ZF to offer beefed up light vehicle 8-speed transmission for medium trucks

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Jim Park, Heavy Duty Trucking (HDT)  /  June 20, 2019

Medium-duty truck builders will soon have a groundbreaking new transmission to add to their data books, and heavy-truck makers will have more steering assist options to offer customers. German automotive supplier, ZF Friedrichschafen AG, recently demonstrated these and other nearly-market-ready technologies at press gathering at the Transportation Research Center near East Liberty, Ohio.

The PowerLine 8HP torque-convertor automatic transmission is the big news here. It's hardly new though. It was officially introduced to the North American market exactly one year ago in Indianapolis. But more than 15 million copies of this transmission have been operating in passenger cars (fitted with the scaled-down 8AP version) across Europe and Asia since 2007. The 8HP is a "muscled-up" version of that same platform. ZF changed little in scaling it up for service in Class 3 to baby 8s save for building in some extra durability.

ZF says the transmission should be on the road next year but wouldn't say which of the major truck makers would be first to market with the PowerLine 8.

ZF did say, however, that this 8-speed will cover all of Allison's 1000, 2000 Series automatic transmissions and a good chunk of its 3000 Series transmissions. "With one product, we cover about 90% of our competitor's volume," said Andre Kohl, ZF's North American business development manager.

It boasts some impressive specs and features, but performance will likely be its biggest selling feature. Reporters had the chance to drive two trucks equipped with the PowerLine 8, and one "baseline" truck for comparative purposes. It's impressive.

Starting out, it will launch in first or second gear, depending on the load, and it will skip-shift when the opportunity presents itself. It has a neutral idle feature that disengages the torque convertor to take the load off the engine when the truck isn't moving. Gear ratios range from 4.89 in first to 0.64 in eighth, which is like double or maybe triple overdrive. There's plenty of latitude in the eight cogs for any driving condition, and ZF did say that fuel economy was a prime driver in the engineering process.

"The PowerLine is at least — not up to — at least 10% better on fuel than any competitive product in same application," said Kohl.

The transmission boasts 30% better acceleration than other transmission and a 45% weight advantage -- the PowerLine 8 weighs a paltry 328 pounds.

Kohl also pointed out that the transmission, as it sits today, is ready for what the OEMs will be asking for in terms of meeting the pending GHG Phase II regs. It's ready for integrated stop/start assist which shuts off and starts the engine while at traffic lights, etc. "We incorporate an accumulator inside the transmission to help with restarting," he said. "This will help truck makers comply with GHG reduction rules in the future with engine stop/start technologies. When they are ready for it, we already are."

It also features twin torsional dampers, which will help with downsped powertrains. These are more common to on-highway Class 8s, but Kohl says downspeeding is coming to medium-duty. There's also a lock-up clutch in first gear for improved energy efficiency. With the PowerLine 8, the torque convertor is used only to launch and stop the truck.

Driving the PowerLine 8 proved pretty well everything Kohl said during his presentation. You literally cannot feel the transmission shifting gears. You can tell the shifts are happening based on the sound of the engine, but they are very quick and really smooth, and there's never a lag in torque as you accelerate.

There's a short off-road loop at TRC that features a hill with a 23% grade. One of the trucks was loaded with 20,000 pounds of steel dunnage for a gross weight of about 37,000 pounds. The truck walked up that grade from a full stop at the bottom, and from a full stop mid-way up the hill (the hill-start assist feature came in handy that time). It even managed an upshift from first to second on one of my runs up the hill with full throttle applied right from the start. 

On the maintenance side you get “best in class” extended oil-change intervals and Kohl said the oil filter is good “for life”. It also features a fully integrated control units inside the casing, with no external sensors or harnesses. That should help with durability.

Building on ReAX

With advanced driver assistance systems now gaining popularity, ZF first introduced its ReAX assisted steering system in March 2015 at the Mid-America Trucking Show. Actually, it was TRW that introduced ReAX, but ZF acquired TRW later that year. At any rate, ReAX was one of the first such systems introduced to the heavy truck market, and the company has now developed a suite of assisted steering applications that offer drivers safety and convenience.

In case you missed it, ReAX is an electric motor integrated into the hydraulic steering gear that provides a boost to the input torque supplied by the driver. It can be controlled to modulate steering force when maneuvering at low speeds and stiffened for highway driving. While that functionality is still present, ZF will soon offer a lane departure prevention function along with a haptic warning to help avoid blind-spot collisions.

Called OnTrax Lane Keeping Assist, the system uses a forward-facing camera to determine the truck's lane position. If the truck drifts toward the lane markers without using the turn signal to indicate a lane change, the system will gently counter steer the truck back into the lane. I tried it on the 7.5-mile oval test track at TRC and found the nudge was certainly noticeable but easy to override — if a lane-change was in fact my intention.

This version of OnTrax LKA will not center the truck in the lane, so the driver has to take control of the wheel after the counter-steering event to prevent the truck from heading toward the opposite side of the lane.   

With the addition of a few radar sensors, LKA is turned into a blind spot detection system called Lane Change Assist, providing drivers with a haptic warning if he or she is about to turn into an already occupied lane. The system shakes the steering wheel with much the same feel as driving over rumble strips. ZF said it opted for the haptic warning rather than an audible warning because of the proliferation of annoying beeps and bells and buzzers now cluttering the soundscape in most modern trucks. This version simply warns the driver, it doesn't prevent the maneuver.

The basic Lane Keeping Assist system will be in production next year with an unnamed OEM, while the lane change assist feature is still a couple of years off because the sensors used aren’t yet in production.

ReAX is also capable of full steering control in an autonomous driving situation. Reporters got a ride in a day-cab International LT that drove a simulated course through a truck terminal using GPS to guide the truck on its predetermined course. It started, stopped, turned right and left (using turn signals) on commands from a Pro AI controller.

This configuration was equipped with two ReAX steering units, one on the steering gear and the other mounted on the steering column. The second was in place for redundancy.

All the technologies presented by ZF will be available through OEM channels within the next year or two. I suspect though that by the time they come to market there will be additional functionality to report on. ZF has a history of innovation, and they won't be sitting still on this stuff for long.

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