You may have noticed that every hybrid launched in the UK so far has combined a petrol engine with an electric motor. So why not use a diesel engine? The answer is that the Japanese manufacturers have led developments and both the home Japanese market and the highly lucrative American market are dominated by petrol engines due to strict emissions regulations. So there is a gap in the market for the Europeans to exploit.
It should come as no surprise that Peugeot is the first to launch a diesel hybrid. They led the diesel charge with common rail injection and diesel particulate filters making them, and diesel engines, major players. To catch up on the hybrid front they have partnered with Bosch and together they have come up with a truly ingenious solution.
The beauty of the HYbrid4 system in the Peugeot 508 RXH is that it leaves the front of the car largely unchanged. The diesel engine still powers the front wheels in the conventional manner. This is a very good thing when it comes to fitting the system into existing ranges. The addition of a nickel-metal hydride battery and a very compact electric motor at the rear axle provides rear-wheel drive.
In addition to a short all-electric range, the outputs of the diesel and electric motors can be combined to any degree to provide either enhanced performance or improved fuel economy. The system has one more trick which is that you can lock it in four-wheel drive. This is thanks to the alternator at the front which can turn diesel power into electrical power to guarantee four-wheel drive even when the hybrid battery is depleted. It also provides a start/stop function for the diesel engine and operates the air conditioning and electrical systems.
The HYbrid4 system is brilliantly packaged allowing Peugeot to apply the system to other models relatively easily. The system appeared first in the 3008 HYbrid4 crossover; although the four-wheel drive capability of both the 3008 and the 508 is the same, the 508 RXH has a higher ground clearance, and so although it’s more expensive, it has better off-road capability. It also looks better than the rather bloated-looking 3008.