CX Automatic: A Smooth Operator

Sept. 28, 2010


An all-yellow team of a C15 (above) or C13 (top) diesel and CX31 transmission is typical of how Caterpillar will initially sell its new automatics starting early next year. Later, they'll be offered as stand-alone products to work with other builders' diesels.
A Kenworth T800 10-wheel dumper is the test bed for continued CX development. This truck has the six-speed version mated to a 435-hp C15.
The gear selector is like that for an Allison, with R, N and D being a driver's main choices. Downshifts can be prompted with the down-arrow button.
A prototype CX31 on a test truck still has the off-road version's iron case. Production units will have lightweight aluminum cases.

What's this — an on-road automatic transmission from Caterpillar? Many folks in the trucking business were surprised when the engine and equipment builder made its low-key announcement earlier this year that it was getting into the vocational-truck transmission market with what it calls the CX series.

Folks familiar with Cat's machinery side probably said, "Oh, sure," because they know about the TH powershift automatics built for Cat's 700 series articulated off-road haul trucks. The TH automatics form the basis for the new CXs, which will come in six- and eight-speed models for heavy trucks working in construction, trash hauling and other severe-service work. The six-speed will compete directly with the well-known Allison 4000 RDS heavy-duty automatic, and drive like it.

"Only smoother," say Cat executives, and they could be right, though my limited experience with a prototype CX six-speed in a Kenworth 10-wheel dump truck would make me call it a draw. I'd probably have to drive Cat- and Allison-equipped trucks back to back to discern a difference in smoothness. More on that in a bit.

Caterpillar executives figure they're jumping into the market at the right time. Automatics go into more than half of all new medium-duty trucks — a segment Cat won't enter for now — and about 10 percent of heavies, but that's growing as truck owners become aware of operating advantages. The Allison Transmission Division of General Motors had this business almost to itself for decades, but that has changed, too.

In recent years, competition has come from automated mechanical transmissions made by Eaton, with its AutoShift and UltraShift; and from ZF Friedrichshafen AG, with its FreedomLine, marketed by ArvinMeritor. The ZF product is not for vocational products, but AutoShifts have gone into some construction trucks as well as thousands of highway tractors. Allison has responded by significantly cutting its prices. Obviously, Cat's CX full automatics will provide more competition, though prices may or may not be affected.

The CXs are much the same as the THs, and use a lock-up torque converter, wet clutches, planetary gear sets, and exterior-mounted solenoids. The solenoids can be serviced or changed without dropping the transmission's oil pan. Weight was cut by fashioning an aluminum case to replace the original iron case. And modified software in the electronic controls enables the CX to run as well on-highway as off-road.

A rear power take-off point was designed into the CX because customers want more power to run equipment, said Larry Riekert, the product's sales and marketing manager. The CX's PTO can transmit up to 300 horsepower, about double the power handled by a typical side-mounted PTO. The CX's rear PTO mount is at a 5 o'clock position, just to the right of its main output shaft, where a coupling to a gearbox or pump is easy to hook up.

Also, a failing PTO box will not dump broken pieces into the transmission, as sometimes happens when it's mounted on the side of the case at a 10 o'clock or 2 o'clock. But side-mount plates in those positions will still be available for customers who want them.

"CX" means Caterpillar Transmission, and it will come in two models: a CX31 six-speed, for engines producing as much as 500 horsepower and 1,650 pounds-feet of torque; and a CX35 eight-speed, for engines making as much as 625 horsepower and 2,050 pounds-feet. With a rear-mount PTO, they'll weigh 925 and 1,125 pounds, respectively. The 31 and 35 in the designations describe the diameters of each unit's clutches in centimeters.

The CX31 will compete with Allison's 4000 Rugged Duty Series, whose top capacity now is 550 horsepower and 1,590 pounds-feet. Allison doesn't presently offer anything stronger for the on-road market now, so the heavier-duty CX35's competition will be from Eaton's 18-speed automated mechanical products.

In general, Cat's CX series will provide another choice for those who believe, or are discovering, the benefits of automatic transmissions — easy operation, greatly reduced driver training, less drive-train maintenance, quicker trip times and sometimes better fuel economy. Compared to any manual transmission, an automatic is a breeze to drive. It leaves the driver free to concentrate on traffic and delivering the load, then lets him or her return quickly to get another.

The "her" is important, for fleet managers running Allisons and AutoShifts find they can easily hire women to fill their ranks. Women have no problem with the size and weight of trucks, but handling a complex manual transmission is more than many of them want to deal with. The same goes for many men. An automatic removes that barrier and about doubles the labor pool for any fleet.

This Cat CX31 was installed in an '05 Kenworth T800 dumper set up with the specs used by a local fleet, which included a 435-hp/1,550-pounds-foot Cat C15, explained Riekert and Bob Keene, a Cat Engine customer satisfaction manager. A prototype CX31 replaced a manual transmission, and Cat engineers and technicians have since used the truck in their testing.

"He's also used it in his regular operations," Keene said of the customer and the truck, "and now it's hard to get it from him when we need it. The drivers don't want to give it up because it's so nice to drive."

And it is. My drive was on and near the premises of Caterpillar's engine manufacturing complex at Mossville, Ill., north of Peoria. Riekert pointed out the Allison-like push-button selector to the right of the driver's seat. I cranked over the engine, released the parking brakes, punched D for Drive, pushed the accelerator and off we went. He rode shotgun as I scooted around the parking lot and over access roads, stopping and starting frequently.

One thing I noticed almost immediately was lively acceleration right from a dead stop. An Allison, on the other hand, tends to be a little sluggish until engine speed climbs to 1,500 rpm. I thought that maybe the CX31's 1st gear was steeper, but Riekert said no, it's slightly faster than a comparable Allison's — 4.40 vs. 4.70. Perhaps the Cat electronic controls on engine and transmission "talk" so well that response is better.

Gear changes at all speeds were smooth and appropriate for each situation. One exception was a slightly crunchy downshift to 1st as I rolled through a Yield sign and mashed the accelerator. It never happened again, though.

I also took the truck out onto nearby highways where 55 and 65 mph were legal. The dump bed had a moderate load of dirt to smooth the ride and give the power train a slight workout. The gutsy C15 propelled us to cruising speeds quickly, and overall gearing allowed a 65-mph pace at an indicated engine speed of 1,500 rpm. Like an Allison, the CX31's 4th gear is a 1:1 direct, while 5th and 6th are overdrives (on the eight-speed CX35, 6th is direct while 7th and 8th are overdrives).

On off-ramps I prompted downshifts through the selector, going from 6th to 5th to 4th, to make use of the engine brake. Each time the gear change was smooth and the retarding was reassuring.

This C15-CX31 combination is typical of how Caterpillar will initially sell the transmissions when they become available early next year: as Cat-Cat packages. As suggested by my experience, performance should be excellent, while service for both engine and transmission will be handled at any Cat dealer. Later, CXs will be offered as stand-alone products to work with other diesels, using a J1939 data link for communications.

By the way, this is not Caterpillar's first foray into on-highway transmissions. Back in the 1970s, it sold thousands of 16-speed semi-automatic gearboxes to the U.S. military for use in Class 8 road tractors. These were not completely successful, and Cat eased out of the business. But the CX series should be another story entirely.