With the ever increasing electrification of ICE (Internal Combustion Engine) ancillaries and sub-systems, holistic approaches to quantification of benefits is essential.
Historically and even in present day, vehicle design is still siloed to an extent. Each department is concerned with the design of their own systems using boundary conditions from previous programmes, or that other departments have provided at a particular point in the programme which might now be obsolete. Systems integration verifications do not happen often enough to avoid “emergency” alterations or indeed finding that a colleague, for example, has assumed a lower (and maybe out of date) maximum discharge rate of the battery and therefore spec’d electrical cables that are not up to the intended use.
Once these vehicle development silos are broken down and engineers are working together, the systems integration becomes more efficient. Constantly updating and discussing issues openly reduces time wasted integrating systems that are incompatible with each other, particularly when considering physical prototypes.
Modern vehicles are becoming ever more complex due to customer demands on technology and due to emissions legislations.
One of the trends that has been increasing over the past decade or so is the electrification of internal combustion engine ancillaries and sub-systems, for example pumps that flow the coolant around the engine and cooling system or indeed the HVAC system. More recently, the electrification of pressure charging devices such as turbochargers and superchargers has given us the opportunity as engine designers to improve the torque delivery of the engine but also, in the case of electrified turbochargers and turbines, given the possibility to recover energy from the exhaust gasses and store it in the form of electrical energy. Electrification of the pressure charging devices has also given us increased freedom of how we control these devices to operate throughout the speed-load range of the engine, particularly for systems which use decoupled electrified turbine and compressor devices.
Figure 1. eTurbo
(Borgwarner, 2017)
Whilst quantifying the benefits in terms of emissions and fuel economy of such electrified systems, we should not just assume that we have a freely available 48V electrical energy storage device to power them. The electrical energy in this device will have been generated from somewhere, most likely from an Integrated Starter Generator, either belt or crank mounted. This will be generating loads on the engine during vehicle operation to maintain the 48V battery charge levels. Such loads need to be considered and will vary according to the BMS strategy and other systems’ demands (Electric air conditioning compressors, coolant pumps, power-steering pumps, PTC heaters, etc.). At any point of the electrical system we will have losses. These can come from cable losses, inverter switching losses, internal resistances of the battery and losses in the motors and generators which should include friction losses. The electrical losses will be temperature and current dependant. These losses will affect the dynamics and availability of optimal levels of electrification and must be considered when evaluating the electrification technology benefits on the overall vehicle.
Claims of technology benefits of 10-15% might soon reduce to figures of around 5% for example or even null, or even worse, detrimental compared to not implementing the technology, once a full systems integration analysis has been undertaken using realistic duty cycles and environmental conditions. Changes in control strategy and hardware must also be considered and analysis re-run as these will also impact the technology benefits.
So in summary, if you’re working in the field of system electrification, make sure you have thought about where your electrical energy has come from and how the electrical storage devices are also used by other systems, not just the one you are designing. Also consider the impact of adding weight. Work as a team to create an optimised and efficient product using modelling tools that allow full vehicle systems integration.
(Audi, 2017)
We use Dymola and Modelica for a variety of reasons:
- Supports multi-physics modelling in one environment: 1d and Multi-body mechanics, Thermo Fluids, Hydraulics, Electrical, Magnetic, Thermodynamics, Chemical, Control.
- Acausal system model definition: the software will automatically determine the calculation order for you as it can deduce what the knowns and unknowns are in the model. The software will also optimise the code for you every time the model is recompiled.
- Model inversion without rewriting any code.
- Open models that allow full customisation without relying on library developers to do so and waiting for later versions to be released.
- IP can be retained within the company designing the system without divulging it to library model developers. Models can also be encrypted to protect IP.
- Fully supports import and export of FMUs using the FMI technology
Written by: Alessandro Picarelli, Engineering Director and Jose Miguel Ortiz Sanchez, Project Engineer
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