Abstract:
Disclosed is an in-wheel drive system including a motor inside a wheel, in which the motor is disposed inside the wheel, with the center of the rotary shaft ahead of and above the center of the wheel, so it provides an effect of more freely designing the inside of the wheel.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to and the benefit of Korean Patent Application No. 10-2013-0153131 filed in the Korean Intellectual Property Office on Dec. 10, 2013, the entire contents of which are incorporated herein by reference. 
       TECHNICAL FIELD 
       [0002]    The present invention relates to an in-wheel assembly and a vehicle with the in-wheel assembly, and more particularly to an in-wheel assembly with a reduction unit in a wheel and a vehicle with the in-wheel assembly. 
       BACKGROUND ART 
       [0003]    An in-wheel drive system means a system that individually drives and brakes wheels, using a motor mounted inside each of the wheels. An in-wheel system operates a motor mounted on each wheel with a power converter. The in-wheel system has the advantage of being able to considerably contribute to improving safety and fuel efficiency of a vehicle, because it can perform posture control and regenerative braking of a vehicle. 
         [0004]    In the in-wheel drive system, however, since a complicated planetary gear is disposed inside a hub bearing, a hub case is necessarily disposed outside the planetary gear to drive wheels and support loads. As a result, there is a problem in that it is required to manufacture a specific hub to use the in-wheel drive system and the in-wheel drive system is not compatible for the existing wheels. 
         [0005]    Since secondary reduction is performed by the planetary gear, the capacity of the planetary gear needs to be increased in order to increase torque. However, because it is required to design the width, outer diameter, and the like of the planetary gear largely in order to increase the capacity of the planetary gear, the manufacturing cost increases. 
         [0006]    A wheel assembly with an in-wheel motor has been disclosed in Korean Patent No. 10-1080664 (published on Nov. 8, 2011), where the direction of the helix angle, that is, the torsion angle of a counter gear at the left wheel is opposite to the direction of the torsion angle of the counter gear at the right wheel, while the direction of the torsion angle of the planetary gear at the left wheel is the same as the direction of the torsion angle of the planetary gear at the right wheel. 
         [0007]    However, in the in-wheel drive assembly having this configuration, the counter gear at the left wheel and the counter gear at the right wheel are different parts with the directions of the torsion angles opposite to each other, resulting in increase in the number of gears. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention has been made in an effort to provide an in-wheel assembly which allows for compact and very free design of the inside of a wheel, and a vehicle with the in-wheel assembly. 
         [0009]    The present invention provides an in-wheel assembly compatible for the existing wheels without a specific hub, and a vehicle with the in-wheel assembly. 
         [0010]    The present invention provides an in-wheel assembly that allows for reduction of the number of gears, and a vehicle with the in-wheel assembly. 
         [0011]    An exemplary embodiment of the present invention provides an in-wheel drive system including a motor inside a wheel, in which the motor is disposed inside the wheel, with the center of the rotary shaft ahead of and above the center of the wheel. 
         [0012]    In the wheel, a caliper may be disposed behind and above the center of the wheel, a strut may be disposed above the center of the wheel, a lower arm may be disposed under the center of the wheel, and a tie rod may be disposed behind and under the center of the wheel. 
         [0013]    A first reduction unit may be connected to the rotor of the motor and a second reduction unit may be connected to the first reduction unit and a hub assembly, so they can transmit torque to the hub assembly. 
         [0014]    The first reduction unit may include a sun gear fitted on the rotary shaft of the motor, at least two planetary gears engaged with the sun gear, a carrier supporting the planetary gears, and a ring gear which is formed around them and engaged with at least two planetary gears. 
         [0015]    The sun gear may be spline-engaged with the rotary shat of the motor. 
         [0016]    The ring gear may be supported by a knuckle fixed to a car body. 
         [0017]    The second reduction unit may be a counter gear engaged with a drive gear engaged with the carrier. 
         [0018]    The direction of the torsion angle of the planetary gear may be opposite to the direction of the torsion angle of the drive gear. 
         [0019]    Radial and axial loads generated in engagement may be resisted by disposing bearings at both sides of the drive gear on the carrier. 
         [0020]    In the bearings, a bearing (first bearing) with a large diameter is disposed between the carrier and the ring gear, at the motor side, and a second bearing smaller in diameter than the first bearing may be used for the hub side. 
         [0021]    The second bearing may be used to make the first bearing support the resultant force of the thrust forces generated by the drive gear and the planetary gear. 
         [0022]    The hub assembly may include a shaft integrally formed with the counter gear, a hub inner race spline-engaged with the shaft and fastened to a disc, and a hub outer race supporting the hub inner race rotatably. 
         [0023]    The hub assembly may include balls between the hub inner race and outer race and appropriate pre-pressure may be applied to the balls by the tightening force of a hub nut after the hub assembly is combined with the shaft. 
         [0024]    The hub outer race may be supported by a knuckle fixed to a car body. 
         [0025]    The knuckle may be fixed to the car body through a strut and a lower arm. 
         [0026]    The rotor of the motor may be rotatably supported by a double row bearing. 
         [0027]    The double row bearing may be an angular bearing. 
         [0028]    Another exemplary embodiment of the present invention for achieving the objects provides a vehicle including the in-wheel drive system. 
         [0029]    According to an exemplary embodiment of the present invention, it is possible to more freely design the inside of a wheel by disposing a motor ahead of and above the center of a wheel and packaging the motor without interference with a caliper, a tie rod, and a lower arm. 
         [0030]    According to an exemplary embodiment of the present invention, it is possible to minimize an increase in width and outer diameter of a planetary gear for increasing torque and to reduce the manufacturing cost through first reduction by connecting the planetary gear and the motor and second reduction by a counter gear. 
         [0031]    According to an exemplary embodiment of the present invention, it is possible to use the system compatibly for the existing wheels, because the counter gear is connected to the hub assembly. 
         [0032]    According to an exemplary embodiment of the present invention, it is possible to since the direction of the torsion angle of the planetary gear and the direction of the torsion angle of the drive gear engaged with the counter gear are opposite to each other in order to cancel out the thrust force generated by the planetary gear and the thrust force generated by the drive gear, it is possible to more freely design the bearings of a reduction unit and reduce the number of gears. 
         [0033]    The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0034]      FIG. 1  is a view illustrating an in-wheel drive system according to an exemplary embodiment of the present invention. 
           [0035]      FIG. 2  is a view illustrating the cross-section of the in-wheel drive system taken along line A-A in  FIG. 1 . 
           [0036]      FIG. 3  is a view illustrating a process of power transmission in the in-wheel drive system illustrated in  FIG. 1 . 
           [0037]      FIG. 4  is a view illustrating the direction of the torsion angle of a planetary gear and the direction of the torsion angle of a drive gear. 
       
    
    
       [0038]    It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various features illustrative of the basic principles of the invention. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment. 
         [0039]    In the figures, reference numbers refer to the same or equivalent parts of the present invention throughout the several figures of the drawing. 
       DETAILED DESCRIPTION 
       [0040]    Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
         [0041]    Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. First, in giving reference numerals to components throughout the drawings, it should be noted that like reference numerals designate like components even though the components are illustrated in different drawings. Although exemplary embodiments of the present invention will be described hereafter, the spirit of the present invention is not limited thereto and may be modified and implemented in various ways by those skilled in the art. 
         [0042]    An in-wheel drive system includes a motor that generates a driving force, a cooler that cools the motor, a reduction unit that transmits a driving force to a wheel, a brake system that generates a braking force, a steering system that steers a vehicle, and a suspension system that supports the wheel against the vehicle. There is a need of a technology of integrating the joints of the components and merging their functions to disposing them inside a wheel. 
         [0043]    In the present invention, an in-wheel motor is disposed inside a wheel, the in-wheel motor is positioned at the upper end ahead of an axle, which is the central axis of the wheel, to drive a vehicle, and then is packed without interfering with a caliper, a tie rod, and a lower arm. A planetary gear is disposed in the motor and performs primary reduction, a counter gear inside a knuckle performs secondary reduction and minimizes an increase in width direction, and the existing wheel can be used as they are by a third generation hub. The helix angles of a counter gear engaged with the carrier of a reduction unit ASSY (Assembly) and the planetary gear are made opposite to each other and a thrust load is offset, such that the reduction unit ASSY is used in the same way even if the directions of the thrust loads at the left wheel and the right wheel are different. 
         [0044]      FIG. 1  is a view illustrating an in-wheel drive system according to an exemplary embodiment of the present invention and  FIG. 2  is a view illustrating the cross-section of the in-wheel drive system taken along line A-A in  FIG. 1 . 
         [0045]    In the present invention, the reason that the position of the motor is determined in this way is for maximizing the size of the motor without interference with the chassis even if the wheel vertically bounces in running or turns by the steering angle in turning. A space that is not occupied by the motor, corresponding to the amount of offset of the motor, is generated at the rear and lower portion inside the wheel, as illustrated in  FIG. 1 . Accordingly, a suspension is more freely disposed at the lower portion. As illustrated in  FIG. 1 , a brake caliper  20  can be easily disposed opposite the side where the motor is offset, inside the wheel. 
         [0046]    Therefore, in the configuration of the system of the present invention, the center of the motor is positioned at a predetermined distance ahead of and above the center of the axle, as illustrated in  FIG. 1 , when seen to the direction of outside from the inside of a vehicle, the caliper  20  is positioned behind and above the center of the axle, and a strut mount, a mount for a lower arm  40 , and a tie rod  50  are disposed above, under, and behind and under the center of the axle, respectively. 
         [0047]    Referring to  FIGS. 1 and 2 , in an in-wheel drive system  100  according to an exemplary embodiment of the present invention, a motor  110  may be disposed inside a wheel  10 , with the center C2 of the rotational axis ahead of and above the center C1 of the wheel  10 . 
         [0048]    That is, the motor  110  may be positioned inside the wheel  10 , with the center C2 of the rotational axis ahead of a vertical reference line L1 (at the front portion of a vehicle) which passes the center C1 of the wheel  10 . The motor  110  may be positioned inside the wheel  10 , with the center C2 of the rotational axis above a horizontal reference line L2 passing the center C1 of the wheel  10 . 
         [0049]    The reason that the position of the motor  110  is determined in this way is for maximizing the size of the motor  110  without interference with the chassis even if the wheel  10  vertically bounces in running or turns by the steering angle in turning. 
         [0050]    As the motor  110  is offset forward and upward, a space is defined at the rear and lower portion inside the wheel  10 . Accordingly, the suspension  60  can be more freely disposed at the lower portion in the wheel  10 . 
         [0051]    The caliper  20  may be disposed behind the vertical reference line L1 (at the rear portion of the vehicle) and above the horizontal reference line L2, inside the wheel  10 . 
         [0052]    A strut  30  may be disposed above the horizontal reference line L2. 
         [0053]    A lower arm  40  may be disposed under the horizontal reference line L2. 
         [0054]    A tie rod  50  may be disposed behind the vertical reference line L1 (at the rear portion of the vehicle) and under the horizontal reference line L2, inside the wheel  10 . 
         [0055]    Therefore, the motor  110  can be packed inside the wheel  10  without interference with the caliper  20 , the lower arm  40 , and the tie rod  50 . 
         [0056]      FIG. 3  is a view illustrating a process of power transmission in the in-wheel drive system illustrated in  FIG. 1 . 
         [0057]    A rotor  111 , a power transmission shaft, is in the motor, as in the cross-section taken along line A-A in  FIG. 2 , and in operation, primary reduction is performed by a sun gear  121  fitted on the end portion of the rotor, a planetary gear  122  engaged with the sun gear, and a carrier  123  supporting the planetary gear. 
         [0058]    Secondary reduction is performed by a drive gear  160  spline-engaged with the carrier and a counter gear  130  engaged with the gear. 
         [0059]    As a hub inner race  142  spline-engaged with a shaft integrated with the counter gear a disc  170  fastened to the hub inner race by hub bolts, and the wheel are rotated, the vehicle is driven. 
         [0060]    A hub outer race  143  supporting the hub inner race with two balls and a knuckle  150  supporting the hub outer race are coupled to the car body through the strut and the lower arm  140  and support the vehicle that is in motion. 
         [0061]    In braking, the caliper  20  supported by the knuckle against the disc rotating with the wheel generates a friction force and braking is performed, while the tie rod  50  generating a steering angle on the wheel is connected to the knuckle and steering is performed. 
         [0062]    Referring to  FIGS. 1 to 3 , in the in-wheel drive system  100  according to an exemplary embodiment, a first reduction unit  120  may be connected to the rotary shaft of the motor  110  and a second reduction unit  130  may be connected to the first reduction unit  120  and a hub assembly  140 . 
         [0063]    In detail, the first reduction unit  120  may include a sun gear  121 , planetary gears  122 , a carrier  123 , and a ring gear  124 . 
         [0064]    The sun gear  121  may be spline-engaged with the rotary shaft  114  of the rotor  111  of the motor  110 . A plurality of planetary gears  122  receives torque from the sun gear  121  in mesh with the sun gear  121  around it. The carrier  123  supports the planetary gear  122 . The ring gear  124  is engaged with the planetary gears  122  around them. The ring gear  124  is supported by the knuckle  150  fixed to the car body. 
         [0065]    As the rotary shaft  114  of the motor  110  rotates, the sun gear  121  connected to the rotary shaft  114  rotates. By the rotation of the sun gear  121 , the planetary gears  122  rotate and revolve around the sun gear  121 . The carrier  123  supporting the planetary gears  122  rotates with the rotation of the planetary gears  122 , so the primary reduction is performed. 
         [0066]    The second reduction unit  130  may be a counter gear  130  engaged with the drive gear  160  engaged with the carrier  123 . 
         [0067]    As the carrier  123  rotates, the drive gear  160  engaged with the carrier  123  rotates and the counter gear  130  engaged with the drive gear  160  rotates, so the secondary reduction is performed and torque increases. 
         [0068]    The torque of the counter gear  130  is transmitted to the hub assembly  140 . 
         [0069]    The hub assembly  140  may include the shaft  141 , the hub inner race  142 , and the hub outer race  143 . The shaft  141  may be integrally formed with the counter gear  130 . The hub inner race  142  is tightened by a hub nut after fitted on the shaft  141  and may be fastened to the disc  170 . The hub inner race  142  is coupled to the wheel  10  by a bolt B. The hub outer race  143  supports the hub inner race  142  rotatably. The hub outer race  143  can be supported by the knuckle  150 . The knuckle  150  can be coupled to the car body through the strut  30  and the lower arm  40 . 
         [0070]    As the counter gear  130  rotates, the hub inner race  142  rotates and the wheel  10  rotates accordingly. 
         [0071]    The caliper  20  is in friction contact with the disc  170  rotating with the wheel  10 , so braking is performed. The caliper  20  is supported by the knuckle  150 . The direction of the wheel  10  is controlled by the tie rod  50  connected to the knuckle  150 . 
         [0072]    The reduction gears of the transmissions in common vehicles have a torsion angle for preventing noise. In-wheel drive systems require the reduction units described above at the left wheel and the right wheel and need many gears for reduction of two or more steps. Accordingly, using the same gears for the left wheel and the right wheel is advantageous for reducing the costs with a simple manufacturing process. To this end, gears with the same direction of a torsion angle may be used for the left wheel and the right wheel, respectively. 
         [0073]    However, since the torsion angle of a gear generates a thrust force, the thrust forces generated in the same direction of a torsion angle may cause a large load on a bearing. It is required to increase the diameter of a bearing in order to increase the lifespan of the bearing, but there is a problem in that it is impossible to increase the diameter of a bearing in order to secure the maximum allowable rotation speed. 
         [0074]    In the present invention, the planetary gear and the drive gear are engaged with the carrier, with the directions of their helix angles opposite to each other, and both ends of the drive gear are supported by bearings with different diameters. 
         [0075]    The thrust forces generated by the planetary gear the drive gear and transmitted to the carrier are cancel out, such that the thrust force transmitted to the inside of the motor is significantly reduced. 
         [0076]    The resultant force of the two thrust forces may be resisted by a bearing with a relatively larger diameter. 
         [0077]    Accordingly, the bearing in the reduction unit has no problem with the lifespan even if it is designed in consideration of only the maximum allowable rotation speed, such that the bearing for the reduction unit can be designed better. 
         [0078]    Since the thrust forces are canceled out in the reduction unit, the same gears can be used for the left wheel and the right wheel, thereby reducing the number of gears. 
         [0079]      FIG. 4  is a view illustrating the direction of the torsion angle of a planetary gear and the direction of the torsion angle of a drive gear. 
         [0080]    In the in-wheel drive system  100  according to an exemplary embodiment of the present invention, in order to solve the problem, the direction G1 of the torsion angle (helix angle) of the planetary gear  122  is made opposite to the direction G2 of the torsion angle of the drive gear  160 , as illustrated in  FIG. 4 . Accordingly, the thrust force generated by the planetary gear  122  and the thrust force generated by the drive gear  160  are canceled out by the carrier  123 , so the thrust force is greatly reduced. 
         [0081]    Therefore, it is possible to consider only the maximum allowable rotation speed in design of a bearing for supporting a drive gear, so the bearing can be designed better. Since the thrust forces are canceled out inside the wheel  10 , it is possible to reduce the number of gears by using the same reduction unit for the left wheel and the right wheel. 
         [0082]    Meanwhile, the rotor  111  of the motor  110  can be rotatably supported by a double row bearing  115 . The double row bearing  115 , an angular bearing, can resist the thrust force generated by the sun gear regardless of the direction. A resolver  116  is disposed on the double row bearing  115  and transmits the information on the rotation of the motor  110  to an inverter. A stator  112  is disposed around the rotor  111  and a coil  113  is wound on the stator  112 . 
         [0083]    In the present invention, the motor, knuckle, planetary gear set, drive gear, counter gear, hub assembly, and disc are assembled in this order. 
         [0084]    The motor includes the stator core  112 , the stator coil  113 , and the rotor  111 . When the motor is a three-phase motor, the stator coil may be a U-shaped coil, a V-shaped coil, or a W-shaped coil. 
         [0085]    The rotor  111  is disposed inside the stator core or the stator coil and rotatably supported by a motor cover through the double angular ball bearing  115 . 
         [0086]    The resolver  116  is disposed behind the ball bearing and transmits the position information for motor control to the inverter. 
         [0087]    The torque outputted from the rotor  111  is transmitted to the wheel through a reduction mechanism. The reduction mechanism includes a planetary gear set and a counter gear and performs 2-step reduction. 
         [0088]    As illustrated in the cross-section taken along line A-A in  FIG. 2 , the planetary gear set is disposed outside the vehicle further than the motor in the tire/wheel assembly. 
         [0089]    The planetary gear set is disposed on the same axis with the center of the motor and includes a sun gear, a planetary gear, a planetary carrier, and a ring gear. 
         [0090]    The sun gear  121  is spline-engaged with the rotor  111  and the ring gear  124  is fixed to the knuckle by bolts, so reduction is performed through the carrier. 
         [0091]    The carrier is composed of three bearings and supported by a reduction cover integrally formed with the rotor  111 , the ring gear  124 , and the hub outer race  143 . 
         [0092]    The counter gear set is disposed outside the vehicle further than the first planetary gear. The counter gear set includes a gear  160  having a small diameter and disposed on the outer carrier of the first planetary gear and a counter gear  130  having a large diameter and engaged with the drive gear. 
         [0093]    The drive gear with a small diameter is fitted on the carrier by splines. 
         [0094]    The counter gear with a large diameter is supported by a bearing at the knuckle side and fixed by a hub nut with the shaft spline-engaged with the hub inner race  142  at the hub side. 
         [0095]    The inner race member of the hub is spline-engaged with the shaft of the counter gear and transmits increased torque to the wheel. The outer race member is disposed outside the inner race member around it, and is fixed to the knuckle by bolts and supports the inner race member. 
         [0096]    The reduction cover is integrated with the outer race member and coupled to the knuckle and is sealed to prevent the oil in the reduction unit from leaking. 
         [0097]    A seal is provided between the knuckle and the motor housing too and prevent the oil in the motor from leaking. 
         [0098]    An in-wheel drive system according to an exemplary embodiment of the present invention was described in detail above with reference to the accompanying drawings. 
         [0099]    As described above, the exemplary embodiments have been described and illustrated in the drawings and the specification. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and their practical application, to thereby enable others skilled in the art to make and utilize various exemplary embodiments of the present invention, as well as various alternatives and modifications thereof. As is evident from the foregoing description, certain aspects of the present invention are not limited by the particular details of the examples illustrated herein, and it is therefore contemplated that other modifications and applications, or equivalents thereof, will occur to those skilled in the art. Many changes, modifications, variations and other uses and applications of the present construction will, however, become apparent to those skilled in the art after considering the specification and the accompanying drawings. All such changes, modifications, variations and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention which is limited only by the claims which follow.