Intelligent energy management takes to the road

Peter Els
Posted: 01/03/2018

It’s no secret that the Automotive industry is under pressure from regulators to cut emissions and improve real world fuel consumption: Not, as in the past, in the laboratory under ideal conditions, but in the real world, with traffic and steep hills.

While it’s not possible to create energy, it is possible to ‘recuperate’ and store energy, such as the kinetic energy converted into heat, vibration and sound energy under braking. In the past this energy would have to have been stored in a flywheel as rotational kinetic energy and (usually) released back into the powertrain by way of a constantly variable transmission.

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Thanks to the rapid progress of electrification, energy harvesting or recuperation, also known as ‘regen’ has been simplified, and the management of the regen and torque boosting process has been optimized.

ENERGY MANAGEMENT IN THE REAL WORLD

Unlike in laboratory tests, such as the New European Driving cycle, real world driving covers a wide spectrum of driving conditions; acceleration, coasting, braking and sailing all make up the average road commute.

The question however, is how to best harvest and use the energy?

Fortunately there is a short term solution that is both cost effective and easy to implement, namely 48-volt electrification. The higher powernet increases the recuperative potential of the recovery systems, allowing effective regen from various sources:

  • Energy harvested from suspension travel, such as Audi’s eROT system that replaces the suspension dampers with horizontal motors, is comfortably stored in the Li-ion battery for use when required
  • Kinetic Energy Recovery systems (KERs) are of particular interest, with a possible recovery of up to about 10 kW

The potential of KERs in reducing emissions is well demonstrated in the 48V Mild Hybrid Electric Vehicle (MHEV), where the replacement of the alternator with a 48V Belt Starter Generator (BSG) in a P0 topology, typically achieves CO2 emissions savings of approximately 13%, measured over the NEDC.

Central to the efficacy of the system is the energy recovery performance, which is highly adaptable and easy to engineer without major design changes to the powertrain. This flexibility means that by reconfiguring the topology, further savings are possible:

Configuring the BSG as a P2 side-mounted Starter Generator could up the CO2 savings to 18%, while switching to a P2 integrated Starter generator extends emissions reduction to 22%.

Energy recuperation is only one half of the equation; the other being extracting useful work from this harvested energy. This is accomplished through torque assist, where the BSG supplements the ICE’s torque during acceleration, or when a gradient is encountered.

While energy recovery and torque assist register significant gains under the NEDC, in real world driving, under the RDE, the results are even more impressive because extended engine-off coasting phases are often encountered. In an evaluation of a 48V P0 system, on public roads in Germany, Continental found that 22% engine-off coasting, with a 9% energy recuperation could realize an 8% fuel saving.

This was achieved over a RDE route with a mix of 20 km urban, 38 km non-urban, and 34 km highway driving. 48V MHEV technology is currently rolling out in series production, with manufacturers such as Renault, Mercedes Benz and Audi all achieving significant emissions reductions with newly launched models, all taking advantage of regen and torque-assist.

Notwithstanding the impressive results achieved with the initial 48V MHEV energy management, first tier suppliers such as Continental and Delphi believe there is further scope for improvement with the imminent roll out of Vehicle to Infrastructure (V2I) connectivity.

CONNECTED ENERGY MANAGEMENT

In 2016 Las Vegas became the first city to introduce a V2I system on public roads. The system transmits information from traffic lights to servers operated by Traffic Technology Services which is in turn relayed to connected vehicles over a 4G LTE connection. This informs drivers of how long it will take the red light to change to green, which would allow the driver to adjust the vehicle’s speed to match the traffic light’s timing on any particular route.

Taking this one step further, a haptic warning could alert the driver to the fact that the traffic light was about to change to red allowing the vehicle to coast and harvest energy. 

This connectivity is not only useful within the confines of the city, in the country it’s possible to use the navigation system to determine the topography of the road ahead – when the vehicle approaches a curve or uphill gradient. 

At the International Federation of Automatic Control, held in Toulouse in July 2017, Continental demonstrated an innovative Connected Optimal Predictive Control for Connected Energy Management in Hybrid Vehicles. 

A Ford Focus demonstrator was connected to continental’s ‘eHorison’, and equipped with automated clutch, HMI haptic pedal for eco-driving functionality, and solar panels; all aimed at conserving energy and reducing CO2 during real world driving through improved onboard connected Energy Management.

The onboard management is supported by intelligent navigation systems with real-time connectivity to the Cloud that can predict driving conditions. The theory behind the real-time optimal predictive algorithms is based on the mathematical Pontryagin’s Maximum Principle (“PMP”) that provides broad solutions for optimization of dynamic systems with integral criteria, within given constraints. 

The calculation of the “trip planning” is made possible by way of embedded controllers synchronized to powerful servers and computers connected to the vehicle. Significant gains of more than - 10% in CO2 reduction have been measured while still maintaining acceptable performance and drivability. 

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With the ICE operating at between 42 and 48% thermal efficiency it’s up to engineers to recuperate ‘wasted’ energy from the vehicle dynamics and turn this into useful work if CO2 emissions are to be reduced and performance maintained. And while this is no simple feat, the emergence of electrification and connectivity is enabling significant strides toward achieving the objectives.

Whether these gains will be enough to get the ICE, even in MHEV format, through the forecast 2025 emissions targets of between 68 to 70 g/ km of CO2 emissions is yet to be seen; but it certainly is a step in the right direction.

SOURCES

Peter Els
Posted: 01/03/2018

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