New international safety standard
The new revised European Machinery Directive 2006/42/ EC demands a more rigorous process of risk analysis and vehicle function verification.
International safety standards such as the harmonised EN ISO 13849-1 standard have also been updated. A significant change is the introduction of a probabilistic approach to vehicle function verification. The challenge for OEMs is to design and verify that vehicle functions meet a specific performance level, determined by a hazard and risk analysis. Verification involves gathering mean time to failure data from individual component suppliers and checking diagnostic coverage and common cause failures in order to ensure the required performance level has been achieved. Only then can OEMs establish an EC Declaration of Conformity and CE mark their vehicles.
To help with this process, standard Sauer-Danfoss products can supply key safety data such as mean time to dangerous failure. New products are also being designed to speed up system development and verification, reduce total installed costs, and ultimately bring vehicles to market faster. These include the OSPE Electrohydraulic Steering Unit and SIL 2 certified H1 Automotive Control.
Safe state steering system architecture
The OSPE electrohydraulic steering unit has been designed to provide the basis for a safe state system architecture. In the event of an electronic or hydraulic system malfunction, a safe state option, activated by an external watchdog controller, can isolate the electrohydraulic section of the steering valve in order to protect the steering system. As a result, OEMs can speed up steering system development and certification.
Another safety feature ensures that the steering ports from the OSP are not blocked in electrohydraulic steering (nonreactive) mode. This is achieved with an extra connection from the hydrostatic steering unit to the cylinder. In contrast to other systems, this keeps the steering wheel fully operational and the driver in complete control.
SIL 2 certified H1 Automotive Control
H1 Automotive Control (AC) is a complete SIL 2 certified solution (Safety Integrity Level 2, according to International Electrotechnical Commission (IEC) standard 61508) that significantly reduces OEM vehicle development and qualification expenses. It offers the precision and consistent performance of intelligent electronics, combined with complete drive system functionality and system qualification. OEMs will be able to reduce time to market for new vehicles and model variants while still customising vehicle behaviour and providing differentiation for their products.
Both the H1 AC hardware and software have been designed to be SIL compliant. The embedded controller incorporates additional watchdog circuitry, which provides real-time fault monitoring of the electronic hardware. Together with optional software used to monitor redundant HMI channels, it provides single fault tolerance for AC transmission systems. The controller is also programmed to bring the H1 pump to a defined safe state in the event of signal loss or interruption. It is SIL 2 certified by TÜV Nord (Technischer Überwachungs-Verein).
H1 AC software is easily configured to meet OEM requirements. Features include engine anti-stall and protection against engine over-speed, extreme high and low hydraulic oil temperature conditions, and hydraulic motor over-speed. In addition, there is automatic compensation for variations in hydraulic oil viscosity that affect control performance. The result is consistent, predictable vehicle performance irrespective of operating temperature.
For more information contact Ron Sheehan, Sauer-Danfoss Hydraulics, +27 (0)11 803 8390, [email protected], www.sauer-danfoss.com
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