TC Components and Power Flow

Torque Converter Components

  1. Impeller - The impeller is driven through the converter cover by the engine flex plate. It is the "input" member of the converter assembly and makes up the second half of the of the converter outer casing.
  2. Stator - This is the stationary or "reaction" member for torque multiplication. It controls oil flow from the impeller in the "reduction" phase of converter operation.
  3. Turbine - The turbine is driven by oil splashed from the impeller. The turbine is the output member of the converter which drives the turbine shaft of the transmission.
  4. Damper Assembly - The Damper is welded to the converter cover. It cushions engine shock to the direct drive shaft of the transmission.
  5. Stator Support - The stator within the converter is splined onto the stator support: the stationary shaft extending from the front of the transmission pump.
  6. Impeller Hub - The hub is a steel collar welded to the impeller which mechanically drives the gears of the transmission pump.

The converter is supported on the stator support [5], which is part of the transmission oil pump assembly. The impeller hub [6] is supported by the transmission pump body bushing.

Power to the Gear Train

Depending on which gear the transmission is in, input from the engine to the transmission is through the turbine input shaft or the direct drive shaft or a combination of both.

How the Converter Works

7

Automatic Hydraulic Clutch

In Reverse, low and second gears, the converter operates in hydraulic or soft drive conditions. In hydraulic drive, the converter functions as an automatic clutch (when the car is stopped) and as a torque multiplier (when engine load requires more torque).
  1. The engine drives the impeller mechanically.
  2. The turbine is driven hydraulically by the impeller.
  3. The turbine drives the tube input shaft for input to the gear train.

Impeller Pumps Fluid

The purpose of the impeller is to put the fluid in motion. Inside the impeller housing many curved vanes, along with an inner ring, form passages for the fluid to flow through. The rotating impeller acts as a centrifugal pump. Fluid is supplied by the hydraulic control system and flows into the passages between the vanes [1]. When the impeller turns, the vanes accelerate the fluid and centrifugal force pushes the fluid outward so that it is discharged from openings around the inner ring [2]. The curvature of the impeller vanes directs the fluid toward the turbine, and in the same direction as impeller rotation [3].

Rotary Force on the Turbine

As shown in View B (above), the turbine vanes [4] in the turbine are curved opposite to the impeller. The impact of the moving fluid on the turbine vanes [5] exerts a force that tends to turn the turbine in the same direction as the impeller rotation. When this force creates a great enough torque on the transmission turbine output shaft to overcome the resistance of motion, the turbine begins to rotate.

Now the impeller and turbine are acting as a simple fluid coupling, but we have no torque multiplication yet. To get torque multiplication, we must return the fluid from the turbine to the impeller and accelerate the fluid again to increase its force on the turbine.

Vanes Reverse the Flow

To get maximum force on the turbine vanes when the moving fluid strikes them, the vanes are curved to reverse the direction of flow [6]. Less force would be obtained if the turbine deflected the fluid instead of reversing it. At any stall condition, with the transmission in gear and the engine running but the turbine standing still, the fluid is reversed by the turbine vanes and pointed back to the impeller. Without the stator, any momentum left in the fluid after it leaves the turbine [7] would resist the rotation of the impeller.

At this point, we have a simple fluid coupling that will cause the turbine to drive the input shaft with no torque multiplication. To gain multiplication, we must add the reaction member or stator.

Torque Multiplication and Coupling

Graphic of Torque Multiplication and Coupling

Torque Multiplication

When torque multiplication is required, the stator [8] above reverses the direction of impeller rotation. A one-way clutch [9] prevents the force of the fluid from turning the stator opposite the impeller and turbine by holding itself motionless on the stator shaft.

As the fluid flows from the stator to the impeller, the impeller has another opportunity to accelerate the same fluid. The fluid [10] leaves the impeller with close twice the energy it had the first time and exerts greater force on the turbine.

We call the flow of fluid [11] through the impeller, to the turbine, through the stator, and back through the impeller the vortex flow. At high impeller speed and low turbine speed. the vortex flow velocity is the sum of the impeller produced velocity, plus the velocity of the fluid returning from the turbine and stator. It is vortex flow that gives us torque multiplication.

By torque multiplication, we mean that there is more torque on the turbine shaft than the engine is putting out because the vortex fluid is accelerated more than once. Torque multiplication is obtained at the sacrifice of turbine rotation. Actually, it's no different from the mechanical advantage which your get from gearing down. You gain torque by sacrificing motion.

Torque multiplication takes place anytime the turbine is turning at less than 9/10 impeller speed. At full stall, the stock AOD converter produces about 1.85-to-1 torque multiplication. As the turbine speed increases in relation to the impeller, torque multiplication decreases.

Coupling Phase

When the coupling phase (view D above) is reached - when the turbine speed is about 9/10 impeller speed - there is no longer any torque multiplication. The converter is then only transmission engine torque to the gear train.

As the turbine begins to rotate and steadily picks up speed, the vortex flow steadily looses speed because of the increasing centrifugal force acting against the flow through the turbine. The rotating impeller produced a centrifugal force in the fluid which caused it to flow from the center outward. The same centrifugal force is acting in the rotating turbine, trying to prevent the fluid from flowing inward. As the vortex flow slows down, torque multiplication is reduced.

As the turbine catches up with the impeller, the angle at which the fluid leaves the turbine is constantly changing [12]. In the coupling phase, the fluid leaving the turbine strikes back at the stator vanes [13]. The one-way clutch unlocks [14] and the impeller, turbine and stator turn together. Allowing the stator to rotate freely during coupling lets the fluid moved by the impeller to flow directly into the turbine.

Converter Automatically Adjusts Torque

Since vortex flow speed is governed by the difference between impeller and turbine speed, the torque converter output to drive shaft torque requirements. When drive shaft torque requirements become greater than the engine output torque, the turbine slows down and causes an increase in vortex flow velocity and therefore an increase in torque multiplication.