WITH UNIMOG, THERE'S NO AUTOMATIC ANSWER
Automated gearbox is Mercedes-Benz's clever answer to the Allison question, and it might well be enough.
How do you answer "the Allison question" from potential buyers when you don't even offer a fully automatic transmission – much less an Allison?
You automate what you have, say the product planners at Mercedes-Benz, maker of the Unimog utility truck.
Unimog 500, the multi-functional, all-terrain truck sold in the United States since 2003, up until now has been equipped with the eight-speed Telligent semi-automatic gearbox. The Telligent is easy to learn and drive, but it requires constant use of the clutch and shift lever. You choose to upshift or downshift by tapping the paddle-like gear selector up or back, then punching the clutch pedal to make it happen.
That clutch pedal is the main problem, figured engineers in Germany, where the U500 is built. So they devised the Electro Automatic Shift, or EAS. It's an example of what is generically known here as an automated mechanical transmission, because electronic controls and servos on the gearbox do the clutching and shifting while the driver merely punches the accelerator or brake pedal, and steers.
EAS has no torque converter or powershift functions, so it's not a full automatic, but Unimog executives believe it's close enough. They could be right, because the Telligent gearbox itself is smooth-acting on or off road, and the EAS function simply adds convenience to this remarkable vehicle.
The U500, as you may recall from our coverage three years ago, is the latest version of the vehicle that was born in post- World-War-II Germany as an agricultural tractor that could also take a farmer's goods to market. Unimog is an acronym for Universal Motor Garact (or Tool). It can be quickly fitted with any of scores of implements that allow one truck to do many things and stay busy year round.
Versatility is the word Bob McTernan, director of Unimog of North America, uses. Unimog is a member of the Freightliner Group of companies, co-based with Freightliner in Portland, Ore.
A basic U500 costs more than $100,000, but its ability to do many things, from plowing snow to digging holes and ditches to cutting grass, can actually save purchasing and ownership dollars. Specialty bodies also can be mounted and dismounted, and Unimog executives recently announced several new units, including a street sweeper, fire-fighting apparatus and a hooklift, which itself can handle several types of platform-based bodies.
Also new is a VarioPower high-pressure hydraulic system that can run implements that traditionally need auxiliary engines.
The U500 is bigger and heavier than it looks in photos. It's a full Class 7 truck whose cab sits high above the road, and whose coil-spring, four-wheel independent suspension makes it as much at home in very rough terrain as on a freeway. It can hustle down the highway at more than 70 mph with surprising comfort and, using a low-low gear set in the transmission, can crawl at less than 400 feet per hour. It can carry loads and pull trailers, and can come equipped with a front-engine power takeoff and multiple hydraulic circuits to power its implements.
Under the tilting composite-fiber cab is a Mercedes-Benz inline six-cylinder diesel, the same one used in Freightliner and Sterling midrange trucks. Set at 260 horsepower and 700 pounds-feet in the 'Mog, it seems more than adequate for what work the vehicle needs to accomplish.
The engine's electronic controls talk with those on the EAS transmission, allowing the driver to do a bunch of things without worrying about what gear he should choose, except that the driver should know that a clutch is there to avoid abusing it.
Indeed, with EAS the clutch can still be used manually, and must be while in the transmission's optional low-range modes. Otherwise, flicking a switch on the steering column causes the clutch pedal to fold up and out of the way, and the tranny becomes a two-pedal type.
That's how it went during a recent demonstration by McTernan and his colleagues at the DuPage County Airport outside Chicago, where I drove a couple of U500s with EAS on streets and access roads. Sadly, rough terrain wasn't part of the program. But I did get a feel for how the EAS works, which is pretty well.
In Auto mode with the clutch pedal folded up, you simply switch to Drive and depress the accelerator. Usually it'll start out in second or third gear and upshift as the engine revs up. It will downshift as road speed falls, eventually going to one of the lower gears and declutching as the truck comes to a stop.
There was some clunking as the transmission descended into its lower gears, but it never missed any. To move out, you take your foot off the brake pedal, which signals the controls that they can engage the clutch as soon as you get your foot on the accelerator.
If you use a very light foot, EAS will "short shift" – upshift at low rpms – but pressing the pedal to get moderate to snappy acceleration causes the engine to rev almost to its 2,600-rpm limit in each gear. I found this a little disconcerting, because I was taught years ago that high revs waste fuel. Shift "progressively," keeping engine speed low until you really need the horsepower that comes at higher rpms, the old pros told me. And you really don't need a lot of horsepower until you're on the highway.
So I used EAS's semi-manual feature: I tapped the paddle selector to initiate an upshift, usually for each gear change. The clutch still works automatically, and I could watch the tachometer or just listen to the engine and command a shift whenever I thought it necessary – which was almost always below 2,000 rpm. I could floor the accelerator and still short shift, and could downshift while braking to get more engine drag. Or I could leave it alone and the automated shifting would proceed as the tranny's controls thought best.
As capable as the EAS is, it's not fully automatic and therefore might not fully answer the Allison question posed by some potential customers. They include municipal fleet managers, who long ago adopted the Allison automatic as a way to avoid training drivers on manual trannies and to reduce the expense and downtime associated with manuals. Engineering an Allison RDS into the low-volume Unimog would not make much economic sense, but EAS is certainly a clever answer, and buyers will decide if it's enough.
— Tom Berg, Senior Equipment Editor
|
