Endless belt power transmission systems or components – Pulley with belt-receiving groove formed by drive faces on... – Fluid pressure actuator for adjustment of member
Reexamination Certificate
1999-09-20
2001-09-11
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
Reexamination Certificate
active
06287227
ABSTRACT:
TECHNICAL FIELD
This invention relates to hydraulic controls and more particularly to hydraulic mechanisms for controlling the ratio in a continuously variable transmission.
BACKGROUND OF THE INVENTION
Continuously variable transmissions (CVT), of the variable pulley or sheave type, employ sheave assemblies having at least one member that is movable to control the diameter at which a flexible transmitter, such as a belt or chain, operates. The transmission has an input sheave and an output sheave, both of which have an adjustable member. The transmission ratio between the input and output sheaves varies between an underdrive ratio and an overdrive ratio.
The CVT ratio is continuously variable between the extremes of the underdrive and overdrive ratios. During the underdrive ratios, the flexible transmitter is positioned at a small diameter on the input sheave and a large diameter on the output sheave. Thus, the input sheave has more than one revolution for each revolution of the output sheave. As the diameter of the input sheave increases, the diameter of the output sheave decreases until a one-to-one ratio exists across the sheaves. During the overdrive ratios, the diameter of the input sheave is maintained larger than the diameter of the output sheave. Thus, each revolution of the input sheave results in more than one revolution of the output sheave.
To accommodate the ratio variance, at least one member of each sheave is disposed to slide axially relative to the other member of the sheave. The movable member has a control piston that is pressurized to urge the member to the desire axial position at which the effective sheave diameter will provide the desired ratio. With the currently available electro-hydraulic controls, when a ratio change is effected, the piston of one of the sheaves is supplied with additional fluid, at a higher pressure, while the piston of the other sheave is exhausted of excess fluid. The exhausted fluid is returned to a transmission sump or reservoir. When a ratio change in the opposite direction is requested, the piston that was exhausted is resupplied with fluid while a portion of the fluid in the other piston is exhausted to the sump.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved control system for a continuously variable transmission.
In one aspect of the present invention, two variable displacement control pumps supply hydraulic fluid to the ratio control pistons of variable sheaves in a continuously variable transmission. In another aspect of the present invention, one of the pumps supplies the primary control pressure to the ratio control pistons. In yet another aspect of the present invention, the other pump supplies a ratio control pressure that is additive to the primary supply pressure at one of the ratio control pistons.
In still another aspect of the present invention, the ratio control pump has a center neutral position. In a further aspect of the present invention, the ratio control pump is moved to one side of the center neutral position when the ratio is being changed to reduce the speed ratio and to the other side of center to increase the speed ratio.
A CVT has two variable sheave members, each of which has a movable half that is controlled by a respective hydraulic piston. The pistons are pressurized to adjust the movable half to a position that will provide the desired speed ratio between the sheave members. The minimum pressure at each piston must be sufficient to support the torque being transmitted by the CVT. The speed ratio between the sheave members is changed, when requested, by increasing the pressure on one of the sheaves while maintaining the torque required pressure on the other of the sheaves.
A variable displacement primary pump supplies the fluid pressure necessary to support the torque requirement of the CVT. A variable displacement ratio pump supplies the added pressure necessary to change the speed ratio in the CVT. The primary pump is connected through check valves to supply fluid to both of the movable sheave halves while the ratio pump is disposed to transfer fluid to one of movable sheave halves. The ratio pump therefore increases the pressure on the movable half that must be adjusted to provide the desired ratio. The ratio pump is variable through a neutral or zero displacement position such that on one side of neutral, the driven sheave is supplied additional pressure, and on the other side of neutral, the drive sheave is supplied with additional pressure. When the ratio adjustment is complete, the ratio pump assumes a displacement sufficient to supply any make-up fluid that might be lost through leakage.
REFERENCES:
patent: 4158290 (1979-06-01), Cornell
patent: 5046991 (1991-09-01), Friedmann
patent: 5108348 (1992-04-01), Bornmann
patent: 6110062 (2000-08-01), Fujikawa
Bucknor Norman Kenneth
Vahabzadeh Hamid
Bucci David A.
General Motors Corporation
Grove George A.
Johnson Vicky A.
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