ENERGY MANAGEMENT FOR NEXT-GENERATION COMMERCIAL VEHICLESThe overall objective of reducing CO2 emissions from commercial vehicles demands the efficient management

of energy for all of the systems involved. Research work at IAV shows how this can be achieved for the next

generation of commercial vehicles using modern development methods and innovative algorithms.

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DEVELOPMENT EnERgy MAnAgEMEnT

REQUIREMENTS ON FUTURE COMMERCIAL VEHICLES

The global warming discussion in recent years has resulted in a sharp rise in public awareness of CO2 emissions. To limit global warming in coming decades, there is a call to reduce worldwide greenhouse gas emissions. Extending the Euro VI emission standard to include regulations limiting CO2 emis-sions from heavy commercial vehicles is being discussed both at national and international levels. It can be expected that future regulations will be geared towards an increase in freight transport.

This means that the commercial vehicle powertrain needs to become even more efficient. This is a demand that is more dif-ficult to satisfy in the light of forthcoming Euro VI emission legislation. Complex systems for reducing engine-out emissions in combination with sophisticated exhaust-gas aftertreatment concepts make a further increase in the efficiency of the inter-nal combustion engine (ICE) more difficult. As a result, ways of reducing CO2 emissions must be identified in the context of optimising the overall vehicle.

ENERGY MANAGEMENT AND POWER CONSUMERS

A raft of measures is necessary to improve the energy effi-ciency of future commercial vehicles. To exploit the full poten-tial in relation to the energy balance of new powertrains, it is essential to optimise the way in which the following systems interact: : internal combustion engine with lower engine-out emissions : exhaust-gas aftertreatment systems with reduction and

regeneration control : thermodynamic recovery of waste heat : drive train and transmission : systems for recovering kinetic energy : secondary propulsion and energy storage systems

(hybrid powertrain concepts) : subsystems and auxiliary drives (cooling water, oil,

compressed air, electricity).A comparison of the Sankey diagrams shown in 1 and 2 illus-trates the differences in energy flow for a conventional power-train and a possible future powertrain. It can be seen that a higher number of systems is involved and that energy flows are more highly branched. Efficient energy management must direct the flows of energy in such a way that the amount of chemical fuel energy required is minimised while keeping transport performance constant.

APPLICATION-SPECIFIC SOLUTIONS

A heavy goods vehicle, for example a semitrailer truck of the 40-t class and a medium-duty commercial vehicle (7.5 to 18-t class), are compared as examples to show the differences in the application-specific frameworks. The two vehicle classes differ widely, not only in terms of the dominant driving profiles.

Long-haul, heavy goods vehicles are typically semitrailer trucks, in other words a combination of a truck tractor and a semitrailer. The truck tractor provides all of the propulsion energy. The measures necessary to meet emission legislation place high demands on the package and the cooling capacity required for the vehicle. As a result, recuperation and hybrid

AUTHORS

TOBIAS TÖPFER, M. SC.is Development Engineer specialising

in Overall Systems/Alternative Powertrains in the Commercial

Vehicles Division of IAV gmbH in Berlin (germany).

DR.-ING. LARS HENNING is Development Engineer specialising

in Powertrain Management in the Diesel Development Division of IAV

gmbH in Berlin (germany).

DR.-ING. PETER ECKERTis Team Manager for

Thermodynamics/Analytics in the Commercial Vehicles Division of IAV

gmbH in Berlin (germany).

DR.-ING. JÖRN SEEBODEis Head of the Department Overall

Systems/Thermodynamics in the Commercial Vehicles Division of IAV

gmbH in Berlin (germany).

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components that demand a large amount of space or are heavy in weight are just as unsuitable for the tractor as technolo-gies that require high additional cooling capacity. The situation found in the

semitrailer is completely different. It pro-vides space, and therefore also offers room for cooling systems. However, suit-able technologies must be relatively low in weight and easy to control. The tech-

nology in the semitrailer must require a low level of maintenance and, except for the open-loop and closed-loop control signals from the truck tractor, must be able to operate autonomously and work

Engine

Engine cooling energy

Mechanicalenergy

Exhaustenergy

Fuel

ene

rgy

Waste heatrecovery

Auxiliaries Exhaust Coolingsystem

Hybridsystem

Drivetrain Wheels

Braking energy

Propulsionenergy

After-treatment

2 Energy flow in a future commercial vehicle powertrain

Engine

Engine cooling energy

Mechanicalenergy

Exhaustenergy

Fuel

ene

rgy

Auxiliaries Exhaust Coolingsystem

Drivetrain Wheels

Braking energy

Propulsion energy

After-treatment

1 Energy flow in the conventional commercial vehicle powertrain

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reliably under extreme outdoor condi-tions. Against the backdrop of these requirements, mechanical or hydraulic hybrid systems may provide alternatives to electric systems.

Medium-duty commercial vehicles that also operate in urban areas must be low-emission. More importantly, besides emitting fewer pollutant gases, they also need to be quieter. Even today, vehicles are required to meet specific conditions for entering Europe’s city centres. In future, zones admitting only local-zero-emission vehicles will become even more widespread. In addition, distances driven in urban areas are usually relatively short. If prolonged or frequent loading and unloading phases are involved, the option of external energy supply is not unrealistic. Electric hybridisation pro-vides the best solution for meeting the requirements in this vehicle class.

The basic principles underlying the two applications under discussion make it impossible to define only one single powertrain layout for the future. This must instead be tailored to the specific requirements in hand, resulting in huge differences in the system architecture of future powertrains for commercial appli-cations, 3.

HOLISTIC DEVELOPMENT METHODOLOGY

As the diversity of powertrain architec-ture and system complexity grow, so too does the cost pressure on the develop-ment side. To maximise development process efficiency, model-based methods must be closely intermeshed with exper-imental approaches. The simulation of the overall vehicle is a central compo-nent of the model-based development process. In this regard, it must be possi-ble to use a vehicle model in various lev-els of detailing on a flexible basis throughout the development process.

In the early concept definition phase, overall-vehicle simulation has the pur-pose of analysing the potential of differ-ent powertrain concepts and architec-tures. In the system and algorithm development phase, simulation is used primarily for selecting individual com-ponents, for designing functions and algorithms, for MIL and SIL testing of control and operating strategies as well as for carrying out the initial pre-calibra-tion of control parameters. The use of

overall-system simulation within a HIL setup on the engine or powertrain dyna-mometer is an important part of the engine and vehicle calibration and test-ing phase. This provides the capability of calibrating the engine and OBD on the dynamometer while taking near-realistic driving conditions into account.

IAV performs the tasks described before using the Matlab/Simulink-based tool Velodyn for ComApps. This is a flex-ible simulation environment for model-ling commercial vehicles and mobile working machinery. It provides an extensive and specific model library. If detailed descriptions of individual com-ponents are necessary, internally devel-oped or commercial simulation tools can be directly integrated into Velodyn or as co-simulations [1, 2].

4 shows an example model structure for a commercial vehicle. As operating behaviour is predominantly determined by running resistances, this model focuses on simulating the vehicle’s longitudinal dynamics. In addition to the model blocks for the surroundings, the driving cycle and the driver, the model structure mainly consists of sub-models for the powertrain

with engine, transmission, hybrid system, recuperation system and the various con-trol units.

ENERGY MANAGEMENT WITH VISION

As a result of its modular structure, the Velodyn for ComApps overall-vehicle simulation environment is an ideal plat-form for developing new energy man-agement systems. Using the example of a 40-t hybrid truck model, a manage-ment system was configured that opti-mises fuel consumption in real time on the basis of a cost-minimisation func-tion involving all powertrain subsys-tems involved. The Equivalent Con-sumption Minimisation Strategy (ECMS) is utilised as the control concept [3]. ECMS is an optimisation method that determines the optimum torque split between the internal combustion engine and the electric motor for the current operating point. The battery’s current state of charge (SOC) is included as a boundary condition. The exhaust gas temperature is also taken into account in the cost function with the aim of

3 Possible layouts for a commercial vehicle powertrain with hybrid components

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operating the exhaust gas aftertreat-ment components within the optimum temperature range.

5 shows a schematic diagram of the energy management system. ECMS is implemented in the hybrid control unit (HCU) and has split factor u as its out-put. This splits the requested total torque between internal combustion engine torque:

EQ. 1 TICE=TReq∙(1–u)

and electric motor torque:

EQ. 2 TEMG=TReq∙u

Input into the HCU is the current torque request TReq and SOC.

By way of example, an extract from the simulation results is presented in 6. It shows the curve of the torque requested by the driver and that of the torque requested by the ICE. It also

shows split factor u and the battery’s SOC resulting from optimisation. Based on the battery’s state of charge, ECMS splits the torque in such a way that, in ranges where requested torque is low, the internal combustion engine is switched off completely, resulting in all-electric driving, (u = 1) or the load point is shifted (u < 0). After prolonged periods of all-electric operation, the load point is shifted to ensure efficient exhaust-gas aftertreatment.

Current work on energy flow manage-ment at IAV also includes developing an alternative strategy to ECMS. For exam-ple, a model-predictive control strategy (MPC) continuously takes account of route information, such as altitude pro-file and vehicle speed, which in modern vehicles is provided by the navigation system. Further input parameters, such as Vehicle2Vehicle communication or weather information, can also be implemented.

SUMMARY AND OUTLOOK

The powertrain will remain one of the key factors in optimising the transport efficiency of future commercial vehicles. A development task posing a particular challenge will be to optimise the integra-tion of recuperation and hybrid systems into the increasingly complex flow of energy. IAV is pursuing different approaches that consider all aspects of energy flow using its knowledge of the subsystems involved. This complex task can be accomplished only by employing modern development tools, such as over-all-vehicle simulation.

REFERENCES[1] Töpfer, T.; Eckert, P.; Seebode, J.; Behnk, K.: Energetische gesamtfahrzeugsimulation als Werkzeug zur Entwicklung hybrider Arbeits-maschinen. 3. Fachtagung für hybride Arbeits-maschinen, 2011[2] Eckert, P.; Henning, L.; Reza, R.; Seebode, J.; Kipping, S.; Behnk, K.; Traver, M.: Management of Energy Flow in Complex Commercial Vehicle Power-trains. Accepted SAE paper 12PFL-0653, 2012[3] Paganelli, g.; Ercole, g.; Brahma, A.; guezennec, y.; Rizzoni, g.: A general Formulation for the Instantaneous Control of the Power Split in Charge-Sustaining Hybrid Electric Vehicles. Proc. AVEC 2000, 5th Int. Symposium on Advanced Vehi-cle Control, Ann Arbor, MI, 2000

0

1

0

-1

0

1

u [-

]

8000 8500 9000 9500

2500

Torque requestedCombustion engine torque

Time [s]

Torq

ue [

Nm

]S

OC

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6 Example showing the course of relevant ECMS signals as a function of time

Vehicle

5 ECMS signal flow

4 Model structure of a commercial vehicle in the simulation environment Velodyn for ComApps

THANKS

The authors wish to thank Kai Behnk for

contributing to this paper.

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