With a capacity of 363 tonnes, Liebherr’s T282B haul truck is one of largest vehicles being produced. Powered by an MTU 20V4000 diesel rated 2722 kW, it was designed to be one of the lightest trucks on the market, with an empty weight advantage of up to 12% over comparable vehicles, according to the company. Much of that can be traced to the use of simulation software from LMS that allowed designers to maintain structural robustness while keeping overall weight down.
There is probably no other type of off-road equipment that has a more grueling life than large mine haul trucks. With load capacities in
excess of 300 tonnes, these behemoths lug iron ore, copper, gold, coal, tar sands, etc., over every type of terrain from boggy flats to spiraling roads that plunge as much as 600 m down into the pit at speeds as high as 64 kph.
Notwithstanding the current downturn, demand for commodities has risen in recent years, prompting mine operators to demand equipment that can help them get precious metals and other materials out of the ground faster and more efficiently. That has led to the growth in size and capacity for the largest haul trucks.
An example is Liebherr Mining Equipment’s flagship T282B diesel-electric haul truck, which the company claims is the largest mining haul truck currently in production. With a load capacity of 363 metric tonnes, the 7.8 m high giant is 15.3 m long, has a wheelbase of 6.6 m
and runs on a set of six 4.0 m tires. It is powered by an MTU 20V4000 diesel rated 2722 kW that is teamed with a Siemens/Liebherr electric drive system. “It’s like driving a two-story house,” said Dr. Vladimir Pokras, analysis and simulation manager for Liebherr Mining Equipment.
For all of the advances in engines,powertrain and structural technology, one of the primary limiting factors in the development of new haul trucks remains tires. Along with their cost, the fact remains that tire size and capacity have proven to be manifestly finite, and in designing new generations of machinery, truck manufacturers must take care that total vehicle weight does not exceed tire capacity. As a result of that, truck manufacturers face the challenge of ensuring vehicle structures remain robust while at the same time trying to shave every kilogram possible from the vehicle structure in favor of greater payload capacity.
Liebherr’s focus led to the T282B truck weighing in at a net weight of 186,880 kg (589,670 kg gross), which is 12% lighter than some competitive vehicles, according to the company. Lighter weight is also a benefit in that lighter trucks use less fuel on their empty return runs and have less tire wear.
Tire wear is also minimized by the
kinematics of the Liebherr dual parallel control arm arrangement and by a differential driving wheel control system that is designed to automatically adjust the torque and speed of the traction motors when turning.
The engineering challenge of integrating advanced features like the differential wheel control system into a lightweight truck strong enough to withstand harsh mining conditions is no easy feat. “Mining trucks are some of the most abused vehicles in the world,” said Pokras. “At many of these mines, operators drive as fast as they can over refrigerator-size boulders and holes as big as bathtubs to haul as many loads as possible.”
Liebherr relied heavily on engineering analysis to design the T282B haul truck to operate efficiently under such heavy-duty conditions. In particular, the company made extensive use of multibody dynamics technology from LMS for full-vehicle simulations that allowed engineers to study the truck’s behavior on various terrains with a variety of load types.
Offering a combination of 1-D and 3D simulation software, testing systems and engineering services, LMS specializes in system dynamics, structural integrity and sound quality to durability, safety and power consumption. The company offers multidomain solutions for thermal, fluid dynamics, electrical and mechanical systems and has operations in Belgium, its headquarters, as well as the U.S., France, Germany, Italy, China, Japan and Korea.
To refine the design of the T28B truck as quickly as possible, multibody simulation models were created up front in the conceptual stage by the analysis and simulation group and modified as more information became available. Initial geometries of major truck parts and assemblies were estimated from preliminary solid models and pieced together as rigid bodies into a first-pass full vehicle multibody model. Then loads from a multibody simulation were generated for the structural group to perform finite element analysis for computing stresses on the frame and other structural components. The mechanical group reused these same loads to design the vehicle hydraulics, suspensions, the powertrain and other systems.
“In this way, LMS multibody dynamics served as a central point where all the designs of individual major components and subsystems came together into a single unified full-vehicle model,” Pokras explained. As component and subsystem designs proceeded, these engineering groups updated their individual solid and finite-element models. The new information was imported into the multibody model where the analysis and simulation group also added greater detail, such as stiffness, damping and mass properties.
“Links with finite-element codes stream lined the iterative process of updating LMS multibody dynamics models,” noted Pokras. “With the ability to quickly enter additional details, we could generate new multibody models much more quickly and with fewer errors than building them from scratch each time. The capability to import finite-element models as flexible bodies in the LMS multibody solution was key to accurate full-vehicle simulation.”
Major structural components throughout the vehicle such as the frame and dump body were modeled as flexible bodies to represent crucial bending and twisting during vehicle operation. The model incorporated more than 70 different joints including rubber mounts, cylindrical and ball bearings, bolted joints, etc.
Analysts also used a wide range of other multibody elements in the detailed vehicle representation. Damping forces of suspension were represented by translational spring-damper-actuator elements. Expression force elements were used to simulate torque for brakes and electric motors, forces for steering and hoist cylinders, and spring forces in suspensions. Rotation stops that limited idler pivoting and dump-body pads were modeled with contact elements. Characteristics of electric motors, hydraulic pumps, oleo-pneumatic struts, tires and other mechanical and electrical components were specified with curve elements.
“The detailed multibody model created with the LMS software predicted vehicle behavior to a reasonable accuracy
for a variety of load cases,” Pokras stated. “The beauty of the approach was that when simulation indicates a potential trouble spot, it was really quite simple to modify the model to investigate other design options.
“In this way, LMS multibody dynamics let us explore alternatives that would be entirely impractical to study with physical mock-ups.”
The multibody dynamics approach was especially helpful in studying many different “what-if” scenarios for the
redesign of an axle box to save weight and allow for easier service accessibility, Pokras added.
After a number of simulation iterations, multibody loads for the final design were entered into LMS durability
software to determine the fatigue life of the critical structural components and assemblies such as the frame and axle box. Tight integration between LMS multibody and durability software enabled fatigue life studies to be performed quickly and accurately, thus providing engineers guidance in the development of lightweight parts to withstand expected operational loads without under or over-designing them. The final step in the development cycle was prototype testing to validate the design before production begins.
“Simulation gives engineers an insight into the behavior and performance of the components, assemblies
and full vehicle that isn’t practical otherwise,” explained James Whitfield, general manager of research and development for Liebherr Mining Equipment. He noted that the role of simulation at Liebherr has shifted from that of a verification tool at the end of design to an up-front development tool that is now totally integrated into day-to-day engineering processes.
www.dieselprogress.com
