22nd ESV Conference 2011
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Schlagworte
- Fahrstabilität (2) (entfernen)
Institut
- Abteilung Fahrzeugtechnik (2)
- Sonstige (1)
New vehicle types are extensively tested to check almost all factors that influence ride and handling. With reference to the Association of German Car Tuners" (VDAT e.V.) valuations, approximately 10% of all cars in Germany are being modified by their owners. 28 % of those modifications" sales are divergent wheel-tire combinations, 13 % are tuning measures on the chassis suspension or wheel spacers. In almost all cases the singular modifications present a general permission for specific vehicles they have been tested in. Combined tuning measures, however, are often checked by just one inspector, following a procedure of mostly subjective assessment criteria. Today, critical attributes are only being observed, in case a vehicle is involved in an accident and the modifications are identified as crash causal factors or as a cofactor on the development of a crash. For the first time, a field study allows a survey of safety affecting chassis modifications. The test layout has to comply with some basic conditions. Different vehicle concepts with a wide margin of modifications are required to get a high transferability of the results. A total amount of more than 150 tested vehicles serves the same purpose. The tests are limited concerning the installation time of measurement techniques and the requirement that no damage, defilement or immoderate wear of the vehicles are accepted by their owners. Due to such factors as well as the driver Ìs acceptance, the vehicles are controlled by its owners instead of robots or test drivers. For keeping down the driver- influence, the lane has narrow boundaries and the driver has to drive in strictly adherence to the given instructions. After gathering all modifications, as well as static and kinematic parameters like the toe and camber angle, dynamic testing of predominantly lateral dynamics is conducted. Besides standardized tests like the ISO 3888-2 (Obstacle Avoidance) or the ISO 14512 (Braking on Surfaces with Split Coefficient of Friction), to test the influence of modified kingpin offsets caused by wheel spacers, some deviant tests are conducted. Those are required due to the demand of objective test results for road tests with vertical induced stimulation of the chassis suspension. Hence, new tests on corner braking with and without vertical stimulation have been developed. The interpretation of data includes thresholds, e.g. the maximum entrance velocity without hitting cones, on the one hand, and the analysis of characteristics of data concerning time and frequency range, "1-second values" and peak response times on the other hand. Besides the thresholds as indicators for the achievable velocities, which are mainly affected by friction coefficients, the vehicle reaction in the course of time characterizes the vehicle reaction in the threshold range and consequently the operational demands on the driver. The field study has started and promises the first long-range analysis of chassis modifications. The results offer a basis for hypothesis and resultant further test layouts for oncoming studies of the identified critical tuning measures.
The ASSESS project is a collaborative project that develops test procedures for pre-crash safety systems like Automatic Emergency Braking (AEB). One key criterion for the effectiveness of e.g. AEB is reduction in collision speed compared to baseline scenarios without AEB. The speed reduction for a given system can only be determined in real world tests that will end with a collision. Soft targets that are crashable up to velocities of 80 km/h are state of the art for these assessments, but ordinary balloon cars are usually stationary targets. The ASSESS project goes one step further and defines scenarios with moving targets. These scenarios define vehicle speeds of up to 100 km/h, different collision scenarios and relative collision speeds of up to 80km/h. This paper describes the development of a propulsion system for a soft target that aims to be used with these demanding scenario specifications. The Federal Highway Research Institute- (BASt-) approach to move the target is a self-driving small cart. The cart is controlled either by a driver (open-loop control via remote-control) or by a computer (closed-loop control). Its weight is limited to achieve a good crashability without damages to the test vehicle. To the extent of our knowledge BASt- approach is unique in this field (other carts cannot move at such high velocities or are not crashable). This paper describes in detail the challenges and solutions that were found both for the mechanical construction and the implementation of the control and safety system. One example for the mechanical challenges is e.g. the position of the vehicle- center of gravity (CG). An optimum compromise had to be found between a low CG oriented to the front of the vehicle (good for driveability) and a high CG oriented to the rear of the vehicle (good for crashability). The soft target itself which is also developed within the ASSESS project will not be covered in detail as this is work of a project partner. Publications on this will follow. The paper also shows first test results, describes current limitations and gives an outlook. It is expected that the presented test tools for AEB and other pre-crash safety systems is introduced in the future into consumer testing (NCAP) as well as regulatory testing.