In the last article hub motor Hub Motor, the revolutionary of the next generation of new energy vehicles? (4) Focuses on Protean hub motor technology. In this issue, let's talk.
Elaphe
Elaphe was founded in the UK in 2006 and has been in development for 15 years. Quantum physicist Andrej Detela, who began working on in-wheel motor solutions in the 1980s, teamed up with Elaphe founder and CEO Gorazd Lampič to create Elaphe. Its mission is to bring hub powertrain solutions to the automotive mass market.
There are four Elaphe hub motor products, namely: S400, M700, M1100, L1500.
Designed for light electric and hybrid vehicles, the S400 is suitable for direct drive applications with light to medium loads and can be integrated with standard disc or drum brakes. Suitable for 13"/14" tires.
The M700 motor is a compact high torque hub motor designed for installation in standard 15/6 inch rims. With a peak torque of over 700 Nm, a peak power of 75 kW and a continuous power of 50 kW, this liquid-cooled motor is suitable for a wide range of passenger car categories. It is compatible with standard disc or drum brakes, enabling the motor to be used in both iWD and 4iWD configurations. Suitable for 15"/16" tires.
The M1100 motor is positioned in the harsh environment of hybrid heavy vehicles such as trains, buses and multi-purpose vehicles. Suitable for 17 inch tires.
The L1500 is the flagship product with integrated standard disc brakes, standard outer calipers and standard wheel bearings, EPB, designed to adapt to the original vehicle steering knuckles. Suitable for 19"/20" tires.
When it comes to the L1500, we have to mention Lordstown Motor, which was founded in the United States in 2018.
Lordstown Endurance is an all-wheel drive (AWD) electric pickup truck under development. Its design includes four independent Elaphe L1500 hub motors. Endurance's production date was postponed beyond April 2022. If nothing else, Lordstown Endurance will be the world's first mass-produced wheel motor electric pickup. Foxconn will acquire the former General Motors plant and produce Endurance for Lordstown Motors.
As for the positioning of Lordstown Motor, you can refer to its comparison with other models in the market, and the company is also raising a large area.
Lordstown Motor's early development plans are as follows, with some delays appearing to be currently available.
The Aptera, which claims to be the world's first solar-powered pure electric vehicle, also uses the Elaphe M700 (standard specification 16-inch) hub motor.
Back to the motor itself, the L1500 was unveiled in 2019 and its design is based on the M700, and both motors have some similarities in structure. The L1500 has 83 parts, of which nearly 60% are standard supplier parts and the rest are mainly cast or customized supplier solutions.
The L1500 uses an external rotor direct drive, and the aluminum rotor housing of the motor contains yoke and permanent magnet, which is connected to the vehicle's steering knuckle by traditional automotive hub bearings.
For the multiphysics structural design of the L1500, you can refer to the details revealed by Elaphe founder and CEO Lampi in a media interview.
Our testing strategy is based on three factors – testing based on OEM and international standards, then internal specifications, and finally internal identification testing, vehicle testing and simulation based on design failure mode and effect analysis exercises.
"These standards also inform our requirements for specific performance parameters for motors and inverters, EMC, electrical safety, durability and cable routing. Analysis based on the ISO 26262 standard is also useful.
Hub motors are subjected to shocks and stresses far more than any electric shaft motor during their service life, as they are in almost constant direct contact with the road. Therefore, Elaphe's development model includes a large number of studies, simulations and tests to iterate on motors that are subjected to various loads over their useful life.
Some of the load acting on the L1500 is generated internally. For example, thermomechanical stresses due to overheating due to copper windings, steel lamination and electromagnetic losses in permanent magnets, as well as frictional losses in bearings and seals.
Excessive preload in the manufacturing process is mainly introduced during the machining and casting processes and can also lead to the accumulation of residual internal stresses in the motor design prior to testing. To this end, Elaphe uses heat treatment to minimize these loads and their impact on structural components.
The external load depends heavily on the type of vehicle with integrated motors, as changes in driving style, driving cycle and vehicle occupancy lead to changes in the vehicle's mass and center of gravity (CoG). For example, electric motors on heavy commercial vehicles and off-road vehicles will be subjected to higher external loads due to the harsher interaction between tires and roads.
In addition, loads caused by the ground or road, which are mainly composed of vibration and bending moments, can act on the electric motor through the tires. Instead, these must be passed through the rims and bearings to the knuckles (and then continue to the vehicle chassis).
To accurately predict and evaluate the structural integrity requirements of motor components in the face of particularly harsh road-induced loads, Elaphe uses SUVs to simulate severe braking and cornering scenarios. The tests investigated CoG acceleration and external lateral loads on all four wheels – particularly severe turns generating about 14,000 N of force on one of the car's right tires.
Additional simulations of external loads on the L1500, such as from potholes, curbs or other problems related to rough roads, were performed according to SAE standards, including SAE J175 and J1981, for impact testing of wheels and tires of road vehicles.
Before iterating on key aspects of the new L1500 design through CAD simulation, Elaphe first selected key peripheral components (including rims, brakes, and bearings) to determine how much space was left for the stator and rotor.
In order to enrich the ideal design of the housing and motor interface, Elaphe's technical experts carried out "topology optimization". These start with a fuzzy CAD approximation of each component with a target structural stiffness level, and then repeatedly expose them to different load simulations (including different combinations and quantities), after dozens of iterations.
For the final verification of the motor of the L1500, you can refer to the following.
Thermomechanical simulations are performed to examine how the air gap between the rotor and stator deforms due to severe heat and shock. These simulations must show that the degree of deformation never exceeds a certain (undisclosed) value, ensuring that no shock occurs between windings or permanent magnets.
Once all design options have been confirmed through CAD and FEA analysis, a prototype of the motor variant can be built and a series of tests can be performed on the company's test bench to verify the accuracy of the simulation.
Testing on the L1500 includes a mechanical shock test. These shocks consisted of 18 shocks, each measuring 100 g (effective), and 60 shocks of 50 g each.
Random vibration durability was also tested by combining a shaker and a hot chamber to apply vibrations of forces up to 2000 Hz and 40 g in the horizontal, vertical and axial directions. As with previous fatigue simulations, both tests were performed in accordance with ISO 16750-3:2007.
In addition to in-house test facilities, Elaphe sometimes uses third-party test facilities for more routine or specialized tests such as vibration, shock, ambient IP rating, and EMC.
Next, combined with the Elaphe patent, let's see how the motor is structured.
PatentED US2015 / 0137669 A1 hub motor comprises at least rotor 1, rotor plate 2, rotor tube 3, bearing system 4 and brake system 5, the connection of which makes the rotor plate 2 screwed or otherwise connected to the rotor tube 3 and the bearing system 4, wherein the opening of the rotor tube 3 and the opening of stator 1 is located from any direction than the maximum braking system 5 or the cross section of the bearing system 4 is larger than the axial plane. The braking system 5 is integrated between the moving parts of bearing system 4 and stator 1. As shown in the figure, with this design, the motor and its components are simple to disassemble and assemble. If not, stator 1 can be assembled into one part or as a component for more parts, such as stator plates and stator tubes. If a piece is used, then casting is a possible production method.
To reduce solder joints and end heights, the stator uses wave winding lines, and patent US 9,601,957 B2 shows a compact multiphase wave winding6. The motor has an even number of magnets on rotor core 12. Magnets magnetize in the radial direction, and the magnetization direction alternates in the tangential direction. The magnetic flux is transmitted through the stator core 3. The number of teeth 4 and slot 5 is less than the number of magnetic cycles K multiplied by 4 to 2 times the number of phases. The number of stator poles remains above 40.
It should be noted that in the early days of the development of hub motor technology, the prototype rotor magnet mainly used N40UH magnets (maximum operating temperature of 180 °C) to ensure good thermal performance, and then with experience and optimized model accuracy, replaced N40UH with N40SH, the latter with a temperature class of 150 °C.
The choice of adhesive for permanent magnets in bonding tanks is tested and validated in a manner similar to rotor and stator structures. Its durability and durability are checked in temperature cycles, load cycles, humidity, shock and vibration.
The image below shows the L1500 stator before (left) and (after) the disc brakes are installed. The windings have been potted with Elaphe's custom resin.
Structurally, it can also be seen that the Elaphe motor controller is not integrated inside the hub, but externally integrated on the chassis, working with other controllers.
The decision to take any technology route is accompanied by the judgment of the market, and according to Elaphe, this choice is driven by a range of reasons.
First, the company observed that the in-wheel motor market has very diverse requirements, with many different vehicles and value propositions. As a result, Elaphe expects each motor to undergo a large number of customizations and different production cycles. Given this need for flexibility for typical hub motor customers, designing motors around integrated inverters will mean increasing design and component costs for each customer. This may reduce adoption due to higher initial prices.
Elaphe believes the advantages are as follows
On the chassis, the environmental and structural loads on the inverter are much lower, and it does not create any subsprung mass or thermal constraints like inside the wheels. Therefore, there are three highly flexible phase cables and two signal cables in the wiring harness for connecting the inverter to the L1500.
The inverter without locking also opens up possibilities for reducing costs within the powertrain range. For example, EV designers can choose to integrate dual inverters in a single enclosure, which can use a single-cycle cooling system, a shared single logic board, faster full-axis control communication, and more.
As packaging and cooling requirements change with different inverter technologies and topologies, mounting the inverter on the vehicle chassis means that it can be replaced relatively easily compared to trying to force an entirely new inverter into the space of the old inverter.
Note: From the above content, it is clear that Protean and Elaphe chose two very different technical routes, such as controller integration. Readers who have read the previous issue will find that the author actually prefers the Protean solution, but Elaphe chooses another one.
Both options have advantages and disadvantages, and each person will have their own opinions and decisions. What I want to say here is that in the absence of any data support, you can challenge and maintain your first thoughts, but don't completely deny it, and keep a skeptical and expectant attitude to confirm it.
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