As one of the few new carmakers in the United States, Rivian has attracted attention from major media and American giants, and everyone is expecting Rivian to bring some fresh blood to the industry, just like Tesla has done.
At the Los Angeles Auto Show on November 28, 2018, Rivian officially released two pure electric vehicle models, the R1T pickup and the R1S SUV.
The two models will be equipped with a maximum of 180 kWh battery pack, with a range of over 400 miles, and a 4-motor drive system. They have a peak output power of 522 kW and a peak torque of 1120 N·m, accelerating from 0 to 60 miles in 3.2 seconds. From the data perspective, Rivian has created multiple new records in the electric vehicle industry, and these two models are also the most popular models in the US market.
After the release, Rivian received investments from companies such as Amazon, Ford, Cox Automotive, and T.Rowe Price, totaling more than 2.85 billion US dollars. In addition, Ford also stated that it would jointly develop a pure electric vehicle model with Rivian when it invested in Rivian, and Amazon’s CEO also plans to purchase 100,000 electric delivery vans from Rivian.
What makes Rivian so strong?
On January 6, 2020, Rivian’s Vice President Richard Farquhar gave an interview to the foreign media Charged, in which he detailed Rivian’s skateboard platform and three-electric technology.
Richard Farquhar, who previously worked as the Director of Powertrain at McLaren Automotive, now leads Rivian’s powertrain, battery, power electronics, and thermal systems engineering teams.
The following is the original interview text from Charged, translated by Translators Dragon.
Charged: Rivian calls its electric powertrain system the “skateboard” platform. What systems are included in the skateboard platform architecture?Richard Farquhar: Skateboard is the core of all vehicles under Rivian, and we are able to create different vehicle models based on this platform.
This platform is composed of an energy storage device (battery), which is located at a lower position between the front and rear axles of the vehicle, with the design intended to improve the vehicle’s dynamic control performance, lower its center of gravity, and increase its polar moment of inertia.
We have equipped each axle of the vehicle with a drive assembly, and each drive assembly has two electric motors. Therefore, Skateboard is equipped with four electric motors, which are independently connected to the four wheels through a fixed gear ratio single-speed transmission.
For each wheel, we also equipped an independent torque control device, which has a fast response and high operational accuracy. Therefore, there is no better design for the vehicle’s handling and driving performance.
However, for us, the off-road handling of the vehicle is the truly important performance. Independent torque control for each wheel helps us to achieve the best vehicle off-road performance.
Skateboard also includes a complete thermal system, which has three thermal control loops in total, used to control the electric drive assembly, battery, and cabin heat. In order to achieve optimal vehicle performance for electric vehicles, we need excellent thermal control and management, which is exactly what we focus on, in order to maximize both performance and efficiency.
The final key element of Skateboard is the chassis system. We have realized comprehensive travel height control in the air suspension, and adaptive roll control on the front-to-back and diagonal axes with a hydraulic system.
In terms of engineering mechanics, we have achieved such a degree in the propulsion and chassis systems that no one can do better than us.
Charged: You just mentioned a symmetrical drive unit, so you equipped Skateboard with four identical electric motors and drive assemblies?
Richard Farquhar: Yes, we equipped Skateboard with four electric motors, located on the left and right sides of the front and rear axles.
The torque and power values of each wheel are identical in order to achieve optimal performance. With our efforts, the total ground torque of each wheel of the test vehicle exceeds 14,000 N·m, and the maximum speed reaches 125 miles per hour (approximately 201 kilometers per hour).
Equipped with a fixed gear ratio single-speed gearbox, there is no need to shift gears or use a two-speed gearbox, which can minimize the efficiency loss caused by gear engagement and maximize our performance goals.
The inverter is an important component of the propulsion system, equivalent to a jewel on a crown, and this device is entirely designed internally by us.
We have developed a dual-power inverter that integrates into the electric drive assembly and efficiently controls two motors on an inverter assembly.
From the battery to the inverter, to the motor, and even to the wheels, we have invested a lot of effort. A double combination inverter is installed on each axle, which enables us to maximize the efficiency of electricity and achieve the maximum range of the vehicle by using the established energy.
Charged: Are the motors also independently designed?
Richard Farquhar: Regarding the motors, we partnered with another company to jointly design the core electromagnetics and motor assemblies, and then encapsulated them into our drive unit.
This is similar to the design of battery modules. We work with multiple partners to obtain battery cells, and then design and develop modules, and accurately encapsulate them according to our needs.
Therefore, for Rivian, motors are unique because we have conducted internal integration of the motor into the electric drive assembly, installation, inverter and motor connection, motor cooling implementation, and how to configure the motor into our transmission.
Charged: You said just now that the maximization of electric vehicle performance is related to thermal management. Could you explain in detail which performance areas will become limiting factors for thermal management?
Richard Farquhar: Electric vehicle system design always revolves around the two topics of trade-offs and performance optimization, and thermal management factors always take precedence.
Regarding the boundary conditions of electric vehicle performance (corner cases), whether it is DC fast charging, power distribution at a constant rate, or traction and high torque, they can all be attributed to the thermal limitations of the motor, inverter, and battery.
Therefore, by using three independent cooling systems and configuring some intelligent valve control devices in the system, we can examine the energy consumption-the heat generated – and achieve optimized cooling in a very intelligent way to achieve optimal performance.
The battery has a dedicated circuit for heating and cooling. We can intelligently adjust the battery temperature to the optimal temperature as needed. If the vehicle is in extremely cold environment, we can heat up the battery to increase its temperature, thereby maximizing efficiency and increasing the vehicle’s range.
The traction system also uses the same principle – an independent circuit to ensure that the motor and inverter are at the optimal temperature. The motor and inverter have a cooling fluid circuit for cooling the stator and power electronic devices.
In addition, there is a third circuit for the cabin and HVAC. Therefore, for these three independent circuits, we have equipped them with intelligent valves and control systems to optimize their performance.
Within the thermal energy system, there is also an intelligent control component. We can intelligently control the vehicle’s thermal management system through the intelligent connected vehicle control function.
For example, if you charge with DC fast charging at super high power, we need to know the optimal temperature for this operation, and then use the cooling system to reduce the battery temperature to that temperature range.
This is not limited to the thermal management system itself. We have also independently developed a complete set of modules and battery packs, used as a mechatronics system, and produced the above equipment in our new Normal assembly plant in Illinois.
In addition to the hardware of the battery management system, we have also developed software, algorithms, and control strategies, and then connected them to the intelligent connected vehicle platform.
Of course, this platform is also independently developed by Rivian. So, we can not only control the functional performance of the battery to optimize battery life and performance, but also change the parameters of the battery management system, which is tailored for individual users to understand their vehicle usage, charging preferences, or energy return rate.
Based on this, we can provide customized services to customize the use of our batteries, thereby optimizing battery life and efficiency, and we strive to provide you with the best performance.
Therefore, we have truly achieved intelligent control of the battery management system (BMS) connected to the Rivian intelligent connected vehicle platform and the user’s vehicle usage.
Charged: Can you explain the design of the battery modules and packs?
Richard Farquhar: If we narrow the focus, we firmly believe that the battery modules and packs currently owned by Rivian have the highest volumetric energy density in the world. Compared with any other similar products currently on the market, the energy density of our battery products is 20%-25% higher, measured in Wh/L.
The key to achieving the above advantages lies in the construction of the battery modules. Each module has two layers, each layer containing 21700 cylindrical batteries.
The energy of each battery module is 15 kWh. Our standard battery pack contains 9 battery modules, while the high-end version has 12, with a total energy of 180 kWh. Therefore, the vehicle’s range can reach more than 400 miles (about 644 kilometers).
The core of this module lies in a cooling plate between the upper and lower cells of the battery. This plate enables us to cool those cells in the most efficient medium, using axial cooling.
We pull the heat out of the center of the cells, which is the most effective way compared to radial cooling. This allows us to package these cells tightly together and achieve the highest volume energy density available today.
Charged: Did you use a thermal interface material between the cells?
Richard Farquhar: We do not use such materials. The cells are only separated by air. We don’t need to place anything between the cells that are packaged together. The space between the cells is intended to ensure that the module itself, the battery pack, and the vehicle are as safe as possible under all conceivable circumstances, safety being a top priority in our work schedule.
When each wheel is equipped with an independent torque control unit, this type of off-road vehicle can go anywhere. We need to consider such driving scenarios.
For example, when climbing rocks and driving up and down steep slopes, we need to provide good protection for the on-board batteries from a structural point of view, ensuring that they are highly integrated with the vehicle body structure. Underneath the battery pack, there is a bulletproof shield, an important part of the vehicle’s main structure, designed to prevent impact events from the ground.
The battery pack is wrapped in extruded aluminum to prevent collision accidents and ensure that the battery will not malfunction in the event of a front or side collision. Passive safety is our highest standard, and the battery cells inside the pack can also withstand the impact and vibration from long-distance off-road driving.
In addition, this type of packaging for the battery pack is also well protected.In the 9 modules inside the battery pack, all high-voltage, low-voltage, and cooling systems are encapsulated in the spine of the battery pack, which is located precisely along the centerline of the vehicle, making such battery components in the center of the battery pack well protected in case of any collision, which has been taken into account with regards to ensuring the integrity of the battery pack from the perspective of passive safety and off-road driving.
Charged: Rivian claims that the vehicle can travel in water up to one meter deep. So, will all the drivetrain component be submerged? Could you talk about the engineering design challenges in the submersion system?
Richard Farquhar: Yes. One of our major requirements is that the vehicle can operate in water up to one meter deep for a period of time. If you look at the vehicle from front to back, all the components I mentioned – our cooling system, HVAC cooling modules, battery pack, drive unit assembly, motor, and inverter – all fall under the submersible category.
So how do these components breathe? How do they operate? What temperature changes occur with long-term submersion? We have already considered these issues in our vehicle design. In fact, if the vehicle travels into deeper areas, it will begin to float up, and its body mass will prevent it from sinking too deep.
The engineering design challenge is in fact about thinking about the laws of physics. Whenever a vehicle with heat flow enters cold water, you will see heat diffusion and thermal expansion and contraction, so there are many temperature protection (delta temperatures) issues that need to be solved, which are known as engineering design challenges.
With temperature changes, how will such equipment breathe? Obviously, you need to seal all the gaps. As long as you have dynamic and static water pressure, these parameters become important components of the design standard level testing standards. Ventilation and drainage are very important, which undoubtedly provide interesting and challenging engineering design challenges for our R&D process.
Charged: Rivian claims to officially start vehicle production work at the end of next year. What stage is the company’s research and development process in currently? What will be the focus of the next stage of work? Will you freeze the design or continue to control the major design changes during production?
Richard Farquhar: We base our product development work on the RDP (Rivian Development Process), and we are very clear about the series of measures established in the process and the milestones that need to be achieved on time in each stage, which are all essential steps to start production.
We have outlined the deliverables and milestones that need to be achieved on time for each stage. Our work is mainly divided into four stages: concept stage, development stage, validation stage, and gradually achieving mass production.We have developed a large number of prototype vehicles, and conducted extensive testing of components and systems. In addition, we have adopted Rivian’s internal processes, which have been continuously improved, enabling collaboration of over a thousand people to deliver such products. Therefore, this is a very clear process, with milestones set along the way.
Regarding the question you want to know – how we manage design changes, in the early stages, we want to maximize the performance attributes of the vehicle. We have defined the vehicle’s performance, functionality, and features, with many ideas and innovations to achieve the above design goals in the most efficient way possible, whether it be in terms of quality, energy, cost, or other aspects.
I think you may say that we have moved into the truly creative and innovative stage through research and development and validation stages. After this, we will focus on reliability, performance, and excellent quality related to product maturity.
We have already built many test cars and are in the early stages of vehicle development, currently working to build more prototype vehicles to test more vehicle attributes and high-level automotive components that are due for production.
We are focused on the so-called validation stage, where we will build dozens of production-intent validation vehicles, aiming to complete all validation, reliability, durability testing, and start the certification process, ultimately delivering a mature vehicle with production quality by the end of next year.
This article is a translation by ChatGPT of a Chinese report from 42HOW. If you have any questions about it, please email bd@42how.com.