Earlier this year, Jaguar launched a premium electric car, the I-PACE, introducing a new luxury competitor to Tesla. The I-PACE has received good reviews, and its larger battery gave it a longer range on a single charge than the Tesla Model X, based on European standardized tests. A few weeks ago, however, US standardized tests results were published and the I-Pace performed worse than the Model X.

Quartz asked Venkat Viswanathan and his team at Carnegie Mellon University to explain the discrepancy—you can read the story here. For transparency, below are the answers we received from Jaguar in response to our questions.


1. What explains the discrepancy between model and actual battery packs?

The Jaguar I-PACE is a desirable, practical and usable all-electric performance SUV that our customers can drive every day, and in all conditions. The certified range figures of 470km/ 292 miles (WLTP) and 234 miles (EPA) reflect this.

Early media tests of the I-PACE have underlined its ability against its competitor set, and its real-world range. For example, Top Gear achieved 291 miles on a single charge.

The model you refer to, developed by Carnegie Mellon University, is not something that Jaguar Land Rover has seen or contributed to the development of, nor supplied data for. The model takes into account a number of different factors, some of which we have published, but some of which we have not, for example frontal area and the rolling resistance of the tyres. We also do not know which wheel and tyre type have been included in the model: as is true of any vehicle, changing from the smallest to the largest will influence range and energy/fuel consumption.

Furthermore, headline battery figures alone, such as nominal capacity, are not a truly robust engineering measure for the energy available during an EPA test cycle. This will vary based on how deeply you are prepared to cycle the battery’s state-of-charge—a variable very well known and understood to contribute to longer-term degradation of Lithium-ion battery packs.

Some attributes which the model uses have been stated, such as nominal battery capacity and drag coefficient, but there are very many more key vehicle characteristics which determine range for a given battery capacity, such as inverter, e-Machine and transmission efficiencies, wheel bearing friction, brake drag, active air suspension and continuously-variable damping loads, as other losses such as HVAC and other 12V electrical system loads.

In the design of these systems there is always a balance of attributes, such as efficiency, strength, durability and NVH, all of which contribute to whole-vehicle attributes such as range, energy consumption, performance and driveability, vehicle dynamics, refinement and cabin noise.

The global media launch of the I-PACE in Portugal this summer, presented journalists with the full opportunity to find this out for themselves. The event included a challenging off-road section comprising steep slopes, loose surfaces and river crossings, several laps of the demanding Autódromo International do Algarve (better known as the Portimão race circuit), as well as a long and challenging road route. With this we were able to demonstrate the I-PACE’s unrivalled balance of repeatable performance under extreme conditions, its agility and ride comfort, refinement, and—of course—real-world range.

Without further understanding of the model used (not least how it compares to our own CAE tools, physical testing and to range certification itself) it is very difficult to comment on a ‘discrepancy’ between the results of Carnegie Mellon’s study, and the Jaguar I-PACE’s certified EPA range of 234 miles or certified WLTP range of 470km.

2. Does the I-PACE have a less efficient motor?

Presumably this means: does the I-PACE have less efficient motors than the other vehicles you listed? We can’t speak on behalf of other manufacturers, but the I-PACE’s state-of-the-art electric motors were designed in-house from a clean sheet, and we have eight patents pending. The motors use synchronous permanent magnets, and provide greater than 95% efficiency over a wide range of speeds—between 30-150km/h.

They are also extremely compact and light: they weigh around 40kg each. For a machine developing 200PS and 348Nm, this delivers exceptional power and torque density. The motor, together with its transmission, weighs just 78kg yet develops 200PS—that’s around half the weight of an internal combustion engine of the same power output

For optimum packaging, the motors are hollow, with the driveshafts passing though the centre. This brings huge benefits, enabling a low trunk floor for maximum cabin and luggage compartment space, and SUV ground clearance.

3. Does the I-PACE on purpose program its battery to avoid full depth of discharge? For example, is the EPA range only for say 20% to 80% of battery capacity?

The I-PACE has a nominal capacity of 90kWh and a useable capacity is 84.7kWh. Like the traction batteries in all electric vehicles and hybrids, the I-PACE’s pack cannot be charged to 100% or run down to a real 0% state of charge because this is detrimental to the cell’s state-of-health and therefore the battery pack’s performance and durability. We manage the depth of energy discharge based on a great number of environmental and driver inputs, primarily to maintain cell state-of-health and consistent performance of the pack over its lifetime.

The battery pack uses state-of-the-art technology, and just like the I-PACE itself, has been engineered and tested to the same exacting standards as every Jaguar and Land Rover vehicle. This is why we have the confidence to protect and reassure our customers by offering a highly competitive 8-year, 100,000 mile/160,000km battery warranty: the battery must retain minimum of 70% state-of-health within the warranty period.

4. If it does constrain the battery, is it to ensure fast-charging at 350kW or even 100 kW doesn’t affect battery life?

As stated above, the I-PACE’s pack cannot be charged to 100% or run down to a real 0% state-of-charge. This is not a constraint: this is because that is inherently detrimental to cells’ state-of-health, which is why every hybrid- and electric vehicle battery pack has a management system which prevents this.

The I-PACE is compatible with 100kW DC rapid charging, and has been future-proofed to take advantage of further developments in the global charging infrastructure. There is not an explicit link between the useable capacity of the battery and repeated rapid charging: we have engineered the on-board charger and the battery management system to modulate charge rate in order to provide optimum protection for the battery, under all conditions and especially at extremes.

5. What manufacturer provides the batteries for the I-PACE?

The battery pack and its management system is designed and developed in-house by Jaguar Land Rover. The motors are also designed and developed in-house. This meant no compromises. It comprises 432 Lithium-ion pouch cells, using Nickel-Manganese-Cobalt chemistry—the best technology available today for energy density, thermal management, and sustained power. Pouch cells also give us the design freedom we want to determine the battery pack’s overall dimensions.

6. If it’s a 95% efficient motor, can you provide any estimates for overall powertrain efficiency?

Motor efficiency is one element of the technical data we’ve released on the I-PACE, but we cannot comment on overall powertrain efficiency as this information is confidential.

7. Can you comment on how different or far away the estimates for the rolling resistance and frontal area are?

Thank you for sharing the MATLAB script—this is very much appreciated—but I’m afraid we cannot discuss the contents of it, since engineering data such as the rolling resistance of the tyres is confidential.

We can say that tyre development was a key part of the programme, to ensure that they delivered the optimum balance of efficiency, grip, dynamics and road noise to enable the I-PACE to meet all of its demanding whole-vehicle targets. As you would expect, it was a similar story with aerodynamics development. The drag co-efficient of Cd 0.29 is very low for an SUV, and is key to range, but this is just one part of the aerodynamics story: lift and yaw characteristics are also essential because of their influence on vehicle dynamics and stability.

Likewise, we can’t share any of our CAE models with you, but thanks to advances in our modelling techniques and CAE tools, we estimate that we saved up to 12 months in the development of the I-PACE. This was a key enabler for us to take the vehicle from concept to series production in just four years.

8. Also, thinking of the Li-ion cells question again, you say the “pack and its management system is designed and developed in-house.” Are the cells themselves manufactured in-house? If not, what vendor do you procure them from?

The battery pack was designed and developed in-house, but, like most of our competitors, we source the cells from a supplier. As part of our launch process, we do not discuss our suppliers, but we can say that the cells are state-of-the-art and come from one of the world’s leading Tier Ones.

9. If we lump all the energy lost due to transmission, brake drag, etc. into one parameter, then it is about 80% for all vehicles apart from the I-PACE, does that imply there are components within the I-PACE that are more inefficient than those compared to the other vehicles?

As the c. 80% efficiency figures you have quoted come from Carnegie Mellon’s model, and are also for vehicles made by other manufacturers, it isn’t appropriate for us to comment on those, nor on the efficiency figure that the model has predicted for the I-PACE.

10. Is there any reason why the EPA vs. WLTP drive cycles have such a large difference in range? Do other vehicles reflect similar differences?

Range figures—and in the case of combustion engine vehicles, fuel consumption figures—are different for any model when certified to the EPA and WLTP test cycles because the cycles are very different. The same applied to EPA and NEDC figures for any given model.



READ SOURCE

LEAVE A REPLY

Please enter your comment!
Please enter your name here