The Project objective will be the development of a new powertrain concept based on a combined energy recovery, storage and re-use system integrated and optimised with the engine system and controls in order to maximize the efficiency of a Natural Gas heavy duty engine.

In that frame, the project has the following objectives:

  1. Internal Combustion Engine optimization.
  2. Heat recovery in the exhaust system of the engine will be obtained by the adaptation of an advanced thermoelectric generator and a turbogenerator able to operate in cascade. 
  3. Beltless engine concept with an advanced 48 V board net architecture is based on the idea of the electrification of all the main auxiliaries as water and oil electric pumps, air condition, brake air compressor, steering pump etc…
  4. Power pack integration. The recovery of energy and the beltless engine impose major changes to the power pack.
  5. Achieve an efficiency at vehicle level well above 50% at acceptable cost.

Power train-concept and estimated temperatures

ICE engine optimization
A relevant engine and powertrain efficiency improvement will be achieved thanks the combined effect of the following innovations:

  • a more powerful turbo to enable higher torque and performance with lower pumping losses at part load;
  • the increased torque allows implement down-speeding strategies with very tall gearing or a hybrid shift strategy
  • a liquid cooled charge air cooler and a redesigned air handling system enables better engine volumetric efficiency helps to refine the engine control strategies the high engine operating points.

This configuration benefit will be further enhanced when an electric torque assist is available as foreseen in the incoming scenario cooperating with the an on-demand electric auxiliary supercharger (running on energy harvested under previous vehicle coasting and braking events) to bring the engine's turbo boost up to the required level within a fraction of a second.

The auxiliary e- supercharger:

  • Helps to bring the transient, real- world torque curve as close to the steady state torque curve as possible and the electricity for the supercharger comes for free under normal driving conditions. The auxiliary e-supercharger is fed with the electric energy produced recovering Kinetic energy and heat and stored in a 48 V battery.
  • Allows to eliminate turbocharger lag at low exhaust gas flow levels. 

Heat recovery

The exhaust system of the ICE will be adapted to host both, an advanced thermoelectric generator (TEG) and a turbo-generator able to operate in cascade to increase the amount of decarbonized on board electric energy.

The thermoelectric generator will be based on innovative thermoelectric elements, leading to an increased electric energy output due to higher temperature levels and thus bigger differences between the hot and the cold side of the TEG modules.

The elements will be specially arranged in a housing to allow the best thermal conditions at the hot and the cold side. As well, high temperature differences and hot-cold-cycles exhibiting high thermal extension and shrinking values have to be accommodated by the housing and the special arrangement of the thermoelectric elements. The thermoelectric generator must be well dimensioned and placed at the right location in the exhaust system considering maximum temperatures. Furthermore, the remaining exhaust gas temperature after leaving the TEG system has to fulfil the full functionality of the state-of-the-art exhaust after treatment.

To ensure lowest possible temperatures on the cold side of the thermoelectric generator, it is necessary to integrate the heat exchanger of the TEG into the engine / vehicle cooling system. As low cold side temperatures are mandatory for a good waste heat recovery rate, the TEG cooling system must be linked into the low temperature circuit of the vehicle cooling system. The elaboration of a suitable thermal management model will help to control the thermal system and to guarantee both, system integrity and high energy return by waste heat recovery.

Of course, the thermoelectric elements must be protected from too extreme temperatures to avoid fast deterioration and early damage of the TEG system.

Therefore and to keep emission regulations, appropriate control of the ICE and probably also a bypass solution is required for the TEG.
The electric energy captured by the TEG, the belt-starter-generator during deceleration events and by other energy harvesting devices as a heat recovery turbo compound is directly used by the electrified auxiliaries, thus avoiding conversion losses and increasing the total system efficiency.

To be able to cope with transient operating conditions, the operating strategy will control the system to a certain extent, for instance, the air conditioning compressor can be shut down while there is a high energy demand of the electrified steering system. When the energy system cannot be balanced any more by the operating strategy, a suitable storage unit based on a an advanced battery and/or a double layer capacitor (DLC) module will be used.

Beltless engine concept with an advanced 48V board net architecture

A beltless engine concept based on a 48-volt electrification will contribute to an optimized drive train. This means the electrification of all main auxiliaries as water and oils e-pumps, air condition and brake air compressor, steering pumps etc.

A smart board net architecture is required comprising the e-auxiliaries, e-generation by an advanced starter-generator and a storage unit to ensure a highly efficient recovery, storage and consumption of electric energy but as well to handle peak demand (e.g. up hill drive at full load).

The development will target the following topics:

  • Efficient e-auxiliaries based on 48 V level and advanced 48V board net architecture with central integrated control unit for all control and power electronic for running the electrified subsystems
  • Efficient and smart solution for generating and storing electric power using a battery and/or a DLC stack for 48 V board net level to deal with basic electric load coupled with the need of high energy peaks e.g. for the starter-generator.
  • Additional DC/DC 24V converter to ensure that the conventional 24 V board net can be further applied for the broad range of conventional electronic application.

Power pack integration

The beltless engine and the heat energy recovery devices impose major changes to the power pack. Besides the new geometrical layout, there are strong effects on the thermal and the electrical system of the power pack, the exhaust system and the exhaust after-treatment.

In a first step, the TEG must be positioned at the right place in the exhaust system to achieve an optimum performance. Thus to select the best position, the amount of energy taken out by the turbo, the absolute temperature level and the exhaust gas backpressure have to be considered. Based on this TEG positioning in the exhaust system, the specifications for the TEG elements and the necessary TEG cooling are elaborated.

As the TEG performance significantly depends on the temperature at the cold side, it is mandatory to design the vehicle cooling system in an appropriate way.

The TEG will impose additional heat power to the cooling system. This heat power is, in principle, originating from the exhaust gas.

Preferably, it shall be dissipated via the low temperature radiator. However, if this is not reasonable or possible due to limitations of radiator performance, additional coolers, fans or increased radiator size might be necessary.

The challenge not to increase the system complexity, and to have an additional weight and higher energy demand, might be solved by the application of a TEG bypass, which is anyway needed to protect the thermoelectric elements, in case of extreme loading of the vehicle cooling system. This means rare, temporary and generally short stops of the TEG waste energy recovery in specific driving situations (e.g. full torque - up hill at high ambient temperatures).

As a whole, to be able to get the optimum performance of the power pack regarding function and energy efficiency, mutual dependencies of the performance of the engine, the electric and electronic system including the battery and of the exhaust after-treatment must be taken into account.

The optimal power pack integration will be achieved by an overall control strategy which shall be derived using an adequate simulation model.

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