With digitisation gradually reshaping the very foundation of diesel engine design, transmission development is especially high on the industry’s agenda at the moment. Prime Mover explored what’s changing in the area between engine and drive shaft.
The advent of high-powered engines providing maximum torque across ever-broadening rev ranges has fundamentally changed the role of the humble gearbox. Once an afterthought, the transmission is now a critical part of the driveline and, in essence, a business tool directly affecting fuel usage and driver recruitment.
Especially in the heavy-duty category, modern transmissions now need to be more durable – and more adaptable – than ever before to confidently handle vehicles grossing 60 tonnes and more, all while being as simple as possible for the inexperienced driver to operate.
The high degree of specialisation required to do so in a fully automatic setting is why many OEMs are still not offering proprietary fluid-drive solutions and continue to finesse automated versions of mechanical transmissions instead.
By using existing and proven gearbox internals with newly developed automated shifting mechanisms, Automated Manual Transmissions (AMTs) are more economic to produce than full automatic systems, yet equally simple to use – allowing transport businesses to take pressure off the drivers so they can focus more on the road. With Australia’s driver shortage getting more severe by the month, driver recruitment is also increasingly tied to the ease of gear shifting.
Suppliers leading the charge
Arguably the most advanced heavy-duty transmission to reach the market in recent years is the ZF TraXon, which has been introduced to the Australian market without a lot of fanfare in the MAN TGX D38 at the end of 2016. Labelled Tipmatic2, the MAN version of the TraXon comes in a 12-speed set-up and has received strong praise from the Australian and European market, where it is also available in a number of Iveco models.
One reason for the praise is the TraXon’s modular design, allowing OEMs to incorporate a choice of dry clutch, dual clutch and hydraulic torque convertor, or even a hybrid-electric motor drive, depending upon the intended application. What’s more, the TraXon can be equipped with ZF’s Intarder hydraulic retardation system, which can exert up to a massive 4,000Nm of driveline braking force.
ZF rival Allison, meanwhile, has recently had a lot of success with the TC10 fully automatic transmission, especially in the US. The ten-speed design features an advanced torque converter as well as a twin countershaft, which is said to help optimise acceleration and minimises fuel consumption in both city and highway conditions. The TC10 is reportedly able to overcome differences in driving styles – and the resultant effects on fuel economy – by ‘learning’ from the driver and optimising gearshifts along the power curve.
First introduced in 2012, the TC10 marked a major departure for Allison, which had been concentrating purely on automatic transmissions in the past. The move to diversify does not mean Allison’s strong focus on the automatic market has been affected, however. In fact, Allison’s full auto offering has seen additional improvements in fluid technology of late, permitting significantly extended service intervals and improved heat dissipation.
The third key transmission brand in Australia, Eaton, has gone as far as forming a Joint Venture (JV) with engine specialist, Cummins, to develop automated transmissions for heavy-duty and medium-duty commercial vehicles. The global JV will reportedly provide customers with transmission technologies and solutions that deliver “optimum fuel efficiency, performance and uptime” while leveraging both Cummins’ and Eaton’s global service and support networks.
The introduction of the Cummins X15 engine to the Australian market was a case in point – according to Cummins, the two companies cooperated closely in the lead-up to the launch to ensure the combined engine and transmission performance was perfectly suited to local conditions.
The X15 features a suite of electronic engine features and a software package that is able to constantly monitor load, speed and gradient in a move to adjust engine speed, power and transmission gear selection in line with the vehicle’s current situation. Abbreviated ADEPT (Advanced Dynamic Efficient Powertrain Technology), the package was designed to work specifically with Eaton’s UltraShift Plus 18-speed AMT to make powertrain control decisions in real time.
The ADEPT package also includes a system dubbed SmartTorque2, which senses both the selected gear and overall engine load as a result of the gross vehicle weight, aerodynamic drag and road grade. As these conditions vary, SmartTorque2 determines the exact amount of torque needed to maintain road speed and momentum.
On the OEM front, Volvo has been successful with the I-Shift AMT – especially since adding an optional crawler gear module to the line-up last year. With a transmission ratio of up to 32:1 (and up to 37:1 in reverse), the new module allows a truck to drive at speeds as low as 0.5-2km/h for improved low-speed manoeuvrability. As such, it enables the same truck to perform more flexibly under different driving conditions, such as on-road and off-road and over-mass applications. The crawler gear module only adds 120mm to the length and 48kg to the weight of the I-Shift system.
Volvo has also developed a dual clutch version of the I-Shift that can pre-select the next gear while driving in the current one. This is achieved by having two concentric input shafts on the transmission and two clutch assemblies, and results in gearshifts that take just a fraction of a second to complete without interrupting power delivery. The Mack version of Volvo’s highly successful truck transmission has been dubbed mDrive and was spec’ed in 95 per cent of all Macks fitted with Volvo-based MP engines that have come off the Wacol assembly line this year.
Inspired by the Volvo Group’s success, Scania has made the transmission of the ‘Next Generation’ Scania – previewed at this year’s Brisbane Truck Show – a key priority. The next gen Opticruise AMT will therefore benefit from a revised software package and an air-operated brake on the layshaft to better synchronise shaft speeds – enabling complete shifts in just 0.4 seconds. The result, Scania says, is a smoother power delivery and negligible loss of vehicle momentum due to gearshifts, especially when upshifting under load on a rising incline.
The US subsidiaries of global powerhouse, Daimler Trucks – Freightliner and Western Star – have been offering the US version of the Mercedes-Benz-derived DT12 AMT for the past five years. Available in the US in the Freightliner Cascadia and Western Star 5700 XE, the 12-speed transmission is said to be especially lightweight due to an aluminium housing and single counter shaft.
Two-pedal operation continues to gather momentum in Japanese-made vehicles, too. Both full automatics and AMTs are taking an increasing share of the market from traditional manual gearboxes and clutches, with Allison now widely considered the default transmission in medium-duty trucks from Japan.
Isuzu, for example, has combined a fluid torque convertor with an AMT in much of the current N-Series – providing a 50 per cent increase in torque which, in Isuzu’s case, allows a four-cylinder engine to have similar start-off characteristics to a six-cylinder alternative, which should save the market-leading brand weight and fuel use.
Hino, meanwhile, expects to spec at least 60 per cent of the all-new 500 Series Wide Cab range with an Allison full automatic, with the rest going toward a newly developed nine-speed all-synchro manual that has been developed in house and a reliable Eaton nine-speed that is optional as a back up.
After a few teething issues when it was first introduced to Australia in the Canter almost a decade ago, the Fuso Duonic dual clutch AMT is now a reliable and smooth performer, too, especially in the demanding rental sector.
What all brands and suppliers have in common is the desire to overcome the stigma of lacklustre performance automated and automatic transmissions have had to bear over the past decade – often due to poorly performing engines. Only as truck engines are becoming more flexible and delivering a broad and flat torque curve, automated and automatic transmissions are able to showcase what they are truly capable of.
If the automotive industry is anything to go by, the revolution has only just begun. As engines become smaller and final drive ratios higher in order to meet ever-more stringent fuel efficiency and emissions standards, transmissions will become crucial, highly integrated tools to manage the drivelines of the future.
Allison can draw on a national network in Australia and works closely with the various OEMs it supplies. Prime Mover research has shown that when examining warranty claim data, failures of transmissions that can be attributed to the transmissions themselves are almost negligible for most local OEMs using Allison technology. Upon investigation, it is more often the case of water contaminating the transmission fluid or badly executed drive shaft modifications that damage the back of the transmission.
For certain applications, some customers have Mack’s mDrive AMT programmed to always start off in first gear rather than the default second or third, preferring to trade off a small saving in fuel consumption for extended clutch and driveline life.
The Mercedes-Benz PowerShift 3 is the new standard across the range in either eight-, 12- or 16-speed configurations. This latest generation changes gears 20 per cent faster than the previous units, and has a new creeper gear function. The new ‘EcoRoll’ function saves fuel by disengaging the drivetrain in overrun mode in certain circumstances and returns to normal if the accelerator, brake pedal or engine brake is applied.