Toroidal drive

Details Toroidal drive Toroidal drive

1998-12-16

2001-02-27

Bucci, David A. (Department: 3682)

Friction gear transmission systems or components

Friction gear includes idler engaging facing concave surfaces

Toroidal

C074S335000

Reexamination Certificate

active

06193627

ABSTRACT:

BACKGROUND OF THE INVENTION
A toroidal drive, having a continuously variable ratio, which has at least two pulleys with toroidal facing surfaces between which friction rollers roll to transmit a torque from one pulleys to the other, are well known. One of the pulleys is connected with an input shaft and the other with an output shaft. To change the ratio, the axes of rotation of the friction rollers relative to the input axis are swivelled so that the friction rollers on the input pulleys move on a contact radius which is different from the contact radius on the output pulleys. The ratio to each other of the contact radii gives the reduction ratio.
DE 28 07 971 A shows a simple toroidal drive of that kind in which the friction rollers are supported in a holding device and swivelled via an axially movable drum.
EP 0 415 391 B1 has disclosed a toroidal drive in which, two friction rollers diametrically disposed relative to an input shaft and between an input pulleys and an output pulleys, are disposed which have semi-toroidal surfaces opposite each other. The friction rollers are supported on eccentric shafts of two roller carriers which are pivoted in a holding device connected with a transmission housing. By means of hydraulic setting devices, the roller carriers can be adjusted in direction of their swivel axis wherein they are simultaneously tilted. Since the friction rollers are situated diametrically to the input shaft, they are swivelled in opposite directions, that is, when one roller is swivelled clockwise, the other is swivelled counterclockwise.
The hydraulic setting device has a double-acting piston, the sides of which are loaded by a pressure difference, which is produced by a valve unit having a piston slide valve with four leading edges. A control unit adjusts the piston slide valve, via control springs, by means of a stepping motor and thus adjusts the reduction ratio desired. A mechanical return system, which contains a cam and lever mechanism, determines the tilting movement of the roller carrier, and acts likewise upon the piston slide valve and ensures that the adjusted reduction ratio be maintained.
The valve device has a strong, non-linear reinforcement of the pressure difference relative to the ratio divergence which can only be overcome with difficulty and particularly, in case of extremely high ratios, for example, by geared systems. Thus yields driving conditions hard to control when starting. In such transmissions the continuously variable reduction step, the so-called variator, is situated in a power branch of a power distribution transmission and can be regulated so that in an operating state the output shaft of a cumulative steps assumes the speed zero and thus stands a vehicle with such an input. During very low output speeds, very high torques appear which, even if desired for starting, cannot be braked by the service brakes when the vehicle is parked and thus result in creeping of the vehicle. In addition, the speed sensors required for regulating the speed are not capable of determining any low speeds which strive against zero.
SUMMARY OF THE INVENTION
The problem on which the invention is based is to improve and more reliably to control the starting characteristics of a vehicle.
According to the invention there is provided a toroidal drive (
1
) providing a continuously variable ratio and having an output pulleys (
6
) disposed co-axially to an input pulleys (
3
), defining opposite semi-toroidal surfaces (
7
,
8
), and at least one friction roller (
9
,
10
) which rolls on said semi-toroidal surfaces (
7
,
8
) and transmits a torque from one pulleys (
3
,
8
) to the other, wherein said friction rollers (
9
,
10
) are pivoted in a roller carrier (
15
,
16
) which is tiltably supported around a swivel axis (
17
,
18
) across an input shaft (
2
) in a holding device (
19
) in a housing (
20
) and adjusted about said swivel axis (
17
,
18
) by a hydraulic actuation device with one cylinder (
26
,
27
) and one double-acting piston (
22
,
23
), wherein a valve device (
28
) with a piston slide valve (
33
) produces by means of leading edges (
38
,
39
,
40
,
41
) a pressure difference in proportional to the desired torque (
40
,
41
) to be transmitted with which are loaded both piston sides (
24
,
25
) and front faces opposite each other (
42
,
43
) of said piston slide valve (
33
).
According to the invention, the valve device produces, in proportion to the desired torque to be transmitted, a pressure difference which is regulated by the return to the opposite front faces of the piston slide valve. Thereby starting characteristics are obtained that can be well controlled and also a stable regulation with good frictional contact ratios between friction rollers and the semi-toroidal surfaces, since when parking no torque crops upon the output shaft while when starting the torque can be increased at will up to the maximum. Since the pressure difference acting upon the piston sides which corresponds to the torque-proportional supporting force, retroacts hydraulically to the piston slide valve of the valve device, it is possible to eliminate the quite complex mechanical return flow of the prior art, in addition, the valve bushing can be firmly connected with the valve housing or be an integral part of the valve housing.
As a rule the piston slide valve has four leading edges in order to set the pressure ratio on the two piston sides. Two leading edges are here associated with one piston side, specifically the one which controls the communication to the feed-in port and the other which controls the communication to the return flow.
According to an embodiment of the invention, the piston slide valve has only two leading edges. These are associated with one piston side while the other piston side is loaded with a constant pressure. Thus the pressure difference results in this simple arrangement from the difference between the constant pressure and the variable pressure.
When the direction of the torque to be transmitted reverses to the coasting operation, the supporting force and thus the pressure difference on the piston sides become negative, that is, the piston side loaded with the higher pressure in the traction operation is loaded with a lower pressure in the coasting operation. This would result in that the pressure force acting upon the piston slide valve changes its direction of action when switching from traction to coasting operation. To prevent this, it is proposed that the front faces of the piston slide valve loaded with pressure of the piston sides be unequally dimensioned and thus synchronized to each other so that the pressure force acting upon the piston slide valve maintains its direction of flow when the direction of the torque to be transmitted is reversed.
The piston slide valve is conveniently loaded on the front side by a control pressure which is proportional to the desired torque to be transmitted. Said control pressure can be adjusted by means of a control unit via a pressure regulator and pressurizes part of the front surface of the whole front surface of the piston slide valve which is designed as step. The remaining part of the front surface is then conveniently loaded by the pressure of one piston side. In the balanced state, the pressure difference set by the piston slide valve on the piston sides corresponds to the pressure preset by the pressure regulator. It is convenient here that the surface part loaded with control pressure be situated on the side of the piston slide valve which has the smaller front face which is loaded by the pressure of a piston side.
One other, naturally more expensive alternative consists in that in case of equal front faces of the piston slide valve which are loaded by the pressure of the piston slides, there be provided on both sides of the piston slide valve surface portions for a control pressure which can be loaded with different control pressures, specifically on the side for setting a traction torque and on the other side for setting a pull torque.
To change the torque to be

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