Tech Briefs
Test-rig automation

Intelligent MODULAR-4 PC boards. GIF's Research & Development center in Alsdorf. Test track section with 30° cambered bend. The acoustic roller test rig.

In the automotive industry, innovative drive concepts and upgraded efficiency systems have to be brought to mass-production maturity against ever-tighter deadlines. The relocation of expensive and time-consuming test drives onto stationary test rigs is a logical consequence of this trend. One of the crucial considerations in test-rig automation is optimized interaction of the hardware and software. For example, not only must large volumes of data be acquired at high speed, but also numerous parameters have to be controlled simultaneously in real time.

The GIF (an acronym for Aachen, Germany-based Industrial Research Association) operates a total of 72 drivetrain and component test rigs in Aachen, and since 1997 in a new R & D center at nearby Alsdorf, with another to open shortly in Wolfsburg. The facility in Alsdorf, on a site measuring 75,000 m² (807,300 ft²), accommodates not only numerous company buildings but also a 1-km (0.6-mi) test route, including inclines, turning loops with bend cambers, and an acoustic measurement section. Extensive visual screening and soundproofing guarantee maximized secrecy so that trial runs of highly secret prototypes can be held.

While complete vehicles are tested on the roller test rigs, the drivetrain test rigs, for example, investigate only engines and transmissions. The more powerful engines, with higher starting torques from low speeds, and new types of material introduce new, untested influences on vibration characteristics and noise emissions. This necessitates intensive studies of the entire drivetrain.

The engineering that underpins the overall test-rig operation is complex and elaborate. Besides test rigs with air-conditioned control rooms, there are extensive supply systems for ventilation, compressed air, and exhaust gas removal. Four-quadrant electric machines with a high dynamic response are used to simulate resistances to vehicular motion. The vehicle's mass can be simulated entirely by the electrical torque or speed-controlled machines or by means of mechanical rotating masses. With a rise time of approximately 20 ms, any conceivable dynamic operating state can be set. Dry-type transformers power the machines, with separate transformers supplying the measuring and in-house networks. The company has its own cooling towers for water. If necessary, air blowers simulate the cooling effect of the air during vehicular motion. For cold-temperature tests, cooling cells can be lowered over the test rigs, creating temperatures as low as -30°C (-22°F).

Each test rig has its own control cubicle, where all the measuring and control cables come together. For the high dynamic-response instrumentation and control operations, industrial PCs are fitted with intelligent expansion cards from the MODULAR-4/486 series of SORCUS Computer GmbH Heidelberg, Germany. The plug-in cards are complete single-board computers with processors from the 486 or 586 generations, cache memories, arithmetical processors, up to 4 MB of static CMOS-RAM, interrupt controllers, timers, two RS-232 interfaces, watchdogs, etc., on one PC card. The OsX operating system accommodated in the EPROM has multi-tasking capability, and has been optimized for handling real-time jobs; up to 1024 tasks can run in parallel.

One important feature for interfacing with the process are the four free module slots on each card, which users can fill with interfaces of their choice. The range of modules available extends from analog and digital input/output (I/O) and serial interfaces of the RS-232/-422/-485 types, plus fieldbus links for PROFIBUS, CAN, etc. all the way to function modules with counters or incremental encoder interfaces. If necessary, the basic card is expanded using a module extender to incorporate five more module slots, thus providing a total of nine slots.

PC cards from SORCUS provide a flexible concept adopted for interface design. Whereas GIF at first managed with four interface modules on the basic card, the complexity of the test rigs has increased so much over the years that the module extender is now standard equipment. Thus one test-rig computer possesses 48 analog input channels, eight PID-controlled analog output channels, 64 digital I/O channels, and six 16-bit counter channels for period measurements. All channels have signal conditioning and are electrically isolated.

For each test rig, there are up to three industrial PCs in a 19-in rack. With the combination of industrial PCs plus intelligent plug-in cards, the GIF provides a sensible division of labor between host computers and the real-time-capability subsystems. While the MODULAR-4 card looks after I/O tasks and is responsible for high-speed control operations, the actual PCs handle the operator control, archival, and visualization software. PDES software was developed specifically for the automation system. GIF engineers have tailored PDES specifically to the SORCUS hardware. All measuring channels and computed variables can be displayed online in user-configurable text and graphics layouts. For limit-value monitoring, measuring points and computed variables can be defined as alarm points. If preset values are exceeded, the system will automatically shut down the test rig. Complex measuring tasks can be user-programmed in the form of a sequential control. Alternatively, real-time data entry provides an option for rerunning motion profiles recorded in the vehicle directly on the test rig.

The challenge for the test rig's hardware and software lies in coping with a large number of real-time processes running in parallel, which would otherwise require more expensive VME/VXI bus hardware. The automation system is responsible not only for data acquisition and control, recording, and data archival at regular intervals, but also for a permanent data ring memory. After a safety shutdown or damage to the system, the data ring memory enables a post-mortem analysis to be performed to determine the precise causes of the fault, and to investigate the factors involved.

A proprietary programming system is unnecessary for real-time programming of the MODULAR-4 cards under OsX. For this purpose the usual standard development environments from Borland under DOS or Windows is used. Libraries for the current high-level languages C, Visual-Basic, and Pascal, including Delphi, are available for DOS and Windows.

Jean L. Broge