Patent Publication Number: US-2022221044-A1

Title: Rotary driving device

Description:
This non-provisional application is based on Japanese Patent Application No. 2021-003308 filed on Jan. 13, 2021 with the Japan Patent Office, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND 
     Field 
     The present disclosure relates to a rotary driving device mounted on a transmission. 
     Description of the Background Art 
     Japanese Patent Laying-Open No. 2020-031492 discloses a conventional rotary driving device in which a driving shaft is provided with an oil passage through which lubricating oil flows, and the driving shaft is rotatably supported in a transmission by a bearing. 
     SUMMARY 
     The driving shaft described in Japanese Patent Laying-Open No. 2020-031492 is provided with an oil passage through with lubricating oil flows from one end to the other end in the axial direction. Generally, the driving shaft is supported by a bearing arranged at one end and a bearing arranged at the other end. In such a configuration that the lubricating oil flows from one end to the other end of the driving shaft, after the lubricating oil passes through the oil passage inside the driving shaft, the lubricating oil is supplied to the bearing arranged at the other end of the driving shaft. Therefore, it takes time to supply the lubricating oil to the bearing, and the bearing may not be sufficiently lubricated immediately after the start of operation. 
     The present disclosure has been made in view of the aforementioned problems, and an object of the present disclosure is to provide a rotary driving device that allows lubricating oil to flow efficiently inside a shaft from one end to the other end thereof so as to shorten a time required for the lubricating oil to reach a bearing that supports the other end of the shaft. 
     A rotary driving device according to the present disclosure includes a shaft which has one end and the other end in an axial direction and is provided with an oil passage through which lubricating oil flows from the one end to the other end, a transmission case accommodating the shaft therein, and a bearing arranged at the other end of the shaft in the transmission case and rotatably supporting the shaft. The shaft includes an end surface located on the other end in the axial direction. The transmission case includes an opposing surface facing the end surface with a gap therebetween in the axial direction. One of the end surface and the opposing surface is provided with a groove so as to generate a negative pressure on the other end when the shaft rotates. 
     According to the configuration mentioned above, since the groove is provided on the end surface located on the other end of the shaft or on the opposing surface facing the end surface with a gap therebetween, when the shaft rotates, the air is discharged through the groove to the periphery of the other end, and thereby a negative pressure is generated on the other end of the shaft. Thus, the lubricating oil supplied to one end of the shaft is sucked toward the other end of the shaft, which makes it possible for the lubricating oil to flow efficiently inside the shaft. As a result, it is possible to shorten the time required for the lubricating oil to reach the bearing arranged at the other end of the shaft while preventing the lubricating oil from leaking to the outside from one end of the shaft. 
     In the rotary driving device according to the present disclosure, the transmission case includes an opposing wall facing the other end of the shaft in the axial direction. In this case, an inner surface of the opposed wall may be provided with an annular member which is coaxial with a central axis of the shaft, and the opposing surface may be formed by an end surface of the annular member facing the end surface of the shaft in the axial direction. 
     According to the configuration mentioned above, by providing the transmission case with the annular member facing the end surface with a gap from the end surface of the shaft in the axial direction, it is possible to efficiently flow the lubricating oil inside the shaft from one end to the other end thereof with a simple structure, which makes it possible to shorten the time required for the lubricating oil to reach the bearing that supports the other end of the shaft. 
     In the rotary driving device according to the present disclosure, the groove may be provided as a plurality of grooves. In this case, the plurality of grooves may be provided around the central axis of the shaft in a radial pattern. 
     According to the configuration mentioned above, the air in the shaft may be more effectively discharged to the outside of the shaft from the other end. 
     The foregoing and other objects, features, aspects and advantages of the present disclosure will become more apparent from the following detailed description of the present disclosure when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view illustrating a configuration of a power transmission device according to an embodiment; 
         FIG. 2  is a cross-sectional view illustrating a positional relationship between a plurality of shafts provided in the power transmission device of  FIG. 1 ; 
         FIG. 3  is a view illustrating a lubrication system provided in the power transmission device according to the present embodiment; 
         FIG. 4  is a schematic cross-sectional view illustrating a rotary driving device provided in the power transmission device according to the present embodiment; 
         FIG. 5  is a perspective view illustrating an annular member provided on a transmission case of the power transmission device according to the present embodiment; 
         FIG. 6  is a view illustrating the flow of air on the other end of the shaft in the rotary driving device according to the present embodiment; and 
         FIG. 7  is a schematic cross-sectional view illustrating how air and lubricating oil flow in the rotary driving device according to the present embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, an embodiment of the present disclosure will be described in detail with reference to the drawings. In the following embodiment, the same or equivalent portions in the drawings will be denoted by the same reference numerals, and the description thereof will not be repeated. 
       FIG. 1  is a view illustrating a configuration of a power transmission device  12  according to an embodiment. The power transmission device  12  according to the present embodiment will be described with reference to  FIG. 1 . 
     As illustrated in  FIG. 1 , the power transmission device  12  is mounted on a vehicle  10 . The vehicle  10  may be an engine-driven vehicle or a hybrid electric vehicle (HEV) provided with a rotary driving machine, i.e., a driving motor, in addition to an engine as a power source. The vehicle  10  may be a battery electric vehicle (BEV) provided with only an electric motor as the power source. 
     The power transmission device  12  is preferably a horizontal transaxle such as an FF (front engine front drive) power transmission device in which a plurality of shafts are arranged in the width direction of the vehicle  10 , but it may be an FR power transmission device or a four-wheel drive power transmission device. The output unit of the power transmission device  12  is, for example, a differential device that outputs a driving force transmitted from the power source via a gear mechanism or the like to a pair of left and right driving wheels. 
     Specifically, the power transmission device  12  includes a first shaft S 1 , a second shaft S 2 , a third shaft S 3 , and a fourth shaft S 4  which are arranged substantially parallel to the width direction of the vehicle  10 . An input shaft  22  is disposed on the first shaft S 1  and the input shaft  22  is coupled to an engine  20  which serves as the power source. A single pinion type planetary gear train  24  and a first electric motor MG 1  are arranged concentrically with the first shaft S 1 . 
     The planetary gear train  24  and the first electric motor MG 1  function as an electric differential unit  26 . The input shaft  22  is coupled to a carrier  24   c  of the planetary gear train  24  serving as a differential mechanism, and the first electric motor MG 1  is coupled to a sun gear  24   s . A ring gear  24   r  is provided with an output gear Ge. 
     The first electric motor MG 1  corresponds to a differentially controlled rotary machine. The first electric motor MG 1  may function as an electric motor or a generator alternatively. Under a regenerative control, the first electric motor MG 1  functions as a generator, the rotational speed of the sun gear  24   s  is continuously changed, whereby the rotational speed of the engine  20  is continuously changed and output from the output gear Ge. When the torque of the first electric motor MG 1  becomes 0, the sun gear  24   s  becomes idle, which prevents the engine  20  from rotating. The engine  20  is an internal combustion engine that generates power by combusting fuels. 
     A reduction gear unit  30  is disposed on the second shaft S 2 . The reduction gear unit  30  includes a large reduction gear Gr 1  and a small reduction gear Gr 2  provided at both ends of a shaft  28 . The large reduction gear Gr 1  is meshed with the output gear Ge. The large reduction gear Gr 1  is meshed with an output gear Gm of a second electric motor MG 2  disposed on the third shaft S 3 . 
     The second electric motor MG 2  may function as an electric motor or a generator alternatively. Under a power-running control, the second electric motor MG 2  functions as an electric motor, and thereby it is used as a power source for the hybrid electric vehicle. The second electric motor MG 2  corresponds to a driving motor. 
     The small reduction gear Gr 2  is meshed with a differential ring gear Gd of a differential device  32  disposed on the fourth shaft S 4 . The driving force from the engine  20  and the second electric motor MG 2  is distributed to a pair of left and right driving shafts  36  via the differential device  32 , and transmitted to a pair of left and right driving wheels  38 . The differential device  32  corresponds to an output unit, and the differential ring gear Gd corresponds to an input gear. 
     The planetary gear train  24 , the output gear Ge, the large reduction gear Gr 1 , the small reduction gear Gr 2 , the differential ring gear Gd and the like constitute a gear mechanism. 
       FIG. 2  is a cross-sectional view illustrating a positional relationship between a plurality of shafts provided in the power transmission device of  FIG. 1 . 
     As illustrated in  FIG. 2 , the fourth shaft S 4  is arranged at the lowest position among the first shaft S 1  to the fourth shaft S 4 , the second shaft S 2  and the third shaft S 3  are arranged at a position above the fourth shaft S 4 , and the first shaft S 1  is arranged at a position diagonally above the fourth shaft S 4  in the forward direction of the vehicle  10 . 
     An oil catch tank  70  is provided inside a case  14  at an upper position. An upper surface of the oil catch tank  70  is formed with an opening. For example, the lubricating oil sucked up due to the rotation of the differential ring gear Gd flows into the oil catch tank  70  through the opening and is accumulated in the oil catch tank  70 . The oil catch tank  70  corresponds to a third oil reservoir  72 . 
     The oil catch tank  70  is arranged above the first electric motor MG 1 . The oil catch tank  70  may be arranged above the second electric motor MG 2 . 
     The vehicle  10  may travel in a BEV (Battery Electric Vehicle) travel mode and an HEV (Hybrid Electric vehicle) travel mode. 
     Specifically, in the BEV travel mode, the engine  20  is stopped, and the second electric motor MG 2  is used as the power source under the power running control. The BEV travel mode is selected when a low driving force is required, in other words, in a low load range. 
     In the HEV travel mode, the engine  20  is used as the power source while the first electric motor MG 1  generates a reaction force under the regenerative control. The HEV travel mode is selected when a driving force higher than that in the BEV travel mode is required, in other words, in a high load range. Instead of or in addition to the HEV travel mode, an engine travel mode in which only the engine  20  is used as the power source may be provided. 
       FIG. 3  is a view illustrating a lubrication system  40  provided in the power transmission device according to the present embodiment. As illustrated in  FIG. 3 , the lubrication system  40  is provided with a suction device including a first oil pump P 1  and a second oil pump P 2 . The first oil pump P 1  is connected to a first oil supply passage  42  and the second oil pump P 2  is connected to a second oil supply passage  44  so as to supply the lubricating oil to each component of the power transmission device  12 . The first oil supply passage  42  and the second oil supply passage  44  are independent of each other. 
     As illustrated in  FIG. 1 , the first oil pump P 1  is mechanically driven by the output unit (the differential device  32 ) via a pump driving gear Gp meshed with the differential ring gear Gd. The second oil pump P 2  is coupled to the input shaft  22 , and is mechanically driven by the engine  20 . 
     The first oil pump P 1  may be driven by the pump driving gear Gp meshed with the large reduction gear Gr 1 , the small reduction gear Gr 2 , or the like interlocked with the differential ring gear Gd. 
     The first oil pump P 1  and the second oil pump P 2  suck the lubricating oil from an oil reservoir  46  arranged at the bottom of the case  14 , and supply the lubricating oil to the first oil supply passage  42  and the second oil supply passage  44 , respectively. The oil reservoir  46  is constituted by the case  14  itself. The oil reservoir  46  is partitioned into a rear portion and a front portion in the front-rear direction of the vehicle  10  by a partition wall  52 . The rear portion is defined as a first oil reservoir  50 , and the front portion is defined as a second oil reservoir  56 . 
     The first oil reservoir  50  is arranged below the differential device  32 . The second oil reservoir  56  is arranged below the first shaft S 1  on which the planetary gear train  24  and the like are disposed. A suction port  58  of the first oil pump P 1  is arranged in the first oil reservoir  50 . A suction port  60  of the second oil pump P 2  is arranged in the second oil reservoir  56 . The suction port  58  and the suction port  60  are connected to the first oil pump P 1  and the second oil pump P 2  via separate oil suction passages, respectively. 
     The first oil supply passage  42  is connected to a discharge port of the first oil pump P 1  so as to supply the lubricating oil to each component of the power transmission device  12 . Specifically, the first oil supply passage  42  is configured to supply the lubricating oil to the bearing  62 , the gear mechanism  64  (such as Ge, Gr 1 , Gr 2 , Gd, Gm, Gp) and the like of each component of the power transmission device  12 , and supply the lubricating oil to the third oil reservoir  72 . 
     The second oil supply passage  44  is connected to a discharge port of the second oil pump P 2  so as to supply the lubricating oil to the input shaft  22 , the planetary gear train  24 , and the first electric motor MG 1  located above the second oil reservoir  56  to cool the input shaft  22 , the planetary gear train  24 , and the first electric motor MG 1 . A heat exchanger  66  is provided in the second oil supply passage  44 , and is configured to cool the lubricating oil and supply the cooled lubricating oil to the first electric motor MG 1  and the second electric motor MG 2  so as to cool the first electric motor MG 1  and the second electric motor MG 2 . The heat exchanger  66  may be an oil cooler that cools the lubricating oil by heat exchange via air cooling or water cooling. 
     The third oil reservoir  72  is arranged at a position higher than a stationary oil level Lst. The third oil reservoir  72  is arranged at a position higher than the first oil reservoir  50  and the second oil reservoir  56 . 
     The third oil reservoir  72  has a first oil outlet  74 . When the lubricating oil stored in the third oil reservoir  72  exceeds a predetermined oil level, the lubricating oil flows into the first oil reservoir  50  through the first oil outlet  74  by gravity. 
     The third oil reservoir  72  has a second oil outlet  80  disposed at a position lower than the first oil outlet  74 . Even when the lubricant oil stored in the third oil reservoir  72  is equal to or less than the predetermined oil level, in other words, even when the lubricant oil does not exceed the predetermined oil level, the lubricant oil may continuously flow into the first oil reservoir  50  through the second oil outlet  80  by gravity without passing through the second oil reservoir  56 . 
       FIG. 4  is a schematic cross-sectional view illustrating a rotary driving device  100  provided in the power transmission device according to the present embodiment. 
     As illustrated in  FIG. 4 , the rotary driving device  100  according to the present embodiment includes a case  14  as a transmission case, a third shaft S 3  coupled to the second electric motor MG 2 , and bearings  62   a ,  62   b  and  62   c.    
     The third shaft S 3  has one end  3   a  and the other end  3   b  in the axial direction. The third shaft S 3  is provided with an oil passage  3   d  through which the lubricating oil flows from one end  3   a  to the other end  3   b . The third shaft S 3  has an end surface  3   c  located on the other end  3   b  in the axial direction. 
     The third shaft S 3  includes a rotor shaft S 31  to which a rotor of the second electric motor MG 2  is fixed, and a coupling shaft S 32  concentrically coupled to the rotor shaft S 31  by spline fitting. In the fitting portion with the rotor shaft S 31 , the outer diameter of the coupling shaft S 32  is smaller than the inner diameter of the rotor shaft S 31 . 
     The rotor shaft S 31  is arranged at the side of the other end  3   b  of the third shaft S 3 . The coupling shaft S 32  is arranged at the side of one end  3   a  of the third shaft S 3 . The motor output gear Gm is coupled to the coupling shaft S 32 . 
     The third shaft S 3  is rotatably supported in the case  14  by bearings  62   a ,  62   b  and  62   c.    
     The bearing  62   a  is arranged at one end  3   a  of the third shaft S 3 . The bearing  62   b  is arranged at the other end  3   b  of the third shaft S 3 . The bearing  62   c  is arranged substantially at the center of the third shaft S 3 . 
     The case  14  accommodates therein the third shaft S 3  and the bearings  62   a ,  62   b  and  62   c . The case  14  supports the bearings  62   a ,  62   b  and  62   c.    
     The case  14  has an opposing wall  141  facing the end surface  3   c  of the third shaft S 3  in the axial direction of the third shaft S 3 . An inner surface  141   a  of the opposing wall  141  is provided with an annular member  142 . 
     The annular member  142  is coaxial with the central axis of the third shaft S 3 . The central axis of the annular member  142  and the central axis of the third shaft S 3  are coaxial with each other. The annular member  142  has an end surface  142   c  facing the end surface  3   c  of the third shaft S 3  in the axial direction. The end surface  142   c  corresponds to an opposing surface of the case  14  facing the end surface  3   c  with a gap therebetween in the axial direction. The gap enables the rotation of the third shaft S 3  to produce a pumping effect. 
     In the present embodiment, it is described that the annular member  142  is a separate member from the case  14 , but the present disclosure is not limited thereto, the annular member  142  may be a part of the case  14  or may be integrated with the case  14 . 
       FIG. 5  is a perspective view illustrating the annular member provided on the transmission case of the power transmission device according to the present embodiment. 
     As illustrated in  FIG. 5 , the end surface  142   c  of the annular member  142  is provided with a plurality of grooves  143 . The plurality of grooves  143  enable the rotation of the third shaft S 3  to produce a pumping effect so as to generate a negative pressure on the other end  3   b  of the third shaft S 3 . The number of grooves  143  may be one as long as a negative pressure may be generated. 
     The plurality of grooves  143  are provided around the central axis of the third shaft S 3  in a radial pattern. Thus, as will be described later, when the third shaft S 3  rotates, the air inside the third shaft S 3  may be more effectively discharged from the other end  3   b  to the outside of the third shaft S 3 . 
     Each groove  143  is provided so as to extend from an inner peripheral edge of the end surface  142   c  to an outer peripheral edge thereof. Each groove  143  may start from the inner peripheral edge of the end surface  142   c  or may start from a position away from the inner peripheral edge. Similarly, each groove  143  may end at the outer peripheral edge of the end surface  142   c  or may end at a position inwardly away from the outer peripheral edge. Each groove  143  may be curved or bend toward the outer peripheral edge. 
       FIG. 6  is a view illustrating the flow of air on the other end of the shaft in the rotary driving device according to the present embodiment.  FIG. 6  is a plan view of the annular member  142  and its periphery as viewed in the direction indicated by an arrow VI in  FIG. 4 . 
     As illustrated by the broken arrows in  FIG. 6 , when the third shaft S 3  rotates, the air is discharged through the plurality of grooves  143  to the outside of the third shaft S 3  in the radial direction from the gap between the end surface  142   c  of the annular member  142  and the end surface  3   c  of the third shaft S 3 . Accordingly, a negative pressure is generated on the other end  3   b  of the third shaft S 3 . Thus, the pressure on the other end  3   b  of the third shaft S 3  becomes lower than the pressure on the one end  3   a  of the third shaft S 3 . 
       FIG. 7  is a schematic cross-sectional view illustrating how air and lubricating oil flow in the rotary driving device according to the present embodiment. 
     When the vehicle  10  is started travelling, the lubricating oil supplied from the first supply passage  42  is introduced into the oil passage  3   d  from one end  3   a  of the third shaft S 3  as indicated by an arrow AR 1  in  FIG. 7 . 
     Generally, a part of the lubricating oil introduced into the oil passage  3   d  leaks from one end  3   a  to the outside of the third shaft S 3  as indicated by an arrow AR 3 , and the rest thereof flows toward the other end  3   b  as indicated by an arrow AR 2 . 
     In the present embodiment, as described above, since the plurality of grooves  143  are provided on the opposing surface, i.e., the end surface  142   c , when the third shaft S 3  rotates, a negative pressure is generated on the other end  3   b  of the third shaft S 3 . Therefore, as indicated by an arrow AR 5 , the air inside the third shaft S 3  is sucked toward the other end  3   b.    
     Thus, the lubricating oil supplied to the one end  3   a  of the third shaft S 3  is sucked toward the other end  3   b  of the third shaft S 3 , which makes it possible to flow efficiently the lubricating oil in the third shaft S 3 . As a result, it is possible to shorten the time required for the lubricating oil to reach the bearing  62   b  arranged at the other end  3   b  of the third shaft S 3  while preventing the lubricating oil from leaking to the outside from one end  3   a  of the third shaft S 3 . 
     (Modifications) 
     Although in the embodiment mentioned above, it is described that the plurality of grooves  143  are provided on the end surface  142   c  of the annular member  142 , but the present disclosure is not limited thereto, and the plurality of grooves  143  may be provided on the end surface  3   c  of the third shaft S 3 . 
     Further, in the embodiment mentioned above, it is described that the annular member  142  is provided, but the present disclosure is not limited thereto, and the annular member  142  may be not provided. In this case, the opposing wall  141  may become thicker, and the inner surface  141   a  may directly face the end surface  3   c  of the third shaft S 3  with a gap capable of generating a pumping effect. However, when the annular member  142  is provided, it is possible to efficiently flow the lubricating oil inside the third shaft S 3  with a simple structure without changing the shape of the case  14 , which makes it possible to shorten the time required for the lubricating oil to reach the bearing that supports the other end  3   b  of the third shaft S 3 . 
     In addition, in the embodiment mentioned above, it is described that the rotary driving device  100  is applied to the third shaft S 3  of the second electric motor MG 2 , but the present disclosure is not limited thereto, and the rotary driving device  100  may be applied to the first shaft S 1  of the first electric motor MG 1  or the second shaft S 2  of the reduction gear unit  30 . 
     Although the embodiments of the present disclosure have been described as above, it should be understood that the embodiments disclosed herein are illustrative and non-restrictive in every respect. The scope of the present disclosure is defined by the terms of the claims, and is intended to include any modifications within the meaning and scope equivalent to the terms of the claims.