Auto to the test

Automatic and automated transmissions are becoming more prevalent in the trucking industry, with a number of choices now available. As the world’s largest maker of fully automatic transmissions, Allison brought truck buyers and journalists to Brisbane from all over Australia, New Zealand and Asia to give them a real hands-on feel for what their fully automatic gearbox can do.

The Mount Cotton training facility in Brisbane, with its on and off-road circuits and large manoeuvring area, allowed drivers to see how an Allison transmission feels from behind the wheel and how it performs in different scenarios.

The event was also an opportunity for people on the ground here in the Asia-Pacific to meet the upper echelons of management of the US company. There have been a number of changes in the structure of Allison in recent years, most notably the floating of its shares on the New York Stock Exchange in March. This event was an opportunity for the company to lay out its future strategies at the same time as demonstrating the effectiveness of its product in real-world trucks.

With 18 trucks and 12 buses available to test drive and a number of static displays of Allison technology and systems, there was plenty to see and a full-day of activity at the Mount Cotton training grounds. The trucks available gave an insight into the new control systems’ effectiveness.

At the core of the Allison technology is the company’s torque converter, it is the common factor in just about every transmission. As a method of launching a truck from stationary and for the transition period between gears, a torque converter ensures smooth transitions of power through the driveline at all times.

The fluid connection between the engine/transmission and the rest of the driveline protects it from any shocks elsewhere. It also gives the driver very precise control in slow manoeuvring situations.

The torque converter also makes taking off on a steep grade a relatively simple task for the driveline to handle. At launch, there is no restriction on the amount of torque available from the engine. The torque converter absorbs as much torque as it can to get the truck moving. It can then provide the driveline with a multiplication of the torque coming through in the first ratio.

The torque converter also provides the gearbox with what Allison calls ‘power shifting’. By enabling the engine to send uninterrupted power down the driveline as the transmission changes up through the gears, faster and more efficient acceleration is possible.

The basic technology inside an Allison transmission is essentially the same as it has been for many years. The torque converter and gearing have been refined and developed, but the core principle is still the same. Where the major changes in technology have happened is in the electronic control of the system. The introduction of sophisticated electronics has transformed the performance and perception of its automatic transmissions.

The most important aspect of any transmission control module (TCM) is the amount and quality of the data it receives. The more information the TCM has at its disposal, the more effectively it can make changes and optimise the performance of the driveline. In recent years, the amount of data available to the Allison TCM has increased with the introduction of technologies like multiplexing and the use of CANbus in the vehicle control systems. This means the TCM knows how much torque is being put out at the rear differential, wheel speed from the ABS, engine rpm, accelerator pedal position etc.

Systems can also monitor how the vehicle is reacting to changes in the transmission and adjust ratio changes accordingly, e.g. loaded or unloaded, uphill or downhill. There are 41 input data functions and 14 output data functions that can be used by other vehicle systems to know what’s going on in the transmission.

One of the new systems this high level of control enables is the RELS feature. Standing for ‘reduced engine load at stop’, this uses brake pressure, zero throttle and vehicle speed data and, when the vehicle comes to a halt, sends the transmission into a partial neutral and blocks the output at the same time. This reduces fuel use when the truck is stationary. When the brake pressure is released and the driver wants to get going again, the transmission drops back into drive immediately.

A core argument advanced by Allison when asserting the effectiveness of the fully automatic transmission over its rivals is based on the company’s interpretation of two different measures of productivity: fuel economy and fuel efficiency.

“For a truck, fuel consumed over distance travelled alone is not a good fuel measure for trucks when accelerations and decelerations are involved,” says Allison Executive Director of Engineering, Steve Spurlin. “Trucks hauls rocks and buses haul people and the idea is to do that in the least time possible – time costs money. Payload and average vehicle speed need to be considered in the metric. An automatic puts more energy into a vehicle faster and, therefore, does more work, which means higher productivity.

“An automatic can accomplish this during acceleration using less fuel. Less fuel used during the transient forces of the duty cycle and more work accomplished due to higher average vehicle speed and reliability of an automatic transmission equals a superior fuel efficiency, when compared to a manual or AMT.”

The Allison uses a feature called auto neutral when the parking brake is applied. The transmission shifts to neutral automatically even if the driver leaves the selector in drive. This combined with RELS is believed to save up to four per cent of fuel in the right application.

Technology is used to specify transmissions to suit the truck and application. The main aim is ensuring the engine is running as close as possible to optimum rpm for a maximum time and the ratios are locked up most of the time without shift cycling.

Load based shift selection (LBSS) allows the transmission to change between different shift calibrations depending on the topography and vehicle load as sensed by transmissions systems. These different patterns are set up to try and maximise fuel economy while maintaining vehicle performance. In the right application, Allison believes there can be a five per cent fuel saving in some cases as a result.

Allison also includes what it calls super economy shift schedule (SESS). This works in conjunction with LBSS and when the truck is cruising allows earlier upshifting to higher gears to reduce engine speed and, consequently, fuel consumption.
If these enhancements are all included in the right application, Alison claims a 14 per cent reduction in fuel consumption compared to Allison transmissions without the latest electronic control systems.

A feature known as vehicle acceleration control (VAC) has been developed to allow truck buyers to set a limit to the acceleration possible. This can improve fuel efficiency by reducing hard acceleration. The system allows full use of available torque from the engine when the truck is fully loaded but less torque when the truck is more lightly loaded.

The development of these kinds of technology moves at a rapid rate. The fifth generation of electronic control systems will be introduced by Allison in January 2013, further refining the way the transmission is controlled and how it monitors vehicle performance.

As a driving experience, the Allison ride and drive illustrated many new features in application specific situations. The Boral truck and dog sees an Allison 4500 fitted behind a Series 60 Detroit. The transmission makes the most of engine brake deceleration by dropping to a lower ratio when the accelerator is released. Acceleration possible is also demonstrated when compared to a manual tipper.

In the Dennis Eagle with an Allison 3500 and a Cummins ISL, the sheer simplicity of the two pedals functioning as stop and go buttons makes life for garbage truck drivers simple. In the cab surrounded by a myriad of controls the driver needs to work with to pick up and empty bins, the starting and stopping function must be easy enough to use to allow them to concentrate on the other functions of the truck.

All of the Japanese truck manufacturers had examples of models fitted with Allison autos, a growing part of the business. There were also examples of Iveco Acco and Freightliner trucks fitted with auto transmissions for specific applications. Probably the most surprising was a Mercedes Benz Atego at 326hp, fitted with an Allison 3000 transmission on a 6×2 configuration for distribution work.

Just by bringing all of these different trucks to one place, as well as allowing drivers to experience their performance first hand, Allison had a chance to demonstrate the breadth of its current product range. The exercise had the effect of showing the industry just how far the latest technology has come in improving the performance of automatic transmissions, after a period where they went out of fashion, as other new technologies moved into their traditional applications.

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