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Terex focuses on productivity with articulated dump truck

Diesel Progress North American Edition,  August, 1999  

The Terex Corp. is a $1.2 billion, diversified global equipment manufacturer based in Westport, Conn. The company is involved in a broad range of construction and mining-related capital equipment operating in two segments - Terex Earthmoving and Terex Lifting.

Terex Earthmoving manufactures and sells heavy-duty off-road trucks and high-capacity surface mining trucks under the brand names of Terex, Unit Rig and Payhauler, as well as large hydraulic mining shovels under the recently acquired brand name O&K. Terex Lifting manufactures and sells telescopic mobile cranes, aerial work platforms, utility aerial devices, telescopic material handlers and truck-mounted cranes, and related products, under the brand names Terex, Lorain, PPM, P&H, Marklift, Koehring, Bendini, Simon, RO, Telelect, square Shooter, Holland Lift and American Crane.

Although Terex has been building off-highway trucks at its U.K. plant in Motherwell, Scotland, for more than 40 years, it is a relative newcomer to the articulated dump truck (ADT) market, having built its first ADT, the 25-ton 32-04, in 1983. Nevertheless, the last 15 years have seen the company become one of the world's leading suppliers of articulated dump trucks.

Terex's ADT product line comprises four models with payloads from 25 to 40 tons, each model having a rugged design chassis and an all-welded dump body fabricated in high strength steel. The vehicles are powered by fuel efficient design, turbo/intercooled Cummins or Detroit Diesel engines built to meet all current regulations for noise and exhaust emissions. The engines drive 6 x 6 drive-lines via ZF powershift transmissions.

Depending on the model, axles are supplied by ZF or Dana Spicer. The Terex ADT range is expanded by special versions for forestry, coal and waste handling, and models developed to high-performance military specifications.

In the off-highway truck market where Terex's four ADT models compete, articulated trucks account for more than 70 percent of all sales below 55 tons. The growing acceptance of the ADT has led to increasing competition for sales of around 5000 units per year, particularly in the 22 to 27.5 ton sector, according to John Rotherford, the company's sales and marketing director.

"The 22 to 27.5 ton sector accounts for around 40 percent of all ADT sales and demands a very competitive overall package," Rotherford says. "Everything has to be just right - including the price, performance and reliability - but also operator comfort and delivery. We are, therefore, always looking for ways to improve our product offering in this sector."

This point is illustrated by the company's decision to replace its popular 25-ton payload 2566C ADT with the model TA25. The TA25 features a 25-ton payload with heaped capacity of 15 cu.yd. It boasts a refined design, quiet, ROPS/FOPS cab engineered to provide excellent operator comfort, an attribute backed by the high power, high torque, emissions-certified engine; electronic transmission control; and automatic limited-slip axle differentials.

The launch of the TA25 also coincided with several other announcements, including a new price structure and a three-year/5000-hour warranty for Terex ADTs. The line is also expected to benefit from a decision to introduce new product designations and a new white and grey color schemeinstead of the well-known all-green livery.

"We introduced the new livery and designations to increase the brand awareness of the Terex product line," continued Rotherford. "The new prices and warranty are a result of the improved design and production methods that have helped to improve our product quality and lower our manufacturing costs."

While Rotherford is confident that the new prices and warranty will increase the competitiveness of the Terex package, he is quick to highlight the benefits of the TA25's new design features, notably the new ZF transmission. Terex's tests have shown that the new transmission makes the TA25 much more productive.

Replacing the ZF 6WG 200 transmission used in the 2566C machine is the 6WG 210 unit from ZF's new Ergopower range of electronically controlled automatic powershifts. The new transmission is coupled to a Cummins 8.3 L, in-line, six-cylinder 6CTA8.3-C diesel engine rated 275 hp at 2000 rpm and a maximum torque of 828 lb.ft. at 1300 rpm - increases of 8 percent in power and 10 percent in torque over the 2566C ADT.

To attenuate both noise emissions and gaseous emissions via reduced fuel consumption, a modulating cooling fan that operates only when needed is fitted.

The 6WG 210 transmission consists of a torque converter close-coupled to a countershaft gearbox with integral output transfer gearing. Kick-down and manual override features are included, as is a torque proportioning output differential that transmits drive permanently to all axles and may be locked in difficult traction conditions. Six forward gears in a 5.56 to 0.61 ratio range give maximum vehicle speeds of 2 to 50 mph. Three reverse gears in a 5.56 to 0.94 ratio range give ground speeds of 2 to 31 mph.

The TA25's axles feature fully floating shafts and outboard planetary reduction gears. Differential couplings between the axles are intended to prevent windup. Each axle has an automatic limited-slip differential, and the leading rear axle has a through-drive differential to drive to the rearmost axle. Differential and transmission output differential are locked simultaneously via a single switch, with automatic locking when reverse gear is selected. The differential ratio is 3.44:1 and the planetary reduction ratio 6.35:1, resulting in a 21.85 overall drivetrain reduction. This arrangement is designed to provide the TA25 with higher rimpull in the lower gears, faster acceleration times and a higher top speed for improved haul road performance and increased productivity.

A key feature of the new transmission is ZF's Ergocontrol electronic transmission control. This is connected to a ZF EST-37 electronic control unit that provides fully automatic gear selection for optimum driveline efficiency by matching gear ratios and shift points to engine speed and load conditions. Ergocontrol is designed to provide smooth, shock-free gear changes by monitoring the transmission to ensure the specified shift curve is maintained and readjusting the shift pressure to the clutch packs as needed.

The TA25's new ZF transmission also gives lower noise levels as a result of new high contact, helical cut gears, shorter and stiffer gear shafts, and a new sound-absorbent transmission housing, Terex notes. Serviceability is improved by a new advanced diagnostic system that allows an engineer to identify the source of transmission faults.

On the hydraulics side, the TA25 ADT features one engine driven gear pump for the hydraulic steering cylinders, one ground driven gear pump for secondary steering pressure in the event of engine failure, and one transmission PTO-powered gear pump feeding the single-stage, double-acting hoist cylinders.

The vehicle's pivot-steer system gives 45 [degrees] of movement to either side with lock-to-lock requiring four wheel turns. Working pressure is 2500 psi. The hoist is joystick controlled, with raise time quoted as 13 seconds loaded and power-down time nine seconds.

The front pivot axle has vertical travel of 5 in. and is supported on flexible air bellows and damped by four heavy-duty design hydraulic absorbers. The rear pivot axles are joined by interaxle balance beams to equalize load and coupled to the frame by three rubber-bushed links with lateral restraint by a transverse link. They have vertical travel of [+ or -] 130 mm and oscillation of [+ or -] 12 [degrees].

The TA 25's braking system comprises air-assisted hydraulic dry discs on each wheel with single calipers and split circuits for the front and rear wheels. The parking brake is a spring-applied/air-released disc on the rear driveline. A secondary brake control actuates service and parking brakes. A guillotine-type engine exhaust brake is standard and designed to operate automatically if the engine approaches overspeed.

To determine the benefits of the new engine and transmission package, Terex and ZF put the TA25 through a three-day test program on a Scottish open cast coal site. The program also involved a Terex 2566C.

The first test involved the trucks working (carrying rated payloads and operating at 100 percent efficiency) over a one-way distance of 350 yd. on a haul road with nominal grade resistance and low to medium rolling resistance. The TA25 outproduced the 2566C by an average 10 percent, achieving a production rate of 475 t/h, Terex said.

Further analysis of the results showed that the TA25 performance advantage came from a 6 to 24 percent higher average speed than the 2566C, according to the company. The TA25 was particularly impressive over the softer, more heavily rutted haul road in the loading area as it pulled away from the excavator fully laden. This advantage was due to the increased rimpull and improved shift arrangement provided by the new transmission. It also demonstrated the much improved acceleration due to Ergopower 6 WG 210's more evenly spaced ratios.

A second performance test compared each truck's acceleration with a full load on a well-maintained haul road. The TA25 completed the 165 yd. course in 28 seconds from a standing start at an average speed of 12 mph, almost 20 percent higher than the 2566C.

Overall, the test results proved that the new engine/transmission package gives the TA25 a clear productivity advantage over the 2566C. "The ZF Ergopower transmission makes the TA25 much more productive than the 2566C," says Rotherford. "It also makes our new ADT more efficient, simpler to operate, more reliable and easier to maintain."

Rotherford's views are shared by ZF's Off-Road Driveline Technology and Axle Systems Division at Passau, Germany. "Our engineers worked very closely with Terex in the development of the TA25 and are very pleased with the results," said Alfred Schobinger, vice president of construction equipment transmission at Passau.