Isuzu Australia Limited (IAL) is in the midst of an extensive Australian evaluation of an advanced diesel electric hybrid as part of the company's wider low emissions initiative.

Trialled against Isuzu's own conventional diesel powered NNR 200 and NPR 300 light duty trucks along with a competitor model, the Isuzu NPR Hybrid Electric Vehicle (HEV) recently completed two days of fuel consumption testing on inner city Melbourne streets with pleasing results.  

According to IAL Product Planning and Engineering Support Manager, Simon Humphries, the second generation HEV N Series (known as ELF in Japan) builds on the technology offered in the first generation N Series Hybrids, which has been available in Japan since 2005.

"While efficiency and performance over the first HEV model was expected, IAL wanted to test the suitability of the latest HEV in our own environment," Mr Humphries says.

"Our road conditions and driving speeds are very different to those in Japan, as its cities are far more congested and offer an ideal operating environment for hybrids."

According to Mr Humphries, IAL's in-house testing of the vehicles, which were all fitted with van bodies and a 660 kg payload, revealed some promising results for both the Hybrid and Isuzu's conventional diesel-powered trucks.

"The testing revealed that Isuzu's HEV performed at its best when average speeds were 15 kilometres per hour or less, with efficiency gains decreasing as the average speed increased," Mr Humphries says.

"In ideal stop-start city driving conditions, the HEV achieved a fuel consumption saving of over 20 per cent and almost 10 per cent in a mixed urban run.

"Also pleasing was the performance of our two conventional diesel-powered trucks which returned fuel efficiency figures of between 8 and 22 per cent better than those achieved by the direct competitor we tested."    

The second generation Isuzu N Series HEV uses battery power to assist the engine when accelerating at low speeds to save fuel.

After a constant driving speed is reached, the highly efficient 3.0 litre SiTEC Series II 150 engine takes over, propelling the vehicle with its conventional diesel power source.

The SiTEC Series II 150 produces 110 kW of power @ 2,600 rpm and torque of 375 Nm @ 1,600 rpm and combines with a synchronous electric motor connected to the driveline via the PTO opening.

The electric motor develops 29 kW @ 1,000 rpm and 274 Nm from zero to about 1,000 rpm.    

A key component of Isuzu's hybrid N Series truck is the use of a low mass 346 volt liquid cooled Lithium-Ion battery pack.

While this battery type can be found commonly in mobile phones, computers and other communications devices it is still rare in vehicles – most hybrids currently on the market opt for the Nickel Metal Hydride batteries, which are generally heavier, less expensive and less efficient.

Like other hybrid technology, the Isuzu HEV charges the battery when the vehicle decelerates or brakes, a system known as 'regenerative braking', which moves power to the battery by recovering the vehicle's kinetic energy.

One of the key fuel saving features on the Isuzu HEV is its use of a special version of the two pedal six speed Automated Manual Transmission, or AMT. 

The AMT uses the same hardware as that found on Isuzu’s latest range of conventional diesel trucks, but the electronics are calibrated for maximum efficiency in a hybrid drivetrain. 

For extra fuel economy and reduced emissions, the HEV shuts down the engine automatically when the vehicle stops or idles in traffic.

When the operator releases the brake pedal, the engine restarts instantly, ready for the driver's foot on the accelerator pedal to propel the vehicle into motion.

Developed on the latest NPR medium wheelbase platform, the Isuzu HEV includes all the features of the latest N Series models, including AMT, Anti-lock Braking System (ABS), SRS driver and passenger airbag, and Anti Skid Regulator (ASR).

According to Mr Humphries, the HEV is only one component of Isuzu Trucks' long term low emissions strategy.

"Our early evaluation results confirm that hybrid vehicles are best suited to quite a specific set of operating conditions, however we will conduct further testing in a broader range of conditions before jumping to conclusions," he says.

"With hybrid vehicles' apparent limitations in mind, Isuzu has undertaken extensive research and development into several other low emission technologies and alternative fuels such as CNG (compressed natural gas) – powered trucks.

"Isuzu CNG trucks have been available in Japan for many years, with a small fleet also operating in Australia – the latest vehicles feature spark ignited, multi-point injection for much improved power and economy, and would be well suited for use in this country.

"Also reassuring from this comparative test, was how well Isuzu's conventional diesel-powered NNR 200 and NPR 300 models performed in the fuel economy comparisons, particularly against their main competitor."