GB2033984A - Infinitely Variable Cone Pulley Transmission - Google Patents

Abstract

A method of correcting for unwanted transmission ratio variations due to component elasticity and traction belt/chain drift which method involves making very small torque-proportional adjustments to one of the cone pulleys; this can be done by providing a resilient lost- motion arrangement in the mechanisms by which axial movement of the transmission-ratio- selection pulley sheave is achieved, or by providing the normally axially fixed other pulley sheave of a pair with means to move it axially a small amount. As shown, driving and driven pulleys 4, 5 and 6, 7 are adjusted by levers 12, 13 torque-responsive contact pressure between the pulley sheaves and belt or chain 8 is generated by means 40-45, and unwanted changes in ratio as a result of changes of torque are corrected by providing resiliency at 47 in the lever 13. Other arrangements have fluid- pressure operated means for pulley sheave adjustment. <IMAGE>

Description

SPECIFICATION Infinitely Variable Cone Pulley Transmission The invention relates to a method for the correction of the transmission ratio of an infinitely variable cone pulley transmission and to the transmission itself.

The infinitely variable cone pulley transmission is of the kind having; a) two cone pulleys arranged on each of the drive-input and drive-output shafts and transmission means e.g. an endless belt or chain circulating between these; b) the cone pulleys of each pair are connected in rotation with one another and with their shaft and at least one cone pulley on each shaft is axially displaceable for the setting and variation of the transmission ratio of the transmission; c) the last mentioned pulley is supported in the axial direction against a transmission ratio setting member; d) the generation of a torque or torquf and transmission ratio dependent pressure force to set at least one cone pulley pair in the required position on its shaft is effected either;; i) by means of a rotating mechanical presser device and rolling bodies cooperating therewith, against which the adjacent cone pulley is supported and which in turn are supported through a support ring axially against the transmission setting member, or ii) by having the cone pulley of each pair which is displaceable for transmission ratio setting formed as a rotating cylinder-piston unit to which the pressure medium for maintaining and varying the transmission ratio and for generating the pressure application force is conducted by way of a control valve.

The invention thus fundamentally relates to all existing forms of construction, of cone pulley transmissions having two cone pulleys arranged on each of drive-input and drive-output shafts, of which at least one pulley on each of the drive input side and drive-output side is axially displaceable for transmission ratio setting and in which the generation of the pressure application forces dependent upon torque or torque and transmission ratio takes place purely mechanically, mechanically-hydraulically or purely hydraulically.

These cone pulley transmissions constructed according to the present-day prior art work very satisfactorily. However, there is the fundamental disadvantage that there tends to be a greater or lesser deviation from the derived or set transmission ratio when starting from a specific transmission ratio under different loads. In other words there is a drift between the pulleys and the endless belt or chain which runs between them.

An equivalent situation does not arise with transmissions which employ interengaging shaped parts, e.g. gears. This drift does not mean that transmission actually slips as would occur when there is a sudden torque surge. Rather this drift means that the endless belt or chain in travelling through the respective cone pulley pair does not circulate over a constant radius but varies this radius according to whether it comes from the unloaded side to the loaded (driveoutput) or whether it circulates from the loaded side on to the unloaded side (drive-input). This variation of radius causes a radial wandering of the endless belt or chain during passage through the cone pulley pair.This drift leads to a falling characteristic curve which means that with a specific transmission ratio setting the transmission moves with increasing size of the transmitted torque towards lower drive-output rotation speeds.

The other factor which causes the transmission ratio characteristic curve to deviate from its ideal course, i.e. a fixed transmission ratio over the entire permissible load range is the elasticities of the loaded components as for example the supporting mechanical or hydraulic or mechanical-hydraulic transmission members, which cannot be excluded in any transmission or mechanism. Even if these loaded parts were completely overdimensioned, which would lead to an uneconomical transmission, these elasticities lead to a further variation in the transmission ratio characteristic curve. However this variation can supplement, partially cancel or even overcompensate the falling characteristic curve mentioned above in connection with the drift, which is dependent in each case upon the construction and nature of the transmission.The last-mentioned over-compensation is always undesired, because then with rising loading the transmission moves towards higher drive-output rotation speeds, which in the case of great masses to be driven effects an increasing overloading of the drive and can lead to torsional vibrations. Therefore it is fundamentally preferable to have a transmission ratio characteristic curve which if anything is somewhat falling. However, this slightly falling characteristic curve however does not occur of its own accord in different transmission types.

Therefore, dependant upon the application requirements of the transmission a transmission must be selected which brings approximately the characteristic curve course which the user requires.

It is therefore the purpose of the invention to modify a cone pulley transmission of the kind outlined in such a way that a desired transmission ratio characteristic curve can be achieved by design without great difficulty in every transmission type, so that there is the possibility of excluding rising transmission characteristic curves. Starting from known transmissions with their respective constructional peculiarities, here a fundamental possibility is to be indicated which, transferred to the respective transmission type, permits the correction and/or desired setting of the transmission characteristic curve with relatively simple means. The measures should only affect the purchase costs of the transmission to an insignificant extent and should be simple to construct.

The invention is based upon the discovery that by making torque-proportional, that is loaddependent, setting operations of a very small order of magnitude, that is in the range often of only a few hundreds of an mm, by reason of elasticity or also due to drift, it is possible to ensure that the desired transmission ratio characteristic curve is achieved.

The method of the invention solves the problem by making a transmission ratio correction in dependence upon the torque transmitted by the transmission by an axial displacement of one of the cone pulleys of a set of pulleys, the magnitude and direction of which displacement corresponding to the desired transmission ratio correction.

It is thus possible by usually only very slight toque-dependent displacement of the relevant cone pulleys to compensate or reverse the deviations from the desired transmission ratio characteristic curve which derive from the mentioned drift and the elasticities of the transmission. Thus firstly the advantage is obtained that transmissions with the desired accuracy of transmission ratio are available, independently of the naturally permissible loading to which the transmission is subjected. Secondly there is the advantage that for all cases it is possible to use all various transmission types so that the most favourable transmission can be selected for the particular use.

According to the present invention the small adjustment referred to can be achieved either: a) by incorporating a motion device in the mechanism by which axial movement of the transmission-ratio-selection cone pulley is achieved, or b) by providing the normally axially fixed other cone pulley of a pair with means to move it axially a small amount.

The lost motion device can be incorporated in a control lever need to axially displace the transmission-ratio-selection cone pulley. This can be done by making the lever more flexible than it would normally be such as by providing the lever with a slot or by reducing its cross-section. In a hydraulically controlled transmission a torque sensor is incorporated between the control lever and the control slide valve in order to vary the axial positions of the two pulley halves in accordance with the torque-dependent pressure applied to the drive-input side and this brings about a correction to the transmission ratio curve.

In the case of a transmission according to Ger.

Pat. Sp. 2,539,094, then it is expedient to apply the following arrangement. The hydraulic supporting of the mechanical, torque-dependent, presser device on the drive-input side is used with its torque-dependent pressure to deliver on the drive-output side through an additional piston an additional supporting force for the otherwise purely hydraulic supporting of the drive-output side.

In the above mentioned specific solutions under a) above the procedure was always directed towards effecting either modifications to the control levers or to an additional displacement of that cone pulley of a pair which is axially displaceable on each of the transmission shafts for effecting a variation, i.e. directed to modifying the axial displacement of the transmission-ratioselection cone pulley, and setting of the transmission ratio.

In the case of hydraulically displaceable cone pulleys the assembly is fundamentally such that the cone pulley serving for the setting and variation of the transmission ratio of the transmission is part of a cylinder-piston unit to which pressure medium is distributed by a control slide valve, so that fundamentally the pressure application conditions between drive-input and drive-output sides of the transmission are given.

The other cone pulley of each shaft is axially fixedly supported and therefore will ordinarily be called the "fixed pulley".

However, in the alternative of b) above in such hydraulically adjustable transmissions the fixed pulley is in fact axially movable a small amount by means of mechanical, mechanical-hydraulic or fuliy hydraulic means, to effect a correction in the transmission ratio.

How the invention may be carried out will now be described by way of example only, with reference to the accompanying drawings in which: Figure 1 shows a mechanical cone pulley transmission with supporting of the cone pulleys against control levers and a presser device on the drive-input shaft; Figures 2 to 5 show a control lever arm of the transmission according to Figure 1 in different working positions and embodiments; Figure 6 shows a mechanically-supported transmission with two mutually opposite, fixedly supported friction pulleys and two axially displaceable friction pulleys with presser device on the drive-input side and with device in accordance with the invention on the drive-output side; ; Figures 7 and 8 show axial sections represented enlarged in partiai manner along the section lines VIl-VIl and VIll-VIll in Figures 6 and 7 respectively; Figure 9 shows a transmission with hydraulic cone pulley supporting with torque sensor on the drive-input side and hydraulically determined decoupling between control lever and control slide valve; Figure 10 shows a mechanical-hydraulic transmission with mechanical presser device supporting on the drive-input side and hydraulic supporting on the drive-output side; Figure 11 shows a diagram to illustrate the transmission ratio correction in accordance with the invention;; Figure 12 shows the simplified diagrammatic representation of a hydraulically displaceable cone pulley transmission with four-edged control slide valve and torque-measuring member, also two diametrically mutually opposite, fixedly supported cone pulleys, and Figures 1 3 to 20 show different mechanical, mechanical-hydraulic or hydraulic devices for transmission ratio correction on the fixedly supported pulleys.

Figures 1 to 5 According to Figure 1, in a gear box 1 there are arranged a drive-input shaft 2 and a drive-output shaft 3 on which pairs of cone pulleys 4, 5 and 6, 7 respectively are seated and between which a traction means i.e. belt or chain 8 circulates.

The cone pulleys 6 and 7 on the drive-output side are mutually axially displaceable but are nonrotatable in relation to the shaft 3 due to a key 9.

On the other hand the cone pulleys 4 and 5 are rotatable and axially displaceable in relation to the shaft 2 but are mutually non-rotatable since the cone pulley 4 surrounds the shaft 2 with a sleeve 10 on which the cone pulley 5 is moveable axially but is prevented from rotating by means of a key 11.

The axial position of the cone pulleys 4 to 7 and thus the transmission ratio between the two transmission shafts are determined by control levers 12 and 13. These are pivotable about journals 14 and 1 5 arranged centrally between the shafts 2 and 3 and formed by blocks 1 6 and 17 which in turn are seated on a spindle 18 with contrary threadings which is likewise rotatably mounted in the box 1. The lateral displaceability of the blocks 1 6 and 1 7 by means of rotation of the threaded spindle 1 8 enables compensation to be made for manufacturing tolerances and inaccuracies and for wear by the readjustment of the pivot bearings for the control levers 1 2 and 13.

The pivoting of the control levers 12 and 1 3 for the variation of the transmission ratio is effected by a setting spindle 1 9 which is mounted rotatably parallel with the shaft 2 in the gear box 1 and can be rotated for example by means of a hand wheel 20, the setting spindle 1 9 having contrary threadings 21 and 22 by means of which blocks 23 and 24 are axially displaceable, these blocks being pivotally connected to the control levers 12 and 13 by means of journals 25 and 26.

The cone pulleys 4 to 7 are supported against the control levers 12 and 1 3 through pivot bearings 27 to 30 and sleeves 31 to 33, rolling bodies 44, a support ring 41 and a sleeve 34 to which the control levers are pivotably articulated by means of journals 35 to 38.

The transmission of rotation between cone pulleys 4 and 5 on the one hand and the shaft 2 on the other takes place through a device for generating torque-dependent and transmissionratio-dependent pressure application forces between the cone pulleys and the traction means 8.

This pressure application device is formed from a hub 40 on the pulley 4, a support ring 41 and a cam sleeve 42 which is fixed axially and nonrotatably on the shaft 2 by circlips 46 and a key 39 respectively. The hub 40 has a plurality of rectangular incisions in to which the rolling bodies 44 serving for torque transmission are inserted.

The support ring 41 is provided with an oblique annular face 43 for supporting and force deflection. Moreover this face has an extension piece 45 for over-run securing of the rolling bodies 44. The more detailed construction of this pressure application device appears from German Patent Specification 2,539,094 and will not be explained in any further detail here.

While the cone pulleys 5 to 7 are firmly supported against their control levers 1 2 and 1 3 in the axial direction, the supporting of the cone pulley 4 takes place directly through the pressure application device against the control lever 1 3. In the event of a torque being applied to the shaft 2, forces arise between the cam sleeve 42 on the one hand and the hub 40 on the other and the conical annular face 43 which forces possess a component in the peripheral direction and a component in the axial direction of the shaft 2.

The force component in the axial direction supports the cone pulley 4 in the axial direction while the force component in the peripheral direction ensures the entraining of the cone pulley 4 and thus also of the cone pulley 5.

The control lever 13 is provided with a slot 47 between the drive-input shaft 2 and the setting spindle 19 in the upper half of the articulation to the journal 25 of the block 23. This slot 47 increases the flexibility of the arm of the control lever 13 between the journals 1 5 and 25 so that it is flexed more than the other arms of the control levers 12 and 13 under the action of the separating forces on the cone pulleys.

The manner of operation of the transmission illustrated is as follows: The intended transmission ratio of the transmission, as characterised by a horizontal line in Figure 11, is set on the hand wheel 20. The transmission characteristic curve of a transmission is composed of the following parts: 1 The drift, and 2 the yieldability of the support members.

The drift always has a lowering action upon the drive-output rotation speed and results in a falling characteristic curve. This characteristic curve is either further increased by the elasticities in the mechanism to give the characteristic curve a shown in Figure 11, or is reduced or even overcompensated for as shown in a rising characteristic curve-b in Figure 11-when the rise of transmission ratio as a result of the yieldability is greater than the transmission ratio drop as a result of the drift.

Without the slotting 47 the transmission would operate as follows. If the torque is introduced on the drive-inputside, that is into the shaft 2, then due to the presser device an axial force occurs which on the one hand acts through the pulley 4 upon the traction means 8 and shifts the latter on to larger running circles, and on the other hand acts upon the control levers. At the same time the traction means at the drive-output side is drawn into the V-gap of the pulleys. This is possible because the cone pulleys at the drive-output side are mounted on the ends of the control levers which ends flex more there than at the drive-input side where the control levers are additionally mounted by means of the journals 25, 26 of the setting spindle 19.Since the running radii at the drive-output side have become smaller and at the drive-input side have become larger, the fall in transmission ratio due to the drift is more or less eliminated by this rise of transmission ratio. If the rise of transmission ratio thus generated is greater than the fall of transmission ratio caused by the drift, then a rising characteristic curve according to b in Figure 11 results.

This rising characteristic curve, as already initially mentioned, is undesired in all cases. If slotting 47 is now provided and the arm of the control lever 13 on the drive-input side is thus made more flexible this has the effect of causing slightly falling transmission characteristic curve as designated by c in Figure 11. This slightly falling characteristic curve permits stable operation.

Thus the slotting 47 causes the associated lever to yield more about the pivot point 1 5 and thus move the cone pulley 6 to the right and thus increase the effective diameter of the pair of cone pulleys 6, 7. In this way the transmission ratio characteristic curve designated by b in Figure 11 is corrected to a characteristic curve which is designed by c in Figure 11.

Figure 2 shows the upper arm of the control lever 13 according to Figure 1 enlarged and in the unloaded condition, while Figure 3 shows this arm of the control lever 1 3 in the loaded condition.

Figure 4 shows a device for limiting the flexure of the upper arm of the control lever 1 3. This device consists of a clip welded at 48 to the left side, which has on the other side a flange 49 with screw 50 adjustable therein, by means of the setting of which the expansion of the slot 47 can be limited.

Finally Figure 5 shows how the upper arm in Figure 1 of the control lever 13 can also be made more flexible by reduction of its cross-section at 51.

Figure 6 According to Figure 6 a drive-input shaft 61 and a drive-output shaft 62 are rotatably mounted in a gear box 60 and carry cone pulleys 63, 64 and 65, 66 which are non-rotatable in relation to one another due to keys 67 and 68. The mutually opposite cone pulleys 64 and 66 are supported axially fixedly to the right against a shaft collar 69, 70 while the transmission of rotation between the respective shaft and the cone pulleys 63 and 65 respectively is effected by presser devices 71, 72 as already explained in detail with reference to Figure 1. The support rings 73 and 74 are supported against setting discs 75 and 76 through anti-friction bearings. The setting discs have external teeth 77 and 78 with which a central pinion 79 meshes which is rotatable in the housing by means of a hand wheel 80.On rotation of the hand wheel 80 the setting discs 75 and 76 are oppositely rotated so that they carry out contrary setting distances due to the threadings 81 and 82 by means of which they are rotatably mounted fast with the gear box casing.

As in the transmission according to Figure 1, in this transmission the presser device 71 ensures the pressure application forces are dependent upon torque and transmission ratio. On the other hand in this respect the normal operation of the presser device 72 is neutralised to some extent by an annular spring 83 which surrounds the balls contained in it and forces the balls radially inwards into the grooves 84 of the presser device.

An effectivness of the presser device 72 can be set by selecting the power of the spring 83 to ensure that the drift-caused transmission ratio drop and the effect of the elasticity of the transmission parts are so compensated for that the desired transmission ratio characteristic curve, for example the characteristic curve c according to Figure 11 is obtained.

Figures 7 b 8 Figure 7 shows an enlarged partial sectional view along the line VIl-VIl in Figure 6 and Figure 8 shows a sectional view along the section line VIlI-VIlI in Figure 7.

As appears especially from Figure 8, the annular spring 83 can be divided into segments 85, for example three on the circumference, which are radially supported by radial pins 86 in support rings 74 and axial pins 87 in the support ring 74.

Figure 9 Figure 9 shows an all-hyc:raulic cone pulley transmission. Again cone pulleys 92, 93 and 94, 95 are arranged on a drive-input shaft 90 and a drive-output shaft 91 respectively. The cone pulleys 93, 95 are fixed axially on the shafts and non-rotatably on the shafts. The cone pulleys 92, 94 are formed as the cylinders 96, 97 of associated pistons 98, 99 which are fixed to their associated shafts. The cone pulleys 92, 94 are axially displaceable on the shafts 90, 91 but held against rotation by keys 100, 101.

The pressure medium is distributed to the cylinder-piston units thus formed by a common pump 102 on the drive-input side through the conduit 103 and on the drive-output side through the control slide valve 104 and the conduit 105.

Depending upon the transmission loading any excess oil under pressure can flow back into the pressure medium reservoir 108 through the conduits 106, 107.

The control slide valve 104 is in communication, through a control piston 109 displaceable in it, with a setting lever 110. The lever 110 is articulated by way of a circumferential groove 111 on the cylinder 96 of the axially displaceable cone pulley 92 on the drive-input side. The transmission ratio is adjustable by means of a hand lever 112 on the lever 11 0. The control piston 109 is loaded by a compression spring 11 3 which reacts against the control slide valve 104.

The device of the invention for effecting a transmission ratio correction is located in the control slide valve 1 04. For this purpose the control piston 109 is charged with the drive-input oil pressure on its side remote from the compression spring 113, through a conduit 114.

The drive-input pressure conduit 103 is connected through a conduit 11 5 with the torque-measuring sensor 11 6 arranged cn the drive-input shaft. This sensor through its control piston 11 7 controls the gap 11 8 thus the outflow of the drive-input pressure oil and thus also the drive-input pressure-medium pressure. The oil under pressure then flowing away is returned through the conduit 107.

With the arrangement as described the regulating operation proceeds as follows.

If on the drive-input side a torque increase takes place, the torque sensor 11 6 constricts the oil returned through the conduit 107 from the drive-input side by means of the control edge 11 8. The pressure rise thus effected-considered firstly only on the drive-input-would lead to a displacment of the cone pulley 92 so that the endless belt or chain 121 on the drive-input assumes a larger running radius and on the driveoutput a smaller running radius. As may be seen from Figure 11 this would signify the undesired high rise in transmission ratio. Simultaneously with the pressure rise on the drive-input side however the pressure in the pressure chamber 122 also increases through the conduit 114.This has the effect that the control slide valve 104 is shifted to the right and enlarges the control gap 123, which leads to a pressure increase on the drive-output side of the transmission. This pressure increase on the drive-output side again returns the belt or chain 121 towards the smaller running radius, whereby the transmission ratio correction is given. Thus according to the design of the control piston 109 and of the compression spring 113 in the control slide valve 104, the transmission ratio characteristic curve can be set in the desired manner. The two separately described operations of course proceed simultaneously side-by-side, so that practically no fluctuation of transmission ratio occurs.

Figure 10 According to Figure 10 a drive-input shaft 1 31 and a drive-output shaft 132 are mounted in a gear box 130. Cone pulleys 133 and 134 are arranged on the drive-input shaft while cone pulleys 135, 136 are seated on the drive-output shaft. A traction means 137, i.e. endless belt or chain, circulates between these. The cone pulleys 133 and 135 are formed as axially fixedly supported pulleys which are connected in rotation with the cone pulleys 134 and 136 by means of keys 138,139.

On the drive-input side the pressing force is again generated in dependence upon torque and transmission ratio by a presser device 140 the support ring 141 of which is formed as a cylinder surrounding a piston 1 42 fast with the shaft. The pressure medium drawn from a pressure medium source 143 is fed through a radial bore 144 to the cylinder chamber between support ring 141 and piston 142. Moreover the pressure medium is present on a control edge 145 which establishes the pressure medium pressure according to the axial position of the cylinder in combination with a thrust ring 146. The thrust ring 146 in turn is supported against a setting disc 147 which can be adjusted by means of a threading 148 fast with the gear box, through its external teeth 149 and by means of a pinion 1 50 operated by a hand wheel.As regards this setting disc on the driveoutput side likewise the construction substantially corresponds to that according to Figure 6.

On the other hand on the drive-input side however the threading 1 58 is not fast with the gear box but is a component of a support cylinder 160 which is axially displaceable on a piston 161 fast with the box but non-rotatable in relation to the gear box 130. The support cylinder 160 forms on the side remote from the thrust ring 156 a pressure chamber 1 62 with which the pressure medium supply on the drive-input side is in communication through a conduit 1 63 in such a manner that on an increase of pressure on the drive-input side it is shifted towards the thrust ring 1 56 against the action of springs 1 64 supported on the gear box, by means of the mechanical connection given by the threading 1 58.

The regulating operation in this transmission proceeds as follows.

On a rise of torque on the drive-input side the presser device 140 shifts the support ring 141 away from the cone pulley 134, whereby the control gap 145 is rediced. This leads to a rise of pressure medium on the drive-input side which leads to the belt or chain 1 37 assuming a larger running radius between the cone pulleys 133 and 134 and correspondingly a smaller running circle on the drive-output side. This signifies, as illustrated with reference to Figure 11, an undesired rise in the transmission ratio characteristic curve i.e. b in Figure 11.However, this rising transmission ratio characteristic curve is corrected in that simultaneously with the rise of pressure oil on the drive-input side this pressure oil rise also passes through the conduit 1 63 to the chamber 1 62 and thus shifts the support cylinder 1 60 to the left against the action of the springs 1 64. Thus the control edge 1 55 on the driveoutput side is further closed, which on the driveoutput side also leads to a rise of pressure oil in the cylinder chamber between cone pulley 1 36 and piston 1 52. Thus the belt or chain 137 is shifted on the drive-output side back again towards a larger running radius and correspondingly on the drive-input side to a smaller running radius. This correction of transmission ratio can be influenced in the desired manner by the size of the piston area in the chamber 1 62 and the strength of the spring 1 64 so that the transmission ratio correction leads to a transmission ratio characteristic curve of the desired kind. The actions as explained in detail above again proceed simultaneously.

Figure 12 Figure 12 shows firstly again the fundamental assembly of a hydraulically displaceable cone pulley belt-type transmission known per se having a torque sensitive member 1 84 on the driveoutput shaft 1 71. This torque sensitive member can also be present in known manner on the drive-input and the drive-output sides. The generation of the pressing forces can take place purely hydraulically or mechanically-hydraulically.

The transmission as illustrated in Figure 1 2 has a drive-input shaft 1 70 and a drive-output shaft 171. Axially displaceable cone pulleys 1 72, 1 73 and axially fixedly supported cone pulleys 1 74 and 1 75 are arranged on these shafts. The cone pulleys 1 72 and 1 73 which are axially displaceable to set the transmission ratio are formed in known manner as cylinder-piston units of pistons (not shown) fast with the shafts. An endless belt or chain 1 76 circulates between the cone pulleys.

The pressure medium supply to the cylinderpiston units formed by the cone pulleys 1 72 and 1 73 leads by way of a four-edged control slide valve 177, which distributes the pressure medium to the cone pulleys in known manner between application pressure on drive-output sides. The four-edged control slide valve is fed with oil by a pump 178. The excess pressure medium can flow away by way of the conduit 179 and may serve for lubricating the traction means 1 76.

The four-edged control slide valve is articulated to a setting lever 181 which slides in a circumferential groove 182 of the pressure cylinder on the drive-input side. To its other end a setting spindle 1 83 is articulated for the setting of the transmission ratio of the transmission.

This transmission is known perse and therefore the manner of its operation not be discussed in detail. By reference to Figures 1 3 to 20 it is intended to illustrate a number of arrangements for transmission ratio correction that can be applied to a transmission of this type.

In the previously described embodiments the correction device has acted either upon the control levers or upon the displacement of the axially movable cone pulley for the setting of the transmission ratio. In contrast in the embodiment of Figure 12 the correction device acts on the axially fixedly supported cone pulley 174, 175. It is always effective on the side on which no direct torque-dependent pressure force prevails, that is to say in the pulley assembly in which the traction means is drawn into the V-gap of the pulleys, in order to push the traction means out again, i.e.

into a larger radius.

Here the otherwise so-called fixed pulley is made at least axially displaceable by a minimum amount. However the pulley is still axially fixed from a transmission ratio setting point of view since in every case the axial displaceability has nothing to do with the voluntary setting of the transmission ratio but serves only to carry out the very small corrective movements required to maintain the desired transmission ratio.

Figures 13 to 20 In Figures 13 to 20 only one pulley assembly is shown in half section. The so-called fixed pulley is shown in detail while the other pulley of the pair is not since it incorporates the known cylinderpiston unit for the voluntary setting of the transmission ratio.

Finally for simplification in these figures the previously utilised term "fixedly supported cone pulley" will not be used, but the term "fixed pulley" will be used, although the pulley referred to in each case is not a fixed pulley in an absolute sense.

According to Figure 13 the fixed pulley 230 is connected in rotation with the cone pulley 232 through the splining 231. With an axially fixedly supported piston 233 it again forms a cylinderpiston unit and is supported against the piston 233 when the transmission is stationary or through an axial bearing 234 on starting up.

In a recess 235 in the flange of the fixed pulley 230 a control piston 236 is axially displaceable which forms control edges 239 and 240 with the pressure medium admission 237 and the pressure medium outflow 238 coming from the cylinderpiston unit. The spacing of these control edges is selected just so that both cannot be open at the same time. Under the pressure of the inflowing pressure medium the end face 241 of the control piston stands under shifting action against a spring 242 which lies on the side of the control piston facing the cone pulley 232.

The effect of this apparatus is as follows. If an increase of the torque takes place a variation of transmission ratio would occur. Now however.

the hydraulic pressure which is increased as a result of torque increase acts upon the end face 241 and the control piston 236 is shifted to the left against the spring 242 and the fixed pulley 230 also shifts to the left under the increased pressure-medium pressure until the control edge 239 is closed again and the control edge 240 is opened. Thus the fixed pulley 230 is shifted somewhat to the left together with the control piston 236 for transmission ratio correction, whereby the endless belt or chain is shifted on to a larger running radius and the transmission ratio variation is compensated.

According to Figure 14 the fixed pulley 260 is connected fast in rotation but axially displaceably with the shaft 262 through a key 261. It forms a cylinder-piston unit with an axially supported piston 263. A control piston 265 is axially displaceable in a recess 264 of the flange of the flxed pulley 260. Under the pressure-medium pressure the control piston 265 bears against a spring 269 which again is arranged on its side facing the other cone pulley 270.

The pressure medium outflow takes place by way of a constriction 271 in the piston 263 and by way of the head clearance of the key 261.

If an increase of torque and thus an increase of pressure takes place here, the piston 265 is pressed to the left against the action of the spring 269. Thus the control edge 267 opens further and the inflow of pressure medium increases. Since the constriction 271 has a fixed cross-section, the pressure medium inflow increases in relation to the pressure medium outflow. Thus a pressure increase on the fixed pulley 260 takes place. This will thus yield to the left and thus bring about the correction of transmission ratio. Thus with this arrangement only the pressure medium inflow is controlled. Thus the axial position of the gap 267 determines the axial position of the fixed pulley and thus the correction of transmission ratio.

It is different in the case of the arrangement according to Figure 1 5 where only the pressure medium outflow is controlled. Here again the fixed pulley 275 is connected fast in rotation with the shaft by a key 276. With an axially fixedly supported piston 277 it forms a cylinder-piston unit to which the pressure medium flows through a radial bore 278.

A control piston 280, which with a pressure medium out-flow 281 forms a control edge 282, is axially displaceable in a recess 279. The control piston 280 is subject, by way of the pressure medium inflow, with its one end face 283 to the pressure-medium pressure while on the other side it is again loaded by a spring 284.

The setting operation here takes place as follows.

If the loading of the transmission and thus also the pressure-medium pressure increases, the piston 280 will yield to the left. Thus the pressure medium return flow on the control gap 282 is reduced or closed so that the pressure-medium pressure rises. This rising pressure-medium pressure also shifts the fixed pulley 275 to the left. Equilibrium then occurs again at the elevated pressure-medium pressure corresponding to the increased torque which pressure with the corresponding shift of the control piston 280 to the left also involves a corresponding shift of the fixed pulley 275 to the left and thus the correction of transmission ratio.

In contrast to the previous solution the following Figures 1 6 and 17 have no control edges.

According to Figure 1 6 the fixed pulley 300 is connected in rotation through a splining 301 with the other cone pulley 302 but is axially displaceable on the shaft 303. With a piston 304 fast with the shaft it forms a cylinder-piston unit to which the pressure medium flows by way of a bore 305. On the side of the piston 304 remote from the fixed pulley 300 there is a spring 306 which seeks to draw the fixed pulley 300 on to the piston. On the other hand the pressurecharged area of the fixed pulley 300 is larger than that of the cone pulley 302 so that per se the fixed pulley 300 seeks to press the cone pulley 302 away, but only just as far as permitted by the spring 306.If here a torque increase and thus also an increase of the pressure-medium pressure takes place, the fixed pulley 300 shifts in the direction towards the traction means 307, as far as permitted by the spring 306, that is to say until a static equilibrium position is reached. This also signifies the desired transmission ratio characteristic curve correction according to the dimensioning of the transmission.

According to Figure 1 7 an arrangement comparable with Figure 16 is made in that the fixed pulley 310 is conducted around the shaftfast piston 311 and fixed in rotation in relation to the shaft by means of a key 312. Between the wall 313 and the piston 311 a spring 314 is arranged so that it seeks to move the fixed pulley 310 is charged with pressure medium.

The embodiments according to Figures 18 and 19 work purely mechanically. They can be used in transmissions with mechanical or equally with hydraulic shift.

According to Figure 1 8 the fixed pulley 290 is supported through a presser device 291 against a collar 292 which is seated axially and circumferentially fixedly on the shaft 293. The fixed pulley 290 is in abutment on springs 294 against the action of the presser device 291.

This purely mechanical presser device ensures that on an increase of torque the balls of the presser device 291 run up somewhat on the cam paths of the presser device and thus press the fixed pulley 290 against the springs 294. Thus in proportion to torque a small readjusting movement takes place for transmission ratio compensation.

The form of embodiment according to Figure 1 9 differs from that according to Figure 1 8 merely in that the springs 295 are in operative connection between fixed pulley 296 and a setting device 297 the setting device being connected with the collar 298 fast with the shaft, through a thread 299. By means of this thread it is possible to effect an adjustment of the initial stress of the springs 295 and thus any desired transmission characteristic curve correction.

Finally according to Figure 20 the fixed pulley 290 is supported through a presser device 191 against the fixed stop 1 92. The fixed pulley is at the same time the piston of a cylinder 193 to which the pressure medium flows by way of a bore 1 94 of the shaft 1 95 through the presser device 1 91. The effective piston area is smaller than that of the side of thedisplaceable cone pulley 196.

The fixed pulley 190 with its flange 197 and an annular space 198 arranged thereon forms a control edge 199 with a radial bore 200 by way of which the pressure medium can flow to the annular chamber 198 and thence away through the bore 201. A fixed stop 202 secures the maximum axial travel of the fixed pulley 190.

Thus this fixed pulley is at the same time formed as torque sensor and carries out the function of the feeler represented in Figure 12 as separate element 184. The axial movements are also used, as well as for transmission ratio correction, by means of the constriction edges 1 99 for torquedependent development of the pressure which charges the cylinder of the other pulley assembly.

The manner of operation of this device consists in that on a torque rise the fixed pulley 1 90 shifts somewhat to the left under the action of the presser device 1 91 whereby the gap of the control edge 1 99 is further closed and the pressure is increased, namely in proportion to the torques conducted through the transmission. The transmission ratio correction is effected by this displacement.

Claims (14)

Claims

1. A method for the correction of the transmission ratio of an infinitely variable cone pulley transmission of the kind having; a) two cone pulleys arranged on each of the drive-input and drive-output shafts and transmission means e.g. an endless belt or chain circulating between these; b) the cone pulleys of each pair are connected in rotation with one another and with their shaft and at least one cone pulley on each shaft is axially displaceable for the setting and variation of the transmission ratio of the transmission; c) the last mentioned pulley is supported in the axial direction against a transmission ratio setting member; d) the generation of a torque or torque and transmission ratio dependent pressure force to set at least one cone pulley pair in the required position on its shaft is effected either;; i) by means of a rotating mechanical presser device and rolling bodies cooperating therewith, against which the adjacent cone pulley is supported and which in turn are supported through a support ring axially against the transmission setting member, or ii) by having the cone pulley of each pair which is displaceable for transmission ratio setting formed as a rotating cylinder-piston unit to which the pressure medium for maintaining and varying the transmission ratio and for generating the pressure application force is conducted by way of a control valve; characterised in that for the transmission ratio correction in dependence upon the torque transmitted by the transmission an axial adjustment is effected on one of the cone pulleys of one pulley set, the magnitude and direction of which corresponds to the desired transmission ratio correction.

2. A transmission for carrying out the method of Claim 1, in which the cone pulleys or the support ring of the presser device arranged on the drive-input side are supported against control levers which are mounted pivotably centrally between the transmission shafts and are articulated on the side of the drive-input shaft remote from the mounting to a threaded spindle for the setting and variation of the transmission ratio of the transmission, characterised in that at least one of the arms of the control levers on the drive-input side has a lower axial support capacity than the other arms.

3. A transmission as claimed in Claim 2, characterised in that the said one arm has a longitudinal slot in it to make it more flexible than it would otherwise be.

4. A transmission as claimed in Claim 3, characterised in that the longitudinal slot is provided with an adjustable stop for varying its flexibility.

5. A transmission as claimed in Claim 2, characterised in that the said one arm has a smaller cross-section than the other arms thus making it more flexible than the other arms.

6. A transmission for carrying out the method according to Claim 1 in which two mutually opposite cone pulleys are formed as axially fixedly supported pulleys while the other two are axially displaceable and the cone pulley displaceable on the drive-input side is supported against the presser device, while the oblique surface pairs are formed as grooves extending substantially parallel with the shaft axis, in which the effective oblique surface inclination is varied over the groove length and in which the balls are displaceable substantially axially with the transmission ratio, and wherein at least one of the support surfaces of the support ring or of the adjacent cone pulley is formed as a wedge surface facing the respective groove, by which the radial forces exerted by the oblique face slope upon the balls are converted into axial support forces, characterised in that on the drive-output side likewise such a presser device is arranged and in that the balls of the presser device are in abutment against a spring which loads them radially towards the transmission shaft.

7. A transmission for carrying out the method according to Claim 1, in which two diametrically opposed cone pulleys are formed as pressure cylinders axially displacedble on shaft-fast pistons, while the pressure medium drawn from a source is distributed to the pressure cylinder on the drive-output side through a control slide valve which is articulated through a transmission setting member to the pulley path on the driveinput side, characterised in that the pressure cylinder, on the drive-input side is connected directly to the pressure medium source in that the connection between setting member and control slide valve contains a piston guided in the control slide valve, and charged against the force of a spring likewise by the pressure-medium pressure on the drive-input side, and in that the return flow of the pressure-medium pressure going towards the drive-input side takes place through a torque sensor formed as a control valve and is connected with the drive-input shaft.

8. A transmission for carrying out the method according to Claim 1, in which on the drive-input side the support ring of the mechanical presser device is arranged on the front of the cylinder of a cylinder-piston unit guided axially on the shaft with axially displaceable cylinder und piston fast with the shaft, to whose cylinder chamber placed between support ring and piston the pressure medium drawn from a first pressure medium source is supplied, while furthermore the cylinder is guided on its rear end remote from the support ring displaceably on the shaft with an axially extending flange, while furthermore on the flange there is guided a thrust ring displaceable mechanically axially for the setting of the transmission ratio and cooperating with the cylinder, and wherein between flange and thrust ring a control edge is formed by way of which the pressure medium supplied to the cylinder chamber flows away, while on the drive-output side the displaceable cone pulley is formed as pressure cylinder of a shaft-fast piston, to which the pressure medium is fed from a second pressure-medium source, the cylinder being guided displaceably on the shaft with an axially extending flange on its side remote from the cone pulley, wherein further on the flange there is guided a thrust ring displaceable mechanically axially for the setting of the transmission ratio and cooperating with the cylinder, and wherein finally between flange and thrust ring a control edge is formed by way of which the pressure medium supplied to the cylinder chamber flows away, characterised in that on the side of the thrust ring remote from the cone pulley a support cylinder is arranged axially displaceably but non-rotatably in relation to the gear box on a piston fast with the gear box, in that the support cylinder on the side remote from the thrust ring forms a pressure chamber, in that the pressure chamber is in communication with the pressure medium supply on the drive-input side in such manner that on an increase of pressure it is displaced against the action of springs supported on the gear box towards the thrust ring, and in that the support cylinder is mechanically connected with the thrust ring.

9. A transmission for carrying out the method according to Claim 1, in which on each shaft a cone pulley is formed as rotating pressure cylinder of a shaft-fast piston to which the pressure medium for setting and maintaining the transmission ratio is distributed by a four-edged control slide valve which is in communication through a setting lever with one of the axially displaceable cone pulleys, while the other two cone pulleys are axially firmly supported characterised in that the firmly supported cone pulleys are connected axially displaceably but non-rotatably in relation to the other cone pulley and with a fixedly supported cylinder or piston form a cylinder piston unit, in that a control piston forming inflow and outflow control edges is displaceably mounted therein between a pressure medium inflow for the pressure-medium pressure prevailing on the other cone pulley of this shaft and the pressure medium outflow, in that the length of the control piston is dimensioned just so that only inflow or output is opened and in that the control piston is subjected with its end face on the inflow side to the pressure-medium pressure on the inflow side against the action of a spring arranged on its side nearer to the other cone pulley.

10. A transmission for carrying out the method according to Claim 1, in which on each shaft one cone pulley is formed as rotating pressure cylinder of a shaft-fast piston to which the pressure medium for setting and maintaining the transmission ratio is distributed by a four-edged control slide valve which is in communication through a setting lever with one of the axially displaceable cone pulleys, while the other two cone pulleys are axially fixedly supported, characterised in that the fixedly supported cone pulleys are connected axially displaceably but non-rotatably in relation to the other cone pulley and with a fixedly supported cylinder or piston form a cylinder-piston unit, in that a control piston forming a control edge is displaceable therein with the pressure medium inflow for the pressuremedium pressure prevailing on the other cone pulley of this shaft, in that the end face of the control piston on the inflow side is subject to inflow-side pressure-medium pressure against the action of a spring arranged on its side nearer to the other cone pulley and in that the pressuremedium outflow from the cylinder-piston unit takes place by way of a constriction.

11. A transmission for carrying out the method according to Claim 1, in which on each shaft a cone pulley is formed as rotating pressure cylinder of a shaft-fast piston to which the pressure medium for setting and maintaining the transmission ratio is distributed by a four-edged control slide valve which is in communication through a setting lever with one of the axially displaceable cone pulleys while the other two cone pulleys are axially fixedly supported, characterised in that the fixedly supported cone pulleys are connected axially displaceably but non-rotatably in relation to the other cone pulley and with a fixedly supported cylinder or piston form a cylinder-piston unit, in that the pressure medium flows to the cylinder-piston unit through a pressure medium inflow with the pressuremedium pressure prevailing on the other cone pulley of this shaft, in that in the cylinder-piston unit a control piston forming a control edge with a pressure medium outflow is displaceable and in that the end face of the control piston on the inflow side is charged by the inflow side pressuremedium pressure against the action of a spring arranged on its side nearer to the other cone pulley.

12. A transmission for carrying out the method according to Claim 1, in which on each shaft a cone pulley is formed as rotating pressure cylinder on a shaft-fast piston to which the pressure medium for setting and maintaining the transmission ratio is distributed by a four-edged control slide valve which is in communication through a setting lever with one of the axially displaceable cone pulleys, while the other two cone pulleys are axially fixedly supported, characterised in that the fixedly supported cone pulleys are axially displaceable but non-rotatable in relation to the other cone pulley of their shaft, in that the fixedly supported cone pulleys form with an axially non-displaceable piston a cylinderpiston unit which is charged with the pressuremedium pressure of the other cone pulley of its shaft, in that the pressure-charged area of the fixedly supported cone pulleys is larger than that of the others of their shaft and in that the fixedly supported cone pulleys are displaceable against the force of a spring towards the other cone pulley of their shaft (Figure 1 6).

1 3. A transmission for carrying out the method according to Claim 1, in which on each shaft a cone pulley is formed as rotating pressure cylinder of a shaft-fast piston to which the pressure medium for setting and maintaining the transmission ratio is distributed by a four-edged control slide valve which is in communication through a setting lever with one of the axially displaceable cone pulleys while the other two cone pulleys are axially fixedly supported, characterised in that the fixedly supported cone pulleys are mounted axially displaceably and rotatably on their shaft and in that the fixed supported takes place through a torqueproportional presser device against the action of a spring; the presser device in turn being fixedly supported.

14. A transmission according to Claim 13, characterised in that the initial stress of the spring is adjustable.

1 5. A transmission for carrying out the method according to Claim 1, in which on each shaft one cone pulley is formed as rotating pressure cylinder of a shaft-fast piston to which the pressure medium for setting and maintaining the transmission ratio is distributed by a four-edged control slide valve which is in communication through a setting lever with one of the axially displaceable cone pulleys, while the other two cone pulleys are axially fixedly supported, characterised in that the fixed supporting is effected through a torque-proportional presser device, in that the axially supported cone pulleys are axially displaceable away from the supporting by at least a small amount and are rotatable on their shaft by at least a small amount, in that the fixedly supported cone pulleys are formed as pistons of a stationary cylinder jacket issuing from the fixed supporting, which jacket is charged with the pressure of the other cone pulley of its shaft but with smaller piston area, and in that the fixedly supported cone pulleys form a setting valve for the outflow of the pressure prevailing on the respective transmission side.

1 6. A transmission according to Claim 15, characterised in that the valve is a radial bore of the shaft in combination with a control edge of the mounting neck of the cone pulley, from which the pressure medium can flow away without pressure.

1 7. A transmission substantially as hereinbefore described with reference to and as shown in the accompanying drawings.