Transmission unit for motor vehicles

Abstract: Transmission unit for motor vehicles of the type containing a continuous variable transmission (2) consisting of an ingoing shaft (3), a driven shaft (4), two pulleys (5-6) situated on the ingoing shaft (3) and the driven shaft (4) respectively, and an endless transmission element (7) provided between said pulleys (5-6), whereby the above-mentioned pulleys (5-6) each consist of two pulley halves (8-9, 10-11) with conical contact surfaces (12) which can be axially adjusted in relation to one another, such that the transmission ratio between the ingoing shaft (3) and the driven shaft (4) can be continuously altered, whereby the transmission element (7) consists of a lubricated belt which is provided with metal parts (13) having contact surfaces (14) which work in conjunction with the above-mentioned conical contact surfaces (12) of the pulley halves (8-9, 10-11), and whereby the contact surfaces (14) of the parts (13) have a profiling (17), in particular a profiling (17) procuring a thin-film lubrication, characterized in that the conical contact surfaces (12) of the pulley halves (8-9, 10-11) concerned are polished.

Description: The present invention concerns a transmission unit for motor vehicles as defined in the preamble of claim 1 and known from US-A-4 794 741. In particular, it concerns a transmission unit containing a continuous variable transmission, consisting of an ingoing shaft, a driven shaft, two pulleys situated on the ingoing shaft and the driven shaft respectively, and an endless transmission element provided between said pulleys, whereby the above-mentioned pulleys each consist of two pulley halves with conical contact surfaces which can be axially adjusted in relation to one another, such that the transmission ratio between the ingoing shaft and the driven shaft can be continuously altered. It is known that with such a continuous variable transmission, it is possible to use a transmission element which consists of a lubricated belt which is provided with metal parts having contact surfaces which work in conjunction with the above-mentioned conical contact surfaces of the pulley halves. The metal parts are connected as such by means of flexible elements, such as cords or such. The belt is lubricated by exposing the belt and/or the pulley halves to oil and/or a cooling liquid. This can be done in any way whatsoever. As described in European patent No. 0.574.085, this can be done for example by squirting the oil and/or the cooling liquid on the transmission element and/or the pulleys by means of one or several feed pipes. In the embodiments known until now, the contact surfaces of the pulley halves are finished by means of conventional grinding. New types of transmission elements have been developed recently whereby the contact surfaces of the parts are provided with a profiling which procure a thin-film lubrication. These profilings are made such that the above-mentioned parts locally penetrate deeper in the oil film situated between the parts and the pulley halves, so that a metal-on-metal contact is obtained locally, as a result of which the risk for the transmission element to slip under a heavy load is minimized. An example of such new type of transmission element is known from US-A-4.794.741. Further, it is known that a new transmission element must always wear in, whereby the contact surfaces of the above-mentioned parts on the one hand, and the pulley halves on the other hand act on one another and adjust to one another as a result of minor wear, after which there will be practically no wear anymore, or at least the wear which is brought about afterwards is so minor that the life of the continuous variable transmission will exceed the normal life of the motor vehicle. In transmission units which are equipped with the above-mentioned recent types of transmission elements, it was found, however, that there is often an unstable wear-in, whereby instead of the contact surfaces getting adjusted to one another, these surfaces start acting on one another more and more aggressively, and the roughness on these surfaces remains or even increases. As a result, the transmission unit is strongly subject to wear, so that the aimed life and quality are not achieved. The invention aims a transmission unit with a transmission element which makes use of the principle of thin-film lubrication, but whereby the above-mentioned disadvantages are excluded with certainty. To this end, the invention concerns a transmission unit as defined by the features of claim 1. Further aspects of the invention are outlined in the dependent claims. As use is made of a combination of a profiled contact surface on the above-mentioned parts and a polished contact surface on the pulley halves, the contact surface of the pulley halves is particularly smooth, and there are no two rough surfaces acting on one another, which finally has for a result that the profiled contact surface of the above-mentioned parts will always smoothly adjust to the contact surface of the pulley halves. This guarantees a stable wear-in. The profile of the contact surfaces of the above-mentioned parts can be of any nature whatsoever and may for example consist of a punched profile, a corrugated profile or a profile formed of local recesses which are obtained for example by sandblasting the surface concerned. The conical contact surfaces are preferably polished with a cloth with particles or with a polishing block. In particular, they are preferably polished by means of a rotating polishing movement. Thanks to this rotating polishing movement is obtained a very smooth surface. In the case where there are nevertheless roughnesses, they do not extend in the sense of rotation of the pulleys, which has for a result that, at the time of the wear-in, the roughnesses on the contact surface of the pulley halves can never co-operate with the profiling on the contact surfaces of the above-mentioned parts, and an unstable wear-in is once more counteracted. A polishing element is hereby preferably used which has such a diameter that this polishing element covers the entire or almost entire radial length of the conical contact surface. As the entire radial length is covered at once, the creation of roughnesses is minimized. It is also preferred that the polishing element, as it carries out a rotating movement around its own axis, is moved over the contact surface of the pulley half to be worked, such according to a circular path in relation to said pulley half. According to a practical embodiment, the pulley half to be worked is driven in a rotating manner, and the rotating polishing element is represented to the rotating contact surface in a fixed place. In order to better explain the characteristics of the invention, the following preferred embodiments are described as an example only without being limitative in any way, with reference to the accompanying drawings, in which: figure 1 schematically represents a transmission unit; figure 2 represents a section according to line II-II in figure 1 in a highly schematic manner, in which the two farthest positions of the transmission element are represented; figure 3 represents a section to a larger scale on the place which is indicated by arrow F3 in figure 1, for an embodiment according to the invention; figure 4 represents a variant of the part which is represented in figure 3; figure 5 schematically represents the method according to the invention. As represented in the figures 1 and 2, the invention concerns a transmission unit 1 containing a continuous variable transmission 2, consisting of an ingoing shaft 3, a driven shaft 4, two pulleys 5-6 situated on the ingoing shaft 3 and the driven shaft 4 respectively, and an endless transmission element 7 provided between said pulleys 5-6. The pulleys 5-6 each consist of two pulley halves 8-9 and 10-11 with conical contact surfaces 12. The pulley halves 8-9, 10-11 respectively can be axially adjusted in relation to one another, such that the transmission ratio between the ingoing shaft 3 and the driven shaft 4 can be continuously altered. The above-mentioned transmission element 7 consists of a lubricated belt which is provided with metal parts 13 having contact surfaces 14 which work in conjunction with the above-mentioned conical contact surfaces 12. The lubrication can be carried out in any way whatsoever. In the given example, this is done by means of a belt lubricating pipe 15 via which a number of squirts of oil and/or cooling liquid 16 are squirted on the transmission element 7 and/or on the pulleys 5-6. Also the metal parts 13 can be linked to one another in any way whatsoever. Examples thereof are sufficiently known from the state of the art and consequently are not further described here. As mentioned in the introduction, the invention specifically concerns embodiments whereby the contact surfaces 14 have a profiling which procures a thin-film lubrication. An example of such a profiling 17 is represented in figure 3. Use is hereby made of a corrugated profile, preferably obtained by means of punching. It should be noted that in reality, the roughnesses of this profiling 17 are very small. In a practical embodiment, the ribs 18 will for example have top sides with a width of a few hundreds of a millimeter, whereas they have a height of for example 0.03 mm. By a thin-film lubrication is meant that the oil film 19 which is present on certain places on the contact surfaces 12 is entirely or almost entirely displaced locally, so that a metal-on-metal contact is obtained and the risk of slipping is minimized. Thanks to the use of a profiling 17 as mentioned above, such a thin-film lubrication is obtained, as the protruding parts of the profiling 17 can easily penetrate in the oil film 19. The invention is special in that a combination is made of the use of contact surfaces 14 which are provided with such a profiling 17 on the one hand, and the use of contact surfaces 12 which are polished on the other hand. Thus, as explained in the introduction, it is excluded that two profilings, namely the above-mentioned wanted profiling 17 on the one hand, and a profiling due to a too rough finishing of the contact surfaces 12 on the other hand, start acting on one another, as a result of which the wanted profiling 17 would disappear in no time due to wear. Thanks to the present invention, there will be only a limited wear on the ribs 18 as the transmission unit wears in, such that a stable profile finally remains, for example having a rib height of 0.01 mm, such for the entire life of the continuous variable transmission 2. As mentioned in the introduction, the profiling 17 can be of any nature whatsoever. As an example is given a profiling 17 with local recesses 20 in figure 4, resulting from the sandblasting of the contact surface 14, such in combination with a contact surface 12 which is polished in compliance with the invention. The contact surfaces 12 are preferably polished in a manner as represented in figure 5. The conical contact surfaces 12 are hereby treated with a rotating polishing element 21, in particular a polishing block. This is represented in figure 5 for one pulley half, but it is clear that the other pulley halves can be treated in a similar manner. A polishing element 21 is preferably used hereby, having such a diameter D that this polishing element 21 covers the entire or almost the entire radial length of the conical contact surface 12, whereby the distance indicated by 'R 1 in figure 5 is meant by this radial length. As represented in figure 5, the polishing element 21 is moved over the contact surface 12 of the pulley half to be treated according to a circular path in relation to this pulley half, while carrying out a rotating movement around its own axis 22, which is realized by driving the pulley half to be treated around its axis 23 in a rotating manner, and by representing the rotating polishing element 21 to the rotating contact surface 12 in a fixed place. It should be noted that by the above-mentioned term 'oil' is implied any type of lubricant and/or cooling medium. By 'metal' parts are understood parts which are exclusively made of metal, as well as parts made of hard materials having a hardness which can be compared to that of the metal parts, as well as parts made of other materials, but whose contact surfaces 12 are made of metal or a material which is comparable as far as hardness is concerned. Although the contact surface 12 of every pulley half 8-9-10-11 is preferably polished, it is clear that the invention also concerns embodiments whereby only one or a restricted number of the contact surfaces 12 are polished. The present invention is by no means limited to the above-described embodiments represented in the accompanying drawings; on the contrary, such a transmission unit, the pulleys used thereby and the above-mentioned method can be made in all sorts of variants while still remaining within the scope of the invention.

Claims: Transmission unit for motor vehicles, said transmission unit containing a continuous variable transmission (2) consisting of an ingoing shaft (3) and a driven shaft (4), two pulleys (5-6) situated on the ingoing shaft (3) and the driven shaft (4) respectively, and an endless transmission element (7) provided between said pulleys (5-6); whereby each of said pulleys (5-6) consist of two pulley halves (8-9, 10-11) with conical contact surfaces (12) which can be axially adjusted in relation to one another, such that the transmission ratio between the ingoing shaft (3) and the driven shaft (4) can be continuously altered; whereby the transmission element (7) consists of a lubricated belt which is provided with metal parts (13) having contact surfaces (14) which work in conjunction with said conical contact surfaces (12) of said pulley halves (8-9, 10-11); and whereby the contact surfaces (14) of said metal parts (13) have a profiling (17), in particular a profiling (17) procuring a thin-film lubrication; characterized in that the conical contact surfaces (12) of said pulley halves (8-9, 10-11) are polished; and in that the contact surfaces (14) of said metal parts (13) have a corrugated profiled structure in the form of ribs (18) obtained by means of punching. Transmission unit according to the preceding claim, characterized in that the conical contact surfaces (12) are surfaces which are obtained as the result of polishing with a cloth with particles or with a polishing element (21) in the shape of a polishing block. Transmission unit according to any of the preceding claims, characterized in that the conical contact surfaces (12) are surfaces which are obtained as the result of a polishing by means of a rotating polishing element (21). Transmission unit according to claim 3, characterized in that said polishing element (21) having a diameter (D), so that this polishing element (21) covers the entire or practically the entire radial length (R) of the conical contact surface (12). Transmission unit according to claim 3 or 4, characterized in that the polishing element (21) is moved over the contact surface (12) of the pulley half (8-9-10-11) to be treated according to a circular path in relation to this pulley half, while carrying out a rotating movement around its own axis (22). Transmission unit according to claim 3 or 4, characterized in that the pulley half (8-9-10-11) to be treated is driven in a rotating manner, and in that the rotating polishing element (21) is represented to the rotating contact surface (12) in a fixed place.

Inventors: ADRIAENSSENS FRANK CORNELIUS M, BROUX JAN MICHEL MARIA, COPS VALENTIN ANTOINE, DEGEEST DIRK GEERT THEO DOMINI, ADRIAENSSENS, FRANK CORNELIUS MARIA, BROUX, JAN MICHEL MARIA, COPS, VALENTIN ANTOINE, DEGEEST, DIRK GEERT THEO DOMINIQUE
Applicants: ZF GETRIEBE N V SINT TRUIDEN, ZF GETRIEBE N.V. SINT TRUIDEN
Application year: 2000
Main classification: F16H55
IPC codes: B24B29, F16H9, F16G5, F16H55, F16H57