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Truck Topics

The Shift Away From Shifting

By Jeff Jensen and Lisa Brooks
Posted May 10th 2002 5:01AM

For decades, automotive technology's advancements have usually outstripped those of the medium and heavy duty truck world. Air conditioning, power steering, power brakes, cruise control - these were all new features found on four-wheelers many years before they made their way into the commercial truck arena.

Automatic-type transmissions have been no exception. The heavy-duty truck market didn't see a viable attempt at automation in shifting until Mercedes-Benz introduced their first automated manual truck transmission in 1990, with Dana-Spicer and Eaton-Fuller following a few years later with limited automation on their 10-speeds.

Since then, the manufacturers have introduced advanced semi-automated manual transmissions with varying degrees of driver/fleet acceptance until the recent arrival of the FreedomLine by ZF Meritor - the first fully automated heavy truck transmission with no clutch pedal.

In the Class 8, tractor/trailer world, automatics have suffered, at least until recently, the stigma of being considered a piece of equipment that a "real truck driver" would never accept. Gear shifting was an art practiced by trucking veterans, and it was felt that an automated transmission would never be able to match the experienced driver's ability to hit just the right shift point.

Despite that, automated transmissions are more attractive than ever. Although the driver shortage may be somewhat in remission right now, the boom part of the boom/bust cycle can't be far off. Sooner or later, the trucking industry will bounce back, and carriers will have little choice but to draw from non-traditional labor sources, recruiting drivers with little or no experience.

Also, today's urban congestion has reduced traffic to a crawl on some interstates, making shifting and clutching a much greater challenge

Because properly shifting a non-synchronized, heavy-truck transmission is one of truck driving's most demanding skills, automating it will remove a major impediment for inexperienced drivers. Automated transmissions offer improvements in safety, productivity and comfort

For the Class 6-7, and to an extent, Class 8 expediting trucks, the automated transmission has been more readily welcomed by the owner/operator. Dan Tilley, Expediting Truck Specialist with Freightliner of Knoxville says, "Automated transmissions are becoming more popular all the time. I suppose that one reason for the demand for automateds is because in the expediting field, we see so many people entering this business from other careers and who are new to truck driving."

"They don't have the years of experience of shifting gears and many don't really see the need for a manual transmission. Add to that, even the veterans who are used to manual shifts are spoiled once they try an automated. I guess they appreciate that they can rest their left leg with an auto, especially in traffic."

Heath Wood of Middle Georgia Freightliner concurs: "A lot of baby boomers are retiring with expediting being a second career choice. Many of them appreciate the automatic type transmission, especially with the husband and wife teams."

"For our dealership, I believe our percentage of automateds installed is around 10 percent right now, but I think you'll see that within 3 years or so, that will increase to 30 or 40 per cent; probably the top choice will be the Allison 6-speed automatic."

From the driver's perspective, even the long-time manual transmission users are looking forward to the automated's:

Rich Moore - "I've been running an FL70 with a Cummins C engine hooked to an Eaton Fuller 6-speed with 600K on the odometer."

"I'd like to go with the Allison full automatic; I've driven them before and I could get used to it very quickly. You have the ease of operation, no shift lever to climb over and it's less fatiguing, especially in traffic."

Overview

The development of the medium and heavy duty non-standard shift transmissions has centered on two basic types; semi-automated and fully-automated.

Semi-automated transmissions are manual gearboxes that perform parts of their shifting functions automatically. The clutch pedal is used only for stopping and starting out. Once the vehicle is in motion, and depending on the make and type of transmission, the shifts will be made by the Electronic Control Module (ECM) or the driver, without use of the clutch.

A fully automated transmission or "two-pedal" system is also a manual transmission, but is quite similar to that of a car's automatic - step on the gas pedal and go. The ECM and sensors control shifts while adjusting engine rpm to road speed, without disengaging the clutch, with the most noticeable difference from the typical automatic being the delay between shifts.

A major concern with automated transmissions has been that of torque converter slippage and it's negative effects on fuel mileage. Because both the semi-automated and fully-automated transmissions use clutch plates (with the Allison being a notable exception), this concern has been eliminated.

An automated transmission shifts up every time it's throttled back to cruise, even when a downshift may be needed soon. It also downshifts whenever the engine gets well below the torque peak and the driver hits the throttle.

The automated transmissions have added benefits for the driver as well - the devices are more forgiving of different driving techniques, and driver error, i.e., missed shifts, especially when climbing and descending hills, is eliminated.

An automated transmission shifts up every time you throttle back to cruise, even when a downshift may be needed soon. It also downshifts whenever the engine gets well below the torque peak and the driver hits the throttle.

According to the experts, automated transmissions are actually easier to maintain than manual transmissions, the main concern being to prevent the fluid from overheating. The pros say just change the fluid and ensure that the transmission coolers are working.

Some of the experts have been generous in their praise of the synthetic transmission fluids, indicating that these non-petroleum fluids have a drain interval of up to four times longer than conventional fluids.

The Choices

Eaton Fuller Autoshift

In this transmission, shifting is accomplished with electric motor-powered shift actuators which also control engine throttle levels. This three-pedal setup requires use of the clutch for starting with the transmission in drive. The transmission then determines the shifts depending on engine rpm and other factors.

With the 10-speed version, the transmission typically starts in second gear. If the driver wants control of shifting, he can shift the selector to hold to keep it in the present gear. He can then push one button to upshift and another to downshift.

The transmission can also be started in first, third, fourth or fifth, merely by using the hold feature.

The unit will refuse to shift when outside the proper rpm range.

Glen Rice - Owner/Operator of "Lil Deuce Coupe", Volvo Class 8 VNL42 with an Eaton Autoshift 10-speed. Glen says, "This is a very smooth, heavy duty truck transmission. Our last truck was an FL70 with an Eaton 6-speed which worked pretty well in spite of computer problems we had with it."

"This Eaton is very pleasant to drive, it doesn't exhibit the jerking sensation that we experienced with the 6-speed. It appears that Volvo will be offering the FreedomLine model later this year, and I'd like to check those out."

George McDonald - Western Star Class 8 Platform with Eaton AutoShift 10-speed: "The big reason I went with this transmission was that it was about 6000 dollars cheaper than the Allison 6-speed. This AutoShift has the clutch for starting and stopping, but it's still great in city or congested traffic."

"The maintenance is nothing out of the ordinary and my fuel mileage is what it should be."

Eaton Fuller Automated - 6 Speed

This two-pedal unit, designed for medium-duty trucks, combines a 6-speed transmission with quiet helical gearing and a multi-disc wet clutch. The transmission's synchronizers are removed.

An inertia brake is added for upshifts on upgrades, because the engines used in these trucks don't have internal brakes. The transmission uses synthetic fluid, but the wet clutch unit uses automatic transmission fluid, with its own pump and clutch hydraulic actuator piston linked to the microprocessor electrically.

When the driver selects Drive, the hydraulically actuated clutch engages just enough to give that gentle push (what Eaton Fuller calls the “urge to move”) that is typical of torque converter automatics, to make starts smoother.

The processor engages the clutch smoothly when you hit the throttle, and then the transmission begins going through the gears, float shifting like it's simpler brothers. On an upgrade, the inertia brake slows engine and gearing together for quick upshifts.

Allison Automatic - 6 Speed

In Allison transmissions, the torque converter replaces the clutch with a hydraulic turbine drive. The converter lets the vehicle start out with no mechanical slippage, just the flow of oil. It multiplies torque about 21¼2 times at the beginning, then gradually locks up as the speed increases.

Allisons have five or six gear ratios provided by planetary gears, multiple-disc wet clutches, and hydraulic pistons. The unit uses the torque converter in the first two gears, locking up completely like a manual at the top of second. All shifts occur under full power. The latest World Transmissions use an electronic processor.

The Allison is complex and expensive but overcomes a multitude of clutch and driveline maintenance troubles in applications with frequent, hard starts and difficult upshifts. Acceleration from zero to 25 mph using the torque converter is nearly twice as fast as with automated mechanical transmissions.

Dan Tilley of Freightliner of Knoxville says, "We're equipping our trucks with Allison 6-speed Automatics in the Class 7 units, with the Eaton 10-speed Autoshift for the Class 8's."

"Between the Freightliners and Sterling expedite trucks we sell, virtually all are automated-equipped nowadays, and our customers report their fuel mileage averages between 9-11 mpg with the automated transmissions."

He adds, "Maintenance intervals are not extreme - just a recommended fluid/filter change every 25,000 miles and the Freightliner and Sterling transmission warranties are 2 years/unlimited mileage."

Another fan of the Allison is Ed Housworth of Housworth Trucking and Leasing in Georgia.

Ed has a 40 truck fleet, and except for 3 trucks, all are manual transmission equipped. Says Ed, "I wish all the trucks were equipped with the Allison 6-speed. My research shows that it's almost indestructible, but it comes with a great warranty, just in case."

"For the few automated trucks in our fleet, the drivers love them and most newer drivers ask about automateds. I've found that the fuel mileage is equal or better in the automated transmissions."

ZF Meritor FreedomLine

The FreedomLine is a premium 12- or 18-speed two-pedal automatic. The transmission is a simple, twin-countershaft, constant-mesh design with all-helical gearing for quiet operation — a rarity in heavy trucks. Its case is aluminum, to keep weight down. This was the first two-pedal design using relatively standard components.

The FreedomLine has an integral single-plate clutch that's operated via an electronically controlled, air-powered piston. It declutches and uses the integral inertia brake to make fast upshifts.

The unit's microprocessor is integral and mounted inside the transmission case, minimizing the number of connectors. Operation is extremely smooth and quiet. Load sensing allows it to do a very skillful job of adapting and skipping full gears or splits when the load and shift points permit.

It drives like the most skillful driver, even as an 18-speed. But the driver can take control and operate it just like SureShift.

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