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Prime Mover Magazine


Isuzu raises bar with upgraded AMT

Having introduced its torque converter- automated manual transmission (TC-AMT) in the lighter end of the N Series range some two years ago, Isuzu Australia Limited (IAL) has announced refinements to the AMT used in heavier versions, including the new NPS 4x4.

According to Simon Humphries, IAL Chief Engineer, Product Strategy, speaking last week at 2018 N Series launch, the programming on this transmission has been significantly improved. He said it matched the TC-AMT versions the commercial vehicle manufacturer introduced a couple of years go, with the smaller 4JJ1 engine.

“So while the gear selector is the same as before, the smarts behind the hardware are quite different,” said Humphries.

The changes are designed to further enhance the drivability of its light-duty range, in a bid to attract greater light commercial vehicle users; those seeking the attributes of higher load carrying capacity and longer life, but in a package that doesn’t significantly diminish the driving experience to which they are accustomed.

Ongoing refinement rather than wholesale change is an important part of IAL’s methodology, and the company has continued to develop the AMT principle while competitors have taken the fully automatic path.

Yet it’s interesting to note that Isuzu’s TC-AMT is literally a hybrid transmission, combining positive features of both automatic and manual versions.

Bolted to the engine’s flywheel, the torque converter, by design, multiplies the torque produced by the engine for improved startability on grades and acceleration up to 10 km/h in second gear, after which the torque converter clutch engages and provides direct-drive power flow to the AMT.

This system is only available with the 3.0 litre 4JJ1 engine in NNR and NLR models.

The higher gross vehicle mass (GVM) models including the NPR, NQR and NPS utilise the larger 5.2 litre 4HK1 engine which due to its higher torque output is deemed not to need the torque multiplication benefits of the torque converter.

Therefore, these variants use a simpler fluid coupling in place of the torque converter to transfer drive from the engine to the AMT via a wet clutch assembly comprising four friction discs and five steel backing plates.

Similar to the TC-AMT, the fluid coupling provides a smooth take-off after which the wet clutch engages to provide direct drive to the AMT as per a conventional clutch.

A major benefit of the wet clutch over a conventional dry unit is that the wet clutch, as its name suggests, runs in transmission oil that is continuously circulated through a radiator-mounted cooler. This significantly mitigates heat build-up due to demanding operating conditions.

Conversely, the conventional clutch relies solely on the air around it to dissipate the heat and is therefore prone to overheating and subsequent wear under arduous operating conditions.

Perhaps the biggest challenge Isuzu has faced with its AMT over the years has been with the software that controls the gearshifts. Put simply, earlier versions were not always adept at choosing the right gear at the right time.

This was most obvious when approaching a roundabout where swift acceleration is needed to enter a gap in the traffic flow. It was here that the AMT could become momentarily bamboozled and by the time it got its act together the gap had well and truly closed. This was a common problem with earlier AMTs of all sizes, including those in larger trucks and prime movers.

According to Simon Humphries, the company has worked hard to overcome this deficiency. Judging by a recent N Series drive event this Achilles Heel has finally been conquered.

“We haven’t been sitting still with the AMT,” said Humphries addressing media at the launch. “The six-speed AMT that is standard in the NQR and NPR models has a revised shift calibration and is now more intuitive.”

“It’s noticeably better in the classic roundabout scenario where you coast up, see an opening and put your foot down to take the lower gear and accelerate into the gap. This is where older AMTs can get a bit confused.”

Another feature the larger AMT now shares with its TC-AMT sibling is a kick-down switch, itself a desirable attribute for metropolitan driving where a swift burst of acceleration is often required. 

“When you put your foot down to what feels like the limit of accelerator pedal travel, you can push through again with a noticeably higher resistance. This initiates the kick-down process and in most cases it will jump down a gear very quickly,” Humphries said. “This is very useful, again, in the roundabout scenario, or indeed any situation where you need to get up and go quickly.”

Humphries went on to describe these changes as an important part of IAL’s strategy to make the driving experience of its light-duty truck range more car-like and therefore more appealing to tradies and others who need to upgrade from car-oriented light commercial vehicles.

“We acknowledge that the N Series is there for many operators who are perhaps growing out of a light commercial vehicle. They want to move up to an N Series because they need more payload and durability but, as much as possible, they don’t want to compromise on their driving experience.”

To this end, IAL has made another small amelioration, making cruise control a standard feature across the entire N Series range.

“I can’t remember the last time I had a car without cruise control,” said Humphries. “Previously it was standard on the premium spec versions with the larger engine and AMT. Now it’s standard across the board.

“The safety and security of cruise control can’t be underestimated and, like I said, we expect it in our cars and now it’s in all our N Series variants.”

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