NL2019030B1

NL2019030B1 - A human-powered vehicle

Info

Publication number: NL2019030B1
Application number: NL2019030A
Authority: NL
Inventors: Joannes Jozef Van Stekelenburg Alexander
Original assignee: Joannes Jozef Van Stekelenburg Alexander
Priority date: 2017-06-08
Filing date: 2017-06-08
Publication date: 2018-12-17

Abstract

This invention relates to a human-powered vehicle comprising: - a frame; - a front and rear wheel; - a primary chain-drive for driving the rear wheel; - a first crankset and foot pedals for driving the primary chain-drive; - a secondary chain-drive for driving the rear wheel; and - a driving and steering assembly for driving the secondary chain-drive by hand and simultaneously steering; wherein the secondary chain-drive comprises: o a first gear arranged on the frame; o a second gear arranged on the driving and steering assembly; o an endless chain arranged around the first and second gears thereby defining an upper chain portion and a lower chain portion; o a first and third guiding element arranged on the frame; and o a second and fourth guiding element arranged on the driving and steering assembly; wherein the first and second guiding element are configured to guide a part of the upper chain portion and the third and fourth guiding elements are configured to guide a part of the lower chain portion, both in a direction parallel to and close to a vertical axis of the front wheel, and wherein the driving and steering assembly comprises: o a driving axle connected to the second gear; and o a second crankset in order to drive rotation of the driving axle and in order to steer the vehicle.

Description

TITLE OF THE INVENTION A human-powered vehicle

BACKGROUND OF THE INVENTION

The invention relates to a human-powered vehicle, in particular a human-powered vehicle which is drivable by using both feet and hands. A human-powered vehicle usually comprises a frame, a front wheel and at least one rear wheel. The front wheel is rotatable about a horizontal axis for riding and pivotable about a substantially vertical axis for steering. The at least one rear wheel is rotatable relative to the frame about a horizontal rotation axis for riding only.

Traditionally, the front wheel is connected to a steer that is operable by the hands of a user, and the rear wheel is driven by the feet, usually using a chain-drive arranged between the frame and the at least one rear wheel.

When the hands are also used to drive the vehicle, the hands/arms have to perform two functions at the same time. The hands have to steer the front wheel about a substantially vertical axis, and the vehicle has to be driven by hand such that the front wheel and rear wheel rotate about their respective horizontal rotation axes, wherein preferably the driving operation is not interfering with the steering operation.

One way to cope with this problem is to use the feet to drive the rear wheel and the hands to drive the front wheel. As the entire driving mechanism for the front wheel will rotate along with the front wheel during steering, the two operations do not interfere with each other, see for examples US2011/018220 and US5908199A. There are even solutions proposed in which the steering function of the hands is taken over by the body of the user, e.g. the head or upper body of a user as is shown in DE102009019138 and US2007/145708A1. A disadvantage of separately driving the front and rear wheel is that the trajectories of the front wheel and the rear wheel do not necessarily have to be equal, so that asynchronous driving of the front and rear wheel is the result.

In DE19606772A1, DE10317206A1 and DE102008054168A1 (extendable) bars and respective hinges are provided between either the steer and the chain-drive or between the steer and the front wheel in order to couple the steering function to the driving function. However, this results in large, complex and fragile structures that have to withstand relatively large forces. In particular in DE102008054168 this also results in a non-traditional way of steering as the steer is pivoted about a horizontal pivot axis in order to pivot the front wheel about a substantially vertical pivot axis.

In WO2011/034289A1, a human-powered vehicle is shown in which a steer and handle bar are provided that implement both the steering function and the driving function and provides power to the rear wheels. The vehicle is equipped with bevel gears to transfer the driving rotation of the steer about a horizontal axis to a shaft having a rotation axis parallel with the pivot axis of the steering column, so that a steering pivotal motion will not interfere with the driving rotation. Other bevel gears are provided to transfer the rotation of said shaft to the rear wheels eventually. A disadvantage of the bevel gears is that steering of the front wheel results in asynchronous driving of the rear wheel due to the steering rotation. Another disadvantage of the bevel gears is that a set of bevel gears extends significantly in three directions and thus needs to be designed small in order to reduce the amount of space required and to reduce the weight.

BRIEF SUMMARY OF THE INVENTION

It is an object of the invention to provide an improved human-powered vehicle which is driven by hand and by feet using both a chain-drive for the feet drive and a chain-drive for the hand drive while, at the same time, the hands are able to steer the vehicle.

This object is achieved by a human-powered vehicle according to claim 1, comprising: a frame; a front wheel which is pivotably mounted to the frame about a substantially vertical axis for steering; at least one rear wheel; a primary chain-drive extending between the frame and the at least one rear wheel for driving the at least one rear wheel; a first crankset and respective foot pedals for driving the primary chain-drive by foot; a secondary chain-drive for driving the at least one rear wheel by hand; and a driving and steering assembly attached to the front wheel for driving the secondary chain-drive by hand and simultaneously steering the vehicle via the front wheel; wherein the secondary chain-drive comprises: o a first gear arranged on the frame; o a second gear arranged on the driving and steering assembly; o an endless chain arranged around the first and second gears thereby defining an upper chain portion and a lower chain portion extending between the first and second gears; o a first guiding element and a third guiding element arranged on the frame; and o a second guiding element and a fourth guiding element arranged on the driving and steering assembly; wherein the first and second guiding element are configured to guide a part of the upper chain portion in a direction parallel to and close to the substantially vertical axis of the front wheel, wherein the third and fourth guiding elements are configured to guide a part of the lower chain portion in a direction parallel to and close to the substantially vertical axis of the front wheel, and wherein the driving and steering assembly comprises: o a driving axle connected to the second gear of the secondary chain-drive; and o a second crankset arranged on the driving axle in order to drive rotation of the driving axle about a longitudinal axis of the driving axle by hand and in order to steer the vehicle.

An advantage of a vehicle according to the invention is that both a part of the upper chain portion and a part of the lower chain portion are guided to extend in a direction parallel and close to the substantially vertical axis of the front wheel so that these parts are able to deform upon steering of the front wheel without interfering with the driving function as the deformation is substantially limited to a predetermined twist of the respective parts about their respective longitudinal axis. Hence, the driving axle can be positioned in different angular positions for steering the vehicle, while still being able to, at the same time, transmit a continuous rotational movement of the driving axle about the longitudinal axis of the driving axle to the secondary chain-drive. Another advantage of the invention may be that the construction and design can be compact and rigid, so that the driving and steering assembly does not occupy too much space and is able to withstand and transmit the relatively large driving forces in combination with the steering forces. A continuous rotation allows for a movement of the arms/hands which is synchronizable with the movement of the legs/feet, and which is more fluently. The ability to synchronize the movement of the arms/hands with the movement of the legs/feet further allows to closely mimic the forward motion of a tetrapod.

In an embodiment, the fourth guiding element is moveably arranged on the driving and steering assembly, wherein the driving and steering assembly comprises a resilient element acting on the fourth guiding element to tension the endless chain of the secondary chain-drive. The resilient element is preferably a spring. A main advantage of the movability of the fourth guiding element in combination with the resilient element is that any loads in longitudinal direction of the chain due to steering can be taken up by the resilient element without causing undesired deformation of the chain in the longitudinal direction thereof. Preferably, the fourth guiding element is moveable in a direction substantially parallel to the substantially vertical axis of the front wheel. This limits the required movement of the fourth guiding element.

In an embodiment, the movement of the arms/hands and the legs/feet during driving of the vehicle are synchronized by providing the secondary chain-drive in series with the primary chain-drive, i.e. the secondary chain-drive is indirectly driving the rear wheel via the primary chain-drive, which may mean that a gear of the primary chain-drive and the first gear of the secondary chain-drive are mounted on a common axle, and wherein both the first and second gears of the secondary chain-drive have the same size/effective diameter.

In an embodiment, the secondary chain-drive comprises a freewheel to allow decoupling of the driving and steering assembly with respect to the at least one rear wheel and/or wherein the primary chain-drive comprises a freewheel to allow decoupling of the primary chain-drive with respect to the at least one rear wheel. The possibility of the chain-drives to decouple with respect to the rear wheel allows a user to stop rotating the chain-drives or to reduce the rotational speed of the chain-drives while the vehicle continues to move, i.e. reducing the rotational speed will not cause any braking forces to be applied to the vehicle.

In an embodiment, the secondary chain-drive is arranged to drive the at least one rear wheel via the primary chain-drive. Preferably, a freewheel is arranged between the secondary chain-drive and the primary chain-drive to allow decoupling of the secondary chain-drive with respect to the primary chain-drive. This allows the user to stop driving the rear wheel with the driving and steering assembly while continuing to drive the rear wheel using the primary chain-drive. It further allows to choose an appropriate orientation of the second crankset relative to the first crankset, so that a user is for example able to drive the vehicle using both hands and feet, wherein an upward movement of the left hand/arm (and thus a downward movement of the right hand/arm) concurs with an upward movement of the right foot/leg (and thus a downward movement of the left foot/leg), which is a natural and fluent way of moving the body and thereby driving the vehicle. This way of driving resembles the moving forward of a tetrapod. The freewheel thus allows for finding an optimal driving position of the hands and feet.

In an embodiment, the secondary chain-drive comprises a member configured to allow rotation of the second crankset in only one direction, i.e. the direction corresponding to driving the vehicle in a forward direction. This member may be a freewheel for instance provided between the driving axle and a frame part, e.g. a frame part of the driving and steering assembly. An advantage of said member is that the second crankset cannot turn in reverse direction providing a more stable and thus comfortable steering of the vehicle.

The presence of said member may result in a configuration in which moving the vehicle in the rearward direction is blocked by said member, which may be disadvantage when e.g. parking the vehicle. The result may be that the tension in the chain-drives becomes too large. To overcome this, a slip device may be provided allowing rotation of the second crankset in the rearward direction only when a predetermined threshold is passed. The predetermined threshold should then be chosen sufficiently large to provide stability during steering and sufficiently low to allow the vehicle to be moved in rearward direction by a user without causing too much tension in the chain-drives.

In an embodiment, the vehicle, and in particular the driving and steering assembly, comprises a steer for steering of the front wheel separate from the second crankset. This allows to use the vehicle in a normal standard manner as well with no driving of the vehicle by hands, but only steering the vehicle using the hands. This may be advantage during low speeds as for instance encountered during climbing on the vehicle and getting of the vehicle.

In an embodiment, the separate steer is arranged above the driving and steering assembly, so that using the separate steer can also be used when traffic demands a better overview of the surroundings.

In an embodiment, the second gear is arranged at a height-level below the second and fourth guiding element. Not only may this provide an efficient guiding by the second and fourth guiding element, it also allows to position the third and fourth guiding element at a relatively large distance to increase the length of chain in between, which results in less deformation of the chain part in between the third and fourth guiding element. Preferably, the first and second guiding element are also positioned at a relatively large distance from each other to obtain a similar advantage for the chain part in between the first and second guiding element.

In an embodiment, a distance between the first and second guiding element is at least 10cm, preferably at least 15cm, and more preferably at least 20cm.

In an embodiment, a distance between the third and fourth guiding element is at least 10cm, preferably at least 15cm, and more preferably at least 20cm.

The inventor has found that the larger the distance between the first and second guiding element on the one hand and the third and fourth guiding element on the other hand results in larger steering angles that can be achieved without interfering with the driving function. For instance, when the distances are 20cm, the obtainable steering angles are 30 degrees in both directions, hence, 60 degrees in total.

In an embodiment, the second gear of the secondary chain-drive is arranged at least 5cm in front of the vertical axis of the front wheel, preferably at least 10cm, in order to provide a stable and comfortable steering of the vehicle.

In an embodiment, the endless chain part of the secondary chain-drive between the first gear and the first and third guiding elements is arranged at most 8cm from a median plane of the frame, preferably at most 6cm, more preferably at most 5cm and most preferably at most 4cm.

In an embodiment, the vehicle comprises only one rear wheel. Preferably, the vehicle is a bicycle.

In an embodiment, the first to fourth guiding elements comprise moveable guiding elements such as wheels or gears to minimize wear between the guiding elements and the endless chain. Additionally or alternatively, the first to fourth guiding elements comprise stationary guiding elements to guide the endless chain. In an embodiment, the first and second guiding elements are moveable guiding elements as these guiding elements need to withstand relatively large forces during driving of the rear wheel using the secondary chain-drive, while the third and/or the fourth guiding element may be stationary guiding elements.

In an embodiment, the primary chain-drive is replaced by a primary belt-drive, in which a belt is used instead of a chain.

In an embodiment, the endless chain of the secondary chain-drive is replaced by an endless belt effectively changing the secondary chain-drive into a secondary belt-drive.

In an embodiment, the vehicle comprises additional motors to aid in driving the vehicle.

When the expression close to the substantially vertical axis of the front wheel is considered clear, this expression may be further clarified by defining close to be within 10cm from the vertical axis, preferably within 8cm, more preferably within 6cm, most preferably within 4cm from the vertical axis, wherein a different range may apply to the part of the upper chain portion than the part of the lower chain portion. Preferably, the part of the upper chain portion is closer to the vertical axis than the part of the lower chain portion as the upper chain portion is the pulling part of the endless chain.

According to another aspect of the invention, there is provided a human-powered vehicle comprising: a frame; a front wheel which is pivotably mounted to the frame about a substantially vertical axis for steering; at least one rear wheel; a chain-drive for driving the at least one rear wheel by hand; and a driving and steering assembly attached to the front wheel for driving the chain-drive by hand and simultaneously steering the vehicle via the front wheel, wherein the chain-drive comprises a gear arranged on the driving and steering assembly, wherein the driving and steering assembly comprises a driving axle connected to the gear of the chain-drive and a crankset arranged on the driving axle in order to drive rotation of the driving axle about a longitudinal axis of the driving axle by hand and in order to steer the vehicle, wherein the chain-drive comprises a freewheel allowing to decouple the chain-drive from the at least one rear wheel, and wherein a member is provided configured to allow rotation of the crankset in only one direction.

This member may be a freewheel for instance provided between the driving axle and a frame part, e.g. a frame part of the driving and steering assembly. An advantage of said member is that the second crankset cannot turn in reverse direction providing a more stable and thus comfortable steering of the vehicle.

All other features and embodiments described above may also be combined or apply to this aspect of the invention, where applicable, and will not be unduly repeated here.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in a non-limiting way with reference to the accompanying drawings in which like parts are indicated by like reference symbols and in which:

Fig. 1 schematically depicts a human-powered vehicle according to an embodiment of the invention; and

Fig. 2 schematically depicts a part of the human-powered vehicle of Fig. 1 in more detail.

DETAILED DESCRIPTION OF THE INVENTION

Fig. 1 schematically depicts a human-powered vehicle 1 having a frame 3, a front wheel 5 and a rear wheel 7. The front wheel 5 is rotatable about a horizontal rotation axis 9 for riding, and pivotably mounted to the frame 3 about a substantially vertical axis 11 for steering. The rear wheel 7 is rotatable relative to the frame 3 about a horizontal rotation axis 13 for riding. A primary chain-drive 15 extends substantially perpendicular to the horizontal rotation axis 13 of the rear wheel 7 between the frame 3 and the rear wheel 7 for driving the rear wheel 7. The primary chain-drive 15 comprises two gears 17a, 17b and in between and around the two gears 17a, 17b an endless chain 19.

The vehicle 1 comprises a first crankset 21 and respective foot pedals 23 for driving the primary chain-drive 15 by foot. In Fig. 1 only one crank 21 and respective foot pedal 23 are shown.

The frame 3 comprises a steering tube 3a for receiving a fore fork 4 and/or handlebar stem 6. The fore fork 4 holds the front wheel 5 and defines the rotation axis 9 for the front wheel 5. The handlebar stem 6 connects a steer 8 and a driving and steering assembly 31 to the fore fork 4. The steering tube 3a defines the vertical axis 11 for the fore fork 4 and handlebar stem 6 and thus for the front wheel 5. The handlebar stem 6 and the steer 8 may be part of the driving and steering assembly 31. A secondary chain-drive 25 is provided for driving the rear wheel 7 by hand, wherein the secondary chain-drive 25 extends substantially perpendicular to the horizontal rotation axis 13 of the rear wheel 7.

The driving and steering assembly 31 is configured for driving the secondary chain-drive 25 by hand and simultaneously steering the vehicle 1 via the front wheel 5. The secondary chain-drive 25 comprises a first gear 27a arranged on the frame 3, a second gear 27b arranged on the driving and steering assembly 31, and an endless chain 29 arranged in between and around the first and second gears 27a, 27b thereby defining an upper chain portion 29a and a lower chain portion 29b extending between the first and second gears 27a, 27b.

The secondary chain-drive 25 further comprises a first guiding element 28.1, a second guiding element 28.2, a third guiding element 28.3 and a fourth guiding element 28.4, wherein the first and third guiding elements 28.1,28.3 are arranged on the frame 3, in this case the steering tube 3a, and wherein the second and fourth guiding elements 28.2, 28.4 are arranged on the driving and steering assembly 31.

The first and second guiding elements 28.1,28.2 are configured to guide a part 30a of the upper chain portion 29a in a direction parallel and close to the vertical axis 11, and the third and fourth guiding elements 28.3, 28.4 are configured to guide a part 30b of the lower chain portion 29b in a direction parallel and close to the vertical axis 11.

The secondary chain-drive is in this embodiment configured to drive the rear wheel 7 indirectly via the primary chain-drive. Gear 27a is therefore mounted to gear 17a, e.g. by mounting both gears 17a, 27a on a common axle. It is to be noted that the gears are depicted highly schematically and thus the sizes of the gears are not exemplary.

The driving and steering assembly 31 comprising a second crankset, of which only a crank 33 is shown, with respective handlebars 35 is able to drive the second gear 27b by rotation about a horizontal rotation axis. The second gear 27b is arranged on a driving axle 37 defining the horizontal rotation axis. The crankset 33 is connected to the driving axle 37.

The handlebars 35 can be used to steer and at the same time drive the vehicle. The steer 8, which is separate from the handlebars and crankset, can be used for steering purposes only.

The vehicle 1 further comprises a saddle 39 on which a user is able to sit. While being seated on the vehicle, the legs and feet are able to drive the rear wheel using the first crankset and foot pedals at the gear 17a, and the arms and hands are able to drive the rear wheel using the second crankset and handlebars at gear 27b and are able to steer the vehicle at the same time.

Fig. 2 depicts a part of the vehicle 1 of Fig. 1 in more detail. Shown in Fig. 2 are the frame 3 with the steering tube 3a, the fore fork 4, the handlebar stem 6 and the driving and steering assembly 31 in this case attached to the handlebar stem 6. Also attached to the handlebar stem 6 is steer 8 separate from the driving and steering assembly. This steer is only for steering purposes.

Attached to the frame 3, in this case steering tube 3a, are first guiding element 28.1 and third guiding element 28.3. Attached to the driving and steering assembly 31 are second guiding element 28.2 and fourth guiding element 28.4. The first and second guiding element 28.1, 28.2 are configured to guide a part 30a of the upper chain portion 29a in a direction parallel to and close to the substantially vertical axis 11 of the front wheel. The third and fourth guiding elements 28.3, 28.4 are configured to guide a part 30b of the lower chain portion 29b in a direction parallel to and close to the substantially vertical axis 11 of the front wheel.

The fourth guiding element 28.4 is moveably connected to the driving and steering assembly 31 via a beam 41 to pivot about a pivot axis 40. A resilient element, in this case a spring 42, is provided between the beam 41 and the driving and steering assembly 31 to urge the fourth guiding element 28.4 upwards to tension the chain 29.

As the first and third guiding elements are arranged on the frame and the second and fourth guiding elements are arranged on the driving and steering assembly which is rotated relative to the frame about the vertical axis 11 to steer the vehicle, the parts 30a, 30b of the chain in between the first, second, third and fourth guiding elements will twist upon steering of the vehicle. However, an advantage of the invention is that due to the chain parts 30a, 30b being aligned with and close to the vertical axis, the deformation is limited and allows simultaneously steering and driving.

The vehicle of Fig. 1 and 2 can be used in one or more of the following modes: 1. Feet drive only, steering using the steer 8; 2. Feet drive only, and simultaneously steering using the second crankset and handlebars 35; 3. Hand drive only, and simultaneously steering using the second crankset and handlebars 35; 4. Hand drive and feet drive, and simultaneously steering using the second crankset and handlebars 35.

To allow one or more of the above modes, the vehicle, although not shown explicitly, be provided with one or more freewheels at appropriate locations.

Mode 1 may for instance be used to climb on the vehicle and start riding as well as slowing down to get off the vehicle.

When a freewheel is used to decouple the second chain-drive from the rear wheel, the introduced degree of freedom may introduce an unstable and/or uncomfortable steering of the vehicle, especially in mode 2. This can be prevented by allowing the second crankset to only rotate in one direction, or by providing sufficient resistance to provide a similar feeling/experience for the user.

Claims

A human-powered vehicle comprising: - a frame; - a front wheel pivotally connected to the frame for steering about a substantially vertical axis; - at least one rear wheel; - a primary chain drive between the frame and the at least one rear wheel for driving the at least one rear wheel; - a first crankset and associated foot pedals for driving the primary chain drive with the foot; - a secondary chain drive for manually driving the at least one rear wheel; and - a drive and steering assembly connected to the front wheel for manually driving the secondary chain drive and simultaneously steering the vehicle via the front wheel, the secondary chain drive comprising: a first sprocket mounted on the frame; o a second gear wheel mounted on the drive and steering assembly; o an endless chain arranged around the first and second gear wheels whereby an upper chain part and a lower chain part are defined which extend between the first and second gear wheels; o a first guide element and a third guide element arranged on the frame; and o a second guide element and a fourth guide element mounted on the drive and control assembly; wherein the first and the second guide element are arranged to guide a part of the upper chain part in a direction parallel to and near the substantially vertical axis of the front wheel, the third and the fourth guide element are arranged around a part of the lower chain part to guide in a direction parallel to and near the substantially vertical axis of the front wheel, and wherein the drive and steering assembly comprises: a drive shaft connected to the second sprocket of the secondary chain drive; and a second crankset mounted on the drive shaft to manually rotate the drive shaft about a longitudinal axis of the drive shaft and to steer the vehicle.

A human-powered vehicle as claimed in claim 1, wherein the fourth guide element is movably mounted on the drive and control assembly, and wherein the drive and control assembly comprises a resilient element that acts on the fourth guide element to drive the endless chain of the secondary chain drive tension.

A human-powered vehicle according to claim 2, wherein the fourth guide element is movable in a direction substantially parallel to the substantially vertical axis of the front wheel.

A human-powered vehicle according to any one of claims 1 to 3, wherein the secondary chain drive comprises a freewheel to enable disengagement of the drive and steering assembly from the at least one rear wheel and / or wherein the primary chain drive comprises a freewheel to enable decoupling of the primary chain drive from the at least one rear wheel.

A human-powered vehicle according to any one of claims 1 to 4, wherein the secondary chain drive is adapted to drive the at least one rear wheel via the primary chain drive.

A human-powered vehicle according to claim 5, wherein a freewheel is provided between the secondary chain drive and the primary chain drive to enable disengagement of the secondary chain drive from the primary chain drive.

A human-powered vehicle according to any of claims 1 to 6, wherein the drive and steering assembly comprises a steering wheel for steering the front wheel which is separate from the second crankset.

A human-powered vehicle according to any of claims 1 to 7, wherein the second gear is mounted at a height below the second and fourth guide element.

A human-powered vehicle according to any one of claims 1 to 8, in particular according to claim 4, wherein the second chain drive comprises a means adapted to allow rotation of the second crankset only in one direction, i.e. say in the forward direction.

A human-powered vehicle according to claim 9, wherein the member is a freewheel.

A human-powered vehicle according to claim 9 or 10, wherein a slip clutch is provided that allows the second crank set to rotate in the rearward direction only when a predetermined threshold is passed.

A human-powered vehicle according to any of claims 1 to 11, wherein a distance between the first and second guide element is at least 10 cm, preferably at least 15 cm, and more preferably at least 20 cm.

A human-powered vehicle according to any one of claims 1 to 12, wherein a distance between the third and fourth guide element is at least 10 cm, preferably at least 15 cm, and more preferably at least 20 cm.

A human-powered vehicle according to any one of claims 1 to 13, wherein the second sprocket of the secondary chain drive is arranged at least 5 cm in front of the vertical axis of the front wheel, preferably at least 10 cm, in order to provide a stable and comfortable provide control of the vehicle.

A human-powered vehicle according to any one of claims 1 to 14, wherein the endless chain part of the secondary chain drive is arranged between the first sprocket and the first and third guide elements at a maximum of 8 cm from a center plane of the frame, at preferably at most 6 cm, more preferably at most 5 cm and most preferably at most 4 cm.

A human-powered vehicle according to any of claims 1 to 15, wherein the vehicle comprises only one rear wheel, preferably a bicycle.