Supercharger Applications

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Abstract: Compared to other boosting options, superchargers offer very rapid response in intake manifold pressure and low exhaust system heat absorption. Therefore, superchargers can be used to improve low speed transient response in downsized and downsped engines. Superchargers have been also used to improve power and torque density in engines using over-expanded cycles, as well as in hybrid vehicle drivetrains.

Introduction

When compared to other intake air boosting options such as turbochargers, superchargers offer several potential benefits including:

While superchargers are perhaps most commonly associated with high performance passenger vehicles, the focus on fuel economy after 2010 has expanded their potential to include other types of vehicle applications.

Figure 1 shows the potential transient response improvement of an engine driven Roots-type supercharger based boosting system relative to a turbocharger for a light-duty 2.2 L diesel engine designed for EPA Tier 2 Bin 5 emissions compliance [2840][2841]. The supercharger does not depend on exhaust energy to power the compressor so that boost pressure can be raised very rapidly. In contrast, at engine conditions where exhaust energy is low (i.e., low engine speed and low load), the turbocharged engine takes a long time to reach full load torque. At higher engine speeds and low load, more exhaust energy is available and the initial turbocharger speed is higher so that the benefit of the supercharger on transient response is much smaller.

Figure 2 compares the expected exhaust temperature profiles over the FTP-75 drive cycle for the same supercharged and turbocharged engine configurations as in Figure 1. The absence of an exhaust turbine, and associated heat capacity, for the supercharged engine means that exhaust temperature rises more rapidly and the aftertreatment system light-off occurs sooner. In his example, the DOC light-off is realized when its outlet temperature exceeds 200°C and which occurred 13 s sooner with the supercharged engine than the turbocharged engine. In other applications, reduction in catalyst light-off times up to 25 s have been reported [2845].