"Yes, this is the first time we're using prismatic cells", says Anand Kulkarni, Chief Product Officer at Tata Passenger Electric Mobility Ltd

The Tata Curvv EV has been launched in India at ₹17.49 lakh. Our assistant editor, Aatish Mishra speaks to Anand Kulkarni, Chief Product Officer at Tata Passenger Electric Mobility Ltd, about the Tata Curvv EV’s architecture, new design language and challenges that they faced with the bigger battery.

Aatish Mishra: Hi Anand. This is an all-new car. You all had a fundamental base to start with—a platform and motors. So, how did you go about creating the Curvv?

Anand Kulkarni: So, we had the architecture. We didn't have the platform. Just as a recap, which I've done a few times now, the acti.EV is an architecture. It's not a platform, as I clarified before. The platform is more about the mechanical assembly of parts, while the architecture focuses on how you bring different components together to execute a certain approach. This is an acti.EV architecture, so in that sense, it was available. However, the platform itself is new. For instance, we didn't have a 4.3-metre platform before, nor did we have something with a 2670mm wheelbase. We also didn't have anything with an 18-inch tyre on a 4.3-metre platform, so in that sense, it’s completely different. Now, what that has given us in terms of an electric vehicle is more space due to the wider footprint, both laterally and longitudinally. It's a bigger product, so you need to have better range. We also innovated with our batteries—instead of using cylindrical cells, we've gone prismatic. As a result, we've been able to pack more energy.

Aatish Mishra: Is this the first time you're using prismatic cells?

Anand Kulkarni: Yes, this is the first time we're using prismatic cells. 

Aatish Mishra: The 8% energy density benefit comes from the prismatic cells?

Anand Kulkarni: There's some inherent benefit from the prismatic cell itself, and there's also an improvement from the way prismatic cells can be packed back-to-back, unlike cylindrical cells that leave some voids. Together, we're seeing a benefit of around 8-8.5%, which has allowed us to increase the battery capacity to 55 kWh. This capacity means you have a 400km real-life usage range, which I think is very good, because not many people drive more than 400 kilometers at a stretch—though some do but the majority don't.

Aatish Mishra: Were there any challenges you faced in terms of engineering due to design demands, like the design team saying they needed a specific feature or silhouette?

Anand Kulkarni: You’re right. The silhouette of the coupe has to be done well, otherwise, it can start to look awkward. The silhouette had to be respected. Since we were placing the battery underneath, there was a certain floor height that had to be maintained. The occupant package had to be carefully managed to avoid any issues. For example, just before you came, Ameya was also mentioning why we couldn't have taken the rear seat further back to create more space. There's a sweet spot in terms of where you place the wheel. If you take the wheel back, you intrude into the boot space. If you move it forward, there isn’t enough space for the occupants. Move it rearward, and the door profile is affected. So, it's a delicate balance. Once we hit that geometric proportioning, and Martin was able to create the silhouette he wanted, everything came together.

Aatish Mishra: From an engineering standpoint, how different is the basic shell or body from a standard SUV or a box-type SUV?

Anand Kulkarni: The fundamentals remain the same; they don’t change much. But with an electric vehicle, there’s a need for reinforcement. We’ve talked about load paths and how we want them to go underneath the car—that’s been sorted out. At the B-pillar and C-pillar areas, the entire structure has been linked to create a very homogeneous and strong body structure. The torsional stiffness is up by 45%, which is amazing. I remember when we were in Bangalore a few years back, we were amazed to hear that some luxury cars in Europe, with aluminum space frame construction, had started to exceed 20 kN per degree. At that time, most other cars, even in Europe, were at 12-13 kN per degree. Now, this car is above 21-22 kN per degree.

Aatish Mishra: And this torsional rigidity comes from where? Is it the battery structure?

Anand Kulkarni: Yes, the battery contributes significantly to this because you have such a stiff structure with 17-18 battery mounting points. The structure itself has been reinforced as well. So, all put together, it has come together really well.

Aatish Mishra: You mentioned that the motors are existing components you have used. Are they the same motors from the Nexon?

Anand Kulkarni: Yes, they are the same motors from the Nexon. But with a larger battery, you can extract more power. The motor was always capable; it’s just that with the 40 kWh battery in the Nexon, you didn’t need or weren’t in a position to extract as much power. Now, we can do that, so it’s become more powerful.

Aatish Mishra: You mentioned something about passing acceleration. Can you elaborate on that?

Anand Kulkarni: Yes, it’s not necessarily about power—it’s about torque. It’s torque on demand, instantaneous torque. The moment you push the throttle, the torque demand translates into instantaneously reaching the highest level of torque. For example, if you’re doing a 60 to 100kmph passing acceleration, this car does it in about four seconds. Most other cars, even with GDI engines or similar, would probably need anywhere between 7.5-8 seconds to up to 12-13 seconds.

Aatish Mishra: What’s the weight of this car?

Anand Kulkarni: 1700kg with the 55 kWh battery and 45 kWh version is 70 kilograms lighter, so around 1620kg

Aatish Mishra: You mentioned the center of gravity is 60 mm lower. Is this lower than the ICE version or lower than similar vehicles?

Anand Kulkarni: It’s lower than other similar mid-SUVs in the market. The center of gravity has been brought down by 60 mm. The roll axis, which is the roll center in the front and rear, is typically like this (illustrating a slope). But here, the roll center is flatter. The center of gravity is above that roll center, creating a roll couple. With the center of gravity coming down, the roll couple has also reduced. So, when you take the car on winding roads, you don’t feel the roll effect as much.

Aatish Mishra: What was the biggest challenge with the Curvv from an engineering perspective?

Anand Kulkarni: The biggest challenge was the timeline and the number of features in the car. It has everything—20 features of level 2 ADAS, standard ABS, ESP, auto park brake, and more. We also had two all-new batteries, which are not from our existing library. Another challenge is the timing of development, especially when safety systems are involved. You need to hit the winter at the right time for ABS, ESP, and other tests. If you miss that window, it could delay your program. These days, with global warming, those windows are shrinking, so that was a challenge. But we managed it.

Aatish Mishra: Is the packaging of the 45 kWh and 55 kWh battery packs the same?

Anand Kulkarni: The battery pack is the same from the outside, but the cells inside and the space utilization are different.

Aatish Mishra: You mentioned the suspension architecture and the roll axis. Can you explain that?

Anand Kulkarni: The suspension is still a MacPherson strut at the front and a twist beam suspension at the rear. It’s been reinforced and tweaked for the higher masses and travels that the car has to manage. The parts are different, but the concept remains the same. 

Aatish Mishra: The 18-inch wheels, better roll control, and lower center of gravity. Has this intentionally been designed to make the car sportier?

Anand Kulkarni: We didn’t set out to create an overly sporty car, but it's designed to appeal to the evolved consciousness of the customer. It’s a streetcar with excellent road manners.

Aatish Mishra: How much of an aero benefit does the roofline provide compared to a flat roof?

Anand Kulkarni: I would guess it’s more than 25-30 counts. The roofline helps in reducing drag by separating the airflow smoothly, unlike a bluff body.

Aatish Mishra: What did you learn from the Gen 2 architecture on the Punch EV that you could integrate into the Curvv?

Anand Kulkarni: A lot. For one, we now understand better how to manage the battery. With a more standardized, symmetric battery, it’s possible to significantly reduce non-cell costs, simplify the design, and gain cost benefits. It’s also easier to manage crash forces and improve body stiffness. We knew this would happen, but seeing the benefits in reduced NVH materials and other components was a plus. These benefits can be carried over to multiple cars and components. The foundation software for the MCU and motors is identical; we do some calibration differences for different cars, but this allows for faster development times, lesser error states, and ability to manage problems better.

Aatish Mishra: So is this going to be your mainstay architecture?

Anand Kulkarni: So this is going to be our mainstay now. Then we bring the Avinya in a couple of years time and a completely different architecture then.

Aatish Mishra: Okay Anand, thank you!