WO2003078867A1

WO2003078867A1 - Variable transmission with clamp force control

Info

Publication number: WO2003078867A1
Application number: PCT/NL2003/000200
Authority: WO
Inventors: Heerke Hoogenberg
Original assignee: Hamapro Holding B.V.
Priority date: 2002-03-20
Filing date: 2003-03-18
Publication date: 2003-09-25
Also published as: NL1020214C2; AU2003225403A1

Abstract

The invention relates to a variable transmission comprising first (3) and second friction discs (5) axially displaceable relative to each other, a first shaft (2) connected to the friction discs (3,5), an endless transmission belt (6) arranged between the friction discs (3,5), a second shaft (7) connected to the transmission belt (6) and clamping means for urging the first (3) and second friction disc (5) toward each other, wherein the clamping means comprise a pressing disc (9) mounted for at least axial displacement on the first friction disc (3) in a at least partly helical guiding (8), wherein the pressin disc (9) supports in axial direction on the second friction disc (5) and the support lies, as seen in radial direction, outside the contact surface of the transmission belt (6) with the second friction disc (5).

Description

VARIABLE TRANSMISSION WITH CLAMP FORCE CONTROL

The invention relates to a variable transmission comprising first and second friction discs axially displaceable relative to each other, a first shaft connected to the friction discs, an endless transmission belt arranged between the friction discs, a second shaft connected to the transmission belt and clampin^sg means for urging the first and second friction disc toward each other.

In continuously variable transmissions wherein use is made of a transmission belt, it is important for the transmission belt to be clamped between the friction discs with sufficient force. If clamping force is insufficient the transmission belt can start to slip relative to the friction discs as a result of the transmitted torque. This is very undesirable.

Different devices are therefore known for providing this clamping force. This clamping force can for instance be generated by springs or by a hydraulic cylinder. Another problem also occurs in such devices, however. Because the transmission belt lies only on a part of the friction discs, the friction discs tend to go askew as a result of the clamping force. The angle between the transmission belt and the friction discs hereby changes, which is also disadvantageous. A solution here of t.he prior art is that the friction discs are given a long axial guiding. This has the drawback however that the dimensions of the transmission hereby increase.

It is an object of the invention to provide a mechanical transmission according to the preamble, wherein the dimensions remain limited and the clamping device does not press the discs askew.

This object is achieved with a variable transmission which is characterized in that the clamping means comprise a pressing disc mounted for at least axial displacement on the first friction disc in an at least partly helical guiding, wherein the pressing disc supports in axial direction on the second friction disc and the support lies, as seen in radial direction, outside the contact surface of the transmission belt with the second friction disc.

Because the support lies outside the contact surface of the transmission belt with the second friction disc as seen in radial direction, an askew position of the friction discs is largely prevented. Because the transmission belt is only clamped locally between the friction discs and because the support lies outside this contact surface, the friction discs tend to move apart. This is however prevented by the at least partially helical guiding. This is because the pressing disc lies, as seen in axial direction, against a side of the helical guiding.

Owing to the helical guiding a pressure force can be exerted by rotating the pressing disc relative to the first friction disc. This rotation can for instance be caused by a torsion spring or a hydraulic rotation cylinder arranged between the first friction disc and the pressing disc.

In a first embodiment of the variable transmission according to the invention, pressing means are arranged between the pressing discs and the first friction disc for pressing the pressing disc and the first friction disc toward each other. These pressing means can comprise at least a spring and/or a hydraulic piston. Using the spring creates a simple construction, while with the hydraulic piston an actively controlled system can be realized. A combination of the two pressing means is also possible.

The invention further comprises a variable transmission according to the preamble, which is characterized in that a connecting sleeve mounted for axial displacement is arranged on both the first and the second friction disc for connecting the friction discs to the first shaft, that the clamping means comprise a first pressing disc mounted for axial displacement on the connecting sleeve in an at least partly helical guiding, wherein the first pressing disc supports in axial direction on the first friction disc and the clamping means comprise a second pressing disc mounted for axial displacement on the connecting sleeve in an at least partly helical guiding, wherein the second pressing disc supports in axial direction on the second friction disc and both supports lie, as seen in radial direction, outside the contact surface of the transmission belt with the first and second friction disc.

In such a variable transmission the friction surfaces are both axially displaceable, with the advantage that axial displacements between the first and second shaft can be easily taken up and the transmission belt can be displaced purely radially.

Both variable transmissions according to the invention can comprise a toothed wheel mounted on the first shaft and coupled thereto, and a lever which is arranged pivotally on the first friction disc, which lever engages with one end on the toothed wheel and with the other end engages at least in tangential direction on the pressing disc.

The torque transmitted by the transmission now runs to the first friction disc via the first shaft, the toothed wheel and the lever. Because the lever is arranged pivotally on the first friction disc, it will exert more or less force on the pressing disc, whereby the generated clamping force depends on the transmitted torque. The squeezing force hereby depends on the torque on the first shaft and on the position of the transmission belt relative to the friction discs. The correct squeezing force sufficient for the transmitted torque is hereby available at all times. This reduces load and wear and increases the efficiency.

The transmission according to the invention preferably comprises first spring means arranged between the first shaft and the toothed wheel, in order to force the other end of the lever into engagement on the pressing disc.

The first spring means ensure that there is no unnecessary play in the transmission which disrupts the behaviour of the transmission.

In a further preferred embodiment according to the invention the toothed wheel is coupled with free movement to the first shaft and the first shaft is further coupled with free movement to a cam rotatably mounted on the first shaft, which cam is adapted to come into contact with the part of the lever between the pivot point and the second end.

When the rotation direction of the transmission is reversed, the toothed wheel would then rotate the lever such that no clamping force at all is exerted. Because the cam is arranged on the first shaft with free movement, the cam is urged against the lever when the rotation direction is reversed, whereby the lever will still bring about the required rotation of the pressing disc in order to obtain the desired clamping force. This latter embodiment preferably comprises second spring means arranged between the first shaft and the rotatably mounted cam, in order to urge the cam against the lever. According to yet another preferred embodiment, the other end of the lever engages on a support surface arranged on the pressing disc. When the pressing disc is rotated, which is necessary in radial displacement of the transmission belt in order to change the transmission ratio, the other end of the lever can thus engage at a different position on the support surface. The torque exerted on the pressing disc can hereby be adjusted to the position of the transmission belt relative to the friction discs. The support surface preferably has at least one tangential directional component. Owing to this angled position of the support surface, the exerted torque can be further influenced subject to the position of transmission belt. In yet another embodiment of the transmission according to the invention the first shaft is coupled to the toothed wheel via a first hydraulic cylinder, which hydraulic cylinder comprises a cylinder space, a piston movable therein, which piston divides the cylinder space into a first and a second chamber, a first channel which has a first valve arranged therein and which is arranged between the first and second chamber, and a second channel which has a second valve arranged therein and which is arranged between the second and first chamber. The play occurring when the transmission rotates between loaded and non-loaded, or when the rotation direction is reversed, can be taken up with this hydraulic cylinder.

In the embodiment with the cam mounted around the first shaft, the first shaft can be coupled to the cam via a second hydraulic cylinder, which hydraulic cylinder comprises a cylinder space, a piston movable therein, which piston divides the cylinder space into a first and a second chamber, a first channel which has a first valve arranged therein and which is arranged between the first and second chamber, and a second channel which has a second valve arranged therein and which is arranged between the second and first chamber. In this embodiment the play is taken up by the two hydraulic cylinders during engine deceleration or reversing of the rotation direction.

The first and/or the second cylinder preferably comprise spring means for urging the respective cylinder into a rest position. Reference is made in the above to a lever. It will be apparent that the lever can also be formed virtually by for instance a rod assembly or for instance a set of toothed wheels.

These and other features of the invention are further elucidated with reference to the annexed drawings .

Figure 1 shows a cross-sectional view of a first embodiment of a variable transmission according to the invention. Figure 2 shows a cross-sectional view of a variant of the transmission according to figure 1.

Figure 3 shows a cross-sectional view of a second embodiment of a variable transmission according to the invention. Figures 4A and 4B show cross-sectional views of a third embodiment of the transmission according to the invention.

Figures 5A-5D show radial cross-sections of the transmission according to figure 4 in four different positions. Figure 6 shows an axial cross-section of the transmission of figure 4 in the position according to figure 5B .

Figures 7A and 7B show cross-sections of a fourth embodiment of the transmission according to the invention.

Figure 1 shows a first embodiment 1 according to the invention. This first embodiment 1 comprises a first shaft 2 to which is connected a first friction disc 3. A second friction disc 5, which is axially displaceable relative to first friction disc 3, is arranged by means of an axial ball guide 4. Between these two friction discs 3,5 is clamped a transmission belt 6, which is connected to a second shaft 7. The second shaft 7 is displaceable in radial direction, so that the transmission ratio between first shaft 2 and second shaft 7 can be varied.

On the periphery of the first friction disc 3 is arranged a helical ball guide 8, on which a pressing disc 9 is mounted. Pressing disc 9 can be axially displaced relative to first friction disc 3 by means of rotation. This rotation is brought about by torsion spring 10.

Pressing disc 9 supports axially on second friction disc 5 by means of balls 11. Because the support of pressing disc 9 via balls 11 on second friction disc 5, as seen in radial direction, lies outside the contact surface of transmission belt 6 with the first and second friction disc 3 respectively 5, the second friction disc 5 will not go askew and on the opposite side the transmission belt 6 is prevented from still being clamped in the extreme case between the first and second friction disc 3 respectively 5, whereby the variable transmission can be damaged. Figure 2 shows a variant of the embodiment according to igure 1. Corresponding parts are designated with the same reference numerals and are not further elucidated. In this variant 15 the second friction disc 5 is arranged for displacement in axial direction on first friction disc 3 by means of dowel pins 16. Pressing disc 9 further supports on second friction disc 5 via balls 17. These balls 17 provide support in both radial and axial direction. The inaccuracy typical of dowel pins 16 is herein removed.

Figure 3 shows a second embodiment of variable transmission 20 according to the invention. This embodiment 20 has a first shaft 21 on which a connecting sleeve 22 is arranged. The first friction disc 25 and the second friction disc 26 are guided in this connecting sleeve 22 by means of an axial ball guide 23,24. Between this first friction disc 25 and second friction disc 26 is clamped a transmission belt 27, which is connected to the second shaft 28. This second shaft 28 is displaceable in radial direction in order to enable the transmission ratio between first shaft 21 and second shaft 28 to be varied.

Further provided on connecting sleeve 22 is a first spiral-shaped ball guide 29, on which a first pressing disc 30 is arranged. The rotation of the first pressing disc 30 is brought about by torsion spring 31. By rotating the first pressing disc 30, an axial pressure force can be exerted on first friction disc 25 via balls 32. In similar manner a second pressing disc 34 is arranged on connecting sleeve 22 via a second spiral-shaped guide 33. Rotation of the second pressing disc 34 is brought about by torsion spring 35. The second pressing disc 34 supports on the second friction disc 26 via balls 36. It is here also the case that the support of the first pressing disc 30 on first friction disc 25 and of the second pressing disc 34 on second friction disc 26, as seen in radial direction, lies outside contact surface 37 of transmission belt 27 and first and second friction discs 25,26.

Figures 4A and 4B show a third embodiment of a transmission according to the invention. Transmission 30 comprises a first shaft 31 and a second shaft 32 to which transmission belt 33 is connected. Transmission belt 33 is clamped between a first friction disc 34 and a second friction disc 35. The first friction disc 34 and second friction disc 35 are mounted axially relative to each other by means of balls 36. A pressing disc 38 is mounted on second friction disc 35 via a helical ball guide 80. Pressing disc 38 supports in at least axial direction on the first friction disc via balls 39.

A toothed wheel 40 is mounted on the first shaft 31. Shaft 31 comprises a flange 41 with two recesses 42 and 43. A cam 44 of flange 45 engages in recess 42, which cam is fixedly connected to toothed wheel 40. Toothed wheel 40 is hereby coupled to first shaft 31 with free movement.

On first friction disc 34 is arranged a lever 46, one end 47 of which is provided with a gear segment which engages on toothed wheel 40, while the other end 48 engages on a cam 49 of pressing disc 38.

When first shaft 31 is driven, toothed wheel 40 will be co-displaced via recess 42 and cam 44. The toothed wheel has the tendency to rotate the lever 46, but the first friction disc 34 will be co-displaced as a result of the resistance of the pressing disc, which resistance is in turn the result of the clamping force. The force on the pressing disc will vary depending on the torque on the first shaft 31, as a result of which the clamping force of friction discs 34, 35 on transmission belt 33 will then vary.

Figure 5A corresponds with figure 4B and is shown by way of comparison with figure 5B. Here the position is shown wherein transmission belt 33 is displaced outward in radial direction, as can be seen in the axial cross-sectional view of figure 6. By displacing the transmission belt 33 in radial direction the friction discs 34, 35 are urged apart, whereby pressing disc 38 rotates relative to friction discs 34, 35. Lever 46 hereby comes to lie in a different position, whereby the torque exerted on pressing disc 38 changes as a result of the position of the transmission belt relative to friction discs 34, 35. When the rotation direction of the first shaft is now reversed, or when the other part of the transmission is used to decelerate when the rotation direction remains the same, for instance during engine deceleration, toothed wheel 40 will then rotate relative to first shaft 31 until cam 50 comes into contact with flange 41 in recess 43 (see figure 5C) . Cam 50 is arranged on a ring 51, on which is arranged a cam 52. This cam 52 lies against lever 46 and prevents the pressure exerted on cam 49 being removed. Pressing disc 38 will again rotate during displacement of transmission belt 33 in radial direction, as a result of which the lever 46 takes up another position.

Further provided is a spiral spring 53 which is arranged between first shaft 31 and flange 45, whereby the other end 48 of lever 46 is urged against cam 49. There is also provided a spiral spring 54 which is arranged between the first shaft 31 and ring 51, whereby cam 52 is urged against lever 46. Figures 7A and 7B show a fourth embodiment according to the invention. This corresponds largely with the third embodiment according to figures 4-6. Corresponding parts are therefore designated with the same reference numerals.

In this embodiment a flange 60 is provided on first shaft 31. A flange 61 is likewise connected to toothed wheel 40. In flange 62 is arranged a chamber 63, into which protrudes a piston-cam 64 arranged on flange 61.

Chamber 63 is filled with a hydraulic liquid. A valve 65 and a pressure relief valve 66 are arranged in piston-cam 64. The hydraulic cylinder, formed by chamber 63 and piston-cam 64, can hereby build up pressure in the one direction and move freely in the other direction. This free movement is brought about by valve 65, while the built-up pressure is limited by pressure relief valve 66.

A ring 67 on which cam 52 is arranged is further mounted around first shaft 31. In ring 67 there is once again arranged a chamber 68 into which protrudes a piston-cam 69 arranged on flange 62. In this cam 69 are also arranged a valve 70 and a pressure relief valve 71. Chamber 68 is also filled with a hydraulic liquid. With these hydraulic cylinders the torque can be transmitted directly from the first shaft to the toothed wheel 40 or to cam 52, while a free movement still remains possible in order to adjust friction discs 34, 35. Further provided are springs 72, 73 for urging respectively piston-cam 64 and piston-cam 71 into a rest position relative to the chamber in question.

Claims

1. Variable transmission comprising first and second friction discs axially displaceable relative to each other, a first shaft connected to the friction discs, an endless transmission belt arranged between the friction discs, a second shaft connected to the transmission belt and clamping means for urging the first and second friction disc toward each other, characterized in that the clamping means comprise a pressing disc mounted for at least axial displacement on the first friction disc in an at least partly helical guiding, wherein the pressing disc supports in axial direction on the second friction disc and the support lies, as seen in radial direction, outside the contact surface of the transmission belt with the second friction disc.

2. Variable transmission as claimed ^'in claim

1, characterized in that pressing means are arranged between the pressing disc and the first friction disc for pressing the pressing disc and the first friction disc toward each other.

3. Variable transmission as claimed in claim 2, characterized in that pressing means comprise at least a spring and/or a hydraulic piston.

4. Variable transmission as claimed in any of the foregoing claims, characterized in that a torsion spring is arranged between the first friction disc and the pressing disc.

5. Variable transmission comprising first and second friction discs axially displaceable relative to each other, a first shaft connected to the friction discs, an endless transmission belt arranged between the friction discs, a second shaft connected to the transmission belt and clamping means for urging the first and second friction disc toward each other, characterized in that a connecting sleeve mounted for axial displacement is arranged on both the first and the second friction disc for connecting the friction discs to the first shaft, that the clamping means comprise a first pressing disc mounted for axial displacement on the connecting sleeve in an at least partly helical guiding, wherein the first pressing disc supports in axial direction on the first friction disc, and the clamping means comprise a second pressing disc mounted for axial displacement on the connecting sleeve in an at least partly helical guiding, wherein the second pressing disc supports in axial direction on the second friction disc and both supports lie, as seen in radial direction, outside the contact surface of the transmission belt with the first and second friction disc.

6. Variable transmission as claimed in any of the foregoing claims, comprising a toothed wheel mounted on the first shaft and coupled thereto, a lever which is arranged pivotally on the first friction disc, which lever engages with one end on the toothed wheel and with the other end engages at least in tangential direction on the pressing disc.

7. Variable transmission as claimed in claim 6, comprising first spring means arranged between the first shaft and the toothed wheel, in order to force the other end of the lever into engagement on the pressing disc.

8. Variable transmission as claimed in claim 6 or 7, wherein the toothed wheel is coupled with free movement to the first shaft and the first shaft is further coupled with free movement to a cam rotatably mounted on the first shaft, which cam is adapted to come into contact with the part of the lever between the pivot point and the second end.

9. Variable transmission as claimed in claim 8, comprising second spring means arranged between the first shaft and the rotatably mounted cam, in order to urge the cam against the lever.

10. Variable transmission as claimed in any of the claims 6-9, wherein the other end of the lever engages on a support surface arranged on the pressing disc .

11. Variable transmission as claimed in claim 10, wherein the support surface has at least one tangential directional component.

12. Variable transmission as claimed in any of the claims 6-11, wherein the first shaft is coupled to the toothed wheel via a first hydraulic cylinder, which hydraulic cylinder comprises a cylinder space, a piston movable therein, which piston divides the cylinder space into a first and a second chamber, a first channel which has a first valve arranged therein and which is arranged between the first and second chamber, and a second channel which has a second valve arranged therein and which is arranged between the second and first chamber.

13. Variable transmission as claimed in any of the claims 8-11, wherein the first shaft is coupled to the cam via a second hydraulic cylinder, which hydraulic cylinder comprises a cylinder space, a piston movable therein, which piston divides the cylinder space into a first and a second chamber, a first channel which has a first valve arranged therein and which is arranged between the first and second chamber, and a second channel which has a second valve arranged therein and which is arranged between the second and first chamber.

14. Variable transmission as claimed in claim 12 or 13, wherein the first and/or the second cylinder comprise spring means for urging the respective cylinder into a rest position.