Cold feet, a hot electric motor, with the battery somewhere in between: temperature control for electric cars is a complex and sensitive subject. This is where efficient multitasking of optimal thermal management works.
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Somehow, we've gotten used to it: setting the temperature control of our car's air conditioning to 20 degrees centigrade and letting the system take care of the rest. Whether it's freezing cold outside or sweltering, the cabin remains comfortable. In many cars, the driver and passengers can even select different temperature levels ' to suit their personal preferences.
Technology operates most efficiently in a special temperature window as well. Excessive variations may even cause damage. Since optimal temperature windows may vary, depending on the component assembly, thermal energy must be skilfully distributed or stored. This is a job for thermal management.
Thermal management modules for powertrains using gasoline engines have been in use since : in Audi's 1.8-l TFSI engine. Just by means of this technology the CO2 emissions of the vehicles using it were reduced by up to four per cent. Since then, the system has been subjected to regular development, especially for meeting the more complex requirements of electrified powertrains.
Current hybrid electric vehicles have up to three cooling circuits operating at different temperature levels: for the IC engine, the electric motor including power electronics, as well as the battery. Even so, these circuits are interlinked via heat exchangers. The individual components are no longer bound to performing fixed roles as heat sinks and heat sources, though can be swapped. In addition, their higher complexity required switching from central to decentralized thermal management for electrified powertrains.
Efficient heating, especially in combination with a heat pump, is decisive for the cabin and the battery of an electric car when starting the vehicle from cold. High cooling power is crucial at hot outdoor temperatures and during fast charging. The new integrated thermal management system from Schaeffler as the central control unit interconnects the coolant and refrigerant circuits. In addition, it uses the waste heat from the electric drive efficiently for optimized energy balance.
The system integrates two electric water pumps. The central electronics unit for the pumps and valves as well as the sensors and chiller as the refrigerant circuit interface. The compact design reduces the space requirement by up to 60 percent compared to conventional, non-integrated systems. At the same time, our new thermal management system with its hydraulically optimized design provides the basis for high overall efficiency.
Because the ample supply of the IC engine's waste heat as a source of heat does not exist in all-electric vehicles, optimized energy management is even more crucial. The objective of the development engineers is to achieve a maximum intersection of high powertrain efficiency as one set and ensured comfort functions and optimal component protection as the other ' by means of sophisticated thermal management.
The interaction between the cooling and the refrigerant circuit in fully electric vehicles is particularly important due to its significantly higher impact on overall vehicle efficiency than in an ICE or hybrid electric powertrain. On cold winter days and nights, the heater in an electric car consumes a similar amount of energy to produce comfortable temperatures in the cabin as the car uses for propulsion. The more efficiently the heater can use the heat dissipated by other units, the higher the car's range. A reversible heat pump in the refrigerant circuit delivers any additionally needed degrees centigrade or Fahrenheit. It can increase the electrical energy diverted from the traction battery by as much as a factor of five and use it not only for heating but also for cooling, as needed.
In contrast to a conventionally powered automobile, in which the IC engine is the central element in the powertrain, the battery ' including thermal management ' is the focus of attention in an electric vehicle. The energy storage device with its liquid electrolytes is highly temperature-sensitive and therefore typically has a dedicated cooling circuit. All of us are familiar with this phenomenon from our smartphones: battery power decreases in cold temperatures due to an increase of internal resistance. The same happens in an electric vehicle, whose energy storage device is nothing but an XXL-sized smartphone battery.
However, the decrease in usable capacity is just one of several issues. High charging currents at low, sub-zero temperatures can damage the battery due to the risk of the lithium ions forming metallic lithium, instead of depositing in the anode as desired, while the battery is being charged. This dreaded process is called 'plating' and can lead to short circuits or even fires. Therefore, predictive thermal management moves the energy storage device into a 'healthy' temperature window prior to the charging process.
The ideal temperature window of a lithium-ion battery ranges between 20 and 40 degrees centigrade. If the battery gets hotter it will not just lose energy but age as well. Due to the fact a normal cooling circuit will soon reach its limits at high ambient temperatures, a refrigerant circuit with a heat pump operating using the same principle as the air conditioning system for the cabin can be activated. The weight of a traction battery, amounting to several hundred kilograms, makes it more difficult to achieve an optimum thermal window. Here, extensive interlinking of the thermal management system and the vehicle control unit helps detect potential stress early and respond accordingly. For instance, if the driver uses GPS navigation to head for a fast-charging station the system can put the battery into the ideal temperature range for charging at maximum power input. The more data that is made available to the predictive management module the more effectively it can respond. Therefore, adequate computing power is becoming an increasingly important pillar of efficient thermal management.
Even though the power dissipation of an electric motor is clearly less than that of an internal combustion engine, it does get hot as well, due to friction and current flow. Overheating of the motor may result in damage, for instance to the winding. Therefore, nearly all electric traction motors are now liquid-cooled. The same applies to the power electronics controlling the complex current flow of an electric vehicle. The cooling circuit controlled by the thermal management system dissipates this thermal energy and conducts it toward a place in the vehicle where it's needed.
Schaeffler's thermal management system controls the complex interaction between the cooling and the refrigerant circuit via a highly integrated cooling module consisting of pumps, valves and the coolant reservoir with a dedicated control unit, complemented by decentralized, smart valves that are coordinated centrally. Based on the prevailing temperatures and operating condition of the vehicle, the central electronics unit controls the actuators and pumps 'also, continuously, the flow of thermal energy. This explains why Jochen Schröder, President of E-Mobility at Schaeffler, says: 'Thermal management is the unsung star of the show when it comes to making vehicles even more efficient and user-friendly.'
The R&D Department Schaeffler
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How much heat comes from an electric motor
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For more information, please visit How Do Electric Cars Generate Heat.
(Mechanical)
(OP)
7 Dec 03 17:37Hello.
If I have a 45kW 3-phase electric motor, can I estimate how much heat is generated from it?
For example, if I know that the power factor is 0.78, is it reasonable to assume all the inefficiencies eventually translate to heat? So that I can say about 10kW of heat is generated?
Thankyou.
Marko.
Replies continue below
(Electrical)
7 Dec 03 18:20Suggestion: The motor manufacturer tech support may provide the motor heat dissipation value (in watts).
The estimate of the motor heat dissipation from the motor efficiency can be derived too; however, the whole loss calculated over the efficiency is not RI^2, watts. Some of losses causing the efficiency to be lower than 1 are covering the windage, and rotor dynamics.
E.g., if the motor is 95% efficient, 45kW is used as a motor output, then 45kW/0.95 - 45kW=2.368kW are losses. If windage and dynamics consumes 2/3 than 1/3 is RI^2 heat dissipation, i.e. about .79kW.
(Electrical)
7 Dec 03 23:30marko333: You do realize that 45kW will be dumped in the "area" of the motor. If the motor is running a leather stacker then all of the motor's consumed energy will be dumped in the immediate area. This is often messed up when people are doing air conditioning calculations.
(Electrical)
8 Dec 03 01:35For a 45 kW motor, the output is 45 kW.If the efficiency is app. 82%, the input is 50 kW. 5 kW is the loss.
For identifying the actual value of the following losses , testing and calculation is requred.
Windage & friction losses
No load magnetic & copper loss
Laod copper loss (stator & rotor)
(Mechanical)
(OP)
8 Dec 03 01:5760hzhmmmm, i do not fully understand what you mean. could you please explain a little more? Are you saying that in the area of the motor, there will be 45kW of heat? I am trying to estimate a heat load for a HVAC calc
I agree that a 45 kW motor will turn that 45kW of energy into some mechanical form.
For a 80% efficient motor, it will draw a total 55kW of energy.
So, that 10kW of energy left over after 45kW are converted to mechanical energy is the result of friction, resistance, slip etc. So generally, does most of this energy loss degrade to heat/noise? Or is only about 1/3 of it converted to heat? Is there a general 'rule of thumb' to estimate this heat loss?
Thankyou
(Electrical)
8 Dec 03 11:29Basically, all losses end up as heat, including friction, windage, core and winding. So just use the efficiency of the motor. A 100 hp motor that has an efficiency of 90% requires about 111 hp of input energy (at full load). It will deliver 100 hp to the shaft and dissipate about 11 hp (8.2kW)as heat. It gets a little more complicated at partial load - you would need a curve of efficiency versus load to be highly accurate.
The power factor doesn't play a role in heat loss determination because it doesn't directly relate to efficiency. In fact, extremely high efficiency motors have poor power factors.
(Electrical)
8 Dec 03 14:15All of the used electrical energy is converted into heat:The loss in the motor itself, the useful part of the energygets converted into mechanical energy first and finally --in the external mechanism -- into heat.
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(Electrical)
8 Dec 03 22:41Suggestion to the previous posting: Normally, RI**2 in watts is considered as a heat source. Although, there is some heat developed in bearings due to bearing friction. Watts that consumed by motor windage losses and motor rotational dynamics do not significantly contribute heat to the room environment.
(Electrical)
9 Dec 03 12:02Suggestion to the previous posting: All losses end up as heat. Some losses are greater than others, but since the original question related to the heat rejected by the motor, the breakdown of losses is immaterial.
(Mechanical)
10 Dec 03 09:50All the input to the motor is finally converted into heat.if the driven equipment is doing the work within the room, for eg a grinding wheel,all the energy is converted into heat with in the room.If the driven equipment is a pump,the mechanical input to pump is converted into pressure energy of the pumped fluid.If the fluid leaves the room,it gets converted into heat at some other place along the pipeline.In this case the heat dissipation in the room is due to inefficiency of the motor only.
Since the most stable form of energy is heat, all energy eventually gets converted into heat energy.
So froma HVAC load estimation point of view,the heat dissipation into the room is very much dependent on the system configuaration as explained in above example
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