Eaton's Ultrashift, is a two-pedal version of their AutoShift transmission

The introduction of automatic transmissions into big rigs has changed the demands on and qualifications of big rig drivers. Fleet owners are increasingly looking to automatic transmissions for their fuel efficiency and the reduced need for driver training. Here's a closer look at the issue.

The Eaton AutoShift won the Technical Achievement of the Year Award for 1997 from Truck Writers of North America. The committee of 13 journalists recognized its potential impact on the future of trucking and its potential to improve safety and operating efficiency.

Initial driver reaction was less than enthusiastic: "Shifting is what separates the men from the boys;" "If you can't handle a transmission, you've got no business driving;" and, "It's just one more thing to break down." These were typical comments, probably from the same old timers who resisted power steering, air conditioning and certainly electronic engines.

In the 1990s, drivers had a right to be skeptical. While the AutoShifts were based on the tried-and-true Eaton Fuller gearboxes, their electronics were new and first generation controls did have problems. Those have been corrected with subsequent generations of electronics, and today, more than 40,000 automatic transmissions are operating on America's highways.

That number includes Freedom Line transmissions from ZF Meritor, the joint venture of ArvinMeritor and ZF Friedrichshafen of Germany. Eaton was the first to fully automate its 10, 13 and 18-speed transmissions, while the Freedom Line was the first to offer two pedal (no clutch, just accelerator and brake) automation. Eaton followed with the UltraShift, their two-pedal version of the AutoShift.

Freedom Line transmissions are made here, but based on ZF's European models. There are 12-speed or 16-speed models. While unfamiliar numbers to American ears, they are proven models and, when the computer does the shifting, as reasonable to use as 10 or 18.

Automated, Not Automatic

These new transmissions are mechanical. They do not have the hydraulic fluid couplings and torque converters we find in passenger cars, light trucks and heavy duty Allison automatics. Those transmissions use fluid torque multipliers and planetary gears. Automated transmissions use clutches and the same gears found in mechanical models.

The computers that control automated boxes are linked to the engine's control module electronically, so they know not only when to shift, but how to shift. The engine controller increases or reduces fuel flow to get the precise rpm the transmission needs to match gears, just as the transmission's X-Y actuator moves the gear selector lever. Every shift is perfectly timed, and all shifts are smooth. The X-Y actuator is the hardware that moves the gear selector linkage, as you would use the shift handle.

The Freedom Line transmission from ZF Meritor, are available in 12- or 16-speed.

A Look at the Benefits

The most direct benefit from making perfectly timed shifts is an increase in fuel economy. Depending on operator technique, savings can reach 5 percent.

Maintenance costs are lower, too. Clutches last longer and less linkage adjustment is needed. There is far less wear and tear on the drivetrain and suspension. Even bushings last longer, since drivetrain shock is virtually eliminated.

As great as the equipment benefits are, the safety benefits are even greater. In situations that call for a driver's full attention, the distraction of shifting is eliminated. The driver can concentrate on driving, not matching gears and engine speeds.

Shifting on grades is not recommended with standard transmissions. The risk of missing a shift, even for a seasoned professional, is too great. Going uphill, your speed is limited by engine rpm if you're in too low a gear, and by power demand if too high a gear. If you try to shift and miss the gear, your best option is pull over, stop, get into a gear that will get you rolling without stalling, and start the climb again.

Going downhill, the dangers of a missed shift are far greater. Without engine braking, your service brakes probably won't be able to control your speed. The technical term is "brake fade." The resulting situation is called a "runaway."

Automatic transmissions overcome these problems and contribute to safety. Uphill or down, if a shift can possibly be made, the computer will make it. And if it can't be made, the computer won't even try until it is knows it can.

Eaton's UltraShift replaces the clutch pedal with this flat-panel push-button control or a shift knob.

Worth the Price?

These benefits come with a price. Going with an automatic transmission adds roughly $3,000-$5,000 to the price of a truck.

And because experienced drivers want to control shifting themselves, with today's automatic transmissions, they can. There is the automatic mode, but you can take over shifting at the touch of a button. The computer is still there to protect from missed or impossible shifts, but you tell it when to do it. Most of the time you keep both hands on the wheel to control the truck, not the transmission.

Fleets like these new transmissions because they improve training. Some schools spend half the students' time learning how to shift. That time could be far better spent driving on streets and highways, gaining driving skills that can only come with practical experience.

Finally, there's a fatigue factor. Drivers with 15 years or more experience, million mile safe drivers, have purchased trucks with AutoShifts and Freedom Line gearboxes. Without exception, they love these transmissions. At the end of a run, they're not as tired, not as sore. They appreciate not wearing out their left legs, right shoulders and arms.

Each year, what marketers call the "take rate" of automatic transmissions continues to grow, as the transmissions continue to improve. Perhaps in the not-too-distant future, they will account for more than half of all new class 8 trucks sold in America.