Test system provides phase-stable rpm simulation for engine electronics
by Silke Thole
In the automotive industry, testing of start-stop systems and hybrid drives as well as the trend towards industry 4.0 pose new challenges to testing technology. Smart Testsolutions GmbH (Stuttgart, Germany) counters these challenges with a new generation of its ISIM-G2 test unit for speed simulation and angle-based trigger signal generation. Application areas of the product are test stands for car engines and modern injection systems.
For the operation of a motor electronics at the test stand, it is necessary to simulate crankshaft and camshaft signals in a phase-stable manner. Decisive factors for the simulation at the test stand are the speed of the drive shaft driving drives the pump shaft of the injection system. In the real vehicle, this task is taken by the crankshaft. At the test stand, the respective rotational speeds of crankshaft and camshaft are simulated for each drive or pump shaft speed.
As long as traditional transmission ratios like 2: 1 from crankshaft to camshaft and 1: 1 from crankshaft to pump shaft were considered standard values, this simulation was comparatively easy to handle. Nowadays however, injection systems based on common-rail technology, in which the ratio of the crankshaft to the pump shaft can sometimes be odd, for example 5: 3.
Further technology trends that that make simulating more complicated are start-stop systems and hybrid drives. „Previously, it was sufficient if the test equipment provided correctly simulated angle signals from a certain speed on, and only in a direction of rotation“, says Wolfgang Neu, CEO of Smart Testsolutions. However the characteristics of modern engines make it necessary to extend the simulation spectrum to zero speed and even to of reverse rotation.
Therefore, Smart Testsolutions equipped the ISIM-G2 with a new, FPGA-based logic design. This can simulate the correct rotational speeds of the crankshaft and camshaft from the rotational speeds of the drive shaft > 0.5 rpm and maintain the relative phase position of the shafts to one another even at very high rotational speeds. Even at high accelerations, the ISIM G2 has a maximum phase error of 0.2 degrees, while in standard operation it is 0.1 degrees.
"In the case of combustion applications, we have to process accelerations of 500 or 1000 revolutions / minute per second; the more and more frequently used hybrid drives are up to 8,000 revolutions per minute in a second," says Wolfgang Neu. Keeping the phase stiffness requires a much faster logic design than before, as well as a new algorithm.
Fuel injection systems process angle-based signals. Therefore, the ISIM-G2 generates angle-based trigger signals as well as angular and speed-proportional analog signals. The duration of a trigger signal can be adjusted freely. In addition, the ISIM-G2 offers more signal type configuration options. For example, it can simulate hall sensors and inductive sensors as well as DG23i sensors, which detect the direction of rotation.
The ISIM-G2 is primarily designed for operation on test stands around injection technology, but can also be used for other application fields. The device can simultaneously simulate up to five completely independent shafts, whereby the dependencies of these shafts are freely adjustable. This allows, among others, rpm simulation with four individually driven wheels.
Another feature of the ISIM-G2 is the web-enabled control software, which allows the device to be operated from any workplace in the local area network via a web browser. "With the integration of a web server into the device, we have pushed the technology sales of our devices to industry 4.0," says Wolfgang Neu.