Article

Direct/Overdrive Adds Efficiency to Bulk-Hauling Volvos

Adaptive Gearing is an offshoot of the earlier Extra Efficiency specification, which uses driveline gearing and electronic controls to “downspeed” the engine and save fuel.

November 2014, TruckingInfo.com - WebXclusive

by Tom Berg, Senior Contributing Editor - Also by this author

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Photo via Volvo Trucks
Photo via Volvo Trucks
Direct drive or overdrive? That’s a years-old question among truck operators concerned with spec’ing transmissions: Should top gear be a direct 1 to 1 ratio, where the output shaft spins at the same speed as the driveshaft with little friction penalty, or a 0.85-or-so overdrive, where the driveshaft spins a little slower, lowering engine cruise speed but suffering a bit of efficiency loss as the extra gear-set churns through lube oil?

Sage managers sometimes choose both with a multi-speed manual box where the very top gear is reserved for running empty or with light loads, and the next lower ratio is used for pulling heavy loads. The concept is not new but Volvo Trucks has come up with a new form of execution with its XE-Adaptive Gearing product, announced in August.  On Tuesday, Volvo demonstrated it to reporters at its plant in Dublin, Va.

Adaptive Gearing is an offshoot of the earlier Extra Efficiency specification, which uses "fast" driveline ratios and electronic controls to “downspeed” the engine and save fuel. Adaptive Gearing doesn’t rely on a driver to remember to choose the correct gear; it’s all automatic.

I-Shift's selector does a lot of things, but it won't prompt an upshift to 12th when its controls know that the rig is heavily loaded. Photo:Tom Berg
I-Shift's selector does a lot of things, but it won't prompt an upshift to 12th when its controls know that the rig is heavily loaded. Photo:Tom Berg
The basic component is Volvo’s I-Shift automated mechanical transmission, whose 12th gear is a 0.78 to 1 "super" overdrive while 11th gear is 1 to 1 direct, said Volvo’s product manager for drivetrains, John Moore. Axle ratios are 2.64 to 1 with a D11 diesel and 2.47 with a D13. The other factor in driveline gearing is tire and wheel size, and two demo tractors ran on popular 22.5-inchers.

A sensor in the tandem’s air-ride suspension tells the I-Shift's electronic controls that the load on the rear axles, and therefore in the entire trailer, is heavy enough to lock out the top gear. Once on the highway, the tractor then runs with the gearbox in 11th-direct, where the engine is better able to pull the load and the transmission doesn’t waste fuel “hunting” for the better gear as terrain and headwinds change. Overdrive is never used, even if the driver tries to force an upshift.

The “load trigger” points vary with the two engines, Moore explained. For a D11-powered tractor with the slower (numerically higher) ratio, the factory-set threshold is 68,000 pounds gross combination weight, or a king pin load of about 19,800 pounds. For a D13-engined tractor with the faster (numerically lower) ratio, the load point is 55,000 pounds GCW with an estimated king pin load of 14,000 pounds.

The VNL demos included a D13-powered sleeper-cab hitched to a flatbed stacked with concrete blocks. I drove it first, and noted that its I-Shift  did as Moore described: At a 65-mph cruising speed on nearby Interstate 81, the I-Shift stayed in 11th-direct with the engine revving at 1,370 rpm, and thumbing the upshift button on the paddle-handle selector had no effect. Locking out overdrive protects the engine from lugging too low under load.

VNL daycab towing an empty flatbed (left) ran in 12th-OD while cruising, but sleepercab with the loaded trailer stayed in 11th-direct. Photo:Tom Berg
VNL daycab towing an empty flatbed (left) ran in 12th-OD while cruising, but sleepercab with the loaded trailer stayed in 11th-direct. Photo:Tom Berg
Driving the second rig, a VNL daycab towing an empty flatbed, showed that Adaptive Gearing’s sensor detected the no-load situation on the tandem and I-Shift’s controls unlocked 12th-OD. It kicked in smoothly in at 65 mph where the engine loafed at 1,069 rpm and 1,151 rpm at 70 mph, according to Moore’s calculations; the tachometer needle, of course, was less precise. The upshift was at a seemingly high road speed because of the 2.64 axle ratio, which allows the engine to downspeed whether in 11th or 12th gear.

I-Shift will downshift as needed, or as road speed drops; as we drifted onto an exit ramp from I-81, engine revs fell way down to 800 before the tranny went to 11th, and further down as I braked for a stop sign. I-Shift automatically downshifts to raise revs and take advantage of the engine brake, and does so aggressively if the engine brake’s control stalk is pulled all the way down. Under power, comparatively high torque courses through the driveline, which is accordingly beefed up. With dual-torque engine ratings, torque is cut by 200 rpm in the lower seven ratios.

With an XE-only spec and 22.5-inch rubber, the axle ratio would also be 2.64 and the engine cruises at a still-low 1,150 rpm at 65 mph. This allows up- and downshifting between 11th and 12th, said Moore. Compared to XE only, Adaptive Gearing can save up to 1% in fuel while running in 11th-direct and 2.75% while in 12th-overdrive.

The best application for Adaptive Gearing is bulk materials hauling where flatbeds and dry or liquid tankers consistently go out loaded and return home empty, Moore said. This best uses the direct-drive/overdrive capability. It’s especially good when encountering headwinds. Freight hauling in vans or reefers is not a proper application if most miles are loaded.

XE-Adaptive Gearing will be optional in January in VNL and VNM models, and only with Volvo D11 and D13 engines mated to an I-Shift. It’ll be approved for gross combination weights of up to 80,000 pounds. 

 

Comments

  1. 1. Fred [ November 07, 2014 @ 04:30AM ]

    Interesting article and concept. Nothing new or newsworthy though. We did this in the 70's with 13 speeds, 12th direct loaded, 13th .87 OD empty. Really not a new concept at all. In the 80's Ryder and Penske both had Eaton build 9 speeds with a short OD, .85 and .83 respectively.

  2. 2. Phil Leopold [ November 07, 2014 @ 06:51AM ]

    The I-Shift with adaptive gearing may not be a new concept but with Volv's I Shift doing the thinking it is really new adaption. Good work Volvo!

  3. 3. Cliff Downing [ November 08, 2014 @ 10:08AM ]

    This concept is good on its face, but the spread is too big. Instead of .78 it should be .86, for roughly a 200 - 250 RPM spread with those tall rear ratios. They do all of their testing on interstate, multi lane type roads and take little into account for two lane, hilly terrain that many pulling bulk loads have to deal with on top of regular freeways. I do this already using 2.64 and an 18 speed. I use direct for the regular haul and can go into .86 over when empty. Until Volvo decides to use .86 on the over, it is no sale.

  4. 4. Gary Dean [ November 12, 2014 @ 10:51AM ]

    Go back to two sticks (5&4), and teach these new drivers how to actually drive a truck. The way I read these articles, a monkey will soon be the top driver.

  5. 5. Dennis [ November 26, 2014 @ 10:04AM ]

    Cliff, .86 vs .78 top gear should not be a deal breaker.

    Which model 18 are you running? I'll assume direct on your 18, where you run loaded, is 7H, and you get the .86 empty in 8L, and 8H at .73 is too tall to run at all with your 2.64 rears. Is this correct?

    Why not run 3.11 rears and use high gear to get the same cruise RPM?

    It seems the only advantage to your gearing on your 18 would be your setup could let you drop one gear when loaded by just moving the thumb. For what it's worth, the iShift can drop a gear from any gear by just moving a thumb.

    The iShift internally is a 2x3x2 where all 12 possible ratios are used. An 18 internally is a 2x5x2 where two of the 20 available ratios are unusable by design, and are near duplicates of usable ratios.

    By using just three speeds in the main section, Volvo can put three very thick gears in about the same space that others cram five thinner gears. This allows the iShift to pass 2350 ft-lbs of input torque with only one countershaft. The iShift weighs less than 600 lbs, where an 18 is closer to 1000 lbs, an important factor for many bulk haulers. A single countershaft design also has less internal friction than twin-countershaft designs.

    A .86 split is very impractical on a 12 speed. This split would be far from half way between the main section gears, requiring much higher engine RPM before the even to odd upshifts. Assuming equal gear spacing 1st thru 12th where 11th is direct, then in theory, if Volvo would move the lower two ratios of the iShift three speed main section up to accomplish a .86 split, then 1st gear ratio would be around 4.52 instead of the more practical 11.73 it is now. (.86 divided by .86 eleven times, once for each downshift, would put first gear at 4.52. Do the math again with a .78 split, .782 may be more precise, and the result is a much more reasonable 1st gear ratio).

 

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