WO2013000492A1

WO2013000492A1 - Hydraulically activated adjustable pulley for a torque transmission device

Info

Publication number: WO2013000492A1
Application number: PCT/EP2011/003226
Authority: WO
Inventors: Francis Maria Antonius Van Der Sluis; Ingmarus Geert Hupkes; Johannes Gerardus Ludovicus Maria Van Spijk
Original assignee: Robert Bosch Gmbh
Priority date: 2011-06-30
Filing date: 2011-06-30
Publication date: 2013-01-03
Also published as: EP2726758A1

Abstract

Hydraulically activated adjustable pulley (50) for a torque transmission device in a vehicular drive line. The pulley (50) is provided with two conical discs (51, 52) on a shaft (53) and with hydraulically activated displacement means (54, 55, 56) for displacing one such disc (52) along such shaft (53) towards the respective other one disc (51). The pulley shaft (53) is provided with an axially oriented channel (58) and with a radially oriented channel (59) branching-off from the axial channel (58) and connecting to the displacement means (54, 55, 56) for allowing hydraulic fluid to flow to and from the displacement means (54, 55, 56). The axial channel (58) either is open towards both axial ends (64, 65) thereof, or is closed-off in the axial direction, with the shaft (53) being provided with a further radially oriented channel (61), likewise branching-off from the axial channel (58).

Description

HYDRAULICALLY ACTIVATED ADJUSTABLE PULLEY FOR A TORQUE TRANSMISSION DEVICE

The present invention relates to a hydraulically activated adjustable pulley for a device for transmitting torque in a vehicle drive line. In such torque transmission device two such pulleys are provided that are interconnected in rotational sense by means of a drive belt or chain. Such transmissions are generally known, for example from EP-A- 0 924 447, and are in particular applied as a continuously variable transmissions in the automotive field. Each pulley comprises two conical discs provided on a shaft, whereof at least one disc is displaceable along such shaft towards the respective other one disc such that the belt can be clamped between and rotates integral with these discs. For such displacement of the at least one pulley disc, the known pulley is provided with hydraulically activated displacement means, such as a piston-and-cylinder-assembly, that act on the displaceable pulley disc. Pressurised hydraulic fluid is allowed to be supplied to and discharged from the displacement means by means of a hydraulic channel provided in the pulley shaft. The known hydraulic channel is provided in the pulley shaft as an axially oriented, blind bore (hole) and at least one radially oriented bore, branching-off from the axial bore and connecting to the displacement means.

The above-described, known pulley and transmission designs function quite well and are universally applied in practice in wide range of motor vehicles. However, in this particular industry there exists the trend towards activating the displacement means by ever higher hydraulic pressure levels, for increasing the efficiency of the transmission, as well as for allowing the miniaturisation thereof. A side effect hereof is that the hydraulic pressure in the axial bore generates an ever higher axial force on the pulley shaft, which axial force is supported by a housing of the transmission via roller bearings by means of which the pulley shaft is mounted in such transmission housing. These roller bearings are, however, typically designed to accommodate radially oriented forces and are substantially less suited to support an axial load. Also, the bearings losses may increase with an increasing axial load.

As an example it is noted that in conventional transmission design the displacement means are typically activated by hydraulic fluid that is pressurised to between 5 to 35 bar, whereas state of the art and future transmission designs may utilise an activation pressure level of 60 bar or more, even up to 80 bar. For a typically applied axial bore having a diameter of 1.25 cm², an axial force of up to 1 kN will thus be generated on the pulley shaft by the pressurised hydraulic fluid. Of course, this axial force could be reduced, simply by reducing the diameter of the axial bore; however, such is generally not possible as the displacement means also demand a considerable flow rate of the hydraulic fluid for the proper operation thereof.

It is an aim of the present invention to, on the one hand, allow the desirable high hydraulic pressure level to be applied for activating the displacement means of the transmission and to, on the other hand, limit the axial force that is generated thereby on the pulley shaft thus avoiding the need to simultaneously equip the transmission with specially designed, i.e. axially strengthened, roller bearing or even axial bearing means.

According to the invention the above aim is realised by either one of two principal solutions in terms of the design of the hydraulically activated adjustable pulley. In a first solution, the axial bore in the pulley shaft is closed-off in both axial directions, i.e. at both axial ends and, additionally, is provided with a further radial bore branching-off from the axial bore, which further radial bore is connectable to a hydraulic control system of the transmission. In a second solution, the axial bore extends over the entire axial dimension of the pulley shaft and opens towards its surroundings in both axial directions.

It may be noted that in the above two solutions, i.e. in both pulley designs according to the invention, the pulley shaft can include separable, modular parts that are mutually fixed in, at least, the axial direction.

In the said first solution according to the invention it is realised that the axial force effected on one axial end of the axial bore of the pulley shaft is compensated by an oppositely directed axial force effective on the respective other, i.e. opposite axial end thereof, whereas in the said second solution no such axial force is effected at all. Either way, favourably no net axial force is generated on the pulley shaft by the pressurised hydraulic fluid in the hydraulic channel in the pulley shaft. As a result, the unfavourable axial loading of the roller bearings of the pulley shaft may be largely avoided, allowing for a simpler, cheaper and more robust design of these roller bearings and of the transmission as a whole. Additionally, friction losses in the roller bearings can be reduced and/or the (displacement means) activation pressure level can be increased relative to the state of the art transmission.

In order to explain the invention in more detail, exemplary embodiments thereof will now be described with reference to the drawing, in which:

Fig. 1 diagrammatically shows a cross-section of the continuously variable transmission with two hydraulically activated adjustable pulleys according to the prior art; Fig. 2 diagrammatically shows a close-up of the known adjustable pulley in cross- section;

Fig. 3 diagrammatically shows a first embodiment of the adjustable pulley according to the invention in cross-section; and

Fig. 4 diagrammatically shows a second embodiment of the adjustable pulley according to the invention in cross-section.

The known continuously variable transmission 1 is illustrated diagrammatically and in cross-section in Fig. 1. A transmission housing 11 of the transmission 1 encloses two adjustable pulleys 3, 7. Both pulleys 3, 7 respectively comprise two conical pulley discs 4, 5; 8, 9 on a pulley shaft 2; 6, which pulley shafts 2, 6 are mounted in the transmission housing 11 by means of two roller bearings 22, 23 each.

One pulley disc 5; 8 of each pulley 3; 7 is fitted axially displaceable on the respective pulley shaft 2; 6 by means of a respective sleeve 20; 25. By controlling the respective axial positions of the displaceable pulley discs 5, 8 of the pulleys 3, 7 in a mutually coordinated manner, the radial positions of the drive belt 10 between the pulley discs 4, 5; 8, 9 of the pulleys 3, 7 is set and hence the speed or transmission ratio of the transmission 1 is determined. To effect the said coordinated control of the displaceable pulley discs 5, 8, the pulleys 3, 7 are each provided with a displacement means associated with the respective displaceable pulley disc 5; 8. It is well-known in the art to provide these displacement means in the form of respective piston-and- cylinder-assemblies 17, 18, 19, 21 , 24; 26, 27.

The piston-and-cylinder-assembly 17, 18, 19, 21 , 24 of a first pulley 3 defines two pressure chambers 3, 14. Pressurised hydraulic fluid is supplied to or discharged from these pressure chambers 13, 14 via a hydraulic channel 12, 15, 16 that is provided in the respective pulley shaft 2. The hydraulic channel 12, 15, 16 is provided in the pulley shaft as an axially oriented, blind bore 12 and two radially oriented bores 15, 16 that branch-off from the axial bore 12 and that connect to a respective one of the two pressure chambers 13, 14 of the first pulley 3.

The piston-and-cylinder-assembly 26, 27 of a second pulley 7 defines just one pressure chamber 28. Pressurised hydraulic fluid is supplied to or discharged from this pressure chamber 28 via a hydraulic channel 29, 30 that is provided in the respective pulley shaft 6. In this case too, the hydraulic channel 29, 30 is provided in the pulley shaft as an axially oriented, blind bore 29 and a radially oriented bore 30 that branches-off from the axial bore 29 and that connects to the pressure chambers 28 of the second pulley 7. A further example of a known pulley design, as applied in the continuously variable transmission, is provided in cross-section by figure 2. This pulley 50 too comprises two conical discs 51 and 52 placed on a pulley shaft 53. Again, one pulley disc 51 is placed on the pulley shaft axially moveable under the influence of a hydraulic pressure to be exerted in the cylinder chamber 54 defined between a piston 55 that is fixed to the pulley shaft 53 and a cylinder 56 that is fixed to the said axially moveable pulley disc 52. The cylinder chamber 54 is connected to a supply line 57 for hydraulic fluid in the transmission housing 11 by means of a radially oriented bore 59 and an axially oriented blind bore 58 of the pulley shaft 53. A seal 60, typically a rotating seal 60, is provided between the rotatable pulley shaft 53 and the stationary housing 11 to avoid or at least minimised the leakage of pressurised hydraulic fluid from the hydraulic connection between the supply line 57 and the axial bore 58.

According to the invention, in the above, known pulley designs, a significant axial force Fax is generated on the respective pulley shafts 2, 6, 53 by the presence of the pressurised hydraulic fluid in the blind axial bore 12, 29, 58 during operation of the transmission 1. This axial force Fax is supported by, i.e. is counterbalanced in the transmission housing 11 via the roller bearings 22, 23 of the respective pulley shaft 2, 6, 53. This axial force Fax puts an additional strain on the said roller bearings 22, 23 and, moreover, results in additional frictional loss.

In order to overcome or at least mitigate the above disadvantage and more in particular to favourably accommodate the desire and trend towards a high activation pressure, two principle solutions are provided by the invention. These principle solutions are reflected by the pulley embodiment examples of figures 3 and 4.

A first embodiment of the pulley in accordance with the invention is illustrated in a diagrammatic cross-section thereof in figure 3. In figure 3 the reference numbers relate to same or at least similar components as in figure 2. However, in contrast with the known pulley design and in accordance with to the invention, the pulley shaft 53 is provided with a further radially oriented bore 61 that is located between the axial bore 58 and the supply line 57. In this manner, the hydraulic fluid is supplied from the supply line 57 to the axial bore 58 in the radial direction, allowing the axial bore 58 to be completely closed in the axial direction.

In figure 3, the open axial end 64 of the known axially oriented blind bore 58 in the pulley shaft 53 is sealed-off with a means 62 fixed to the pulley shaft 53. In this particular example a stop 62 is plugged into the entrance opening of the axial bore 58, however, obviously many alternatives are available in the art for realising an axially closed channel 58 inside the pulley shaft 53. For example, an axial channel may extend the full length of pulley shaft 53, such that its opens towards both, mutually opposite axial directions, however, sealed-off by two stops fixed to the pulley shaft 53, i.e. one stop being provided at each axial end of the axial channel.

In this first embodiment of the invention as represented by the pulley design of figure 3, the pressurised hydraulic fluid in the axial bore 58 generates an axial force F'ax on the stop 62. This further axial force F'ax is generated in addition and directed oppositely to the axial force Fax that is generated on the end surface of the axially oriented blind bore 58. As a result the said axial forces Fax and F'ax cancel each other, thereby favourably and significantly reducing the axial force and mechanical load experienced by the bearings 22, 23 of the pulley shaft 53 during operation of the transmission 1.

A second embodiment of the pulley in accordance with the invention is illustrated in a diagrammatic cross-section thereof in figure 4. In figure 4 the reference numbers relate to same or at least similar components as in figures 2 and 3. However, in contrast with the known pulley design and in accordance with the invention, the pulley shaft 53 is provided with a channel for hydraulic fluid in the form of an open- ended axially oriented bore 63 that thus extends over the full axial length of the pulley shaft 53. One axial end or entrance opening 64 of the axial bore 63 is connected to the supply line 57 provided in the transmission housing 11 and the other one, i.e. opposite, axial end or entrance opening 65 of the axial bore 63 remains open as well, at least in relation to the pulley 50 as such.

Naturally, the pressurised hydraulic fluid can not be allowed to freely flow from the axial bore 63. This means that, in practice, two seals 60, 66 are provided between the rotatable pulley shaft 53 and the stationary housing 11 , one on either axial end 64, 65 of the axial bore 63 thereof. In order to minimise the (resultant) axial force on the pulley shaft 53, these two seals 60, 66 should be designed to have the same diameter. By this latter measure it is effectively realised that the axially oriented surface area of the shaft 53 on which the pressurised hydraulic fluid is allowed to act, is the same in the opposite axial directions.

The invention will now be defined further along a set of claims and also relates to all details therein in addition to all details and aspects of the preceding description and drawings discussed therein, which are directly and unambiguously derivable there from, at least by a person skilled in the art. For example, although the present invention has been discussed in relation to the pulley 50 with a single pressure 54 corresponding to the second pulley 7 of figure 1 , it can just as well be applied in the design of the first pulley 3 of figure 1 with the two pressure chambers 13, 14.

Claims

1. Hydraulically activated adjustable pulley (50) for a torque transmission device in a vehicular drive line with two conical discs (51 , 52) on a shaft (53) and with hydraulically activated displacement means (54, 55, 56) for displacing one such disc (52) along such shaft (53) towards the respective other one disc (51), whereof the shaft (53) is provided with an axially oriented channel (58) and with a radially oriented channel (59) branching-off from the axial channel (58) and connecting to the displacement means (54, 55, 56) for allowing hydraulic fluid to flow to and from the displacement means (54, 55, 56), characterised in that the axial channel (58) is closed-off at both axial ends thereof and in that the shaft (53) is provided with a further radially oriented channel (61) likewise branching-off from the axial channel (58), which further radial channel (61) is connectable to a supply line (57) for hydraulic fluid of the torque transmission device.

2. Hydraulically activated adjustable pulley (50) according to claim 1 , characterised in that the axial channel (58) is provided in the shaft (53) either as a blind bore or as an open-ended bore, whereof the entrance opening or openings are sealed by a means (62) that is fixed to the shaft (53).

3. Hydraulically activated adjustable pulley (50) according to claim 1 or 2, characterised in that the pulley (50) is provided with at least two bearings (22, 23) that are fixed to the shaft (53) for rotatably mounting the pulley (50) in a housing (11) of the torque transmission device.

4. Hydraulically activated adjustable pulley (50) for a torque transmission device in a vehicular drive line with two conical discs (51 , 52) on a shaft (53) and with hydraulically activated displacement means (54, 55, 56) for displacing one such disc (52) along such shaft (53) towards the respective other one disc (51), whereof the shaft (53) is provided with an axially oriented channel (63) and with a radially oriented channel (59) branching-off from the axial channel (63) and connecting to the displacement means (54, 55, 56) for allowing hydraulic fluid to flow to and from the displacement means (54, 55, 56), characterised in that the axial channel (63) extends over the entire axial dimension of the shaft (53).

5. Torque transmission device provided with the hydraulically activated adjustable pulley (50) according to claim 3, characterised in that one axial end or entrance opening (64) of the axial channel (63) is connected to a supply line (57) for hydraulic fluid of the torque transmission device and in that the other one, i.e. opposite, axial end or entrance opening (65) of the axial channel (63) is contained by the torque transmission device as well.

6. Torque transmission device according to claim 5, characterised in that at least two seals (60, 66) are provided between the pulley (50) and a housing (11) of the torque transmission device for limiting a leakage of hydraulic fluid from the displacement means (54, 55, 56), the axially oriented channel (63) and the radially oriented channel (59) of the pulley (50).

7. Torque transmission device according to claim 6, characterised in that the at least two seals (60, 66) are ring-shaped and have mutually corresponding diameters.

8. Torque transmission device according to claim 5, 6 or 7, characterised in that the pulley (50) is provided with at least two bearings (22, 23) that are fixed to the shaft (53) for rotatably mounting the pulley (50) in a housing (11) of the torque transmission device.

9. Hydraulically activated adjustable pulley (50) or torque transmission device according to one of the preceding claims, characterised in that the shaft (53) includes at least two separate, modular parts that are fixed to one another.