The Lucid Air intends to redefine the approach to the electric car with an unparalleled level of engineering. Peter Rawlinson, the brand’s CEO, takes us to the heart of the electric sedan.
Presented at the end of 2016, the Lucid Air intends to climb to the top of the hierarchy, whether in terms of automotive or electrical technology. Succeeding the company Atevia, also known to experts for the supply of Formula E batteries, Lucid has a strong expertise. Behind the project hides Peter Rawlison, an engineer by training who notably worked at Jaguar and Lotus. But he was above all the chief engineer to develop an electric sedan, today known as the Tesla Model S.
Now, the Lucid Air is a reality and is coming to American roads. The opportunity for the sedan to make its first concrete proofs, but also to reveal most of its mysteries. It is quite difficult to find where to start regarding the Lucid, as the plumage and the ramage are one, and so many innovations are. But who says electric car, says above all traction battery. And to talk about it, nothing better than a presentation by Peter Rawlinson himself, who will make you regret not having had him as a physics-chemistry teacher, at a time when you had nothing better to do. what to draw cars on notebooks.
This is one of the most important parts of the Lucid Air, and not the least. The electrical unit has been fully developed in-house from scratch. It is the autonomy at the center of the specifications that determined all the engineering around this battery, exclusively composed of cylindrical cells. What therefore looks like a vulgar radio-controlled car battery is, after extensive research, the starting point which allows, among other things, the Lucid Air to climb to the top of the basket in terms of autonomy.
Like Tesla or Rivian, Lucid therefore chooses cylinder-shaped cells, for technical reasons, but also for thermal reasons. More affordable and already integrated into a clean case, they have an inherent mechanical resistance, especially in the event of thermal runaway. Lucid Motors uses 21-700 (or 2170) cells in its packs from Samsung SDI for the Dream Edition and from LG Chem for the other models in the range. The brand indicates that the chemistry is different, without going into detail. In both cases, however, there are 6,600 of these cells, divided into 22 modules of 300 batteries each.
The reason for this pattern: Ohm’s law. A basic electrical rule moreover, but which imposes a challenge for the manufacturer. Because now, the power is the product of the resistance (expressed in Ohms) and the intensity squared. Or P=I²xR. And the more the intensity increases, the more the heat increases, bringing with it physical losses. Therefore, to reduce the intensity, it is necessary to increase the voltage, expressed in volts, while taking into account the power requirements.
The Lucid teams have therefore chosen to combine the two types of assembly with, per module, 10 series groups of 30 cells mounted in parallel. This therefore gives 220 cells connected in series and 30 groups in parallel, for a maximum voltage of 924 V, or 800 V depending on the nominal value, as we learn. one of the reports from the EPA. This also makes it possible to understand the slightly smaller capacity of the cells on board the Lucid Air Grand Touring, which displays a total useful capacity of 112 kWh, against 118 kWh in the Dream Edition.
Each module has a cooling plate placed on the back of the cells, into which the glycol is injected. Peter Rawlinson thus explains that if the heat dissipates in several directions, it is more important axially than radially. Also, lateral cooling, although it can be effective, imposes the installation of channels between the cells, widening the pack while being more complex to industrialize. This is how the engineers decided to use the architecture of Atevia’s racing batteries by attaching the cooling plates to the back of the cells, where the contact is most important.
To take better advantage of this technical solution, the batteries are directed downwards (the positive pole towards the ground), so that the plates and the heat transfer liquid form an additional firewall to ensure the protection of the passengers in the event of a problem. . Below the modules is a small space with the floor of the case to ventilate the battery. The box has side openings to allow gases to escape in the event of thermal runaway and once formed, the pack is an integral part of the structure of the Lucid Air.
With this layout, Lucid therefore had to find a solution to connect the cells to each other via the aluminum busbar. An element that has itself could also be the subject of a long description. But we will content ourselves with specifying that this process of manufacturing this element is unprecedented, since it is directly molded with the box which contains the cells. A unique and patented solution to optimize industrialization. This is where the cells are connected by two ribbon wires, without the secrets of soldering being revealed. One is wider and less resistant in order to reduce heat and losses. The other, thinner and more resistant, acts as a fuse in the event of a problem. For comparison, Tesla uses round wire connections, which have the natural disadvantages of increasing heat and resistance. Lucid indicates that the air would lose 100 hp with this solution per wire.
Lucid’s other prowess in component development is none other than the engine. The brand has thus imagined one of the smallest electric machines in the world, which also has the advantage of including the transmission and the inverter in a single and unique pack. Side figures, the set weighs only 73 kg for a maximum power output of 679 hp. This therefore represents a density of 9.30 hp/kg. That’s almost 3.5 times better than the rear unit of the Porsche Taycan depicted in this infographic (the others being the motors of the Tesla Model 3 and Model S without being named).
Peter Rawlinson is currently less transparent in his explanations for obvious reasons of industrial secrets. But with the miniaturization of the elements, by rethinking the arrangement of the magnets on the rotor, and the shape of the coils in the stator, Lucid promises a denser magnetic field. A total of 24 square copper wires are braided and pressed into the stator. These Lucid-specific innovations allow the motor to develop more reluctance torque for the same amount of magnets. Also, Lucid affirms that, if its engine uses the techno’ with permanent magnets, it is also possible to be freed from its natural resistance. It would thus behave like an induction motor (or almost) at the highest speeds. Especially since this machine can go up to 20,000 rpm. But no details are yet known about this process.
Remains to solve the cooling problems. Because the more a wire heats up, the more resistant it is. For this, the engineers said they discovered several dead zones in the stator winding. Areas which do not ensure the conduction of electric currents and which can be used for cooling, as close as possible to the wires which physically give off heat. Cooling is logically provided by oil. It is injected directly into the coil via the axial channel collector. A piece that is the subject of several patentsboth for its form and operation, and for its integration in the center of the stator.
This mechanical assembly, encapsulated in its casing, is sandwiched between the planetary gear transmission, where the teeth have been patented: according to the designers, their shape has been optimized to transmit the maximum torque while offering as little resistance as possible. Opposite is the reducer. Above the electrical machine is positioned the inverter. This device is based on MOSFETs (for Metal Oxide Semiconductor Field Effect Transistors) which optimize efficiency to amplify and switch circuit voltages. The system is made with silicon carbide (SiC) rather than standard silicon, more regularly associated with an IGBT system (for insulated gate bipolar transistors).
This brings many advantages in terms of cooling, volume and electrical resistance (again). But it was above all its ability to manage high-frequency switching with high voltages that interested the Lucid teams. This technology acquired in Formula E and inherited from Atevia therefore makes it possible to gain even more efficiency in the process of converting currents according to the acceleration or deceleration phases. But it is more expensive to apply.
On-board charger: the dream box
The last piece that stands out within the Lucid Air is called Wunderbox. Installed at the front, also used to absorb deformation in the event of an impact, it controls the entire 900+ V system of the electric sedan. It is through it that the AC and DC currents pass for recharging the Lucid Air.
Recharging on alternating current (domestic socket, public terminal, etc.) is done via the Type 2 port, with a power that can increase to 22 kW of power, according to the information communicated by the European sheet (19.2 kW in Level 2 in the USA). It also has a direct current charging capacity (on Mode 4 fast charging stations) that can target 350 kW of maximum power. Peter Rawlinson is convinced that the power can go further, but no charging network promises as much. Not even Electrify America, which Lucid has a business partnership with (sedans take advantage of 3 years of free recharge) but also for the development of the car.
Peter Rawlinson preferring to calculate the autonomy gained by recharge time, this is how the Lucid Air communicates its data. In AC charging, it would take 128 km of autonomy gained per hour. On the fast terminals, 32 km per minute could be recovered, or 482 km in 20 minutes. This corresponds to nearly 60% battery, or the equivalent of 20-80%.
Among other features, the Wunderbox can convert the voltage of older generation charging stations to calibrate to the car’s 900 V system. It should therefore be able, by a turbo effect unexplained for the moment, to rectify a 400 V current and vice versa. In addition, it is she who provides the reverse charging function. This is not yet effective, but it will be able to power a house via the Lucid Connected Home (V2G) or another electric vehicle (V2V).
A new benchmark?
The Lucid Air isn’t just a new electric car. Nor is it just another competitor to the Tesla Model S, its spiritual half-sister. It is a new reference in terms of engineering whatever its aspects. Designed from the inside out, all the elements have been thought of one another, to form a harmonious whole, as efficient and effective as possible. On paper, the promises are great.
For this, Lucid relies on more than 10 years of experience, especially in competition, and on several million kilometers of road tests. It’s been six years since the Lucid Air was introduced. Six years during which engineers have partly developed these technologies to serve efficiency. On the benches of the EPA, the Lucid Air Dream Edition Range (on 19-inch wheels), aims for a range of 836 km. The Grand Touring version is credited with 830 km or 754 km depending on its configuration.
It just has to prove itself on the road in our hands. Stay connected !