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 interrupted and that power isn’t getting transferred down the drivetrain to the wheels. In a fully automatic transmission, the torque converter allows you to shift transmission gears without interrupting the torque going from the engine to the wheels.
Since automatic gearboxes and
AMT solutions gradually drive manual gear shifting options from the market of
transmissions for trucks and commercial vehicles, we will review these types of
gearboxes in more detail.
Insight into automatic transmissions for trucks and commercial vehicles
The common automatic transmission includes the torque converter, mechanical part, control system and auxiliary mechanisms. The torque converter serves as a hydraulic transmitting mechanism, in which the power is transferred by the flow of ATF. The torque converter consists of the pump impeller, turbine runner, and startor. The locking mechanism ensures better fuel economy. The torque converter provides the connection between engine and transmission, reduces dynamic loads, prevents the engine from stopping during overloads, and increases torque from the engine when starting from a standstill and under difficult road conditions.
Automatic transmissions have 3 planetary gears and friction clutches, which ensure the transmission gear shifting process. The gear ratio value changes gradually without disrupting the power flow. The gear transmission shifting is performed by the control system in automatic mode. Many models of automatic transmissions are equipped with a hydrodynamic retarder, which serves to slow down the vehicle and reduce wear of brake pads. The retarder is usually installed in automatic transmissions for buses and machinery and vehicles operating in mountainous areas. Advanced electronic control units (ECU) of automatic transmissions ensure high adaptability to road conditions and driving style, and allow implementing additional functions. At the request of the customer, the automatic transmission may be equipped with the button- or lever-type automatic transmission shifters.
Allison Transmission, one of
the world’s largest manufacturers of automatic transmissions for trucks and
commercial vehicles, equip its transmission solutions with the truck transmission diagnostics
system named Prognostics, which allows the driver to monitor the status of the
main vehicle components. The function Oil Life Filter controls fuel
consumption, saving the fuel while driving and during idle running of the
engine. The function Filter Life Monitor informs the driver about the necessity
to change the transmission filter. The function transmission Health Monitor monitors the
status of transmission drive circuits and warns the driver about the necessity
of well-timed maintenance and readjustment.
Allison 2000 Series
Allison 4000 Series
Today Allison Transmission offers a wide range of transmission solutions for trucks and commercial vehicles (transmission models of the Series 1000, 2000, 3000, and 4000). Another automatic transmission solution TC10 was designed by Allison for tractive vehicles. Allison transmissions of Torqmatic Series are used for buses. Heavy-duty trucks, which are used in mining and building industry, are frequently equipped with Allison 5000, 6000, 8000 and 9000 Series transmissions.
Allison 9000 Series
Volvo, a well-known
manufacturer of trucks, also provides efficient automatic transmission
solutions, such as Powertronic.
The Powertronic is a fully 6-speed automatic transmission with
electronic control, which is designed for movement with frequent stop-start
operations. The Powertronic truck transmission is equipped with the torque converter
to ensure high propulsive force when starting from a standstill without any
interruptions of torque transmitted to the drive wheels. Therefore, this transmission
is an ideal option for Volvo trucks operating on building sites and in urban
traffic.
Volvo Powertronic
The
company Voith offers the family of automatic transmissions named DIWA, which
are intended for city-buses and suburban buses. The main feature of these
automatic transmissions is that the engine torque is transmitted mechanically
as well as hydraulically. Starting from a standstill is performed
hydraulically, and as the speed of movement increases the hydraulics
participation is gradually replaced by the mechanical part. It should be noted
that the engine power is divided before the torque converter engagement and
combines afterwards. Thus, the torque converter and two planetary gears form the
1-st hydro-mechanical gear. Therefore, DIWA transmission operates with high
efficiency in a wide range of speeds, ensuring smooth starting from a
standstill and steady acceleration. Then, the transmission system activates
purely mechanical torque transfer, which operates with less losses. The torque
converter simultaneously operates as a hydraulic retarder, which ensures
immediate activation of the hydraulic brake regardless of the engaged gear.
High
efficiency of this transmission is achieved thanks to the combination
“differential-torque converter”. While common automatic transmissions shift
gears 2-3 times at the start, Voith DIWA continues using the 1-st gear –
simultaneously engaging the torque converter and mechanical truck transmission parts.
Therefore, a smaller number of shifts makes the bus movement smoother and
reduces the wear of friction discs. The torque converter in DIWA is located in
the middle of the gearbox, such positioning helped to get rid of excessive
tubes and connection hoses.
The
German company ZF also offers remarkable transmission solutions for trucks and
commercial vehicles. For example, the 6-speed automatic transmission ZF EcoLife
is intended for trucks and buses. This transmission has an efficient cooling
system, which allows operating in more severe temperature conditions when the transmission oil temperature in the heat exchanger reaches up to 120°C. In addition, ZF
engineers used here the torque converter with higher rates of acceleration when
the engine RPM parameter is low. The built-in torque vibration damper reduces
fuel consumption when starting from a standstill by means of rapid disabling of
the torque converter lock-up.
ZF Ecolife
ZF Powerline
Another
6-speed automatic transmission ZF-PowerLine, intended for light commercial
vehicles, is notable for its fuel economy thanks to an advanced torque
converter. It should be noted that the automatic transmission torque converter in ZF gearboxes is
used at the beginning of the movement and it stops operating when the car accelerates
up to the speed of 10-15 km/h. in this case there is no need in using
“prolonged” 1-st gear. The family of ZF transmissions Ecomat was specifically
designed for city buses and special purpose vehicles.
Insight into automated manual transmissions (AMT) for trucks and commercial
vehicles
Today, electronics plays a major role in controlling of different systems implemented in trucks. Currently, the microprocessor regulates the operation of not only the engine ignition, but also of the clutch and gearbox. The main advantage of the electronic control over mechanical, hydraulic or pneumatic options is better responsiveness and the possibility to combine a large number of parameters. Different operation modes may be changed by reconfiguring the software, rather than making changes in the transmission design. Thus, electronics ensures more cost-efficient operation of the vehicle and safer driving experience. Therefore, more and more trucks (especially heavy-duty trucks) are equipped with automated manual transmissions. Many people confuse this type of transmission with the automatic gear shifting solution, but automatic transmissions, unlike AMT, have torque converters.
Drivers share their AMT experience
The design of the automated
transmission may include an electromechanical, electro-pneumatic or
electro-hydraulic drive, which converts signals received from the electronic
control unit (ECU) into an angular displacement of the clutch fork. The AMT
itself features the electromotor with the servo drive, which moves the clutch
fork. This seemingly simple technical solution is controlled by the complicated
software, which processes signals from the joystick lever, located in the cab
of the truck, when the driver shifts gears. Therefore, there are only two
pedals in the cabin of the truck equipped with the AMT – gas and brake. Such truck
transmission appeared in the late 90’s and initially this technology was
perceived by drivers with distrust. In addition, back in those days, automated
transmissions were significantly more expensive than manual transmissions. But
these days, with development of more advanced and cost-efficient technologies, more
and more trucks are equipped with automated transmissions. Eaton was the 1-st
company on the market of automated transmissions with its AutoShift
transmission launched in the 90’s. Since then, the product portfolio of Eaton
has been supplemented with a 6-speed midrange UltraShift and 10-, 11-, 13- and
18-speed heavy UltraShift Pluses.
Eaton UltraShift Plus
The automated mechanical transmission (AMT) is gaining popularity in the automotive industry, due to its combination of the advantages of mechanical transmissions and automatic transmissions in terms of fuel consumption, low cost, improved driving comfort and shifting quality. Nowadays, automated manual truck transmissions are produced by a wide range of companies: ZF, Volvo, Daimler AG, Eaton, Mack, Detroit Diesel, Mercedes, Man, etc. Now let’s take a closer look at remarkable AMT solutions offered by these companies.
Volvo Trucks offers the
6-speed automated manual transmission I-Sync, which is intended for Volvo FL
trucks. This truck transmission is specially designed for the D7 engine and for
running on urban streets and suburban areas. The electro-hydraulic drive
ensures smooth gear shifting when driving in dense city traffic with frequent
stops
. The I-Sync transmission is available in two versions
- for D5K engine and for D8K engine. The lever, mounted behind the steering
wheel, allows the driver to select the manual or automatic gear-shifting mode.
There is no clutch pedal in trucks with I-Sync transmission – the manual
gear-shifting is performed with the help of the abovementioned lever. In the
automatic mode, I-Sync transmission independently shifts gears at a well-chosen
moment. The torque capacity of this transmission may reach up to 1050 Nm,
making I-Sync transmission an ideal option for trucks operating in urban areas.
Volvo’s I-Sync transmission
Another
well-known AMT solution developed by Volvo Trucks is the I-Shift transmission.
This transmission is based on manual constant-mesh gearbox. The main component
of this “smart” transmission is the electronic control unit (ECU), which
controls the transmission clutch operation and the process of gear shifting. The ECU shifts
gears very accurately thanks to the analysis of data on truck speed, weight,
required torque, road grade and other parameters. The system also exchanges
data with the engine, which, in turn, regulates the RPM rate and engine braking
for maximum efficiency. This transmission solution is designed to save up to 5%
of fuel. This automated transmission may have one or two speed-reducing gears,
as well as the option with additional reverse gears. Speed reducing gears
significantly improve the capacity of start from a standstill, reduce the load
on the clutch to 75 %, and help to avoid additional repair services.
Volvo I-Shift
Mack
Trucks offers mDrive (12-speed) and mDrive HD (13- and 14-speed variants) automated
transmissions intended for different models of Mack trucks.
mDrive
mDrive HD
Mack
truck transmissions are developed to operate smoothly with Mack MP engines and axles
so there’s no issue of compatibility or performance. With durable materials, simple
operation and American manufacturing, these transmission solutions ensure not
only efficient gear shifting, but also fuel economy, reduced wear, and
convenient driving experience.
Detroit
Diesel Corporation, a subsidiary of Daimler Trucks North America (itself wholly
owned by German Daimler AG), offers automated manual transmission DT12 intended
for heavy-duty trucks. This truck transmission ensures smooth gear shifting performance,
durability and ease of operation.
DT12
The DT12
transmission links engine to axles, and communicates with the DD13 and DD15 on
an integrated electronics network to share damage-reducing data such as transmission clutch
overloading and driveline protection. The DT12 uses information from a
topographical map to manipulate both engine and gearbox functions, taking
advantage of the truck's surroundings.
The family of automated
transmissions Mercedes-Benz PowerShift includes several models of
transmissions. The process of gear shifting in trucks equipped with the
12-speed PowerShift is implemented quickly and smoothly. This transmission has
a “maneuvering” mode and gears for the main-line traffic at high speeds and a
low RPM level. Line-haul trucks Mercedes-Benz Actros are equipped with an
upgraded version PowerShift 2. Thanks to the use of the advanced sensor system,
gears are shifted more rapidly and smoothly. Building trucks Mercedes-Benz
Actros are equipped with the 12-speed AMT PowerShift Off-road, which several
modes of operation and 4 reverse gears. The design of this gearbox also includes
a tilt sensor and an advanced system of smooth starting from a standstill. The
8-speed AMT PowerShift GO 240-8 is installed on tourist coaches Mercedes-Benz
Travego и Tourismo.
Informative video about Mercedes PowerShift
MAN Nutzfahrzeuge Gruppe
produces automated TipMatic transmissions, which create a perfect synthesis of
comfort and efficiency. The 12-speed TipMatic transmission with the “off-road”
mode and 2 reverse gears was designed for heavy-duty trucks TGX and TGS.
Automated MAN TipMatic gearshift system
This automated transmission
may have a direct gear or overdrive gear. Modes of operation are selected with
the help of the switcher on the center console, while gears are shifted by
means of the under-steering shifter. The TipMatic transmission may be equipped
with the retarder MAN PriTarder or with the ZF intarder. On request, TipMatic
may be equipped with special control programs: Profi (manual shifting mode
kick-down), Fleet (for inexperienced drivers).
Despite the fact that more and
more manufacturers of trucks prefer to install automatic or automated
transmissions in their products, manual transmissions still have a significant
share in the segment of commercial trucks. There are still many admirers of reliable
and reasonably priced manual transmission solutions,
who
like to be in charge of the gear shifting process with the help of the truck manual transmission shifter.
Ten-speed transmissions
remain the most common manual type for heavy highway trucks, though 13- and
18-speed boxes are popular among long-distance truck drivers and are commonly
applied with high-horsepower engines. Trucks used in construction and other
vocations tend to have 11-speed “low-low” gearboxes with three ratio ranges
instead of the two in highway transmissions. Such well-known companies as
Eaton, ZF, and Volvo do not give up on manual transmission options for trucks
and commercial vehicles. The adoption of fully automatic transmissions and AMTs
in trucks has been driven largely by drivers’ demands for comfort and
convenience as well as safety issues. Therefore, it is hard to make accurate
predictions for such a hi-tech industry, where companies put a great deal of
effort and significant financial resources to develop extremely complicated
technical solutions which 10 or 15 years ago seemed incredible. Who knows,
maybe in the not so distant future all commercial operations will be performed
by self-driving trucks.
