Citroën, now part of PSA Peugeot Citroën, has often marched to different drummer with its different designs like the Traction Avant, 2CV, and DS21. It has done it again with the PSA Peugeot Citroën HYmotion4 system. Unlike other hybrids with the electric motor integrated with the transmission, Hymotion4 uses an internal combustion engine to drive either the front or rear wheels and an electric motor to drive the other axle.

This is not the first Citroen to use two independent powerplants. That honor goes to the 1961-71 Citroen Safari. The Safari was a Citroen 2CV with its two-cylinder, air-cooled engine up front driving the front wheels and an identical engine in the trunk powering the rear wheels. One advantage of the Hymotion4 concept is that it is relatively easy to provide all-wheel or four-wheel-drive capability. Unlike the Safari, where the two engines were controlled mechanically, electronic 'drive-by-wire' controls are used with Hymotion4.

Another advantage is that existing engine, transmission, and other components can be retained pretty much unchanged and electric components can be added in modular fashion. It is quite easy to provide an all-electric mode for urban driving. The downside is that two separate propulsion systems can take up more space.

A conventional starter and alternator are still required on the engine since the electric motor cannot be used as a starter. However, when the vehicle is moving the engine can be started by motion - sort of like 'popping the clutch' in a manual transmission car to start an engine when the battery is dead - provided the road is not too slippery. Power flow control in the HYmotion4 system is integrated with the electronic stability control system to balance power between the front and rear axles for optimum vehicle dynamic behavior.

PSA Peugeot Citroën showed four vehicles using Hymotion4 at the 2008 Paris Auto Shows - the Peugeot RC and Peugeot Prologue, Citroën Hypnos, and Citroën C4 WRC. The Prologue and Hypnos are five-door, compact crossover concept vehicles. Up front they feature a 2.0 liter, 163 horsepower HDi (High pressure Direct injection) diesel equipped with a particulate filter for emissions control, and a 37 horsepower electric motor in the rear for a maximum of 200 horsepower. Combined fuel consumption is 57 mpg and CO2 emissions of only 109 g/km, or zero in electric-only mode. Both have regenerative braking and Stop & Start technology.

Things are turned around in the Peugeot RC HYmotion4 concept. A turbocharged 1.6 liter, 218-horsepower four-cylinder gasoline engine is located in the rear and a 70 kW electric motor is located between the front wheels. The 3,141 pound four-door coupe accelerates from 0-62 mph in just over four seconds when both gasoline and electricity are bringing to bear their 313 horsepower. Having the electric motor at the front instead of the rear axle means more kinetic energy can be recaptured through regenerative braking to keep the lithium-ion battery pack charged. According to Peugeot, the RC can get 52 mpg with CO2 emissions of just 109 g/km.

The Citroen C4 WRC HYmotion4 is the first World Rally Championship race car equipped with a hybrid energy recovery system. The HYmotion4 system enables a proportion of the kinetic energy produced during braking to be recovered by the 125 kilowatt electric motor/generator in the rear and stored in a 990 cell lithium-ion battery pack located over the fuel tank. This energy can be used either to deliver extra power when accelerating or to drive the car using emission-free electrical power alone, with no engine noise or exhaust fumes.

Article key :  Hi-Tech Modular Hybrids, Hi-Tech, Hybrids, New Car