Ludwigsburg, Germany-based MANN+HUMMEL, original equipment supplier to the automotive industry, has developed a new type of secondary air charger which reduces cold-start emissions from petrol engines through the injection of fresh air into the exhaust system. Unlike the well-known electrically driven secondary air pumps, the secondary air charger works as a turbocharger. The drive is achieved through the pressure difference on the throttle valve, thus requiring no electrical energy. It takes up less than one third of the space of a secondary air pump, and weighs only 300 g.
For many years, the principle of secondary air injection has proved effective in reducing cold-start emissions in petrol engines. During the first 30-60 seconds of the cold start, fresh air is injected into the exhaust system close to the discharge valves. As uncombusted hydrocarbons and carbon monoxide then ignite, the uncombusted components of the exhaust air are reduced. In addition, the exothermic reaction heats the catalytic converter system, so that it can reach its conversion temperature far more quickly.
Measurements on test rigs and vehicles have shown that the secondary air charger, when used as a turbocharger, provides a higher flow rate than an electrical pump, particularly at higher counter-pressures. The key components of the secondary air charger are the thermoplastic impellers. A roller bearing with life-time lubrication can operate at 140,000 rpm, with proven component strength.
The engineers at MANN+HUMMEL verified the operational reliability of the secondary air charger through periodic operation and under vibration loads. In the endurance test, the charger speed and pressure behind the compressor remain practically unchanged. During the vibration test, the secondary air charger can withstand temperature cycles of -20 to 120C without loss of performance. Testing showed that its acoustic characteristics were comparable with those of the electrical secondary air pump.
With its compact design, the secondary air charger can be easily integrated into the intake system, for example into the air filter housing, the engine intake manifold or the clean air line. Some of the pipework and the holders are therefore no longer necessary, and only a small amount of extra space is required.
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