Hairpin technology
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Hairpin technology is a winding technology for stators in electric motors and generators and is also used for traction applications in electric vehicles. In contrast to conventional winding technologies, the hairpin technology is based on solid, flat copper bars which are inserted into the stator stack. These copper bars, also known as hairpins, consist of enameled copper wire bent into a U-shape, similar to the geometry of hairpins.[1]
In addition to hairpins with U-shape, there are two other variants of bar windings, the so-called I-pin technology and the concept of continuous hairpin windings.
I-Pins are straight copper wire elements that are inserted into the stator slots. Unlike Hairpins, these Pins are not bent prior to insertion into stack. However, contacting is necessary on both sides of the stator. In the concept of continuous hairpin windings, so-called winding mats are produced and afterwards inserted into the stack from the inner diameter.
Structure of a hairpin stator[edit]
The structure of a hairpin stator differs from conventional stators only in the type of winding system - other components of the stator stay mostly the same. [1] [2] The stack of sheets, e.g., consists of many layers of individual sheets, each insulated by a thin coating. [3] The housing is another subcomponent that does not require modifications in general. The thin, round wire of the conventional winding technology is substituted by copper bars, which better fit the slot geometry and therefore provide a higher slot-filling degree than regular winding. [4] To create the necessary winding scheme, the free ends of the hairpins are twisted and subsequently contacted by a welding process. In addition to the impregnation process for the entire stator, which is also necessary for conventionally wound stators, a layer of insulation resin is applied to the ends of the hairpins. [5] Hairpin stators are most commonly used for synchronous machines. [6]
Hairpin stator manufacturing[edit]
The hairpin stator process chain is based on an indirect winding approach. Due to the solid conductor cross section, the hairpins can be shaped into their final geometry ahead of the actual assembly process. [7] In contrast to conventional stator production, in which winding-based assembly processes predominate, a forming process is applied. [8] [9]
The production of a hairpin stator can be divided into 4 steps:
Hairpin production[edit]
In the first process, a flat copper wire, which is usually already enameled, is continuously unwound and straightened in several stages to reduce residual curvature and stresses. In preparation for welding of the copper ends in a later process step, this insulation is partially removed. Here, laser-based and mechanical processes are feasible. Depending on hairpin geometry, the hairpin wire is cut to length and bent, in varying order. Hairpins are formed into a three-dimensional geometry either in a single-stage process using special CNC bending equipment or in multiple stages in which a die bending process follows a swivel bending process.[7][9] [4]
Assembly and twisting[edit]
The insertion process of hairpins in a stator stack is limited by overlaps in the winding head geometry. In addition, a reliable insertion process of hairpins into the stator must be ensured. The hairpins are usually pre-assembled in a so-called assembly nest. [10] Individual pins are arranged in accordance with the defined winding scheme within the pre-assembly process. In general, a single hairpin stator has about 3-16 different hairpin geometries. [11] The stator slots are lined with insulation paper to separate the winding system from the ground potential of the sheet stack of the stator. In the next assembly step, the entire hairpin basket is inserted axially into the stator stack. To support the insertion the hairpins are sometimes equipped with chamfers during the cutting process – in addition grippers for precise positioning might be used.
According to the winding scheme, each layer of hairpin ends is twisted. Each layer of hairpin ends is twisted in accordance with the winding scheme. During the associated rotation the tool has to be moved in an axial motion for height compensation. To ensure axial accessibility for the hairpin ends must be radially exposed in a preparatory step. [4]
Welding and interconnection[edit]
In the following step, hairpin ends are electrically contacted with each other to form the windig scheme of an electric motor. Using a laser, the hairpin ends are partially melted and joined together to form an electroconductive connection. An optimal welding process is marked by homogenous weld geometries as well as minimal thermal input into the hairpins. Repeatable welding strategies require a stable condition of the stator ahead of the welding process. Height and lateral offset of the hairpin end relative to each other can cause welding defects. These can be prevented by corrective processes that are dependent on the adherence to tolerances within all upstream processes.[12] [13] Phase jumps and the main electroconductive connection of the entire winding can be carried out through connective elements or assemblies that are connected to the previously welded hairpin ends. [14] This can also be done by using laser welding. [15] Examples of interconnection elements are contact rings, terminals, and so-called bridges.
Insulation[edit]
After the winding process, the welded copper ends are reinsulated and the entire stator is impregnated. Powder coating or polyurethane-based resins are commonly used to insulate the copper ends. Usually, dipping, trickling, or potting processes are used for this purpose. The impregnation process of the stator itself does not differ a lot from the ones used for conventionally stators, hence dipping or trickling processes are used. The purpose of impregnation is to protect the stator against thermal, electrical, ambient, and mechanical influences. [6] [16]
Testing[edit]
Depending on the process and product design, a large variety of tests are performed throughout the entire production process. Within the scope of end-of-line testing, ensuring function- and safety-relevant properties of the stator is a key objective. Common tests are, e.g.:
- Partial discharge testing[17]
- Surge voltage testing[18]
- Resistance testing[17]
- Geometric testing[19]
Advantages and disadvantages on the process and on the product side[edit]
The advantages and disadvantages of a hairpin stator largely depend on the final application.[10] Due to deterministic assembly processes, good speed-torque behavior, and high fill factors the hairpin technology has moved into the focus of automotive applications in recent years. Additionally, the hairpin production process is highly suitable for automation. As a result, shorter cycle times and increasing quantities lead to decreasing production costs.[10]
To ensure functionality, particularly in traction drives, a major challenge for the implementation of the hairpin technology is process reliability. In this regard, bending and welding processes are the most challenging processes. In case of the bending process, high requirements for an undamaged insulation as well as exact geometry must be met. Incorrectly welded hairpin ends can cause electrical losses – up to a non-functioning stator.[10]
Key target parameters for stator design are high fill factors within the stator slots and a small winding head. Due to the rectangular and enlarged conductor cross section, fill factors reach up to 73% and are thus significantly higher compared to conventionally wound stators (approx. 45-50%).[20] Furthermore, a small winding head leads to an increase in relative active material in the stator and thus, the proportion of the winding system that generates power increases. However, the larger cross section of hairpins can result in additional electrical losses, e.g., due to current displacement effects such as the skin effect.[21]
Hairpin technology in the automotive industry[edit]
In recent years, hairpin technology is increasingly applied in automotive applications. The Volkswagen Group, in particular, relies on hairpin stators in its latest generation of electric vehicles. Next to the Volkswagen ID.3[22] and ID.4[23] the Audi e-tron GT[24] models as well as the Porsche Taycan[25] have traction motors based on hairpin technology. With the introduction of the iX3, BMW also started to install hairpin stators in its electric vehicles. In 2021, General Motors unveiled its new motor line up which includes a 64kW ASM for hybrid applications as well as a 255kW PSM for use in the new Hummer EV.[26]
The first production vehicle with hairpin technology was the Toyota Prius hybrid model in 2012.[27]
Research in the field of hairpin technology[edit]
With an increasing interest in hairpin technology in the automotive industry, an improvement in the maturity of hairpin stators is required. To accelerate the optimization process of the technology, both government and industrial research projects focusing on hairpin technology are being funded. These include (research area, consortium leadership):
- Pro-E-Traktion (Production, BMW AG)[28]
- HaPiPro2 (Production, PEM of RWTH Aachen University)[29]
- AnStaHa (Production, Karlsruhe Institute of Technology)[30]
- IPANEMA (Machine Learning, API Hard- and Software GmbH)[31]
- KIPrEMo (Artificial Intelligence, FAPS of FAU Erlangen-Nürnberg)[32]
- KIKoSA (Artificial Intelligence, FAPS of FAU Erlangen-Nürnberg)[33]
Further reading[edit]
- Kampker/Schnetter/Vallée: Elektromobilität. 2nd rev. edition, 2018, Springer Berlin Heidelberg, ISBN 978-3-662-53136-5
- Gläßel, Tobias: Prozessketten zum Laserstrahlschweißen von flachleiterbasierten Formspulenwicklungen für automobile Traktionsantriebe. FAU Studien aus dem Maschinenbau Band 354. Juli 2020, Erlangen, FAU University Press, ISBN 978-3-96147-356-4
- VDMA/Raßmann: Produktionsprozess eines Hairpin-Stators. 1st edition, Oktober 2019, ISBN 978-3-947920-08-2
External Links[edit]
- VDMA: Production process of Hairpin stators
- Schaeffler eDrive Plattform: Benefits and Disadvantages of a Hairpin stator
References[edit]
- ↑ 1.0 1.1 Porsche. "The powertrain: Pure Performance". Retrieved 2022-07-27.
- ↑ German Patent and Trade Mark Office. "Hairpin motor, power assembly, and vehicle". Retrieved 2022-05-13.
- ↑ Tong, Wei (2014). Mechanical design of electric motors. Radford, Virginia: CRC Press. ISBN 978-1-4200-9144-1. Search this book on
- ↑ 4.0 4.1 4.2 PEM RWTH. "Produktionsprozess eines Hairpin-Stators" (in German). Retrieved 2022-05-24.CS1 maint: Unrecognized language (link)
- ↑ Tong, Wei (2014). Mechanical design of electric motors. Radford, Virginia: CRC Press. ISBN 978-1-4200-9144-1. Search this book on
- ↑ 6.0 6.1 Karlsruhe Institute of Technology (KIT). "Wissen kompakt: Produktion elektrischer Traktionsmotoren" (PDF) (in German). Retrieved 2022-04-21.CS1 maint: Unrecognized language (link)
- ↑ 7.0 7.1 German Patent and Trade Mark Office. "Flat wire motor stator plane hairpin forming device". Retrieved 2022-05-13.
- ↑ Kampker, Achim (2018). Elektromobilität (in German). Aachen: Springer. p. 333. ISBN 978-3-662-53136-5.CS1 maint: Unrecognized language (link) Search this book on
- ↑ 9.0 9.1 German Patent and Trade Mark Office. "Motor hairpin type conducting bar winding device". Retrieved 2022-05-13.
- ↑ 10.0 10.1 10.2 10.3 Gläßel, Tobias (July 2020). Prozessketten zum Laserstrahlschweißen von flachleiterbasierten Formspulenwicklungen für automobile Traktionsantriebe (in German). Erlangen: FAU Universitiy Press. p. 19. ISBN 978-3-96147-356-4.CS1 maint: Unrecognized language (link) Search this book on
- ↑ Kampker, Achim (2018). Produktionsprozess eines Hairpin-Stators (in German). Aachen: Springer. p. 10. ISBN 978-3-947920-08-2.CS1 maint: Unrecognized language (link) Search this book on
- ↑ "Vorrichtung und Verfahren zur Ausrichtung einer Hairpinwicklung". register.dpma.de. Retrieved 2022-08-09.
- ↑ German Patent and Trade Mark Office. "Driving motor hairpin connection alignment apparatus". Retrieved 2022-05-13.
- ↑ German Patent and Trade Mark Office. "Verbindungsbauteil zur Verbindung von elektrischen Leitern einer hairpin-Wicklung eines Stator einer Elektromaschine" (in German). Retrieved 2022-05-13.CS1 maint: Unrecognized language (link)
- ↑ Gehring Technologies GmbH + Co. KG. "Welding". Retrieved 2022-05-24.
- ↑ Gehring Technologies GmbH + Co. KG. "Impregnation". Retrieved 2022-05-24.
- ↑ 17.0 17.1 Marposs. "Elektrische Prüfungen: Montage von Statoren, Funktionskontrollen: Teilentladungsprüfung". Retrieved 2021-07-21. Unknown parameter
|url-status=ignored (help) - ↑ Schleich. "MTC3". Retrieved 2021-07-21.
- ↑ Hexagon Manufacturing Intelligence. "Dimensionale Prüfung von Hairpin Statoren". Retrieved 2021-07-21.
- ↑ Kampker, Achim (October 2019). Produktionsprozess eines Hairpin-Stators (in German). Aachen: VDMA. p. 2. ISBN 978-3-947920-08-2.CS1 maint: Unrecognized language (link) Search this book on
- ↑ Pfung, Thomas (2018). "Die Schaeffler eDrive Plattform". Retrieved 2021-07-15.
- ↑ Volkswagen. "Von Feder und Dämpfer bis Rotor und Stator". Retrieved 2021-07-21.
- ↑ Munro Live (2021-07-06). "Volkswagen ID.4: Electric Motor Teardown and Analysis". Retrieved 2021-07-21.
- ↑ Audi. "Antrieb und Rekuperation". Retrieved 2021-07-21.
- ↑ Porsche Newsroom. "Der Antrieb: Performance pur". Retrieved 2021-07-21.
- ↑ General Motors (2021-09-21). "GM Reveals All-New EV Motors to Power an All-Electric Future". Retrieved 2021-09-23.
- ↑ Weber Auto (2017-05-27). "Das Prius C P510 Transaxle". Retrieved 2021-07-21.
- ↑ Lehrstuhl für Fertigungsautomatisierung und Produktionssystematik (FAPS), Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU). "Pro-E-Traktion: Automatisierte und robuste Produktionssysteme für E-Traktionsantriebe". Retrieved 2021-07-20.
- ↑ PEM RWTH Aachen University. "HaPiPro2". Retrieved 2021-07-20.
- ↑ Schinarakis, Kosta (2019-09-06). "Flexible Fertigung von Elektromotoren für Fahrzeuge". Retrieved 2021-07-20.
- ↑ PEM RWTH Aachen University. "IPANEMA". Retrieved 2021-07-20.
- ↑ Lehrstuhl für Fertigungsautomatisierung und Produktionssystematik (FAPS), Friedrich-Alexander-Universität Erlangen-Nürnberg. "KIPrEMo – Künstliche Intelligenz für die flexible und effiziente Produktion von Präzisionsbauteilen für die E-Mobilität". Retrieved 2021-07-20.
- ↑ Lehrstuhl für Fertigungsautomatisierung und Produktionssystematik (FAPS), Friedrich-Alexander-Universität Erlangen-Nürnberg. "KIKoSA – Künstliche Intelligenz zum prozesssicheren laserbasierten Kontaktieren von Statoren für elektrische Antriebe". Retrieved 2021-07-20.
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