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About modern hybrid drivelines
As it was told, the modern hybrid drives are equipped with the energy buffer. In addition they also have motor/generator devices that can use/provide the energy from/for the mentioned energy buffer. According to the energy type used in the recently proposed modern hybrid drivelines electric and hydraulic technologies are the most promising ones. One has to say that other technologies also have been tested, like hybrids based on fly-wheel or compressed air as energy storage devices. According to the present state, they are not as interesting as the electric and hydraulic technologies.
Regarding the way how these systems are introduced in the automotive applications, two basic architectures are dominant: parallel and serial hybrids. Using combination of the mentioned technologies and architectures, numerous final concepts of the hybrid drivelines are possible and VOLUMTRAN is one of them.
Hybrid technologies 
As it was mentioned, modern hybrid drives are mostly based on  electric and hydraulic technology. Each technology has strong and week points. In scope of the VOLUMTRAN project special attention was given to potentials that can be reached by synergy between these two technologies.
Electric hybrid technology
In this case the energy buffer is/are battery and/or capacitors while the electric machines that can work as motor/generator will be used to turn the electrical energy to the mechanical and inversely. Electric buffer and motor/generator are connected by the drivers that can accommodate the current and tension between the batteries and the motor/generator, according to given driving situation. Using state of the art electric components it is relatively easy to make quiet and cost effective electric system that can maintain the highway speed (about 15-20 % of nominal power), but electric hybrid with similar overall fuel efficiency as the hydraulic hybrid, regarding regenerative braking, will be roughlly two times more expensive.
Hydraulic hybrid technology
Comparing with the electric hybrid; a hydraulic accumulator is equivalent of the electric batteries and/or capacitors while the hydraulic motor(s)/pump(s) are equivalent of the electric motor(s)/generator's). Additionally, the oil flow is equivalent to the electric current, while the oil pressure is equivalent of the electric tension. Hydraulic motor/pump machines can meet vehicle demand for power by simple displacement variation so additional devices, as drivers at electric hybrids, are not needed. Using state of the art hydraulic components it is relatively easy to make hydraulic hybrid, which for same fuel efficiency regarding regenerative braking, will be roughly two times less expensive than similar electric system, but hydraulic hybrid at highway speed will be less efficient and it will generate more noise than electric system.
Hybrid Architectures 
Adding additional systems to existing one, logically will add additional cost. Or one can say that the biggest problem of the modern hybrid solutions is price that has to be paid for given improvement. Impact of the additional systems on to the  overall cost can be reduced by hybrid architecture. Hybrid architecture relates to concept of interconnection between different subsystems of the hybrid drive. Using advanced architecture strategy  'hybridisaton' of the driveline  can be donne with acceptable cost. Two main architecture strategys are paralel and serial one. Combination of those architectures is possible with so called power split devices. Still, trend is toward pure serial hybrids, without elements of standard mechanical transmission.

Parallel hybrid
If there is a mechanically conection between the engine and wheels it is parallel hybrid. Parallel hybrids can be seen as the ‘conservative’ approach where standard, mechanic part of the driveline is combined with the additional part, electric, hydraulic or pneumatic capable to store/restore energy. Strong points of this approach are good efficiency of the mechanical transmission and known technology. Drawbacks are reduced freedom of the vehicle design and hybrid control strategie designe due to the limits imposed by the mechanical conection.
Serial hybrid
If there is no mechanical connection between the engine and wheels, it is serial hybrid. This can be seen as the more advanced option as the overall vehicle construction is simplified. Strong points of the serial hybrids are flexibility of the connections between different components and complete freedom in the optimization of the system component parameters. Flexible connection allows more freedom in the vehicle design regarding placement of the system components while complete freedom in parameter optimization will allow waste choice of the hybrid strategies that can be applied, providing the best overall performance. 
VOLUMTRAN project can provide serial hybrid with all benefits that this architecture can offer.