Shock absorbers, often also known as vibration absorbers, are used to collect the vibrational energy of moving masses and convert it into heat. Used in conjunction with the wheel suspension and spring system, they largely determine whether the driver of the vehicle finds the road handling comfortable and safe. Designing and manufacturing modern gas or oil pressure absorbers for the automotive industry are a science in their own right; today’s individual absorber types are completely custom-made for certain vehicle types or model series. Automotive manufacturers pursue completely different concepts when it comes to the detail, even establishing an individual brand or model image. Thanks to intelligent technology, drivers of higher-priced models can now choose for themselves if they want their journey to be soft or hard-sprung.
Test rig simulates reality
Single or dual tube pistons essentially consist of the absorber tube, piston, piston rod, gaskets, valves and rubber-mounted fixing points and are true masters when it comes to converting vibration energy. Before they are manufactured in series and installed in vehicles in thousands, the automotive manufacturer needs to be absolutely sure that the vibration absorber will satisfy the real-life demands over many years. That’s why new absorber models are comprehensively tested in advance on special simulation and test rigs. Almost all conceivable applications and loads that are likely to arise in rugged, everyday use are simulated with regard to the respective vehicle model, its weight and special features. Various road surface conditions are included, as are temperature fluctuations and use in different climate zones.
Compact test rigs include process control technology
“It’s our job to develop and construct a rig in such a way that the performance requirements specified by the vehicle manufacturer can be simulated efficiently and reliably,” said Günter Gröpler, Founder, SAR Gröpler GmbH. Based in the Swabian town of Dettingen/Erms and specialising in this type of test rig, the company has over 40 years’ experience in the industry. Alongside mobile test rigs, SAR Gröpler GmbH also manufactures machinery for the production and filling of shock absorbers. Other focus areas include development & production of hydroelectric power plants and the retrofit of old plants. “Thanks to our test rigs, customers can be certain that the type of shock absorber subsequently installed in the vehicle satisfies everyday demands,” opined Jan Gröpler, Junior Manager, SAR Gröpler GmbH.
Test rig requires efficient safety technology
The test rig that stands just before the final inspection area at a well-known German car manufacturer measures around 2 x 2 metres at ground level and is around 3 metres high. The vibration absorber to be tested is initially clamped vertically on to the upper and lower lug between two retaining pins. Once the safety gates are closed, a multi-stage test and simulation program begins, based exactly on the customer’s requirements. Two motor-driven spindles contract the shock absorber; the massive eccentric on the lower part of the rig is set in motion. Controlled by proprietary software, the rig now simulates on-road use with a variety of speeds, hubs, gas pressures, vibration forces and frequencies.
This is where it gets hard and fast: forces of up to 40 KN are exerted; sensors regularly measure the absorber’s reaction, the gas pressure and other relevant parameters. The item under test must meet the stipulated performance features even under extreme conditions; obviously it must neither squeak nor creak. The software displays progress clearly on the central operator panel; at the end of the test series, all measured data such as speed, load, friction and absorption are also displayed. “Based on these results, the manufacturer makes corrections and fine adjustments to the valves, for example, or changes the oil pressure”, explained Gröpler.
Manipulation-proof safety gate system
Automation and safety technology from Pilz is used to ensure that set-up, operation and maintenance of the test rig at SAR Gröpler is simple, efficient and above all, safe. “The risk assessment in accordance with EN ISO 12100 showed that risks emanate, in particular from the eccentric and that a risk of crushing and injury in the event of a power failure cannot be ruled out, so that safety functions up to PL e of EN ISO 13849-1 are required,” explained Timo Lurf, Head of Pilz’s technical office in Reutlingen. The focus was, therefore, on finding reliable, safety-related solutions for the two safety gates in the upper area and for the safety gate in the eccentric area. That’s why the safety gate system PSENslock from Pilz is used on all three gates.
The non-contact, low-wearing and fully-coded system with an electromagnetic holding force of up to 1000 N offers maximum manipulation protection, thanks to RFID transponder technology. Whether connected separately or in series, PSENslock is suitable for safety gate monitoring up to PL e. Thanks to flexible connection options (M12 connector, 5-pin or 8-pin), wiring is simple and can be achieved quickly, without great effort. The safety gate system combines safety, automation and diagnostic functions in one device; and thanks to IP56 protection, it is also suitable for rugged environments.
The flexible and configurable control system PNOZmulti 2 fulfills its role as the central safety component in the test rigs from SAR Gröpler GmbH. It monitors all the sensor technology and the installed emergency stop pushbuttons, as well as controlling the stroke movements. The housing width of the base unit is only 45 mm. On the left-hand side, it is possible to connect communication modules with serial or ETH interface, or fieldbus systems such as PROFIBUS-DP, CANopen, EtherCAT or Powerlink. There are still 20 safe inputs available, up to eight of which can be configured as non-safety-related outputs, plus 4 safe semiconductor outputs (each with PL e).
With the new illuminated display, you can save time and costs during configuration and diagnostics and reduce the engineering work significantly. With the PNOZmulti Configurator, configuration is simple and intuitive via drag & drop. What’s more, in conjunction with PNOZmulti 2 as a contact expansion module, the safety relay PNOZsigma provides multiple shutdown paths. Finally, Pilz emergency stop pushbuttons are fitted to all relevant parts of the rig, the control cabinet and the operator terminal. As a result, the rig can be brought to a safe standstill within fractions of a second.
One-stop automation and safety technology
SAR Gröpler GmbH offers its customers the security of knowing that the shock absorbers tested on its rigs meet the required quality features. With wide-ranging industry expertise, competence in the field of risk analysis and CE certification as well as an extensive portfolio of sensor and control technology, as a complete safe automation supplier, Pilz offers customers like SAR Gröpler one-stop, economical and tailor-made solutions for automation and safety tasks.