This invention relates to a drive unit for an electric vehicle, and to a method of using such a drive unit.

Electric vehicles are becoming increasingly popular. However, they have very tight demands for space, particularly given the size of the batteries needed to provide the desired speed, power and range. As such, reducing the size of any of the components of the drive train of such a vehicle is desirable.

According to a first aspect of the invention, we provide a drive unit for an electric vehicle, comprising:

• a first output and a second output;

• a housing;

• a motor in the housing having:

o a body;

o an output driven by the motor for rotation relative to the body; and o a bore through the body;

• a shaft passing through the bore such that the shaft is free to rotate in the bore relative to the body of the motor and the output of the motor, the shaft having a first end and a second end, the first output being formed in the first end of the shaft;

• a first epicyclic gear and a second epicyclic gear both in the housing and each having:

o a sun gear having a diameter;

o a plurality of planet gears;

o a planet carrier supporting the planet gears such that the planet gears each engage the sun gear; and

o an annular gear having an internal diameter and being arranged around the planet gears so as to engage each planet gear;

in which the first and second epicyclic gears connect the output of the motor and the first and second outputs so as to provide a differential between the first and second output and to transmit torque generated at the output of the motor to the first and second outputs and in which a ratio of the internal diameter of the annular gear to the diameter of the sun gear for the first and second epicyclic equals the Golden Ratio ( 1.618... ) ± 15%.

Thus, this provides a compact speed reduction drive unit that can also act as a differential between its two outputs.

The first output may be coupled to the first epicyclic gear, and the second output may be coupled to the second epicyclic gear, with the first and second epicyclic gears being coupled together. This is a way of achieving a reduction ratio with a differential function given the basic ratio for each of the epicyclic gears is the Golden ratio.

Typically, the output of the motor may be coupled to the sun gear of the first epicyclic gear. The first output may be coupled to the planet carrier of the first epicyclic gear. The annular gear of the first epicyclic gear may be coupled to the sun gear of the second epicyclic gear. The planet carrier of the second epicyclic gear may be fixed relative to the housing. The annular gear of second epicyclic gear may be coupled to the second output. Thus, this achieves the speed reduction differential function, whilst remaining compact.

There may be at least 5, 8 or 10 planet gears for each of the first and/or second epicyclic gears. Typically, the ratio for each of the first and second epicyclic gears measured between Annular to sun gear diameters will be the Golden Ratio ( 1.618... ), within 10%, 5%, 2% or 1 %. As such, the total ratio of the first and second epicyclic gears measured from the sun gear of the first epicyclic gear to the first and second output shafts will be 5.24 ± 15%, 10%, 5%, 2% or 1 %.

The output of the motor may be in the bore of the motor; as such, the output of the motor may be arranged to rotate relative to the shaft in the bore.

The unit may also comprise a torque vectoring motor for the first and/or second outputs. As such, each torque vectoring motor may be arranged to apply a torque between the housing and the output for which the torque vectoring motor is provided. As such, this allows for the torque generated by the unit to be preferentially directed to one or other of the first or second outputs. This can be useful in electric vehicles, for example for steering or stability control purposes.

Each torque vectoring motor may comprise:

• a reaction body;

• an output driven for rotational motion relative to the output; and

• a bore through the body.

Therefore, for a torque vectoring motor on the first output, the shaft or part of the first output may pass through the bore of the torque vectoring motor, and the output of the torque vectoring motor may act upon the shaft or the part of the first output. For the torque vectoring motor on the second output, part of the second output may pass through the bore of the torque vectoring motor, and the output of the torque vectoring motor may act upon the shaft or the part of the second output.

Each sun gear, planet gear and annular gear may comprise a helical gear, in that they are formed with helical teeth.

According to a second aspect of the invention, there is provided a method of using the drive unit of the first aspect of the invention to drive an electric vehicle, the method comprising the steps of generating torque using the motor and transmitting torque to a first wheel of the electric vehicle from the first output and a second wheel of the electric vehicle from the second output.

The method may also comprise selectively delivering torque between the first and second wheels by causing each torque vectoring motor to apply at torque to its respective output.

There now follows, by way of example only, description of an embodiment of the invention, described with reference to the accompanying drawings, in which:

Figure 1 shows a cross section through a drive unit for an electric vehicle in accordance with an embodiment of the invention; and Figure 2 shows a schematic view of the gear arrangement of the drive unit of Figure 1.

A drive unit 1 for using in driving the driven wheels of an electric vehicle is shown in the accompanying drawings. It is designed to have a peak power of 150 kilowatts and a peak torque of 2800Nm at the vehicle axle .

The drive unit 1 has first output 2 and second output 3. These are, in use, coupled to the driven wheels (typically via drive shafts) of the vehicle. The drive unit also comprises a hollow shaft motor 4. This motor 4 has a body 9 with a bore 5 through it, and a rotating output 6 within the bore 5. A shaft 7 passes through the bore 5 but is free to rotate within the bore independent of the output 6. A first end 8 of the shaft 7 forms the first output 2.

An epicyclic gear arrangement 10 is provided to couple the output 6 of the motor 4 to the first 2 and second 3 outputs of the drive unit 4. This comprises a first epicyclic gear 1 1 and a second epicyclic gear 12.

The first epicyclic gear 1 1 comprises:

• a sun gear 13 coupled to the output 6 of the motor;

• a plurality of planet gears 14 (typically up to 10) on a planet carrier 15, with the planet gears 14 each meshing with the sun gear 13, and the planet carrier 15 being coupled to the shaft (and so to the first output);

• an annular gear 16 which meshes with the planet gears 14.

The second epicyclic gear 12 comprises:

• a sun gear 17 coupled to the annular gear 16 of the first epicyclic gear 1 1 ;

• a plurality of planet gears 18 (typically 10) on a planet carrier 19, with the planet gears 18 each meshing with the sun gear 17, and the planet carrier 19 being fixed relative to a housing 20 of the drive unit 1 ;

• an annular gear 21 coupled to the second output 3.

The first 1 1 and second 12 epicyclic gears thus act to transmit the torque generated by the motor 4 to the first 2 and second 3 outputs, which also acting as a differential to accommodate for relative rotational motion between the first 2 and second 3 outputs. The first 11 and second 12 epicyclic gears are arranged so as to each have a ratio of the golden ratio - 1.618... - measured from diameter of annular gear to diameter of sun gear. This means that, overall, the first and second epicyclic gears have a ratio of 5.24. The various sun 13, 17, planet 14, 18 and annular 15, 21 gears are all helical, in that they have helical teeth.

The use of the hollow shaft motor 4 and the epicyclic gears 11, 12 both allow for a particularly compact low weight drive unit 1 which is useful in the confined spaces available in electric vehicles.

It is easy to add torque vectoring - that is directing the torque to one or other of the first 2 and second 3 outputs, by the use of torque vectoring motors on each output 2, 3. This can be seen in Figure 2, but is not shown in Figure 1. In this particular embodiment, a hollow shaft reaction motor 21, 22 is placed around each of the first 2 and second 3 outputs, and acts directly on the outputs to add or subtract torque therefrom. Combined with the differential nature of the drive unit 1, this allows torque to be selectively applied to either output 2, 3.