Machine Design

Software simulates many disciplines in one model

Large off-road vehicles are made of many subsystems such as mechanical devices in the driveline, thermodynamic systems in the radiator, electrical and hydraulic components, as well as digital controls. Until recently, simulating complex products meant working on individual systems and hoping they functioned properly in the physical prototype.

An older version of a Caterpillar rear suspension, axle, transmission, and driveshaft appear in the upper left. The design uses a single bearing at the peak of the A frame. Simulations in Dynasty showed the bearing undersized for a 360-ton payload. The redesign for the company's largest mining truck shows the four alternative bearing links.
Dynasty software lets Caterpillar engineers take new vehicles for test rides long before physical prototypes are available. Taking sharp turns lets user see, for example, whether or not there is sufficient room for wheel dynamics and how the dump body shifts in turns.
Dynasty software, working with another Caterpillar developed program (Rocks3D -- it models the behavior of a loose load such as the 20,000 rocks in this image), animated the 797B as it traverses a set of potholes with a 20,000-lb payload.

The recently available Dynasty software simplifies the task of working with many subsystems by painting a comprehensive picture of what is happening in each as well as predicting the overall machine performance.

Dynasty lets users focus on performance modeling, not the underlying math and physics. Users build schematic machines by dragging and dropping components and connecting them together. The software comes with more than 230 components such as engines, controls, electronics, fluids, linkages, body structures, and drivelines. Users can also create and reuse their own components.

After building a model, the program converts components and associated design and performance data to symbolic equations. The application optimizes the equations for rapid simulation.

Users get point-and-click access to simulation results without having to predefine sensors at particular locations, a must for some dynamic-simulation programs. Results are tabulated, plotted, and viewed as 3D animations. They can also be exported to other programs such as Matlab for control studies or Nastran for stress results. In the later case, Dynasty lets user place virtual strain gages on parts. The deformations they record can be sent to FEA programs such as Nastran or Ideas. This lets users sample operating conditions of components as diverse as fuel pumps and cooling systems.

The software also provides dynamic structural stress-and-strain predictions of fuel injectors and fuel-system pumps, analysis of cooling systems, and development and validation of the control systems.Another plus for the software is that it lets users see complex designs as coupled systems rather than disconnected problems. Dynasty shows how components or subsystem-level changes affect overall machine performance. The software is also useful diagnosing, and responding to customer-equipment problems.

Engineers at Caterpillar Inc. developed the simulation software and used it to design the 797B mining truck, the company's largest piece of equipment. The truck went from concept to production in roughly in half the time it would have taken if working only with a large physical prototype.

The size and cost of building the 797B meant trial-and-error approaches would not work on components affecting the truck's ride, stability, and structural integrity. Dynasty helped users optimize the performance of the 797's subsystems, such as the 24-cylinder engine, transmission, torque converter, and suspension before the prototype.

In the 797 program, we imported the truck's CAD geometry, along with mass and stiffness data, to represent the frame, suspension, and dump body. These flexible bodies were connected to other mechanical and hydraulic-system components to develop a more detailed model.

Simulations indicated that we needed to change the rear suspension. Previous mining trucks use an A-frame attached with a single joint at the tip of the frame, where the axle and chassis connect. The software indicated that one bearing large enough to handle stresses from the 360-ton payload would not fit within the space available. After simulating several alternatives, engineers designed a four-link frame that better balances chassis loads. Distributing loads to four bearings also reduced driveshaft angles and improved drive-train efficiency.

Most engineers can use the software after a 4-hr introductory class. Advanced, discipline-specific classes are also available. Comprehensive documentation covers the underlying physics of components. The system runs on Windows 2000 (with at least 128-Mbytes RAM and 175 Mbytes on the hard drive) or on HP-UX 10.2 or 11.0 and a HP workstation with a PA-Risc V2.0 and similar RAM and disk space. Dynasty also requires C or Fortran compilers.

Dynasty comes from Caterpillar Inc., (309) 675-5919, [email protected]
-- Patrick Ormistron

Patrick Ormistron is a product-design engineer at Caterpillar, a manufacturer of construction, mining, and forestry equipment in Peoria, Ill.

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