FIELD

The present description relates generally to adjusting air flow from a compressor in response to a catalyst temperature.

Background/Summary

Engines may use a turbocharger to improve engine torque/power output density. A turbocharger may include a compressor and a turbine connected via a drive shaft, where the turbine is coupled to an exhaust manifold and the compressor is coupled to an intake manifold. Exhaust gases may drive the turbine, which supplies energy to the compressor to increase air flow to the engine.

The turbine may be arranged upstream of a catalyst configured to treat certain combustion byproducts in an exhaust gas flow. A temperature of the catalyst may be controlled to provide a desired conversion rate of the byproducts while also mitigating degradation to the catalyst. During some operating conditions, temperature control of the catalyst may be relatively difficult. For example, during higher loads or higher driver demands, the catalyst temperature may exceed an upper threshold temperature, which may increase a likelihood of catalyst degradation.

Examples of addressing catalyst temperature control may include derates to reduce peak engine power and torque to avoid increasing the catalyst temperature above the upper threshold temperature. However, this may reduce customer satisfaction. Other examples may include introducing one or more heat sinks between the turbine and the catalyst, cooling the exhaust gas via coolant, injecting air or water into an exhaust passage to decrease an exhaust temperature, and compressors with a ported shroud.

However, the inventors have identified some issues with the approaches described above. For example, packaging space is constrained in modern designs. Thus, the introduction of additional heat sinks or an auxiliary pump may demand a redesign while also increasing manufacturing complexity. Injecting boosted fresh air from downstream of the compressor to upstream or downstream of a charge-air-cooler (CAC) may increase a cooling system demand, which may be at its limit during peak engine power and torque conditions when catalyst temperatures increase. Thus, the peak power and torque derate may still be needed.

In one example, the issues described above may be addressed by a method for flowing bleed air from a bleed port of a compressor to a portion of an exhaust passage upstream of a catalyst in response to a catalyst temperature. In this way, a catalyst conversion efficiency and longevity may be improved.

As one example, the bleed port may provide bleed air to an exhaust passage without adjusting a compressor load efficiency. Additionally, by drawing air from the bleed port at a location where pressures are less than a compressor outlet pressure, the air temperature may be less than the temperature at the compressor outlet, reducing cooling requirements. Alternatively, compressor size may be maintained or reduced, which may maintain or improve a surge margin and decrease lag, compared to existing methods which need to increase compressor size. By doing this, catalyst temperatures may be maintained without increasing a packaging size of the turbocharger and the exhaust system.

It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.

