Strain Analysis – Future Oriented Measurement at VW

 

The car of the future shall have reduced energy consumption, reduced emissions and it has to consist of materials which will fit in a resource saving ecological circuit. One of the VW key terms is to develop lightweight construction combined with hybrid technology. To get to this point reliable data are a must. The Wolfsburg sub department "strain analysis" is a part of the main department EGPF "fatigue analysis". For any complex and challenging measurement tasks the VW engineers prefer the TEAC data recorder RD-145T .
The VW group committed itself in 1990 to reduce fuel consumption within the following 15 years by a quarter. Since 1995 the fleet consumption averages to seven liters per 100km.

VW is committed to make further steps in this direction. Dr. Friedrich-Julius Quissek, manager of R & D of the VW group says: "It is our goal to offer a car in any market segment which is a technology leader in lowest consumption. The use of the TDI technology is only one of the concepts, reducing weight of any component of a car is another one". The engine takes therefore a key position. In the market segment of small cars the "three liters car" (which means a car that consumes three liters per 100km) is discussed. As in any other European automotive group VW has made also lots of effort in development. The magic limit is expected to be overcome by new developed engine concepts. The hard competition has changed a lot of the basic structures of the VW R & D. Parallel networked development of new platforms led to enormous synergy potentials. Examinations and simulations in the early stages of development allow getting a bigger picture of the gathered results. The "Simultaneous Engineering Teams" ensure the success of this strategy. They work together interdisciplinary in development, construction, test department, and computation.

The result of this concept is among others the cars of the A0 class like VW Lupo and Seat Arosa.

 

Measuring Rapid Dynamic Forces

 

An all new three cylinder diesel engine incorporates pump jet injection technology with a balancer shaft, 1.4 liters displacement at 55 kW will be the engine of choice for this two cars. VW expect it to be less resource consuming and last but not least to be cheaper in operation.

Because of conceptual limits a three cylinder engine's mass compensation isn't as perfect as engines with more cylinders. A balancer shaft was integrated to avoid exposing customers to engine vibrations. The softer burning of fuel caused by the pump jet injection makes this little power plant a really comfortable engine. Because of its compact design the balancer shaft is driven of the same chain as the oil pump. VW engineer Holger Bünning had to find out if the chain would be able to fulfil the requirements of the hard every day operation spanned over its whole life cycle. To have a realistic constellation for the tests he had to find a method to measure the extremely dynamic forces applied to the chain which passes four chain wheels while the engine is running. At least he only possibility to do this was to use extremely small strain gages and to transmit the measured values over a telemetric system. Büning said, "we had the problem to measure in extremely limited room and to handle measured values in the range of 0.3mV/V".

 

TEAC RD-145T

 

The high flexibility provided by the TEAC RD-145T, was proved again; especially the maximum averaged sample rate of 192 kHz. In double speed mode the maximum number of 16 channels may be reduced. If only four of the 16 channels were selected the band width rises up to remarkable 20 kHz. This ensures the recording of meaningful data. The extremely low white noise of the TEAC RD-145T was a further advantage when recording the sensitive signals. Before the measurement could be started the strain gages had to be applied to the chain links and calibrated to the respective force. After this the chain had to be mounted to the engine. The measurement data were transmitted by a telemetric system. Easy to read but the VW staff had a real tricky job to do which forced them to employ a lot of new methods. The measurement engineers were mainly interested in the following parameters:

 

 

* Force values along the whole distance of the chain

* Maximum forces

* Amplitude values of chain load depending on the engine revolutions

 

 

The exact values of the relevant parameters are a basic knowledge which is needed to optimize components efficiently like the chain itself, deflection angle, placement of the pinion, and the chain tensioning device.