Dual Clutch Transmissions

Dual Clutch Transmissions are quickly becoming the standard for performance and efficiency in roadcars. This will be a brief review on how they work and how they compare to other transmission designs.

How They Work

Figure 1
Image via Wikimedia Commons

Dual clutch transmissions (DCT) are a type of automatic transmission that uses two clutches for odd and even and gear sets. Figure 1 is a diagram of a typical DCT. Essentially it is two separate manual transmissions that are combined as one in a single housing. Unlike manual transmissions, most DCTs have electro-hydraulically actuated clutches that are operated automatically. Some vehicles with DCTs offer modes in which the driver can control gear shifts manually via paddle shifters or other means.

Advantages

Shift times are very important in performance vehicles, because while a transmission is shifting gears the vehicle is moving without torque being sent to the wheels. Other benefits of faster shift times include a smoother/seamless acceleration, and increased fuel economy. As compared to traditional transmissions, DCTs are able to offer much faster shift times between gears. This is because alternate gears can be pre-selected. For example the vehicle could be propelled by the fourth gear with one clutch engaged and as soon as the vehicle upshifts to the fifth gear the even gear clutch disengages and the odd clutch which is already pre-selected to the fifth gear can then engage. These shifts can be as fast as 8 milliseconds; a typical manual transmission shift time averages around 500 milliseconds.

Disadvantages

The main disadvantage to DCTs is their high cost. This is attributed to their complex design, economies of scale (since they are not produced at the rate of other traditional transmission designs), and maintenance costs which are attributed to their complexity. DCTs rely heavily on computers to dictate gear shifts further adding to their cost. Although DCTS can provide smooth shifts while accelerating quickly, they sometimes have problems shifting to often at low speeds when the throttle is being applied intermittently. This can cause a jerky ride compared to traditional transmissions.

Applications

Due to the inherent disadvantages of DCTs they are usually reserved for higher end sports cars. Some examples of vehicles that use DCTs include:

Bugatti Veyron
Image by Brian Snelson via Flickr

BMW Z4
Image by Dein Nordrhein-Westfalen via Flickr

Nissan GTR
Image by Sebastien Cosse via Flickr

Some examples of inexpensive models available with DCTs include:

Volkswagen  GTI
Image by Justin Capolongo via Flickr

Dodge Dart
Image by Michael Gil via Flickr

Future of Transmission design

With ever increasing pressure on automakers to design more fuel efficient vehicles, transmission design is an obvious way to increase efficiency and performance. Another recent transmission design is the Continuously Variable Transmission (CVT). CVTs have no gears but instead use a belt that can be adjusted to an infinite number of effective gear ratios. This design can be more cost effective than 

DCTs while also providing increased fuel economy over traditional transmissions. The main disadvantage behind CVTs is they are not capable of handling the high amounts of torque that DCTs can. Thus they are not suitable for performance/heavy duty oriented vehicles, and are mostly limited to smaller economy vehicles. Transmission design will always be an important element in vehicle design, and with advances in technology and manufacturing techniques DCTs may become a mainstream component in consumer vehicles. 

What is mechanical engineering?

Mechanical engineering is a discipline of engineering that uses principles of applied sciences to design, manufacture, and maintain mechanical systems. Humans have been mechanical engineers since the early discoveries of simple machines like the wheel or lever. The field truly emerged during the Industrial Revolution in Europe when production of goods shifted from being handmade to being manufactured by machines, and since then the world has exploded in technical innovations thanks to the ever-evolving field of mechanical engineering. Mechanical engineering tasks overlaps many other areas of engineering such as electrical, manufacturing, or aerospace engineers. The projects that mechanical engineers (of MEs for short) work on are very diverse and practically unlimited, a few common industries MEs work in are: transportation, robotics, HVAC, and medical devices.

Ferrari F136 FL V8 engine
(Image by: Ferrari http://auto.ferrari.com/)

Ferrari 458 speciale
(Image by: Ferrari http://auto.ferrari.com/)

Pictured above is a great example of a project that mechanical engineers would be heavily involved in, from the design and testing phase, to the designing the equipment and steps used in manufacturing the vehicle's components. In developing a car as complex as the Ferrari 458 speciale it takes a tremendous effort in coordinating between different types of engineers and designers. The Ferrari F136 FL engine is an example of mechanical engineering at its pinnacle, it produces 562 hp at 9000 rpm. To create this amount of power at such high rpm creates enormous amounts of stress on all components of the car from the transmission to the breaks, engineers must calculate these stresses and choose appropriate materials or alter the design of a specific assembly so it can function properly.

The Ferrari 458 is a modern engineering marvel and displays the incredible complexity of what mechanical engineers can create. The 458 is built with almost no compromise for cost. This is not usual, in most projects limitations and compromises are integral to the job. Common limitations in mechanical engineering projects include: budget, material properties, and government regulations. These limitations create many barriers to engineers, but these limitations drive innovations in design, manufacturing processes, and material science. There are examples of these innovations all around us, another car example to illustrate this point is the invention of the catalytic converter.

Cut away view of a catalytic converter
(Image by: http://www.chemhume.co.uk/)

In 1975 the United States EPA created stricter exhaust emissions regulations. To meet and exceed these new standards engineers came up with the catalytic converter. These work by catalyzing a redox reaction to convert toxic pollutants such as unburned hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx) into less toxic exhaust gases like nitrogen, water, and carbon dioxide. Today the designs of catalytic converters have greatly improved and they eliminate a large portion of smog and greenhouse causing gases.

The catalytic converter is just one of the many innovations mechanical engineers have created to make a better world for everyone. Often time projects that mechanical engineers work on can seriously impact the public's health and safety. That is why it is vital for engineers to have a strong ethical commitment to the people they serve to help make safe designs for the environment and the people that interact with them.