|VTES electric supercharger. Click to enlarge.
UK-based Controlled Power Technologies (CPT) says that its switched reluctance motor-powered electric supercharger (earlier post)—VTES (Variable Torque Enhancement System)—is ready for production applications.
CPT suggests that configuring the high dynamic (10-90% rise time < 300 ms) VTES in series with a conventional fixed geometry turbocharger offers a combined transient effect which cannot be matched by other series air charging systems, and thus offers support for more extreme and more cost-effective—and therefore more broadly applied—engine downsizing.
|VTES series boosting layout (upstream). Click to enlarge.
Guy Morris, CPT’s engineering director presented the latest findings of the company’s research, development and testing program at the 13th Supercharging Conference in Dresden, Germany (25-26 September).
Extreme engine downsizing typically means replacing a 2.5-liter engine in a full-size family saloon or MPV with a 1.2-liter turbo-charged engine, CPT says. Motorists, however, still have certain minimum expectations for vehicle performance. Boosting the charge of air into the engine by mechanical supercharging or exhaust turbocharging is the most effective way to satisfy this requirement, but only if sufficient low-speed transient torque is delivered quickly enough to meet customer expectations for vehicle drivability. The reference point remains the response time of the larger, naturally-aspirated engine that is being replaced.
In recognition of this requirement, customer correlated engineering evaluation of the more radical (>40%) downsizing solutions, necessary to deliver optimum CO2 reduction, emphasizes the need to maximize the “near instantaneous” (typically <0.5s) torque available through intake charge boosting. Until recently the only intake charging solution with the potential to deliver significant torque enhancement in <0.5s was a mechanical supercharger, either operating on its own or combined, for better overall efficiency, with a conventional turbocharger.
...With serial upstream boosting VTES enables a significantly downsized, conventionally turbocharged engine to deliver dramatically (>50%) enhanced low speed transient torque. Through the use of highly dynamic switched reluctance direct drive motor technology, CPT has been able to deliver a cost effective system with low application effort and minimal investment, thereby offering a genuinely quick to market alternative solution to this challenging problem.—Morris and Criddle (2008)
Comparison of torque from a fixed geometry turbo (FGT) and a FGT with VTES in a 1.2-liter direct injection Otto engine. Click to enlarge.
CPT test data presented in the paper show that when applied to a radically downsized and down-speeded engine, the VTES technology significantly increases the initial transient response, delivering significantly more torque at low engine speeds, thereby enhancing a car’s low speed drivability characteristics. The combination of a highly dynamic electric supercharger, in series with a conventional fixed geometry turbocharger, also makes it relatively easy to optimize the overall response of the system, compared to other air charging methods.
The VTES system can also help reduce soot and particulate emissions from diesel engines, particularly when the driver accelerates at low engine revs, which, in turn, creates an opportunity to reduce the size and cost of the diesel particulate filter (DPF).
Fast response air-boost systems are essential for delivering radically-downsized engines. Even the most dynamically optimized turbocharger cannot deliver an air-side response approaching the fuel control capability of the latest injection systems. The consequence is ‘air limited’ combustion, which imposes many compromises on the engine developer.
Series boosting solutions are gaining popularity because of their extended low speed boosted air delivery capability, but their dynamic performance is still frustratingly linked to engine speed and air mass flow rates. The provision of a cost-effective electric supercharger, in series with a conventional fixed geometry turbocharger, offers a combined transient effect, which as yet cannot be matched by other air charging systems.—Guy Morris
The VTES electric supercharger, which operates independently of engine speed, can significantly increase the air charge density over the first 10 combustion cycles of a low speed transient, thereby enabling real improvements in both transient torque and emissions performance. Fitted with a low inertia compressor, the supercharger accelerates from its 5,000 rpm idle speed to a maximum speed of 70,000 rpm in less than 0.35 seconds. The system is highly dynamic and the intake charge boosting and resulting torque enhancement is achieved very typically in less than a quarter of a second (250 ms).
G. Morris and M. Criddle (2008) “Transient Torque Enhancement and Emissions Reduction Potential of a Highly Dynamic Supercharger” [To request a copy of the paper, contact Dipl.-Ing. Carsten Guhr, Lehrstuhl Verbrennungsmotoren, Institut für Automobiltechnik Dresden - IAD Technische Universität Dresden.]