Raleigh SC30 converted to an electric bicycle with an aftermarket electric conversion hub motor kit
A wheel hub motor, also known as a hub motor or in-wheel motor, is a type of motor that is built into the hub of a wheel. These motors are often used in electric bicycles. While they were initially popular in early electric cars, they haven't been widely successful in modern production cars because it affects weight distribution of the car and increases unsprung weight .
Patents for electric bicycles with hub motors were granted as early as 1895.[3] Bicycle hub motors are simple, durable, and affordable compared to other designs, but less suitable for high speeds.[4] Hub motors rose in popularity over other designs in the late 2000s and 2010s.[5]
Several electric, combustion, and steam powered in-wheel motor designs were patented in the 1880s and 1890s.[7] Among those who were awarded patents: Wellington Adams of St. Louis in 1884;[8] Edward Parkhurst of Woburn in 1890;[9] Albert Parcelle later in 1890;[10] Charles Theryc in 1896, who cites no transmission losses thanks to an absence of classic transmission rods from engines to wheels;[11] C F Goddard in 1896 who cites a piston hub motor for horseless carriages powered by expanding gas of some kind;[12] and W C Smith in 1897 who cites an explosive gas expansion motor inside a wheel hub that utilized cams on a track in the hub to transmit power to the wheel.[13]
An electric wheel hub motor car was raced by Ferdinand Porsche in 1897 in Vienna, Austria. He developed his first cars as electric cars with electric wheel hub motors that ran on batteries.[14] A racecar by Lohner–Porsche fitted with four wheel-hub motors debuted at the World Exhibition in Paris in 1900. Alongside it a commercial model was introduced, the Lohner–Porsche Chaise, with two front wheel-hub motors. It was well-received, and several models based on its design were produced by Lohner and other manufacturers until the 1920s.[15][6]
Honda FCX Concept 2005 in-wheel motor with high-voltage wires in orange. Running high voltage outside the chassis can be avoided by using near-wheel motors, which have similar advantages to in-wheel motors.
Hub motors are attractive from a design standpoint because of their flexibility. They can be used for front-, rear-, or individual-wheel drive. They are compact and hence allow for more room for passengers, cargo, or other vehicle components. They allow for better weight distribution compared to a single motor, and they eliminate the need for many of the drive components in traditional vehicles like transmissions, differentials, and axles, which reduces wear and mechanical losses.[18][19] High-voltage in-wheel motors must be robust against damage to their high-voltage cables and components.[2]
Unsprung weight
One disadvantage of a wheel hub motor is that the weight of the motor is not supported by the suspension's shock absorbers, adding to the vehicle's unsprung weight which adversely affects handling and ride quality. Despite this reduction in ride quality with electric hub motors, it is still better than the ride quality of equivalent combustion engine vehicles, but vehicle handling is still negatively affected.[18]Protean Electric and Lotus found that most negative effects of added unsprung mass could be eliminated by adding suspension damping, and that the ability to utilize accurate torque vectoring actually improved car's handling so much that the net effect of the whole arrangement was positive.[20]
Without being supported by the suspension's shock absorbers, in-wheel motors are themselves less shielded both from shocks and debris, reducing their durability. Some designs reduce unsprung weight by reducing the weight of the motor, for example by using a coreless design or Litz wire coil windings. These weight-saving designs may have a negative effect on motor durability.[19]
Similar to in-wheel motors, electric vehicles can be designed with near-wheel motors, sometimes called wheel-end motors. This design shares the same advantages as in-wheel motors while avoiding unsprung weight and wear issues, as the motors are near the wheels but inside the chassis, supported by the suspension. Near-wheel motors are less compact than in-wheel motors, but as of 2022 they are more reliable and more cost-effective,[22] they avoid the risks associated with out-of-chassis high-voltage components,[2] and they simplify vehicle design and assembly. American Axle has developed 100 kW wheel-end motors which will debut in the REE Automotive commercial vehicle product line.[23]
Concept cars
An early modern concept car utilizing electric hub motors was the IZA, presented in at the IEEE conference in 1997, built with four 25 kW (34 hp) motors.[24]
Concept cars that were announced without publicly presenting a physical model include: SiemensVDO eCorner concept, 2006;[37] and ZAP-X, 2007.[38]
Mini QED electric vehicle
MAZ-7907 truck. Each wheel has its own electric motor
Hiriko Fold with in-wheel motor, steering actuators, suspension, and braking, controlled by a drive-by-wire system
Production vehicles
Production vehicles with in-wheel motors include:
Lohner–Porsche Chaise, Mixte, and others. Several models based on this design were produced by Lohner and other manufacturers in the early 1900s.[15][6]
Lightyear 0, briefly produced in 2022 before its manufacturer filed for bankruptcy.[39][40]
Lordstown Endurance, briefly produced in 2022 before its manufacturer filed for bankruptcy.[41]
Planned production vehicles include:
Aptera, a solar powered three wheeler using hub motors from Elaphe Propulsion Technologies[42] is planned, as of 2023, for production in 2024.[43]
^ abVos, R.; Besselink, I. J. M.; Nijmeijer, H. (22–26 August 2010). Influence of in-wheel motors on the ride comfort of electric vehicles. Proceedings of the 10th International Symposium on Advanced Vehicle Control (AVEC10). Loughborough, United Kingdom. pp. 835–840.
^Whitehead, Andrew; Hilton, Chris. "In-Wheel Motors Roll Again". IEEE Spectrum (July 2018): 27. The Lotus engineers were able to eliminate much of the effect of the added unsprung mass by using slightly more suspension damping. What's more, they found that when that unsprung mass came from actual motors attached to the wheels, the ability to power each side of the car independently improved the car's handling substantially. We've now carried out similar studies on other vehicles. And in all cases, we've found that once the dampers are retuned and we add individual wheel control, the net effect on the vehicle's handling is for the better. So unsprung mass really isn't a showstopper after all.
.jpg)
Mini QED electric vehicle
MAZ-7907 truck. Each wheel has its own electric motor
Hiriko Fold with in-wheel motor, steering actuators, suspension, and braking, controlled by a drive-by-wire system
