CPT: Low cost performance boost for small, fuel efficient engines

A low cost technical solution to soaring fuel prices could be as simple as electric superchargers boosting the performance of small internal combustion engines, says the UK-based vehicle CO2 emissions specialist, Controlled Power Technologies. CPT’s micro-hybrid technologies are designed to support the transition from current powertrains to the still distant mass market adoption of affordable mild hybrid vehicles.

According to CPT, the prospect of oil racing towards US$150 a barrel can only accelerate the global trend towards smaller, more efficient engines. The engineering challenge facing the industry, however, is downsizing engines without compromising the drivability and performance that motorists have come to expect from their vehicles.

Nick Pascoe, chief executive of CPT is helping to address this downsizing issue at the prestigious JSAE (Society of Automotive Engineers of Japan) international annual congress held in Pacifico Yokohama from 21 to 23 May 2008.

‘Legislators have recognised the political urgency for reducing carbon emissions in response to increasing consumer concern,’ says Pascoe. ‘However, vehicle manufacturers will only sell reduced CO2 vehicles if the price is affordable to the mass market consumer,’ he adds.

That only happens when the technologies required to achieve the reduction are sufficiently mature to ensure industry financial risk is minimised. Since the technical risk drives the cost, the only solution is taking smaller, incremental steps – hence the pressing need for low cost micro-hybrid solutions.

Engine downsizing has been shown to be one of the most cost effective routes to vehicle CO2 reduction and European carmakers are already moving rapidly towards a 30 percent reduction in the displacement of their mid-sized engines, to around 1.4 - 1.6 litres, offering the potential to deliver up to 15 percent reduction in CO2 emissions. Most cars in India already have small engines, but even on the bigger luxury cars sold here, smaller, more fuel efficient engines could become the norm very soon.

In a surprising reinforcement of the smaller engines trend, the US market is also now taking CO2 reduction seriously and viewing the option of perhaps a 40 percent reduction in engine displacements. This will be achieved through integrating advanced boosting technologies into optimised induction and exhaust systems, as a potential alternative to embracing higher cost, lower emission diesel engines. Asian and other markets, where small displacement engines already dominate, are well placed to take this trend to extremes.

However, for small engines to be effective in urban environments, they need near instant full torque availability for the driver demanding strong acceleration. Such responsiveness is essential to avoid fuel being unnecessarily wasted because otherwise the driver must continually select lower ratio in order to keep up with traffic flow.

To achieve this, smaller engines could require sophisticated boosting/forced induction systems. However, there are simpler and more cost-effective solutions now available that can prevent such systems becoming more complex and expensive than the engine itself.

‘Our production-ready variable torque enhancement system (VTES) for example, provides full boost within 350 milliseconds and significantly improves low speed torque response for naturally-aspirated or turbocharged gasoline and diesel engines. VTES can be implemented on current vehicles, using existing 12 volt electrical architecture, and is therefore more cost effective than any equivalent mild hybrid solution,’ says CPT’s Pascoe.

In essence, the CPT VTES system employs an electric motor driving a supercharger compressor to provide a charge of air to the engine for short periods, when the driving conditions demand it. The transient boost increases engine torque at low engine speeds.

When used in series with a conventional turbocharger, the 2kW of electrical power typically translates into 20kW at the crankshaft. The drain on the battery is minimal and its charge soon restored by the engine alternator.

‘When correctly matched to the engine, VTES can dramatically increase the air charge density over the critical first 10 combustion cycles of a low speed transient operation, delivering real improvements in both torque and emissions performance, where it matters most,’ says Pascoe.

In addition to its electric supercharger, the CPT family of low carbon powertrain related products includes a stop-start system now moving close to production readiness and an exhaust energy recovery system in an advanced stage of development.

The CPT ‘SpeedStart12’ stop-start system can crank up to 2.8-litre petrol or 2.0-litre diesel engines, also using standard 12 volt architecture. It packages into the space of a typical alternator and all electronics are integrated into the unit.

Importantly, its switched reluctance motor provides the power density to re-start an engine within 400 milliseconds, the start time necessary for a driver to perceive a dependable ‘instant’ re-start. It also provides very efficient power generation, achieving up to 3kW with up to 80 per cent efficiency.

‘There is also a tremendous incentive to minimise or recover the energy rejected by the engine as heat,’ says Pascoe. ‘One of the main sources of waste heat is exhaust gas with approximately 30 percent of the hydro-carbon fuel energy used by a vehicle lost down the exhaust pipe. Although some of the exhaust can be used to power a turbocharger at certain points in the operating cycle, and heat is required to operate a catalyst, there is still plenty of energy worth recovering,’ he adds.

‘Our TIGERS product is again based on a very efficient switched reluctance motor operating as a generator and sized to produce up to 6kW of power. This level of power generation can be used either to meet the growing power requirement of future cars or to boost the crankshaft power available,’ says Pascoe.

The innovative and highly efficient application of ‘switched reluctance’ machines in all three CPT micro-hybrid technologies has, until now, represented an untapped opportunity for the automotive sector. OEMs stand to benefit greatly from the inherent robustness and reliability of such machines, already demonstrated in other industries.

‘Switched reluctance motors are well suited to the requirements of the automotive industry,’ says Pascoe. ‘They can be produced for high volume series production at low cost; they are manufactured mostly from easy-to-recycle steel, copper and aluminium and avoid the use of exotic, expensive and heat sensitive materials. These compact motors are easy to package and offer excellent energy efficiency and controllability.’