Continuously variable transmission

Details Continuously variable transmission Continuously variable transmission

1999-05-18

2002-01-08

Bucci, David A. (Department: 3682)

Endless belt power transmission systems or components

Pulley with belt-receiving groove formed by drive faces on...

Fluid pressure actuator for adjustment of member

C474S018000, C474S019000

Reexamination Certificate

active

06336878

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to continuously variable transmissions (CVT) of the type employing rotary input and output shafts, adjustable pulleys on the shafts, and an endless flexible element (such as an endless flexible chain or belt and hereinafter called chain for short) which is trained over the pulleys. Transmissions of such character are preferred by numerous makers of motor vehicles or power trains for use in motor vehicles because they exhibit important advantages over other types of continuously variable transmissions, e.g., those which employ planetary gears. Thus, the ride in a motor vehicle comprising a power train embodying a continuously variable transmission which comprises input and output shafts with adjustable pulleys and an endless chain trained over the pulleys is more comfortable to the operator and other occupants of the motor vehicle, and the engine can be operated with considerable savings in fuel consumption.
Published German patent application Serial No. 195 44 644 A1 discloses a continuously variable transmission with two adjustable pulleys and an endless chain which serves to transmit torque from the adjustable pulley on the input shaft to the adjustable pulley on the output shaft. Each pulley comprises a first flange which is fixedly secured to the respective shaft, and a second flange which cannot rotate with reference to the respective shaft but is movable axially toward and away from the associated fixed flange. First plenum chambers are provided at those sides of the axially movable flanges which face away from the associated first flanges. The pressure of a hydraulic fluid in such chambers is regulated in dependency upon the magnitude of the torque being transmitted to the input shaft at any given time. Such mode of operation is desirable because it ensures that the chain cannot slip, or is less likely to slip, relative to the adjacent surfaces of the flanges. Changes in the ratio of the transmission are effected by changing the pressure of fluid in additional plenum chambers which are outwardly adjacent the respective first plenum chambers. A torque sensor is integrated into the just described conventional transmission to monitor the magnitude of the torque being transmitted from a prime mover (such as an internal combustion engine) to the input shaft of the transmission.
As a rule, and as already mentioned hereinbefore, the first plenum cambers are located between the additional plenum chambers and the axially movable flanges of the respective pulleys. The arrangement is normally such that each first plenum chamber is immediately adjacent the respective axially adjustable flange. On the other hand, the additional plenum chambers are immediately adjacent to pistons which are directly connected to the respective axially movable flanges. A third plenum chamber is or can be provided between each first plenum chamber and the respective additional plenum chamber. The third plenum chamber receives and/or discharges hydraulic fluid by way of a throttling orifice, and its purpose is to compensate for those rises of fluid pressure which are attributable to forces developing as a result of rotation of the shafts and pulleys when the transmission is in use. However, the utilization of such third plenum chambers results in considerable pumping losses because of uninterrupted flow of pressurized fluid from the first plenum chambers. In addition, the third plenum chambers impose a lower limit upon the duration of changes of the transmission ratio. The reason is that, when the volume of a third chamber is being reduced, some of the fluid must be expelled from the third chamber into the atmosphere by way of one or more narrow flow restrictors which impose a lower limit upon the speed of adjustment of the transmission ratio.
The aforementioned published German patent application Serial No. 195 44 644 A1 further discloses a hydromechanical torque sensor which is installed to transmit to the pulley on the input shaft the entire torque being supplied by a prime mover. More specifically, the torque sensor comprises an axially fixed first cam and an axially movable second cam, and the cams are provided with confronting ramps engaging spherical distancing or spreading members which are disposed between the two cams. The second cam is movable axially of but cannot rotate relative to the input shaft of the transmission. It is necessary to ensure that the pressure of hydraulic fluid in the first plenum chambers is variable at least as a function of the transmitted torque; this ensures that the flanges bear upon the marginal portions of the chain without any or with minimal slip. In other words, if the magnitude of the transmitted torque increases, then the torque sensor must ensure that the fluid pressure in the first chambers increases accordingly. Analogously, if the magnitude of transmitted torque is reduced, the torque sensor initiates a reduction of fluid pressure in the first plenum chambers because the likelihood of slippage between the flanges of the pulley on the one hand, and the marginal portions of the chain on the other hand, is less pronounced. When the transmission ratio reaches a certain value, the first and the adjacent second chambers are permitted to communicate with each other by way of the respective axially movable flanges to thus account for an increased area of contact with the chain, i.e., the pressure of fluid in the first plenum chambers is reduced.
The just outlined construction and mode of operation of the torque sensor which is disclosed in the aforementioned published German patent application ensure that the pressure between the conical surfaces of the flanges and the marginal portions of the chain can be regulated as a function of the momentary transmission ratio, i.e., of the radii of those arcuate portions of the endless chain which are trained over the two pulleys. This renders it possible to ensure that the torque sensor operates not unlike a multistage torque sensor.
However, the just described torque sensor also exhibits certain drawbacks. For example, the space requirements of the torque sensor, as seen in the axial direction of the input shaft, are rather pronounced which is evidently undesirable in many types of motor vehicles. Moreover the torque sensor is quite complex and comprises a rather substantial number of component parts.
Published German patent application Serial No. 42 01 692 A1 discloses a continuously variable transmission which comprises a dual cylinder-and-piston arrangement wherein the axially movable flange of each of the two pulleys is associated with a double-acting cylinder and piston unit, and such units are radially offset relative to each other. The arrangement is such that each cylinder-and-piston unit can furnish a fluid at a desired pressure, i.e., each of the units can pressurize the fluid to a desired extent independently of the pressure in the other unit. Thus, the radially inner plenum chamber contains a body of fluid the pressure of which is just sufficient to ensure the transmission of a desired torque from the pulley on the input shaft to the pulley on the output shaft. On the other hand, the fluid in the radially outer cylinder-and-piston units is pressurized only when the transmission ratio must be changed, i.e., if the ratio of the transmission is to be changed in actual use, e.g., in the power train of a motor vehicle.
Another feature of the continuously variable transmission which is disclosed in the published German patent application Serial No. 42 01 692 A1 is that the running endless flexible chain contributes to an increase of the force acting between such endless chain and the flanges of the pulley on the input shaft of the transmission. Such force is compounded by the force which is furnished by pressurized fluid in the second plenum chambers.
Further double-acting cylinder and piston units are disclosed in published German patent application Serial No. 41 33 724 A1. The two plenum chambers which are associated with each axially movable flange are axially off

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