Patent Publication Number: US-2002011148-A1

Title: Axial actuator

Description:
BACKGROUND OF THE INVENTION  
       [0001] The present invention relates to an axial actuator, for converting a rotary motion into a translational motion, in particular for controlling the axial position of variator disks of an infinitely variable vehicle transmission (continuously variable transmission or CVT), to a variator and to a CVT.  
       [0002] International Patent Application WO/00/03157 has disclosed an axial actuator with at least one first pair of spiral tracks which extend in such a way as to be rotatable along the lateral surface of a cylinder about an axial axis, there being arranged between the first pair of spiral tracks a radially guided axial needle or roller ring, the running length of which corresponds essentially to the length of the tracks. In a variation of this embodiment, a second pair arranged offset relative to the first pair of spiral tracks is provided to eliminate transverse forces and achieve as high tipping stability as possible. However, an axial actuator constructed in this way is not very suitable for transmitting high or very high axial forces.  
       [0003] German Patent DE 199 42 462 C1 shows an axial actuator having an intermediate member having two adjuster rings with at least three pairs of helical raceways mutually movable against each other, characterized by at least three interconnected distance members arranged between the two adjuster ring, the distance members following the form of the helical raceways and reducing the friction between the two adjuster rings, whereas a rotation of one adjuster ring causes an axial movement of the other adjuster ring.  
       [0004] The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.  
       SUMMARY OF THE INVENTION  
       [0005] It is therefore an object of the present invention to propose an axial actuator for high and extremely high axial loads which can still be operated with an economical use of energy. The inventor has furthermore set himself the object of proposing an axial actuator of this kind accommodated in a variator of a continuously variable transmission, and a continuously variable transmission of this kind per se.  
       [0006] The object is achieved by an axial actuator in accordance with claim  1 .  
       [0007] By means of the configuration, in accordance with the invention, of an axial actuator with at least three ramps, which run concentrically around an axial axis, it is possible to create an arrangement which is very uniform and absolutely stable in terms of tipping. A flanged cage placed between the two mutually complementary ramp groups, carrying spiral flanges and having rolling-contact elements, which are preferably arranged in the central area of the spiral flanges, allows absolutely reliable and repeatable actuation of the axial actuator. This applies particularly to high axial forces since, in contrast to the axial actuators known from the prior art, a large transmission area for axial forces is obtained without the unit surface pressure being too high.  
       [0008] In an advantageous embodiment of the invention, the axial actuator is, in accordance with claim  2 , constructed with a driving device for the rotatable control element. The configuration of the driving device as a multi-chamber pump to be found here increases the efficiency of the axial actuator in an advantageous manner while using a very small, spaced-saving pump which can operate at a low oil pressure with a small quantity of oil. Moreover, gentle, jolt-and jerk-free and, at the same time, accurately definable actuation of the linear motion element is possible in a short response time. Claim  3  describes a variator for a CVT with an axially adjustable variator disk mounted on a shaft and having longitudinal pressurized-oil holes which, via radial holes, supply an annular slot from which, in turn, radial holes lead into pressure chambers of the driving device. This refinement is a very elegant solution to the supply of energy to the driving device and its chambers, which can be achieved within the minimum of space and with a very small number of components.  
       [0009] The advantageous embodiments of a variator according to the invention which are described in claims  4  and  5  relate to the axially displaceable arrangement of the variator disk on the shaft by means of splines or a crossed-roller bearing arrangement. One or other construction will be preferred depending on the particular goals of the application, a decision being taken as to whether a sliding- or a rolling-friction version is the more advantageous in any particular application.  
       [0010] In an advantageous refinement of the invention, the axial actuator claimed, accommodated in a variator, is doubled in number for use in operating a CVT in accordance with claim  6 . Here, it is ensured, inter alia by subjecting the output-side variator to a torsion spring that presses the loose disk against the fixed disk of the variator, that at the moment when an energy drop occurs on the input side, the loose disk on the output side is moved into the forwardmost position under spring control.  
       [0011] Further advantages and features of the configurations according to the invention can be found in the following description, in which an exemplary embodiment of the invention is outlined briefly with reference to drawings to allow a better understanding of the invention. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0012]FIG. 1 shows a section through two variators of a continuously variable transmission (CVT) in a sectional representation, the two variators being oriented toward one another and each accommodating an axial actuator according to the invention;  
     [0013]FIG. 2 shows the input-side (upper) variator from FIG. 1 in section on a somewhat larger scale;  
     [0014]FIG. 3 shows the output-side (lower), variator from FIG. 1 in section on a somewhat larger scale;  
     [0015]FIG. 4 shows a variator similar to that in FIG. 3, although a so-called crossed-roller bearing arrangement is used here instead of splines between the shaft and the looser disk;  
     [0016]FIG. 5 shows a section through the input-side variator, as seen in the direction of arrow C in FIG. 1;  
     [0017]FIG. 6 shows a section through the output-side variator as seen in the direction of arrow C in FIG. 1;  
     [0018]FIG. 6 a  shows an illustration which is identical to the illustration in FIG. 6, with the exception that a crossed-roller bearing arrangement has been shown instead of splines (cf FIG. 4);  
     [0019]FIG. 7 shows a section through the input-side variator arrangement as viewed in the direction of arrow B in FIG. 1;  
     [0020]FIG. 8 shows a section through the output-side variator arrangement as viewed in the direction of arrow B in FIG. 1;  
     [0021]FIG. 9 shows a section through the input-side variator, in particular through the pressure chambers of the driving device in accordance with arrow D in FIG. 1;  
     [0022]FIG. 10 shows a section through the output-side variator viewed in direction D in FIG. 1;  
     [0023]FIG. 11 like FIG. 1, shows the variators of a CVT, but instead of showing them in section, shows them as encapsulated with the loose disks retracted to the maximum possible extent;  
     [0024]FIG. 12 shows the arrangement of the two variators of a CVT in accordance with FIG. 1, as seen in direction E in FIG. 11;  
     [0025]FIG. 13 gives a schematic representation of some of the components of variator VI without the housing;  
     [0026]FIG. 14 gives a schematic view of a rolling contact element for a crossed-roller bearing arrangement;  
     [0027]FIG. 15 gives a schematic view of another rolling contact element for a crossed-roller bearing arrangement; and  
     [0028]FIG. 16 gives a schematic view of a flanged cage in perspective representation. 
    
    
     DETAILED DESCRIPTION  
     [0029]FIG. 1 shows two variators V 1  and V 2 , which are shown arranged in the installed position relative to one another. (Technically identical or similar components of the two variators V 1  and V 2  are identified by the same reference numerals to simplify the description). The input-side variator V 1  is shown at the top in FIG. 1 and FIG. 2. The output side variator V 2  can be seen at the bottom in FIG. 1 and FIG. 3. A shaft  1 , horizontal in FIG. 2, is here of onepiece construction with a variator disk  51 , which lies opposite a variator disk  5  (loose disk) to the left of it. The variator V 1  is supported axially and radially in the same gear case (not shown) by means of a bearing arrangement  23  and a housing  3 . The same applies to variator V 2 , components  3  and  23  being shown only in part in the figures for the sake of clarity.  
     [0030] At this point, it should be stated that it has been assumed that continuously variable transmissions are known from the literature, in particular from an article by Dr.-Ing. Hartmut Faust and Dr. Ing. Andre Linnenbrucker entitled “Development of Continuously Variable Transmmissions at LuK”:  
     [0031] For this reason, the technology and details or particular features of continuously variable transmissions will not be repeated here. Three further literature references may also be mentioned here:  
     [0032] (1) Dr. techn. R. Fischer, Dipl.-Ing. D. Otto:  
     [0033] Wandleruberbruckungssysteme (converter lock-up systems); 4 th  international LuK symposium 1994, “Leichter Schalten umweltfreundlicher und komfortabler Fahren” (Easier gear changing, more comfortable and environmentally friendly driving); pp 133ff.  
     [0034] (2) Dr. techn. R. Fischer:  
     [0035] Das TorCon-System—Ein neues Wandleruberbruckungskonzept als Beitrag zur Okonomie und Fahrtfreude (The TorCon System  
     [0036] A new converter lock-up concept as a contribution to economy and driving pleasure): VDI Report No. 1175, “Getriebe in Fahrzeugen 1995” (Vehicle Transmissions) pp 301 ff.  
     [0037] (3) Dave Piper:  
     [0038] Automatic Transmissions—An American Perspective; VDI Report No. 1175, “Getriebe in Fahrzeugen 1995” (Vehicle Transmissions), pp 25 ff.  
     [0039] The axial component of the contact force, which is transmitted by the loose disk  5  and a chain (not shown) that moves between the cones of the disks  5  and  51 , is taken by a radial/thrust bearing  23 , which is mounted in a fixed position on a gear case (not shown) and supports the fixed disk  51  and the shaft  1  on the left. To adjust the distance between the loose disk  5  and the fixed disk  51 , the loose disk  5  is moved axially toward the fixed disk  51 . This is accomplished by means of an axial actuator AST with a linear-motion element  4 , relative to which the loose disk  5  is rotatably arranged and which transmits the axial force for the adjustment of the loose disk  5  via a thrust bearing  9  situated between the linear-motion element  4  and the loose disk  5 . As can be seen from FIG. 1 and FIG. 2, the loose disk  5  is of one-piece construction with an axial sleeve  50 , which, on the outside, engages in splines  40  on the shaft  1  and, on its outside, guides the linear-motion element  4  radially by means of a radial bearing  7 . The linear-motion element  4 , which is provided with three ramps  403 , is controlled via flanges  111  of a flanged cage  11  that rest against the ramps  403  and, for their part, contain rolling-contact elements, by ramps  203  of a control element  2 , which are complementary to the ramps  403 , said control element being guided radially on the outer circumference of the linear-motion element  4  by means of a bearing  8  (see also FIGS. 6 and 6 a ). A flanged cage of this kind has been described, for example, in the as-yet unpublished German Patent Application 199 42 462.4. The control element  2  is supported by a thrust bearing  10  on a housing  3 . The housing  3  is supported radially against a rear, externally cylindrical end  201  of the control element  2  by a radial bearing  6 . The rear end  201  of the control element  2  contains annular slots RI and R 2 , which are open toward the shaft  1  and are aligned with radial holes S 1  and S 2  respectively, these in turn being supplied with pressurized oil by longitudinal pressurized-oil holes A 1  and B 1  respectively in order to control the axial actuator AST described here in the manner described below.  
     [0040] To make the axial actuator to be described easier to understand, a brief explanation will be given of the way in which the continuously variable transmission illustrated in FIG. 1 operates. An engine, which imparts rotation to the shaft in order to supply power, may be imagined at the left-hand end of the shaft of the upper variator VI. This power is to be transmitted to the shaft  27  of the lower variator V 2 .  
     [0041] Transmission is accomplished by means of a V-belt (not shown here) or a corresponding chain with a variable radius of warp depending on the distance between the fixed and loose disks  51  and  5  of the variators.  
     [0042] In actual fact, the position of the chain disks  51  and  5  of the two variators Vi and V 2  shown in FIG. 1 does not correspond to any operating position since the two disks are at the maximum spacing here. In reality, the disks move axially backward and forward by a distance H (FIG. 1). To set the configuration in FIG. 1 for start-up, i.e., the lowest ratio of torque transmission from variator VI to variator V 2  and from shaft  1  to shaft  27 , the loose disk  5  of, the variator V 2  must be imagined as having been displaced to the left by distance H. In this position, a transmission chain would have the least amount of wrap on variator V 1  and the greatest amount of wrap between the disks  51  and  5  of the variator V 2  on shaft  27 . In this case, it would therefore be a reduction ratio.  
     [0043] To change the transmission ratio to a speed-increasing ratio, the disks  5  must be moved toward the disks  51  up to a maximum distance H until, in the extreme case, the radii of wrap are precisely the reverse of those described above.  
     [0044] To displace a loose disk  5  of a variator, an axial actuator AST is controlled as follows (this will be easier to understand if the apparatus is considered in a static condiiton, i.e., shaft  1  and shaft  27  are thought of as not rotating): pressurized oil is pumped via a longitudinal pressurized-oil hole A 1  and a radial hole S 2  into an annular slot R 1  arranged in the rear end of the control element  2  and pointing toward the shaft  1 , this slot communicating with the chambers K 1  and K 3  of the driving device P (see FIG. 9). An annular slot R 2  communicating with the chambers K 2  and K 4  is supplied with pressurized oil in a similar manner via a longitudinal pressurized-oil hole B 1  and a radial hole S 2 . The chambers K 1 -K 4  are formed by two axially nested concentric housing halves  300  and  200 , the outer housing half  300  having an end  301  with a central round aperture  302 , a cylindrical wall  303  extending axially from the end  301  to the control element  2 , and two chamber walls  305  extending radially inward from the wall  303  to the round aperture  302 . The inner housing half  200  contains a cover ring  206 , which extends radially inward essentially from the cylindrical wall  303  to the central round aperature  302 . A cylindrical wall  204  of the control element  2  extends axially from the cover ring  206  to the aperture  302 . Extending radially from the cylindrical wall  204  of the inner housing half  200  to the cylindrical wall  303  are outward-pointing chamber walls  205 , which are offset by 180° and form a leaktight seal with the cylindrical wall  303 . Two mutually opposite chamber walls  305  extend from the cylindrical wall  303  of the outer housing half  300  to the cylindrical wall  204  of the inner housing  200 . This gives four separate chambers K 1  to K 4  (in variator V 1 ), the chamber pair K 1  to K 3  and the chamber pair K 2  and K 4  each communicating with one another via annular slots R 1  and R 2 . If pressurized oil is now supplied via the pressurized oil hole A 1 , the volume of the chamber K 1  and the chamber K 3  is necessarily increased. This is accomplished by virtue of the fact that the pressure increase in the chambers K 1  and K 3  causes a force to be exerted on the chamber walls  205 , as a result of which—the pressurized oil being supported against the chamber walls  305 , which are fixed relative to the transmission—the control element  2  (as seen in FIG. 9) is rotated in the counterclockwise direction. The chamber walls  205  serve, as it were, as turbine blaues or pump vanes.  
     [0045] Rotation of the control element  2  relative to the housing  3 —initiated by the supply of pressurized oil via the hole A 2  as just described—reduces the volume of pressurized oil in the chambers K 3  and K 4 , which carry oil away again by means of the longitudinal pressurized-oil hole B 1  via an annular slot R 2  and radial hole S 2 . A detailed description of the supply and discharge of pressurized oil will not be given here since this will be available to a person skilled in the art from conventional pressurized-oil control systems. As outlined in FIG. 11 and also in FIG. 2, the linear-motion element  4  is fixed in terms of rotation but not in terms of axial motion relative to the housing  3 . For example, the linear-motion element  4  is mounted in a manner fixed in terms of rotation relative to housing  3  by means of retention pins  4   a , which are mounted on the circumference of the linear-motion element  4  and pass through longitudinal slots  3   a  formed in the housing  3 . Rotation of control element  2  about the axis of the shaft  1  has the effect that ramps  203  arranged on the control element  2  and rising toward the linear-motion element  4  cause the linear-motion element, which can, of course, not rotate with the rotating control element  2 , to move to the right. For this purpose, the linear-motion element has ramps  403  that are complementary to the ramps  203  and likewise rise in a spiral. To ensure that the two ramp groups  203  and  403  do not rest upon one another as a sliding pair, a flanged cage  111  is arranged between them, its spiral flanges  111 , of which there are three in this case and which preferably carry rolling-contact elements, thus forming a spiral thrust bearing. As can be seen from FIGS. 9 and 8, the adjustment angle to obtain the axial adjustment of the loose disk  5  by the distance H is about 700. However, precise relative dimensions will not be given here. The specific dimensions depend on the specific requirements. To simplify the shape and position of the components just described, said shape and position being somewhat complicated to describe, some of the relevant components described are shown again in schematic representation in FIG. 13, the housing  3  with its outer housing half  300  not being shown in this case for reasons of clarity. As a result, the shape of the inner housing half  200  can be clearly seen. However, it can be clearly seen from FIG. 13 how the control element  2  with its ramps  203  and the linear-motion element  4  with its spiral ramps  403  are positioned relative to one another. The flanged cage  11  between them, with flanges  111  which are likewise of spiral configuration, carries rolling-contact elements  110 , for example. The flanges  111  of the flanged cage  11  are connected to one another at the circumference by a cylindrical part-sleeve  112  (FIG. 2), it likewise being possible for the cylindrical sleeve  112  to carry rolling contact elements (not shown) to provide radial support for the flange cage  11  relative to the control element  2  and/or the linear-motion element  4 .  
     [0046] With the arrangement according to the invention of axial actuators in variators of a CVT as just described it is possible to create a highly economical arrangement, the advantages obtained by means of the present invention being very extensive. The design allows high efficiency with a high transmission ratio and a low energy requirement. Compared with known continuously variable transmissions, only a tenth to a fifth of the energy consumption required there is employed. The construction of the driving device with pressure chambers requires only a small pump, which operates at a low oil pressure with a small quantity of oil, and the variator has no rotating parts. Fast adjustment of the variator is promoted if oil flowing out of chambers K 1  and K 3  is fed immediately to chambers K 2  and K 4 .  
     [0047] A helical spring  13  is shown on the shaft  27  illustrated at the bottom in FIG. 1 and in FIG. 3, this spring being secured in the housing  3 , on the one hand, and in the control element  2 , on the other hand, with the result that the two elements, namely the control element  2  and tbe housing  3 , have an inbuilt preload relative to one another and thus adjust the chambers K 1  to K 4  and the position of the loose disk  5  in such a way that the distance between the loose disk  5  and the fixed disk  51  is minimal when operation is interrupted on the oil pressure supply side, e.g. because the engine has stalled or there is a power failure. If there is assisted onward rotation of the shafts  1  and  27  or the entire transmission unit, a speed-increase or speed-reduction ratio favorable for restarting is thus automatically established.  
     [0048]FIGS. 4 and 6 a  show a special form of an axially displaceable but rotationally fixed support coupling between, the loose disk  5  and the shaft  1 . This is a so-called crossed-roller bearing arrangement  60 . In this arrangement, grooves are arranged longitudinally on the circumference of the shaft and in the variator disk, and cylindrical rollers  61  are placed crosswise in these grooves. This allows symmetrical torque transmission from the loose disk to the chain (not shown).  
     [0049]FIG. 14 shows a rolling-contact element  61 , and cylindrical roller with a diameter A and a height A-X. This makes the diameter of the rolling-contact element  61  greater than its length. Since the rolling-contact elements  61  roll axially in grooves and there are no intermediate elements (cages and the like) between the rolling-contact elements  61 , the rolling contact elements must be fixed in their end positions or in the instantaneous positions. This is advantageously possible when all or at least the first and the last rolling-contact element  62  (see FIG. 15) have a height which is greater than their diameter, e.g. a height A+2Y. This is not expensive and can be achieved simply by coating the rolling-contact element  62 . If, for example, a plastic coating is applied, this gives a material which is softer than the rolling-contact element itself and hence flexible and, furthermore, is rougher than the rolling-contact element itself. When installed, the flexible region is compressed. If there are no translational forces acting, the rolling-contact elements are held in their position by means of the coated end faces, whatever their position. The length of the grooves and the number of rolling-contact elements are matched to the respectively required stroke (displacement distance H for the loose disk  5 ). The number of grooves (5 in the example shown) depends on the intended quality of axial guidance and thrust torque to be transmitted. This results in an astonishingly simple but very advantageous shaft/hub connection, which operates with very little wear and very reliably.  
     [0050] The exemplary embodiments explained in this description do not limit the scope of protection of the present application. Analogous modifications likewise form part of the subject matter of the present application.