Method of forming torque converter stator

A method of forming a stator for a torque converter is provided. The method includes casting a stator casting to include a body and blades on an outer circumferential surface of the body. The body includes excess material at an axial surface thereof. The method also includes machining the excess material to balance the stator casting. A torque converter is also provided. The torque converter includes a turbine, an impeller and a stator axially between the turbine and the impeller. The stator includes a stator casting including a body and blades on an outer circumferential surface of the body. The body includes a material segment at an axial surface thereof.

The present disclosure relates generally to torque converters and more specifically to stators of torque converters.

BACKGROUND

In order to balance a stator casting prior to use, a brim or a hat of the stator is machined. Such machining may not allow enough imbalance correction, may cause a large increase in scrap and may hurt torque converter characteristics.

SUMMARY OF THE INVENTION

A method of forming a stator for a torque converter is also provided. The method includes casting a stator casting to include a body and blades on an outer circumferential surface of the body. The body includes excess material at an axial surface thereof. The method also includes machining the excess material to balance the stator casting.

A torque converter is also provided. The torque converter includes a turbine, an impeller and a stator axially between the turbine and the impeller. The stator includes a stator casting including a body and blades on an outer circumferential surface of the body. The body includes a material at an axial surface thereof including a first circumferential segment and a second circumferential segment. The first circumferential segment is thicker than the second circumferential segment.

DETAILED DESCRIPTION

The disclosure provides a method of balancing a stator hub by machining as necessary extra material added to the turbine side of the stator hub in the casting. Thereby, machining is done at the hub and not the hat area thus a design of the blades and core ring of the turbine and/or impeller is not altered.

FIG. 1shows a cross-sectional side view of a torque converter10in accordance with an embodiment of the present invention. Torque converter10is rotatable about a center axis11and includes a front cover12for connecting to a crankshaft of an internal combustion engine and a rear cover14forming a shell16of an impeller or pump18. Front cover12includes cup shaped section12afor connecting to a rear cover14and a hub section12bincluding a pilot12cfor aligned with the crankshaft. Torque converter10also includes a turbine20, which is positioned opposite impeller18, and a damper assembly22fixed to turbine20. Torque converter10further includes a stator24according to an embodiment of the present invention formed in accordance with the method described below with respect toFIGS. 2aand 2b. Stator24is axially between impeller18and turbine20and includes a stator casting26, which includes a plurality of blades28and a stator body30. Stator24also includes a one-way clutch32held within an annular recess34formed in stator body30by a centering plate36. One-way clutch32includes an inner race38, an outer race40and rollers42radially between inner race38and outer race40. Stator casting26is rotationally fixed to outer race40, and depending on the operating conditions of torque converter10, inner race38and outer race40are rotationally fixed to each other or rotatable relative to each other. A first axial thrust bearing43ais provided between stator24and impeller18and a second axial thrust bearing43bis provided between stator24and turbine20.

Turbine20includes a plurality of blades44supported on a rounded portion46of turbine20at a rear-cover side of turbine20. Turbine20further includes an inner radial extension48protruding radially inward from rounded portion46. On a front-cover side of turbine20, turbine20is connected to damper assembly22. Damper assembly22includes two cover plates50,52supporting an inner set of springs54axially therebetween, with the turbine-side cover plate50being riveted to turbine20by a plurality of circumferentially spaced rivets56. Damper assembly22further includes a centrifugal pendulum vibration absorber58at a radially outer end60of cover plate50and a drive flange62positioned axially between cover plates50,52. Drive flange62includes a drive hub64at an inner radial end thereof including splines66on an inner circumferential surface thereof configured for nonrotatably connecting to a transmission input shaft. Cover plates50,52transfer torque from turbine20to drive flange62via springs54. Drive flange62in turn drives the transmission input shaft via hub64. Radially outside of springs54, cover plates50,52are riveted together by a plurality of circumferentially spaced rivets68. Rivets68pass through cover plates50,52into circumferential spaces formed between outer tabs70extending from a radial outer end of drive flange62.

A radially outer end of cover plate52forms a spring retainer76retaining a set of radially outer springs78. A further plate80of damper assembly22is riveted to a front cover side of cover plate52and extends into circumferential spaces between springs78to contact circumferential ends of springs60. Plate80further includes projections82extending axially away from cover plate52.

Torque converter10also includes a lockup clutch84formed by an inner axial surface86of front cover12, a clutch plate88and a piston90. Clutch plate88includes friction material88a,88bon both axial surfaces thereof. A first friction material88ais configured for contacting inner axial surface86and a second friction material88bis configured for contacting piston90. Clutch plate88further includes drive projections94on a radial outer end thereof extending through circumferential spaces between projections82and into the circumferential spaces between springs78.

FIGS. 2ato 2cillustrate a method of forming stator24in accordance with an embodiment of the present invention. Stator24includes blades28for redirecting the torque converter fluid supported radially between an outer circumferential surface96of stator body30and an inner circumferential surface98of a brim100. On an outer circumferential surface102of brim100, stator24includes a hat104protruding radially outward from brim100to define a radially outermost edge of stator24. Stator body30includes annular recess34formed in an impeller-side axial surface106thereof receiving one-way clutch32(FIG. 1). Annular recess34is defined by two step portions—an radially inner step portion108receiving inner race38, outer race40and rollers42and a radially outer step portion110receiving centering plate36. Radially inner step portion108includes a radially extending surface112extending radially outward from an innermost circumferential surface114of stator casting26and an axially extending circumferential surface116extending from a radially outer edge of radially extending surface120. Radially outer step portion110includes a radially extending surface118extending radially outward from axially extending circumferential surface116of step portion108and an axially extending circumferential surface120extending from a radially outer edge of radially extending surface118to axial surface106. In this embodiment, axial surface106extends axially and radially away from surface120radially toward blades28and axially toward impeller18(FIG. 1) to form a tapered surface122between recess34and blades28.

Opposite of axial surface106, casting26, at a turbine-side axial surface124of stator body30, includes an excess material ring126at a radial outer end of body30, just inside of blades28. In other embodiments, the excess material ring126may be formed on the impeller-side axial surface106. Axial surface124includes a flat thrust surface128extending perpendicular to a center axis of stator24for contacting axial thrust bearing43b. Radially outside of thrust surface128, axial surface124includes a tapered surface130extending axially and radially away from flat surface128radially toward blades28and axially toward impeller18(FIG. 1). Excess material ring126is provided at an outer radial edge of tapered surface130, between tapered surface130and blades28to allow for balancing stator casting26after it is casted. Material ring126protrudes axially past a plane132of turbine-side axial edges134of blades and axially past a plane136of tapered surface130. In this embodiment, material ring126is step shaped and includes a radially extending surface138extending radially outward from tapered surface130and an axially extending circumferential surface140extending axially from a radially outer edge of radially extending surface138to plane132.

FIG. 2billustrates the machining of material ring126during a balancing operation to provide for imbalance correction. During the balancing, innermost circumferential surface114is provided onto a support and stator casting26is rotated about its center axis by a portion of the 360 degree revolution, which is less than or equal to 120 degrees. While stator casting26is being rotated for a degree amount that is less than or equal to 120 degrees, a machining tool is applied in a tool direction142to apply a radially inward force to create a balancing cut at a common depth to remove a portion of material ring126, in particular an arc portion (i.e., a circumferential segment of less than or equal to 120 degrees of ring126), which is illustrated by hatching, as necessary to properly balance stator casting26. More specifically, a majority of radially extending surface138extending radially outward from tapered surface130and an axially extending circumferential surface140are removed over the circumferential range, i.e., the range of less than or equal to 120 degrees. The exact angle on each part produced varies based on the amount of correction needed. 120 degrees is set as a maximum threshold because any material removed over this ranged no longer is beneficial for changing the component imbalance due to the short distance to the centerline of the imbalance vector.

FIG. 2cillustrates stator casting26after the machining of material ring126described with respect toFIG. 2b. As shown inFIG. 2c, over the circumferential range in which a portion of the excess material ring126is removed, a material arc segment144remains on axial surface124of body30radially outside of tapered surface130and radially inside of blades28. Material arc segment144is of sufficient size and configuration such that stator casting26is properly balanced during operation of torque converter10. In this embodiment, material arc144still protrudes axially past planes132,136, but to a less degree than material ring126, and includes a tapered axial surface146extending axially and radially away from the remaining portion of radially extending surface138to the remaining portion of axially extending circumferential surface140such that surface146is tapered toward blades28. Removing of the circumferential segment to form material arc144leaves an arc segment148of material ring126intact on axial surface124, as schematically shown inFIG. 2c. Because arc segment148is of the same shape as material ring126when view cross-sectionally as inFIG. 2c, circumferential segment148is thicker than material ring, more specifically in both the axial and radial directions.

To further illustrate the shape of segments144,148,FIG. 3schematically shows a plan view of stator casting26after the machining of material ring126. Arc segment144has a smaller circumferential length than thicker arc segment148, with arc segment144extending 120 degrees or less and arc segment148extending 240 degrees or greater.