Bottom Line
Shifting on the fly

By Paul Abelson
senior technical editor

 

Even though fuel prices have come down from their historic highs of this past summer, general economic conditions dictate that truckers operate as frugally as possible.

Frugal doesn’t necessarily mean cheap. There are times when it is worthwhile to spend a little more in order to get greater value. This is especially true when making equipment decisions for your truck. That’s why automated and automatic transmissions can often be frugal choices.

All transmissions perform two major functions. They provide a mechanism to match the somewhat limited range of engine operating rpm with actual and desired truck speed. They also multiply the torque to meet the power required for acceleration, cruising, hill climbing and even braking.

For years, one mark of a professional driver was how skillfully he or she shifted gears with the unsynchronized manual gear boxes. It took time to learn double-clutching and matching engine and road speeds in the transmission. Students spent weeks in yards learning to shift when that time could have been better spent on the streets learning safety.

Although transmission makers advise against the practice, skilled drivers have learned to “float the gears.” They release torque and shift into neutral. Then they either let engine rpm drop (if upshifting) or increase rpm (if downshifting) and, at the precise moment, shift into the right gear. This not only  demonstrates skill, but also saves clutch wear – when done right.

This is the method used by some automated manual transmissions. It works because the computers controlling the system never get distracted and never miss shifts.

The first model, Eaton Fuller’s Top 2, floated between direct and overdrive in top gears. The idea was to lessen a driver’s workload, because about 95 percent of shifts in over-the-road trucks are made between the top two gears while on the highway.

About a decade ago, Eaton introduced the AutoShift transmissions – computer-controlled versions of their line of proven manual transmissions. They use the principle of floating gears, but have a computer doing the shifting and controlling the engine’s throttle. That opened up the use of automation to all trucking, not just long haul.

The computers in the transmission and engine communicate to coordinate throttle movement and the actions of the X-Y actuator, the device that moves the shifter mechanism instead of the gearshift handle we’re all used to.

The AutoShift uses the clutch only to disengage when stopping or to engage when starting. All gears are changed by floating.

Within a few years, Meritor introduced the FreedomLine, based on ZF’s European style fully synchronized manual transmission. It operates like the manual transmission found in cars and pickups with synchronizers, eliminating the need for double-clutching.

A computer actuates the clutch with every shift. Because the FreedomLine doesn’t have to hesitate in neutral, waiting for rpm to match, shifts are faster.

And because the computer controls the air that activates the clutch, there is no clutch pedal.

That made it the first two-pedal (throttle and brake) setup. Meritor sells and services the FreedomLine.

In 2004, Eaton introduced the UltraShift with a two-pedal setup. The clutch is computer-activated. Otherwise, UltraShift works just like AutoShift.

AutoShift, UltraShift and FreedomLine are all automated, based on manual transmission designs.

Volvo’s entry is the I-Shift, a 12-speed transmission that works with the company’s proprietary engines. It is available with Eco-Roll, which disengages the engine in top gear on long, slight downgrades to save fuel. A direct drive model is available. Like all latest-generation automated transmissions, I-Shift is programmed for each specific engine.

Allison makes a true automatic with a hydraulic torque converter and planetary gears. Like the transmission in a car, its torque converter allows slippage when at idle, then adjusts its vanes to vary torque multiplication and input rpm. Because fully automatic transmissions use hydraulics in every gear, fewer gears are needed to cover the operating range. For better mpg, the converter locks up at speed.

Automated transmissions are several thousands of dollars more than manuals, and automatics may be more than $10,000 higher.

Allison transmissions are justified when constant torque is needed, such as on heavy haul or hilly terrain. They have the least shock load on drivetrains and suspensions.

The cost advantages of automated and automatic transmissions come from improved fuel economy and reduced maintenance costs. While it may seem counterintuitive, Technology & Maintenance Council member fleets report lower maintenance costs because of smoother operation and the elimination of missed shifts.  

Fuel economy was measured using SAE/TMC Type II procedures. AutoShift savings were between 4 percent and 5 percent because computers were shifting at optimum rpm. Eaton’s Gen 3 electronics incorporated into their LEP (linehaul efficient performance) show a 2 percent improvement over previous UltraShift models. HV (Highway Value) models show 7.5 percent better fuel mileage than manual transmissions, partly because of having shift points and rpm tailored to each specific engine.

Fuel economy and reduced maintenance offer savings and also improve safety. You can manually shift both types, so you always have control. If the transmission cannot physically make the shift, it won’t start it. You’ll never get hung out in neutral going up or down a grade. The latest UltraShifts even have Hill Assist, which minimizes rollback when going from brake to accelerator on grades up to 10 percent. LL

 

Paul Abelson can be reached
at truckwriter@anet.com.

Aug/Sept Digital Edition