Torque converter for an automatic transmission

Claim 1

A torque converter for a motor vehicle driven by an engine, the torque converter having a converter cover secured to a crankshaft of the engine, an impeller secured to the converter cover, an input shaft for an automatic transmission, a turbine secured to the input shaft at a turbine hub, and a lockup clutch including a lockup piston axially slidably mounted on the turbine hub and a torsion damper which comprises a drive plate secured to the lockup piston and a driven plate between the drive plate and the lockup piston, the turbine hub having a disc formed on a periphery of the turbine hub, a pilot boss having an axial hollow therein, and an annular inner boss and an annular outer boss extending from said disc in a direction toward the crankshaft, the improvement in the torque converter wherein: said pilot boss has a small diameter portion, an intermediate diameter portion and a large diameter portion which are accurately concentric to each other and are inserted between said crankshaft and said input shaft; an outer end of said small diameter portion of the pilot boss being engaged with a hole formed in the crankshaft at an axis thereof; said intermediate diameter portion supports said converter cover; said large diameter portion of the pilot boss rotatably supports said lockup piston interposing said annular inner boss so as to accurately coaxially align each axis of said crankshaft, of said converter cover and of said lockup piston; said pilot boss being formed with a bore extending in a radial direction therein with respect to an axis of the torque converter and communicating with said axial hollow and a release side oil chamber formed between the converter cover and said lockup piston for supplying release oil to said release side oil chamber; thrust bearing means being inserted in a recess formed in said pilot boss, said recess communicating with the axial hollow, for receiving an axial thrust force of said turbine hub; the lockup piston being axially slidably mounted on said annular inner boss interposing sealing means for preventing oil from leaking out of said release side oil chamber; the driven plate being coaxially slidably mounted on said annular outer boss via a spline therebetween; and an oil passage being formed in the input shaft communicating with said axial hollow of said pilot boss for supplying said release oil to said release side oil chamber via said bore so as to disengage the lockup piston from the converter cover.