Transmission Solutions for Trucks and Commercial Vehicles

All motorized vehicles have a transmission, which transmits torque from the engine to the driving wheels. At the same time, the function of the standard transmission is to adjust the speed of the vehicle depending on road conditions, vehicle loading level, etc. Producers of automobile gearboxes offer new technical solutions, which use fuel more efficiently, are easier to operate, and ensure comfortable driving, as well as enhanced reliability and maintainability. Therefore, modern gearboxes for trucks and commercial vehicles are innovative high-tech products with integrated electronic control systems.

Eaton’s 18-speed AutoShift transmission

When moving, vehicles are affected by different resistance forces, such as friction force from interaction with the road surface. Therefore, vehicles have to accumulate power required to overcome resistance forces for starting from a standstill and accelerating. The road resistance is called tractive resistance, and the traction, which overcomes this resistance, creates the tractive effect. In addition to road resistance, vehicles have to withstand air resistance. For trucks it is especially important, as air resistance is proportional to the area of the vehicle frontal projection and its speed raised to the third power (s^3). Thus, truck manufacturers have to pay close attention not only to the gearbox and the gear ratio parameter (min and max), but also bring these parameters into correlation with power, vehicle’s own weight, gross vehicle weight, etc. When selecting gearbox for a vehicle, specialists take into account power-to-weight ratio, i.e. ratio of maximum engine power to its gross weight.

Learn how MAN’s trucks are assembled

The gearbox characteristics have a significant effect on fuel efficiency. Well-known companies such as Eaton, Allison, ZF are continuously developing new gearbox solutions, which provide significant advantages for owners of commercial trucks. It should be noted, that the transmission performance depends on road conditions, engine operating cycle (long periods of driving with constant speed or frequent stops and starts), vehicle average speed, etc.

Trucks vary greatly in size, power, and configuration; smaller varieties may be mechanically similar to some passenger automobiles. These vehicles can be very large and powerful, and may be configured to adjust specialized equipment, such as in the case of fire trucks and concrete mixers and suction excavators. Modern trucks are largely powered by diesel engines, although small to medium size trucks with gasoline engines exist in the US, Canada, and Mexico. Modern trucks are designed to run long distances. Therefore, these vehicles should be equipped with very reliable and durable gearboxes.

The truck transmission is a combination of interrelated units, which help to transmit the engine torque to the driving wheels. Moreover, the torque value and its direction may be changed depending upon other factors. Transmissions of different brands and models of trucks have their peculiarities, which are determined by such factors as the number of driving axles, individual design features of the vehicle, etc. Manual truck standard transmissions necessarily include such components as clutch, gearbox, propshaft, transfer case.

Truck components and their assembly

As for the torque, which is transmitted with the help of the transmission to the leading wheels of the truck, it is directly proportional to transmission gear ratios. Gear ratios are determined by engineers for each particular vehicle during the process of its development. The torque value is determined by technical and dynamic characteristics, which should be implemented in the model being developed.

Transmission trends in the segment of trucks and commercial vehicles

Crawling through narrow urban areas in the traffic with frequent stop and go, moving through the dugout tire tracks of a mudded building site, or rolling through residential refuse duties – targeted application of Class 6 - 8 trucks or commercial vehicles can set specific requirements for gearboxes compared to their on-highway counterparts. Yet, it hasn’t stopped a general trend of automation in trucks and commercial vehicles, which especially affected gearboxes.

The manual gearbox has been tested for decades by millions of commercial truck drivers, who consider this solution to be the most suitable solution for trucks: manual gearboxes are simple, relatively inexpensive in production as well as in maintenance, and they ensure reduced fuel consumption. However, manual gearboxes have one significant disadvantage, which may overshadow all merits mentioned above and incur displeasure among drivers: manual gear shifting and simultaneous manipulations with pedals may be quite troublesome, especially in city traffic. No wonder that nowadays manufacturers of trucks, with the latest technologies at their disposal, try to satisfy the requirements of drivers and make the process of gear shifting more convenient and fail-safe. According to numerous research works, North America is following Europe in the trend of “shiftless-ness” as automatic and automated manual gearboxes continue to gain popularity in the segment of commercial trucks. The reasons include enhanced fuel efficiency and easier driver recruiting and productivity than with manuals, along with greater safety.

Learn how to tackle the challenge of shifting an 18 speed transmission

On small trucks you might find manual gearboxes that resemble shifting solutions applied in passenger cars. They often have approximately six gears and commonly have a synchronizer. For these trucks the simple H-pattern is easy-to-operate. It does, however, get a little more complicated when you are dealing with bigger trucks and commercial vehicles with more gears. On these bigger trucks there are usually additional controls to help manage the control of the different gears. In older trucks, the control is often a separate lever mounted on the floor or more recently – a pneumatic switch mounted on the "H" lever; in newer trucks the control is often an electrical switch mounted on the "H" lever. Multi-control gearboxes are built in much higher power ratings, but rarely use synchromesh. There are several common alternatives for the shifting pattern – Range, Splitter, Range-Splitter. Today's truck manual gearboxes are most commonly "range-splitter".

Modern automatic transmissions have significant differences from their predecessors, which were used in commercial trucks. The main difference lies in the quantity of gear ranges and in the very principle of truck transmission control. The quantity of gears in old automatic gearboxes was limited to 5, and the control was performed with the help of hydraulics. Nowadays, transmission manufacturers offer automatic gearboxes with more than 5 gears, which are controlled by means of electronics. Moreover, modern automatic gearboxes are equipped with the torque converter lock-up.

The list of advantages of modern automatic gearboxes for commercial trucks includes smooth gear shifting process. Fuel consumption on rural roads is comparable to the level of consumption when using the manual gearbox. The automatic transmission allows drivers to drive the truck more easily and safely, paying more attention to the road and not being distracted by manual gear shifting. The main competitive drawbacks of automatic gearboxes for commercial trucks are increased fuel consumption, maintenance and automatic transmission problems resulting in costly repair services.

Manual vs Automatic Transmission in Trucks

The automated manual transmission (AMT) is considered to be another promising transmission solution for trucks and commercial vehicles. AMTs are similar to manual transmissions in terms of functional capabilities and operating principles. It may be said that AMT is almost the same as the manual gearbox, but it includes servo and hydraulic drives, which control the clutch operation and gear shifting process. AMTs are notable for their efficiency. In addition, automated transmissions are not so expensive in maintenance and repair as automatic transmissions, and fuel consumption of automated transmissions is compatible to the level of manual gearboxes (sometimes AMTs may be even more fuel saving). If trucks with automatic gearboxes are easy to use, but require considerable expenses for fuel and services, then trucks with AMTs turn out to be not only convenient but also economically viable.

What is good about AMTs

However, it should be noted that when you shift a manual gearbox or AMT and engage the clutch, the engine torque is i