Electric Drive Units (EDUs) are at the heart of modern electric vehicles, combining the electric motor and transmission into a single, compact system. These units are crucial for achieving the efficiency, performance, and reliability expected in electric cars.
A key challenge in the design of EDUs is ensuring effective lubrication. Proper lubrication minimizes friction, reduces wear on components, and helps dissipate heat, all of which are critical for maintaining the longevity and efficiency of the system. Additionally, as EDUs operate at high speeds and under varying loads, optimizing lubrication becomes essential for achieving peak performance while meeting stringent durability requirements.
This simulation case explores the behavior of lubrication within an EDU, focusing on how oil is distributed and interacts with critical components under realistic operating conditions.
Objective of Part III: Examine Critical Regions in the Transmission
While Part II. focused on the E-engine, Part III shifts the focus to the transmission. This part shares similarities with the gear box cases on our website (Gear Box Lubrication with shonDy and Gear Box Lubrication at Low Temperature with shonDy ). Accordingly, the objective here is also comparable: to ensure effective lubrication of the bearings and to achieve an optimal distribution of lubricant throughout the transmission system. Proper lubrication reduces friction and wear, contributing to the overall efficiency and longevity of the EDU.
Case Description
The general setup of the transmission is depicted in the image below. To avoid duplication, this section exclusively describes the transmission setup. For details on the E-engine configuration, please refer to Part II. .
The rotational speeds of the various shafts and bearings are as follows:
| Component | RPM | Component | RPM |
|---|---|---|---|
| Input Shaft | 2000 RPM | Input Bearing | 666 RPM |
| Intermediate Shaft | 666.5 RPM | Intermediate Bearing | 215 RPM |
| Output Shaft | 147.3 RPM | Output Bearing | 50 RPM |
The simulation starts with approximately 1.6 liters of oil in the sump. A particle size of 0.064 mm was used, resulting in a total of around 5 million particles. The red box in the image represents an outlet located in the sump of the transmission box. This outlet is connected to the inlets of the rotor from Part II. . The outlet withdraws 12 l/min of oil, which is redistributed to the rotor inlets.
Monitoring occurs through sample windows positioned around the bearings. The image below highlights the samples located on one side of the transmission.
- As shown in the image above, the samples labeled with the number 1 represent those positioned at the front of the transmission box.
- The samples labeled with the number 2 are located at the back of the transmission box (not visible in this image).
Results
In the diagrams below, the data from the two samples on the same shaft (1 and 2) are displayed together within each diagram. This comparison provides a clear overview of lubrication behavior across the front and back of each shaft.
Input Shaft
Key observations:
- Bearing 2 (back) receives significantly more lubricant than Bearing 1 (front).
- Bearing 2 reaches steady-state conditions after approximately 3 seconds of simulation time, with the lubricant volume stabilizing at around 11 ml.
- Bearing 1 does not reach steady state during the 5 seconds of simulation time:
- In the first half of the simulation, Bearing 1 receives almost no lubricant.
- In the second half, the situation improves slightly, but the bearing still receives minimal lubrication.
- By the end of the simulation, the total lubricant volume in the sample is less than 1 ml.
The rendered image below provides a visual representation of the lubricant distribution.
- Bearing 2 is fully lubricated, with fluid visible between the bearing balls.
- Bearing 1, in contrast, has only a few drops of lubricant, indicating insufficient coverage.
Intermediate Shaft
Key observations:
- Bearing 2 receives significantly more lubricant than Bearing 1, similar to the input shaft.
- Bearing 1 receives no lubricant throughout the entire simulation, highlighting a critical lubrication gap.
- By the end of the simulation, the lubricant volume in the Bearing 2 sample is approximately 4 ml, which is less than the volume observed in Bearing 1 of the input shaft.
- Bearing 2 appears to be approaching steady state near the end of the simulation, but extending the simulation time would be necessary to confirm this.
The rendered image below illustrates the lubricant distribution in the bearings of the Intermediate Shaft:
- Bearing 2 is adequately lubricated, with fluid visible between each roller of the bearing.
- Bearing 1, on the other hand, shows no visible lubricant within the bearing.
Output Shaft
Both bearings reached a steady state, with Bearing 1 stabilizing after 3.5 seconds and Bearing 2 after 2 seconds.
Bearing 1 stabilized at 6 ml, while Bearing 2 stabilized at 2 ml. This makes the output shaft different from the other shafts, as it is the only one where the front bearing receives more lubricant than the rear bearing. Additionally, the output shaft is the only shaft where the nearby casing is equipped with a guide rail, which actively direct fluid from the gears to the bearings.
The image on the left shows a section of the casing along with the output shaft, where the guide rail is clearly visible. The output gear carries lubricant to the top of the casing and then throws it onto the guide rail, which distributes the fluid laterally to the bearings.
This process is illustrated in the second image, where the casing is hidden, showing only the gear and the bearings. The reason why Bearing 2 receives less lubricant than Bearing 1 is also visible:
- For Bearing 1, the fluid is directly guided to the bearing.
- For Bearing 2, the fluid first flows on the differential gear casing before reaching the bearing.
Nevertheless, in both bearings, the lubricant fills the gaps between the rollers, ensuring proper lubrication.
Summary
This simulation examines lubricant distribution in the transmission of an Electric Drive Unit (EDU), revealing imbalances across the input, intermediate, and output shafts.
- Input Shaft: Bearing 2 reaches steady state at 11 ml, while Bearing 1 remains under-lubricated (<1 ml). This imbalance highlights a potential design issue requiring further optimization.
- Intermediate Shaft: A similar issue occurs, with Bearing 2 receiving 4 ml while Bearing 1 stays completely dry, indicating a lubrication gap.
- Output Shaft: Unlike the other shafts, Bearing 1 (6 ml) receives more lubricant than Bearing 2 (2 ml) due to guide rails directing oil from the gears.
These results emphasize the need for further optimization to ensure balanced lubrication, enhancing the efficiency and durability of the EDU. This could be achieved through additional guide rails or active lubrication.
