Patent Publication Number: US-2023142241-A1

Title: Integrated Drive System and Electric Vehicle

Description:
TECHNICAL FIELD 
     The present application relates to the technical field of drive, in particular to an integrated drive system and an electric vehicle comprising same. 
     BACKGROUND ART 
     Electric vehicles can generally be driven in two ways. One is a centrally mounted conventional transmission system, in which an electric machine is mounted in the engine compartment and transmits torque to the wheels via a gearbox, a differential and a drive shaft, etc.; the other is an integrated drive system, in which an electric machine and gearbox are mounted together in or near the wheel. Compared with a conventional transmission system, the efficiency of an integrated drive system is markedly increased, e.g. by 20% or more, due to the elimination of the centrally mounted transmission system, and an integrated drive system also achieves modular design and independent control of the wheels, thus expanding the technical flexibility and feasibility of implementation of advanced driver assistance systems (ADAS) (e.g. automatic parking). 
     Existing integrated drive systems mainly use low-speed, high-torque electric machines; such electric machines have an external rotor connected to a wheel hub, and the output torque of the electric machine is transmitted directly to the wheel hub, so the rotation speed of the electric machine is the same as the rotation speed of the wheel. In general, the maximum rotation speed of the electric machine is about 1,500 r/min. External rotor electric machines have the disadvantages of low power density, high weight, large volume, severe NVH and a high cost, etc. This is unacceptable in systems with a higher rated power, because the corresponding electric machine dimensions and mass are greater, thereby increasing the unsprung mass of the vehicle and thus affecting the operability and comfort level of the vehicle. To overcome these shortcomings, an integrated drive system has appeared which uses an internal rotor electric machine and a single-stage planetary gearbox; this system can increase the power density of the drive electric machine, the weight of the electric machine can also be reduced slightly, and adverse effects caused by unsprung mass can also be reduced to a certain extent. However, in comparatively long buses or heavy trucks, this type of integrated drive system using an internal rotor electric machine and a single-stage planetary gearbox is unable to meet requirements completely, because the torque that needs to be transmitted to the wheels is very large and there is very limited space in the rims of the drive wheels. 
     As well as being used to drive the wheels of electric vehicles, integrated drive systems using the combination of an electric machine and a gearbox may also be used to drive other apparatuses, such as wheeled mobile machinery, transportation equipment, etc., and these are likewise affected by the shortcomings mentioned above. 
     Thus, there is a need for a new integrated drive system that is capable of meeting the requirements of a large transmission ratio, structural compactness and high load capacity. 
     SUMMARY OF THE INVENTION 
     An objective of the present application is to provide an improved integrated drive system, to overcome the problems in the prior art. 
     To this end, according to one aspect of the present application, an integrated drive system is provided, comprising: an electric machine, comprising a housing and an output shaft; and a planetary gear transmission mechanism, comprising a first-stage planetary gear mechanism and a second-stage planetary gear mechanism, wherein a first output torque of the first-stage planetary gear mechanism is transmitted to a driven object, a second output torque of the first-stage planetary gear mechanism is transmitted to the second-stage planetary gear mechanism, and a third output torque of the second-stage planetary gear mechanism is transmitted to the driven object. 
     Optionally, the first-stage planetary gear mechanism comprises a first-stage sun gear, first-stage planet gears meshed with the first-stage sun gear, a first-stage ring gear meshed with the first-stage planet gears, and a first-stage planet gear carrier supporting the first-stage planet gears; and the second-stage planetary gear mechanism comprises a second-stage sun gear, second-stage planet gears meshed with the second-stage sun gear, a second-stage ring gear meshed with the second-stage planet gears, and a second-stage planet gear carrier supporting the second-stage planet gears; and the output shaft of the electric machine is fixedly connected to the first-stage sun gear, the first-stage planet gear carrier may be fixedly connected to the driven object, the first-stage ring gear is fixedly connected to the second-stage sun gear, the second-stage planet gear carrier is fixedly connected to the housing of the electric machine, and the second-stage ring gear may be fixedly connected to or integrally formed with the driven object. 
     Optionally, the first-stage planet gears are distributed uniformly around the first-stage sun gear in the circumferential direction, and the second-stage planet gears are distributed uniformly around the second-stage sun gear in the circumferential direction. 
     Optionally, the first-stage planet gears are supported on the first-stage planet gear carrier by means of first-stage planet gear shafts, and the second-stage planet gears are supported on the second-stage planet gear carrier by means of second-stage planet gear shafts. 
     Optionally, the first-stage ring gear is fixedly connected to the second-stage sun gear via a coupling plate. 
     Optionally, the driven object is a wheel. 
     Optionally, the wheel comprises a rim and a hub, the first-stage planet gear carrier may be fixedly connected to the rim or the hub, and the second-stage ring gear may be fixedly connected to or integrally formed with the rim. 
     Optionally, the wheel further comprises a cover plate, the cover plate being fixedly connected to the rim, and a brake disk being provided on the cover plate. 
     According to another aspect of the present application, an electric vehicle is provided, comprising: the integrated drive system described above; and a chassis on which the integrated drive system is mounted. 
     Optionally, the chassis is provided with a brake caliper which cooperates with the brake disk of the integrated drive system. 
     The integrated drive system of the present application employs a two-stage closed planetary gear transmission mechanism, and is capable of achieving a larger transmission ratio, thus allowing the use of a high-speed internal rotor electric machine with a maximum rotation speed as high as 10,000 r/min, and can also achieve the distribution of torque, to reduce the force acting on each gear and meet high torque output requirements, in order to increase service life. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present application are described in detail below with reference to the drawings. It should be understood that the embodiments described below are merely intended to explain the present application without limiting the scope thereof. In the drawings: 
         FIG.  1    is a schematic sectional view of an integrated drive system according to an embodiment of the present application. 
         FIG.  2    is a schematic diagram of torque distribution in the integrated drive system shown in  FIG.  1   . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Preferred embodiments of the present application are described in detail below with reference to examples. In the embodiments of the present application, the case of an integrated drive system for an electric vehicle is taken as an example to describe the present application. However, those skilled in the art should understand that these exemplary embodiments do not imply any limitation of the present application. The integrated drive system of the present application may also be used in other fields, such as wheeled mobile machinery, robots, transportation equipment, etc. 
     In the absence of conflict, features in the embodiments of the present application may be combined. In different drawings, identical or similar components are indicated with identical reference labels, and other components are omitted for conciseness, but this does not mean that the integrated drive system of the present application cannot include other components. It should be understood that the component sizes, proportional relationships and the number of components in the drawings do not limit the present application. 
       FIG.  1    shows schematically a sectional view of an integrated drive system according to an embodiment of the present application. As shown in  FIG.  1   , the integrated drive system of the present application substantially comprises an electric machine  30  and a planetary gear transmission mechanism, to impel a driven object to move. A wheel of an electric vehicle is taken as the driven object below to describe an embodiment of the present application. The driven object could of course also be another object, such as a transportation or winching drum. 
     The wheel  40  comprises a rim  41  and a hub  42  (as force-bearing components of the driven object for example), the rim  41  and hub  42  forming a rigid support structure, and a tire  47  may be provided at an outer side of the rim  41 . The electric machine  30  comprises a stator  31 , a rotor  32 , an output shaft  33  and a housing  34 ; the rotor  32  drives the output shaft  33  to rotate, to provide an electric machine torque P 0  (shown in  FIG.  2   ). Furthermore, the housing  34  comprises a bearing  35 , to support the output shaft  33 . The planetary gear transmission mechanism may be mounted in a space enclosed by the rim  41 , or mounted close to rim  41 . The planetary gear transmission mechanism comprises a two-stage planetary gear mechanism, i.e. a first-stage planetary gear mechanism  10  and a second-stage planetary gear mechanism  20 , which form a closed two-stage planetary gear transmission mechanism. As shown in  FIG.  2   , a first output torque P 1  of the first-stage planetary gear mechanism  10  is transmitted to the rim  41  or hub  42  of the wheel  40 , a second output torque P 2  is transmitted to the second-stage planetary gear mechanism  20 , and a third output torque P 3  of the second-stage planetary gear mechanism  20  is transmitted to the rim  41  or hub  42 . 
     A larger transmission ratio can be achieved by two-stage planetary gear transmission, and a high-speed internal rotor electric machine with a maximum rotation speed of as high as 10,000 r/min can be used as the electric machine  30 ; additionally, torque distribution can be achieved, such that the electric machine torque P 0  is distributed across the two-stage planetary gear mechanism, thus reducing the force acting on each gear, so high-torque output requirements can be met. Furthermore, service life can be increased and the amount of space taken up can be minimized. 
     According to an embodiment of the present application, as shown in  FIG.  1   , the first-stage planetary gear mechanism  10  comprises a first-stage sun gear  11 , first-stage planet gears  12  meshed with the first-stage sun gear  11 , a first-stage ring gear  15  meshed with the first-stage planet gears  12 , and a first-stage planet gear carrier  14  supporting the first-stage planet gears  12 . The second-stage planetary gear mechanism  20  comprises a second-stage sun gear  21 , second-stage planet gears  22  meshed with the second-stage sun gear  21 , a second-stage ring gear  25  meshed with the second-stage planet gears  22 , and a second-stage planet gear carrier  24  supporting the second-stage planet gears  22 . The output shaft  33  of the electric machine  30  is fixedly connected (e.g. by splines) to the first-stage sun gear  11 , the first-stage planet gear carrier  14  may be fixedly connected to the rim  41 , the first-stage ring gear  15  is fixedly connected to the second-stage sun gear  21 , the second-stage planet gear carrier  24  is fixedly connected to the housing  34  of the electric machine  30 , and the second-stage ring gear  25  may be fixedly connected to or integrally formed with the rim  41 . It should be pointed out that the first-stage planet gear carrier  14  may also be fixedly connected to the hub  42 . In this way, the rotation speed provided by the output shaft  33  of the electric machine  30  is reduced by means of the two-stage planetary gear mechanism, and the output torque PO provided is distributed between the first-stage planetary gear mechanism  10  and the second-stage planetary gear mechanism  20 . 
     Two first-stage planet gears  12  and two second-stage planet gears  22  are shown in  FIG.  1   , but the number of planet gears in each stage is not limited, and may for example be 2, 3, 4 or more. The first-stage planet gears  12  may be distributed uniformly around the first-stage sun gear  11  in the circumferential direction, and the second-stage planet gears  22  may be distributed uniformly around the second-stage sun gear  21  in the circumferential direction. 
     As shown in  FIG.  1   , the first-stage planet gears  12  may be supported on the first-stage planet gear carrier  14  by means of first-stage planet gear shafts  13 , and the second-stage planet gears  22  may be supported on the second-stage planet gear carrier  24  by means of second-stage planet gear shafts  23 . Needle roller bearings  17  may be provided between the first-stage planet gears  12  and the first-stage planet gear shafts  13 , and needle roller bearings  27  may be provided between the second-stage planet gears  22  and the second-stage planet gear shafts  23 . The first-stage planet gear shafts  13  may be fixedly connected to the first-stage planet gear carrier  14 , and the second-stage planet gear shafts  23  may be fixedly connected to the second-stage planet gear carrier  24 . The first-stage ring gear  15  may be fixedly connected, for example by splines or another suitable connection means, to the second-stage sun gear  21  via a coupling plate  16 . 
     In this way, the output shaft  33  (providing the electric machine torque PO) drives the first-stage sun gear  11 , the first-stage sun gear  11  drives the first-stage planet gears  12 , and the first-stage planet gears  12  drive the first-stage ring gear  15  (providing the first output torque P 1 ), and drive the first-stage planet gear carrier  14  via the first-stage planet gear shafts  13  (providing the second output torque P 2 ). The first-stage planet gear carrier  14  then drives the second-stage sun gear  21 , the second-stage sun gear  21  drives the second-stage planet gears  22 , and the second-stage planet gears  22  drive the second-stage ring gear  25  (providing the third output torque P 3 ). Because the second-stage planet gear carrier  24  is fixedly connected to the housing  34  of the electric machine  30 , the second-stage planet gears  22  only drive the second-stage ring gear  25 . In this way, the distribution of torque across the two-stage planetary gear mechanism is achieved. 
     When the planetary gear transmission mechanism is mounted in the space enclosed by the rim  41  of the wheel  40 , the wheel  40  may further comprise a cover plate  46 ; one end of the cover plate  46  is fixedly connected to the rim  41 , and another end forms a seal with the housing  34  of the electric machine  30  via a sealing member  45 , thereby shielding or covering the planetary gear transmission mechanism. In addition, a brake disk  43  may be provided on the cover plate  46 . When the integrated drive system is mounted on a vehicle, the brake disk  43  can cooperate with a brake caliper  44  mounted on the chassis (not shown) to brake the vehicle. 
     Furthermore, in the example shown in  FIG.  1   , the output shaft  33  passes through the second-stage sun gear  21  and is then connected to the first-stage sun gear  11 , and the second-stage sun gear  21  can rotate freely on the output shaft  33 . However, the first-stage planetary gear mechanism  10  and second-stage planetary gear mechanism  20  may also be arranged in other ways, for example with the output shaft  33  connected to the first-stage sun gear  11  directly, without needing to pass through the second-stage sun gear  21 . 
     It should be pointed out that the integrated drive system shown in  FIG.  1    is just one specific example capable of realizing the concept of the present application. The electric machine, planetary gear mechanism and wheel of the integrated drive system of the present application may also be arranged in other ways, for example with the planetary gear transmission mechanism mounted at a position close to the wheel instead of in the space enclosed by the rim, and the two-stage planetary gear mechanism in the planetary gear transmission mechanism may also be arranged in different ways, for example with left and right positions exchanged, as long as it is able to perform the abovementioned functions of speed reduction and torque distribution. 
     Design parameters such as the ratios of numbers of teeth of the various gears and ring gears of the planetary gear transmission mechanism can be determined according to parameters such as the electric machine rotation speed, the torque that needs to be transmitted and the ratio of torque distribution; no further details are provided here. 
     According to another embodiment of the present application, the present application further discloses an electric vehicle, comprising the abovementioned integrated drive system, and further comprising a chassis on which the integrated drive system can be mounted. Correspondingly, since the electric machine is mounted on the chassis, the second-stage planet gear carrier may also be fixed to the chassis directly. 
     During use, the integrated drive system of the present application may employ a high-speed internal rotor electric machine, the maximum rotation speed of which can be as high as 10,000 r/min, and the closed two-stage planetary gear speed reduction mechanism can achieve a larger transmission ratio to reduce the wheel rotation speed. Furthermore, this type of planetary gear transmission mechanism can achieve two-stage distribution of torque, thereby reducing the force acting on each gear, can increase input torque and thereby increase the vehicle&#39;s load capacity, and can increase service life and minimize the amount of space taken up. 
     The present application has been described in detail above with reference to particular embodiments. For example, an integrated drive system for an electric vehicle is taken as an example in preferred embodiments to describe the present application, but applications can be found not only in the field of electric vehicles but also in any drive system combining an electric machine with a gearbox. For example, the wheel could be replaced with another rotary component of a drum for example as the driven object. 
     The embodiments described above and shown in the drawings should all be understood as being exemplary, without limiting the present application. Those skilled in the art could make various alterations or amendments thereto without departing from the spirit of the present application, and all such alterations or amendments shall fall within the scope of the present application.