Vehicle Control Unit – The
Mastermind Behind All Vehicle Functions
The vehicle control unit (or VCU) acts as the mastermind of a modern vehicle – whether they are battery electric vehicles or fossil-fueled cars. But within BEVs specifically, the range of functions of the central control unit has extended significantly. Tasks that go beyond the mere regulation of propulsion have been integrated, and thus, the engine control unit became the vehicle control unit.
Concentrating vehicle functions within an overarching control unit enables vehicle manufacturers to centrally consider the reciprocal influence of different factors. However, this requires precise individual adjustments of the VCU for each specific vehicle application.
ADDITIONAL FUNCTIONALITY RANGE OF THE VEHICLE CONTROL UNIT IN BATTERY ELECTRIC VEHICLES
Within the architecture of a traditional combustion vehicle, there are separate electric control units for different power train components. Respectively, there is one for engine control, one for gear control, one for transfer gearbox control (if applicable), and one for potential axle differential lock control.
However, an electric vehicle’s power train is not separated this way. There is no separately controllable gearbox, and instead of a transfer gearbox, modern, fully electric all-wheel vehicles use one engine per axle – sometimes even one per wheel. The vehicle control unit handles both torque and rotational speed from starting to maximum velocity, as well as torque distribution between drive axles or potentially the wheels of an axle.
This is how the vehicle control unit became the “power train mastermind” – a development that was necessary specifically for battery electric vehicles. Of course, local functions can be outsourced to sub control units linked to the VCU. For example, a control unit for the engine control inverter. However, there is a strong trend towards bundling as many functions as possible within the VCU.
SAME VCU BASIC FUNCTIONS FOR ALL BEVs
In principle, vehicle control unit functions are the same in all battery electric vehicles. Therefore, it stands to reason to try to develop a “universal control unit” that only needs to be adapted via small software adjustments or changing parameters, and that can be used across a multitude of vehicles. Nonetheless, in practice, there is a difference between the software and the hardware section. Magna as a development service provider can make the necessary arrangements according to each customer.
For example, established OEMs usually already produce one or more BEVs and have a strong interest in using as many common parts as possible. In this case, a new vehicle project should at least be implemented with the same hardware, so that the adaptations to the respective vehicle type can be solved with software. This narrows the leeway for development.
On the other hand, new market entrants commissioning only one vehicle project can more easily expect a tailor-made solution.
Yet, modular hardware architecture does facilitate the usage of common parts, like in different variations of the same vehicle model, for example. Two-wheel drives and all-wheel drives can, in principle, both be realized through the same drive control unit. In this case, adjustments only need be made to the software, which can be easily achieved.
REPROGRAMMING VERSUS PARAMETERIZATION
Programming the software can pose similar challenges to implementing VCU hardware. Depending on the client’s (i.e., the OEM’s) requirements, the VCU’s software contains exactly those functions that are required in the vehicle. The basic functions of the vehicle control unit are always the same in principle.
However, depending on the application, additional functions may be added. Furthermore, the programming must also be adapted to the components used in each case. For example, batteries from different suppliers, even if they always have the same function and possibly the same or similar specifications, are not exactly the same – so they must be addressed differently by the VCU. Inverters from different manufacturers often also require different ways of control.
The problem of receiving components from different suppliers does not usually arise in development projects by classic OEMs that already have one or more BEVs in production, since OEMs typically do not use different components for different vehicle types. On the other hand, new market entrants commissioning only one vehicle type may require using non-standard components that need to be considered when developing the software.
However, not every new project necessitates a complete reprogramming. In most cases, the software can be adapted to the new requirements through parameterization. This not only significantly shortens development time but also reduces development costs. An experienced development partner like Magna can offer the optimal software solution for any specific requirements from business partners like vehicle manufacturers.
THE TREND TOWARDS INCREASED FUNCTION INTEGRATION IN ECUs
Instead of using multiple electronic control units, also called an ECU, for different necessary functions of a BEV, there is an increasing trend to concentrate as many functions as possible within a single ECU. For example, not only drive functions, but charge control or thermal management could also be left to the vehicle control unit (VCU).
This is made possible by area or domain controllers that address individual functions via the respective software modules. Regarding thermal management, the VCU can control all relevant pumps and valves directly to regulate temperature.
With other functions, however, it makes more sense to interact with other ECUs through interfaces. For example, there is an interface to the control unit of the brake control to request deceleration from the VCU even though the vehicle uses an independent brake control system.
Factually, the vehicle control unit is an amalgamation of integrations of functions and interfaces to other systems. However, there is a clear trend towards the integration of as many functions as possible into a correspondingly high-performance control unit.
COMPREHENSIVE COMPETENCE WITH OTHER CONTROL AND REGULATING SYSTEMS
All systems are interconnected with each other in any modern vehicle. That is why an established development partner with additional experience and competence in other areas besides vehicle control unit development can bring additional know-how to the table.
This applies, for example, to driving dynamics control and torque distribution, which not only need to be adjusted differently according to vehicle model and model version, but also according to selected driving mode. All modern cars – especially electric cars – have a range of different driving modes ready for the driver to choose from to his or her personal preferences.
These different modes not only influence the engine response to and the characteristics of the accelerator pedal, but also affect torque distribution, the height and build-up curve of steering forces, and possibly also chassis level and damper behavior. To ensure a satisfying end customer experience, the individual vehicle systems must match with each other, or rather, be a perfect overall fit.
In addition to the VCU, the superordinate control strategy of the entire powertrain also determines the optimized driving behavior of the future battery electric vehicle in terms of efficiency, safety, driving dynamics and comfort to achieve utmost end-customer satisfaction.
Magna as a systems partner offers decades of experience in different areas. Particularly, the implementation of driving dynamics control of battery electric vehicles into the vehicle control unit forms the core know-how of drive control, which Magna continues to further develop and enhance.
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