Thermal Management System in Hyundai Kona Electric
There has been a lot of discussion about what the batteries would look like and plenty of comment about the lack of a heater in the U.S., so Electric Revs got a comprehensive look at the battery modules.
According to the article, the battery cells were made by LG with a cathode that is 60 per cent nickel, 20 per cent manganese, and 20 per cent cobalt. Each 64-kWh pack has five modules that are located under the floor in the main cabin with two stacked modules under the rear seats. There are 294 cells in the battery pack and are wired into 98 cell groups of three cells apiece.
The modules sit on top of cold plates that channel fluid. As the article described, “Inside the 64 kWh pack there are three coolant sub-loops running through the five modules. One sub-loop runs through the driver-side floor module and one of the stacked modules. A second sub-loop runs though the passenger-side floor module and the other stacked module. The third sub-loop cools only the middle floor module.”
A heat pump and dedicated battery heater will be available for Canadian sales, but not in the U.S., which leads to the assumption that sales will be focused on California and other temperate locations rather than the Northeast or Midwest.
“Despite the lack of a dedicated battery heater, the U.S. version of the Kona does have the ability to scavenge heat from the electric motor and power electronics in addition to the heat dissipated by the battery itself to help keep the battery warm when operating in colder conditions,” the article noted.
A thermal management loop with computer-controlled valves allows the battery pack sub-loops to run separately or is included with the coolant that runs through the motor, motor inverter, other power electronics, and the on-board battery charger. The valves have three modes: Heating, Low-Temperature Radiator, and Chiller.
“During much of the year in mild climate conditions, the thermal system typically starts up in LTR mode,” according to the article, “which circulates coolant through a single interconnected loop to warm the battery up to its optimal operating temperature when cold and to maintain that temperature with the help of a radiator and fan.”
Chiller mode runs the coolant through an on-board chiller when temperatures get too hot. The chiller uses the car’s air conditioning loop to reduce the temperature. Heating, or ‘Winter Mode,’ uses a heater (when present) to raise the temperature of the coolant before it runs under the battery modules.
This thermal management system will also be included in the 2019 Kia Niro EV and the 2020 Kia Soul EV.
Hyundai’s new 2019 Kona Electric, with its 64 kWh battery and an EPA-rated 258 miles of range, has gotten many positive initial reviews but until now we haven’t known much about some important aspects of its internal powertrain design.
We knew the basic size, shape, and layout of the pack. We were pretty sure the battery cells inside the Kona pack were liquid-cooled unlike all previous plug-in cars from Hyundai and its sister company Kia. Those earlier designs used a fan to actively blow cabin air through the inside of their packs.
However, many questions remained unanswered.
The electric motor and related power electronics usually need liquid cooling but would they now be on their own separate cooling loop or would there be some way to exchange heat between them and the battery’s new coolant loop?
And just how does heating the battery work in colder weather? And what do the battery cells even look like? For the Kona Electric, we had some tentative hints in our “first drive” review but it was still a bit of a mystery.
These two images above show a topless battery pack with the left (driver’s) side of the seat and floor also removed along with part of the rear seat. Each of the dark grey strips seen under the floor is an individual lithium-ion pouch cell mounted in a carrier frame (as illustrated below) and collectively packaged into a battery module.
The cells in the Kona Electric are made by LG and use cathode chemistry known as NMC 622 which stands for a ratio of 60 per cent nickel, 20 per cent manganese, and 20 per cent cobalt. The cells in the Kia Niro EV are similar but are made by SK InnovationAccording to Jerome Gregeois, a senior manager at the Hyundai Kia America Technical Center, the full 64 kWh pack consists of five modules. Three are under the main cabin floor and two stacked modules are under the rear seats. Each module consists of cell groups as seen in the illustration below (the second stacked module below the rear seats is not shown).
The 294 cells in the pack are wired together three at a time into 98 cell groups which are shown as alternating blue and brown bands in the image. Each of the three-floor modules has 20 cell groups. The two stacked modules each contain 19 cell groups.
Here’s an “exploded” illustration of the pack.
The battery modules sit above cooling plates that channel the same type of water and glycol mix that is used for cooling conventional gasoline engines except the heat emitted from batteries is not normally as intense.
Inside the 64 kWh pack, there are three coolant sub-loops running through the five modules. One sub-loop runs through the driver-side floor module and one of the stacked modules. A second sub-loop runs though the passenger-side floor module and the other stacked module. The third sub-loop cools only the middle floor module.
What about when the pack needs to be warmed in winter conditions?
When Hyundai initially briefed the media on the US version of the Kona Electric there was some ambiguity about whether the car would have a dedicated battery heater. The company engineers have designed the Kona as a global vehicle with a menu of engineering choices that can be tailored to each marketing region to optimize for price and performance in different climate conditions.
At least for the 2019 model year, all Kona Electric’s sold in the US will come without a dedicated battery heater while all Canadian versions will include one. Similarly, all US deliveries will come with 5.5 kW PTC direct resistive cabin air heating alone while all Canadian deliveries will include a heat pump (reversible A/C system) to more efficiently assist cabin heating.
These choices implicitly assume that most, or at least a very large fraction, of the US deliveries will go to areas of California that rarely experience severe cold weather. Skipping the heat pump and dedicated battery heater saves money and helps lower the consumer price of the vehicle.
Despite the lack of a dedicated battery heater, the US version of the Kona does have the ability to scavenge heat from the electric motor and power electronics in addition to the heat dissipated by the battery itself to help keep the battery warm when operating in colder conditions.
There is one overall thermal management loop with computer-controlled valves that allow a battery pack sub-loop to either run separately or join together with the coolant that runs through the motor, motor inverter and other power electronics, and the on-board (AC) battery charger.
When a dedicated 2 kW battery heater is available (as in the Canadian version), it is used primarily at sub-zero temperatures (0C or 32F) or when the driver enables an optional “Winter Mode”. The battery heater, if present, is located outside the battery pack and warms the liquid “coolant” just before it enters into the pack.
The winter mode uses extra energy to warm the battery pack to allow for full regenerative braking and quicker fast DC charging. Colder pack temperatures force the battery management system to restrict the amount of power that can recharge the battery in order to avoid damaging the carbon-graphite anode. This is an issue common to most lithium-ion batteries. Cold temperatures are not much of an issue for power coming out of the battery except under rare and extreme conditions like down near -40 degrees.
Three coolant loop modes
The three modes (Heating, LTR or Low-Temperature Radiator, and Chiller) correspond to the three different computer-controlled valve settings and coolant flow diagrams.
During much of the year in mild climate conditions, the thermal system typically starts up in LTR mode (labelled “Cool Condition” above) which circulates coolant through a single interconnected loop to warm the battery up to its optimal operating temperature when cold and to maintain that temperature with the help of a radiator and fan.
The three-way valves switch to Chiller Mode (labelled “Hot Condition” above) when the battery starts to get too warm. Hyundai hasn’t said what the exact parameters are. The coolant flows through a “chiller” which exchanges heat with the vehicle’s air conditioning refrigerant loop.
In the Chevrolet Bolt EV, the A/C system begins helping to chill the battery coolant when it reaches much above 32C (90F). But the Bolt has a dedicated coolant loop just for the battery and no valves to allow the exchanging of heat with the motor and power electronics loop.
When temperatures are really cold, the dedicated battery heater kicks in (if present) even if “Winter Mode” isn’t enabled. Like a hot battery in Chiller Mode, the battery coolant sub-loop circulates independently because the battery heater is only needed to warm the battery and not the rest of the components.
This thermal management strategy is somewhat similar to that used by Tesla, and the startup automaker Rivian among others.
The recently introduced Tesla Model 3 can flexibly connect its coolant loops and does not have a dedicated battery heater but it does reportedly have the ability to generate excess heat from its motor and power inverter by deliberately operating inefficiently which is then used in place of a dedicated heater.
Rivian also has a similar flexibly configurable thermal loop that includes a dedicated battery heater.
Owner experiences will demonstrate over the next year how well Hyundai’s design and configuration choices perform in the real world.
Hyundai and Kia are using this new overall battery pack and thermal management design in the 2019 Kia Niro EV and the 2020 Kia Soul EV as well as in the 2019 Hyundai Kona Electric.
The companies also market a smaller 39.2 kWh version of the battery pack outside of the US and Canada. That smaller pack reportedly skips the two modules under the rear seat and reorganizes the three modules under the floor into 90 cell groups using pairs of the same cells used in the 64 kWh version of the pack. This smaller pack continues to use the same liquid-cooled thermal management design as the larger 64 kWh pack.
According to Kia, the North American version of the 2019 Niro EV will come standard with a heat pump to more efficiently assist with cabin heating and the dedicated battery heater will be an optional feature. In the 2020 Soul EV, both the heat pump and battery heater are listed as optional features.
Audi A3 sportsback E-tron
The voltage of the 8.8 kWh battery pack ranges between 280 and 390 volts, depending upon the level of charge. The battery comprises 96 prismatic cells—currently from Sanyo—arranged into eight modules of twelve cells each. Including the battery management controller and the battery junction box for the connections, the battery system weighs 125 kilograms (275.6 lb). The bottom shell of its housing is made of diecast aluminium, the top shell of polymer.
The high-voltage battery has an ideal operating temperature of around 25 ˚C (77 ˚F). It, therefore, has a liquid cooling system in which four cooling plates regulate the temperature of the eight modules. Cooling is by means of a separate, flexibly controlled low-temperature loop, which also includes the power electronics and charger, as necessary. The Audi A3 Sportback e-Tron can generally also be driven solely on electric power in the heat of mid-summer and the below-freezing temperatures of winter.
Installed under the rear seat, the flat battery is extremely well protected in an area where the high-strength and ultra-high-strength steel components of the occupant cell form an especially strong structure. The housing is bolted to the vehicle floor at five points. In the event of a crash sufficiently severe to trigger the belt tensioners or airbags, the system is disconnected from the power supply.
The 12-volt battery for the low-voltage consumers and the 40-litre (10.6 US gal) fuel tank is located over the rear axle. The luggage compartment remains spacious. In the standard configuration, it has a capacity of 280 litres (9.9 cu ft) and 1,120 litres (39.6 cu ft) with the rear seat backrest folded down.
With a volume of just eight litres (0.3 cu ft) and weighing just ten kilograms (22.0 lb), the power electronics in the engine compartment, which include a DC/DC converter for connecting to the 12-volt electrical system, are compact and lightweight. Six high-performance transistors convert the direct current supplied by the battery into the three-phase current for the electric motor.
When charging the A3 Sportback e-Tron, the charger converts the incoming alternating current into direct current for the battery. The charging port is located in the Singleframe grille behind the four rings, which fold out to the side. Besides a status light, there are also two buttons here. The driver uses them to either start the charging process immediately or via a timer for the next trip. Timer charging can also be programmed via a special menu in the MMI navigation plus or the new Audi connect e-Tron services.
The Audi A3 Sportback e-Tron comes standard with a charging system comprising a control unit with graphical display, and a portable charging unit for the car with two power cables with the 120V and 240V plugs. For use at home, the e-Tron charging cable can be mounted in a wall box (standard with the e-Tron plus package)—snap the unit into place, and have access to Level 2 charging. The charging dock can be locked to protect the equipment against theft, and a PIN code provides additional security.
240-volt charging replenishes the battery in about 2 hours and 15 minutes; recharging through a 120-volt outlet takes approximately 8 hours. Home installation of a 240-volt outlet and home charging station is optional.
The available A3 e-Tron smartphone app allows drivers remotely to check on the status of their A3 e-Tron. It can be used to check battery status and for “charge planning”—setting times for charging to automatically begin. The driver can also use the app to adjust climate control remotely for added comfort and energy savings.
Tesla Model S Cooling System
The Tesla models S battery cooling system consists of a patented serpentine cooling pipe that winds through the battery pack and carries a flow of water-glycol coolant, thermal contact with the cells is through their sides by thermal transfer material. Again this will remove heat from the side of the cells rather than from the tabs, and overheating a Tesla battery pack under hard driving is easy to do.