Best-in-class Thermal Assessment of Electric Powertrain

Mario Theissl, CEO, Theissl Systems GmbH

THEISSL systems enables precise measurement of temperature and torque in electric drive units with its minimally invasive sensor telemetry technology that is tailored specifically to each customer application. These systems can be seamlessly integrated into existing drive components with minimal need for system modifications, allowing for highly accurate measurements under real-world test bench and vehicle conditions.

With project-specific telemetry units for E-machine rotors gearbox shafts and clutches, the original characteristics of the DUT are inherently preserved while making optimal use of the available installation space. All systems are entirely contactless, transmitting wirelessly to the evaluation unit to ensure reliable performance on high-speed rotating components.

At the core of thermal EDU characterization is the choice of the right sensor elements. Therefore, as a full-service partner, THEISSL systems supports the entire measurement process starting from the definition of test points and the selection of suitable sensors all the way to data analysis after a successful test run.

Even in demanding applications, such as rotor temperature measurements in electric drives, up to 32 thermocouples can be used to gain vast knowledge of the thermal behavior of the DUT. Another variant of our telemetry boards is just 10.5 mm wide, foldable, and bendable around tight radii, which enables temperature measurements on gear teeth and bearing inner rings on transmission shafts. Furthermore, it could be mounted on the rotor shaft, for gearbox input torque measurement e.g. to determine system efficiency.

This measurement technology was implemented in a VW ID.3 demonstrator vehicle, which is showcased at CTI 2025 in Berlin. The system captures inner and outer bearing ring temperatures, gear tooth temperatures, as well as torques at the gearbox input shaft and side shafts. In the E-drive rotor temperature measurement, a telemetry system capturing 16 individual test points was complemented by four additional sensors on the stator windings, giving unprecedented insights into the thermal behavior of the
vehicle’s drive train.

This data, collected over more than 10,000 km of test drives then formed the basis for the training of a Thermal Neural Network (TTN) modelling the thermal behavior of the E-machine. Due to the large number of temperature measurement points, the temperature estimator for the rotor magnets achieved a highly respectable accuracy of ±1.5 K.

Application example: Thermal testing of the electric drive unit of the VW ID.3

A New Material Solution for Low Wear, Low Friction, and Electrical Insulation in Automotive Transmissions

Geoff Lewis, Technical Director, Duvelco

What is a New Material?

Being ‘new’ is claimed with some regularity in the world of polymers; however, step changes in performance are less frequent. Here, I am going to look at an innovation that may pass the test and rightfully be called a new material. The polymer in question has the trade name Ducoya.

In terms of chemical type, it is a semicrystalline thermoplastic block copolymer bearing the unfamiliar name PMDA-ODA or, in long form, PyroMellitic DiAnhydride – 4,4‘-OxyDiAniline. The repeat unit is shown below:

This is a polyimide with an ‘I’; not a polyamide. Polyimides are a vast and rapidly growing class of polymers. The number of polyimide papers written annually has exploded in recent years. Polyimides include thermosets, thermoplastics, amorphous, semicrystalline, and photo-imageable materials.

The above graph shows the number of papers regarding polyimide. Source: Researchgate – Number of citations per year from 1975 to 2019, Web of Science.

Some may recognise this molecule as being from the 1960s; however, that is not the new part. This molecule, initially developed for NASA’s space programme, has long seemed too difficult to source and too expensive for many automotive applications.

This is especially the case as the industry moves into an era of cost-competitive BEVs, and, from a European and North American perspective, an era of low-cost, possibly subsidised Chinese BEV imports to compete with.

So, if it isn’t the molecule, what is new?

The innovation here is a new, patented manufacturing process that also covers the resulting material. Many high-performance plastics, including those produced by the traditional PMDA-ODA Manufacturing method, utilise monomers dissolved in harmful, high-VOC solvents. The environmental and high-cost considerations of these solvents mean they must be separated, distilled, and reused, consuming a large amount of energy in the process.

Ducoya avoids most volatile solvents used in the process and instead employs supercritical carbon dioxide and a catalyst.

Therefore, it is straightforward to separate the polymer from supercritical carbon dioxide by lowering the pressure. The carbon dioxide is repressurised and stored for reuse. This single step greatly streamlines manufacturing at scale, making the polymer considerably more accessible for automotive applications. However, this is not the end of the story. While the original aim of the invention was to simplify manufacturing at scale, when the properties of the resulting polymer were compared with those of its traditional predecessors, something remarkable emerged – dramatically improved mechanical and tribological properties.

The above graph consists of Ducoya preliminary data – arithmetic mean of five specimens, and best traditional values taken from published datasheets, none of which reported data over 260 °C.

The above graph consists of Ducoya preliminary data – arithmetic mean of thirty specimens, and best traditional values taken from published datasheets, none of which reported data over 260 °C.

Datasheet1

Ducoya G021 ISO is a filled version of Ducoya, containing 15 % wear- and friction-optimised graphite. Initial investigations of tribological properties in dry conditions indicate a significant improvement in wear factor compared to the best traditionally produced polyimides of this type. While much work remains to be done with this
specific molecule, this result seems to confirm earlier work by Irisawa et al. on several polymers, showing that the wear rate is inversely proportional to the product of tensile strength and elongation.

Of particular importance is the continued performance of this molecule at significantly elevated temperatures. This is because, when dry friction occurs – whether by design or due to off-design operation under adverse conditions – temperatures on the wear surface can rise substantially compared to the bulk material. For instance, regular operation at 120 °C can quickly lead to temperatures exceeding 240 °C on the wear surface under harsh sliding conditions (High PV value).

It should be noted that this general hypothesis applies only to materials of the same type (in this case, PMDA-ODA polyimides) and only when tested under identical conditions. Further work will determine whether this prediction holds for Ducoya G021 in comparison with other PMDA-ODA polyimide polymers.

Why would this be important to Battery Electric Vehicles?

As BEVs increase in torque, while package space and cost must decrease, this can lead to higher PV values as the available load area diminishes. This also reduces the weight of single-speed and multi-ratio transmissions. Epicyclic transmission layouts may particularly benefit from this improvement. Furthermore, Ducoya, being wear-resistant, although still relatively soft compared to metal, allows metallic debris, such as burrs and wear particles from gears, to embed in its material and be removed as contaminants from the lubricating oil. While this embedding must be limited, removing metallics before they can interfere with the proper functioning of the electric motor – often sharing the same lubricating oil as the transmission – can only be beneficial.

Conclusion

An interesting new material that adds a new dimension to accessibility and performance in automotive applications. Here, we have focused on mechanical and tribological properties.

Future Work

Future publications will describe why this unusual and newly applied process using supercritical carbon dioxide should lead to such improved mechanical and tribological performance.

Opportunities arising from the resulting electrical performance in conjunction with the latest high-precision
moulding techniques will be highlighted.

In addition, test results will be published in which the relationship between t·ε2 and wear rates in various
situations, as described above, will have been investigated.

1 DuPont Vespel® SP-21 ISO Reference No. VPE-A10863-00-B0614 published 2010 and 2021.

Proposal of Next-generation HEV System

Kazuyoshi Hiraiwa, President, FINEMECH
Shinji Morihiro, Representative, M Powerlabo

Background of the proposal

In recent years, the problem of BEV has become apparent, and the value of HEVs has been reevaluated. Under these circumstances, we would like to propose a next-generation HEV system.

Purpose of the proposal

This proposal is based on the THS (Toyota Hybrid System). This is because the THS is superior to the series model in terms of power transmission efficiency as an E-CVT. The THS used in the Prius is simple system but it is generally said to have problems with starting acceleration performance and high-speed fuel economy. Looking at the specifications of the Prius, in order to ensure starting acceleration performance, the capacity of the MG2 (Motor Generator 2) for driving in recent models is larger than that of the initial model. However, the increased capacity of the MG2 makes to a deterioration in high-speed fuel economy. On the other hand, Toyota has added a four-speed automatic transmission planetary gear mechanism to the THS for LEXUS to improve both fuel efficiency and acceleration performance. However, this can only be applied to FR cars due to the axle length.

This proposal aims to improve fuel efficiency and acceleration performance by applying a dog-clutch parallel-shaft transmission mechanism to the THS, while also realizing a configuration that can be installed in FF vehicles. (see Figure 1)

Proposal Overview

The power transmission route between the ring gear and the output shaft of the planetary gear for torque division is the „mechanical route“ (M route), and the route that transmits power from the sun gear to the output shaft via MG1 and MG2 is the „electric route (E route)”. If the route between the input shaft and the output shaft is a „direct connection route (D route)”, a dog clutch type transmission mechanism is provided for each route (see Fig. 2). That is, there are only three sleeves. Normally, both the M route and the E route are transmitted as an E-CVT, but when switching from H-1 to H-4, which will be described later, the gear is shifted through the D route to avoid loss of output shaft torque when driving on one route while driving on the other route, and when shifting under high load.

MG capacity (at ICE power 1) is assumed as follows: This takes into account that if the input shaft is fixed and used as a PHEV, the driving force equivalent to that of an ICE can be obtained. Also, the specs of the early PRIUS were almost this ratio.
MG1 0.4
MG2 0.6

Basic rule of Sleeve switching (Dog clutch)

Torque is set to 0 and the engagement is related, and the engagement is carried out with a speed difference of 50rpm or less.

Operation

First, we will explain the shifting operation of the E-CVT in HV mode. If the sleeves are S1, S2, and S3, then the H-1 is a combination of the M route (S1) and the E route (S2) with Lm and Le. Switching from H-1 to H-2 is done as follows: When driving on Lm on the M route, the MG2 torque is reduced to zero at the mechanical point (when MG1 stops), making it easier to switch the E route from Le to Me, and the output torque can be shifted without change. That is, the switching from H-1 to H-2 is carried out with gear ratios near the mechanical point of H-1.

Also, switching between H-2 and H-3 is done through the D-route Ld (D-1). In other words, if the gear ratio is equal to the value of Ld while driving in H-2, the speed of the S3 and the opponent’s gear matches, so it is easy to shift S3 and switch to D-1 at this point. S1 and S2 can be freely operated while driving in D-1, so if you revive the power generation of MG1 and the drive of MG2 by connecting H-3 in the operation chart, it will switch to H-3. This can also be done without any change in output torque.

Similarly, it is easy to switch from H-2 to H-4 via D-3. You can switch in the same way in these reverse orders.

In addition, the above switching is done with a fixed gear ratio, but especially in low to medium load driving, it is possible to switch without the drive of the D-route in any gear ratio. This means that you can drive on one route, M route and E route, while switching between the other. In this way, in low- to mediumload driving, it is possible to switch between any gear ratio without little change in output torque.

Kickdown

If you press the throttle pedal sharply while cruising on the H-3, follow these steps:
When the ICE power is increased and the gear ratio is equal to the value of D-1, switch S3 to Ld (D-1) and operate S1 and S2 to switch to the desired drive mode while driving with D-1.

If you press the throttle pedal sharply while cruising on the H-4, follow these steps:
When the ICE power is increased and the gear ratio is equal to the value of D-2, switch the S3 to Hd (D-2), and operate the S1 and S2 to switch to the desired drive mode while driving with D-2.

Of course, if the amount of throttle pedal depression is not very large, you can switch at any gear ratio by switching while driving on either the M route or the E route mentioned above.

MG1 & MG2 Stops

It is widely known that power loss due to dragging torque of MG1 and MG2 occurs when the ICE stops at medium or high speeds, or when MG2 is driven at low load at high speeds. The system allows MG1 and MG2 to be stopped as needed. (See Figure 5)

This means that if the ICE stops while driving at medium to high speeds, you can stop MG1 by putting S1 in neutral. If you want to revive the connection of MG1, rotate MG1 to synchronize and shift S1 again. In addition, the gear ratio near the mechanical point of the H-4 and the low-load high-speed driving on the D-1 and D-2 can keep the MG2 at a standstill if the S2 is neutral. This avoids loss of drag torque and improves fuel economy.

Application to PHEV

As is well known, PHEV is established by increasing the battery capacity and providing a means to fix the input axis, allowing MG1 to participate in driving in addition to MG2 in EV mode. In this case, by driving one of the M routes and the E route while switching between the other using the same method as above, you can switch between EV mode while preventing loss of output torque. This means that it is possible to smoothly switch between the MG2’s three-stage drive and the MG1’s two-stage drive without losing drive torque. Of course, this is when switching, not to mention that after the switch is complete, you can drive both MG2 and MG1, or even one of them. It can also be driven by stopping one side, allowing for a variety of drives.

Advantages of this system

• The multi-stage THS reduces the capacity of the MG2 while ensuring acceleration performance in the low speed range and driving torque during reverse driving.
• In HV mode, the drive mode can be switched without changing the output torque. Moreover, in medium and low load driving, it can be switched with any gear ratio.
• No oil pump or friction clutch required.
• MG2 and MG1 can be stopped when it is not needed.
• By reducing the size and stopping of the MG2, fuel efficiency can be improved by about 6 ~ 8 % during high-speed cruising.
• When applied to a PHEV, it makes EV mode driving in multiple modes to achieve smooth shifting.
• While having the above functions, it fits into a size that can be installed on an FF car.

When compared to the THS+4AT and Renault systems, we can see that this system has many advantages. (See Figure 6).

References

• TOYOTA Hybrid System, Development of Multi Stage Hybrid Transmission , K. Okuda, Y. Yasuda, M. Adachi, A. Tabata, H., Suzuki, K. Takagi(Toyota), T. Atarashi, R. Horie (Aisin AW), 2017 SAE World Congress, No.2017-01-1156 (2017/4/4-6)
• Renault HEV System, The new DHT from Alliance Renault/Nissan, Antoine Vignon (Renault FRANCE), CTI Symposium 2017 Berlin