Endless belt power transmission systems or components – Pulley with belt-receiving groove formed by drive faces on...
Reexamination Certificate
1999-09-29
2001-08-07
Fenstermacher, David (Department: 3681)
Endless belt power transmission systems or components
Pulley with belt-receiving groove formed by drive faces on...
C474S015000
Reexamination Certificate
active
06270436
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a continuously variable belt-drive mechanism, particularly for motor vehicles, with at least one variator. The term “variator” as used herein means a pulley comprised of at least two conical disks arranged concentrically on a driving shaft of a prime mover unit or on an element that is connected to the driving shaft. At least one of the conical disks is axially movable, and an endless flexible torque-transmitting device (subsequently referred to as a belt) occupies the axial space between the conical disks at a location of variable radius. A disk-tightening device pushes the conical disks axially towards each other so that, by virtue of the frictional engagement between the conical disks and the belt, the latter receives the torque to be transmitted and passes it on to at least one pulley disk.
Continuously variable belt-drive mechanisms of this kind are used in particular in motor vehicles as continuously variable transmissions and as drivers of auxiliary devices. In transmitting torque from the variator to other pulley disks, the critical factor is the frictional engagement between the belt and the conical disks. The disk-tightening devices used to produce the frictional engagement are in many cases energy-storing elements, such as helix springs, pushing against the axially movable conical disks. However, with an arrangement of this kind, the contact pressure between the belt and the conical disks is independent of the amount of torque that is to be transmitted.
Also known are variators with disk-tightening devices in which the amount of contact pressure depends on a centrifugal force, i.e., increases at greater rpm speeds, whereby the contact pressure is only coarsely adapted to the amount of torque that is to be transmitted.
In DE-OS 35531830, a disk-tightening device is proposed where the conical disks are pushed against a belt by a torque-dependent force. The conical disks are moved by pull rods with pivotal connections at both ends that are expensive to manufacture. Besides the cost factor, the proposed disk-tightening device also requires a great amount of space in the axial dimension.
OBJECT OF THE INVENTION
Therefore, the object of the present invention is to provide a continuously variable belt-drive mechanism that can be accommodated within a reduced amount of axial space and is more cost-effective to manufacture.
SUMMARY OF THE INVENTION
The object of the invention is met by a continuously variable belt-drive mechanism comprising at least one variator with at least two conical disks arranged concentrically on a driving shaft of a prime mover unit or on an element that is connected to the driving shaft. At least one of the conical disks is axially movable, and an endless flexible torque-transmitting device (subsequently called a belt) occupies the axial space between the conical disks at a location of variable radius. A disk-tightening device pushes the conical disks axially towards each other so that, by virtue of the frictional engagement between the conical disks and the belt, the latter receives the torque to be transmitted and passes it on to at least one pulley disk. The disk-tightening device consists at least of an arrangement of mutually complementary guiding means connected, respectively, to the axially moveable conical disk and to an element that is axially fixed on the driving shaft. Dependent on the magnitude of the torque to be transmitted and/or dependent on a transmission ratio that is externally settable, the guiding means are effecting an axial displacement of the conical disk that occurs as a result of a rotational displacement that the guiding means perform in relation to each other.
A continuously variable belt-drive mechanism of this kind can be employed, e.g., to drive auxiliary devices in an arrangement where at least one auxiliary device is driven by the torque-transmitting engagement of a pulley with the belt. Normally, several auxiliary devices such as, e.g., an alternator, a power-steering pump, an air-conditioning compressor, a water pump, and/or similar units can work on one belt drive. The diameter of each driven pulley determines a base value of the transmission ratio to the variator. In addition, by varying the radius at which the belt passes over the variator, the transmission ratio can be varied within a range of 2:1 to 4:1 (between the largest and smallest possible ratio) if the diameter of the conical disks is 150 to 300 mm. Particularly preferred is a diameter of 180 to 220 mm, resulting in a range of transmission ratios of 2.5:1 to 3:1.
The continuously variable belt-drive mechanism can also be used in the drive train of a prime mover unit, e.g., an internal-combustion engine, with at least one variator arranged on the driving shaft and, preferably, a second variator on the driven shaft, so that the two variators together constitute a continuously variable transmission. The variators are controlled in such a manner that the radii at which the belt engages each of the variators are complementary to each other. A torque-transmitting unit such as a friction clutch or laminar-disk clutch, a fluid coupling, or a hydrokinetic torque converter can be arranged in the torque-flow path between the prime mover unit and the driving variator. By using two variators, the numerical value for the range of transmission ratios will be squared.
One embodiment according to the invention can be provided with a disk-tightening device comprising at least three axially rising spiral ramps that are evenly distributed on the at least one axially movable cone disk and on a component that is axially fixed on the driving shaft. The respective ramps on the axially movable cone disk and on the axially fixed component are rotatable in relation to each other.
A disk-tightening device can also consist of spiraling grooves that are evenly distributed in the at least one axially movable cone disk with a complementary arrangement of grooves in a hub that is fixed on the driving shaft and with roller elements being guided in the grooves.
To simplify mounting on the driving shaft, the variator can have a hub on which the conical disks are seated. The hub has a flange-like extension by which the variator is centered on the driving shaft and, e.g., axially bolted to the latter in a rotationally fixed connection.
It is advantageous if the axial space between the conical disks where the belt is seated is V-shaped, i.e., widening in the outward radial direction. The belt has corresponding sloping flanks so that, by applying a force generated, e.g., by an adjustable belt-tensioning device, the belt can be moved to a smaller running radius, whereby the transmission ratio is changed. A move to a greater radius can be effected by reducing the tensioning force. It can also be advantageous, e.g., in a continuously variable transmission, if the transmission ratio is set through the contact pressure of the disk-tightening device, increasing the contact pressure in one variator and decreasing it in the other, whereby the running radius of the belt is increased in one variator and decreased in the other and the transmission ratio is changed accordingly. It is advantageous if the aperture angle a of the individual conical disks (i.e., the angle between the conical surface and a plane perpendicular to the axis of rotation) is in a range of 5°<&agr;<20°, the preferred value being &agr;≈20°. It can be particularly advantageous if the running surfaces do not have a linear profile in the radial direction but are slightly inward-curved to optimize the relationship of the contact force as a function of the radius.
According to the invention, the at least one axially movable conical disk has axially rising ramps arranged on the side facing away from the space that holds the belt. The ramps bear against complementary ramps arranged on an element that is fixed on the driving shaft. It is advantageous if the element carrying the complementary ramps is a radially projecting hub flange that is axially fixed and non-rotatable on the
Gerhardt Friedrich
Haas Wolfgang
Reik Wolfgang
Schmitt Ruben
Darby & Darby
Fenstermacher David
LuK Lamellen und Kupplungsbau GmbH
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