Ch46 Torque Converters

A stall test rpm that is significantly lower than specification (400 to 600 rpm lower), could indicate

A freewheeling stator.

One-way clutch

A roller or sprag-type device that allows rotation in one direction but locks in the opposite direction. Aka over-running clutch.

Stall test rpm higher than 100 rpm from specification usually indicates

A slipping clutch or a torque converter fluid issue.

Coupling phase

A torque converter operating phase when the turbine and the impeller are at close to the same speed.

Torque converter

A type of fluid coupling that is also capable of multiplying torque.

Variable pitch stators can

Alter a torque converter's multiplication factor by changing their blade angles.

Stall test rpm lower than 100 rpm from specification typically means

An engine that is performing poorly.

The torque multiplication phase occurs

Anytime the converter is multiplying torque.

The coupling phase occurs

Anytime the turbine and the impeller speeds are w/in 10% of each other.

A torque converter's impeller can only drive the turbine to

Approximately 90 to 95% of impeller speed. this speed difference, aka slippage, robs efficiency. Today's torque converters are equipped with a lock-up clutch to eliminate the 5 to 10% slippage.

The impeller is part of the converter housing that is

Bolted to the engine, so it always turns with the engine.

A torque converter's torque multiplication factor can be controlled by

Changing the curvature of the elements, the turbine, the stator and the impeller, the sizing of the elements, and the clearance between the elements.

Automatic transmissions have a limited number of gear ratios available when

Compared to standard transmissions. To provide enough torque multiplication, automatic transmissions need a torque converter to supply the extra degree of torque multiplication.

Transmission fluid that does not cool down

During the cool down phase of a stall test could indicate a stuck or seized stator.

Torque converters are connected to the

Engine crankshaft or flywheel thru flex plates, so they can expand and contract while under load.

Rotary flow

Fluid flow inside the torque converter that follows the rotation of the housing.

Vortex flow is always present in the torque converter, but is greatest at

Full stall

During torque multiplication, the stator is

Held stationary by the one-way clutch; during coupling phase, the stator is freewheeling.

The turbine position in relation to the

Impeller can affect the torque multiplication factor of the torque converter.

Torque converters and fluid couplings both have an

Impeller or pump and a turbine inside a shell that is shaped like a hollowed-out donut. Aka torus.

Torque converter lock-up can be pre-programmed or

Modulated. Programmed lock-up is for fuel economy. Modulated lock-up is for vehicle performance.

Torque multiplication phase

Occurs whenever the impeller is turning significantly faster than the turbine.

Fluid is returned from the converter to the transmission cooler thru a passage formed between the inside

Of the stator support shaft and the outside of the turbine shaft.

The stator is mounted on a

One-way clutch and can freewheel in one direction, but it locks up if it tries to turn in the opposite direction.

Light-duty torque converters should be

Replaced with a new one when a transmission overhaul is required.

The torque converter fluid flow can be

Rotary or vortex. Rotary flow in the torque converter is fluid that follows the rotation of the converter housing. Vortex flow is the flow of fluid from the impeller, thru the turbine, thru the stationary stator, and back to the impeller.

The turbine is

Splined to the transmission input shaft to deliver power to the transmission.

Impeller

The bladed element in a torque converter or fluid coupling that is fixed to the housing and, therefore, rotates with it.

Stator

The element inside a torque converter most responsible for torque multiplication.

Vortex flow

The flow of fluid from the impeller, thru the turbine, thru the stator, and back to the impeller.

Torus

The hollowed-out donut shape of the rear of the converter housing and the turbine.

Transmission fluid is normally delivered to the rotating torque converter thru a passage formed between

The inside of the converter's pump drive hub and the outside of the stator support shaft.

Turbine

The torque converter element that is splined to the transmission input shaft.

Heavy-duty torque converters should be overhauled when

The transmission requires an overhaul.

Rotary flow is always present in the

Torque converter but is greatest at the converter's coupling phase, when the turbine speed is w/in 10% of impeller speed.

Fluid couplings are similar to

Torque converters because they transfer power from the source to a driveline through fluid. A fluid coupling, however, cannot multiply torque.

The torque converter has two distinct phases of operation. The

Torque multiplication phase and the coupling phase.

Stall testing can help determine

Whether the engine, the transmission, or the torque converter is the source of a driver complaint.

Torque converters have an extra element inside, called a

stator, which is the primary component that enables a torque converter to multiply torque.