The conventional 12V electrical system of the production vehicle was extended by a 48V electrical system. In addition to a powerful 48V battery and a DC/DC converter to supply the 12V system, this also includes a highly efficient belt starter generator, which replaces the traditional alternator and supplies the electrical systems with power. At the same time, the belt starter generator can support the combustion engine with an electric torque and in conjunction with an additional electric compressor, significantly improve the response behavior independent of the operating point of the combustion engine.
As a development service provider with outstanding expertise in the field of electrification and vehicle electronics, FEV has implemented efficient mild hybridization in its concept vehicle, from mechanical to electrical design and integration to an optimum operating strategy. The control software based on the FEV PERSIST software architecture was developed by engineers from FEV.
In the A48V concept vehicle, this is done on a rapid control prototyping control unit and takes over the control of the 48V components and the coordination of higher-level functions such as mild hybrid boosting or the forward-looking sailing and recuperation strategy. Due to the intense component orientation, the software architecture is very flexible and modularly expandable.
In order to supply the vehicle with electrical energy, the electrical machine is operated as a generator. The mechanical energy required to generate electricity can either be generated by the combustion engine or provided by the vehicle's kinetic energy during braking. The belt starter generator feeds the 12V electrical system via the DC/DC converter and simultaneously charges the 48V battery.
The recuperation process can be initiated by the driver by applying the brake or by a predictive algorithm that takes into account the current traffic situation and ideally performs a braking maneuver without using the mechanical brake system, thus significantly increasing the efficiency of the recuperation function.
The belt starter generator enables a very comfortable and fast start of the combustion engine. The high torque capacity ensures that the idle speed is reached quickly even at low ambient temperatures. This means that the driver can no longer perceive the resonances that can occur with conventional 12V stop/start systems. Compared to the conventional starting system of the A45 AMG, a belt starter generator can reduce the starting time by up to 65 percent, the amount of energy required for starting or the overshoot of the combustion engine speed, depending on the calibration. Only the significantly reduced starting time permits the use of a sail function in which the combustion engine can be switched off, since it can be restarted almost without delay if the driver wants to accelerate.
The electric booster and the belt starter generator are used on the A48V to increase response and available torque, especially at low engine speeds. The use of an electric compressor enables an almost delay-free boost pressure build-up in operating areas where the exhaust gas turbocharger has weaknesses due to its principle. The maximum torque can thus be achieved at 1,600 rpm which is 650 rpm earlier than in the A45 AMG. With the help of the belt starter generator, torque can be applied instantaneously, making the vehicle and the driving impression much more agile.
In combination, the use of a belt starter generator and electric booster can extend the effectively usable speed band downwards, thus enabling more comprehensive downsizing or downspeeding.
In overrun mode, in which the combustion engine is towed along but does not have to provide propulsion, it makes sense from an energy point of view to open the transmission clutch and decouple the engine from the rest of the drive. In this way, the kinetic energy of the vehicle can be used more efficiently to overcome the driving resistances, since the frictional power of the combustion engine does not have to be overcome additionally. The combustion engine is either operated at idling speed, in which the friction power is lower due to the lower engine speed, or switched off completely. Switching off the combustion engine requires a particularly comfortable and fast starting system in order to ensure the acceptance of the driver for such a function. A 48V belt starter generator offers this possibility.
To optimize fuel consumption, the A48V is equipped with a sail function where the combustion engine can be switched off. During sailing operation, the electrical systems are powered by the 48V battery. This includes an electric vacuum pump, which ensures operation of the brake booster and power steering even when the engine is switched off.
In order to increase efficiency advantages of the sailing function and to increase the acceptance of the driver, the vehicle is equipped with a predictive algorithm, which decides on the basis of a camera-based sensor system, which analyzes the current traffic situation, whether the sailing or recuperation operation is more energy-efficient. When driving undisturbed, the function will automatically initiate sailing operation and switch off the combustion engine.
If another road user is detected, the function predicts the speed curve of the A48V and decides whether the recuperation mode must be initiated in order to avoid undesired tailgating. In this case, the function controls the recuperation torque, with the aim of decelerating the A48V without driver intervention and thus without using the mechanical brake system, so that the energetic potential can be optimally utilised.