Torque Converters

Comprehensive practice flashcards covering torque converter components, fluid flow mechanisms, stall speed measurement, internal and external influences, and selection guidelines.

What is the primary function of a torque converter in an automobile?

The torque converter is what transfers the torque from the engine to the transmission.

At what operating point does a torque converter achieve maximum torque?

The maximum torque comes at maximum stall speed.

What happens to the stator when stall RPM is reached?

When stall RPM is reached, the stator stops spinning.

In this diagram of vortex flow, what do labels A, B, and C represent?

A represents the Impeller (Pump), B represents the Turbine, and C represents the Stator.

What are the roles of the stator and the sprag in a torque converter?

The stator helps smooth out rotary flow and multiply torque, while the sprag operates as a one way clutch.

What two types of fluid flow occur in torque converters?

Vortex Flow and Rotary Flow.

How is vortex flow defined in a torque converter?

Vortex flow is the flow of fluid from the pump through the turbine and back through the stator.

How does fluid movement transition into rotary flow as turbine and pump speeds equalize?

As speeds start to equalize nearing a $1:1$ ratio, oil flow slows and allows the stator to unlock and rotate with the pump and turbine.

What occurs when vortex flow ends, and what is the typical range of torque multiplication in converters?

When vortex flow ends, torque multiplication ends; torque converters have a $2.0 - 2.9$ torque multiplication.

What two methods are used to measure stall speed?

Foot Brake Stall and Flash Stall.

What is foot brake stall, and what serves as its limiting factor?

Foot brake stall is the maximum RPM reached at WOT with the transmission in gear and the brakes locked; the limiting factor is the holding capability of the brakes.

What is flash stall speed and how does inertia affect it?

It is measured with no brakes applied; the throttle is pushed wide open and inertia helps the engine reach a higher stall speed than would be achieved with foot brake stall.

When launching a vehicle using flash stall, how should the low RPM be configured?

Set low RPM to $1000\text{ RPM}$ less than the rated stall speed.

How does adjusting launch RPM affect the tires and torque multiplication?

Raising launch RPM softens the hit on the tires; the less RPM from stall speed, the more torque multiplication will be available.

What four external vehicle factors influence stall speed?

1. Engine Torque, 2. Vehicle Weight, 3. Overall Gear ratios, and 4. Tire Diameter.

What four internal factors control stall speed within a torque converter?

1. Blade angle, 2. Clearances (between pump and turbine, as well as turbine and stator), 3. Stator blade design, and 4. Torque converter diameter.

How do blade angle and converter diameter correlate with stall speed?

A more negative blade angle produces a higher stall speed, and a smaller torque converter diameter results in a higher stall.

How are converter fins manipulated to tighten or loosen a converter?

To tighten a converter, fins are bent towards the flow (Negative Angle); to loosen a converter, fins are bent away from the flow (Positive Angle).

What stall range is recommended for street applications, and what operational caution must be followed?

Choose a stall range between $1,200$ and $1,500\text{ RPM}$ below the engine's peak torque; cruise RPM must be greater than stall RPM.

What stall range is recommended for racing applications?

A stall range between $600$ to $700\text{ RPM}$ below peak torque.

How do camshaft or final drive gearing alterations influence stall speed?

The stall speed will change even if the actual torque converter is not changed.

What is the primary benefit and disadvantage of selecting a higher stall speed?

A higher stall speed helps the vehicle launch, but it may be less efficient at high speed.