Hardened test modules upgrade transmission development

A fully instrumented pallet is connected to a transmission test stand at GM’s Ypsilanti, MI, transmission development center. Smart pallets equipped with IP-65 hardened test modules have reduced idle time at the test stand from 8 to 10 hrs per test to less than 1 hr.

Working with HBM, the company solved the throughput problem by using a fleet of "smart pallets." Rather than tie up the single test stand for instrumenting and de-instrumenting on line—a process that can take several days—the GM staff now makes all the pre-connections offline.

The pallets on wheels contain the transmission and all the electronic test instrumentation. With everything prewired, the engineers wheel the pallet into place, lock it down, and make just five connections—power, signal, hydraulic in, hydraulic out, and mechanical—and start collecting data within minutes.

The palletizing scheme, which was put into operation in late 2004, should help the engineers increase testing throughput and density and quality of data, by possibly 10 to 1. Collecting more and better data allows GM to rely more on computer modeling and finite element analysis (FEA) for design and to dispense with destructive testing.

We created 20 smart pallets in a variety of sizes to match transmissions for everything from compacts to Corvettes to pickups and SUVs. Each pallet also has a fixture to lock the trannie in place, and each has a processor module on board. Depending on the test, other modules are daisy-chained so that only one signal lead, rather than 20–50, needs to be connected at the test stand. The other modules variously handle temperature, speed and torque, pressure, and acceleration. Each pallet is equipped with MGCsplit data-acquisition modules. Hardened to IP-65 standards, the MGCsplit modules survive next to hot, gritty transmissions.

The purpose of the testing program is solely transmission development. Engineers assess performance of entire new transmissions or new components in an existing transmission, whose characteristics are known. GM also runs accelerated life testing on new designs and components to ensure reliability and reduce warranty exposure. For that reason, the test protocols monitor speed, temperature, pressure, and torque in all cases, and they may also monitor other parameters depending on the circumstances.

An actual test may take anywhere from 15 min to several weeks. For each test, a team of test engineers assembles the necessary instrumentation package, installs the instruments on the pallets, and connects them to the processor module. Then, they mount the sensors on the transmission, 20 to 50 depending on the test, make all the connections, and check everything out. Such instrumenting may take from 6 to 20 hrs.

If a problem arises, pre-test checkout and troubleshooting can take up to 50 hrs. The difference now is that the test stand can be running another transmission while the problem job is dealt with offline. And since the pallets are essentially "random access," GM test engineers can vary the queue order for the test stand at any time.

The electronics inside includes 24-bit analog-to-digital converters on each channel for superior resolution and 19.2-kHz sampling rates for simultaneous measurement. Effective analog resolution is 20 bits. Precision is selectable from 0.0025% to 0.1% of full scale. The IP-65 hardened modules support all mainstream transducers and testing software and are compatible with USB, Ethernet, RS-232C, CANbus, and ProfibusDP.

Each of the modules is a complete, self-contained analyzer, with built-in intelligent data-reduction capability, and each can perform simultaneous output to a hard disk and an external PC. Modules can be connected daisy-chain fashion via a single cable.

Despite the higher performance capability, the cost of this testing system is comparable with other available systems. The cost advantage increases with the number of modules and channels in the total data-acquisition package.

In fact, GM standardized on this module as much for the higher speed and wide operating range as for its hardened enclosure. The company's engineers can select data-acquisition rates from 20 to 19,200 Hz per channel with the touch of a button. With older modules, they often had to reset signal conditioning every time they wanted to vary the data-acquisition rate.

Regardless of test complexity or the number of I/Os involved, electronic installation at the test stand is always the same: 2–3 min to make one signal and one power connection. Mechanical and hydraulic connections take another 25–30 min.

Turnarounds at the test stand run less than 1 hr, vs. 8–10 before. GM is now making greater use of its test stand, as the stand does not need to sit idle while engineers set up the instrumentation and perform troubleshooting.