Patent Publication Number: US-2020300355-A1

Title: Lubrication system for a planetary gear

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a national stage application (filed under 35 § U.S.C. 371) of PCT/SE2018/050951, filed Sep. 18, 2018 of the same title, which, in turn, claims priority to Swedish Application No. 1751272-4 filed Oct. 13, 2017; the contents of each of which are hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a lubrication system for a planetary gear, a powertrain comprising a lubrication system and a vehicle comprising a powertrain. 
     BACKGROUND OF THE INVENTION 
     A planetary gear comprises a sun gear, a ring gear and a number of planet gears supported by a planet gear carrier. The planetary gear may be used in a powertrain for a vehicle. The sun gear is rotationally fixedly arranged on an inlet shaft and the planet gear carrier is rotationally fixedly arranged on an outlet shaft coaxially arranged with the inlet shaft. The components of the planetary gear may be lubricated and cooled by a lubrication system supplying lubricant via a lubrication channel in one of the shafts to a lubrication passage in the planet gear carrier. During operation, the lubricant is forced radially outwardly through the lubrication passage by means of the rotation of the planet gear carrier. The lubrication passage delivers lubricant to the sun gear and to the planet gear bearings, which are arranged radially outside the sun gear. During certain operating conditions, the rotational speed of the planet gear carrier is relatively low. In these cases, there may be a risk that the speed is not high enough to provide enough lubricant all the way radially outwardly to the planet gear bearings which may cause the sun gear to get to much lubricant and the bearings to little lubricant. During other operating conditions, the rotational speed of the planet gear carrier is relatively high. In these cases, the lubricant is forced radially outwardly to the planet gear bearings with a significantly higher force, which may cause the sun gear to get to little lubricant and the bearings to much lubricant. Due to the variation of the rotational speed of the planet gear carrier a pumping effect may occur in the lubrication passage which may cause an imbalance of the intended lubricant distribution between the sun gear and the planet gear bearings. Improvements in the field of lubricating planetary gears are therefore desirable. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to address and at least alleviate the above-mentioned problem. A further object is to reduce the pumping effect in a lubrication passage. Another object is to ensure a required lubricant flow to a sun gear and to planet gear bearings during different operating condition. 
     In accordance with the present invention, there is provided a lubrication system for a planetary gear comprising a sun gear rotationally fixedly arranged on a first shaft, a number of planet gears rotatably supported by planet gear bearings and a planet gear carrier rotationally fixedly arranged on a second shaft. The lubrication system comprises a lubrication passage adapted to direct lubricant from one of the shafts to the planet gear bearings. The lubrication passage comprises a first passage part extending through the planet gear carrier from an inlet opening to a first outlet opening. The first passage part comprises a second outlet opening having a center axis and adapted to direct lubricant through a third passage part, having a first cross-sectional area, to a first engagement area between the sun gear and the planet gears. The second outlet opening is located at a shorter first radial distance from a rotation axis of the sun gear than the first outlet opening. A flow restrictor is arranged in the first passage part. The flow restrictor delimits a gap, having a third cross-sectional area, between an interior surface of the first passage part and the restrictor and comprises at least one restriction having a lubrication inlet end, a lubrication outlet end and a second cross-sectional area. The lubrication inlet end is arranged at a second radial distance from the rotation axis, which is substantially the same as the first radial distance from the rotation axis to the center axis. The position of the flow restrictor defines the proportions of lubricant to be directed from the first passage part to the bearings and the first engagement area so that a predetermined part of the lubricant leaving the first passage part is directed through the first outlet opening and a remaining part of the lubricant is directed through the second outlet opening. This may ensure a required balanced lubricant flow to the first engagement area and to the bearings during different operating conditions and may reduce the pumping effect in the lubrication passage. 
     According to an optional aspect of the invention, the lubrication inlet end is arranged at a second radial distance closer to the rotation axis than the first radial distance of the center axis. Hereby lubricant is allowed to be dependent on the rotation speed of the planet gear carrier in a predetermined manner since the axial position can be selected such that relatively more lubricant will be supplied to the first engagement area than to the bearings at high rotational speeds to compensate for higher losses at the first engagement area than in the bearings. In addition, this may ensure a required balanced lubricant flow to the first engagement area and to the bearings during different operating conditions and may reduce the pumping effect in the lubrication passage. According to some embodiments, the second radial distance is in the range 0.80-0.95 times the first radial distance. This may improve the lubricant flow to the first engagement area and to the bearings during different operating conditions. 
     According to an optional aspect of the invention, the first cross-sectional area is greater than the second cross-sectional area. This may improve the lubricant flow to the first engagement area and to the bearings during different operating conditions. According to some embodiments, the first cross-sectional area is 2.25 times the second cross-sectional area. 
     According to an optional aspect of the invention, the third cross-sectional area is greater than the first cross-sectional area. This may improve the lubricant flow to the first engagement area and to the bearings during different operating conditions. According to some embodiments, the third cross-sectional area is 2 times the first cross-sectional area. 
     According to an optional aspect of the invention, the flow restrictor is bottle-shaped and comprises a body, a neck and a central longitudinal flow path. The restriction is arranged in the flow path. Hereby the flow restrictor may be achieved in a relatively simple manner. At some embodiments, the gap extends around an outer periphery of the neck. This may improve the lubricant flow to the first engagement area when the lubrication inlet end is arranged at a second radial distance closer to the rotation axis than the first radial distance of the center axis. 
     According to an optional aspect of the invention, the flow restrictor is a stand-alone insert adapted to be inserted into the first passage part. Since the flow restrictor is a stand-alone insert shaped and configured to be received within an existing lubricant passage a particular planet gear carrier is not required in order receive improved lubricant distribution characteristics, on the contrary the insert can be installed in already existing planet gear carriers to improve their lubricant distribution characteristics. Further, the insert can easily be manually or automatically inserted and removed from a lubricant passage, which have been fitted with such flow restrictor. Another advantage is that the insert is simple to manufacture, and can be manufactured in large numbers for subsequent installation in any planet gear carrier. 
     In accordance with the present invention there is also provided a powertrain comprising a lubrication system according to what is mentioned above. 
     In accordance with the present invention there is also provided a vehicle comprising a powertrain according to what is mentioned above. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and are intended to provide further explanation of the invention as claimed. Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described in detail with reference to the accompanying drawings in which: 
         FIG. 1  is a schematic view of a vehicle having a planetary gear. 
         FIG. 2  is a schematic perspective view of the planetary gear. 
         FIG. 3  is a cross-sectional view of the planetary gear along a line A-A at  FIG. 2 . 
         FIG. 4  is a locally enlarged view of the planetary gear shown in  FIG. 3 . 
         FIG. 5  is a locally enlarged view of the planetary gear shown in  FIG. 3  showing a flow restrictor according to one embodiment. 
         FIG. 6  is a locally enlarged view of the planetary gear shown in  FIG. 3  showing a flow restrictor according another embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention will now be described with reference to the drawings in which some exemplary embodiment are shown. Well-known functions or constructions will not necessarily be described in detail for brevity and/or clarity. 
       FIG. 1  shows a vehicle  1  having a powertrain  2  in which an internal combustion engine  3  is connected to traction wheels  4  via a gearbox (not shown). At some embodiments the vehicle  1  may be a hybrid vehicle comprising the internal combustion engine  3  and an electrical machine  5  adapted to be powered by at least one battery  6 . The powertrain  2  comprises at least one planetary gear  7  adapted to control, for example, the torque transfer in the powertrain  2 . The planetary gear  7  may be arranged at different positions in the powertrain  2  depending on the actual design of the powertrain  2 . 
       FIGS. 2 and 3  shows that the planetary gear  7  comprises a sun gear  9 , a ring gear  10  and a number of planet gears  11  which are rotatably mounted on a planet gear carrier  12  and adapted to intermesh with the sun gear  9  and ring gear  10 . Further, the planet gears  11  are adapted to revolve around an exterior circumference of the sun gear  9 . The sun gear  9  is rotationally fixedly arranged on a first rotatable shaft  14 , which may be an inlet shaft, and the planet gear carrier  12  is rotationally fixedly arranged on a second rotatable shaft  15 , which may be an outlet shaft. One end of the second shaft  15  extends into an inner space  16  at the end of the first shaft  14  and is supported by a bearing  17  arranged in the inner space  16 . The first shaft  14  and the second shaft  15  are coaxially arranged with each other and rotatable about a common rotation axis  18 . 
     The planet gear carrier  12  comprises hubs  20  adapted to support the respective planet gear  11 . Each planet gear  11  is rotatably arranged on a hub  20  and rotatably supported by means of at least one planet gear bearing  21 . Further, each planet gear  11  comprises planet gear teeth  22  adapted to be engaged with sun gear teeth  23  of the radially inner sun gear  9  and ring gear teeth  24  of the radially outer ring gear  10 . The contact area between the planet gear teeth  22  and the sun gear teeth  23  defines a first engagement area  25 . The contact area between the planet gear teeth  22  and the ring gear teeth  24  defines a second engagement area  26 . 
     The planet gear carrier  12  comprises a locking portion  28  adapted to be engaged by a locking member (not shown). The locking member is rotationally fixedly arranged on the first shaft  14  and is movably arranged in an axial direction in relation to the first shaft  14  between a first operating condition and a second operating condition. In the first operating condition, the locking member is in engagement with the locking portion  28  and the rotational movement of the first shaft  14  is transmitted to the second shaft  15  via the planet gear carrier  12 . In this operating condition, the second shaft  15  and the planet gear carrier  12  rotate at the same rotational speed as the first shaft  14  and the sun gear  9 . In the second operating condition, the locking member is out of engagement with the locking portion  28  and the rotational movement of the first shaft  14  is transmitted to the second shaft  15  via the sun gear  9 , the planet gears  11 , the ring gear  10  and the planet gear carrier  12 . In this operating condition, the ring gear  10  is provided with a torque and the second shaft  15  and the planet gear carrier  12  may achieve a lower rotational speed than the first shaft  14  and the sun gear  9 . At some embodiments, the torque may be provided by the gearbox, which is adapted to control the torque. At some embodiments, when the planetary gear is used to achieve hybrid operation, the ring gear  10  is connected to a rotor in an electrical machine adapted to control the torque. 
     The planetary gear  7  comprises a lubrication system  30 . The lubrication system  30  comprises an elongated axial lubrication channel  31  arranged in a central portion of the second shaft  15  and connected to a lubricant pump (not shown). At some embodiments, the lubrication channel  31  may be arranged in the first shaft  14 . Further, the lubrication system  30  comprises at least one radial lubrication channel  32  adapted to direct lubricant from the axial lubrication channel  31  radially outwardly and out of the second shaft  15 , or where appropriate the first shaft  14 , to a lubrication passage  35  in the planet gear carrier  12  via an outlet opening  33  and an annular space  34 . The lubrication passage  35  is adapted to direct lubricant from one of the shafts  14 ,  15  to the planet gear bearings  21 . The outlet opening  33  and the annular space  34  are arranged in positions radially inwardly of the planet gear carrier  12 . 
     The lubrication passage  35  comprises a first passage part  38  extending through the planet gear carrier  12  and having a radial extension essentially corresponding to the radial extension of the planet gear carrier  12  between an inlet opening  39  arranged at an inner periphery of the planet gear carrier  12  and a first outlet opening  40  arranged at an outer periphery of the planet gear carrier  12  in the vicinity of the hub  20 . Further the first passage part  38  has a second outlet opening  41  arranged in the sidewall of the first passage part  38  between the inlet opening  39  and the first outlet opening  40  in the axial direction of the first passage part  38  and having a center axis  19  ( FIG. 5 ). At some embodiments a lubrication passage  35  is arranged between the axial lubrication channel  31  and each hub  20  i.e. each planet gear  11 . The first passage part  38  may have any cross-sectional shape that suits the particular application. In a preferred embodiment, the cross-sectional shape is circular. 
     During operation, the rotational speed of the planet gear carrier  12  forces the lubricant in the first passage part  38  radially outwardly. The lubricant receives a velocity in an axial direction through the first passage part  38  ensuring that the lubricant leaves the planet gear carrier  12  through the first outlet opening  40  and the second outlet opening  41 . The lubricant leaving the first outlet opening  40  flows substantially radially outwardly through a second passage part  43  of the lubrication passage  35 . The second passage part  43  comprises a first channel  44  comprising a first inlet opening  50  and a first outlet opening  51 , an inner space  45  of the hub  20  and at least one second channel  46  comprising a second inlet opening  52  and a second outlet opening  53 . The first channel  44  is formed in the hub  20  and adapted to direct lubricant radially outwardly from the first passage part  38  to the inner space  45 . The second channel  46  is formed in the hub  20  and adapted to direct lubricant from the inner space  45  to the planetary gear bearings  21 . The planet gears  11  rotates with a low friction on the hub  20  by means of the planet gear bearings  21 . The lubricant distributed by the lubrication passage  35  provides an effective cooling and lubrication of planet gear bearing  21 . 
     The second outlet opening  41  is, with reference to  FIGS. 3, 4 and 5 , adapted to direct lubricant through a third passage part  48 , having a first cross-sectional area A 1 , to the first engagement area  25  between the sun gear  9  and the planet gears  11 . The center axis  19  of the second outlet opening  41  is located at a shorter first radial distance R 1  from a rotation axis  18  of the sun gear  9  than the first outlet opening  40 . The lubricant leaving the second outlet opening  41  flows substantially perpendicular to the lubricant in the first passage part  38  and substantially in the axial direction of the planet gear carrier  12  through the third passage part  48 . The third passage part  48  comprises a third channel  54  comprising a third inlet opening  55  and a third outlet opening  56  at a periphery portion of the sun gear  9 . The periphery portion of the sun gear  9  constitutes the first engagement area  25 , i.e. the contact area between the planet gear teeth  22  and the sun gear teeth  23 . 
     The third passage part  48  is formed in the planet gear carrier  12  and adapted to direct lubricant from the first passage part  38  towards an end surface  58  of the sun gear teeth  23 , or more precisely into spaces between the sun gear teeth  23 . Further, the third channel  54  has the first cross-sectional area A 1  and may be arranged with its center axis  19  in parallel with the common rotation axis  18  and at the first radial distance R 1  from the rotation axis  18 . When the planet gear  11  shown in  FIG. 3  rotates, lubricant is distributed by the rotation from the first engagement area  25  to the second engagement area  26  i.e. to the contact area between the planet gear teeth  22  and the ring gear teeth  24 . The lubricant distributed by the lubrication passage  35  therefore provides an effective cooling and lubrication of the sun gear teeth  23 , the planet gear teeth  22  and the ring gear teeth  24 . 
     At some embodiments, the sun gear teeth  23  may comprise, as best shown in  FIG. 4 , a zone with at least one lubrication-guiding surface  57  adapted to direct lubricant from the third passage part  48  along the sun gear teeth  23 . The lubrication guiding surface  57  forming an angle less than 90 degrees in relation to the rotation axes  18  of the sun gear  9 . At some embodiment, the angle may be less than 45 degrees. At a preferred embodiment, the angle may be 40 degrees. A lubrication-guiding surface  57  may be formed at the end of each sun gear tooth  23  and adapted to direct the lubricant from the third passage part  48  along the teeth  23  in their axial direction. The lubricant receives a velocity in the axial direction along the guiding surface  57  ensuring that the lubricant arrives at the correct location and is used for lubricating and cooling the first engagement area  25  and, by the rotation of the planet gear  11 , the second engagement area  26  ( FIG. 3 ). 
     With reference to  FIG. 3 , the first passage part  38  is adapted to supply lubricant to a radially outer region  74  of the planetary gear  7  i.e. to the bearings  21  via the first outlet opening  40  and to supply lubricant to a radially inner region  75  of the planetary gear  7 , i.e. to the first engagement area  25  via the second outlet opening  41 . During operation the lubricant is forced radially outwardly through the first passage part  38  by means of the lubricant pump and the rotational speed of the rotating planet gear carrier  12 . During certain operating conditions, the rotational speed of the planet gear carrier  12  is relatively low. In these cases, there may be a risk that the speed is not high enough to provide enough lubricant all the way radially outwardly to the bearings  21  which may cause the first engagement area  25  to get to much lubricant and the bearings  21  to little lubricant. During other operating conditions, the rotational speed of the planet gear carrier  12  is relatively high. In these cases the lubricant is forced radially outwardly to the bearings  21  with a significantly higher force which may cause the first engagement area  25  to get to little lubricant and the bearings  21  to much lubricant. Due to the variation of the rotational speed of the planet gear carrier  12  a pumping effect may occur in the lubrication passage  35  which may cause an imbalance of the intended lubricant distribution between the first engagement area  25  and the bearings  21 . 
     To solve or at least alleviate this problem a flow restrictor  60  may be arranged in the first passage part  38 . The axial position of the flow restrictor  60  defines the proportions of lubricant to be directed from the first passage part  38  to the bearings  21  and the first engagement area  25  so that a predetermined part of the lubricant leaving the first passage part  38  is directed through the first outlet opening  40  and a remaining part of the lubricant is directed through the second outlet opening  41 , substantially independent of the rotation speed of the planet gear carrier  12 . At some embodiments the axial position of the flow restrictor  60  may be such that the lubricant is allowed to be dependent on the rotation speed of the planet gear carrier in a predetermined manner, for example, the axial position can be selected such that relatively more lubricant will be supplied to the first engagement area  25  than to the bearings  21  at high rotational speeds to compensate for higher lubricant losses at the first engagement area  25  than in the bearings  21 . 
     The flow restrictor  60  may be adapted to be inserted into the first passage part  38  and thus, the first passage part  38  may be adapted to receive the flow restrictor  60 . The flow restrictor  60  may be a stand-alone insert adapted to be inserted into the first passage part  38 . The flow restrictor  60  can be manually or automatically inserted and removed, as appropriate, from passages  38 , which have been fitted with such flow restrictor  60 . Further, the flow restrictor  60  may be manufactured of any suitable material, including metals, plastic, composite materials or other durable materials. 
     The flow restrictor  60  may, which can be seen in  FIG. 5 , be bottle-shaped and may comprise a body  61 , a neck  62  and a central longitudinal flow path  66  which serves as a lubricant inlet passage to the first channel  44 . The body  61 , the neck  62  and the flow path  66  may have any cross-sectional shape that suits the particular application. In a preferred embodiment, the cross-sectional shapes are circular. The body  61  includes an annular wall  63  having an exterior surface  64 . The exterior surface  64  may include at least one exterior shoulder  65 . An interior surface  67  of the first passage part  38  may include at least one interior shoulder  68  disposed at a predetermined location between the first outlet opening  40  and the second outlet opening  41 . By disposing the interior shoulder  68  at a predetermined location, insertion of the flow restrictor  60  into the first passage part  38  can be performed easily by pushing the flow restrictor  60  so that its exterior shoulder  65  is brought into contact with the interior shoulder  68 . Further, when brought into contact with each other the shoulders  65 , 68  prevent the flow restrictor  60  from sliding axially within the first passage part  38  towards the inner periphery of the planet gear carrier  12 . At some embodiments the flow restrictor  60  may be held in position by a press fit and may have a width of the body  61  which at least slightly exceeds the width of the first passage part  38  so that when the flow restrictor  60  is inserted within the first passage part  38  it will remain in place and the pressure of the lubricant will not cause the flow restrictor  60  to be forced out of the first passage part  38 . At some embodiments, the flow restrictor  60  may be held in position by the hub  20 , which is arranged to extend over the mouth of the first passage part  38 . 
     The neck  62  includes an annular wall  70  having an exterior surface  71 , which together with the interior surface  67  of the first passage  38  is adapted to delimit the radial direction of a gap  72 . The gap  72  extends around an outer periphery of the neck  62  and is open towards the radially inner periphery of the planet gear carrier  12  and closed by a bottom surface of the body  61  towards the radially outer periphery of the planet gear carrier  12 . The axial extent of the gap  72  may be determined by the length of the neck  62 . Further, the gap  72  has a third cross-sectional area A 3 . 
     The flow path  66  comprises least one restriction  79 . The restriction  79  has a lubrication inlet end  77 , a lubrication outlet end  78  and a second cross-sectional area A 2 , which is smaller than the cross-sectional area of the rest of the flow path  66 . The restriction  79  may be formed in any suitable manner, such as by an inwardly tapering portion of the flow path  66 . At some embodiments, at least one restrictor insert (not shown) may be installed in the flow path  66  to decrease the cross-sectional area of the flow path  66  to constitute the restriction  79 . At some embodiments, at least a part of the restriction  79  may extend through the neck  62  in its axial direction. At other embodiments, the entire length of the flow path  66  may be shaped as a restriction. 
     Further, the restriction  79  may be arranged with, which can be seen in  FIGS. 5 and 6 , the lubrication inlet end  77  at a second radial distance R 2  from the rotation axis  18 . At some embodiments the lubrication inlet end  77  may, which can be seen in  FIG. 5 , be arranged at a second radial distance R 2  from the rotation axis  18  which is substantially the same as the first radial distance R 1  from the rotation axis  18  to the center axis  19  i.e. R 1 =R 2 . At other embodiments the lubrication inlet end  77  may, which can be seen in  FIG. 6 , be arranged at a second radial distance R 2  closer to the rotation axis  18  than the first radial distance R 1  of the center axis  19  i.e. R 1 &gt;R 2 . At some embodiments, the second radial distance R 2  may be in the range 0.80-0.95 times the first radial distance R 1 . 
     During operation, the rotational movement of the planet gear carrier  12  forces the lubricant in the first passage part  38  radially outwardly. The lubrication flow receives a velocity in an axial direction through the first passage part  38  ensuring that the lubricant flow leaves the planet gear carrier  12  through the third passage part  48  and the restriction  79 . The axial position of the flow restrictor  60 , the size of the first cross-sectional area A 1 , the size of the second cross sectional area A 2  and the size of the third cross-sectional area A 3  may have an influence on the flow of lubricant in the lubrication system. At some embodiments the first cross-sectional area A 1  may be greater than the second cross-sectional area i.e. A 1 &gt;A 2 . At an alternative embodiment A 1 =2.25(A 2 ). Further, at some embodiments, the third cross-sectional area A 3  may be greater than the first cross-sectional area A 1  i.e. A 3 &gt;A 1 . At an alternative embodiment A 3 &gt;2A 1 . Further, at some embodiments, the length of the third passage part  48  and the size of the first cross-sectional area A 1  on one hand and the length of the restriction  79  and the size of the second cross-sectional area A 2  on the other hand may be chosen such that and the pressure drop in the third passage part  48  may be ⅓ of the pressure drop in the restriction  79 . 
     The present invention is not limited to the embodiments describe above, but relates to and comprises all embodiments within the scope of protection of the attached independent claims. The vehicle  1  may for example be a truck, a bus, a passenger car, any commercial vehicle or any constructional vehicle or the like. 
     As used herein, the term “comprising” or “comprises” does not exclude other features, elements, steps, components, functions or groups thereof. Further, the indefinite article “a” or “an” does not exclude a plurality.