Friction gear transmission systems or components – Electric or magnetic control
Reexamination Certificate
1999-11-22
2002-05-14
Fenstermacher, David (Department: 3682)
Friction gear transmission systems or components
Electric or magnetic control
C476S004000, C476S040000
Reexamination Certificate
active
06387009
ABSTRACT:
TECHNICAL FIELD
This invention relates to traction drive transmissions having a slip control and control method to limit the slip between members of the traction drive.
BACKGROUND OF THE INVENTION
Infinitely variable transmissions generally employ a continuously variable unit (CVU) and a gearing unit. The gearing unit has a summing differential that combines the engine input power to the transmission with the output power of the CVU for delivery to an output shaft of the transmission. The gearing will commonly permit a geared neutral wherein the output shaft is stationary while both the input and output of the CVU are rotating. The CVU includes a traction drive assembly commonly in the form of a full toroidal type unit or a half toroidal type unit. Both of these devices transmit power from an input disc to an output disc via transfer rollers through a traction force. The CVU generally includes two input discs, two output discs and a plurality of transfer rollers disposed between respective input disc/output disc pairs.
The traction force is carried through an oil film between the discs and the transfer rollers. During the transmission of torque between the discs, a slip occurs at the interface of the discs and the rollers. When the relation between the traction force and the slip characteristic is evaluated, it appears to be similar to a viscous shear force. The traction force is proportional to the normal force between the discs and the rollers. The normal force can be imposed through a hydraulically actuated piston attached to one of the input discs while the other input discs is grounded.
The transfer rollers are rotatably supported on trunnions that have a hydraulic force applied thereto to maintain the transfer rollers in the desired position between the respective pairs of input and output discs. The hydraulic force applied to the trunnions establishes the traction force between the discs and the rollers. The traction force divided by the normal force represents the coefficient of traction. The maximum torque capacity of the CVU is determined by the geometry of the discs and rollers, the normal force and the coefficient of traction of the fluid which varies with temperature. If the torque being transmitted exceeds the maximum torque capacity, detrimental slippage will occur between the discs and the rollers which can damage the CVU.
One system for controlling the normal force and traction force is shown in U.S. Ser. No. 09/323,259 filed Jun. 1, 1999 and assigned to the assignee of this application. Another control system for a toric type drive is described in U.S. Pat. No. 5,067,372 issued on Mar. 4, 1997.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved traction drive and control having a method of determining the slip speed.
In one aspect of the present invention, sensors are placed to record the input disc speed, the output disc speed, the traction roller speed and the traction roller angle. In another aspect of the present invention, the speed of the discs and rollers and the roller angle is recorded when the torque transmission is approximately equal to zero.
The maximum coefficient of traction varies with fluid temperature and the speed ratio of the CVU. The speed ratio of the CVU is a function of the angle at which the traction rollers are positioned. This angle is varied to vary the speed ratio. Speed sensors are positioned to determine the input disc speed, the output disc speed and the traction roller speed. These sensors are relatively inexpensive and provide accurate and repeatable data. An angle sensor is provided to determine the operating angle of the traction rollers. It is difficult with the sensors presently available to accurately determine the roller angle unless an inordinately expensive sensor is employed. However, the presently inexpensive angle sensors do provide acceptable repeatability. With the present invention the exact angle need not be known as long as the data can be repeated. In other words, if the sensor indicates the data is being taken at the proper angle, the exact value is not required.
The data is collected when the CVU is transmitting approximately zero torque. At this operating condition, the slip between the discs and the traction rollers is zero. This establishes a baseline for that angle of the traction rollers. The system repeats the reading at the data point when the torque is zero and updates a table of values for the various angles. When torque is being transmitted, the control system can determine the slip between the rollers and the discs from the stored data and adjust the normal force, if required, to maintain the slip speed within a desired range near the maximum coefficient of traction permitted by the traction fluid.
REFERENCES:
patent: 3596467 (1971-08-01), Avery
patent: 6162144 (2000-12-01), Haka
Fenstermacher David
General Motors Corporation
Hodges Leslie C.
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