Driving Cat's CX Automatic
Its smooth operation shows, and ruggedness is likely, because the transmissions are based on those from earth-moving trucks.
Tom Berg
Equipment Editor
Caterpillar's entry into the automatic transmission business, announced at trade shows earlier this year, surprised many folks in this industry, but maybe it shouldn't have.
After all, the Peoria-based corporation's primary occupation is building earth-moving machinery, and they all have Cat's own automatic transmissions. Why not adapt one or two of those to on-highway trucks?
That's the genesis of the new CX series, which is based on TH powershift automatics made for Cat's 700 series articulated off-road haul trucks. CX means Caterpillar Transmission, and there'll be two models: a CX31 six-speed, for engines producing as much as 500 hp and 1,650 lbs.-ft. of torque, and a CX35 eight-speed, for engines making as much as 625 hp and 2,050 lbs.-ft. The 31 and 35 in the designations describe the diameters of each unit's clutches in centimeters (equivalent to 12.2 and 13.8 inches, respectively).
CXs will be for on/off-highway heavy trucks working in construction, trash hauling and other severe-service work. They're not meant for highway-only vehicles, though some might find their way into heavy P&D trucks and tractors. There are no plans to scale down the TH products to medium-duty size, although Cat executives have discussed it. The CXs will be available early next year.
Cat people figure they're jumping into the market at the right time. Automatics go into more than half of all new medium-duty trucks and about 10% of heavies. The heavy duty business is growing as truck owners become aware of operating advantages over manuals - easy operation and therefore easy training of neophyte drivers; quicker trip times and higher productivity; reduced maintenance; and sometimes better fuel economy.
The Allison Transmission Division of General Motors pioneered this business and was alone in it for decades. But in recent years, automated mechanical transmissions, or AMTs, from Eaton and ZF Meritor have been making inroads.
AMTs offer many of the same benefits, and while Allison people feel their full automatics are superior, they've responded with substantial price cuts. Cat's fully automatic CX31 six-speed will compete directly with Allison's 4000 RDS, and the CX35 eight-speed will go up against Eaton's 18-speed AutoShift, but prices may or may not be affected.
Like the off-road Cat THs, the CXs 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 a CX to run as well on-highway as off-road.
Side- and rear-mount power take-off points will be available. The CX's rear PTO can transmit up to 300 hp, about double that handled by a typical side-mount, said Larry Riekert, the product's sales and marketing manager. 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 10 o'clock or 2 o'clock. 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.
My experience was with a CX31 installed in an '05 Kenworth T800 dumper set up with the specs used by a local fleet, which included a 435-hp/1,550-lbs.-ft. Cat C15. Riekert and Bob Keene, a Cat Engine customer satisfaction manager, said 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 Cat'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 to give the tranny a bit of a workout and feel it up- and downshift.
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 slow until engine speed climbs to 1,500 rpms. 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 versus 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 happened only once, and is not surprising for a prototype unit. It'll no doubt be taken care of as engineers fine-tune the CX's mechanical and electronic components.
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 powertrain 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 to 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 braking was reassuring.
This C15-CX31 combination is typical of how Caterpillar will initially sell the transmissions: as Cat-Cat packages, though probably with more C11s and C13s, which are popular in vocational trucks. Ruggedness should be a given because the TH series has an excellent durability record, Riekert says. 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 Cat'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, and a few to civilians, for use in Class 8 road tractors. These were not overly successful, and Cat eased out of the business. But the CX series should be another story entirely.
