The future of the car is electrifying!
Global regulations for vehicle emissions are becoming ever more stringent; emissions have to go down more and more. It is not possible to get the engines cleaner soon enough, so in order for car manufacturers to be able to keep meeting these standards, they have to resort to building electric cars and/or electrification of their existing car platforms, which have internal combustion engines (ICE); hybrids. Electric motors do not emit any fumes, so if you can use those to propel a vehicle, or have them support fuel driven vehicles, there is significant reduction of the total bulk of emissions.
The standard for electrification of motor vehicles, including hybrids and BEV (Battery Electric Vehicle) typically is a high voltage architecture. The typical voltage lays around the 400 Volts mark. In some high performance applications even near the 800 Volts mark.Though these high voltage architectures can bring a significant amount of horsepower and torque, they also have some major drawbacks; big batteries are needed, there is danger of electrocution, it is quite expensive to develop and build and the batteries need thermal management to obtain optimal power and lifespan.
Developing a new full electrical car platform is very expensive for most car manufacturers, so if adapting existing platforms to electrification is possible, this would be very cost effective. One of the major problems however, is placement of the battery pack; an existing ICE platform usually does not allow for easy integration; the floor is set up to take an exhaust and a fuel tank. Slipping in a battery pack is difficult.
So, there is the high cost of high voltage configurations and architectures and the demand for simple solutions for electrification. This is where 48 Volt steps in as a solution.
48 Volt on the rise
In the past, 48V was regarded as a solution for glorified stop/start systems, but did not quite catch on. Since then, the perception has changed quite dramatically.In the field of electrification, 48V systems can offer up to 90% of the performance of high voltage systems, for 30-60% of the cost.The key contributor to the cost reduction, is also the heart of the system; the generator. In its construction, the 48V generator is very similar to a conventional 12V alternator. This makes it very easy to integrate into the car. It simply sits at the same location, so there is no need for big changes.Then, if the generator is also used as an electric motor, it becomes evidently a useful piece of equipment. Enter the Belt Driven Starter Generator (BDSG).
Two in one
The BDSG is a generator and an electric motor in one. It only consumes as much space as a conventional alternator, so there is no need to rearrange the car’s engine bay.
In alternator mode, the BDSG charges 48V and is part of a smart charge system. This means the generator only charges when the battery condition requires it. In any other situation, there is no charge and consequently fuel is saved and CO2 emissions reduced. The ideal time to engage charging is during braking and off-throttle, hence acting as regenerative braking.
Dual layout: 48V and 12V
The fact that the BDSG is charging 48 Volt, does not mean the whole board net is working on 48 Volt. It would not make sense to change the board net voltage from 12 Volt to 48 Volt, as that would mean everything would have to change; from light bulbs to entertainment systems, to ignition system, to comfort systems, etc. Every electrical component would have to be changed.
Therefore the 48 Volt charging system and the rest of the 12 Volt electrics are separated. The 48V BDSG charges a compact 48 Volt battery pack, through designated power lines. Both positive and negative. Connected to this 48 Volt battery pack is a DC/DC power converter, which converts 48 Volt into 12 Volt, which in turn powers the traditional 12 Volt board net, including the 12 Volt (start) battery.
The 48V BDSG can work as an electric motor and since it is connected to the ICE’s crankshaft via the multi-V belt, the electric motor can assist the ICE during acceleration. This means the ICE does not need to consume as much fuel as before. Burning less fuel equals less CO2 emissions; objective achieved! A configuration like this qualifies as a mild hybrid system, in which the vehicle is electrically assisted, but is not able to propel itself in full electric zero emissions mode (ZEV – Zero Emission Vehicle).
The mild hybrid system is usually charged through regenerative braking and/or off-throttle coasting. There is no plug-in function. In some cases, a mild hybrid system also allows for a so-called sail mode, where the ICE is shut off when the accelerator pedal is released. All in the name of fuel saving and reduction of CO2 emissions.
Not just for Mild Hybrid
Due to the increased power levels, 48 Volt systems have significant benefits, which expand beyond drivetrain electrification. Think of active chassis management, electric AC compressors, various heating systems, AWD drive systems and full hybrid architectures. Even an electric supercharger is offered!
Valeo has developed various 48V components to suit electrification needs, as well as electric AC compressors and electric superchargers.The available electrical power in a 48 Volt system allows virtually all ICE driven accessories, such as water pump, AC compressor and power steering pump, to be positioned away from the ICE and become electrified. This then reduces the resistance and load on the ICE, which – again – saves fuel. In terms of electric propulsion, 48 Volt allows electric motors to become strong enough to provide electric drive and thereby ZEV capabilities. This means various full hybrid architectures are possible; an electric motor on the ICE’s crankshaft, on the gearbox input or output shaft, and/or (rear) wheel drive.
A car manufacturer may decide to do a combination of the above; 48 Volt BDSG, combined with a gearbox drive and additional rear wheel drive. This then brings a clean and safer vehicle, which is relatively cost effective to develop and yet performs excellently in everyday life. Granted, the ZEV range of a 48 Volt system may be smaller than that of a high voltage solution, but it is a perfect trade-off for most daily drivers.
Starting the engine and e-motor deployment
When the ICE is very cold, the initial start is performed through a conventional 12V starter motor. Each engine start thereafter is done through the 48 Volt BDSG unit. This allows for a smooth and extremely fast stop/start system.
Another benefit of starting with the BDSG is that starts can be performed at higher ICE rpm. This means the ICE can be shut off and restarted well before the vehicle comes to a standstill; the rpm of the BDSG can be easily matched to the engine speed. Having this possibility has another benefit. If starting the ICE can be done at higher speeds, then you have the possibility to shut down the ICE when the throttle pedal is released; a so-called Freewheel-Engine off function.
If the driver then presses the accelerator pedal again, the BDSG quickly starts the motor and the car’s DSG gearbox closes one of the clutches again to drive the wheels again. Should the driver press the brake pedal, one of the DSG clutches closes and the BDSG falls into regeneration mode and charges the battery.
Another cool thing for the Golf 1.5 eTSI is that it uses the GPS information to decide when this is most useful to do.
The BDSG is also used to give the ICE a boost and support it, should the driver suddenly press the accelerator pedal hard at low rpm. The ICE will reach its maximum torque around 25% sooner, thus enhancing efficiency significantly.
The future is now
Valeo has concentrated on finding vehicle solutions that reduce CO2 emissions for many years and currently is in the middle of vehicle electrification. It is a total supplier of equipment and systems to vehicle manufacturers in every category; low and high voltage.
Alongside developments in the field of Advanced Driving Systems (including autonomous driving) and vehicle connectivity, this sets Valeo at the right place for future developments today.