FIELD OF THE INVENTION

The present invention relates to a power unit for a pedal vehicle and more particularly to a power unit according to preamble of claim 1. The present invention further relates to a method for operating a power unit and more particularly to a method according preamble of claim 17.

BACKGROUND OF THE INVENTION

In the prior art, it is known that utilize two separate motors in an electrical pedal vehicle. The motor unit of a pedal vehicle comprises a pedal shaft, chainwheel arranged to transfer torque to a vehicle wheel and a main epicyclic gear set arranged to control transmission ratio between the pedal shaft and the chainwheel. The power unit comprises an assist motor connected to an assist gear of the main epicyclic gear set and arranged to transmit torque to the assist gear. The power unit further comprises a control motor connected to a control gear of the main epicyclic gear set and arranged to transfer torque to the control gear. Accordingly, the assist motor is arranged to provide assist power to the pedal shaft or output shaft via the epicyclic gear set for the user for assisting the user during pedalling. On the other hand, the control motor is arranged to change the transmission ratio of the motor unit and between the pedal shaft and the chainwheel.

The control motor comprises a rotor connected to the control gear of the epicyclic gear set. The rotation of the rotor is transmitted to the control gear. Therefore, rotation speed of the rotor of the motor is arranged to control the rotation speed of the control gear of the epicyclic gear set in a first and second rotation direction and thus the transmission ratio between the pedal shaft and the chainwheel. This construction with the, control motor and the epicylic gear set provides a continuously variable transmission.

In the above mentioned, construction, the control motor needs to be able to control all the torque driven through the power unit. Therefore, the control motor needs to be able to control all the torque the rider is producing on the pedal shaft. By nature, humans are able to generate very high torques although total power is very limited which is contrary to nature of electric motors which can produce very high power but torque can be very limited. This possesses a new issue in the electric bike power unit equipped with a continuously variable transmission. In certain situations, where the control motor is not able to control the torque driven through the power unit. In these situations, the transmission ratio cannot be kept at a target level which in practice means that the transmission starts to slip. This behaviour is unwanted during pedalling or cycling and feels uncomfortable to the user. High torques are often driven through the power unit when speed of the pedal vehicle is slow, for example when the user is stomping on the pedals.

In the prior art, the slipping behaviour is avoided by adding a freewheel or the like one-way clutch to the power unit by implementing between the control motor and output shaft. The freewheel prevents the output shaft from rotating slower than the input shaft.

However, with this prior art solution one major benefit of continuously variable transmission is revoked. By nature, the electric motors can be rotated to either direction with equal torque and power output. When incorporating a mechanical freewheel to the construction, the control motor can only be rotated to one direction essentially removing 50% of the usable RPM (revolutions per minute) range.

BRIEF DESCRIPTION OF THE INVENTION

An object of the present invention is to provide a power unit and method so as to overcome or at least alleviate the prior art disadvantages.

The objects of the invention are achieved by a power unit which is characterized by what is stated in independent claim 1. The objects of the present invention are also achieved with a method which is characterized by what is stated in independent claim 17.

The preferred embodiments of the invention are disclosed in the dependent claims. The invention is based on the idea of providing a power unit for pedal vehicle. The power unit comprises a pedal shaft, an output shaft arranged to transfer torque to a vehicle wheel and a main epicyclic gear set arranged to control transmission ratio between the pedal shaft and the output shaft. The power unit further comprises a control assembly arranged to adjust the transmission ratio of the main epicyclic gear set, the control assembly comprising a control motor and a control gear of the main epicylic gear set. The control motor is connected to the control gear of the main epicyclic gear set.

According to the present invention the control assembly of the power unit further comprises a non-backdrivable gear mechanism arranged between the control motor and the control gear. The non-backdrivable gear mechanism is arranged to transmit rotation from the control motor to the control gear and to prevent transmission of rotation from the control gear to the control motor.

The non-backdrivable gear mechanism is further arranged to be rotated from the side of the control motor and arranged such that rotation of the non- backdrivable gear mechanism from the side of the control gear is prevented.

Accordingly, the non-backdrivable gear mechanism is arranged to transmit rotation in a first and second rotation direction from control motor to the control gear and arranged to prevent transmission of rotation from the control gear to the control motor.

Further, the non-backdrivable gear mechanism is arranged to transmit rotation in a first and second rotation direction from control motor to the control gear and arranged to prevent rotation of the control gear when the control motor is not rotated.

The output shaft may be a chainwheel, pulley for belt drive or cardan shaft. The output shaft is arranged to transmit the torque to the wheel of the pedal vehicle.

In one embodiment, the main epicyclic gear set comprises a sun gear, a ring gear, plurality of planet gears between the sun gear and the ring gear and a planet carrier connected to the planet gears.

In one embodiment, the power unit comprises an arrangement in which the pedal shaft is connected to the sun gear, the planet carrier is connected to the output shaft, and the control motor is connected to the ring gear. The ring gear forms the control gear of the control assembly. The assist motor is connected to the sun gear or to the planet carrier.

In another embodiment, the pedal shaft is connected to the planet carrier, sun gear is connected to the output shaft, and the control motor is connected to the ring gear. The ring gear forms the control gear of the control assembly. The assist motor is connected to the planet carrier or the sun gear.

In a further embodiment, the pedal shaft is connected to the ring gear, the planet carrier is connected to the output shaft, and the control motor is connected to the sun gear. The sun gear forms the control gear of the control assembly. The assist motor is connected to the ring gear or to the planet carrier.

In a yet further embodiment, pedal shaft is connected to the planet carrier, the ring gear is connected to the output shaft, and the control motor is connected to the sun gear. The sun gear forms the control gear of the control assembly. The assist motor is connected to the planet carrier or to the ring gear.

As should be noted from above, the epicyclic gear set may be configured in different manners in relation to the pedal shaft and the output shaft. Further, the control motor and assist motor may be configured in alternative ways in relation to the main epicyclic gear set.

In one embodiment, the non-backdrivable gear mechanism comprises a first operating state in which the non-backdrivable gear mechanism is arranged to transmit rotation of the control motor from the control motor to the control gear, and a second operating state in which the control motor is kept in place and rotation of the non-backdrivable gear mechanism is prevented such that the control gear is kept in place.

The first and second operating state may be provided with any of the above configurations. Further, the first and second operating state may be provided with the non-backdrivable gear mechanism in the control gear or between the control motor and the control gear.

In one embodiment, the non-backdrivable gear mechanism comprises gear pair arranged to transmit rotation from the control motor to the control gear and to prevent transmission of the rotation from the control gear to the control motor.

In one embodiment, the gear pair of the non-backdrivable gear mechanism comprise a first gear and a second gear connected to each other, the first gear being connected to the control motor and the second gear being connected to the control gear.

Accordingly, in one embodiment the non-backdrivable gear mechanism comprises: a worm gear mechanism, a cycloidal gear mechanism, or a strain wave gear mechanism, or a high ratio spiroid gear mechanism, or a compound planetary gear mechanism or any other type of non-bakcdrivable gear mechanism.

In another embodiment, the non-backdrivable gear mechanism comprises a gear pair having a first and second parallel axis gears.

In some embodiments, the first gear is a pinion gear and the second gear is a drive gear, in known manner.

In one embodiment, the non-backdrivable gear mechanism is arranged to form a first reduction gear set between the control motor and the control gear.

The non-backdrvable gear mechanism is commonly known arrangement in which the input shaft can rotate the output shaft but the output shaft cannot rotate the input shaft. This means that if the input shaft is not rotating the output shaft is locked in place. Additionally, the non-drivable gear mechanism can function as a reduction gear set in which high-speed low-torque input shaft rotates low-speed high-torque output shaft.

In some embodiments, the power unit further comprises an assist motor connected to an assist gear of the main epicyclic gear set and arranged to transmit torque to the output shaft.

In one above mentioned embodiment, the arrangement of the power unit further comprises that the assist motor is connected to the sun gear or to the planet carrier.

In another above mentioned embodiment, the arrangement of the power unit further comprises that the assist motor is connected to the planet carrier or the sun gear.

In a further above mentioned embodiment, the arrangement of the power unit further comprises that the assist motor is connected to the ring gear or to the planet carrier.

In a yet further above mentioned embodiment, the arrangement of the power unit further comprises that the assist motor is connected to the planet carrier or to the ring gear.

In one embodiment, the pedal shaft is connected to the sun gear, the output shaft is connected to the planet carrier, control motor is connected to the ring gear, the non-backdrivable gear mechanism is arranged between control motor and the ring gear. The control motor, the non-backdrivable gear mechanism and the ring gear form the control assembly.

In another embodiment, the pedal shaft is connected to the sun gear, the output shaft is connected to the planet carrier, the control motor is connected to the ring gear, the assist motor is connected to the sun gear, the non-backdrivable gear mechanism is arranged between control motor and the ring gear, the control motor, the non-backdrivable gear mechanism and the ring gear form the control assembly.

In a further embodiment, the pedal shaft is connected to the sun gear, the output shaft is connected to the planet carrier the control motor is connected to the ring gear, the assist motor is connected to the planet carrier, the non- backdrivable gear mechanism is arranged between control motor and the ring gear. The control motor, the non-backdrivable gear mechanism and the ring gear form the control assembly.

The power unit is arranged in connection with the pedal shaft of the pedal vehicle. The power unit comprises a housing accommodating the main epicyclic gear set, the assist motor and the control motor. The housing comprises a hub arranged around the pedal shaft and an arm extending from the hub. In the above disclosed embodiments, the assist motor is arranged in the hub and the control motor is arranged in the arm.

The power unit is arranged in connection with the pedal shaft of the pedal vehicle. The power unit comprises a housing accommodating the main epicyclic gear set and the control motor. The housing comprises a hub arranged around the pedal shaft and an arm extending from the hub. In the above disclosed embodiments, the control motor is arranged in the arm.

In one embodiment of the power unit, the pedal shaft is connected to the planet carrier, the output shaft is connected to the ring gear, the control motor is connected to the sun gear, the non-backdrivable gear mechanism is arranged between control motor and the sun gear. The control motor, the non-backdrivable gear mechanism and the sun gear form the control assembly.

In an alternative embodiment, the pedal shaft is connected to the planet carrier, the output shaft is connected to the ring gear, the control motor is connected to the sun gear, the non-backdrivable gear mechanism is arranged between control motor and the sun gear, the assist motor is connected to the ring gear. The control motor, the non-backdrivable gear mechanism and the sun gear form the control assembly.

In one embodiment, the power unit comprises a housing accommodating the main epicyclic gear set, the control motor and the assist motor, the housing comprising a hub arranged around the pedal shaft and an arm extending from the hub, and that the control motor is arranged in the hub and the assist motor is arranged in the arm.

In another embodiment, the power unit comprises a housing accommodating the main epicyclic gear set and the control motor, the housing comprising a hub arranged around the pedal shaft, and that the control motor is arranged in the hub.

In one embodiment, the power unit further comprises at least one second reduction gear set between assist motor and the main epicyclic gear set or between the assist motor and the assist gear.

The present invention further relates to a method for operating a power unit of pedal vehicle having a pedal shaft and an output shaft for transferring torque to a vehicle wheel. The method comprises controlling transmission ratio between the pedal shaft and the output shaft with a main epicyclic gear set, transmitting torque to an assist gear of the main epicyclic gear set with an assist motor for transmitting torque to an output shaft of the pedal vehicle, and adjusting the transmission ratio of the main epicyclic gear set with a control motor by transmitting torque to a control gear of the epicyclic gear set. The control motor and the control gear forming a control assembly of the power unit.

According to the present invention, the control assembly further comprises a non-backdrivable gear mechanism arranged between the control motor and the control gear. Further, the method comprises operating the power unit in a first operating mode in which the non-backdrivable gear mechanism transmits rotation from the control motor to the control gear such that the control motor is operable adjusting the transmission ratio of the main epicyclic gear set, and operating the power unit in a second operating mode in which control motor is kept in place and the non-backdrivable gear mechanism prevents transmission of rotation from the control gear to the control motor such that rotation of the control gear is prevented.

In one embodiment, in the second operating mode adjusting the transmission ratio of the main epicyclic gear set is prevented with the non- backdrivable gear mechanism.

Further, in one embodiment, in the second operating mode adjusting the transmission ratio of the main epicyclic gear set is prevented with the non- backdrivable gear mechanism as disclosed above.

In some embodiments, the main epicyclic gear set comprises a sun gear, a ring gear, plurality of planet gears between the sun gear and the ring gear and a planet carrier connected to the planet gears and arranged to receive rotation of a crankshaft.

In one embodiment, the method comprises transmitting power from the control motor to the ring gear of the main epicyclic gear set in the first operating mode.

In another embodiment, the method comprises transmitting power from the control motor to the sun gear of the main epicyclic gear set in the first operating mode. Further, the power unit may comprises an assist motor connected to an assist gear of the main epicyclic gear set.

In one embodiment, the method comprises transmitting power to the assist gear of the main epicyclic gear set with the assist motor for transmitting power to an output shaft of the pedal vehicle.

In another embodiment, the method comprises transmitting power from an assist motor to the sun gear of the main epicyclic gear set.

In a further embodiment, the method comprises transmitting power from an assist motor to the ring gear of the main epicyclic gear set.

In a yet further embodiment, the method comprises transmitting power from an assist motor to the planet carrier of the main epicyclic gear set.

Torque from the control motor to the control gear of the main epicyclic gear set may be transmitted in the first and second operating modes.

One advantage of the non-backdrivable gear mechanism is that fewer mechanical parts are required for achieving the same functionality to the power unit. This will reduce the cost, weight and assembly time of the power unit.

Furthermore, the non-backdrivable gear mechanism allows the utilizing full RPM range of the control motor. Accordingly, the control motor can be used and rotated in both directions. This doubles the usable gear range of the power unit and allows to optimize the design of the control motor. Space in the power unit is limited and weight is an important factor in any pedal vehicle components, it is essential to keep the size of the electric motor as small as possible. When less focus is needed for enabling that the control motor can achieve sufficient RPM range, control motor may be designed for higher torque. In other words, the same size electric motor can provide more torque or a smaller electric motor can be used to achieve the requirements.

A further advantage is achieved for situations when the power unit is operated in fully mechanical mode. For example, when speed of the pedal vehicle is low and torque on the pedal shaft is high, the power unit may be configured to operate in fully mechanical mode, for example in speed say 15 km/h, which would allow to use of the pedal vehicle comfortably, even without electric power available, as a single speed pedal vehicle. In this case, smaller transmission ratios can be achieved by rotating the control motor to the second rotation direction, which in the case of a freewheel is not possible.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in detail by means of specific embodiments with reference to the enclosed drawings, in which

Figure 1A shows schematically one embodiment of power unit of the pedal vehicle;

Figure IB shows schematically one embodiment of power unit of the pedal vehicle in connection with a transmission system of a pedal vehicle;

Figure 2 shows schematically one embodiment of an epicyclic gear set;

Figure 3 shows schematically one embodiment of power unit of the pedal vehicle;

Figure 4 shows one schematic diagram of the power unit of figure 3;

Figure 5 shows schematically another embodiment of power unit of the pedal vehicle; and

Figure 6 shows one schematic diagram of the power unit of figure 5.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1A shows schematically a power unit 2 for a pedal vehicle. The power unit 2 comprises a housing 4. The power unit 2 further comprises hub 6 or hub part to be arranged around a pedal shaft 10 of the pedal vehicle. The power unit 2 also comprises an arm 8 or arm part extending from the hub 6. The housing 4 forms both the hub 6 and the arm 8, and encloses the components of the power unit 2. The power unit 2 comprises a hub motor 20 arranged to the hub 6 and in connection with the pedal shaft 10 inside the housing 4. The power unit also comprises an arm motor 30 arranged to the arm 8 and inside the housing 4.

The housing 4 represents also body of the power unit 2.

The power unit 2 comprises two motors, a control motor arranged to adjust transmission ratio of the power unit 2 and an assist motor arranged to assist pedalling of the pedal vehicle. The control motor may be a hub motor or an arm motor, and the assist motor may be an arm motor or a hub motor, respectively, depending on the embodiment.

Figure IB shows schematically transmission system of a pedal vehicle. The transmission system comprises the pedal shaft 10 to which pedal cranks 12 are connected. At the distal end of the pedal crank 12 there is a pedal 13 for pedalling the pedal vehicle. There is further a chainwheel 17 operatively connected to the output shaft for transmitting torque from the pedal shaft 10 via the chainwheel 17 with a chain 16 to a rear wheel sprocket 18 arranged to the rear wheel of the pedal vehicle. The power unit 2 is arranged to or in connection with the pedal shaft 10.

The chainwheel 17 forms an output shaft of the transmission system.

Figure 2 shows schematically an epicyclic gear set 40. The main epicyclic gear set comprises a sun gear 48, a ring gear 42, plurality of planet gears 44 between the sun gear 48 and the ring gear 42 and a planet carrier 46 connected to the planet gears 44. The basic operating principle of the epicyclic gear set or planetary gear set is commonly known and it is not described in detail in this application.

Figure 3 shows one embodiment of the power unit 2 according to the present invention. In this embodiment, the assist motor 21 is provided as a hub motor and arranged in connection with the pedal shaft 10 or around the pedal shaft 10. The assist motor 21 is arranged inside the housing 4 and to the hub 6 of the housing 4. The control motor 31 is provided as an arm motor. The control motor is arranged inside the housing 4 and to the arm 8 of the housing 4.

Figure 4 shows schematically a diagram of one power unit 2 according to the figure 3. The power unit 2 comprises main epicyclic gear set 40 arranged to control transmission ratio between the pedal shaft 10 and the chainwheel 17. The power unit 2 further comprises the assist motor 21 connected to an assist gear of the main epicyclic gear set 40 and arranged to transmit torque to the chainwheel 17. The assist motor 21 is provided as the hub motor. The power 2 unit also comprises the control motor 31 connected to a control gear of the main epicyclic gear set 40 and arranged to adjust the transmission ratio of the main epicyclic gear set 40. The transmission ratio is adjusted between the pedal shaft 10 and the chainwheel 17 with the epicyclic gear set 40. The control motor 31 and the control gear form a control assembly of the power unit 2.

The epicyclic gear set is provided between the pedal shaft 10 and the chainwheel 17 for adjusting the transmission ratio.

As shown in figure 4, the sun gear 48 of the epicyclic gear set 40 is connected to the pedal shaft 10. The assist motor 21 is also connected to the sun gear 48. Further, the control motor 31 is connected to the ring gear 42 of the epicyclic gear set 40. Thus, the ring gear 42 is the control gear in this embodiment. The carrier 46 is connected to the chainwheel 17.

As shown in figure 4, a non-backdrivable gear mechanism 100 is provided between the control motor 31 and the ring gear 42.

The non-backdrivable gear mechanism 100 is arranged to transmit rotation from the control motor 31 to the ring gear 42 and to prevent rotation of the ring gear 42 when the control motor 31 is not rotated, meaning is kept in place. The non-backdrivable gear mechanism 100 is further arranged to be rotated from the side of the control motor 31 and arranged such that rotation of the non- backdrivable gear mechanism from the side of the ring gear 42 is prevented. This means that the non-backdrivable gear mechanism is arranged to transmit torque from the control motor 31 to the ring gear 42 in a first and second rotation direction of the control motor 31 and prevent torque transmission from the ring gear 42 to the control motor 31. Further, the non-backdrivable gear mechanism 100 locks the ring gear 42 in place when the control motor 31 is not rotated.

In the embodiment of figure 4, the non-backdrivable gear mechanism 100 may be a worm gear provided between the control motor 31 and the ring gear 42.

Alternatively, the non-backdrivable gear mechanism 100 may be a cycloidal gear mechanism, or a strain wave gear mechanism, or a high ratio spiroid gear mechanism, or a compound planetary gear mechanism or any other type of non-bakcdrivable gear mechanism.

For example, in figure 2 arrow 43 denotes rotation direction of the ring gear 42, arrow 45 rotation direction of the plant gears 44, arrow 47 rotation direction of planet carrier 46 and arrow 49 rotation direction of the sun gear 48. The rotation direction of each gear may vary depending on the configuration of the drive unit.

In the embodiment of figure 4, the control motor 31 provides torque to the ring gear 42 in the first and second rotation direction of the ring gear 42 for adjusting the transmission ratio of the epicyclic gear set 40. The assist motor 21 provide torque to the sun gear 48 which is connected to the pedal shaft 10. Thus, the assist motor provides assist power or torque further to the chainwheel 17 via the planetary gears 44 and the planet carrier 46.

The embodiment of figure 4 could be modified by connecting the assist motor 21 to the planet carrier 46 instead of sun gear 48.

The non-backdrivable gear mechanism 100 may be a worm gear 100 arranged to transmit torque of a rotor of the control motor 31 from the control motor 31 to the ring gear 42. Further, the non-backdrivable gear mechanism 100 is arranged to prevent rotation of the ring gear 42 when the rotor of the control motor 31 is kept in place and not rotated.

Accordingly, in the first operating mode of the power unit 2 and in the first operating state of the non-backdrivable gear mechanism 100, the non- backdrivable gear mechanism 100 is arranged to transmit rotation or torque from the control motor 31 to the ring gear 42. Similarly, in the second operating mode of the power unit 2 and in the second operating state of the non-backdrivable gear mechanism 100, non-backdrivable gear mechanism 100 prevents rotation of the ring gear 42 and torque transmission from the ring gear 42 to the control motor 31.

Figure 5 shows another embodiment of the power unit 2 according to the present invention. In this embodiment, the control motor 32 is provided as a hub motor and arranged in connection with the pedal shaft 10 or around the pedal shaft 10. The control motor 32 is arranged inside the housing 4 and to the hub 6 of the housing 4. The assist motor 22 is provided as an arm motor. The assist motor 22 is arranged inside the housing 4 and to the arm 8 of the housing 4.

Figure 6 shows schematically a diagram of one power unit 2 according to the figure 5. The power unit 2 comprises the main epicyclic gear set 40 arranged to control transmission ratio between the pedal shaft 10 and the chainwheel 17. The power unit 2 further comprises the assist motor 22 connected to an assist gear of the main epicyclic gear set 40 and arranged to transmit torque to the chainwheel 17. The assist motor 22 is provided as the arm motor.

The power 2 unit also comprises the control motor 32 connected to a control gear of the main epicyclic gear set 40 and arranged to adjust the transmission ratio of the main epicyclic gear set 40. The transmission ratio is adjusted between the pedal shaft 10 and the chainwheel 17 with the epicyclic gear set 40.

The epicyclic gear set 40 is provided between the pedal shaft 10 and the chainwheel 17 for adjusting the transmission ratio.

As shown in figure 6, the planet carrier 46 of the epicyclic gear set 40 is connected to the pedal shaft 10. The assist motor 22 is also connected to the ring gear 42. Further, the control motor 32 is connected to the sun gear 48 of the epicyclic gear set 40. Thus, the sun gear 48 is the control gear in this embodiment. The ring gear 42 is connected to the chainwheel 17. Thus, the assist motor 22 is connected to the chainwheel 17.

This configuration is preferable, as the torque provided by the assist motor 22 is not transmitted to or has no effect on the control motor 32.

As shown in figure 6, a non-backdrivable gear mechanism 100 is provided between the control motor 32 and the sun gear 48. The control motor 32, the non-backdrivable gear mechanism and the sun gear 48 form a control assembly of the power unit 2.

The non-backdrivable gear mechanism 100 is arranged to transmit rotation from the control motor 32 to the sun gear 48 and to prevent transmission of rotation from the sun gear 48 to the control motor 32. The non-backdrivable gear mechanism 100 is further arranged to be rotated from the side of the control motor 32 and arranged such that rotation of the non-backdrivable gear mechanism from the side of the sun gear 48 is prevented. This means that the non-backdrivable gear mechanism is arranged to transmit torque from the control motor 32 to the sun gear 48 in a first and second rotation direction of the control motor 32 and prevent torque transmission from the sun gear 48 to the control motor 32. Further, the non-backdrivable gear mechanism 100 locks the sun gear 48 in place when the control motor 32 is not rotated.

In the embodiment of figure 6, the non-backdrivable gear mechanism 100 may be a worm gear provided between the control motor 31 and the sun gear 48.

Accordingly, the non-backdrivable gear mechanism 100 may be a worm gear 100 arranged to transmit torque of a rotor of the control motor 32 from the control motor 32 to the sun gear 48. Further, the non-backdrivable gear mechanism 100 is arranged to prevent rotation of the sun gear 48 when the rotor of the control motor 32 is kept in place and not rotated.

Alternatively, the non-backdrivable gear mechanism 100 may be a cycloidal gear mechanism, or a strain wave gear mechanism, or a high ratio spiroid gear mechanism, or a compound planetary gear mechanism or any other type of non-bakcdrivable gear mechanism.

Accordingly, in a first operating mode of the power unit 2 and in a first operating state of the non-backdrivable gear mechanism 100, the non- backdrivable gear mechanism 100 is arranged to transmit rotation or torque from the control motor 32 to the sun gear 48. Similarly, in a second operating mode of the power unit 2 and in a second operating state of the non-backdrivable gear mechanism 100, the non-backdrivable gear mechanism 100 prevents rotation of the sun gear 48 and torque transmission from the sun gear 48 to the control motor 32.

In the embodiment of figure 6, the one-way clutch 100 may be a worm gear provided between the control motor 32 and the sun gear 48.

In the embodiment of figure 6, the control motor 32 provides torque to the sun gear 48 via the non-backdrivable gear mechanism for adjusting the transmission ratio of the epicyclic gear set 40. The assist motor 22 provides torque to the ring gear 42 which is connected to the chain wheel 17. Thus, the assist motor 22 provides assist power or torque to the chainwheel 17 via the ring gear 42. This is preferable configuration as the ring gear 42 has the largest diameter in the epicyclic gear set 40 and thus the assist torque of the assist motor 22 is high.

The non-backdrivable gear mechanism 100 is provided as reduction gear set between the control motor 31, 32 and the control gear 42, 48. The reduction gear set functions such that the high-speed low-torque input shaft, the control motor 31, 32, rotates low-speed high-torque shaft, the control gear 42, 48.

Accordingly, in the embodiment of figures 3 and 4, the non- backdrivable gear mechanism 100 is provided as reduction gear set between the control motor 31 and the ring gear 42.

Further, in the embodiment of figures 5 and 6, the non-backdrivable gear mechanism 100 is provided as reduction gear set between the control motor 32 and the sun gear 48.

It should be noted that in all embodiments non-backdravable gear mechanism may be any type of non-bakcdrivable gear mechanism arranged to transmit rotation from the control motor 31, 32 to the control gear and to prevent transmission of rotation from the control gear to the control motor 31, 32.

The present invention further provides a method for operating a power unit 2 of the pedal vehicle. The method is utilized by the power unit as disclosed above.

It should be noted that the power unit 2, the pedal shaft 10 and the chainwheel 17 together provide a transmission arrangement of the pedal vehicle. This concerns all the embodiments of the invention.

The method comprises controlling transmission ratio between the pedal shaft 10 and the chainwheel 17 with the main epicyclic gear set 40, transmitting torque to the assist gear 48, 42 of the main epicyclic gear set 40 with the assist motor 21, 22 for transmitting torque to the chainwheel 17 of the pedal vehicle, and adjusting the transmission ratio of the main epicyclic gear set 40 with a control motor 31, 32 by transmitting torque to a control gear 42, 48 of the epicyclic gear set 40. The control motor 31, 32 and the control gear 42, 48 form the control assembly of the power unit.

The method comprises operating the power unit 2 operating the power unit 2 in a first operating mode in which first operating mode the non-backdrivable gear mechanism 100 transmits rotation from the control motor 31, 32 to the control gear 42, 48 such that the control motor 31, 32 is operable adjusting the transmission ratio of the main epicyclic gear set 40. The method further comprises operating the power unit 2 in a second operating mode in which control motor is kept in place and the non-backdrivable gear mechanism 100 prevents transmission of rotation from the control gear 42, 48 to the control motor 31, 32 such that rotation of the control gear 42, 48 is prevented.

According to the method, in the second operating mode adjusting the transmission ratio of the main epicyclic gear set 40 is prevented with the non- backdrivable gear mechanism 100.

Further, in the second operating mode adjusting the transmission ratio of the main epicyclic gear set 40 is prevented with the non-backdrivable gear mechanism 100 according to any one claims 1 to 16.

In a preferred embodiment, the method comprises operating the power unit 2 in the second operating mode when the transmission ratio is at a predetermined boundary value or less.

In the embodiment of figures 3 and 4, the method comprises transmitting power from the control motor 31 to the ring gear 42 of the main epicyclic gear set 40 in the first operating mode.

In the embodiment of figures 5 and 6, the method comprises transmitting power from the control motor 32 to the sun gear 48 of the main epicyclic gear set 40 in the first operating mode.

The method may also comprise transmitting power to an assist gear 48, 42 of the main epicyclic gear set 40 with an assist motor 21, 22 for transmitting power to an output shaft 17 of the pedal vehicle; or

In the embodiment of figures 3 and 4, the method comprises transmitting power from an assist motor 21 to the sun gear 48 of the main epicyclic gear set 40, or transmitting power from an assist motor 21 to the planet carrier 46 of the main epicyclic gear set 40.

In the embodiment of figures 5 and 6, the method comprises transmitting power from an assist motor 22 to the ring gear 42 of the main epicyclic gear set 40.

The invention has been described above with reference to the examples shown in the figures. However, the invention is in no way restricted to the above examples but may vary within the scope of the claims.