The present invention relates to a linkage for use in drawing a self-propelled trailer.

In expectation of future legislation restricting and/or making uneconomical the use of petrol and diesel automotives within urban areas, there is a desire to find alternative methods for so called 'last mile' delivery, that being transportation of goods between a transportation hub and a final delivery address, which has traditionally being performed using diesel vans. One method of interest is the use of cargo bicycles.

The Carla Cargo bike trailer (www.carlacargo.de) is a brand of electric self-propelled trailer having linkage that includes a ball joint for connection with a bike and a pivotable front wheel. Because the linkage is stiff in a longitudinal axis extending between the bike and trailer, the trailer is able to propel the cyclist through force transferred through the linkage.

US2008023234 discloses a self-propelled trailer for a bicycle. Electric motors that power the trailer are controlled by a force/pressure meter located between the bicycle and the trailer.

US4771838 describes a self-propelled trailer having a linkage that allows the towing vehicle to move relative to the trailer in a longitudinal direction (i.e. towards/away from each other) by virtue of a vertically orientated link member that connects about its base to the trailer through a ball and socket joint which allows the link member to pivot in any direction away from vertical. As the link member pivots, it acts on control lines that control motors that drive near and far side wheels of the trailer independently. Through altering the speeds of the wheels of the trailer independently, the trailer can be caused to change direction to match that of the towing vehicle. RO102236 and WO2012/163529 relate to linkages that comprise spring damper systems between a tow and a trailer.

The present invention was conceived as a linkage for drawing a self-propelled trailer with a bicycle, though the principle may be employed for drawing a trailer with other types of tow.

According to a first aspect there is provided a system for controlling the speed of a self-propelled trailer, the system comprising: a linkage for connection between a tow and a self-propelled trailer, the linkage having a first part which when in use is associated with the tow and a second part associated with the trailer, at least one of the first and second parts being arranged to move relative to the other in response to differing speeds of the tow and trailer; the linkage comprising at least one couple that, when in use, allows relative movement in a vertical direction between at least one of the trailer and tow, and the first and second parts; and the system comprising means for altering the speed of the trailer in response to detecting relative movement between the first and second parts indicative of a differential in the speed of the tow and trailer

The linkage favourably restricts displacement between the first part and the tow, and the second part and the trailer in a line of travel of the tow. This means the speed of the first part will match that of the tow and the speed of the second part will match that of the trailer. In this way movement between the first and second parts can be used as an indicator of a speed differential between the tow and trailer. Movement between the first and second parts can be used to control the speed of the trailer.

According to another aspect there is provided a linkage for connection between a tow and a trailer. The linkage may have a first part which when in use is associated with the tow and a second part associated with the trailer, the first and second parts arranged for movement there between in response to differing speeds of the tow and trailer. The linkage may comprise at least one couple that, when in use, allows relative movement in a vertical direction between at least one of the trailer and tow, and the first and second parts.

In this way the linkage can accommodate for a height and/or attitude differential between the tow and trailer, e.g. whilst the tow and trailer are tracking over uneven terrain, such as to remove or at least minimise the differential' s influence on the separation distance between the first and second parts. Additionally the decoupling also allows each of the bike and trailer to track the surface of the ground without influencing each other.

The following may apply to either of the aspects provided above. Accommodating for height and/or attitude differential may be achieved through the couple allowing the tow or trailer to rotate relative the first and second parts about an axis lying in a substantially horizontal plane .

The couple may be arranged between the tow and the first part in order to allow relative movement in a vertical direction between the tow and first and second parts. The couple may also, when the tow is moving, allow relative rotational movement about a vertically extending axis, favourably substantially vertical axis, between the tow and the first and second parts. This allows the tow to rotate relative to the trailer or vice-versa so that one can change its direction of travel across the ground relative to the other in order to facilitate steering. The linkage may comprise a second couple that allows relative rotational movement about a vertical axis between the trailer and the first and second parts. In this way both the tow and the trailer can change direction relative to the first and second parts. Favourably the linkage comprises a wheel that in use carries a nose weight of the trailer. In order to do this it is preferred that the wheel provides a front wheel of the trailer, and as such may be mounted proximate the linkage under the front of the trailer. By arranging the wheel to carry the nose weight of the trailer, it avoids or at least minimises said weight being carried by either the first and second parts. This aids to ensure consistent friction, favourably minimal fiction, between the first and second parts irrespective of their relative positions to one another and changes in nose weight caused, for example, by variations of cargo weight and position in the trailer. This allows the first and second parts to move relative to one another predictably with change of speed of the tow relative the trailer or vice-versa.

The wheel may be arranged to rotate with the first and second parts relative to the trailer about the vertically extending axis This facilitates steering of the trailer and, where the tow is a light weight wheeled vehicle such as a bicycle, reduces the propensity for the rear wheel of the tow to skid laterally towards an imaginary line extending between a front wheel of the tow and a front wheel of the trailer.

A problem with providing a front wheel is that it causes a disparity of height between the back of the tow and the front the trailer. To compensate for this the linkage may include a further couple that allows relative movement in a vertical direction between at least one of the trailer and tow, and the first and second parts. One of the couples may also allow the tow to rotate relative to the trailer in order to enable the tow to steer.

In one embodiment, the linkage may comprise a third part linked to the first part by the couple, the third part comprising means (e.g. one part of a ball and socket joint) for connection to the tow. The third part may comprise, when in use, means that couples to the tow in a manner that allows relative movement in a vertical extending axis, favourably substantially vertical axis between the tow and the third part. More favourably it allows rotation between the tow and the third part in axes that extend laterally from the line of travel of the tow and perpendicular to one another.

In another embodiment, the linkage comprises coupling means (e.g. part of a ball and socket joint) for coupling with the tow and which, when in use, provides the couple between the tow and the second part; and a second couple between the first part and trailer that allows relative rotation therebetween about a substantially horizontal axis extending laterally to the line of travel of the tow.

The first and second parts are favourably arranged for linear, e.g. sliding, movement (as opposed to a rotational movement) relative to the other, as a consequence of a differential between the speed of the tow and trailer. The linear movement favourably occurs in a direction extending between the trailer and the tow and/or a line of travel of the tow. The first and second parts are favourably in contact so as to transmit lateral steering force from the tow when the tow changes direction.

The second part may comprise a linear bearing. The first part may comprise a shaft. The shaft may have any desired cross-sectional shape. The linear bearing may act to guide movement of the shaft so as to minimise motion other than linearly in an axis lying substantially in a horizontal plane between the trailer and tow. The shaft may extend into the linear bearing.

Rotational movement of the shaft about its axis may be restricted through provision of an anti-torque device, e.g. the addition of a further linear shaft coupled running parallel with the linear shaft, or through the cross-section profile of the bearing.

At least one of the first and second parts may comprise a stop arranged to engage the other part to provide a maximum separation distance between the tow and the trailer, e.g. to prevent detachment; and/or to provide a minimum separation distance between the trailer and the tow to prevent overrun. The self propelled trailer may be controlled so that it does not provide more than a net neutral effect from the perspective of the tow. In other words the trailer may be controlled to avoid applying a force through the linkage such as to propel or retard the tow. The speed of the trailer is favourably controlled in order that it tends towards the speed of the tow. In this way the trailer can be caused to follow closely behind the trailer without the tow having to draw the load of the trailer.

The system may comprise a detector, e.g. a linear displacement transducer such as a linear variable displacement transducer or a linear magnetic transducer, arranged to transmit a signal in response to detecting movement, e.g. linear movement, between the first and second parts indicative of a differential in the speed of the tow and the trailer. The system may further comprise a controller arranged, in response to receiving said signal, to operate a speed control mechanism to adjust the speed of the trailer. The speed control mechanism may comprise a motor, e.g. an electric motor. The motor may be used to accelerate the trailer. Additionally, the motor may be used to decelerate the trailer, e.g. through an 'engine braking' effect. The trailer may comprise regenerative breaking means in order, for example, to charge an electrical power store used to power the motor. The system may comprise a sensor that provides a signal indicative of the ground speed of the trailer. This may, for example, take the form of a sensor that provides a signal indicative of the frequency of revolution of a trailer's wheel.

The system may comprise means to determine an indicator of the speed of the tow. The advantage of knowing the speed of the tow and the trailer is that it allows a command to be given to provide a target speed for the trailer, as opposed to simply causing an acceleration or braking action. Favourably an indicator of the speed of the tow is derived using the ground speed of the trailer and an indication of magnitude of movement detected between the first and second parts. The magnitude of movement may be used to determine a rate of change of magnitude of movement between the first and second parts. This method allows the speed of the tow to be determined, or at least estimated, without a separate sensor on the tow. Alternatively an indication of the tow speed may be taken from a sensor mounted on the tow, e.g. a signal from a speedometer.

Alternatively, rather than determining an indicator of the speed of the tow, the system may be arranged to receive a force signal from the tow and use this to control acceleration and deceleration of the trailer. Where the tow is a vehicle with pedals, this may be a torque on the pedal, crank, chain or wheel. The system may use both the force signal and signal from the detector to control acceleration and deceleration of the trailer. By using signals from both, it is possible to ensure that the trailer acts as a net neutral load from the perspective of the tow.

The system may further include means to sense steering angle between the trailer and the tow. The controller may use the sensed steering angle to control the speed of the tow. Because the trailer will have a smaller turning circle than the tow during a turn, the sensed steering angle can be used to ensure the trailer travels at a reduced speed compared with the tow in order not to overrun during turning.

The controller is favourably mounted directly to the trailer.

According to another aspect there is provided a trailer comprising the linkage or the system described above. The trailer favourably comprises front and rear travelling wheels.

The linkage may be used for drawing the trailer by hand or with an animal, i.e. the tow is a human and/or animal. Alternatively the tow may be a towing vehicle such as, but notlimited to: self-powered vehicles such as cars, lorries, quadricycle, electric bikes and two-wheeled self balancing electric vehicles, or non powered vehicles including bicycles and tricycles. The tow may be itself a trailer, powered or unpowered, following a primary tow vehicle. The tow may comprise one any one of a: bicycle, tricycle, electric bicycle and pedicycle. The tow may be a vehicle weighting, unloaded, less than 200Kg. The invention will now be described by way of example with reference to the following figures in which:

Figure 1 is a perspective view of a linkage arranged to extend between a bicycle and a trailer;

Figure 2 is a side view schematic of the linkage linked to a bicycle for connecting the bicycle with a trailer;

Figure 3 is a side view schematic of the linkage linked to a bicycle for connection to a trailer, shown with a height differential between the bicycle and trailer;

Figure 4 is a plan view schematic of the linkageconnected between a bicycle and a trailer travelling in straight line; Figure 5 is a plan view schematic of the linkage connected between a bicycle and a trailer showing the bicycleand trailer in a turn;

Figure 6 is a side sectional view of the linear bearing and first shaft; and

Figure 7 is a side view schematic of an alternative linkage connected to a bike for connection to a trailer. With reference to the Figures there is shown a linkage 3 arranged for connection between a bicycle 1 and a self propelled trailer 2. The linkage 3 forms part of a system for controlling the speed of the trailer 2 in order for it to respond to changes in speed (forward and backwards) of the bicycle 1.

The linkage 3 includes a wheel assembly 4 including a linear bearing 4A, a first shaft5, and a second shaft 6. The first shaft 5is arranged between the linear bearing 4Aand the second shaft 6. The first shaft 5is seated in the linear bearing 4A arranged to slide relative to the bearing 4a in a longitudinal axis X-X ,which when the bicycle is travelling in a straight line, corresponds with the direction of travel of the bicycle 1. The linear bearing is arranged to constrain lateral movement between it and the shaft 5 in all other directions. Through this decoupled arrangement, the bicycle exert effectively no drawing or breaking force on the trailer 2 or vice versa through the linkage 3 in the direction of travel of the cycle over the range of free travel of the first shaft 5 relative to the linear bearing 4 A. As such, the separation distance between the bicycle and trailer changes as a consequence of different velocities of the bicycle and trailer. A change in the relative positions between the shaft 5 and bearing 4A is used to control the speed of the trailer 2 in a manner to be further described in order to cause the trailer 2 to follow closely behind the bicycle 1. To ensure the relative movement between the linear bearing 4A and shaft 5 provides a consistent indicator of the different speeds between the bicycle 1 and trailer 2, it is desirable that the stiction/friction between the shaft 5 and bearing 4A remains as close to constant as possible, and favourably as low as possible, irrespective of the relative positions of the shaft 5 and bearing 4A with respect one another, and the gross weight of trailer 2. To achieve this, the linkage 3 is arranged to minimise the load carried by both the first shaft 5 and linear bearing 4A. Additionally it is desired to minimise the application of force on both the first shaft 5 and linear bearing 4A, that would urge movement of the shaft 5 relative to the bearing 4A in any direction other than in the direction of travel of the bicycle 1 e.g. that might happen as a result of the bicycle 1 and trailer 2 turning or passing over uneven ground. The first shaft 5 and second shaft 6 are connected about a first hinge 7, e.g. a clevis, that allows rotation about axis Y-Y which in an expected orientation of use lies in a horizontal plane normal to X-X.

The other end of the second shaft 6 comprises a socket 6A for engagement with a ball joint connector e.g. a tow bar ball, 8 that is rigidly fixed to the rear of the bicycle 1. Together socket 6A and connector 8 form a second couple 9 that allows relative movement between the bicycle 1 and second shaft 6 in substantially all directions, including rotation about X-X, but restricts lateral movement in X-X.

The wheel assembly 4 further include a pivot bearing 4B, that forms part of a third couple 10 with a corresponding bearing (not shown) of the trailer chassis 2 that connects the wheel assembly 4 and linear bearing 4A to the trailer 2. The third couple 10 allows relative rotation between the wheel assembly 4 including the linear bearing 4A and the trailer 2 about vertical axis Z-Z Wheel 4C is mounted to the wheel assembly 4 to allow relative rotation of the wheel 4C about Y-Y axis. The wheel 4C is positioned adjacent the linear bearing 4A, towards the front of the trailer 2, in order to carry the nose weight of the trailer 2 and thus avoid the linear bearing 4A and shaft 5A doing so.

Through the linkage 3 arrangement described above, the first shaft 5 is rigidly fixed for movement with the bicycle 1 in the longitudinal direction of the linkage (direction of travel of the bicycle X-X), and the linear bearing 4A is rigidly fixed for movement with the trailer 2 in X-X. Fig 3 illustrates how the linkage 3 accommodates for relative vertical movement between the bicycle 1 and trailer 2 as a result, for example, of travelling over a curb or uneven ground. Shown exaggerated for ease of comprehension, the combination of the hinge 7 and couple 9 allows both the bicycle 1 and second shaft 6, and the first shaft 5 and second shaft 6 to rotate relative to one another about the horizontal Y-Y direction. This arrangement thus isolates the load from the bicycle 1 onto the bearing 4A throughfirst shaft 5(and vice-versa) which would otherwise likely increase the friction between shaft 5 and the bearing 4A. When the bicycle 1 moves to be higher than the trailer 2, the hinge 7 and couple 9 similarly accommodate relative rotation between the bicycle 1 and second shaft 6, and first shaft 5 and second shaft 6 in the other direction.

With reference to Fig 4, the system for controlling the speed of the trailer 2 further comprises a speed sensor 11, a linear displacement sensor 12, and a controller 13 arranged to receive signals from the speed sensor 11 and linear displacement sensor 12 to control a motor 14. The speed sensor 1 1 may be arranged to transmit a signal to the controller 13 indicative of the frequency of rotation of wheel 4C or other wheel 2A associated with trailer 2, used by the controller 13 to determine an indication of the ground speed of the trailer 2. The linear displacement sensor 12 may take the form of a linear variable differential traducer comprising a magnet 12A that is arranged to move with the first shaft 5 and an inductive rail 12B arranged to move with the linear bearing 4A and outputs signals to the controller 13 indicative of relative position of shaft 5 with respect linear bearing 4A. In use, when the bicycle 1 starts to move away from the trailer 2 because its speed is greater than that of the trailer 2, or starts to move towards the trailer 2 because its speed is less than that of the trailer 2, a displacement occurs between the first shaft 5 and linear bearing 4A indirection X-X of travel of the bicycle 1. In response, the linear displacement sensor 12 sends a signal indicative of the magnitude of the displacement to the controller 13. The controller 13 uses these signals over time to determine a rate of change of displacement between the first shaft 5 and the linear bearing 4A. From this information together with an indicator of the speed of the trailer 2 as determined using the signals from the speed sensor 11, the controller 13 determines the speed of the bicycle 1 and controls the motor 14 in order to accelerate/decelerate the trailer 2 towards the speed of the bicycle 1. Depending on the magnitude of the displacement, the controller 13 may cause the trailer to accelerate so that it is temporarily at a speed greater than the bicycle 1 in order to move the first shaft 5 and linear bearing 4A back towards a control position. The motor 14 and controller 13 are powered from an electrical store such as a rechargeable battery (not shown) carried on the trailer 2.

With reference to Fig 5, couple 9 allows for rotation of the bicycle 1 relative to the linkage 3 in vertical axis Z-Z to allow for steering of the bicycle 1 and trailer 2. Additionally because the bicycle 1 is free to rotate about X-X relative to the linkage 3, the bicycle 1 is able to lean into turns and thus has improved stability during cornering. Similarly, couple 10 allows the linkage 3 including wheel 4C to rotate relative to the trailer 2 about Z-Z so that the wheel follows the direction of travel of the bicycle 1. This facilitates steering of the trailer 2 by minimising lateral sliding of a rear wheel 1A of the bicycle 1 towards an imaginary line extending between the front wheel IB of the bicycle 1 and the wheel 4C under the trailer 2.

With reference to Fig 6, the first shaft 5 includes a cavity 5A that opens at the trailer end 5B of the shaft 5, and an end cap 5C seated over said trailer end 5B. Within the cavity 5A reside two dampers 5D, which may comprise coiled springs or elastomeric bungs. One of the dampers 5D sits at a bike end of the cavity 6 A, the other is retained in the cavity 5A by end cap 5C. Extending through end cap 5C and opening 5B into cavity 5 A is a stop shaft 14 that is fixed to move with the linear bearing 4 A and trailer 2, and move relative to first shaft 5. The stop shaft 14 includes a stop actuator 14A fixed to the so the stop shaft 14 that sits within the cavity 5A. The position of the stop actuator 14A within the cavity 5A changes with relative movement between the first shaft 5 and linear bearing 4A. As the separation between the bicycle 1 and trailer 2 increases, the stop actuator 14A tends towards the end cap 5C compressing one of the dampers 5D against end cap 5C until the actuator 14A can move no further towards the end cap 5C, preventing further separation of the shaft 5A and linear bearing 4A. Similarly, as the separation between the bicycle 1 and trailer 2 reduces, the separation between the bicycle end of the cavity 5A and stop actuator 14A decreases until the opposite damper is fully compressed by stop actuator 14A. Figure 7 illustrates an alternative embodiment of linkage 3 ' comprising a shaft 5' and linear bearing 16 arranged for sliding movement relative one another in response to a speed differential between the bicycle 1 and trailer 2. The linear bearing 16 comprises a connector 16A adapted to be mounted to ball connector 8 fixed to bicycle 1, to form a couple that allows rotation of the linkage 3 ' relative to the bicycle 1 in substantially all directions whilst inhibiting lateral movement between the bicycle 1 and linear bearing 16 in X-X.

Shaft 5' is coupled about couple 17 to wheel assembly 4' to allow relative pivoting of the linkage 3 ' and wheel assembly 4' about Y-Y. The wheel assembly 4' comprise a mounting pivot (not shown) to allow relative rotation of the wheel assembly 4' including wheel 4C relative to trailer chassis about Z-Z to facilitate steering. The wheel 4C is also free to rotate about Y-Y relative to the wheel assembly 4 in order to allow the wheel 4C to roll along the ground.

The combination of a couple on either side of the shaft 5' and linear bearing 16 that each provide pivoting about Y-Y allows for relative vertical movement between the bicycle 1 and linkage 3', and the trailer 2 and linkage 3 \ This allows the linkage 3' to compensate for a height and/or attitude differential between the trailer 2 and bike 1 - though not to the extent of the first embodiment, whilst minimising forces on the linkage 3 ' that could interfere with relative movement between the shaft 5' and linear bearing 16.

With either of the embodiments described above, the system can be used in order for a tow to pull multiple trailers, in a train formation, each linked to the one in front through one of the linkages described above. Because each trailer can be arranged to act as a net neutral load, the number of trailers, and load carried by each trailer is not limited by the towing force that can be generated by the tow.

The linkages described above may further include one or more steering angle sensors that identify a steering angle(s) based on the relative positions of linkage parts about one or each of the couples that provide relative rotation about Z-Z. This can be used y the controller to identify that the tow and trailer are in a turn and the tightness of the turn and in response reduce the speed of the trailer relative to the tow in order to avoid the trailer overrunning during a turn as a consequence of its tighter angle of turn compared with the tow.

Variations to the above described embodiments are envisaged. For example, an indicator of the ground speed of the trailer may be determined using means other than RPM such as for example GPS. Notwithstanding, at the time of writing this is not preferred because the lag to obtain such information and its relative inaccuracy for the required purpose. Rather than determining the speed of the bike (or other tow) from the speed of the trailer, the speed of the tow could be obtained directly using an additional speed sensor mounted on the tow.

Rather than determining an indicator of the speed of the tow, the system may be arranged to receive a force (e.g. torque) signal from the tow to the trailer. This may be a force on the pedal (where present), crank, chain (where present) or wheel. This arrangement need not include the linear displacement sensor; however by using signals from both, the speed of the trailer can be controlled whilst ensuring the trailer does not act to propel or retard the tow. This may be of particular benefit when the tow is a bicycle, pedelec or similar where it is desired that combination of said tow with trailer fall with a class of vehicle subject to relatively little legal regulation.