Toroidal type continuously variable transmission

Details Toroidal type continuously variable transmission Toroidal type continuously variable transmission

2000-06-26

2004-05-25

Joyce, William C. (Department: 3682)

Friction gear transmission systems or components

Friction gear includes idler engaging facing concave surfaces

Toroidal

C476S041000

Reexamination Certificate

active

06740001

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-183247, filed Jun. 29, 1999 the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a toroidal type continuously variable transmission mounted in a vehicle such as an automobile.
A toroidal type continuously variable transmission described PCT National Publication No. 6-502476 is a known example of a transmission that is mounted in a vehicle such as an automobile. The transmission of this type comprises an input shaft rotatable by means of a drive source that includes an engine, an input disk rotatable integrally with the input shaft, an output disk opposed to the input disk, power rollers arranged between the input and output disks, and a push mechanism for pressing at least one of the disks toward the other. As the input and output disks are pressed against the respective traction surfaces of the power rollers by the push mechanism, the rotation of the input disk is transmitted to the output disk through the power rollers. As the angle of inclination of the power rollers, which are rockably arranged between the input and output disks, changes, the reduction ratio of the toroidal type continuously variable transmission changes.
In some cases, a loading cam mechanism may be used as the push mechanism. The loading cam mechanism comprises a loading cam mounted on the input shaft and a cam roller in contact with the cam. The loading cam, which is located behind the input disk, is rotated by means of the drive source that includes the engine. The cam roller is located between the loading cam and the input disk and is rotatable around an axis that extends at right angles to the axis of the input shaft. When the drive source rotates the loading cam, the cam roller presses the input disk toward the output disk.
The loading cam mechanism presses the input disk toward the output disk with a push force proportional to a torque from the drive source that is applied to the input shaft. Since the loading cam mechanism mechanically presses the input disk in response to only the input torque from the drive source, there is no necessity for computer control. Thus, the toroidal type continuously variable transmission using the loading cam mechanism has an advantage over the one that uses a hydraulic loading mechanism (mentioned later) in being simpler in construction.
The efficiency of power transmission between the input and output disks and the power rollers varies depending on various conditions, such as the input torque from the drive source, gear ratio of the toroidal type continuously variable transmission, rotational frequency of the input disk, temperature of the a lubricant, etc. In the case where the loading cam mechanism is used as the push mechanism, however, the push force is settled without regard to the aforesaid conditions including the gear ratio, rotational frequency, lubricant temperature, etc. Depending on these conditions, therefore, the loading cam mechanism sometimes may fail to press the input and output disks with an optimum push force.
FIG. 4
shows the relation between a push force Fac generated by the loading cam mechanism of the half-toroidal type continuously variable transmission and an appropriate push force Fan
1
. If the input torque from the drive source is fixed, the push force Fac generated by the loading cam mechanism is substantially fixed despite the change of the gear ratio, as shown in FIG.
4
. On the other hand, the appropriate push force Fan
1
is represented by an upwardly convex curve.
FIG. 5
shows the relation between the push force Fac generated by the loading cam mechanism of the full-toroidal type continuously variable transmission and an appropriate push force Fan
2
. The lower the gear ratio, the smaller the appropriate push force Fan
2
is, as shown in FIG.
5
.
Thus, in the case of the half-toroidal type continuously variable transmission that uses the loading cam mechanism, the generated push force Fac is greater than the appropriate push force Fan
1
, as shown in FIG.
4
. In the case of the full-toroidal type continuously variable transmission also, the generated push force Fac is greater than the appropriate push force Fan
2
, as shown in FIG.
5
. In either case, the push force Fac lowers the power transmission efficiency of the continuously variable transmission. In the case of the full-toroidal type, in particular, the transmission efficiency lowers substantially.
In the toroidal type continuously variable transmission described in PCT National Publication No. 6-502476, the hydraulic loading mechanism is used as the push mechanism. The hydraulic loading mechanism comprises a pressure source such as a hydraulic pump, a cylinder rotatable integrally with the input shaft, and the back surface portion of the input disk that serves as a piston portion in the cylinder. The input disk is pressed toward the output disk by means of the pressure of oil that is fed from the pressure source into the cylinder. The transmission described in PCT National Publication No. 6-502476 is provided with only one cylinder and one piston portion.
A push force that is generated by the hydraulic loading mechanism is controlled to be at an appropriate value by means of a well-known control device such as an ECU (engine control unit). This control device obtains the appropriate push force in accordance with the conditions including the input torque, gear ratio, rotational frequency, lubricant temperature, etc. Thus, the power transmission efficiency of the toroidal type continuously variable transmission can be improved by using the hydraulic loading mechanism.
In the push mechanism of the toroidal type continuously variable transmission, however, the push force should be enhanced in proportion to the input torque from the drive source. In the toroidal type continuously variable transmission that uses the hydraulic loading mechanism, therefore, the pressure of the oil to be fed into the cylinder must be increased when the input torque is high. Sealing the high-pressure oil requires the sliding resistance of seal members between the piston portion and the cylinder to be increased, thus entailing a higher power loss. Since the high-pressure oil must be fed into the cylinder, moreover, the pressure source and therefore the toroidal type continuously variable transmission itself are expected to be large-sized.
The pressure of the oil to be fed into the cylinder may possibly be adjusted to a lower level by increasing the pressure receiving area of the piston portion (input disk) on which the oil pressure acts. In this case, however, the size of the toroidal type continuously variable transmission itself increases, and the manufacturing costs of the input disk and the like pile up inevitably.
BRIEF SUMMARY OF THE INVENTION
Accordingly, the object of the present invention is to provide a toroidal type continuously variable transmission, of which the power transmission efficiency can be restrained from lowering and which can be restrained from being large-sized.
In order to achieve the above object, a toroidal type continuously variable transmission according to the present invention comprises an input shaft rotatable by means of a drive source, a first cavity including a first input disk rotatable together with the input shaft and a first output disk opposed to the first input disk in the axial direction of the input shaft, a second cavity including a second input disk rotatable together with the input shaft and a second output disk opposed to the second input disk in the axial direction of the input shaft, a hydraulic loading mechanism including first and second hydraulic chambers arranged in the axial direction of the input shaft and adapted to press one of the disks in the first cavity toward the other so that the input and output disks approach each other when pressurized oil is fed into the hydraulic chambers, and an interlocking portio

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