Which Part of the Torque Converter Is the Driving Part?

The impeller—also called the pump—is the driving part of a torque converter. It is bolted to the engine’s flexplate and rotates with the converter housing, pushing transmission fluid toward the turbine to transmit power. In contrast, the turbine is the driven member connected to the transmission input shaft, while the stator redirects fluid to enable torque multiplication at low speeds.

How the Torque Converter Transmits Power

In an automatic transmission, the torque converter uses fluid dynamics to transfer engine power to the gearbox. As the engine turns, the impeller accelerates transmission fluid outward. That energized fluid strikes the turbine blades, spinning the turbine and driving the transmission input shaft. The stator, positioned between them, redirects returning fluid to boost efficiency and torque at low vehicle speeds. At cruising speeds, a lock-up clutch may engage to create a direct mechanical link, reducing slip and improving fuel economy.

Key Components and Their Roles

The following list outlines the primary parts of a torque converter and how each contributes to power transfer and efficiency.

• Impeller (Pump): The driving member, fixed to the converter cover and engine flexplate; it propels fluid toward the turbine.
• Turbine: The driven member, splined to the transmission input shaft; it receives fluid energy and converts it into rotational motion for the gearbox.
• Stator: Sits between impeller and turbine, mounted on a one-way clutch; it redirects returning fluid to multiply torque when there’s a large speed difference between impeller and turbine.
• Lock-up Clutch: Engages at steady speeds to eliminate hydrodynamic slip by mechanically linking the converter cover to the turbine, improving efficiency and reducing heat.
• Converter Cover/Housing: Bolts to the engine flexplate and turns with the crankshaft, carrying the impeller and enclosing the fluid circuit.

Together, these components ensure smooth vehicle launch, torque multiplication at low speeds, and efficient cruising through reduced slip when the lock-up clutch engages.

Why the Impeller Is Considered the Driving Member

The impeller is physically connected to the engine via the converter cover and flexplate, so it spins whenever the engine runs. By accelerating fluid and directing it toward the turbine, the impeller initiates power transfer. Its speed and the fluid’s momentum determine how much torque reaches the turbine. During acceleration, the stator’s redirection of fluid amplifies torque, but the process is always initiated by the impeller’s motion—hence its designation as the driving part.

Common Misconceptions

Some terms and functions are easily conflated in discussions of torque converters. Here’s what often gets mixed up—and why it matters.

• “The turbine drives the system.” The turbine is the driven member; it only turns because the impeller accelerates fluid into it.
• “The stator drives the turbine.” The stator doesn’t drive anything directly; it redirects fluid to improve torque multiplication and efficiency.
• “Lock-up replaces the impeller’s role.” Lock-up bypasses hydrodynamic slip at cruise, but the impeller remains the driving part whenever the clutch is open and during most acceleration.

Keeping these roles distinct helps diagnose performance issues and understand when fluid dynamics versus mechanical lock-up are at play.

Practical Implications for Diagnostics and Maintenance

Because the impeller is the driving member, issues like low fluid level, degraded fluid, or impeller damage can cause sluggish launches, overheating, or shudder under load. If symptoms appear mainly at steady cruise, the lock-up clutch or its control system may be involved instead. Regular fluid checks and timely service help maintain proper hydrodynamic coupling and reduce wear on the converter and transmission.

Summary

The impeller (pump) is the torque converter’s driving part, bolted to the engine and responsible for accelerating fluid toward the turbine. The turbine is the driven member, the stator optimizes fluid flow for torque multiplication, and a lock-up clutch reduces slip at cruise. Understanding these roles clarifies how automatic transmissions deliver smooth, efficient power.

What are the 4 parts of a torque converter?

The torque converter is what transmits that torque from the engine to a rotating driven load. In an automatic transmission car, the torque converter connects the power source to the load. Torque converters are comprised of five main components: the impeller, the turbine, the stator, a clutch, and the fluid.

Which of the following is the driving member of the torque converter and is part of or attached to the shell?

A torque converter is a fluid coupling that transmits power from the engine to the transmission. The main parts of a typical torque converter include: 1. Impeller: The impeller is the driving member of the torque converter that is connected to the engine crankshaft.

What is the driven part of a torque converter?

impeller
In a torque converter there are at least three rotating elements: the impeller, which is mechanically driven by the prime mover; the turbine, which drives the load; and the stator, which is interposed between the impeller and turbine so that it can alter oil flow returning from the turbine to the impeller.

What part of the torque converter drives the input shaft?

impeller
When the engine is running, it drives the impeller, a curved blade fan located at the front of the torque converter. The impeller is immersed in transmission fluid. As it rotates, it creates a flow of fluid towards the turbine, which is connected to the transmission input shaft.