April 4, 2005 Mercedes-Benz has always been at the forefront of the development environment- and resource-friendly propulsion systems and has explored natural gas, LPG, electric propulsion and fuel cell technologies in recent times. This pioneering position will be further enhanced this year when it becomes the first manufacturer to offer a plug-in hybrid-drive version of its Sprinter commercial van. Plug-in means that the vehicle is equipped with a power socket which enables the batteries to be recharged even when the engine is not running, for example overnight. A hybrid-drive Sprinter with no recharging socket is also planned.
In the hybrid-drive Sprinter (with or without a recharging socket) an electric motor is integrated into the drive train between the transmission and clutch. It obtains its energy from a nickel/metal hydride battery which it constantly recharges when on the move, acting as a generator and using the energy produced when braking or on downhill gradients (recuperation). The basic vehicle is a Sprinter 311 CDI (3.5 t GVW, kerb weight 1960 kg) with an automatic transmission.
A hybrid-drive van can provide zero-emission, exceptionally quiet operation when travelling in towns and other emissions-sensitive areas. Other advantages include an unrestricted operating range thanks to the internal com-bustion engine, familiar operation which is largely the same as for a conventional vehicle and a high level of operating safety. Last not least, the operator is rewarded with a reduction in diesel fuel consumption of between 10% and 50% depending on the type of operation.
Plug-in hybrid drive with a 70 kW electric motor
Since the two drive units – the internal combustion engine and the electric motor - are intelligently configured in parallel, the hybrid Sprinter can be optimally operated to suit the situation: emission-free, low-noise operation in sensitive areas (city, warehouses) under pure electrical power and fuel-reducing hybrid operation by supporting the internal combustion engine with electrical power at low speeds and when accelerating. When the accelerator is fully depressed for maximum performance, both power units operate together. This so-called boost function is appropriate when more performance is required for acceleration or on uphill gradients. During normal operation the driver is able to select the required drive unit at the push of a button.
In the plug-in hybrid drive system in the Mercedes-Benz Sprinter, an electric motor with an output of 70 kW is combined with the conventional diesel engine. It obtains its energy from a nickel/metal hydride (NiMH) battery with a capacity of 14 kWh. This allows an operating range of up to 30 kilometres under purely electric propulsion. The battery is recharged from the mains power supply, e.g. overnight, with a recharging time of approximately six hours. The energy generated when braking is also used to recharge the battery.
Workmen, disaster relief organisations or the fire services can also use the 40 kW electric motor in the Sprinter with plug-in hybrid drive as a generator to operate tools and machinery while in the field. The additional electrical equipment weighs 350 kg. If lithiumion batteries are used in place of the NiMH batteries, the weight penalty is reduced to 160 kg.
Hybrid drive with a 30 kW electric motor
The Sprinter with hybrid drive and no recharging socket has a smaller electric motor with an output of 30 kW and smaller batteries with a capacity of only 3 kWh. These allow purely electric operation with a range of 3 to 4 km, which is perfectly adequate for almost all pedestrian areas. The additional weight of this simpler variant is approx. 100 kg.
Looking at the overall picture, it cannot be denied that as a result of the second power unit, hybrid drive has certain penalties in terms of payload and purchase price. That said, however, nine EU countries are already offering incentives for the purchase of hybrid vehicles, e.g. preferential taxation or subsidies, as well as tax relief on the operation of such vehicles. In London, for example, gas-powered or hybrid drive vehicles are already exempt from road toll charges.
In view of expected, increasingly stringent emissions regulations, restrictions on access to inner city areas, tolls and vehicle taxes, and with the aim of reducing fuel consumption in general, this form of drive system is gaining in worldwide importance. Hybrid drive with its combination of well-proven components, i.e. the internal combustion engine and the electric motor, is ideally suited to bridge the interim period before the fuel cell reaches series production maturity.
Customer trials of the Mercedes-Benz Sprinter with plug-in hybrid drive will commence within the next few months.