Electric wheel hub drive for a vehicle, in particular a bicycle, including a stator with an ironless hollow cylindrical stator winding

#The present invention relates to an electric wheel hub drive for a vehicle, in particular a bicycle, according to the preamble of independent claim 1. The wheel hub drive comprises a hub housing which is pivot-mounted about an axis. The wheel hub drive further comprises a brushless electric motor arranged coaxially with regard to the axis and including a rotor and a stator, wherein the electric motor is provided for driving the hub housing. In case of such brushless electric motors, an alternating magnetic field is generated by means of stator coils. In contrast thereto, the rotor does not have any winding but one or a plurality of permanent magnets interacting with the alternating magnetic field of the stator in such a manner that the rotor starts rotating.

#Such electric wheel hub drives are known from the prior art and are used, for instance, as auxiliary drives for bicycles. Most diverse requirements are put on such wheel hub drives. Usually, the hub housing and the electric motor are coaxial with regard to each other, the motor and, where applicable, an interposed gear system being enclosed by the hub housing. Hence follows that, at first, there is only little space available for the motor and the gear system which means that the wheel hub drive has to deliver a relatively high power at a minor structural size. Beyond that, customers still are expecting that the torques of such wheel hub drives increase even more. Direct high-torque drives can be realized only if the electric motor is of relatively large size in the radial direction. To obtain a high torque with electric motors or wheel drive hubs that are small in the radial direction, planetary gear systems are used that are connected or posed between electric motor and hub housing. In case of high-performance drives, a relatively large amount of waste heat is usually produced. Such waste heat has to be dissipated outwards in order to prevent any damages of the motor or the interior of the wheel hub drive, in particular the gear system.

#An electric wheel hub drive of the kind as mentioned above is known, e.g. from EP 1 601 083 A1, EP 1 601 085 A1 and from EP 1 640 261 A1. All of said three documents disclose a wheel hub drive in which the electric motor and the gear system are enclosed by the hub housing. The rotor of the electric motor has been designed as an internal rotor and includes at its outer circumference a ring of permanent magnets arranged to one other in a row and being alternately oppositely poled. The alternating magnetic field is generated in the stator of the electric motor. To this end, the stator comprises hollow-cylindrical stacks of sheet by which the rotor is enclosed. A plurality of poles of said stacks of sheet is distributed in circumferential direction and wound up with stator windings to which power can alternately be applied. In EP 1 601 083 A1 it is referred to the problem of heat dissipation. According to said document, it is already known to provide a cooling liquid between a housing of the electric motor and the hub housing which may be favorable for dissipating heat from the stator of the electric motor. EP 1 601 083 A1 however states that such kind of cooling causes an increased effort, as the cooling liquid would, on the one hand, have to be introduced into the hub housing and, on the other hand, have to be safely encapsulated therein. Accordingly, EP 1 601 083 A1 suggests to arrange the stator at the side so that no motor housing has to be provided. Thus, the waste heat developing in the stator might be dissipated outwards more easily. In contrast thereto, EP 1 640 261 A1 suggests to provide the hub housing with an air pump for supplying environmental air through the hub housing for cooling the electric motor.

#In the following, one example of an embodiment of the present invention will be explained in detail with regard to the drawing.

#FIG. 1 is a longitudinal sectional view of an electric wheel hub drive 1 according to the invention.

#In the present example, the wheel hub drive 1 is an auxiliary bicycle drive. The wheel hub drive according to the invention substantially includes a pivot-mounted hub housing 3, a brushless electric motor for driving said hub housing, and a planetary gear system connected between said electric motor and said hub housing.

#The pivot-mounted wheel hub housing 3 is made of aluminum and consists of three parts, viz. a hollow-cylindrical hub housing center part 22, a left hub housing cover 21 and a right hub housing cover 20. Said right and said left hub housing covers 20 and 21 are bolted together with said hub housing center part 22 by means of screws 18. Owing to the multiple-part design of hub housing 3, the wheel hub drive according to the invention can be dismounted easily for service or maintenance or repair purposes. Hub housing center part 22 normally includes two hub flanks 23 to which the spokes 24 of the rear wheel are applied. Pivot-mounting of hub housing 3 is done via two ball bearings, viz. the right ball bearing 25 between said right hub housing cover 20 and said stationary axis 2 and the left bearing 26 between said left hub housing cover 21 and also said stationary axis 2. Axis 2 is a commonly used, hollow-cylindrical rear wheel axis which is connected to the rear bicycle fork 5 of which only the left branch is shown. Quick releases or fasteners for fastening axis 2 to rear wheel fork 5 are also not shown. Between the wheel hub drive and the right fork branch the drive sprocket for the chain drive and, if need be, a brake disk are also provided on the same axis.

#Hub housing 8 entirely encloses the electric motor and the planetary gear system. In the drawing, the electric motor is shown on the right side, the planetary gear system is shown axially following thereto on the left side of the drawing. Hub housing 8, electric motor and planetary gear system are concentrically arranged with regard to axis 2.