Transmission (Gearbox) Systems in Motor Vehicles

Transmission is a mechanical component that transmits power from a vehicle’s engine to the wheels, enabling motion. important performs two essential functions: not only ensuring the vehicle’s forward movement but also providing the driver with speed and torque control. Over the years, transmissions have evolved through technological advancements to enhance vehicle versatility. Today also play a role in influencing direct driving dynamics, making the driving experience more flexible.

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In motor vehicles, the ability to accelerate rapidly and maintain speed is highly desired. Load-carrying capacity and achieving the desired speed under load depend on the engine’s torque, or more precisely, its tractive force. To enable the engine’s generated power to propel the vehicle and provide sufficient tractive force, the rotational force must be increased and transmitted all the way to the wheels.

Functions of Transmissions

Speed Variation

The process required to enable driving at different speeds is gear shifting. Depending on the type of transmission, usage and performance vary accordingly. This process either increases or decreases the vehicle’s speed.

Torque Control

Torque is the force with which the wheels contact the road surface. Transmissions regulate torque to adjust the vehicle’s acceleration and traction. feature enables better performance on steep inclines or slippery surfaces. If we disregard certain high-performance and powerful vehicles where manual transmissions deliver the best torque control under identical conditions, manual transmissions remain superior.

Reverse Gear

Transmissions provide a reverse gear to move the vehicle backward. This function is present in nearly all transmissions and, due to the single-stage design of most vehicles, the range of rotational speeds offered is not significantly different across types.

Fuel Economy

Transmissions can improve a vehicle’s fuel economy. Depending on whether the transmission is automatic or manual, the vehicle can consume energy more efficiently. If a driver experiences difficulty with manual operation, switching to a vehicle with an automatic transmission can yield fuel economy benefits.

Driving Experience: Transmissions offer drivers greater control and driving enjoyment. Manual transmissions provide a stronger sense of interaction and control, while automatic transmissions offer a more comfortable driving experience.

What Are the Types and Features of Transmissions?

Manual transmissions give drivers complete control over gear shifting.

They can offer advantages in fuel efficiency, depending on usage patterns.

They give drivers a greater sense of control over their vehicle.

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In modern traffic, shifting gears can be cumbersome, requiring frequent actions during stop-and-go conditions. These actions can cause time and create discomfort for other drivers during these intervals.

Manual transmissions are more efficient in performance and acceleration when operated by skilled drivers.

Types of Manual Transmissions

Sliding Gear Type

Gears are slid onto a splined shaft to achieve various transmission positions. This system type is used in older vehicles and typically only for reverse gear.

Sliding Dog Type

All gears are permanently engaged. Gear shifting is achieved by sliding a dog clutch. Shifting to a higher gear requires a brief disengagement of the clutch, while shifting to a lower gear requires a brief application of throttle.

Synchromesh Type

In synchromesh gearboxes, the synchromesh system ensures that the rotational speeds of the splined shaft and the gear are equalized before engagement. This eliminates the need for double-clutching or throttle blipping during gear changes, making gear engagement easier and protecting the gearbox.

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Locked Synchromesh Type

A locked synchromesh gearbox includes a locking mechanism that prevents gear engagement until the rotational speeds of the dog clutch and gear are matched. The lock disengages only when speeds are synchronized, allowing gear engagement. Complete In synchromesh gearboxes, all gears except reverse are equipped with a locked synchromesh system.

Automatic Transmission (Torque Converter Transmission)

Automatic transmissions perform gear shifts automatically, freeing drivers from the effort of manual gear changing.

Automatic transmissions offer easier operation due to their smooth acceleration and reduced physical input during stop-and-go traffic.

Fuel economy may be slightly lower in some cases, but this depends heavily on usage; it is not always true that manual transmissions provide better fuel efficiency.

Gear transitions are significantly smooth and faster than in manual transmissions.

Some automatic transmissions include manual features such as paddle shifters to provide drivers with greater control.

An automatic transmission is a mechanism that transfers engine power to the wheels without a clutch. Gear ratios change automatically via a torque converter, which replaces the clutch. It typically consists of three main units.

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Torque Converter

The torque converter functions like an automatic clutch and additionally amplifies engine torque. Its main components are an impeller, a turbine, and a stator. The torque converter is filled with automatic transmission fluid (ATF), and torque transfer is achieved through fluid flow. The pump, driven by the engine, flings fluid outward via centrifugal force through its vanes. The high-speed fluid enters the turbine wheel. Inside the turbine, curved vane channels convert the fluid’s kinetic energy into mechanical rotation. The fluid exits the turbine in a direction opposite to the pump’s rotation but at a lower speed. It strikes the stator vanes, which attempt to rotate the distributor in the opposite direction to the pump and turbine. However, since the stator rotates in only one direction, it redirects the fluid flow to an optimal angle and sends it back toward the pump.

Planetary Gear Set

The planetary gear set receives driving power from the turbine in the torque converter and functions like an auxiliary transmission. As shown below, the planetary gear set consists of a sun gear, a planet gear, and a planet carrier. These input, output, and fixed gears are designed to transmit and reverse engine torque. Brakes in the automatic transmission control gear ratios by locking each component of the planetary gear set.

Hydraulic Control System

Designed to select the appropriate input, output, and fixed gears of the planetary gear set based on the vehicle’s work conditions such as speed, throttle opening, and engine load.

Semi-Automatic Transmission:

Semi-automatic transmissions incorporate features of both manual and automatic transmissions. They offer drivers the option of either manual or automatic operation.

This type of transmission is commonly found in sports cars. Vehicles normally operated in automatic mode can deliver enhanced performance by switching to manual mode. Hence, they are used in such vehicles.

Fuel economy varies depending on driver preferences and driving style. Each transmission type has its own advantages and disadvantages, and the optimal choice depends on the driver’s needs, preferences, and usage conditions. Vehicle owners can select the most suitable transmission type by carefully evaluating their options.

Single-Clutch Semi-Automatic Transmission

Although single-clutch transmissions are no longer common today, many manufacturers have used this type across various car models. This automatic transmission type functions as a manual transmission that shifts gears automatically on the driver’s behalf. BMW, FIAT, PEUGEOT, HONDA, and CITROEN models use this transmission type. Examples include Fiat Dualogic, Opel Easytronic, Toyota Multimode-MMT-M/M, and Peugeot–Citroën ETG5–ETG6.

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Double-Clutch Semi-Automatic Transmission

Double-clutch semi-automatic transmission systems are a popular feature in many modern automobiles. Renault EDC (Efficient Dual Clutch), Volkswagen DSG (Direct-Shift Gearbox), and Ford Powershift are widely used automatic transmission systems by automakers. Instead of the torque converter found in conventional automatics, these systems use a dual-clutch mechanism. One clutch handles gears 1, 3, and 5, while the other handles gears 2, 4, and 6. While one gear is engaged, the next gear is pre-selected and ready for immediate engagement.

Continuously Variable Transmission (CVT)

Continuously Variable Transmission (CVT) means continuously variable power transfer. Its operating principle uses a unit called a “variable pulley” to adjust the gear ratio seamlessly between the lowest and highest possible values. This ensures that an optimal gear ratio is always available. The engine can always operate within its most efficient range, whether prioritizing performance or fuel economy. The variable pulley consists of two pairs of conical disks. A special chain moves within the groove of these disks and serves as the power transmission element.

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