Developing a new model involves more than just designing the shape and engineering the structural design. Those two aspects are probably the first two-thirds of the project and once the design is ‘frozen’, there is a final third phase which is crucial for the success of the new model: real-world testing. All the simulations (digital testing) may have shown that the new car will run well and has met all the targets but in the real world, there are many variables which can present new technical issues that must been resolved before the new model can be allowed for sale.
Mercedes-Benz uses a ratio of 35%:65% between digital testing and real-world testing. While the engineers at the German company have many decades of experience in real-world testing, a new challenge has now begun with the advent of electric cars and Mercedes-Benz will soon be launching a range of all-electric cars in high volumes. The model is the EQC and it is now being put through trials in cold and hot weather conditions, the latter in temperatures of up to 50° C. Particular attention is given to aspects which are very demanding for electric cars, ie air conditioning and charging, as well as cooling the battery, drive system and control units in extreme heat. Naturally criteria such as driving dynamics and ride comfort are not overlooked and subjected to equally stringent tests.
The biggest challenge is dry heat; while the battery of an electric car ‘merely’ loses power in the cold, exposure to great heat carries the risk of battery damage. Optimum management of these physical characteristics is the aim of the extreme tests presently being done in Spain. One main focus is on the battery’s cooling circuit and the engineers want to see how it copes with high power requirements. How does an almost fully charged battery respond to further charging? What influence does the heat have on operating range? Battery draining tests (driving until the battery is completely drained) are also part of the test programme.
Another aspect is air conditioning of the cabin, a basic expectation nowadays and more so in tropical areas. ‘Pre-climatisation’ (cooling or warming the cabin) is an important comfort factor and the length of time required has to be determined. Then there is the question of whether the time is sufficient for pre-climatisation and is the calculated range correct when the temperature is taken into consideration?. Furthermore, the noise characteristics of individual components such as the air conditioning compressor in the heat are specifically examined.
Fine dust is also a particular challenge and the technicians will be examining all the areas where dust might be deposited in the components. Accumulation of dust might not be damaging in all cases but it could still have a negative effect so the sealing concept has to work well and only in such real-world testing can this be determined.
Different countries present different circumstances and therefore international operability of each individual system has to be assured A few examples: are the slightly differently designed traffic signs recognised? Are toll stations reliably recognised? Are speed limits correctly detected by the camera of the assistance systems?
A special role is also played by the acoustics of an electric car – unlike in a combustion-engined car, there is hardly a sound from the electric powertrain. This makes sounds such as the rolling of the tyres or wind noise more prominent. Where these requirements are concerned, the engineers benefit from their long experience in testing NVH (noise, vibration and harshness).
Many of the prototypes will be ‘international travellers’ as they will be driven in various European countries as well as Dubai, South Africa, the USA and China.
Many people may not understand the importance of this testing phase but for a manufacturer, it is crucial because every part and system must be reliable and durable. Offering a long warranty is one thing but the customer should not be inconvenienced by a breakdown, especially if the brand is a premium one like Mercedes-Benz.