Reusable Test Suites Cut Test Development Time

At Yazaki, a designer and manufacturer of automotive electronic control units (ECUs), a standardized test platform based around the HP TS-5400 family of functional test systems has helped achieve a consistent flow of test and evaluation information from design through end-of-line testing. Striving for a seamless flow of reusable test suites has enabled the company to slash its test-development cycle time significantly since it standardized on the test platform.

Yazaki produces body-control ECUs for most of the world’s automakers. Body-control modules typically handle lighting, windshield washers and wipers, door locks, horns, chimes and remote keyless entry.

Yazaki has successfully combined these and other functions into one module, helping to reduce the complexity of new automobiles. One PCB contains the Motorola HC11 microprocessor for all these functions along with its associated circuitry and approximately 200 components (Figure 1).

Body ECU Test Suite

Test-system objectives included using a generic test system that was easily adaptable from program to program across multiple geographic locations. Yazaki wanted to reuse code from module to module and location to location. It also wanted only one learning curve for its testing process. In addition, test engineers wanted an expandable test framework, since the complexity of ECU modules is growing exponentially.

With this in mind, the company selected a standard test platform that is used in its Detroit-based design organization and its companion manufacturing organization, NACOM, in Griffin, GA. The test system offers features tuned for automotive applications, such as switchable loads, sophisticated measurement hardware, and a test development environment with software libraries. These libraries include knock and crank waveforms, inductive fly-back voltage and current analysis routines, and simulation of variable reluctance sensors.

The test executive is HP’s Test Exec SL. It contains a search function that makes it easy to reuse both standard tests provided by HP and new tests developed by Yazaki.

The company has three major testing milestones:

Design validation (DV).

Production verification (PV).

End-of-line testing.

DV and PV include parametric and durability testing. With a standard platform installed in Detroit and Griffin, test routines written at one location can be used at the other site.

DV and PV

Test design runs in parallel to the actual ECU module design. This approach allows full DV and PV tests to be completed concurrently. DV is performed primarily in Detroit; PV is executed largely at NACOM.

Yazaki calls its parametric and functional test suite the Initial Characteristic Checker (ICC). ICC is a system that records parametric data for functional performance evaluations of a single stand-alone module. ICC tests ensure that consistency exists from module to module and that the modules are meeting specifications across all possible conditions of the automotive environment.

During DV testing, data is recorded on more than 100 ECU modules using the built-in datalogging functions of the test executive. For a full battery of I/O tests, this consists of 100 to 200 routines per module. Some of the typical measurements include output state (on/off), operating current, sound pressure on the chimes, timing on the intermittent wiper system, sensitivity to operating voltage, serial communication response, and steering actuator frequency.

The module connects to a series of input switches and to appropriate loads mounted on load cards. These loads can be switched in and out of the circuit.

This is useful for several reasons. First, the tester can measure the output of a device without a load applied, not only to check the state but also to measure leakage current. Second, there often are protection devices such as zener diodes across an output stage, and it is useful to remove the load and inject a current into the output to measure the resulting clamp voltage.

Finally, with a load connected, it is often desirable to measure load current. The load cards have built-in current sense capability on each channel (Figure 2).

With a flexible load strategy, the cards can be easily removed for servicing and exchanged for other load cards needed for testing different modules. The system allows multiple modules of differing functionality to be tested using a single set of common load cards.

Durability Testing

While ICC tests use resistive loads to ferret out design defects such as timing errors and to check overall functionality, durability testing attempts to catch stress-related faults and, as such, typically uses actual loads. The purpose of durability testing is to ensure the module will not fail over the lifetime of the car. For example, 50,000 to 500,000 cycles are executed for typical durability test programs.

To address durability testing needs, the test system was modified to incorporate much of the same hardware and test executive environment used by the ICC. In this situation, the test system records data simultaneously on multiple modules that are in an environmental chamber to track either permanent or intermittent data failures.

The test equipment monitors every cycle by multiplexing a voltmeter to 14 outputs on each of 22 modules using a series of VXI switch cards. The system’s ISO 9141 controller is also multiplexed to all the modules. This allows one serial controller to command all the modules in sequence and then to measure the responses on the respective outputs.

In the past, Yazaki R&D facilities undertook DV tests in isolation from the PV tests conducted at NACOM. With the company’s durability tester running the same software environment as its ICC and with NACOM using the same platform, both organizations enjoy the time-to-market benefits of a single learning curve.

End-of-Line Testing

The manufacturing process relies on end-of-line testing to ensure 100% customer satisfaction. This testing verifies that the ECUs are fit to release to automotive customers.

The end-of-line testing approach differs from the ICC approach where tests are designed to confirm full specification adherence. End-of-line tests rely heavily on DUT-assisted test to check the module as quickly as possible. This test method isolates sections of the DUT by means of the serial communications line.

Instead of applying all inputs, waiting for debounce and settling time of input switching and other analog inputs, serial commands can be sent to the module to cause just one output to change state. Tests can then be performed on just that output without controlling any other input circuits or waiting for the module to get into a testable state. In essence, the module “assists” testing by providing internal routines that appropriate serial commands can access.

The choices of communication protocols vary per automobile manufacturer. Built into the tester is the capability to produce all the standard serial data protocols, including ISO 9141, J1850 and CAN. Today, many cars have a diagnostic bus based on one of these protocols. As more electronics are installed in cars, service centers will use diagnostic tests to locate defective modules.

The end-of-line tester is the same platform as the ICC and durability testers. In this way, ICC, durability and end-of-line testing can be conducted using the same methodology.

Rapid Test Development

The speed and usability of Yazaki’s test system are important to meet the objectives of developing the right tests once and reusing that code in future tests. Test development is shorter because ECU designers use the hundreds of built-in libraries of instrument setup and measurement routines that are standard with the system.

For example, developers can save time by quickly finding and executing a choice of nine configuration actions and six analysis actions for the 20-MHz digitizer, seven setup actions and 10 measurement actions for the dual-channel frequency counter, 11 configuration actions and seven measurement actions for the digital multimeter, and 16 configuration actions for the arbitrary waveform generator. In the past, programmers had to write similar routines themselves and, in most cases, the resulting code was not easy to reuse.

Test executives provide search mechanisms to make these libraries of reusable functions easy to find and select. When the test executive places the selected routine in the test-sequence list, the user simply edits parameters as well as the allowable high and low limits if working on a measurement action. This point-and-click programming approach frees the test developer from writing tedious code (Figure 3).

Leveraging software development on new test systems involves using existing libraries. Industry-standard tools can be used to develop new tests and create new libraries. Once a test plan is written, the test executive allows the designer to debug the tests by:

Pausing, single stepping and looping.

Allowing direct control of instruments and switches.

Providing waveform displays.

Supplying seamless integration with the programming language that was used to develop the test.

Benefits of Intelligent Test

The HP test systems have provided considerable test-cycle-time reduction. In addition, Yazaki has increased throughput by establishing a single learning curve and by sharing test code among all installed systems.

Test engineering continues to find ways to improve the testing cycle. For example, the test design specifies several segments of durability testing. Rather than having NACOM perform three segments in series, Yazaki runs one of those segments in parallel because it has the same test suite. If each of these segments takes 30 days, then they can cut that overall test time by 30% and still have consistent data.

Referring to hardware, a standard test platform enables part-swapping capabilities. Consequently, the company is assured that component replacement is readily available in the case that hardware problems arise. These systems also offer a flexible approach to the design and manufacturing process which reduces cost and lead time to the customer.

Test systems are no longer just the means to a myriad of data points. Standardized test platforms are helping to get the job done faster and better and with long-term support.

About the Authors

Phil Paquette, a senior engineer at Yazaki, has been with the company for five years and presently is the program leader for the design of automotive electronics modules. Paquette graduated from the University of Michigan with a B.S.E.E. degree. Yazaki EDS Engineering, 7611 Market St., Canton, MI 48187, (313) 207-2519.

Brian Wood, who has been with Hewlett-Packard since 1973, is a member of the Automotive Electronics Test Group. Currently, he is an applications engineer for the HP TS-5400 testers. Wood earned a B.S.E.E. degree from the University of Arizona. Hewlett-Packard, 815 14th St. S.W., Loveland, CO 80537, (970) 679-2915.

January 1997