As the drive motors used in new energy vehicles are evolving toward lighter, more compact designs with higher power density, and as their operating environments become increasingly harsh, higher thermal management and protection requirements are being imposed on these motors; consequently, the temperature rise of the drive motor has become a critical factor determining whether the motor can operate under continuous load for extended periods. If the heat generated by the motor during operation is not dissipated promptly, it can lead to an excessive temperature rise, which accelerates the aging of the insulation materials, reduces the motor’s service life, or even cause demagnetization of magnetic materials such as NdFeB. Therefore, temperature rise (or, more precisely, heat dissipation) is a particularly important performance indicator for drive motors in new energy vehicles.
The stator windings generate heat due to copper loss within the winding chamber; this heat is transferred to the stator core and the air (the air within the slot insulation) through thermal conduction and convection via the slot insulation and the winding surface. The encapsulation process using the thermally conductive epoxy compound JOME3113 not only eliminates the air gap within the stator winding insulation slots but also establishes a thermal path between the stator and the motor housing.
1. The relationship between thermal conductivity, heat dissipation performance, and power increase.
Using high thermal conductivity encapsulant to establish a thermal path between the stator and the housing to enhance the overall heat dissipation performance of the motor is a feasible approach. However, no specific studies have yet been conducted to demonstrate the relationship between the thermal conductivity of the encapsulant and the increase in motor power rating.
When the thermal conductivity of the JOME3113A/B thermal encapsulant is adjusted to approximately 1.5 W/(m·K), the temperature rise of the newly manufactured electric vehicle motor after encapsulation is approximately 15–20°C lower than that of a motor manufactured using the VPI impregnation process; this result is quite significant. 2. The motor performs suboptimally under high-temperature operating conditions after the stator windings have been fully encapsulated.
Generally, the nominal operating range of a new energy vehicle motor
Temperature range: -40°C to 180°C.
3. Comprehensive consideration of thermal conductivity and cost
The most effective way to enhance the thermal conductivity of potting compound is to add an adequate amount of thermal conductive fillers; these fillers create thermal conduction pathways within the epoxy resin matrix, thereby improving the overall thermal conductivity of the potting compound.
However, thermal conductive fillers are generally more expensive than conventional inorganic fillers. The higher the amount of thermal conductive filler added, the better the thermal conductivity of the potting compound, but the cost increases accordingly. Currently, in various other applications, thermal conductive potting compounds with a thermal conductivity ranging from 1.0 to 1.5 are most commonly selected for motor applications.
- Encapsulation process compatibility For the drive motors of new energy vehicles, vacuum casting combined with heating curing is considered the more ideal approach; therefore, when designing the curing process for the JOME3113A/B thermal conductive encapsulant, the following factors should be primarily taken into account:
The crosslinking density of heat-curing epoxy systems is generally higher than that of room-temperature amine-based systems, resulting in superior performance under high-temperature operating conditions;
The heating and curing system allows for the adjustment of the viscosity of individual components during the initial curing stage by means of temperature control, thereby facilitating the proper wetting of the mixture onto the stator windings.
5. The issue of motor weight increase caused by thermal encapsulant
A large number of experiments have demonstrated that epoxy resin-based high-thermal-conductivity encapsulant adhesives generally exhibit a relatively high specific gravity; however, the specific gravity varies depending on the choice of thermal conductive fillers. Typically, for adhesives with a thermal conductivity of approximately 1.0, the specific gravity ranges between 1.8 and 1.9; whereas for adhesives with a thermal conductivity of approximately 1.2, the specific gravity can range between 2.1 and 2.3.
In the cost analysis of thermal conductive encapsulants, the thermal conductive filler often accounts for the largest portion of the total cost; the cost of an encapsulant with a thermal conductivity of 3.0 is typically several times higher than that of an encapsulant with a thermal conductivity of 1.0!
For conventional motors, a value of 0.8–1.2 W/m·K is sufficient; for motors with high power density, the target ranges from 1.5–2.0 W/m·K or higher; only for specialized motors does the pursuit of 3.0 W/m·K or even higher values become relevant.
Vacuuming before and after applying adhesive
1: Degassing before potting (static degassing)
After mixing the glue, transfer it into the vacuum tank and evacuate it for 5–15 minutes; once the liquid surface stops producing bubbles, remove it and fill the container. The advantage is that the process is simple and controllable, eliminating concerns about the glue bubbling or exploding inside the stator. However, there is a clear drawback: during filling, some new bubbles may still be introduced, as the operation is performed under atmospheric pressure.
2: Apply adhesive and then perform vacuuming.
After the adhesive is applied to the stator, the workpiece is simultaneously placed into the vacuum chamber for evacuation over a period of 3–10 minutes to forcibly remove any air trapped within the iron core slots. The advantage of this method is that it effectively clears all dead-air bubbles from the gaps between the coils. The disadvantage is the narrow time window: the adhesive must be in a flowing state for degassing to occur; if evacuation is performed once the adhesive’s viscosity has increased, it will be ineffective.
Recommendation: Before filling with adhesive, perform a degassing cycle (to remove any bubbles introduced during mixing); after filling the stator, place it in a vacuum chamber for a vacuuming cycle (do not fill to capacity – leave a 20–30% margin to prevent adhesive leakage!).