Many modern engines are adopting turbochargers to provide customers with the same level of driving performance while reducing fuel consumption and emissions. To match the drivability of normally aspirated engines, full turbo boost pressure must be present at low engine speed. This is achieved by the use of boost pressure control systems, such as wastegate actuators, to control the pressure of exhaust gases entering the turbocharger. The actuator is situated close to the turbine of the turbocharger where exhaust gas temperatures – which can reach as high as 1050°C - as well as limited packaging space result in very high actuator temperatures of more than 220°C.
Guide bushings perform a critical function by accurately guiding a metal connecting rod within the wastegate actuator. They must ensure smooth, consistent operation of the connecting rod, with minimum hysteresis, to ensure accurate control of the turbocharger at all boost pressures and engine speeds.
A global leading supplier of innovative turbocharging systems selected Vespel® SP-21 bushings to ensure reliable performance and long life of the wastegate actuator. During rigorous application testing, the company observed that other potential solutions, such as thermoplastic bushings, can actually get hot enough to melt. Because the Vespel® bushings have no melting point, intermittent exposure to these high temperatures was not a problem. The superior property retention of Vespel® at extreme temperatures, even in the presence of aggressive exhaust gases, provided solutions where other polymer failed and assured the operation of the sliding shaft remained consistent over the entire testing cycle.
• Consistent and stable friction performance in a non-lubricated environment
• Long-term wear resistance even at elevated temperatures
• Resistance to aggressive exhaust gases
• Long-term thermal stability
• Good strength and impact resistance for robust assembly processes
The Vespel® guide bushings ensure the smooth, precise movement of the non-lubricated pneumatic wastegate actuator connecting rod. Vespel® SP bushings can provide a stable coefficient of friction over the life of the actuator and can reduce actuator hysteresis for accurate control of the turbocharger throughout the operating range. Thanks to the long-term thermal and chemical stability of these parts, these benefits can be maintained even in the high temperature and aggressive environmental conditions typically found near the exhaust stream of turbocharged engines.