Background Art Generally, a conventional transmission device known as a variator (V) is classified into a step variable unit (SVU) and a continuously-variable unit (CVU). For the SVU, configurations of a gear mechanism and a chain mechanism exist to this point. For the CVU, configurations of various traction drive mechanisms such types as variable pulley-belts, toroidals, ball-discs, etc. exist to this point. Since the SVU of the gear mechanism has a very high torque capacity, it is thus generally used in devices requiring high power. However, the SVU has the disadvantage of unsmooth speed change. The CVU by friction mechanism has the advantage of smooth speed change, but a disadvantage that its torque capacity is smaller than that of the SVU by the gear mechanism, and it thus can not be widely applied.

Generally, a power split transmission system (PSTS) has a configuration

in which power input from a power source is split and supplied to the transmission system so that power to be transmitted to a variator can be as small as possible. A gear linkage using one or more planetary gear units (PGUs) referred to as a power split means.

In Figs. 1 and 2, a structure of the PSTS using one PGU 10 is schematically shown. As shown in the Figs. 1 and 2, the PGU 10 may generally be represented as a black box with three connecting elements (A, B and C). Input/output elements of the variator 100 are connected to two of the three connecting elements of the PGU 10, respectively. A power source 1 and a load 2 are connected to the two connecting elements of the PGU 10, respectively. Power input by the power source 1 such as an engine or a motor and the like is split into two paths for the PGU 10 and the variator 100 and then combined again to be the output to load 2. Herein, the term"connecting element"refers to a component to be connected to an external device such as a variator or a power source. The three connecting elements of the PGU 10 used in a conventional PSTS are the components of a ring gear (R), a sun gear (S) and a carrier (C). Generally, the PGU 10 further has one pinion (P) in addition to the components of R, S and C. The pinion is used as a relay element to internally link the R, S and C, not as an element to link with external devices. Pinions are classified into single pinions (SPs) and compound pinions (CPs). The use of a PGU with only the SP used in a conventional PSTS has been known.

As shown in Fig. 3, a structure of the PSTS using two PGUs (PGU1 and PGU2) has also been known. An example illustrated in Fig. 3 (a) may be generalized as the structure shown in Fig. 3 (b). In such a conventional PSTS configuration, the two connecting elements of PGU1 10 and PGU2 20 are coupled at port a and port b (for example, the carrier of the PGU1 coupled to the sun gear of the PGU2, and the sun gear of the PGU1 coupled

to the carrier of the PGU2 in the illustrated example), wherein PGU1 10 and PGU2 20 each have three connecting elements, respectively. The power source 1 and the load 2 are connected to the connection points (port a and port b). The transmission 100'is connected between the remaining un-coupled connecting elements not coupled, that is, between the ring gear (port c) of the PGU1 and the ring gear (port d) of the PGU2.

Such a conventional variator has the disadvantage that it is difficult to be applied structurally with respect to high power. For example, a friction variator has a low torque capacity. According to the Hertz contact theory, a difference occurs in contact pressure and elastic stress depending on the dimension and the direction of the radius of curvature of a contact (portion).

A conventional friction variator has a structure that when any two things (a ball, a roller, a cone or a disc) selectively contact each other and thereby its torque capacity can not but be low. Also, a conventional CVU has the disadvantage that the range of transmission gear ratio thereof is not wide.

If a conventional CVU is used in a PSTS, it is impossible to achieve a desired wide overall speed ratio (OSR). Therefore, for a conventional PSTS, respective clutches must be provided for each of a low speed range and a high speed range, separately, so as to achieve a required OSR by employing a multiple-mode method by means of respective power split means for each range. The multiple-mode method is highly complicated, and leads to increased weight.

As mentioned above, a conventional PSTS using one or two PGUs has been known in which only a simple PGU having a single pinion gear, a ring gear (R), a sun gear (S) and a carrier (C) is used. In such a conventional PSTS, the gear size must become very large if designed to achieve varied ranges of required OSR by means of only simple PGUs. Accordingly, simple PGUs are restricted in their application. In addition, for a PSTS using two

PGUs, a power source and a load are connected to the connection points of the PGU1 and the PGU2, and the transmission device is connected only to the un-coupled connecting elements, which results in a very restricted design. Therefore, it is very difficult to design a PSTS of varied structure conforming to various speed requirements from the conventional PSTS using two PGUs.

Disclosure of Invention Accordingly, it is an object of the present invention to provide a device, a system and an improved apparatus to solve problems of the aforementioned conventional power split transmission system and the limitations on conventional CVU.

For the purpose, it is another object of the invention to increase to a torque capacity of a variator by providing a traction drive CVT device having a quadric crank mechanism for stable speed change operation and a friction wheel mechanism in which the spherical inside and outside faces contact each other.

It is another object of the invention to provide flexibility for various designs in a power split transmission system by configuring the power split means to comprise the S, S and C or the R, R and C as components and then providing the PGU with one or more CPs, wherein the power split means splits input power from a power source to allow only a part of the power to be transmitted to a transmission device.

It is still another object of the present invention to provide flexibility for various designs in a power split transmission system. This is done by providing a power split means so that a power source and a load are connected to two connecting elements other than the connection points where the PGU1 and the PGU2 are coupled each other, wherein the power

split means splits input power from a power source to allow only a part of the power to be transmitted to a transmission device.

It is still another object of the present invention to provide a continuously-variable transmission system whose torque capacity and speed change range is significantly increased. It can consequently be employed in applications of high power such as a passenger car or higher level applications, by providing a power split type traction drive CVT system in which a continuously-variable transmission device having a quadric crank mechanism and spherical rotors is combined with a power split means.

In order to achieve the aforementioned objects, in accordance with one aspect of the present invention, a transmission system is provided for continuously converting and transmitting input rotational force, the transmission system comprising: a driving rotor having a first spherical surface on at least a part of its surface which is rotated by the input rotational force; a driven rotor having a second spherical surface on at least a part of its surface which receives and transmits the rotational force from the driving rotor; a counter rotor assembly having a driving counter rotor and a driven counter rotor for relaying the rotational force between the driving rotor and the driven rotor, the driving counter rotor having a third spherical surface on at least a part of its surface for traction drive with the driving rotor and the driven counter rotor having a fourth spherical surface on at least a part of its surface for traction drive with the driven rotor ; and a quadric crank mechanism having the rotatable counter rotor assembly fixed thereto and for adjusting the location of the counter rotor assembly. The quadric crank mechanism comprises: a fixed link fixed to the frame of the CVT device ; a crank having a first rotatable pivot fixed to one end of the fixed link and a first joint on the other end thereof, for

location adjustment ; a rotatable coupler fixed to the first joint of the crank at one end, and having a second joint on the other end thereof, the coupler having the rotatable counter rotor assembly fixed thereto ; and a rotatable follower fixed to the second joint of the coupler and having a second rotatable pivot fixed to the other end of the fixed link, the follower movable depending on the movement of the crank. The counter rotor assembly has a coupling shaft for connecting the driving counter rotor to the driven counter rotor so as for the rotors to be rotated together, and the coupling shaft is configured to be a hollow shaft and the rotatable coupler of the quadric crank mechanism is fixed into the inside of the hollow shaft. In a preferred embodiment of the invention, the first pivot of the quadric crank mechanism is located at the center of a spherical surface (first spherical surface) of the driving rotor ; the second pivot is located at the center of a spherical surface (second spherical surface) of the driven rotor ; the first joint is located at the center of a spherical surface (third spherical surface) of the driving counter rotor and the second joint is located at the center of a spherical surface (fourth spherical surface) of the driven counter rotor.

In accordance with another aspect of the invention, a power split transmission system of a power conversion unit is provided, wherein for splitting input power into two paths and transmitting and outputting the power, the transmission system comprises: a power split means comprising either a planetary gear unit (PGU) having at least one compound pinion gear, two sun gears and one carrier or one planetary gear unit having at least one compound pinion gear, two ring gears and one carrier; and a transmission means which is either a step variable transmission means or a CVT means for receiving a part of the split power from the power split means, converting and transmitting the rotational force back to the power split means. In this aspect of the invention, a first

connecting element of the PGU is connected to a power source directly or through a reducer (amplifier); a second connecting element of the PGU is connected to a load directly or through a reducer (amplifier) ; and the transmission means is connected between the first connecting element and the third connecting element of the PGU, or between the third connecting element and the second connecting element directly or through a reducer (amplifier).

In a still another aspect of the invention, a power split transmission system of a power conversion unit is provided, wherein the transmission system comprises: a power splitting means having a combination of two PGUs from a first gear link unit having one sun gear, one ring gear, one single or compound pinion gear and one carrier, a second gear linkage having two sun gears, at least one compound pinion gear and one carrier, or a third gear linkage having two ring gears, at least one compound pinion gear and one carrier, for splitting input power into more than one path, transmitting and outputting the power using two PGUs and a transmission means which is either a step variable transmission means or a CVT means for receiving a part of the split power from the power split means, converting and transmitting its rotational force back to the power split means. In this case the combination of the two PGUs comprises: a first connecting element which is a first component of a first PGU; a second connecting element which is a first component of a second PGU; a third connecting element consisting of a connection of a second component of the first PGU and a second component of the second PGU ; and a fourth connecting element consisting of a connection of a third component of the first PGU and a third component of the second PGU. The first connecting element is then connected to a power source directly or through a reducer (amplifier) ; the second connecting element is connected to a load directly

or through a reducer (amplifier) ; and the transmission means is connected between the first connecting element and the first connection point, or the first connection point and the second connecting element, or the first connection point and the second connection point, directly or through a reducer (amplifier).

In still another aspect of the invention, a transmission system of a power conversion unit is provided, wherein the transmission system comprises a CVT device having a quadric crank mechanism and spherical rotors, and a power split means using one or two PGUs. In still another aspect of the invention, a motorcycle, a vehicle, an industrial machine, a bike, a toy, a robot or the like, comprising a CVT device or a transmission system as described are provided.

Hereinafter, the present invention will be described in detail by way of the various embodiments and examples of the invention. It will be apparent to those skilled in the art that the following embodiments, however, are for illustration only, not for limiting the scope of the invention. Therefore, simple variants and modifications can be recognized by those skilled in the art, and those variants and modifications fall within the true spirit and scope of the invention.

Brief Description of the Drawings These and other features, aspects, and advantages of the present invention will make it easier to understand with regard to the following description, appended claims, and accompanying drawings, in which like components are referred to like reference numerals. In the drawings : Figs. 1 and 2 show block diagrams of an exemplary power split transmission system comprising a planetary gear unit (PGU) with three

connecting elements (A, B and C) ; Figs. 3 (a) and (b) schematically show an exemplary power split transmission system comprising a combination of two conventional PGUs ; Figs. 4 to 6 illustrate configuration and operation of embodiments of a CVT device using a quadric crank mechanism and spherical rotors in accordance with the invention; Figs. 7 to 11 show variants of a CVT device using a quadric crank mechanism and spherical rotors in accordance with the invention; Figs. 12 and 13 show a driving unit for controlling the speed of a CVT device using a quadric crank mechanism and spherical rotors in accordance with the invention; Figs. 14 (a), (b) and (c) schematically show an exemplary PGU comprising a compound pinion (CP) gear; Figs. 15 to 17 show block diagrams of exemplary power split transmission systems comprising a combination of two PGUs having two connecting elements (A and B) and two connection points (C and D) ; Fig. 18 shows types of frictional surfaces implemented in a traction drive system ; and Fig. 19 shows performance curves for the embodiment in Fig. 14 (c).

Best Mode for Carrying out the Invention Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Figs. 1 to 3 were already described in conjunction with the prior art.

Figs. 4 to 13 illustrate a traction drive continuously-variable transmission (CVT) device, using a quadric crank mechanism and spherical rotors in accordance with an aspect of the present invention. Hereinafter, a traction

drive CVT device having spherical rotors (friction wheels) in which one spherical surface contacts another spherical surface will be described, but the present invention is not limited to this example. It should be noted that it is possible to configure a counter rotor assembly, a driving rotor and a driven rotor by means of a quadric crank mechanism according to the invention, using friction wheels having various types of contact surfaces such as typical flat friction wheels, conical friction wheels, cylindrical friction wheels and the like, instead of spherical rotors.

Figs. 4 and 5 are schematic diagrams to illustrate a structure and mechanical relationship of a traction drive CVT device in which one spherical surface contacts another spherical surface according to one embodiment of the invention. Figs. 6 (a) and (b) show schematic diagrams to illustrate the operation of the embodiment of Fig. 4. As shown in the drawings, a preferred embodiment of the invention is a traction drive CVT device 100, for continuously transmitting input rotational force, comprising a driving rotor 120 at an input side, a driven rotor 180 at an output side, a counter rotor assembly 140 for relaying the rotors, and a quadric crank mechanism 150 for adjusting the location of the assembly 140.

The driving rotor 120 is rotated by means of input rotational force. The input rotational force can be provided by an engine, a motor or by human power. At least a part of the surface of the driving rotor 120 is in the form of a spherical surface. The spherical surface is required only for traction drive. That is, it is not essential for each rotor according to the invention to be in a shape illustrated in the figures. For example, if an external spherical surface is used, it may be a solid sphere, or generally have a quadrangular shape externally if an internal spherical surface is used. The invention needs only a spherical surface for a contact area for power transmission by the traction drive. In the area other than the spherical

surface, it may be in various shapes. The possibility of so many variant shapes also applies to the driven rotor and the rotors on both ends of the counter rotor assembly as well as the driving rotor. The driven rotor 180 receives the rotational force from the driving rotor 120 through the counter rotor assembly and outputs the rotational force, wherein at least a part of the surface is in the form of a spherical surface in the area required for traction drive as in the driving rotor 120. The spherical surface may exist inside or outside as in the following embodiments.

The counter rotor assembly 140 transmits rotational force between the driving rotor 120 and the driven rotor 180. The counter rotor assembly 140 has a driving counter rotor 142 and a driven counter rotor 146. The driving counter rotor 142 is a part to be friction-driven through rolling contact with the driving rotor 120. The driven counter rotor 146 is a part for friction-driving with the driven rotor 180 through rolling contact. On at least a part of the respective surfaces of the driving counter rotor 142 and the driven counter rotor 146, a spherical surface required for friction is provided respectively. The location of the counter rotor assembly is adjusted by the quadric crank mechanism 150. As such, while the spherical surfaces of the driving rotor and the driven rotor and those of the rotors of the counter rotor assembly contact each other to achieve rolling, power, that is, rotational force, is transmitted by means of frictional force.

Referring to Fig. 5, the mechanism on the contact portion F1 between spherical surfaces is described as follows. Since an interior spherical surface of the driving rotor 120 and an exterior spherical surface of the driving counter rotor 142 of the counter rotor assembly 140 have different radii, a point of contact is theoretically obtained on the contact portion.

However, in effect a local elastic deformation by the normal force at the contact portion occurs and thus a circular contact area is formed. As

according to the Hertz theory, in this case, the contact stress is distributed to have, on the one hand, the highest pressure in the center and, on the other hand, zero at the boundary. According to'the law of action and reaction'by the driving torque of the driving rotor 120, tangential force is formed on the contact portion. Then power is transmitted to the driving counter rotor side of the counter rotor assembly 140 due to the tangential force and the tangential velocity on the contact portion. In this case, if the tangential force on the contact portion is within the maximum static frictional force (a value obtained by multiplying the normal force on the contact portion by a frictional coefficient), the absolute velocities of the two contacting rotors (the driving rotor and the driving counter rotor) are equal at the center of the contact portion and thus rolling is achieved. On the other hand, if the tangential force is above the maximum static frictional force, the absolute velocities of the two rotors is different from each other, and thus sliding occurs, which in turn gives adverse effect on power transmission. Preferred embodiments of the invention have an advantage that such sliding is minimized by implementing a CVT device using a quadric crank mechanism and/or spherical rotors.

In a preferred embodiment of the invention, a first pivot 151 of the quadric crank mechanism 150 is located at the center of a spherical surface configured on the driving rotor 120 ; a second pivot 157 is located at the center of a spherical surface configured on the driven rotor 180 ; a first joint 153 is located at the center of a spherical surface configured on the driving counter rotor 142; and a second joint 155 is located at the center of a spherical surface configured on the driven counter rotor 146. In another example, the first pivot 155 and the first joint 153 may alternately be located on the driven rotor at the output side, and the second pivot 157 and the second joint 155 may be located on the driving rotor at the input

side. As such, the present invention has an advantage that the contact portion can always be kept stable regardless of the crank location if the locations of pivots of the quadric crank mechanism correspond with those of the centers of the rotors. In this case, the present invention has another advantage in that a structure can be more easily configured (which allows precise control of the motion of the quadric crank mechanism) by adjusting the radii of curvature of respective spherical surfaces, relative locations of the centers of the spherical surfaces, and length of each link (bar) of the quadric crank mechanisms. Since the motion of the quadric crank mechanism is implemented by means of rotational angle adjustment of a crank, a variety of speed ratio ranges can be obtained depending on the range of rotational angle of a crank. It is possible to properly modify shapes of respective parts so that the speed ratio according to such a rotational range of a crank may be maximized.

Referring back to Fig. 4, the speed ratio p between the rotational speed of the driving rotor 120 and that of the driven rotor 180 can be defined as shown in the equation 1, on the condition that the driving rotor 120, the driven rotor 180 and the rotors of the counter rotor assembly which implement traction drive between the rotors 120 and 180 respectively carry out only rolling without sliding, according to the principle of the speed change of traction drive: [Equation 1] #=#2/#1=r1/r2 r3/r4 25 where, is an angular velocity of the driving rotor 120 ; X 2 is an angular velocity of the driven rotor 180 ; ri is a perpendicular distance from the contact point F, to the rotating axis of the driving rotor ; r2 is

a perpendicular distance from the contact point F, to the rotating axis of the driving counter rotor of the counter rotor assembly 140; r3 is a perpendicular distance from the contact point F2 to the rotating axis of the driven counter rotor of the counter rotor assembly 140 ; and r4 is a perpendicular distance from the contact point F2 to the rotating axis of the driven rotor 180. According to the equation 1, it is noted that it is possible to change a speed ratio by changing the locations of the contact po. ints F, and F2 relative to the rotating axes of the driving rotor 120 and the driven rotor 180 fixed with respect to the frame of the CVT device. The change of the locations of the contact points Fi and F2 can be achieved by changing the location of the counter rotor assembly 140, wherein the location of the counter rotor assembly 140 is determined by shifting the crank location of the quadric crank mechanism 150.

Evidently as shown in Fig. 6, the motion of the counter rotor assembly 140 corresponds to that of the crank 154 which moves within the rotational angle range 0 1 for location adjustment. In response to the motion of the crank 154, the follower 158 also moves within the corresponding rotational angle range E) 2. In this case, although the rotational angle range of the crank 154 is constant, the variables ri, r2, r3 and r4 in the equation 1 may be varied depending on shapes of spherical surfaces to be contacted for friction driving and the relative sizes of spherical surfaces to be contacted. As such, the speed ratio range may also be defined widely or narrowly enough within a desired range, depending on the various values of ri, r2, ra and r4. Therefore, the CVT device in accordance with the invention has, theoretically, an advantage that the transmission range, that is, the range in which a speed ratio may change can be wide enough as desired. Fig. 6 shows the case that the ranges of the variation of the angular velocities 0 1 and 6 z of the crank 154 and the follower 158 are

limited to the first and third quadrants, respectively. In this case, as can be appreciated from the equation 1, the speed ratio has only positive values.

Alternately, in a different structure, the range of the rotational angle variation of the crank may be in the first and second quadrants (that is, the contact point Fi at the driving side is located at the left side of the rotating axis of the driving rotor 120), or the range of the rotational angle variation of the follower may be across the third and fourth quadrants (that is, the contact point F2 at the driven side is located at the right side of the rotating axis of the driven rotor). In this case, the range of speed ratio may reach from negative to positive values. A negative speed ratio means that the rotation speeds of the driving rotor and the driven rotor are actually opposite, that is, the rotation is carried out in opposite directions as compared to a positive speed ratio. In this case, the contact point of the crank 154 or the follower 158 may be located on the rotating axis of the driving rotor or that of the driven rotor, respectively (that is, the rotational angles 6 1 and 6 2 are zero). If the rotational angle 6 1 of the crank 154 is zero, ri =0 and thus the speed ratio becomes zero. This means that the counter rotor assembly 140 and the driven rotor 180 actually do not move although the driving rotor 120 is rotated. If the rotational angle 6 2 of the follower 158 is zero, r4 =0 and thus the speed ratio is infinite. This means that the counter rotor assembly 140 and the driving rotor 120 actually do not move although the driven rotor 180 is rotated.

In this embodiment, the counter rotor assembly 140 may be provided with a coupling shaft 144 for connecting the driving counter rotor 142 to the driven counter rotor 146 so as to allow the rotors 142 and 146 to be rotated together. In this case, the coupling shaft 144 may be configured to be a hollow shaft, so that the coupler 156 of the rotatable quadric crank mechanism 150 can be fixed into the inside of the hollow shaft. In

this embodiment, it is possible to advantageously design the rotors on both ends of the counter rotor assembly 140 to be spaced apart as desired, and also to design a more compact device. In a different example, the coupling shaft 144 may be in another shape, but a hollow shaft. In this case, the shaft 144 may be in any shape in order to perform only the function that the rotors 142 and 146 on both ends can be rotated together.

Figs. 7 to 11 show schematic diagrams for illustrating structures of CVT devices in various embodiments that are modified from the embodiment in Fig. 4. These embodiments can be distinguished from one another by the types of contact portions of the rotors. The types of contact portions may be made to implement interior-exterior, exterior-interior and exterior-exterior contact, respectively, and thus nine combinations thereof can be conceived. These various embodiments are similar in that all of them use spherical rotors and a quadric crank mechanism except that the types of the contact portions on the spherical surfaces are different, and share the advantages according to the use of them and operate in a similar way.

A preferred embodiment of a traction drive CVT device in accordance with the invention has been described previously by referring to the schematic diagrams illustrated in Figs. 4 to 6. The type of frictional surfaces in this embodiment is the interior spherical surface-exterior spherical surface contact and the exterior spherical surface-interior spherical surface contact. In the embodiment shown in Fig. 7, a spherical surface of the driving rotor 120 for the contact with the driving counter rotor 142 is an interior spherical surface, and a spherical surface of the counter rotor assembly 140 for the contact with the rotor 120 is an exterior spherical surface. On the other hand, a spherical surface of the driven

counter rotor 146 of the counter rotor assembly 140 for the contact with the driven rotor 180 is an interior spherical surface, and a spherical surface of the driven rotor 180 for the contact with the driven counter rotor 146 is an exterior spherical surface. In such an interior spherical surface-exterior spherical surface contact structure, both of the contact areas show a relatively wide circular shape (band). The alternate embodiment in which both of the contact areas show a relatively wide circular shape (band), that is, the contact of the spherical surfaces is realized with the exterior-interior and interior-exterior contact structures, may be further represented by the embodiment already described by referring to the schematic drawings shown in Figs. 4 to 6 (interior spherical surface-exterior spherical surface contact and exterior spherical surface-interior spherical surface contact), the embodiment shown in Fig.

9 (exterior spherical surface-interior spherical surface contact and interior spherical surface-exterior spherical surface contact), and other embodiments not shown (exterior spherical surface-interior spherical surface contact and exterior spherical surface-interior spherical surface contact), other than the embodiment shown in Fig. 7 (interior spherical surface-exterior spherical surface contact and interior spherical surface-exterior spherical surface contact with respect to the order of power transmission).

In the embodiments shown in Fig. 8 (interior spherical surface-exterior spherical surface contact and exterior spherical surface-exterior spherical surface contact) and in Fig. 10 (exterior spherical surface-exterior spherical surface contact and interior spherical surface-exterior spherical surface contact), and an embodiment not shown (exterior spherical surface-exterior spherical surface contact and exterior spherical surface-interior spherical surface contact), one of the contact portions is

of an exterior-exterior spherical surface contact and the other is of an exterior-interior or interior-exterior spherical surface contact. The type of an exterior-exterior spherical surface contact has a characteristic of a narrow contact area. Therefore these embodiments have an advantage that it is possible design to conform to various motion conditions since such a narrow contact area type can be employed together with the wide contact area type. Lastly, the embodiment shown in Fig. 11 (exterior spherical surface-exterior spherical surface contact and exterior spherical surface-exterior spherical surface contact) is the exterior-exterior contact type in that all of the contacting spherical surfaces of the driving rotor 120, the driving counter rotor 142, the driven counter rotor 146 and the driven rotor 180 are exterior spherical surfaces. Such a contact type is a little bit similar to previous types, but the embodiments according to the present invention are characterized in that the location of the counter rotor assembly is adjusted through a quadric crank mechanism. The present invention thereby still has an advantage that more stable and exact speed control can be achieved when compared to that of conventional devices.

In Fig. 18, the frictional surface type of interior spherical surface-exterior spherical surface contact achieved according to one embodiment of the invention is compared with that of a conventional traction drive CVT device. Fig. 18 (a) shows a disc-ball contact, Fig. 18 (b) a ball-ball contact, Fig. 18 (c) a toroidal contact, and Fig. 18 (d) an interior-exterior contact employed in a preferred embodiment according to the present invention. The following Table 1 illustrates maximum contact stress depending on the ratios of radii (rl/ro) of friction rotors in each case, which well illustrates that the maximum contact stress is small for the interior spherical surface-exterior spherical surface friction type

implemented in the present invention. In this table, the maximum contact stress values are relative values with reference to the disk-ball contact type. A value of relatively small maximum contact stress means that the corresponding transmission device has a higher torque capacity than a transmission device of the disk-ball contact type under the same level of size. The relative values in Table 1 are based on the Hertz contact theory in which the maximum contact stress is proportional to a 2/3th power of the sum of the inverse of the radii of curvature of contacting objects. For example, if r,/ro=2. 0, the maximum contact stress was 1.310 in a ball-ball contact, 1.1 in a toroidal contact and 0.630 in an interior-exterior contact.

In addition, it is noted that the smaller ri/ro, that is, the ratio of radii of friction rotors, become such as 1.5,1.2 and so on, the smaller the value is.

It can be appreciated from the aforementioned relative values that the interior-exterior contact always has higher torque capacities than the disc-ball or ball-ball contact under the same level of size. On the contrary, as compared to a toroidal contact, if ri/ro is larger than 2.0, the relative values still tend to be smaller. Since there is no preferred embodiment if ri/ro is larger than 3.0, however, it is not regarded that the toroidal contact is better than the interior-exterior contact in practice.

[Table 1] 1.0 1.2 1.5 2.0 3.0 Ball-ball 1.587 1. 498 1. 406 1. 310 1. 211 1.000 Toroidal 1.842 1. 631 1. 406 1. 1 0. 886 0. 0 Int.-ext. 0.000 0.303 0. 481 0. 630 0. 763 1. 000 In a CVT device with the aforementioned configuration, a power source is connected to the driving rotor 120, and a load is connected to the driven rotor 180. Alternately, it is possible to configure the device in which

the power source is connected to the driven rotor 180 and the load is connected to the driving rotor 120. The traction drive CVT device using the aforementioned quadric crank mechanism and the spherical rotors can be used independently, and can be comprised in a power split, CVT device by being combined with a power split means according to the invention, which will be described below, or a conventional power split means.

Although torque capacity in the aforementioned traction drive CVT device according to the invention is improved over the conventional one, power transmission beyond that required in a passenger car is limited. However, if a transmission system is configured by combining a power split means with a CVT device as in further another aspect according to the invention, it is possible to use a traction drive CVT device with low power transmission capacity in a high power machine which power level is higher than that of a passenger car.

A power split transmission system (PSTS) according to the invention may comprise a traction drive CVT device having a quadric crank mechanism or spherical rotors of the aforementioned configuration, or a conventional step variable transmission device or a CVT device. The conventional CVT device may be one of the belt-variable pulley type, cone traction wheel type, disc type, and spherical surface-sphere type transmission means. The step variable transmission may be either a gear means or chain means. The PSTS further comprises a power split means which would preferably be configured using a PGU (planetary gear unit).

In accordance with the invention, the PGU included in the power split means comprises a compound gear (CP), a carrier and two sun gears (S) or two ring gears (R). Alternately, a power split means may be used in which two PGUs (PGU1 and PGU2) are coupled into a combination by means of two components, respectively. In this case, the PGU of the power

split means is provided with two or three connecting elements to which a power source for supplying input rotational force, a load to which power is finally outputted, and a transmission device may be connected, respectively. The connecting elements may be connected to the power source, the load and the transmission device selectively through an additional device such as a reducer or amplifier.

Referring to Fig. 14, a schematic diagram of a PGU for configuring a PSTS according to the invention is shown. The structure shown in Fig.

14 (a) is for a PGU (10') consisting of a compound pinion gear (CP), a carrier (C) and two sun gears (S). The structure shown in Fig. 14 (b) is for a PGU (10") consisting of a compound pinion gear (CP), a carrier (C) and two ring gears (R). If a PGU having the structures shown in Fig. 14 is connected to the power source 1, the load 2 and the transmission device 100 as described with reference to Figs. 1 and 2, a power split transmission system (PSTS) is thus configured.

Referring to Fig. 2, an equation between the transmission ratio of the transmission (means) p and the overall speed ratio (OSR) of the whole transmission system 6 is represented as follows, while the PGU is represented as a black box: [Equation 2] <BR> <BR> <BR> <BR> B<BR> <BR> <BR> # = # - A An equation between variator power ratio (VPR) v and 6 is: [Equation 3] 1-, 5 A where A and B are system parameters defined depending on the gear type and size, and first, second and third connecting element settings for the PGU. Fig. 14 (c) shows an embodiment of a transmission system according

to the invention having one PGU shown in Fig. 14 (a) and configured in conformity to the structure shown in Fig. 2. In the embodiment shown in Fig. 14 (c), a carrier (C) is connected to the power source (i); a first sun gear (S1) connected to the first pinion gear (P1) of the compound pinion gear is connected to the load (o); a second sun gear (S2) connected to the second pinion gear (P2) of the compound pinion gear is connected to the input of the CVU ; and the first sun gear (S1) is connected to the output of the CVU.

A conventional PGU is compared to the embodiment of a transmission system using one PGU according to the invention shown in Fig. 14 (c) in the following Table 2, wherein the conventional PGU consists of one sun gear, one ring gear, one carrier and one single pinion gear, and the inventive PGU in the embodiment consists of two sun gears, one carrier and one compound pinion gear.

[Table 2] Conventional Conventional Conventional Embodiment model 1 model 2 model 3 1 of the (prior art 1) (prior art 2) (prior art 3) invention lst connecting Carrier (-) Sun gear (1. 0) Ring gear (-) Carrier element (2.22) (inputelement) 2nd connecting Sun gear (-) Ring Carrier (-) 1st sun gear element gear (5.56) (1.11) (output element) 3 d connecting Ring gear (-) Carrier (3.28) Sun gear (-) 2nd sun gear element (1.0) (intermediate connecting element) Pinion gear Single (-) Single (2.28) Single (-) Compound (1.11,1.22) Definition of A 2Rc Rp-Rc Rc +Rp (Rp'-Rp)Rc Rc-Rp Rp+Rc 2Rc (Rc-Rp)RF

In Table 2, Rc corresponds to the pitch radius of a carrier, Rp to the pitch radius of a first pinion of a single pinion or a compound pinion and Rp 'to the pitch radius of a second pinion of a compound pinion, respectively.

The numbers in parentheses indicate values for A in a specific design. As can be obviously seen from Table 2, in the conventional three models and the embodiment 1 according to the invention, values for A are differently defined, which indicates different performance of each transmission device.

The embodiment according to the invention has following advantages in design flexibility. For example, a small passenger car (whose displacement is about 800cc) such as Matiz (trademark) of Daewoo Motors needs an OSR of 0.06 to 0.25. Generally, when configuring a transmission system using one PGU shown in Fig. 14 (c), it is appropriate to design the system so that the value of A is between 0.06 and 0.25, preferably 0.18. As can be seen from Table 2, it is impossible to design an appropriate PGU for configuring a transmission system to obtain a proper value A, by means of the conventional models 1 and 3. On the other hand, on condition that the conventional model 2 has a single step reducer (amplifier) for reversing the direction between an element. (connecting element or connection point) facing a load and the load of a transmission system, the design values in the parentheses of Table 2 can be obtained. In the embodiment 1 according to the invention, it is possible to obtain the design values in the parentheses of Table 2 without any additional device. Furthermore, design flexibility can be achieved with the construction of the invention in that other preferred design values can be obtained as desired by means of other possible embodiments according to the invention and/or by attaching additional devices. In addition, the magnitude of design values of the conventional model 2 is relatively large, as compared to that of the design values by the embodiment 1. Smaller design values mean that the

dimension of a transmission becomes smaller, and thus can be understood as a very advantageous point with respect to weight or fuel consumption of the system and so on. As such, as compared to the conventional models using one PGU, the transmission system of an embodiment according to the invention which employs a power split means having two sun gears, one carrier and at least one compound pinion gear, provides significant flexibility in an actual design, and can be advantageously produced as a small type in addition.

Referring to Figs. 15 to 17, schematic structures of two PGUs for a PSTS according to the invention are illustrated. The PGU 1 or the PGU2 may be a gear link unit comprising one sun gear, one ring gear, one single or compound pinion gear, and one carrier as its components, or a gear linkage comprising two sun gears, at least one compound pinion gear and one carrier, or a gear linkage comprising two ring gears, at least one compound pinion gear and one carrier. In the PGU1 and the PGU2, two of three connecting elements other than the pinion gear (s) are combined to one another to form two connection points (C and D). The power source 1 and the load 2 are connected to the two remaining connecting elements A and B, respectively. The transmission 100 is connected between the connecting element at the power source side A and the connection point C as shown in Fig. 15, or between the connection point C and the connecting element B on the load side as shown in Fig. 16, or between 2 connection points C and D as shown in Fig. 17.

As such, performance of a conventional transmission system comprising two PGUs is totally different from that of a transmission system comprising two PGUs according to the invention, because of the difference in connecting the connection points C and D and the connecting elements A and B to the power source and the load, or to input/output elements of

the CVU. The following equation 4 is for the relation of VSR (p) to OSR (S) and VPR (p) to OSR (S), when the PGU1 and 2 are represented as black boxes in a conventional model: [Equation 4] <BR> <BR> <BR> <BR> C (d-B) (A-a B)<BR> <BR> d-A (A+B) d where A, B and C are system parameters defined depending on the type, size and connection method of components in the PGU1 and PGU2 respectively. The equation 4 is changed into the following equation 5 if the PGUs and the CVU are connected as described in the invention: [Equation 5] <BR> <BR> <BR> <BR> Ad-CB (C-6) (Ad-CB)<BR> <BR> 8-C' C (A+B) 8 From the change through the equations 4 and 5, it can be easily seen that the performance of transmissions is totally different in the above two cases by carrying out an analysis similar to that about a transmission comprising one PGU.

The CVT device and the power split CVT system according to the invention as described above can be applied to various fields, and can be provided for all types of machines which require the speed change function.

In a traction drive CVT device according to the invention, power by a human (for a bike), an engine (for a motorcycle, a vehicle, etc.) or a motor (for an industrial machine, a robot, a toy, etc.) as a power source is applied to a driving rotor at an input side of the CVT device directly or through an additional device such as a clutch, a torque converter or a reducer (amplifier).

To the driven rotor at the output side of the CVT device, a load such as a wheel or propeller shaft or a shaft for moving robot arms and the like is connected directly or through an additional device such as a differential

gear or a reducer (amplifier), etc. In the power split CVT device, the power source and the load are connected to a power split means comprising PGUs, and rotors at the input/output sides of the CVT device are also connected to the power split means. The CVT device or the power split CVT device according to the invention can be used not only in vehicles, industrial machines or large robots which require high power, but also in medium/small-sized motorcycles, robots or bikes which require not-very-high or low power, and in small radio controlled vehicles or toys such as typical dolls which require relatively small power. In addition, the present invention may be easily employed in sporting equipment such as physical exercise gears since the mechanism to use power by human hands or feet as a power source can be easily configured with simple mechanical devices. In particular, the transmission system according to the invention has an advantage of reducing overload on machines while running in rugged mountain areas where changing speeds is frequently required.

Therefore the transmission system can be used in military vehicles, for example, tanks or armored cars, etc.

As described above, the CVT device according to the invention improves conventional traction drive CVT devices, thereby increases torque capacity, implements precise speed control, and has a wide-range speed ratio suitable for a power split means.

In particular, the CVT device according to the invention achieves an effect that the counter rotor assembly is exactly transferred to a desired location and a stable contact state is kept in place, so that a desired speed ratio can easily be achieved, by employing a quadric crank mechanism for adjusting the location of the counter rotor assembly. By making the location of the pivot points of the quadric crank mechanism correspond with the centers of the rotors, contact portions can always be stably

secured independently of the location of the crank on the quadric crank mechanism. The contact area is widened, stable flow of an oil film is kept and use of fluid viscosity is maximized, so that the torque capacity is increased, by the configuration in which an exterior spherical surface-interior spherical surface contact, or an interior spherical surface-exterior spherical surface contact can be achieved between the spherical surfaces of the rotors and the counter rotor assembly. It is also possible to design the spherical surfaces of the driving rotor, the driven rotor and rotors on both ends of the counter rotor assembly to be on the inside or the outside of the rotors at discretion. The CVT device according to the invention has an advantage of design flexibility for easily conforming to desired specifications of a machine. A transmission device according to the invention, that is, a variator, can be used independently without a power split means. Since an interior-exterior or vice versa contact is achieved for a spherical surface contact between a driving rotor and a connection rotor, and a driven rotor and a connection rotor, torque capacity is significantly improved. By employing a quadric crank mechanism, the speed change range is widened, so that desired performance is obtained although the variator according to the invention is independently used.

In a power split transmission system according to the invention, since the power split means comprises one or two PGUs and design flexibility is secured while a transmission system with significantly improved power split effect is achieved, the power split transmission system according to the invention can have even more flexibility for achieving an optimum OSR range required in a transmission system. In particular, in a 4-port system in which 2 PGUs are combined, when the port A and the port B are selected for the input/output elements as shown in Figs. 15 to 17, transmission performance different from that by selecting the port C and the port D in

a conventional manner is obtained to implement a variety of transmission devices.

If a transmission system is constructed by incorporating the traction drive CVT device according to the invention, it is possible: first, to minimize power transmitted to a CVT device by maximizing the speed range thereof; and, second, to configure an infinite variable transmission device in which backward, stop and forward movements can be made without a clutch or a torque converter by making the speed change range of the CVT device from negative to positive values and then to the infinite by means of a quadric crank mechanism. In the embodiment of the invention shown in Fig. 14 (c) for numerical illustration of the noted difference, if the OSR ranges from-0.07 to 0.25,-0.07 indicates a backward movement, 0.0 a neutral position and positive values forward movements. Fig. 19 shows performance curves to illustrate relationship between the VSR and the OSR for the embodiment of the invention in Fig.

14 (c). The VSR has positive values from-0.07 to 0.00 of the OSR in the graph, passing through zero and then monotonously decreasing to negative values. Thereafter, the VSR goes to the negative infinite when the transmission gear ratio reaches the system parameter A (designed as 0.18 in this embodiment) and then decreases from the positive infinite to positive finite values. That is, the most significant advantage of the invention is to easily obtain a CVT device in which a transmission gear ratio of the CVT device can vary from a positive value through zero, then to the negative infinite, and then from positive infinite to a finite positive value during a series of the OSR transmission process from-0.07 to + 0.25, as described above by means of the aforementioned quadric crank mechanism and the spherical friction wheels.