The word “transmission” or “gearbox” is one of those terms that many are familiar with but most people are unfamiliar with the differences between the many types of transmission in use today. The transmission is one of the vital components of any vehicle with an internal combustion engine. This guide will explain some of the most popular types of car transmission used today and how they work.
What is the transmission?
The transmission is a device designed to change the speed of the engine based on the amount of power needed. The transmission helps to transmit the power from the engine to the wheels in an optimal way.
Try to imagine a car without a transmission. With each crankshaft revolution, the driving wheels would turn the same number of times. Such a vehicle would be uncontrollable since it would always turn the driving wheels; stopping would mean turning off the engine, and starting would mean that the car would suddenly jump as soon as you turned the key. Its performance would be poor and it would use a lot of fuel. Having a transmission ensures that your car’s engine revs are optimally used, performance is improved, and you can put it in neutral. The neutral gear uses a clutch mechanism that disconnects the engine revs from the driving wheels. Transmission is simply an irreplaceable component of any car.
Throughout history, automotive engineers designed and introduced numerous types of transmissions. We can divide them into two distinctive groups: automatic and manual. Automatic transmissions have evolved a lot more than manual transmissions, especially in the last few decades. This guide will explain what you should know about car transmissions and how to spot the difference between the different types.
1. Manual Transmission
Manual transmission has been around since the beginning of the automotive age. In order to properly operate the vehicle, the driver is required to press the clutch pedal, disengaging the gearbox from the engine, manually choose the desired gear, and depress the clutch pedal to engage the transmission. Using the manual transmission demands a certain level of skill and coordinating your left leg (clutch), right foot (gas), and right hand (gear lever). Shifting requires coordinated movement in order to operate the car smoothly which is often quite challenging to learn.
The benefits of manual transmissions are the analog feel, high level of driver engagement, and sense of control. That is why manual transmission is still commonly seen in enthusiast vehicles and some sports cars. Although the manuals have lesser performance and slower shifting times, they are still highly regarded as the proper transmission by some driving purists. However, with technological improvements to automatic transmissions, manual transmissions are becoming less common.
2. Automatic Transmissions
Most modern cars have an automatic transmission, a technology that has been around since the 1940’s. The concept of an automatic transmission is simple. The driver puts the vehicle in “D” (for drive), and the gearbox will execute shifting automatically. There is no clutch pedal, just the brake and the accelerator, which makes using a car with an automatic transmission much easier to operate.
The automatic gearbox is a much more complicated device than the manual, especially modern transmissions with complex electronics. The classic automatic transmission has a torque converter that replaces the clutch mechanism of manual transmission and it shifts gears smoothly without the driver’s input. The benefits of automatic are a more relaxed driving experience, efficiency, and practicality.
The automatic gearboxes started as 2 or 3-speed units, while modern automatic transmissions have 8-speed or even 10-speed boxes. The more gears the transmission has, the better it can use the engine power for high efficiency and performance. Modern advances have improved the shifting times in automatics and made them much quicker than the manuals could ever be. That is one reason automatic transmission is dominating the industry right now, and it is irreplaceable for some types of vehicles like SUVs or pickup trucks. Many modern automatic transmissions also have a “manual mode” or feature that allows the drivers to control the gearbox by choosing the desired gear themselves.
3.Continuously Variable Transmission (CVT)
The CVT is an automatic transmission since it has no clutch pedal and doesn’t require the driver to change gears. There are several types of CVT transmissions, but the most common is the pulley-based CVT which uses a V-shaped belt or chain to connect two cones, one which is powered by the engine and the other which is connected to driving wheels. When moving the cones towards and away from each other, the CVT transmission creates a different turning ratio, which results in varying numbers of the turns of the driving wheels. That is why the CVT is often called “gearless transmission.” It doesn’t have a pre-designed set of mechanical gear ratios but a continuous set of ratios used through the rev range.
The benefits of CVT transmission are the optimal use of the engine power and torque (since the gearbox is always in the right ratio), compact dimensions, and lower weight. However, the CVT transmission is rarely used in passenger vehicles since it cannot endure heavy use and towing, and it is not ideal for highway driving. The CVTs are commonly found in scooters, some machines, and the Toyota Prius.
4. Dual-Clutch Transmission
One of the most interesting automatic transmissions found in modern vehicles is the DCT or dual-clutch transmission. This design is best known for its compact size and lightning-fast shifts, which made it popular in sports cars and high-performance vehicles. The DCT is an automatic transmission, but it features two clutches, one for even gears and the other for odd gears. The DCT does not have a torque converter like a conventional automatic. It can change gears very fast since the system can swiftly use one or the other clutch pack connected with the 1-3-5 or 2-4-6 gears.
Volkswagen successfully introduced the DCT in 2003 with the Golf MK4 R32, and it has been subsequently used in many other vehicles. A DCT is lighter than an automatic transmission, which makes it easier to mount in front-wheel-drive models with transversally installed engines. It has also proven durable even for high-performance use and unbeatable in shift times, making it a favorite with the sports car crowd. In most cases, vehicles equipped with a DCT-type gearbox have paddles behind the steering wheel.
5. Sequential Manual Transmission
The sequential manual transmission is rarely used in passenger vehicles but it is a top choice for racecar drivers. This highly sophisticated unit uses the feel and control of the manual transmission with the swiftness and precision of an automatic. It is designed for extreme race track use. Sequential manual transmissions have a clutch, but it is only used for starting and selecting the first gear. After that, the driver selects the gears by gear lever or paddle shifts. The driver can concentrate on driving while the gears are changed quickly without the need for pressing the clutch every time.
Despite the benefits, this type of transmission is not used in consumer vehicles because of the high cost. Additionally, there are no skipping gears or “kick down” functions. The sequential manual transmission can only change into the next gear up or down, not skip two or three gears like the common automatic transmission.
6. Semi-Automatic Transmissions
Over the years, numerous companies experimented with hybrids of manual and automatic gearboxes and created the semi-automatic transmission. The basic idea was to combine the efficiency and control of a manual with the comfort of an automatic. So far, semi-automatics have had mixed success and are not commonly used in consumer cars.
The semi-automatics can use a clutch for starting the car, but the rest of the gear changes are done automatically without the driver’s control. The other way is to have a clutch-less design (e.g. Porsche Sportmatic), which is started just like any automatic transmission and then shifted like a manual. Even though the basic concept is sound, semi-automatics proved to be problematic and lack the performance or response of automatic or manual transmissions.