Technology and Innovation Articles

DBS Electric Supercharger (eSC) for Engine Downsizing

18 June 2017 #Technology and Innovation Articles

Global pressure to reduce vehicle emissions is changing how vehicles are designed and manufactured fundamentally. Automotive OEMs must identify ways to reduce CO2 emissions, whilst also increasing power as demanded by consumers. Reducing engine displacement with boosting is one of the most cost effective ways of achieving this since smaller engines give lower fuel consumption at part load and are lighter. This enhancement has minimal impact on the powertrain configuration and manufacturing costs.

Internal combustion engines with displacement < 1.0L suffer from an inherent lack of torque (figure 2). A turbocharger is commonly utilised to address this problem by boosting the engine. However, the exhaust only has sufficient energy to drive the turbocharger at higher engine rpm (around 3,000 rpm and above). At lower rpm, the exhaust is unable to spool up the turbocharger (often with operating speeds above 150,000 rpm) to deliver the required boost. As a consequence, these engines suffer from lack of torque at lower rpm despite utilising a turbocharger. Since these engines are often used in small city cars, low speed torque is an important aspect of the performance.

Electric supercharger (eSC) technology has the potential to address the lack of torque, which is a consequence of turbo lag. An eSC consists of a turbocompressor driven by a high speed motor. The system is powered by the car’s battery, making it independent of engine speed and can operate to provide almost instant boost when required.

Responding to these changing demands, boosting companies have developed a number of solutions to these challenges, but none have yet improved significantly the low-end torque or optimised transient response on smaller engines (<1.2L). This is exactly where DBS’ innovative TurboClaw® electrically-driven supercharger, (eSC) could make a difference.

Dynamic Boosting Systems’ patented TurboClaw® technology features unique design attributes that mitigate many backswept-turbomachinery performance issues, whilst also delivering superior engine performance. TurboClaw® is a turbocompressor with fundamentally different blade geometry as compared to conventional back-swept design, and offers game-changing advantages such as:

Figure 1: Conventional back-swept impeller (L), and TurboClaw® (R)

  • Efficiency improvement at low volumetric flow rate.
  • Lower speed operation to achieve same compression ratio and volumetric flow rate. This allows use of standard off-the-shelf grease lubricated bearings.
  • Simple 2-D blade geometry.
  • Compact and robust design.

The DBS eSC with its innovative low specific speed TurboClaw® turbomachinery delivers better performance than backswept turbomachinery designs because it is decoupled from engine speed and operates at significantly lower speeds than available alternatives, providing further benefits in terms of reliability and cost. Results from eSC trials, sponsored by the UK Department of Trade and Industry’s Technology Strategy Board (TP BS088J) are depicted below.

Figure 2: Torque vs speed characteristic obtained from eSC trials by AVL.

The above test results indicate a 30% increase in engine torque at 1,000 rpm. The performance advantage over turbocharger is evident benefits between 1,000 and 3,000 rpm. DBS eSC can be utilised independently or in tandem with a turbocharger. The torque improvement enables a 1.0L engine to deliver performance characteristics similar to a 1.4L naturally aspirated engine. Performance of eSC was validated through hardware in loop (HIL) test as depicted in figure 3 below.

Figure 3: Hardware in loop (HIL) test setup.


Continuous development

Figure 4: eSC with standard diffuser (L), eSC wit compact diffuser (R)

DBS has developed the next generation of its eSC product based on TurboClaw® technology. Critical improvements include compact packaging (around 1 litre in volume and weighing less than 5kg), high efficiency, low cost manufacture, (target €100, £ 81, USD$ 120), and high temperature operation, (to 230° C). The new product underwent Hardware in the Loop (HiL) and vehicle evaluation in 2015/16 to confirm performance improvements.

The improved design includes a high-speed permanent magnet brushless DC (BLDC) motor developed by DBS.

Motor Design Features

  • High speed and power density with overall motor/drive efficiency > 95%.
  • Low maintenance long life design – with oil lubricated or grease packed bearings available as standard.
  • Low rotor diameter to minimise windage (air friction) losses and inertia.
  • Water or air cooled casing to suit customer requirements.
  • Induction motor as well as PM versions available.

    Figure 5: Controller developed by DBS for eSC.

The company has also developed power electronics to drive the motor at standard automotive voltage of 12V / 24V.

Electronics

  • DBS designs and manufactures its own electronic circuits for motor control, system control and instrumentation. These enable DBS to precisely match customer requirements with minimal additional integration effort required by the customer.
  • DBS has experience of designing electronics for automotive requirements, including the selection of appropriate components for these demanding applications.
  • The control software is also developed in-house and can be readily tailored to customer requirements.

Future development and productionisation

  • Improved response time to less than 0.4 seconds: DBS has identified below listed improvements to achieve target response time.
    • Lower inertia of the rotating assembly.
    • Lower diameter of the impeller and shaft.
    • Selection of lighter materials to reduce mass of rotating components.
  • Productionise and optimise the design for lower cost.
  • Target price of €100, £ 80 when manufactured in production volumes.

DBS is seeking to collaborate with a Tier 1 automotive company for productionising eSC technology and commercialising it.

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