The present invention relates to a continuously variable transmission incorporating a push-type drive belt with increased ratio coverage and, more in particular to a control method for such a transmission. The continuously variable transmission is generally known, for example from European patent application EP1529985-A. In the design of such transmissions it typically aimed at maximising the available range of transmission ratios provided by the transmission, i.e. its ratio coverage, given the required throughput of driving power per unit of mass and/or volume of the transmission. Various manners of accomplishing this aim exist, often requiring extensive research and significant redesign of the pulley and/or the drive belt components of the transmission. Presently, it is therefore an object to realise the same in a cost effective and preferably simple manner, in particular without substantial changes to the existing transmission designs being required.

In accordance with the present disclosure, the above object is realised in the transmission according to claim 1 and, more in particular, with the ratio control method according to claim 5 hereinafter. In this novel transmission and/or with the novel control method a radial position of the drive belt between the pulley discs of at least one of the transmission pulleys is determined such that the ring set of the drive belt extends, at least partly, beyond the outer circumference, i.e. to the radial outside of the respective pulley, however, only over a segment of the curved trajectory of the drive belt at the respective pulley.

The present disclosure makes use of the circumstance that during operation of the transmission the curved pulley trajectory of the drive belt spirals radially inwards as seen in the direction of movement of the drive belt, due to the elastic deformation of the pulleys and of the drive belt itself. In particular, the radius of curvature of the drive belt's curved pulley trajectory between the pulley discs is larger at the point of entry of the drive belt there between than at the point of exit from in-between such pulley discs. As a result, the ring set of the drive belt can be located inside the outer circumference of the pulley discs where the drive belt exits (from in-between the discs of) the pulley, thus being constrained thereby in the axial direction, even though it is located to the radial outside of pulley discs of that pulley at the said point of entry.

The above-mentioned elastic deformation and, hence, also the amount of radially inward spiralling of the drive belt is proportional to not only to the force with which the drive belt is clamped between the pulley discs, but also to the radial position of the drive belt between such discs. Therefore, in accordance with the present disclosure, the most extreme radial position of the drive belt (at entry) between the pulley discs is advantageously set in proportion to such clamping force.

In practical transmission designs, the radially inward spiralling of the drive belt typically amounts up to 1 to 2 millimetres or more, such that according to the present disclosure the ring set can extend beyond the circumference of the pulley, at the point of entry of the drive belt between the pulley discs thereof, by at most the same amount. Thus, the largest controlled radial position of the drive belt can be increased by the same amount relative to the conventional control method, whereby the ratio coverage of the transmission is favourably increased without any modification being required to the transmission other than incorporating therein a somewhat longer drive belt to make possible the said increased radial position thereof. Alternatively, the diameter of the pulleys -and thus an envelop of the transmission as a whole- can be reduced, while favourably maintaining the ratio coverage of the transmission.

It is noted that it is known from EP 1529985-A to provide the transmission with guiding means, separate from the pulley discs, for imposing an ultimate axial position on the ring sets, such that these can be brought beyond the outer circumference of the pulleys without the risk of one or more endless rings of the ring set separating from the drive belt. However, this known transmission thus requires additional components in the form of the guiding means, raising the complexity and cost thereof.

The novel control method according to the present disclosure will now by way of example be elucidated further along a drawing in which:

figure 1 provides a schematic perspective view of the continuously variable transmission with a drive belt running over two pulleys;

figure 2 shows a cross section of the known drive belt oriented in the circumference direction thereof;

figure 3 provides a width-wise oriented view of a transverse member of the known drive belt;

figure 4 provides a cross-section of the prior art transmission part including the pulley and the belt, the latter being represented in an ultimate radial position relative to the pulley;

figure 5 in a schematic side elevation of the prior art transmission illustrates an aspect of the operation thereof; figure 6 illustrates the same aspect of the prior art transmission in a cross-section of the pulley and the belt thereof;

figure 7 illustrates the novel transmission during operation in a schematic side elevation thereof; and

figure 8 illustrates the novel transmission of figure 5 in a cross-section of the pulley and the belt thereof.

In the figures, identical reference numbers relate to identical, or at least comparable technical features.

The schematic illustration of a continuously variable transmission in figure 1 shows a drive belt 3 that runs over two pulleys 1 , 2 and that includes two sets of a number of flexible rings 31 and a number of transverse members 32 that are consecutively arranged along the circumference of the ring sets 31 in an essentially contiguous row, while being contained and guided thereby. The transmission pulleys 1 , 2 each include a pair of conical discs 4, 5 that define a tapered circumferential groove that opens towards the radial outside whilst enclosing an acute angle; the so- called pulley angle Φρ. Circumference sections of the drive belt 3 are located in the pulley grooves, while being clamped by and between the pulley discs 4, 5 of the respective pulley 1 , 2.

The axial separation between these pulley discs 4, 5 can be controlled, typically by way of only one pulley disc 4 of the pulleys 1 , 2 being arranged axially movable relative to a respective pulley shaft 6, 7, in order to control a speed ratio between the pulleys 1 , 2. In the illustrated configuration of the transmission, the upper pulley 1 will rotate more quickly than the lower pulley 2. By changing the distance between the two conical discs 4, 5 of the pulleys 1 , 2, the radial positions or running radii R1 , R2 of the drive belt 3 at the pulleys 1 , 2 are changed in mutually opposite radial directions and, as a result, the ratio between rotational speeds of the two pulleys 1 , 2 is varied. More in particular, the speed ratio is defined as a rotational speed of an output pulley 2 of the transmission, which output pulley 2 is associated with a load, divided by a rotational speed of an input pulley 1 of the transmission, which input pulley is associated 1 with an engine or motor driving the load. In figure 1 the transmission is thus depicted in its smallest speed ratio.

In figure 2, an exemplary embodiment of the drive belt 3 is shown in cross section oriented in circumference or length direction L thereof, i.e. facing in a direction perpendicular to the axial or width direction W and the radial or height direction H of the drive belt 3. In this figure 2, the ring sets 31 are shown in cross- section and one transverse member 32 of the drive belt 3 is shown in a front elevation. The ring sets 31 are in this case constituted by five individual flat, thin and flexible endless rings each, which endless rings are mutually concentrically nested to form the respective ring set. In practice, however, these ring sets 31 often comprise more than five endless rings, e.g. nine or twelve or possibly even more.

The transverse members 32, a side view whereof is included in figure 3, take- up a clamping force exerted between the discs 4, 5 of each pulley 1 , 2 via contact faces 37 thereof, one such contact face 37 being provided at each axial side of the transverse member 32. These contact faces 37 are mutually diverging in radial outward direction such that an acute angle is defined there between that is denoted the belt angle <J>b of the drive belt 3 and that closely corresponds to the pulley angle Φρ. The transverse members 32 are able to move, i.e. to slide along the ring sets 31 in the circumference direction L, so that a torque can be transmitted between the transmission pulleys 1 , 2 by the transverse members 32 pressing against one another and pushing each other forward along the circumference of the ring sets 31 in a direction of rotation of the drive belt 3 and the pulleys 1 , 2.

The transverse member 32 of the drive belt 3, which is also shown in a side elevation in figure 4, is provided with two cut-outs 33 located opposite one another, which cut-outs 33 each open towards a respective axial side of the transverse member 32 and each accommodate a small circumference section of a respective ring set 31 . A first or base portion 34 of the transverse member 32 thus extends radially inwards from the ring sets 31 , a second or middle portion 35 of the transverse member 32 is situated in between the ring sets 31 and a third or top portion 36 of the transverse member 32 extends radially outwards from the ring sets 31 . The radially inner side of each cut-out 33 is delimited by a so-called bearing surface 42 of the base portion 34 of the transverse member 32, which bearing surface 42 faces radially outwards, generally in the direction of the top portion 36 of the transverse member 32, and contacts the inside of one of the ring sets 31.

A first or rear surface 38 of the two main body surfaces 38, 39 of transverse member 32 that face in mutually opposite circumference directions L, is essentially flat. The other or front main body surface 39 of the transverse member 32 is provided with a so-called rocking edge 18 that forms, in the radial direction H, the transition between an upper part of the front surface 39, extending essentially in parallel with its rear surface 38, and a lower part thereof that is slanted such that it extends towards the rear surface 38. The said upper part of the transverse member 32 is thus provided with an essentially constant dimension between the main body surfaces 38, 39, i.e. as seen in the circumference direction L, which dimension is typically referred to as the thickness of the transverse member 32. Furthermore, the transverse segment 10 is shown to be provided with a projection 40 that protrudes from its front main face 38 thereof and with a corresponding hole 41 that is provided in its rear main face 39. In the drive belt 3, the projection 40 of the trailing transverse segment 32 is at least partially located in the hole 41 of the leading transverse segment 32, such that mutual displacement of these adjacent transverse segments 32 in a plane perpendicular to the circumferential direction of the drive belt 3 is prevented or, at least, limited.

The transverse members 32 and the (endless rings of the) ring sets 31 of the drive belt 3 are typically made of steel.

In the conventional transmission, a largest running radius imposed on the drive belt 3 (at either pulley 1 ; 2) is limited by the (endless rings of the) ring set 31 still being located in-between the pulley discs 4, 5 in order to avoid that the ring set 31 or an individual endless ring thereof can separate from the drive belt 3 in the axial direction. This latter requirement of the known design and controlled operation of the transmission is illustrated in more detail in figure 4, wherein the drive belt 3 is depicted in such largest or maximum running radius R-max relative to the centre of rotation of the respective pulley 1 ; 2. In figure 4 the horizontal dashed line indicates the outer extent and diameter of the pulley discs 4, 5, immediately radially inward whereof the ring sets 31 are located. Obviously, such maximum running radius R- max at both pulleys 1 , 2, also determines the maximum and minimum speed ratio provided by the transmission, i.e. determine the total ratio coverage of the transmission, at least in combination with a minimum radial position of the drive belt 3 as determined by the diameters of the respective pulley shafts 6; 7.

It is noted that, in the present disclosure and for the sake of simplicity, the running radius of the drive belt 3 is defined by the radially outer extent of the ring sets 31 relative to the rotational centre thereof, whereas this parameter is often associated with the rocking edge 18 in the art instead.

In the art, it has been observed that during operation of the transmission the actual curved pulley trajectory of the drive belt 3 between the pulley discs 4, 5 of the pulleys 1 , 2 does not necessarily follow a circular arc, but can spiral radially inwards to a smaller or greater extend in the direction of rotation DR of the drive belt 3. This aspect of the transmission operation is schematically illustrated in figures 5 and 6, in a side elevation of the transmission and in a cross-sectional view of the output pulley

2 respectively.

In figure 5 the trajectory of the drive belt 3 is schematically indicated by the dash-dotted line T3 that tracks the radial outer extent of the ring sets 31 . A clear difference can be observed between the running radius R-in of the drive belt 3 when entering (between the discs 4, 5 of) the output pulley 2 and such running radius R-out when exiting from that output pulley 2. This radially inward spiralling of the drive belt

3 at the output pulley 2 is caused, at least predominantly, by the elastic deformation of the pulley discs 4, 5 and of the pulley shaft 7 that increases, not only in dependency on the applied load, but also -and to a large extent- in dependency on the running radius of the drive belt 3. Thus, in figure 5, the inward spiralling of the drive belt 3 at the input pulley 1 is minimal, even negligible.

In figure 6, a bending of the shaft 7 is the primary cause of the deformation of the output pulley 2 and has been exaggerated to more clearly illustrate the running radii of the drive belt 3 at entering (R-in) between and at exiting (R-out) from in- between the pulley discs 4, 5. In reality, the pulley discs 4, 5 will also bend or flex in the axial direction to a certain extent.

Both in figure 5 and in figure 6 the curved pulley trajectory of the drive belt 3 satisfies the above-explained requirement that the radially outer extent of the ring sets 31 remains within the outer circumference or radial dimension RD of the pulley discs 4, 5 of the pulleys 1 , 2. However, according to the present disclosure, the ring sets 31 is already sufficiently constrained in the axial direction if it is located within the radial dimension RD of the pulley discs 4, 5 for only a part of the said curved pulley trajectory of the drive belt 3. This insight opens up the possibility to increase the said maximum running radius R-max. More in particular, such maximum running radius R-max is determined not by the running radius of the drive belt 3 at entering R-in between the pulley discs 4, 5, but rather by the running radius thereof at exiting R-out from in-between the pulley discs 4, 5, which latter running radius at exiting R- out should be smaller than the radial dimension RD of the pulleys 1 , 2, in particular of the pulley discs 4, 5 thereof. In formula:

R-in > RD > R-out (1 )

Thus, during operation of the transmission and at least at one pulley (1 , 2) thereof, the ring set 31 extends at least partly beyond a radial dimension of the pulley discs 4, 5 at a point of entry of the drive belt 3 between the pulley discs 4, 5 of such respective pulley 1 , 2 and, simultaneously, is fully contained between, i.e. constrained in the axial direction by the pulley discs 4, 5 at a point of exit of the drive belt 3 from between the pulley discs 4, 5 of such respective pulley 1 , 2.

The above-described, possible trajectory of the drive belt 3 in accordance with the present disclosure is schematically indicated in the figures 7 and 8 in a side elevation of the transmission and in a cross-sectional view of the output pulley 2 respectively.

In figure 7 the trajectory of the drive belt 3 is schematically indicated by the dash-dotted line T3 that tracks the radial outer extent of the ring sets 31. The running radius of the drive belt 3 (as defined by the radially outer extent of the ring sets 31 thereof) at entering R-in (between the discs 4, 5 of) the output pulley 2 exceeds the radial dimension RD of the output pulley 2, whereas such running radius at exiting R- out when from that output pulley 2, due to the radially inward spiralling of the drive belt 3 in the said curved pulley trajectory thereof at the output pulley 2 and in accordance with the present disclosure. As a result of this trajectory that is imposed on the drive belt 3 by a control system of the transmission through the control of the clamping forces exerted on the drive belt 3 by the input and output pulleys 1 , 2, the said smallest speed ratio between these pulleys 1 , 2 is favourably decreased relative to the prior art transmission depicted in figure 5.

In figure 8, the output pulley 2 of figure 7 is shown in a cross-section corresponding to that of figure 6 with the elastic deformation thereof being exaggerated to more clearly illustrate the running radii of the drive belt 3 at entering R-in between the pulley discs 4, 5, as well as at exiting R-out from in-between these pulley discs 4, 5 in relation to the radial dimension RD thereof.

The above principle in accordance with the present disclosure, namely of controlling the running radius of the drive belt 3 (as defined by the radially outer extent of the ring sets 31 thereof) at entering R-in between the discs 4, 5 of the pulley 1 ; 2 to exceed the radial dimension RD of the respective pulley 1 ; 2, while ensuring that such running radius at exiting R-out the pulley 1 ; 2 remains within the radial dimension RD of the respective pulley 1 ; 2, can also be applied to the input pulley 1 to favourably increase the largest speed ratio of the transmission relative to the prior art transmission. This alternative arrangement of the transmission is illustrated in the box inserted at the top right corner of figure 7.

In practice, the radially inward spiralling of the drive belt typically amounts up to 2 millimetres or so, such that according to the present disclosure the ring set 31 can extend beyond the radial dimension RD of the pulley, at the point of entry of the drive belt between the pulley discs thereof, by at most the same amount. For example, if the running radii R1 and R2 of the drive belt 3 vary between 30 and 75 mm in the conventional transmission, the novel transmission that is controlled in accordance with the present disclosure for the maximum running radius R-in at pulley entry of both the input pulley 1 and the output pulley 2 provides a highly significant increase in ratio coverage of almost 6%, namely the ratio coverage of the said typical, conventional transmission amounts to (70 mm/30 mm) ² , i.e. 5.44, whereas the novel transmission provides a ratio coverage of (70+2 mm/30 mm) ² , i.e. 5.76.

The present disclosure, in addition to the entirety of the preceding description and all details of the accompanying figures, also concerns and includes all the features of the appended set of claims. Bracketed references in the claims do not limit the scope thereof, but are merely provided as non-binding examples of the respective features. The claimed features can be applied separately in a given product or a given process, as the case may be, but it may also be possible to apply any combination of two or more of such features therein.

The invention(s) represented by the present disclosure is (are) not limited to the embodiments and/or the examples that are explicitly mentioned herein, but also encompasses amendments, modifications and practical applications thereof, in particular those that lie within reach of the person skilled in the relevant art.