Lock-up piston in a torque converter

Details Lock-up piston in a torque converter Lock-up piston in a torque converter

1999-08-24

2001-03-13

Marmor, Charles A. (Department: 3681)

192 clutches and power-stop control

Vortex-flow drive and clutch

Including drive-lockup clutch

C192S213000

Reexamination Certificate

active

06199675

ABSTRACT:

BACKGROUND OF THE INVENTION
A. Field of the Invention
The present invention relates to a lock-up piston in a torque converter, and more particularly to a piston that includes a disc-shaped portion and an annular tube-shaped portion formed on an outer periphery of the disc-shaped portion, the annular tube-shaped portion extending in an axial direction.
B. Description of the Related Art
A torque converter is a device which has three types of internal vaned wheels: an impeller, a turbine and a stator. Torque converters typically configured to transmit torque via movement of hydraulic fluid within the device. A torque converter typically includes a front cover that is fixed to the impeller. The impeller typically includes an impeller shell welded to the front cover, and a plurality of impeller blades. The front cover is coupled to a torque producing mechanism, such as the crankshaft of an engine. The turbine is typically coupled to a transmission shaft. Torque is transmitted from the front cover to the impeller, the blades of the impeller urge the hydraulic fluid toward the turbine causing the turbine to rotate, and the turbine causes the transmission shaft to rotate.
A lock-up clutch within the torque converter is disposed between the turbine and the front cover. The lock-up clutch is typically coupled to the turbine for rotation therewith. When the lock-up clutch is engaged with the front cover, torque is directly transmitted from the front cover to the turbine.
Usually, the lock-up clutch includes a piston that can be brought into contact with the front cover in response to fluid pressure changes. The piston typically includes an annular flat portion on an outer peripheral portion thereof, the annular flat portion having an annular shaped frictional facing fixed thereto. A retaining plate is fixed to a portion of the piston for supporting a torsion spring that elastically couples the piston to a driven plate that is connected to the turbine.
The piston is selectively moved in an axial direction in and out of engagement with the front cover by changes in hydraulic fluid pressure within portions of the torque converter. When the annular shaped frictional facing fixed on the outer periphery of the piston is in direct contact with a corresponding frictional surface of the front cover, torque from the front cover is transmitted through the lock-up clutch to the turbine.
Preferably, the frictional surface of the front cover should be flat. In reality, however, undulations and irregularities caused by, for instance, welding, sometimes develop in the frictional surface. With such undulations present, when the friction facing of the piston is in contact with the frictional surface of the front cover, the rigidity of the piston prevents complete planar surface to surface contact between the frictional surface on the front cover and the frictional facing on the piston. Specifically, only the undulated portions of frictional surface of the front cover closest to the piston make contact with the frictional facing on the piston. As a result, the performance of the lock-up clutch is degraded and slippage of the lock-up clutch may occur. Therefore, under such circumstances, the lock-up clutch is unable to operate properly and may not sufficiently absorb or dampen vibrations during slippage of the lock-up clutch, and further may not transmit torque to the turbine in an efficient manner due to the slippage.
Further, in a known configuration of a piston of a lock-up clutch, the piston is formed on an outer radial periphery thereof with an annular rim or tubular portion which restricts radially outward movement of torsion springs. Typically the torsion springs are moved radially outward by centrifugal force. Therefore, such an annular rim or tubular portion is necessary to retain the torsions springs. Unfortunately, such an annular rim or tubular portion provides the piston with even greater rigidity, thereby further adding to the problems discussed above.
SUMMARY OF THE INVENTION
An object of the present invention is to improve the frictional engagement performance of a piston of a lock-up clutch by making the portion of the piston that undergoes friction engagement more flexible.
In accordance with one aspect of the present invention, a lock-up piston in lock-up clutch of a torque converter includes a disc-shaped member. The disc-shaped member includes a central disc-shaped plate portion, an flat annular portion formed at the outer periphery of the disc-shaped plate portion, and an annular rim portion formed at an outer peripheral edge of the flat annular member. The flat annular portion is configured for frictional engagement with a front cover of the torque converter and the annular rim portion extends in an axial direction towards a turbine side of the torque converter. The lock-up piston is configured such that the flat annular portion is more flexible that the central disc-shaped plate portion.
Since the flat annular portion has a lower rigidity than the disc-shaped plate portion, when the flat annular portion frictionally engages the front cover, the flat annular portion is able to conform to the shape of the front cover. Therefore, if the front cover has irregularities or an undulating surface, the flat annular portion may still make reliable frictional engagement therewith. As a result, the friction performance of the lock-up piston is improved. Since the central disc-shaped plate portion can maintain the same rigidity as that of a prior art central disc-shaped plate portion, the piston has sufficient strength to withstand the hydraulic fluid pressure exerted on the piston.
Preferably, in one embodiment of the invention, the flat annular portion of the lock-up piston has a thinner plate thickness than the central disc-shaped plate portion.
Preferably, the plate thickness of the flat annular portion of the lock-up piston is in the range from 50 to 80% of the plate thickness of the central disc-shaped plate portion.
Alternatively, a thickness of the annular rim portion is thinner than the thickness of the disc-shaped plate portion.
Preferably, the thickness of the annular rim portion is in the range from 50 to 80% of the thickness of the disc-shaped plate portion.
Alternatively, a plurality of apertures are formed in the annular rim portion.
Preferably, the plurality of apertures is in the form of a plurality of notches opened axially toward the turbine.
Preferably, an axial length of the notches is in the range from 30 to 90% of an axial length of the annular rim portion.
Preferably, a sum of circumferential length of all of the plurality of notches is no greater than 30% of a circumferential length of the annular rim portion.
Preferably, the circumferential length of each of the notches is in a range from 5 to 20 mm.
Alternatively, the plurality of apertures is in the form of a plurality of holes closed on an axial end of the annular rim portion close to the turbine.
Preferably, each of the holes has a circumferential length larger than an axial length thereof.
Preferably, the axial length of each of the holes is in a range from 20 to 70% of an axial length of the annular rim portion.
Preferably, a sum of circumferential lengths of the plurality of holes is in the range from 50 to 80% of the circumferential length of the annular rim portion.
In each of the above configurations and embodiments, the flat annular portion is more flexible than in prior art configuration making it possible for more reliable contact with possibly uneven surfaces on a front cover of a torque converter.


REFERENCES:
patent: 4809830 (1989-03-01), Schierling et al.
patent: 4934495 (1990-06-01), Lemon
patent: 6079529 (2000-06-01), Hinkel et al.
patent: 6079531 (2000-06-01), Ohkubo et al.
patent: 19622691 (1996-12-01), None

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