With its recent models, Hyundai has shown how far it has come in a relatively short time. And now, making the company even more the one to watch, Hyundai has released information on an LPG-fuelled hybrid about to go into production. At the time of writing it was unknown whether the car would be made available outside of South Korea, but here in Australia – with our widespread LPG fuelling infrastructure and low LPG prices – it would surely be an immediate success.
Not the First Hyundai Hybrid
It’s important to realise that the LPG hybrid is not Hyundai’s first attempt at hybrids.
In 2004 the company developed a Getz hybrid prototype, with 50 vehicles supplied as a demonstration fleet to the Korean Ministry of Environment. Hybrid versions of the Hyundai Accent and Kia Rio were then developed, with 350 of these vehicles supplied to the Korean government. Since then, the company states that “thousands” more hybrids have been tested in government fleet use.
However, the LPI Hybrid Elantra pictured here will be the first hybrid Hyundai to be sold to the public.
Technology
The Elantra LPI Hybrid is a parallel-type hybrid. A continuously variable transmission (CVT) is used and the electric motor is mounted between the CVT and the internal combustion engine (ICE) – very much in the manner of Honda hybrids.
The ICE is a ‘Gamma’ 1591cc DOHC four valve engine – a modified version of one of the engines fitted to the non-hybrid Elantra. Bore is 77mm and stroke is 85.44mm. The compression ratio has been lifted from 10.5:1 to 12:1 and the valve timing altered to allow the use of an Atkinson Cycle, the latter approach also used in the Toyota Prius. Mechanical efficiency is improved by a 14 per cent reduction in valve spring load and a 30 per cent reduction in piston ring tension. Both the tappets and the piston skirts use special low-friction coatings. Finally, continuously variable intake camshaft timing and electronic throttle control have been adopted.
The result is a peak power of 86kW at 6000 rpm and 201Nm at 4500 rpm. Diagrams contained in a technical paper written by Hyundai engineers appear to show that the ICE has a very flat torque curve and best Brake Specific Fuel Consumption at about 75 per cent load and 3000 rpm.
No specific detail has been released on the liquid LPG system, however cutaway views of the car show the use of two LPG tanks mounted fore-aft under the rear of the car and multipoint indirect injection.
The flywheel-mounted electric motor is a permanent magnet synchronous design. When powering the car, it can develop a peak power of 15kW and peak torque of 105Nm; when acting as a generator it can develop maxima of 15.7kW and 125Nm. Peak efficiency of the electric motor is listed as 94 per cent and it has a mass of 20.5kg. Its volume is quoted as being 2.2 litres. The motor is natural air cooled (ie forced air or liquid cooling are not used).
The motor control unit is 4.6kg in mass and 5 litres in volume.
The battery pack in the LPG hybrid Elantra uses lithium polymer cells, supplied by LG Chem. It has a nominal output of 180V and a capacity of 5.3 amp-hours. Peak discharge power is 17.8kW and peak recharge is 14kW. Battery efficiency is listed by Hyundai is being a surprisingly high 90 per cent. The battery uses forced air cooling.
The self-discharge of the pack is 0.1 per cent per day (compared with the 2 per cent per day for Ni-MH used in previous Hyundai hybrids) and the Li-Polymer battery pack is 30 percent lighter in weight and 50 per cent smaller in volume than the previous Hyundai Ni-MH designs. (However, the new pack also has a 18 per cent smaller electrical capacity.)
A battery management system controls the rate of charge and discharge and monitors battery temperature.
Hyundai state that the battery pack has passed the company’s internal 300,000km durability test.
The CVT transaxle has a torque capacity of 182Nm and internally variable ratios from 0.427 to 2.369, with a final drive ratio of 4.91. A torque converter is not used; instead, moving away from a standstill is achieved by means of a wet multi-plate clutch.
The CVT is made by Van Doorne’s Transmissie, now a fully-owned subsidiary of Bosch. The transmission uses a metal belt drive and two variable diameter pulleys, each comprising two conical sheaves. When the distance between the sheaves is altered, the effective diameter of the pulley changes. One set of sheaves alters in one direction (eg growing smaller) while at the same time the other alters in the other direction (in this example, increasing in size). This allows the transmission ratio to steplessly alter. The belt, made up of many small steel elements, works as a ‘push’ belt rather than a ‘pull’ belt.
The distance between the two pulleys is 156mm and the overall length of the motor and CVT is 405mm.
Other highlights of the CVT include a chain-driven external gear type oil pump and torsional damper. In case of failure of the electronics, the transmission is also equipped with an all-hydraulic limp-home facility.
To prevent rolling back on hill starts, the hybrid control system applies the brakes until sufficient torque is being developed by the powertrain. This system uses a clinometer to sense road gradient.
A DC/DC converter is used to power the car’s nominal 12V system. The converter has a maximum output power of 1.7kW and a power density of 0.68kW/litre. It is forced-air cooled.
Fuel Economy
Hyundai suggests that the LPG hybrid has a fuel economy of 5.8 litres/100km – amazingly good for a vehicle running on LPG. The car emits just 102 g/km of CO2 and so qualifies as a Super Ultra Low Emissions Vehicle. Over the conventional 1.6 litre auto trans Elantra, the company claims a 41 per cent improvement in fuel economy – however it is not clear whether this is comparing the hybrid to petrol equivalent economy, or LPG versus LPG.
Conclusion
Using liquid LPG technology in a hybrid vehicle potentially realises a very low emission vehicle that, in countries with cheap LPG, would have running costs lower than literally any other approach to driving. We can’t wait for it to arrive!
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