Tech Briefs

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March 2002
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Audi injects track technology into cars

Audi believes its technology behind the Le Mans-winning twin-turbo R8 will benefit personal vehicles.

Although examples of track-to-road technology transfer are relatively few and sometimes questionable, Audi says that a new gasoline-direct-injection (GDI) system now under development in an engine based on the 2.0-L alloy block used in some A4 and A6 variants is directly linked to experience gained with the 2001 Le Mans race-winning twin-turbo Infineon Audi R8. With GDI, the R8 had a higher power output and lower fuel consumption (about 8%) than equivalent V8 engines using conventional injection technology.

The indirect gasoline injected 2.0-L FSI Audi production engine produces 97 kW (130 hp), but with GDI this has risen to 112 kW (150 hp) with fuel consumption improvements in some regimes of up to 15%, claims the company. The Audi engine, now undergoing an extensive test program, uses an 11-MPa (230-psi) high-pressure, common-rail-injection system with a single-piston injection pump supplying precisely the correct amount of fuel to maintain the desired pressure in the system. It also features a new cylinder head with four valves per cylinder. Valve operation is via roller cam followers. The system uses an upgraded version of Audi's air-guided combustion process with continuous control of charge movement.

The Audi FSI gasoline-direct-injection engine with alloy block is being developed for production.

There is also a further development of the exhaust-emissions control system with NOx storage-type catalytic converter and NOx sensor. According to Audi, a major contributing factor to achieving emissions improvements is the stratified charge principle at part load, with the engine needing a fuel-air mixture capable of immediate ignition around the spark plug. The remainder of the combustion chamber is filled with a leaner mixture containing a considerable amount of excess air. As a result, the engine can be run without the incoming mixture flow being throttled.

The injector is in the side of the cylinder head. Unlike most Audi engines, the cylinder head has four, not five, valves, which frees space for the injector in the combustion chamber. The engine has an exhaust gas recirculation facility that returns about 30% of gas back to the combustion chambers.

Audi is working with lighting suppliers to develop smart lighting systems, including variable headlights. Click to enlarge

Another Audi technology project is the development of new lighting. Working with major lighting suppliers, the company is developing both headlight and taillight systems. In common with several other OEMs, Audi is considering the linking of headlight direction to steering angle. Subject to European legislation, this may be fitted to production cars next year. It would be controlled by speed and steering angle but would not involve the use of moving parts or actuators. Rain sensors would automatically adjust the lights to reduce glare on wet surfaces. Deepening the lit area in dipped mode would be achieved by linking the lighting system to sensors monitoring yaw rates and road speed. The central control unit for the system would need information on the type of road the car was using. This information might be achieved via video images sent from cameras in the headlights or by an onboard satellite navigation system. The lighting system would then conform to the type of road, whether urban, rural, or high speed.

Audi is also working toward the use of intelligent electronics to obviate the need for dedicated rear fog lights, which are often used in the wrong conditions or forgotten by drivers and left illuminated in good visibility. Adjustable light intensity using LED technology would allow them to be incorporated into a single rear light design. Light intensity would be automatically adjusted to suit weather conditions and time of day. It would also be possible to adjust the intensity of rear fog lights according to the closeness of a following vehicle.

- Stuart Birch

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Multi-axial simulation from MTS

The Series 353.10 High Frequency MAST from MTS Systems is suitable for squeak and rattle, modal, and durability testing of vehicle components and subassemblies.

Engineers from MTS Systems Corp. developed the Series 353 High Frequency MAST to enable automotive engineers to simulate an automotive-component operating environment for conducting noise and vibration studies. The patent-pending design concept employs a hexapod or Stewart platform. It is controlled in six-degrees-of-freedom by six inverted-design servohydraulic actuators, providing coherent response to 500 Hz. MTS uses an ultra-stiff swivel design to connect the actuators to a cast and bolted aluminum table. The actuators are arranged in prismatic form, which, in combination with the swivels, prevents potential control problems caused by backlash, and also problems that could be caused by fit and maintenance. The machine's small footprint allows it to be adapted easily to space constraints in a variety of component-testing laboratories.

Noise and vibration testing is accomplished with focused NVH software tools. Time-history reproduction (or sine sweep and sine dwell testing) provides for the duplication of recorded service behavior. Real-world conditions are simulated with the assistance of digital control and MTS RPC Pro analysis and simulation software. The software package provides a suite of analysis tools to optimize both the design and development of testing technologies appropriate to the capabilities of the system. Diagnostic tools in the software minimize the amount of time invested in testing, and the software integrates seamlessly to all MTS controllers, minimizing configuration time and possible setup errors. An event action matrix lets the user directly couple the test with controller features such as limit detection, mode switching, and set-point control.

All multi-axial simulation tables offered by MTS feature degree-of-freedom control, which allows control in Cartesian coordinates, an easier task than dealing with the complex motions of the actuators. Degree-of-freedom control also allows the user to define unique control conditions directly from the software, such as defining the center of rotation of the platform above the table surface.

Flat performance from any single control variable such as displacement, velocity, or acceleration would make accurate high-frequency simulation difficult to attain. MTS solves this problem by using all three of the control variables simultaneously as feedback and command parameters to the controller, which provides for emphasis of displacement at low frequencies, velocity at middle frequencies, and acceleration at high frequencies. The result is the best possible and most consistent performance across a wide frequency spectrum, according to the company.

For durability testing applications, the Series 353 High Frequency MAST provides the relatively high stroke and force required for event-based control, or control that can reproduce specific force-time events. However, when the equipment is used for NVH testing of components, it will be required to deliver relatively low stroke and force to the test specimen, replaced by energy-based control, or control that produces a given power spectral density specification.

Squeak and rattle testing requires some of the performance capabilities of both durability testing and NVH testing. This may require force and stroke performance or energy-based excitation to attain specimen vibration rates throughout the system's entire 500 Hz bandwidth. Evaluation of both NVH and squeak and rattle tests is aided by the suite of I-DEAS NVH engineering software offered by MTS. These tools enable the engineer to first measure and then thoroughly analyze a product's acoustic and vibration characteristics. By employing quantitative metrics or qualitative jury studies, unacceptable features of these noises can be identified and evaluated and specific targets can be set for more desirable sound output.

- Jean L. Broge

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