electric motor has a housing to which the fan is attached. It is therefore possible to implement a particularly stable and space-saving arrangement. In particular, no intermediate connecting parts are necessary between the electric motor and the fan. The fan itself can also be embodied as in previous systems. 
     In one particularly advantageous modification of the subject matter of the invention, the friction clutch and the electric motor are combined to form one structural unit. This facilitates the installation or disinstallation of the drive unit. Furthermore, the entire drive with the drive unit can therefore be configured in a compact fashion. Furthermore, the parts of the friction clutch and of the electric motor can, if appropriate, be accommodated in a protected fashion in a common housing. 
     The friction clutch and the electric motor are advantageously connected to form one unit, which is advantageous in terms of optimum utilization of space. 
     The invention also relates to an arrangement for cooling an internal combustion engine having a radiator for cooling the internal combustion engine, and a fan which interacts with the radiator, wherein a drive unit for the fan is present in accordance with the details explained above. The cooling arrangement for the internal combustion engine can therefore be embodied in accordance with the advantages specified above. 
     The drive unit preferably comprises a friction clutch and an electric motor which are combined to form one structural unit, wherein the structural unit is connected to the radiator. The fan generates an air current which is conducted past faces of the radiator in order to effectively bring about a transmission of heat from areas of the radiator to the air flowing around. 
     Moreover, it is advantageous that the drive unit comprises a friction clutch and an electric motor which are embodied separately. This permits advantageous installation, disinstallation and utilization of an existing installation space. 
     Furthermore, it is possible that the friction clutch can be arranged on the internal combustion engine. This can be advantageous depending on the application or prevailing installation conditions. 
     Finally, it is also advantageous that the electric motor is attached to the radiator, in particular the entire drive unit composed of the clutch and electric motor. This may be advantageous in terms of a compact design of the drive unit or for reasons of installation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages and features of the invention will be explained in more detail with reference to three exemplary embodiments of the invention which are illustrated in a highly schematic form. 
         FIG. 1  shows a schematic view of a drive unit according to the invention which is attached on the radiator side; 
         FIG. 2  shows an alternative drive unit according to the invention which is arranged on the motor side; and 
         FIG. 3  shows a third inventive embodiment variant of a drive unit, with an electric motor being arranged on the radiator and a friction clutch being arranged on the motor. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a highly schematic view—which omits components—of a drive unit  1  according to the invention in the installed state, for example, in a vehicle with an internal combustion engine  3 , for example a diesel engine, with the internal combustion engine  3  being only shown in block form. The drive unit  1  is to be understood as being the part of the drive for an impeller wheel  2 , and in this context the drive unit  1  does not include the internal combustion engine  3  itself. 
     The drive shaft  4  is connected to the drive unit  1  via a flange  4   a  of a drive shaft  4  (shown only partially) of the internal combustion engine  3 . 
     The impeller wheel  2  (illustrated only partially or in a hub region) is accommodated on a central impeller wheel hub  2   a  which is connected in a rotationally fixed fashion to a fan shaft  5  via which the impeller wheel  2  can be driven in rotation. The fan shaft  5  is embodied over its main longitudinal extent as part of an electric motor  6  and forms a rotor  8  of the electric motor  6 . The rotor  8  is surrounded by a stator  7  of the electric motor  6 . The stator  7  is attached in a positionally fixed fashion to a radiator section  9  and to a vehicle frame (not illustrated) via the radiator section  9 . The stator  7  is supported with respect to the rotating rotor  8  by means of bearings  10  and  11 , for example roller bearings. 
     A friction clutch  12  is provided between a drive flange  17  connected in a rotationally fixed fashion to the flange  4   a , and the electric motor  6 , on that side of said electric motor  6  which faces toward the internal combustion engine  3 . The friction clutch  12  is embodied as an electromagnetically actuable friction disk clutch. For this purpose, an electromagnet arrangement  13  with a positionally fixed electromagnet  14  is provided, the electromagnet  14  generating magnetic forces as a result of energization of the electromagnet arrangement  13 , as a result of which an armature disk  15 , which can be moved axially with respect to the fan shaft  5  in a resettable fashion, is attracted to a friction ring section  16  that is rotationally fixed to fan shaft  5 . In this way, it is possible to establish a coupling connection for a maximum cooling power in the case of power peaks of the radiator, and as a result also of the fan  2  with a direct transmission of rotational speed taking place from the drive shaft  4  to the fan shaft  5 , and therefore to the fan  2 , via the drive flange  17  and the friction ring section  16 . 
     The drive flange  17  is rotatably mounted on the fan shaft  5  by means of a bearing  18 , at the axial end of the fan shaft  5  which is directed toward the internal combustion engine  3 . When the electromagnet arrangement  13  is not energized, the armature disk  15  is separated from the friction ring section  16  by resettable spring means, for example by means of a spring ring  19 , as a result of which no drive connection is produced between the drive shaft  4  and the fan shaft  5 . 
     However, in this state, the drive unit  1  can drive the fan via the electric motor  6  if a comparatively low cooling power is required for the radiator (not illustrated). The fan  2  can be operated in an infinitely variable fashion, for example to approximately 5 kW power via the controllable electric motor  6 . Unless current is applied to the electric motor  6  and the electromagnet arrangement  13 , the impeller wheel remains stationary or does not experience any motor drive effect. 
     The drive unit  1  with the electric motor  6  and the friction clutch  12  can advantageously extend in the radial direction with respect to the rotational axis S of the fan shaft  5  over a region a which is almost completely in the diameter region of the impeller wheel hub  2   a  according to  FIG. 1 . According to the exemplary embodiments in  FIG. 2  and  FIG. 3 , a drive unit according to the invention can also be located completely within the radial extent of an impeller wheel hub. 
     It is also advantageous that the drive unit  1  can, for example, be fixedly arranged with the drive flange  17  on the radiator section  9 . Vibrations or oscillations which occur during operation of the internal combustion engine  3  are therefore not transmitted to the impeller wheel  2 . A circumferentially extending gap (not illustrated) which is present radially on the outside of the impeller wheel  2 , with respect to the adjoining sections, for example an air guiding ring on the radiator, can therefore be selected to have the minimum size, if appropriate in the millimeter range. Disruptive air eddying formations at the radial outer edge of the impeller wheel  2  can therefore be advantageously avoided or minimized. If a drive unit were to be mounted on the internal combustion engine  3 , a significantly larger size would have to be disadvantageously selected for this gap in order to prevent contact between the impeller wheel and air guiding ring means. This has a negative effect on the formation of flow by the impeller wheel. 
     An alternative arrangement according to the invention with a drive unit  20  is shown in  FIG. 2 . Said arrangement likewise serves to drive an impeller wheel  21  on an impeller wheel hub  21   a . Furthermore, an internal combustion engine  22  for driving the impeller wheel  21  is present. An electric motor  23  of the drive unit  20  for a drive operation of the impeller wheel  21  which can be controlled in an infinitely variable fashion is present spatially between the internal combustion engine  22  and the impeller wheel  21 . The electric motor  23  comprises a rotor  24  which is fixedly connected to the impeller wheel hub  21   a  and which is mounted by means of bearings  21  and  26  with respect to a stator  27  which is arranged in a positionally fixed fashion on the internal combustion engine  22 . The cylindrical stator  27  therefore has a gap with respect to the impeller wheel hub  21   a  on the fan-side end of said stator  27 . 
     Furthermore a friction clutch  28  is present between the internal combustion engine  22  and the electric motor  23 . The friction clutch  28  comprises an electromagnet arrangement  29  with an electromagnet  30 , by means of which, when the electromagnet  30  is energized, an axially displaceable armature disk  31  can be connected to a section  33   a  of a belt pulley  33  in a frictionally or non-positively locking fashion via spring means, for example a spring ring  32 , which can be displaced in the axial direction with respect to the rotor  24 . The belt pulley  33  is rotatably mounted on the stator  27  by means of a roller bearing  34  and can be driven in rotation by the internal combustion engine  22  by means of belts (not illustrated). For this purpose, a belt support section  33   b  is present on the outer circumference of the belt pulley  33 . 
     When the electric motor  23  is operating, the impeller wheel hub  21   a  and therefore the impeller wheel  21 , are made to rotate in a regulated, infinitely variable fashion, by rotating the rotor  24  with said electric motor  23 . 
     When the electric motor  23  and the electromagnet arrangement  29  are not energized, the impeller wheel  21  is not driven in rotation. If only the electromagnet arrangement  29  is energized when the electric motor  23  is not being operated, the rotor  24  which runs on the outside and therefore also the impeller wheel  21 , are driven directly via the shifted friction clutch  28  via the belt pulley  33  and the engaged friction clutch  28 . 
     In the arrangement of the inventive drive unit  20  shown in  FIG. 2 , the electric motor  23  and the friction clutch  28  are embodied as a structural unit which is positioned between the impeller wheel  21  and the internal combustion engine  22 . 
     A further arrangement of an inventive drive unit  34  is shown in  FIG. 3 . According to this embodiment, the drive unit  34  is divided into two units. A first unit is formed by the electric motor  35 , which is held fixedly connected by its stator  36  to a radiator section  38 . The stator  36  is mounted, by means of bearings  39  and  40  on the rotor  37  which rotates together with an impeller wheel hub  41   a . An impeller wheel  41  is secured to the impeller wheel hub  41   a . The rotor  37  forms part of an impeller wheel shaft  42 . The impeller wheel shaft  42 , which is illustrated in an interrupted fashion in  FIG. 3 , can be connected in a rotationally fixed fashion to a drive shaft (not shown) of an internal combustion engine  43  via a friction clutch  44 , and can be disconnected from a drive effect of a drive shaft by means of the friction clutch  44 . The friction clutch  44  is only illustrated in a highly schematic fashion or in a box form. The friction clutch  44  can be embodied, in particular, in the form of an electromagnetic clutch which can be shifted. 
     LIST OF REFERENCE NUMERALS 
     
         
           1  Drive unit 
           2  Impeller wheel 
           2   a  Impeller wheel hub 
           3  Internal combustion engine 
           4  Drive shaft 
           4   a  Flange 
           5  Fan shaft 
           6  Electric motor 
           7  Stator 
           8  Rotor 
           9  Radiator section 
           10  Bearing 
           11  Bearing 
           12  Friction clutch 
           13  Electromagnet arrangement 
           14  Electromagnet 
           15  Armature disk 
           16  Friction ring section 
           17  Drive flange 
           18  Bearing 
           19  Spring ring 
           20  Drive unit 
           21  Impeller wheel 
           22  Internal combustion engine 
           23  Electric motor 
           24  Rotor 
           25  Bearing 
           26  Bearing 
           27  Stator 
           28  Friction clutch 
           29  Electromagnet arrangement 
           30  Electromagnet 
           31  Armature disk 
           32  Spring ring 
           33  Belt pulley 
           33   a  Section 
           33   b  Belt support section 
           34  Drive unit 
           35  Electric motor 
           36  Stator 
           37  Rotor 
           38  Radiator section 
           39  Bearing 
           40  Bearing 
           41  Impeller wheel 
           41   a  Impeller wheel hub 
           42  Impeller wheel shaft 
           43  Internal combustion engine 
           44  Friction clutch