Partial hybrids offer emissions compromise

Partial hybrid cars with low voltage engine boosters can reduce emissions and retain driving performance at a much lower cost than full hybrids, according to a firm that has produced a powertrain demonstrator.

Controlled Power Technologies claims that its retro-fitted hybrid technology can deliver between 15 and 25 per cent CO2 reduction with an additional cost to the vehicle manufacturer of between €750 (£635) and €1500 (£1269).

This compares with a CO2 reduction upwards of 30% for full plug-in electric hybrids but with additional manufacturing costs of between €6000 (£5077) and €10,000 (£8461). 

‘The concept approaches full hybrid CO2 reduction potential, but at a much lower cost and without compromising dynamic performance,’ said Guy Morris, engineering director and chief technical officer at CPT.

So-called ‘micro’ and ‘mild’ hybrids incorporate a downsized internal combustion engine alongside a combination of stop-start functions, electric superchargers, integrated starter generators, and energy storage systems. They cannot, however, drive on electric alone like full hybrids.

The batteries used to power these add-ons tend to be small, low cost and can be charged quickly from mains outlets.

CPT’s initial demonstrator, called the low carbon super hybrid, is based on the engine from the 1.4 Bluemotion Volkswagen Passat family saloon.

‘That vehicle is pretty good on CO2, but dreadfully boring to drive – and that’s the problem, you tend to have the opportunity to give performance or economy but not both,’ Morris told The Engineer.

CPT claims its technology can increase power from 122 to 140 bhp and torque from 200 to 260 Nm whilst achieving a CO2 emission rate of 130g/km.

‘The concept behind the low carbon super hybrid is to configure a solution with an electric supercharger instead of a very large electric motor, which allows you to use a relatively small battery but fully recover that performance.’

CPT are collaborating with the Advanced Lead Acid Battery Consortium (ALABC) on their micro-mild demonstration technology and Morris argues that lead-acid batteries are a far better option for this application.

‘There’s no question, if you want to store energy electrically lithium ion and lithium polymer are very definitely the best battery technologies available, but the caveats are cost, safety and the general strategic accessibility of raw materials,’ he said.