Testing automatic transmission components under real-world conditions is challenging for many manufacturers. It is difficult and costly to measure performance of critical components such as torque converters in an operating transmission. On-vehicle testing can determine the life of the components but provides little or no information on parameters such as torque, hydraulic pressure, and temperature.

In current practice there are two basic methods of testing critical automatic transmission components. The first involves running full vehicle tests on a dynamometer or proving ground. This approach provides valuable information in evaluating the durability of the overall design, but is a relatively poor tool for component-level design. The expense, lead time, and cost to measure parameters on individual components restrict use of this method. The second approach is to test transmission components in a laboratory, normally by driving one side of the component while the other is fixed to the machine. The dynamometer typically cycles through a series of loads. But, there is no way to correlate the loads seen by the component with real-world conditions. With one side spinning and the other fixed, conditions differ from those in a real transmission. The method provides general information, but has a limited ability to evaluate the relative performance of alternate designs.

A new test rig overcomes these drawbacks by recreating actual operating conditions. Developed by COM Inc., Dexter, Mich., it uses two dynamometers, the first simulating the automobile driving the transmission, and the second simulating the resistance of the driveline, tires, and road. COM's design involved putting sensors on components attached to both dynamometers and using telemetry collars to transmit these signals to a data-acquisition device. Sensors measure rpm, torque, strain, temperature, pressure, and other parameters. The system, for example, can record the amount of torque that causes a clutch to break away and begin slipping under a real-world control profile. This allows users to change friction materials or plate geometry, and immediately measure the impact on the torque converter.

Inputs to the dynamometer are based on measurements taken in road tests, and include the rpm, and torque into and out of the transmission.

Determining the signal for the second dynamometer is more complicated. A mathematical model transforms road-test data into the operating signal. A traditional approach uses a PLC in between the graphical interface and the machine to control on/off positions, timing, logic, counting, and sequencing. PLCs are frequently used to control complicated machinery because they possess the stability and real-time capabilities needed to ensure that machines remain under control in case of a fault. Operating systems like Windows NT use up a lot of cycles on the PC platform and when they take control of the CPU they hold onto it for a long time in machine-control terms. A failure of the operating system could leave the machine in an unknown and possibly dangerous state. In measuring or controlling a real-time process, computer power has to be available when it is needed. But incorporating both a PLC and a personal computer would drive up the cost of the machine.

Data-acquisition processors (DAPs) have an onboard microprocessor that runs a multitasking, real-time operating system optimized for high-performance data-acquisition and control applications. The intelligence on the DAP board is designed to extend the power of the Windows user interface by executing all processor intensive routines in real time and performing data reduction so that the software on the PC can handle more demanding applications than usual.

COM's engineering team configured the DAP to provide a software control loop for the test rig. The Windows interface provides the basic dynamic commands to the rig. Each of these commands goes through a finite-state machine developed by COM engineers. The DAP communicates with Windows through a watchdog interface. Should Windows fail to respond to the watchdog timer, the finitestate machine takes over and brings the test rig to a safe stop.