Abstract:
An adjusting device including a CVT planetary roller transmission having two axially-spaced sun wheels that are rotatable about a common axis of rotation and at different speeds of rotation. Planet wheels contact and ride against peripheral surfaces of each of the sun wheels, and an axially displaceable ring wheel lies radially outwardly of the sun wheels and engages a peripheral groove formed in the sun wheels. When the ring wheel is axially displaced relative to the sun wheels the axes of rotation of the planet wheels tilt relative to the sun wheel axis resulting in a difference in the rotational speed of the sun wheels changes. The device can be employed as an adjusting device for adjusting the rotational speed of connected units, and also as a drive line component having a variable transmission ratio and situated in a power train of a motor vehicle.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an adjusting device with a CVT planetary roller transmission. 
         [0003]    2. Description of the Related Art 
         [0004]    In particular in motor vehicles, due to the increasing automation of the power train, adjusting devices are needed for a great variety of purposes, for example to actuate a clutch, to change the transmission ratio of a transmission having a continuously variable transmission ratio, to drive ancillary units such as generators, fluid pumps, etc. 
         [0005]    An object of the present invention is to provide an adjusting device, particularly for motor vehicle power trains, which enables continuous adjustment of a particular unit. 
         [0006]    Common to all of the adjusting devices in accordance with the present invention is a CVT planetary roller transmission with which continuous variation of a rotary transmission ratio is possible, which is either used directly or is usable to adjust a positioning element. 
       SUMMARY OF THE INVENTION 
       [0007]    A first adjusting device in accordance with the present invention includes a CVT planetary roller transmission which has two sun wheels that are axially spaced from each other and are rotatable about the same axis of rotation at different speeds, and each having sun wheel outer peripheral surfaces. A ring wheel is provided having a radially inner peripheral surface, and planet wheels with planet wheel peripheral surfaces that are in frictional contact with the inner peripheral surface of the ring wheel and with the sun wheel peripheral surfaces. The surfaces that are in frictional contact with each other are so shaped that when there is an axial shift of the ring wheel relative to the sun wheels and an accompanying tilting of the axes of rotation of the planet wheels, a difference in speed of rotation between the sun wheels changes. An actuator is provided for axially shifting the ring wheel and a positioning element that is rotatable about the same axis as one of the sun wheels, which is coupled to that sun wheel via an axial drive in such a way that it is shifted axially when it rotates relative to the sun wheel. 
         [0008]    When the adjusting device in accordance with the invention is used to actuate a clutch, a clutch lever that sets the clutch torque of a friction clutch bears against an actuating element which relates to one of the sun wheels in a way that transmits axial force, which actuating element additionally relates to the positioning element that is coupled to the other sun wheel in a manner that transmits axial force. 
         [0009]    The clutch lever advantageously bears against the actuating element at a place that is situated between the places at which the actuating element bears against the clutch lever and against the positioning element. 
         [0010]    Advantageously the ring wheel is held so that it cannot rotate, the first sun wheel is rotationally driven by a drive engine, and the second sun wheel is coupled through the axial drive to the positioning element, whose position changes a clamping force with which an endless torque-transmitting means of a belt-driven conical-pulley transmission with continuously variable transmission ratio bears against a conical pulley. 
         [0011]    In another embodiment of the adjusting device in accordance with the present invention the ring wheel is held so that it cannot rotate, the first sun wheel is rotationally driven by a drive engine, and the second sun wheel is coupled through the axial drive to the positioning element, whose position changes the transmission ratio of a CVT planetary roller transmission. 
         [0012]    Another embodiment of an adjusting device in accordance with the present invention includes a CVT planetary roller transmission which has two sun wheels that are axially spaced from each other and are rotatable about the same axis of rotation at different speeds, and each having sun wheel outer peripheral surfaces. A ring wheel is provided having a radially inner peripheral surface, and planet wheels with planet wheel peripheral surfaces that are in frictional contact with the inner peripheral surface of the ring wheel and with the sun wheel peripheral surfaces. The surfaces that are in frictional contact with each other are so shaped that when there is an axial shift of the ring wheel relative to the sun wheels and an accompanying tilting of the axes of rotation of the planet wheels, a difference in speed of rotation between the sun wheels changes. The ring wheel is held so that it cannot rotate and is axially immovable, the first sun wheel is rotationally driven and is subjected to an axial force directed at the second sun wheel, and the second sun wheel drives a fluid pump and is subjected to an axial force in the direction of the first sun wheel by a piston-cylinder unit that is under the pressure of the fluid transported by the fluid pump. 
         [0013]    Another embodiment of an adjusting device in accordance with the present invention includes a CVT planetary roller transmission which has two sun wheels that are axially spaced from each other and are rotatable about the same axis of rotation at different speeds, and each having sun wheel outer peripheral surfaces. A ring wheel is provided having a radially inner peripheral surface, and planet wheels with planet wheel peripheral surfaces that are in frictional contact with the inner peripheral surface of the ring wheel and with the sun wheel peripheral surfaces. The surfaces that are in frictional contact with each other are so shaped that when there is an axial shift of the ring wheel relative to the sun wheels and an accompanying tilting of the axes of rotation of the planet wheels, a difference in speed of rotation between the sun wheels changes. The ring wheel is rotationally driven and is axially movable by an actuator, the first sun wheel is held so that it cannot rotate, and the second sun wheel is non-rotatably connected to an output shaft. 
         [0014]    Another embodiment of the adjusting device in accordance with the present invention includes a CVT planetary roller transmission which has two sun wheels that are axially spaced from each other and are rotatable about the same axis of rotation at different speeds, and each having sun wheel outer peripheral surfaces. A ring wheel is provided having a radially inner peripheral surface, and planet wheels with planet wheel peripheral surfaces that are in frictional contact with the inner peripheral surface of the ring wheel and with the sun wheel peripheral surfaces. The surfaces that are in frictional contact with each other are so shaped that when there is an axial shift of the ring wheel relative to the sun wheels and an accompanying tilting of the axes of rotation of the planet wheels, a difference in speed of rotation between the sun wheels changes. The ring wheel is held so that it cannot rotate and is axially movable by an actuator, the first sun wheel is rotationally driven and the second sun wheel drives an output shaft through a transmission that includes a shiftable reversing set to reverse the direction of rotation of the output shaft. 
         [0015]    Another adjusting device in accordance with the present invention includes a CVT planetary roller transmission which has two sun wheels that are axially spaced from each other and are rotatable about the same axis of rotation at different speeds, and each having sun wheel outer peripheral surfaces. A ring wheel is provided having a radially inner peripheral surface, and planet wheels with planet wheel peripheral surfaces that are in frictional contact with the inner peripheral surface of the ring wheel and with the sun wheel peripheral surfaces. The surfaces that are in frictional contact with each other are so shaped that when there is an axial shift of the ring wheel relative to the sun wheels and an accompanying tilting of the axes of rotation of the planet wheels, a difference in speed of rotation between the sun wheels changes. The first sun wheel is rotationally drivable by a drive engine, the ring wheel is axially movable by an actuator and rotationally drivable by an electric motor, and the second sun wheel rotationally drives an output shaft. 
         [0016]    In the above-identified embodiment of the adjusting device in accordance with the present invention a clutch can be positioned between the drive engine and the first sun wheel. 
         [0017]    In addition, the rotation of the ring wheel and of the electric motor can be blockable. 
         [0018]    Another embodiment of the adjusting device in accordance with the present invention includes a CVT planetary roller transmission which has two sun wheels that are axially spaced from each other and are rotatable about the same axis of rotation at different speeds, and each having sun wheel outer peripheral surfaces. A ring wheel is provided having a radially inner peripheral surface, and planet wheels with planet wheel peripheral surfaces that are in frictional contact with the inner peripheral surface of the ring wheel and with the sun wheel peripheral surfaces. The surfaces that are in frictional contact with each other are so shaped that when there is an axial shift of the ring wheel relative to the sun wheels and an accompanying tilting of the axes of rotation of the planet wheels, a difference in speed of rotation between the sun wheels changes. The first sun wheel of a first CVT planetary roller transmission is rotationally drivable by a drive engine, the second sun wheel of the first CVT planetary roller transmission is connected in a rotationally fixed connection to the first sun wheel of a second CVT planetary roller transmission, whose second sun wheel drives an output shaft, the second sun wheel of the first CVT planetary roller transmission and the first sun wheel of the second CVT planetary roller transmission are non-rotatably connected to an electric motor, and the ring wheels of the CVT planetary roller transmissions are held by at least one actuator so that they cannot rotate and are axially movable. 
         [0019]    Another embodiment of the adjusting device in accordance with the present invention includes a CVT planetary roller transmission which has two sun wheels that are axially spaced from each other and are rotatable about the same axis of rotation at different speeds, and each having sun wheel outer peripheral surfaces. A ring wheel is provided having a radially inner peripheral surface, and planet wheels with planet wheel peripheral surfaces that are in frictional contact with the inner peripheral surface of the ring wheel and with the sun wheel peripheral surfaces. The surfaces that are in frictional contact with each other are so shaped that when there is an axial shift of the ring wheel relative to the sun wheels and an accompanying tilting of the axes of rotation of the planet wheels, a difference in speed of rotation between the sun wheels changes. The first sun wheel is rotationally drivable by a drive engine, the ring wheel is held so that it cannot rotate and is axially movable by an actuator, the second sun wheel is non-rotatably connected to the ring wheel of a second CVT planetary roller transmission, the rotationally fixed connection is connected in a rotationally fixed connection to an electric motor, the ring wheel of the second CVT transmission is movable by an actuator, and the second sun wheel of the second CVT transmission rotationally drives an output shaft. 
         [0020]    Another embodiment of the adjusting device in accordance with the present invention includes a CVT planetary roller transmission which has two sun wheels that are axially spaced from each other and are rotatable about the same axis of rotation at different speeds, and each having sun wheel outer peripheral surfaces. A ring wheel is provided having a radially inner peripheral surface, and planet wheels with planet wheel peripheral surfaces that are in frictional contact with the inner peripheral surface of the ring wheel and with the sun wheel peripheral surfaces. The surfaces that are in frictional contact with each other are so shaped that when there is an axial shift of the ring wheel relative to the sun wheels and an accompanying tilting of the axes of rotation of the planet wheels, a difference in speed of rotation between the sun wheels changes. The first sun wheel is held so that it cannot rotate, the ring wheel is rotationally drivable by a drive engine and an electric motor, the second sun wheel is non-rotatably connected to the first sun wheel of a second CVT planetary roller transmission whose ring wheel is held so that it cannot rotate and is axially movable by means of an actuator and whose second sun wheel rotationally drives an output shaft. 
         [0021]    The above-identified adjusting devices in accordance with the present invention can be used for a great variety of application purposes in which continuous adjustment of the operation of a unit is necessary. 
         [0022]    Especially advantageously, an adjusting device is used in a vehicle power train to adjust the operation of a unit. 
         [0023]    Embodiments of the above-identified adjusting devices in a vehicle power train with an adjusting device situated between a vehicle drive engine and an output shaft for driving a vehicle wheel can form a vehicle transmission with variable transmission ratio. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    The structure, operation, and advantages of the present invention will become further apparent upon consideration of the following description, taken in conjunction with the accompanying drawings in which: 
           [0025]      FIG. 1  is a side view of a CVT planetary roller transmission; 
           [0026]      FIG. 2  is a longitudinal cross-sectional view of the transmission in accordance with  FIG. 1 , taken along the line A-A of  FIG. 1 ; 
           [0027]      FIG. 3  is an enlarged side view of a planet wheel of the transmission shown in  FIG. 1 ; 
           [0028]      FIG. 4  is a side view of parts of the transmission shown in  FIG. 1  to illustrate a change of transmission ratio; 
           [0029]      FIG. 5  is a longitudinal cross-sectional view through a system for use of a CVT planetary roller transmission to actuate a clutch; 
           [0030]      FIG. 6  is a schematic view of an arrangement for use of a CVT planetary roller transmission to change the contact pressure in a belt-driven conical-pulley transmission; 
           [0031]      FIG. 7  is a schematic view of an arrangement in which a CVT planetary roller transmission is used to adjust the transmission ratio of a CVT transmission; 
           [0032]      FIGS. 8 and 9  are schematic views of an arrangement in which a CVT planetary roller transmission is used to set the speed of rotation of a hydraulic pump as a function of the pump discharge pressure; 
           [0033]      FIGS. 10 through 12  are schematic views of an arrangement including a CVT planetary roller transmission for adjusting the transmission ratio and reversing the direction of rotation of an output shaft; 
           [0034]      FIGS. 13 and 14  are schematic views showing the arrangement of  FIGS. 10 through 12  as used to drive a pump; 
           [0035]      FIGS. 15 and 16  are schematic views of an arrangement including a CVT planetary roller transmission for adjusting a transmission ratio, followed by a planetary transmission for reversing a direction of rotation; 
           [0036]      FIGS. 17 through 21  are schematic views of various arrangements including one or two CVT planetary roller transmissions in a hybrid power train of a vehicle. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0037]    In accordance with  FIGS. 1 and 2 , a CVT planetary roller transmission, i.e., a planetary roller transmission with continuously variable transmission ratio, includes two sun wheels  12   a ,  12   b , three planet wheels  14  and one ring wheel  16 . Sun wheels  12   a ,  12   b  taper toward their sides facing each other, so that their sun wheel peripheral surfaces  18   a ,  18   b  are in the shape of a truncated circular cone. The contour line of sun wheel peripheral surfaces  18   a ,  18   b  is a straight line in the illustrated example. Sun wheels  12   a ,  12   b  are situated at an axial distance from each other on a shaft  20  having an axis of rotation  22 . One sun wheel  12   a  is axially movable relative to shaft  20 , and is rotatable relative to shaft  20  by means of a bearing  24 , for example a ball bearing. The other sun wheel  12   b  is rigidly attached to shaft  20 . 
         [0038]    A spring  26  is propped between sun wheel  12   a  and a shoulder  28  of shaft  20 , and presses sun wheel  12   a  in the axial direction into contact against planet wheels  14 . 
         [0039]    Planet wheels  14  each have an axis of rotation  30  and taper starting from a central area toward their faces, so that their planet wheel peripheral surfaces  32  are substantially in the shape of a circular cone. In the example illustrated, the contour lines of the planet wheel peripheral surfaces  32  are convexly curved. Planet wheels  14  have a circumferential groove  34  with rounded flanks  36  between the planet wheel peripheral surfaces  32 . Planet wheels  14  are situated coaxially to shaft  20 , and each have one of their planet wheel peripheral surfaces  32  in frictional contact with one of the sun wheel peripheral surfaces  18   a ,  18   b.    
         [0040]    Projections  40  of a star-shaped separator element  38  rotatably situated on shaft  20  extend into intermediate spaces between the planet wheels  14  and into the grooves  34  of planet wheels  14 , so that the planet wheels are held at the same circumferential spacing from each other. 
         [0041]    Ring wheel  16  is advantageously an annular member and has a bulge in the form of a pointed arch with a convex cross section on its inner peripheral surface  42 . Ring wheel  16  is situated concentrically to shaft  20 . Inner peripheral surface  42  is in frictional contact with each flank  36  of groove  34 . 
         [0042]    The planet wheels  14  are held axially by the frictional contact of the planet wheel peripheral surfaces  32  with the sun wheel peripheral surfaces  18   a ,  18   b  and the inner peripheral surface  42  of ring wheel  16 . When there is an axial movement of ring wheel  16  relative to sun wheels  12   a ,  12   b , planet wheels  14  tilt relative to axis  22  of shaft  20 . Planet wheel peripheral surfaces  32 , groove  34  and inner peripheral surface  42  of ring wheel  16  are advantageously shaped so that in the tilted state the axes of rotation  30 , the axis of rotation  22 , and lines through the two points of the frictional contact of inner peripheral surface  42  with the flanks  36  of groove  34  intersect at a point SP (see  FIG. 4 ). The result is a well-defined precessional movement of the planet wheels  14 . 
         [0043]    To move ring wheel  16  axially relative to shaft  20 , a displacing device  44  (see  FIG. 2 ) is situated around ring wheel  16 . In the illustrated example, displacing device  44  is designed similarly to a clutch actuator, and is therefore not explained in greater detail. 
         [0044]    The operating principle of the planetary transmission will be explained below on the basis of  FIG. 4 , based upon the following definitions: 
         [0045]    r s1  is the distance between axis of rotation  22  of shaft  20  and the point of frictional contact of sun wheel peripheral surface  18   a  with planet wheel peripheral surface  32 ; 
         [0046]    r s2  is the distance between axis of rotation  22  of shaft  20  and the point of frictional contact of sun wheel peripheral surface  18   b  with planet wheel peripheral surface  32 ; 
         [0047]    r P1  is the distance between axis of rotation  30  of planet wheel  14  and the point of frictional contact of planet wheel peripheral surface  32  with sun wheel peripheral surface  18   a;    
         [0048]    r P2  is the distance between axis of rotation  30  of planet wheel  14  and the point of frictional contact of planet wheel peripheral surface  32  with sun wheel peripheral surface  18   b;    
         [0049]    n s1  is the speed of rotation of sun wheel  12   a;    
         [0050]    n s2  is the speed of rotation of sun wheel  12   b;    
         [0051]    n P  is the speed of rotation of planet wheels  14 ; and 
         [0052]    ΔS is the axial distance of sun wheels  12   a ,  12   b  from each other. 
         [0053]    In general, the following equation applies to the transmission of torque by planetary transmission  10 : 
         [0000]        n   s1   ×r   s1   =n   P   ×r   P1  and  n   s2   ×r   s2   =n   P   ×r   P2    
         [0054]    The description of the operating principle begins with the planet wheels  14  in a non-tilted condition. In that condition and with a symmetrical arrangement of the planetary transmission  10 , the following equalities are true: 
         [0000]        r   s1   =r   s2   ; r   P1   =r   P2 , and therefore  n   s1   =n   s2 . 
         [0055]    The transmission ratio I between drive and take-off is then i=1. 
         [0056]    When ring wheel  16  is moved axially relative to sun wheels  12   a ,  12   b , planet wheels  14  are carried along with it by virtue of contact with the flanks  36  of the grooves  34 , and consequently the axes of rotation  30  of the planet wheels  14  are tilted relative to the axis of rotation  22  of the sun wheels  12   a ,  12   b . If axis of rotation  30  is tilted toward sun wheel  12   a , as shown in  FIG. 4 , then r s1 &gt;r s2  and r P1 &lt;r P2 , i.e., n s1 &lt;n s2 . If axis of rotation  30  is tilted toward sun wheel  12   b , the relationships just stated above are accordingly reversed. The transmission ratio between n s1  and n s2  thus changes in accordance with the magnitude and direction of axial displacement of displacing device  44 . At the same time, the transmission ratios between ring wheel  16  and each of the sun wheels  12   a ,  12   b  change in the opposite direction. 
         [0057]    The conical outer surfaces  18   a ,  18   b  of sun wheels  12   a ,  12   b  can be formed so that the distance ΔS (see  FIG. 5 ) between the opposed side faces of the sun wheels  12   a ,  12   b  remains constant when the axes of rotation  30  of the planet wheels  14  are tilted, i.e., when the transmission ratio is shifted. Contact pressure between the sun wheels  12   a ,  12   b , the planet wheels  14 , and the ring wheel  16  is ensured by the spring  26 . 
         [0058]    The CVT planetary roller transmission, as illustrated in its basic construction, can be modified in many ways. The sun wheels can differ in size. The contours of the peripheral surfaces can be concave, convex, or rectilinear, in coordination with each other. 
         [0059]    The adjusting device can be designed in various ways. 
         [0060]    The inner peripheral surface of the ring wheel can be in frictional contact with the planet wheel peripheral surfaces at only one point. 
         [0061]    A planet wheel carrier whose supports extend from the carrier can be situated so that another gear can be engaged with it. 
         [0062]    Spring  26  can be replaced by other biasing means. 
         [0063]    As usual with planetary transmissions, first sun wheel  12   a  and ring wheel  16  can be used in different ways as inputs, with the shaft  20 , which is connected to second sun wheel  12   b  in a rotationally fixed connection, serving as an output shaft. 
         [0064]    Various applications and end uses of the described CVT planetary roller transmission will be explained below on the basis of  FIGS. 5 through 21 . 
         [0065]      FIG. 5  shows a half-sectional view through an embodiment of the planetary roller transmission, designated overall as  50 , for actuating a friction clutch. A clutch lever  52 , designed in a known manner as a diaphragm spring with radially inwardly projecting tongues, bears at a support point  54  against a lever-like actuator  56 , which is pivotally attached at pivot  58  to a radially outer extension  60  of the first sun wheel  12   a  of planetary roller transmission  50 . The ring wheel  16  of the planetary roller transmission is axially movable by means of a suitable actuator (not shown). The second sun wheel  12   b  is rotatable by a recirculating ball screw  62  relative to a sleeve-shaped positioning element  64 , the positioning element being moved in one direction or the other in the axial direction when there is relative rotation between the second sun wheel  12   b  and the positioning element  64 , depending upon the direction of the relative rotation. The end of the positioning element  64 , which is on the left side of  FIG. 5 , bears against the actuator lever  56 . 
         [0066]    If the radial distance between support point  54  and pivot  58  is designated as b and the radial distance between support point  54  and the contact point between the positioning element  64  and the actuator lever  56  is designated as a, and the force applied by the clutch lever  52  to the actuator  56  is designated as X, the result is K 1 =X×b/(b+a) for the force K 1  acting on the first sun wheel  12   a , and K 2 =X×a/(a+b) for the force acting on the positioning element  64 . The sleeve-shaped positioning element  64  is non-rotatably connected to the first sun wheel  12   a  and is axially movable relative thereto. The second sun wheel  12   b  is supported on a transmission bell housing  68  through a thrust bearing  66 . 
         [0067]    Corresponding to the division of the force X acting from the clutch lever  52  into the forces K 1  and K 2 , a bias in the planetary roller transmission is set in such a way that a necessary torque can be transmitted. In the neutral position of ring wheel  16 , in which the two sun wheels  12   a  and  12   b  do not turn relative to each other, positioning element  64  remains unchanged in its axial position. If the ring wheel is shifted axially, for example with a solenoid, the sun wheels rotate relative to each other and the positioning element  64  is moved in one or the other axial direction, depending upon the direction of the relative rotation. Depending upon the transmission ratio set between the two sun wheels with the help of the axial shifting of the ring wheel  16 , the clutch is rapidly disengaged or engaged. The axial force transmitted by the actuator (not shown) to the ring wheel  16  can thus be increased as needed with the help of the planetary roller transmission  50 , and the clutch can be controlled very precisely in accordance with need. 
         [0068]      FIG. 6  shows a basic arrangement in which a CVT planetary roller transmission  50  is used to change the contact pressure with which conical places on a conical disk pair  70  are pressed against the endless torque-transmitting means of the belt-driven conical-pulley transmission  72 . A drive engine  74 , preferably an internal combustion engine, drives a shaft  76 , to which the first sun wheel  12   a  of the planetary roller transmission  50  and one of the conical disks of the conical disk pair  70  are rigidly connected. However, the other conical disk of the conical disk pair  70  is connected to shaft  76  so that it is rotationally fixed but axially movable, and is coupled to the second sun wheel  12   b  through a recirculating ball screw  62 . The ring wheel  16  of the planetary roller transmission  50  is held so that it is rotationally fixed and is movable in the direction of the double arrow by means of a suitable actuator (not shown). It is clearly evident that when the planet wheels are in the non-tilted position no shift occurs in the distance between the conical disks of the conical disk pair  70 . Depending upon the tilting of the planet wheels to one position or the other, the distance between the conical disks of conical disk pair  70  becomes greater or smaller. With the help of the planetary roller transmission  50  employed as an adjusting device, the contact pressure can be precisely changed while significantly increasing the force applied by the actuator to the ring wheel  16 . 
         [0069]      FIG. 7  shows an arrangement of a planetary roller transmission  50  similar to that of  FIG. 6 , with planetary roller transmission  50  being employed there to change the transmission ratio of a toroidal transmission  80 . The adjustment of a toroidal body  82  is performed similarly to the adjustment of the axially movable conical disk of the arrangement shown  FIG. 6 , so that a detailed description is omitted. 
         [0070]      FIGS. 8 and 9  show a change of planetary roller transmission  50  to regulate the speed of rotation of a fluid pump  84  to transport a gaseous or liquid fluid. 
         [0071]    Drive engine  74 , preferably an internal combustion engine, is non-rotatably connected to a first gear  86  that engages with a second gear  88 , which is rigidly connected through a sleeve  90  to the first sun wheel  12   a  of the planetary roller transmission  50 . The sleeve  90  is rotatably supported on an axle  92 . Second gear  88 , which is axially movable relative to first gear  86 , is elastically biased toward planet wheel  14  by a spring  94 . Ring wheel  16  is held stationary. 
         [0072]    Second sun wheel  12   b  is non-rotatably connected to an impeller of pump  84  and is axially biased in the direction of the first sun wheel  12   a  by means of a piston-cylinder unit  96 , which is pressurized with pressure that exists in a return line leading from the discharge line of pump  84  to a fluid supply, in which return line a throttle  98  is situated. 
         [0073]    At low pressure in the piston-cylinder unit  96 , the planet wheels  14  are pivoted into the position shown  FIG. 8 , so that second sun wheel  12   b  rotates at a higher speed than first sun wheel  12   a . If the pressure in piston-cylinder unit  96  increases, the planet wheels  14  are increasingly pivoted into the position shown in  FIG. 9 , in which the speed of rotation of first sun wheel  12   b , and hence the speed of rotation of the pump, is reduced. Pump  84  can be, for example, the lubricant pump of an internal combustion engine, or a supply pump for hydraulically operated units. The system pressure is adjustable by means of the bias of spring  94 . 
         [0074]      FIGS. 10 through 12  show the use of a planetary roller transmission  50  as a reversing transmission. There the ring wheel  16  is driven by a rotationally driven gear  100 , where the engagement between ring wheel  16  and gear  100  permits a shifting of ring wheel  16  relative to gear  100  in the direction of the double arrow by means of an actuator (not shown). First sun wheel  12   a  is held so that it cannot rotate. Second sun wheel  12   b  is non-rotatably connected to an output shaft  102 . 
         [0075]    In the neutral (non-tilted) position of the planet wheels  14 , output shaft  102  does not rotate, corresponding to the stationary first sun wheel  12   a  (see  FIG. 11 ). If ring wheel  16  is moved axially relative to axis  22  of the planetary roller transmission (see  FIG. 10 ), the output shaft rotates in one direction, for example the forward direction. If ring wheel  16  is moved in the other direction, output shaft  102  rotates in the opposite direction, for example the reverse direction (see  FIG. 12 ). 
         [0076]      FIG. 13  shows an arrangement of planetary roller transmission  50  for a reversing pump  104  to drive two oppositely acting piston-cylinder units  125 ,  126 . 
         [0077]      FIG. 14  shows the application of a planetary roller transmission  50  in an arrangement in accordance with  FIG. 13  for a reversing pump  104  that drives an oscillating motor  106 . 
         [0078]    The remaining drawing figures show CVT planetary roller transmissions in which the planetary roller transmission  50  is situated in the torque transmission path from a drive engine to the driven wheels of a vehicle, i.e., it forms at least part of the vehicle drive train. 
         [0079]      FIGS. 15 and 16  illustrate how a drive train can be realized that includes a planetary roller transmission  50  to change the transmission ratio of a transmission  110 , and in addition permits reversal between forward and reverse. 
         [0080]    As shown in  FIG. 15 , a drive engine  74 , preferably an internal combustion engine, is connected through a clutch  122  to the first sun wheel  12   a  of a planetary roller transmission  50 . Ring wheel  16  of the planetary roller transmission  50  is held so that it cannot rotate, but is axially movable by means of a suitable actuator (not shown). The transmission ratio between the speed of rotation of the first sun wheel  12   a  and the second sun wheel  12   b  is changeable by moving ring wheel  16  axially. Second sun wheel  12   b  is operatively connected to a downstream transmission  110  by an input gear  108  that is non-rotatably connected with second sun wheel  12   b . A ring wheel  112  designed with two sets of inner teeth that are at different radial positions meshes with input gear  108 , and in the position shown in  FIG. 15  with first output gear  114 , which is non-rotatably connected to an output shaft  102 . Ring wheel  112  is axially movable by means of a suitable actuator (not shown), so that in a position in which it has been moved to the right (see  FIG. 16 ) it continues to mesh with gear  108  but no longer with first output gear  114 , but instead with planet gears  116 , whose carrier is held stationary and which mesh with second output gear  118 , which is non-rotatably connected to output shaft  102 . 
         [0081]    The condition shown in  FIG. 15  corresponds to rotation of output shaft  102  for forward travel of the vehicle. The condition shown with  FIG. 16  corresponds to rotation of output shaft  102  for reverse travel of the vehicle. 
         [0082]      FIGS. 17 and 18  show a utilization of the CVT planetary roller transmission  50  in a power-branched hybrid power train with a drive engine  74 , preferably an internal combustion engine, and an electric motor  120  that is preferably operable both as an electric motor and as a generator. The electric motor  120  is drivingly connected to the ring wheel  16  through a drive gear  123 , and is axially movable by means of a suitable actuator (not shown). Drive engine  74  is drivingly connected through a clutch  122  to the first sun wheel  12   a  of the planetary roller transmission  50 . The second sun wheel  12   b  of the planetary roller transmission is non-rotatably connected to output shaft  102 . A large variety of drive configurations can be achieved, depending upon the actuation of the two motors, the position of the ring wheel  16 , and the engagement state of the clutch  122 . 
         [0083]    The arrangement shown in  FIG. 18  differs from that of  FIG. 17  in that the rotation of electric motor  120  and hence that of ring wheel  16  can be blocked by a suitable blocking means  114 . The clutch  122  of  FIG. 17  can be eliminated in this arrangement. 
         [0084]      FIG. 19  shows the use of two planetary roller transmissions  50   1  and  50   2  in a power-branched hybrid drive. Internal combustion engine  74  is connected through a clutch  122  to the first sun wheel  12   a , of the first planetary roller transmission  50   1 , whose second sun wheel  12   b , is non-rotatably to the first sun wheel  12   a   2  of a second planetary roller transmission  50   2 , whose second sun wheel  12   b   2  is non-rotatably connected to the output shaft  102 . The ring wheels  16   1  and  16   2  of both planetary roller transmissions are held stationary, and are axially movable by means of a common actuator (not shown) or by separate actuators. Electric motor  120  is operatively connected to the second sun wheel  12   b   1  of the planetary roller transmission  50   1  or to the first sun wheel  12   a   2  of the planetary roller transmission  50   2 . With the arrangement shown in  FIG. 19  it is possible to achieve a high overall transmission ratio spread of the transmission, while the transmission ratio spread of the individual planetary roller transmissions is small. 
         [0085]    In the arrangement shown in  FIG. 20  the two planetary roller transmissions  50   1  and  50   2  are not connected one after the other through the sun wheels  12   b   1  and  12   a   2 , but rather the second sun wheel  12   b   1  of the first planetary roller transmission  50   1  is non-rotatably connected to the ring wheel  16   2  of the second planetary roller transmission  50   2 , whose second sun wheel  12   b   2 , in turn, is non-rotatably connected to the output shaft  102 . The ring wheel  16   1  of the first planetary roller transmission  50   1  is held so that it cannot rotate. The first sun wheel  12   a   2  of the second planetary roller transmission  50   2  is likewise held so that it cannot rotate. Once again, it is possible to achieve a large transmission ratio spread of the overall transmission ratio, while the transmission ratio spread of the individual planetary roller transmissions is smaller. 
         [0086]      FIG. 21  shows another modified arrangement of a hybrid drive with two planetary roller transmissions  50   1  and  50   2 . In that arrangement the drive engine  74 , preferably in the form of an internal combustion engine, and the electric motor  120  are both drivingly connected to the ring wheel  16   1  of the planetary roller transmission  50   1 , whose second sun wheel  12   b   1  is drivingly connected to the first sun wheel  12   a   2  of the planetary roller transmission  50   2 . The ring wheel  16   2  of the second planetary roller transmission  50   2  and the first sun wheel  12   a   1  of the first planetary roller transmission  50   1  are held so that they cannot rotate. Again, it is possible to achieve a high transmission ratio spread of the overall transmission while the transmission ratio spread of the individual transmissions is small. 
         [0087]    In the embodiments shown in  FIGS. 20 and 21 , a reversal of the direction of rotation, i.e., forward and reverse travel, is possible because one of the sun wheels is fixed in each case. The ring wheels of both planetary roller transmissions can again be operated by their own actuators or by a common actuator. 
         [0088]    The actuators for adjusting the ring wheel can be designed in a great variety of ways, and act together with the ring wheel, if the latter is rotatable, through thrust bearings. The actuators can be formed, for example, by a linearly movable component through an electric motor having a rotatable spindle, a magnet that is controllable with regard to its stroke, a hydraulic unit, etc. 
         [0089]    Although particular embodiments of the present invention have been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit of the present invention. It is therefore intended to encompass within the appended claims all such changes and modifications that fall within the scope of the present invention.