The high demands for safety, functionality and aesthetics during a car’s development are obvious in all its parts. These demands are usually at odds with cost effectiveness. Finding a reasonable compromise is always a difficult task for designers, structural engineers and technologists. At TÜV SÜD we support our customers in the testing area, from development through type approval to conformity of production (CoP) tests. To provide high quality services, we regularly invest into new testing equipment, which helps our customers to verify the functionality of components and assemblies, and thanks to that, speed up the development process. One of such investments is the new test pendulum for physical simulation of parking collisions.
The front and rear bumpers have long been, not only a steel moulding that connects and reinforces the front longitudinal beams but they are also part of a sophisticated deformation zone system. The front of a car is a textbook example of often opposing demands. If we consider the first aspect - safety, we will encounter demands for adequate deformation zones and component response for four types of impact.
Types of Impact
The first and most serious for the occupants are high speed impacts, which are tested according to valid legislation for example with a frontal impact at a speed of 56 km/h into a deformable barrier with partial overlap (40% of the vehicle width) according to ECE Regulation 94 or the full vehicle width into a rigid barrier at 50 km/h according to ECE Regulation 137. This type of impact is considered in the construction of the longitudinal beams in the engine compartment, by the bumper reinforcement, the transfer of forces between the longitudinal beams and sills, and the tunnel, etc. Greater demands on these parts beyond the legislative requirements have been introduced by the ENCAP (European New Car Assessment Programme) organisation with its consumer tests, where the impact energy is even higher.
The second type of impact are low speed impacts (RCAR – Research Council for Automobile Repairs), where a vehicle crash occurs at a speed of 15 km/h with a rigid barrier and most impact energy should be absorbed by the bumper reinforcement, the deformation elements below it and the plastic or composite parts of the bumper. This type of impact simulates frequent accidents caused by incomplete braking in stop-start traffic, etc. The purpose is to minimise vehicle damage and repair costs as much as possible after such a collision.
The third type of impact are parking lot collisions, which occur at very low speeds and the plastic and composite parts of the bumpers, lights, radiator grills, etc. must safely withstand them. Testing the correct functioning of the bumpers (front and rear) is done using a special pendulum with a rigid impactor. In the longitudinal direction, the impact occurs at a speed of 4 km/h and the test in the oblique direction towards the corners (at an angle of 60°) occurs at a speed of 2.5 km/h. The effective pendulum weight must be equal to the vehicle’s unladen weight.
The requirements for meeting ECE Regulation 42 Uniform provisions concerning the approval of vehicles regarding their front and rear protective devices are inter alia:
- the lighting and signalling devices shall continue to operate correctly,
- the vehicle’s bonnet, boot lid and doors shall be operable in the normal manner,
- the vehicle’s fuel and cooling systems shall have neither leaks nor constricted fluid passages which prevent normal functioning,
- the vehicle’s exhaust system shall not suffer any damage,
- the vehicle’s propulsion, suspension (including tyres), steering and braking systems shall remain in adjustment and shall operate in a normal manner.
The fourth type of impact are pedestrian impacts according to ECE Regulation 127. For these collisions, the front part of the car must be designed as favourably as possible to these vulnerable road users. It is not just about transmitting the smallest possible force during a pedestrian impact, but also so that the pedestrian’s subsequent motion is directed over the bonnet and not under the vehicle. Suitability is judged by impact tests when measured impactors simulating, for example, the head or legs, are propelled at the front of the vehicle and bonnet.
What about the functionality and aesthetics of cars?
If we focus on aspects of functionality and aesthetics at the front of the vehicle, account must also be taken of both external aerodynamics that affect fuel consumption, noise, driving dynamics, etc., as well as internal aerodynamics, where we deal with sufficient air supply to the cooling system, brakes, intake etc. This cocktail of requirements is supplemented by a sufficiently large curvature on the outer edges of the bodywork (“external projections”), resistance to environmental influences (UV radiation, extreme temperatures, etc.), colour fastness of the mostly plastic components, etc. It is clear from the above, that the design of the construction, the materials and surface finishes are very complex and the size of the test matrix confirming the right choice is considerable.
Innovation in vehicle resilience testing
One of TÜV SÜD Czech’s most recent significant investments in the field of testing is a new pendulum made by ENCOPIM for testing the resilience of the front and rear of the vehicle to parking collisions. As mentioned above, the most important requirement is that, after such an impact, the vehicle should still have functioning lights and signalling devices, functioning fuel, cooling and exhaust systems and functioning mechanisms for opening the hood and the boot lid. Beyond these legal requirements, TÜV SÜD Czech performs tests according to customer methodologies at extreme temperatures, for example from -10 °C to 65 °C.
In the initial phase of developing a new model (the whole bodywork does not yet exist), the bumper cover is tested with all grilles, decorative trims, fixtures, brackets, covers and other parts on a fixture that simulates fixing points and stabilising elements of the future bodywork. This highly accurate device is attached to a test vehicle that is weighted according to the customer’s specifications. The pendulum for verification of non-destructive energy absorption capacity is also weighted at a vehicle’s unladen weight and impacts on the test vehicle.
The new pendulum can be weighted to an effective weight of up to 3,500 kg and a test can be performed at an impact speed of up to 10 km/h. The main advantage of the new system is that the kinematics are closer to an actual impact in traffic. The percussion mechanism is replaced by a parallelogram, and only a horizontal deformation force occurs during impact. Another advantage is the possible varied load cells configuration that accurately determines the force flows between the impact plate and the pendulum. From the point of view of operative efficiency, the pendulum is automatically height-adjustable, and there is no unnecessary downtime during setting change for another project.
In addition to the mentioned ECE Regulation 42, the pendulum also complies with the American FMVSS 581 (Pendulum test device as per TP-581-01) and Canadian CMVSS 215 and manufacturer’s methodologies, for example with EP 83 300.90 and GB 17354-1998.
The entire workplace is complemented latest lighting, recording and measuring technology to produce results beyond ISO 17025, which our accredited laboratory must fulfil. Thanks to the LED lighting system supplied by the German company HS Vision, there is no thermal influence on the test sample during the test. For various vehicles front-end deformation analyses, we are also now equipped with a filming shaft, which gives customers a high-speed camera record from under the vehicle. Our services also include measurements and analyses, where, at the customer’s request, we instrument test samples, e.g. potentiometers or strain gauges, and we evaluate deformations.
Another novelty at this workplace is the temperature chamber for tempering not only the samples mounted on the fixture, but also the entire vehicle. In the newly built chamber, a vehicle over 5m in length can be tempered to -25°C. Very low temperatures are critical because of plastic embrittlement. The demands of most automobile manufacturers on their suppliers, in this case the bumper system supplier, is uncompromising — even at low temperatures components must not break or otherwise be visibly damaged.
When defining assignments for all suppliers, we considered not only legislative requirements and current manufacturer’s methodologies, but we also configured the entire centre to be as modern and extensive as possible, and with regard to the effectiveness of testing and the safety of our team. New projects, including all alternatives and levels of equipment, will soon be underway at this new centre.
For further information please contact Martin Sotola, Vehicle Safety Business Unit Manager or Jiří Vojtíšek, Head of the Strength Testing Laboratory