Patent Publication Number: US-2009230791-A1

Title: Drive unit having optimized cooling

Description:
The invention concerns an electric drive unit with at least one steering motor and a drive motor arranged co-axially therewith, according to the preambles of claim  1  and claim  6 . 
     Conveyor trolleys have known drive units in which a wheel of the vehicle is driven by a drive motor and steered by a steering motor. 
     One such is described in DE 199 49 351 A1, which discloses an electric drive unit for a conveyor trolley in which a drive motor and a steering motor are arranged co-axially and both these electric motors are mounted vertically in the vehicle. A reduction transmission is arranged between the drive motor and the steering motor. 
     DE 103 28 651 A1 shows an electric drive unit in which, likewise, a drive motor and a steering motor are arranged co-axially and mounted vertically in the vehicle. The drive motor is directly above the steering motor. 
     In the known drive units, the electronic units of the drives are fixed on the outside of the housing of the drive unit. This allows the heat produced to be dissipated easily. If the electronic units are integrated on or in the drive unit, a reliable heat reduction must be ensured. 
     The purpose of the present invention is to provide a compactly built drive unit which enables good dissipation of heat. 
     This objective is achieved with a drive unit having the characteristics of claims  1  and  6 . 
     According to the invention, the objective is achieved by an electric drive unit comprising a steering motor and a drive motor arranged co-axially with one another. The steering motor drives a wheel of the vehicle in a steering movement and the drive motor drives the vehicle wheel in a propulsion movement. The first of the two motors has a hollow drive shaft through which passes a second drive shaft of the second motor. The second drive shaft continues on to project through a first axial outer wall of the drive unit. This axial outer wall is in the axial direction on the side opposite to the drive wheel and separates the entire drive unit from its external surroundings. Outside the said outer wall the second drive shaft is connected in a rotationally fixed manner to a fan impeller. The fan impeller blows air in the radial direction along the first outer wall and enables effective cooling of the drive unit. 
     In one embodiment, the first outer wall is provided on its outside with cooling fins, along which the air blown by the fan flows. This improves the cooling of the drive unit. Advantageously, the cooling fins extend in a radial direction. 
     According to a another embodiment, the drive unit has a second outer wall which forms a cooling channel with the first outer wall. The air blown by the fan impeller moves radially outward through this cooling channel. To enable cooling air to access the fan impeller, the second outer wall has an aperture in an axial direction. Advantageously, the second outerwall too has cooling fins. In addition, components of the electronic units of the two drive motors can be attached on the inside and/or outside of the first and/or second outer wall. By positioning the electronic units close to the air-cooled, cooling fins, cooling of the drive unit is improved still further. In one embodiment, cooling fins can even be made integrally with the first and/or second outer wall. 
     In a further embodiment, on the second outer wall, as viewed in a radial direction, a deflector is provided on the outside, which deflects the air blown in the radial direction so that it flows along the outside of the radial outer wall. 
     Another embodiment of the drive unit again comprises a steering motor and a drive motor arranged co-axially with one another. The steering motor drives a wheel of the vehicle in a steering movement and the drive motor drives the vehicle wheel in a propulsion movement. A first one of the two motors has a hollow drive shaft through which a second drive shaft of the second motor passes. A second fan impeller is attached to the rotor of the second motor. Advantageously, this fan impeller blows air around the stator of the second motor. For this, a second cooling channel is formed in the radial outer wall, through which the air blown by the second fan impeller is blown, in an axial direction, onto the outside of the second motor. 
     According to another embodiment, the drive housing is connected by way of an axial bearing to a vehicle frame. The space between the outer ring of the bearing and the vehicle frame is advantageously filled with a heat-conducting material to improve the dissipation of heat from the housing of the drive unit by heat conduction into the vehicle frame. 
     In a further embodiment, the outer ring of the bearing is designed to promote high heat conduction. The inner ring of the bearing is formed so that the bearing has a specified service life. In the design of the outer ring, the heat transfer by conduction, between the housing of the drive unit and the outer ring and between the outer ring and the vehicle frame, is also taken into account. The larger the two contact surfaces are the more heat can be transferred by conduction. The size of the contact surfaces depends on the radial overlap and thus on the radial width of the outer ring. 
     In one embodiment, a vehicle brake is arranged between the second motor and the first axial outer wall. Advantageously, the first motor is the steering motor and the second motor is the propulsion motor. 
     According to a further embodiment, another electronic control unit is arranged under the first motor and is directly connected to the first motor. 
    
    
     
       To explain the invention and its embodiments more clearly the description of a drawing is given below. The drawing shows: 
         FIG. 1  is a structure of a drive unit, and 
         FIG. 2  is a mounting of the drive unit in the vehicle frame 
     
    
    
       FIG. 1  shows an electric drive unit with a steering motor  1  and a drive motor  4  arranged co-axially with one another and having respective stators  28 ,  16  and rotors  29 ,  14 . The drive unit has a rotation axis D. A first drive shaft  2  is made hollow. Through the first drive shaft  2  passes a second drive shaft  3 . The second drive shaft  3  also extends through a braking device  26  and through a first axial outer wall  5  and on its outer side  6  is connected rotationally fixed to a fan impeller  7 . The braking device is located in the axial direction between the propulsion motor  4  and the first outer wall  5 . Components of an electronic unit  11  are attached directly on the first outer wall  5 . A second axial outer wall  9  is arranged so that together with the first outer wall  5 , it forms a cooling channel  10 . Cooling fins  8 ,  27  extending radially, are attached on the two outer walls  5 ,  9 . Also attached on the second axial outer wall  9  are components  11  of the electronic unit. The components  11  of the electronic unit may be for example an electronic power circuit and/or an electronic signal circuit of the drive motor  4  and/or an electronic signal circuit of the steering motor  1 . The electronic unit also is made integrally with one of the two outer walls  5 ,  9 . When the drive motor  4  is rotating, the fan impeller  7  is driven so as to blow air in a radial direction through the cooling channel  10 . To enable the fan impeller  7  to blow air, the second outer wall  9  has an axial aperture  26 . Particularly effective cooling is enabled by the arrangement of the components  11  of an electronic unit on the first and second outer walls  5 ,  9 . 
     Onto the second outer wall  9  is attached a deflector  12 . Thanks to this deflector  12 , the air blown in a radial direction is deflected so that, after deflection, it flows in an axial direction along a housing  19  of the drive unit. A radially outer wall  13  is also provided with further cooling fins  18  arranged axially. An electronic unit  24  is fixed directly under the two motors  1 ,  4 , nested one inside the other, and is also provided with cooling fins  25  on its radially outer side. The electronic unit  24  contains at least part of the electronic circuitry for the steering motor  1 . The housing  19  of the drive unit is mounted in a vehicle frame  21 , via a bearing  20 . 
     On its lower side, the rotor  14  of the propulsion motor  4  is provided with a second fan impeller  15 . This second fan impeller  15  blows the air in the inside space of the housing of the drive motor  4  so that it flows around the stator  16 . For this, a cooling channel  17  is formed in the radially outer wall  13 , through which the blown air can flow in an axial direction over the propulsion motor  4 . 
     To clarify the invention, the direction  30 ,  31  of air flow blown by the fan impellers  7 ,  15  are shown in the drawing. A direction  32  of the improved heat transfer out of the housing  19  of the drive unit is also indicated. It can also be seen that the electronic unit  24  and the steering motor  1  are thermally decoupled. Furthermore, the thickness of an outer wall  33  of the steering motor is increased so as to improve heat conduction. 
       FIG. 2  shows a mounting of the housing  19  of the drive unit in a vehicle frame  21 . A radial width  36  of an inner ring  39  is designed at least so that the bearing  20  reaches a specified lifetime and is substantially smaller than a radial width  37  of an outer ring. The housing  19  rests on the outer ring  22  of the bearing  20  and is advantageously connected in a rotationally fixed manner thereto by a screw joint. 
     The radial width  37  of the outer ring  22  is wider than necessary for the attainment of the aforesaid service life. This allows large radial overlaps  35 ,  34  to be formed between the housing  19  and the outer ring  22  and between the outer ring  22  and the vehicle frame  21 . The large contact areas, between the housing  19 , the outer ring  22  and the vehicle frame  21 , ensure high heat conduction. The radial width  37  of the outer ring  22  is chosen such that the bearing  20  does not exceed a certain first temperature level. This first temperature level is the temperature at which the lubricant of the bearing  20  would be degraded and perhaps leak out of the bearing  20 . As a further design feature the radial width  37  is designed so that the first motor  1 , with its associated electronic unit  24 , do not exceed a specified second temperature level. Advantageously as a further embodiment, the higher of the two temperature levels is taken into account for the design of the outer ring  22 . The radial width  37  of the outer ring  22  is substantially larger than the radial width  36  of the inner ring  38 . Advantageously, the radial width  37  of the outer ring  20  is more than twice as large as the radial width  36  of the inner ring  38 . 
     REFERENCE NUMERALS 
     
         
           1  first motor 
           2  first drive shaft 
           3  second drive shaft 
           4  second motor 
           5  first axial outer wall 
           6  outer side 
           7  first fan impeller 
           8  cooling fins 
           9  second axial outer wall 
           10  first cooling channel 
           11  components of an electronic unit 
           12  deflector 
           13  radially outer wall 
           14  rotor 
           15  fan impeller 
           16  stator 
           17  second cooling channel 
           18  cooling fins 
           19  housing 
           20  bearing 
           21  vehicle frame 
           22  outer ring of the bearing 
           23  heat-conducting material 
           24  electronic unit 
           25  cooling fins 
           26  aperture 
           27  cooling fins 
           28  stator 
           29  rotor 
           30  flow direction 
           31  flow direction 
           32  flow direction 
           33  outer wall 
           34  radial overlap 
           35  radial overlap 
           36  radial width 
           37  radial width 
           38  inner ring 
         D rotation axis