EP4247699A1

EP4247699A1 - Gear system, pedal cycle, and method of retrofitting gear system

Info

Publication number: EP4247699A1
Application number: EP21839852.7A
Authority: EP
Inventors: Edward Johnston
Original assignee: Individual
Current assignee: Individual
Priority date: 2020-12-16
Filing date: 2021-12-14
Publication date: 2023-09-27
Also published as: GB2602447A; WO2022129026A1; GB202019856D0

Abstract

There is provided a gear system (100) for a pedal cycle (150). The gear system (100) comprises an epicyclic gear set (102) having a sun gear (104), one or more planet gears (106) meshed with the sun gear (104), and a ring gear (112) meshed with the one or more planet gears (106). Each of the planet gears (106) is connected to a planet carrier (110). The sun gear (104) has a connecting portion (118) for connecting to a component (122) of the pedal cycle (150). The gear (100) system comprises a control arrangement that is arranged to control a speed of rotation of the ring gear (112), so as to provide a variable gear ratio to the gear (100) system.

Description

Gear system, pedal cycle, and method of retrofitting gear system

Field of the invention

The present disclosure relates to a gear system for a pedal cycle, a pedal cycle incorporating the gear system, and a method of retrofitting a bicycle with the gear system. More particularly, the gear system incorporates a control arrangement that is arranged to provide a continuously variable transmission.

Background

Pedal cycles such as unicycles, bicycles and tricycles are well-known. Most pedal cycles use derailleur gears which have been known for approaching a century. Derailleur gears provide a certain number of fixed gear ratios. It has also been known for continuously variable transmission (CVT) systems to be utilised in pedal cycles. CVTs provide a continuous spectrum of gears rather than a certain number of fixed gear ratios. Known CVTs for bicycles are based on friction systems, which for example use rotating balls or cones.

Summary of invention

According to a first aspect of the invention there is provided a gear system for a pedal cycle comprising: an epicyclic gear set having a sun gear, one or more planet gears meshed with the sun gear, and a ring gear meshed with the one or more planet gears; each of the planet gears connected to a planet carrier; the sun gear having a connecting portion for connecting to a component of the pedal cycle; the gear system comprising a control arrangement that is arranged to control a speed of rotation of the ring gear, so as to provide a variable gear ratio to the gear system..

According to some examples, the control arrangement is arranged to restrain rotation of the ring gear.

According to some examples, the control arrangement comprises an electric motor for controlling the speed of rotation of the ring gear. According to some examples, the control arrangement comprises a one-way transmission between the electric motor and the ring gear.

According to some examples, the control arrangement comprises an escapement mechanism for controlling the speed of rotation of the ring gear.

According to some examples, the gear system comprises a solenoid that is arranged to control the escapement mechanism.

According to some examples, the control arrangement comprises a disc connected to the ring gear, the disc having a plurality of holes around a periphery of the disc, a peg of the solenoid arranged to selectively engage with the holes of the disc to control rotation of the disc and to consequently control rotation of the ring gear.

According to some examples, pedal input is provided to the gear system via the planet carrier, and output from the gear system is via the sun gear.

According to some examples, the connecting portion of the sun gear is constructed and arranged to engage with and provide drive to a wheel-hub, and the planet carrier comprises a sprocket arranged to be driven by a belt or chain.

According to some examples, the planet carrier is constructed and arranged to be connected to a pedal crank of the pedal cycle, and a sprocket being located on the connecting portion of the sun gear, the sprocket arranged to provide drive to a belt or chain.

According to some examples, the control arrangement is configured to selectively enable any one of: restrained rotation of the ring gear in a forward direction; locking of the ring gear.

According to some examples, the control arrangement has a sprint setting, wherein when the sprint setting is invoked the ring gear is locked.

According to some examples, the control arrangement is configured to control rotation of the ring gear at a speed that provides a gear ratio of 3:1 or higher.

According to some examples, the control arrangement is configured to control rotation of the ring gear at a speed that provides a gear ratio lower than 1 :1. According to some examples, the gear system comprises an electricity generator for recharging a battery of the control arrangement.

According to some examples, the electricity generator comprises a brushless, ironless generator.

According to some examples, the gear system comprises a pitch sensor for sensing whether the pedal cycle is going uphill, downhill or is on flat terrain, the electricity generator configured to generate electricity only when it is detected that the pedal cycle is travelling downhill.

According to some examples, the gear system comprises an automatic gear mode and when in the automatic gear mode the control arrangement is configured to control the speed of rotation of the ring gear so as to cause a constant or near-constant pedalling cadence of the pedal cycle.

According to some examples, the gear system is configured to be retrofitted to the pedal cycle.

According to a second aspect there is provided a pedal cycle comprising a gear system according to the first aspect.

According to some examples, the pedal cycle comprises a bicycle.

According to a third aspect there is provided a method comprising removing at least part of an existing gear system of a bicycle and retrofitting the gear system of the first aspect to the bicycle.

Brief description of drawings

Figure 1 schematically shows a gear system according to an example;

Figure 2 schematically shows a gear system according to an example;

Figure 3 schematically shows a pedal cycle according to an example;

Figure 4 schematically shows a user interface according to an example. Detailed description

The present disclosure relates to a gear system for a pedal cycle. The gear system incorporates a control arrangement for controlling a gear ratio of the gear system. The gear system may be arranged to provide a continuously variable transmission. In examples, the gear system is arranged to be retrofitted to an existing pedal cycle, so that an existing pedal cycle can be converted from a traditional, derailleur gear type bicycle to a CVT pedal cycle quickly and easily. The described gear system has utility for commuters who value a range of gears and smooth cycling, for mountain bikers who require particularly low gear ratios for climbing steep hills, and racing cyclists who require high gear ratios for high speed cycling and sprinting.

Figures 1 and 2 schematically show a side view of a gear system 100. The gear system 100 is arranged to be fitted to a pedal cycle 150 (see Figure 3). In the example of Figure 1 , the gear system 100 is arranged to be mounted to a rear wheel hub 152 of pedal cycle 150. In the example of Figure 2, the gear system 100 is arranged to be mounted to a bottom bracket 156 of pedal cycle 150. Each of these example embodiments will be discussed in turn in more detail below.

With reference to Figure 1 , the gear system 100 comprises an epicyclic gear set 102, which is schematically shown in cross-section. The epicyclic gear set 102 comprises a sun gear 104, and one or more planet gears. In the example of Figure 1 , two planet gears 106 and 108 are shown. In some examples, more planet gears are provided. For example, four planet gears may be provided. The planet gears 106 and 108 are arranged to mesh with the sun gear 104. The planet gears 106 and 108 are connected to a planet carrier 110. A ring gear 112 encircles the planet gears 106 and 108 and the sun gear 104. In the example of Figure 1 , the planet carrier 110 comprises a sprocket or gear. In other words, it may be considered that a sprocket is provided which acts as planet carrier 110. The planet carrier 110 carries a chain 116 (see also Figure 3). Accordingly, planet carrier 110 is arranged to be rotationally driven by chain 116. It may be considered in some examples that planet carrier 110 is located where a conventional gear cassette would be located in a conventional derailleur system, and in some examples it may also be considered that the planet carrier 110 effectively replaces the conventional cassette. In some examples it may be considered that the planet carrier 110 comprises a single sprocket. The epicyclic gear set comprises a rear face or plate 113. Together, the rear face 113 and carrier 110 form a cage around sun gear 104 and planet gears 106 and 108. In the example of Figure 1 , a shaft 115 passes through planet gear 106, and a shaft 117 passes through planet gear 108. The shafts 115 and 117 also connect planet carrier 110 and rear face 113. Therefore, as planet carrier 110 is caused to rotate by being driven by chain 116, rear face 113 also rotates. This causes planet gears 106 and 108 to travel around the circumference of sun gear 104.

The sun gear 104 comprises a connecting portion 1 18 for connecting the sun gear 104 to a component 122 of the pedal cycle. In some examples, it is considered that the connecting portion 122 projects from the sun gear 104. In some examples the connecting portion 118 comprises a sleeve. In some examples the connecting portion

118 comprises a shaft. In the example of Figure 1 , the planet carrier 110 and the rear face 113 comprise a central hole shown schematically at 119. The hole 119 enables the epicyclic gear set 102 to be fitted on or over component 122. For example, hole

119 enables the epicyclic gear set 102 to be slotted on or over a rear wheel hub 152 of the pedal cycle.

In one example, the connecting portion 118 is splined and is arranged to cooperate with corresponding splines of a wheel hub 152 (e.g. rear wheel hub) of the pedal cycle 150. Since different derailleur gear manufacturers have different size and I or spline patterns, a suitable connecting portion 118 may be provided for each of the different size and I or spline patterns. Thus, in some examples the sun gear 104 (via its connecting portionl 18) is arranged to provide drive to a wheel of a pedal cycle. In such examples, it may be considered that the output of the gear system 100 is at the sun gear 104. In such examples, belt or chain 116 is driven in a conventional manner off a front chainring 155, which chainring is driven by rotation of pedals 154. In such an example the path of drive is: rotation of pedals 154 causes rotation of chainring 155 which causes drive of chain or belt 116. Drive of chain or belt 116 causes rotation of planet carrier (sprocket) 110. This causes the planet gears to travel around the circumference of sun gear 104, whilst also driving rotation of sun gear 104. Rotation of sun gear 104 causes rotation of connecting portion 118, and consequently rotation of component 122 e.g. wheel hub 152. In some examples, a 12 tooth sprocket is used as the sun gear and slid on to a splined hub of the pedal cycle. In some examples a conventional chainring of 52 teeth is used as the ring gear, giving a top gear ratio of (52+12)/12 i.e. 5.3:1. The epicyclic gear equation then yields the answer of a 20-tooth planet gear. The present disclosure further considers making a circular chain. By breaking down a bicycle chain into its constituent parts e.g. pins, rollers and links, the links are replaced with two discs into each of which are drilled a plurality of equally spaced holes (e.g. 20 holes) on a PCD (e.g. an 81 .18 mm PCD). Then the two discs are joined together, with the pins carrying the rollers. Therefore in some examples the roller gear may be the planet gear. Then, 2 or 3 planet gears may be mounted onto a planet carrier (plus the input driver sprocket) and laid on the 52 tooth chainring (i.e. the ring gear). This presents teeth of the ring gear facing outwards and the rollers of the planet gear also facing outwards. Therefore, in some examples a conversion gear is provided. Taking a 12 tooth standard sprocket to mesh with the planet gear, a 12 tooth roller gear is provided to mesh with the ring gear. These two gears, sprocket and roller are mounted onto the same shaft and locked to the shaft. Each planet gear now has a conversion gear mounted with it on the planet carrier. With the ring gear locked, the planet gears move around the ring gear and in doing so rotate the sun gear (52+12)/12 (5.3:1 ) times per revolution. In examples, to control the ring gear a worm wheel is attached to it as described with reference to Figure 1 , with a difference that the conversion gear now acts as an idler gear and changes the direction of rotation.

A second example embodiment will now be described with reference to Figure 2, where components equivalent to those of Figure 1 share like reference numerals.

In the example of Figure 2, the connecting portion 118 is arranged to locate in a bottom bracket 156 of the pedal cycle 150 (see Figure 3). Again, different connecting portion sizes and/or patterns may be provided for different bottom bracket sizes and/or patterns. In the example of Figure 2, pedal crank 153 is fixed to planet carrier 110. Rotation of pedal crank 153 via pedals 154 causes corresponding rotation of planet carrier 110, and ultimately rotation of sun gear 104 and connecting portion 118 via epicyclic gear set 102. In some examples, pedal cranks 153 are connected directly to planet carrier 110. In such an example, a conventional fixed gear may be provided on the rear wheel of the pedal cycle 150. In some examples, a single gear is provided at the rear wheel of the bicycle, since the continuously variable gear ratios are provided by the gear system 100. In some examples, the sun gear 104 carries a freewheel mechanism. Then, the gear 151 attached to the rear wheel-hub can be a fixed gear, because the freewheel is provided at the bottom bracket 156. For example, the gear 151 on the rear wheel-hub can be a 12-tooth sprocket. This is a relatively small gear and has little rolling weight.

In the example of Figure 2, a sprocket 121 is fixed to rotate with connecting portion 118. Therefore, as pedal cranks 153 rotate this causes corresponding rotation of sprocket 121 via connecting portion 118. Drive is then carried to rear wheel via chain 116.

It will be noted that in examples there is no need for multiple chainrings on the bottom bracket 156, or a multi-gear cassette on the rear wheel hub 152. For example, in the embodiment of Figure 1 the planet carrier 110 may comprise a single sprocket connected to a single chainring on the bottom bracket via chain 116. In the embodiment of Figure 2, a single sprocket 121 on the bottom bracket 156 may be connected to a single sprocket on the rear wheel hub 152 via chain 116. Therefore, the chain or belt 116 can always run straight, not skewed as with derailleur gears. Benefits of the chain or belt 116 running straight include less power loss, less wear and more efficient transmission. The manner in which the continuously variable gearing is provided will be discussed in more detail below.

In examples the gear system 100 comprises a control arrangement for controlling speed of rotation of ring gear 112. A gear ratio of the gear system 100 between input and output (e.g. between planet carrier 110 and sun gear 104) can be controlled at least in part by controlling speed of rotation of the ring gear 112. For example controlling speed of rotation of the ring gear 112 enables a continuously variable transmission to be realised. To this end the control arrangement may be termed a speed controller. As will be explained in more detail below, the control arrangement may be powered by an electric motor. The control arrangement may therefore be termed an electric speed controller.

A first example of a control arrangement is shown at 101 . Control arrangement 101 comprises an electric motor 120. The electric motor is arranged to control a speed of rotation of the ring gear 112. In some examples the electric motor 120 is configured to enable one or more of: rotation of the ring gear forwards (a clockwise direction when viewing Figure 3); rotation of the ring gear backwards (an anti-clockwise direction when viewing Figure 3); holding of the ring gear stationary. In some examples, when the ring gear 112 is held stationary the gear system 100 is in “top gear”. But, in at least some examples, the intention is to rotate the ring gear 112 to produce different gear ratios.

When the ring gear 112 is locked stationary (e.g. by the electric motor 120 providing a counter force) then input on the planet carrier 110 (such as pedal input) has something to react against in driving the sun gear 104. Once this “lock” is removed and replaced by driving of electric motor 120 to rotate the ring gear 112, it will be up to the electric motor 120 to provide the reaction between planet carrier 110 input and the sun gear 104 output. Therefore, the present inventor has identified that a one-way transmission system is needed at this point.

According to some examples, the gear system 100 comprises a one-way transmission 126. The one-way transmission 126 enables one-way drive from the electric motor 120 to the ring gear 112. That is, rotation of electric motor 120 provides drive to the ring gear 112, but the ring gear 112 cannot “drive” the electric motor 120. In examples, the one-way transmission 126 comprises a worm drive 130. In examples, the worm drive 130 comprises a worm gear or worm screw 132 which meshes with ring gear 112. A shaft 131 of the electric motor 120 drives the worm gear 132. It will be understood that in some examples the function of the electric motor 120 is to overcome the friction of the worm gear, and to control the speed that the ring gear 112 rotates. That is in examples the primary function of the electric motor 120 is not to provide assisted drive to the pedal cycle. In examples, the electric motor 120 operates to counter a rotational motion of the ring gear 112 that is imparted by the cyclist pedalling. That is the electric motor 120 provides a counter force to the pedal power of the cyclist, to give the cyclist’s pedalling motion a force to react against. Without the control arrangement the ring gear 112 would be free to rotate more quickly, but without providing a reactive pedalling force (akin to a “neutral” gear). Therefore it may be considered that the control arrangement is arranged to cause controlled rotation of ring gear 112. In some examples, “controlled rotation” includes holding the ring gear 112 stationary. In examples, the gear system comprises a controller 134. For example, the controller 134 may comprise a microcontroller or microprocessor. In some examples, the controller 134 comprises a memory 136 and a processor 138. The controller 134 is configured to control the electric motor 120. For example, the controller 134 is configured to control a speed and/or direction of rotation of electric motor 120.

In some examples, the controller increases the speed of rotation of the ring gear 112 (by increasing the speed of the electric motor 120) to lower the gear ratio. Conversely, reducing the speed of rotation of the ring gear 112 increases the gear ratio.

In some examples, a conventional lever (for example located on the bicycle’s handlebars 170) could be used to adjust the speed of the electric motor 120 to increase or decrease the gear ratio.

A second example of the control arrangement is shown at 103. The control arrangement 103 may be considered to comprise an escapement mechanism. The control arrangement 103 comprises a disc 182. In some examples the disc 182 comprises a clearance hole 183, similar to clearance hole 119 of planet carrier 110. Although not shown in Figure 1 , the disc 182 is attached to the ring gear 112. That is, control of rotation of disc 182 controls rotation of ring gear 112.

In examples, the disc 182 has holes equally spaced around its periphery. For example there may be twenty holes. In some examples the holes are 10mm in diameter with a ‘land’ of 3mm between holes.

A solenoid 184 is attached to the pedal cycle frame and mounted perpendicular to the disc 183, and an armature of the solenoid 184 is used to ‘rock’ an escapement mechanism, as follows.

The solenoid 184 is energised and the armature ‘rocks’ the escapement such that a holding peg 186 withdraws from one of the holes in the disc 182, then the peg 186 enters the next hole, the disc 182 rotates one half pitch, the solenoid 184 returns pulling out the free peg 186 and re-inserting the peg 186 in the next hole to arrive and so on. This has a result that one whole pitch of rotation has been allowed.

Thus, the speed of rotation of the ring gear 112 is controlled by controlling rotation of the disc 182. Therefore the gear ratio is controlled by the rate at which the solenoid is energised. In some examples energising the solenoid would be from 2 to 60 cycles per second, or faster if more holes in the disc were used.

It will be appreciated that the control arrangement 103 (e.g. escapement mechanism) does not and cannot ‘drive’ the ring gear 112. Rather, the control arrangement controls the tendency of the ring gear to rotate freely once it has been unlocked.

A controller (e.g. controller 134) may control the solenoid 184.

It will be appreciated that the control arrangement 103 may also be incorporated in the example gear system of Figure 2.

It will therefore be appreciated that the function of the control arrangement 101 , 103 is to control the gear ratio of the gear system, rather than to provide pedal assistance to the pedal cycle.

In some examples, buttons may be provided to enable the gear ratio to be adjusted. An example “dashboard” or user interface 172 is shown in Figure 3. The user interface 172 may, for example, be attached to handlebars 170 of the pedal cycle 150. In this example the user interface 172 comprises an “up” button 174 for increasing the gear ratio and a “down” button 176 for decreasing the gear ratio.

In some examples, one or more settings or modes of the gear system 100 are provided. In some examples these modes may be accessed via user interface 172. For example, a sprint mode may be invoked by pressing “SPRINT” button 178 on user interface 172. In some examples, prior to sprint mode, the control arrangement 101 , 103 is enabling the ring gear 112 to rotate forward at a certain speed. When sprint mode is invoked the control arrangement 101 , 103 will immediately stop, consequently locking the ring gear 112, instantly or near-instantly putting the pedal cycle 150 into what would traditionally be called top gear. . For example, gear ratios of 3:1 or above or 5:1 or above may be provided. This is particularly useful for professional cyclists who require short, sudden sprint bursts. The gear system is also able to provide such high gear ratios in a compact manner, because large chainrings often seen on track bikes and the like are not required.

Conversely, the gear system 100 can provide gear ratios lower than 1 :1. For example, gear ratios of 1 :0.8 or lower or 1 :0.6 or lower may be provided. In examples, such low gear ratios are provided by increasing the speed of the electric motor 120, and consequently the ring gear 112, in the forward direction. Such low gear ratios may be useful, for example, for mountain bikers facing tough climbs, or indeed road cyclists facing particularly steep inclines. In some examples, the low gear ratio mode may be invoked immediately or nearly immediately by pressing “LOW’ button 180 on user interface 172.

As briefly mentioned above, in at least some examples the gear ratio comprises a ratio between input at the planet carrier 110 and output at sun gear 104. In some examples, it may be considered that the planet carrier 110 rotates with the pedal cranks and the sun gear 104 rotates with the rear wheel of the pedal cycle.

In some examples, the gear system 100 comprises a battery 142. The battery 142 stores electrical energy for powering the control arrangement 101 , 103. In some examples the battery 142 comprises a rechargeable battery. In some examples, an electricity generator 140 such as a dynamo is also provided for charging the battery 142. For example, the electricity generator 140 may be driven by one of the wheels of the pedal cycle 150. For example, the electricity generator 140 may be driven by a front wheel of the pedal cycle. In some examples, the electricity generator 140 may be arranged to power a speedometer. In some examples, the electricity generator 140 comprises a brushless, ironless generator. Such a generator has high generating efficiency (90% +), and very low, no load torque. Such a generator makes it suitable for cyclists who otherwise may not wish to carry the weight and resistance of traditional dynamos.

In some examples, no electricity generator is provided and the battery 142 may either be simply replaced by a new battery whenever it is depleted, or the battery 142 can be recharged by plugging in to a suitable charging socket.

In some examples, the gear system 100 comprises a pitch sensor 144. The pitch sensor 144 is in communication with controller 134. The pitch sensor 144 may comprise one or more accelerometers or the like. The pitch sensor 144 can sense whether the pedal cycle 150 is going uphill, downhill, or is on flat terrain. According to some examples, the controller 134 is configured to cause the electricity generator 140 to generate electricity only when it is detected that the pedal cycle 150 is travelling downhill. In some examples, the battery 142 and gear system 150 can be used to not only perform the function of providing a CVT, but additionally or alternatively for turning the pedal cycle 150 into an automatically geared pedal cycle 150. For example, the gear system 150 and battery 142 can be arranged to provide automatically the right gear to maintain the desired cadence (pedalling rhythm) whenever required. For example, an “AUTO” button 181 could be provided on user interface 172 to place the pedal cycle into an automatically geared pedal cycle. For example, the controller 134 may be arranged to control the control arrangement 101 , 103 (e.g. control speed of electric motor 120, control firing of solenoid 184) to maintain the cadence detected at the time the AUTO button 181 was pressed. To this end, a sensor may be provided for detecting speed of rotation of pedal cranks 153. For example, the sensor could comprise a rotary encoder or an optical sensor. Alternatively, a user could specify a desired cadence via user interface 172. Whichever way the desired or target cadence is set, in AUTO mode the controller 134 then monitors the actual cadence and adjusts the gear ratio to bring the actual cadence back towards the target cadence. Say for example the target cadence is 60 revolutions per minute (RPM). As the cyclist becomes tired, the actual cadence may start to drop below 60 RPM, in which case the controller may act to speed up the electric motor 120 so that the gear ratio drops, thus reducing pedalling resistance to the cyclist and bringing the cadence back up to the target of 60 RPM. Likewise, if the cyclist starts pedalling too quickly, the controller 134 may cause the gear ratio to increase, so as to increase pedalling resistance and bring the cadence back towards the target of 60 RPM. Maintaining constant cadence is a valuable skill for efficient cycling. Not only can the AUTO function be used for the purposes of providing efficient cycling through constant cadence, but can also be used as a training tool for teaching more serious cyclists the “feel” of constant cadence cycling.

Another occasion where a sprint may be required is in a race on a climb where a rider may wish to break away from the peloton. However, on a climb going into top gear would not be a good idea. Therefore a “break” mode may also be provided, which when invoked would start to increase the gear to match the increased power being unleashed by the rider. Subsequently, to return from “sprint” or “break” the rider may invoke the “auto” mode or a “manual” mode. In some examples the manual mode returns the rider back to the gear status prior to the sprint or break functions being activated.

Therefore, in examples there may be provided one or more of the following rider-selectable functions:

1 . Manual

2. Up

3. Down

4. Auto

5. Break

6. Sprint

In some examples the controller 134 is configured to process voice commands. That is, a rider could invoke one or more of the functions above by voice control. The words ‘Up’, ‘Down’, ‘Sprint’, and ‘Auto’ could directly invoke those features. But since the rider may programme the controller to match his/her voice, then code words could be used, such as ‘Bill’, ‘Tom’, ‘Ken’ and ‘Dave’ (by way of non-limiting example) to invoke the desired feature. This may assist a rider in making surprise moves against opponents.

A worked example will now be described where a 12t sprocket (where t = tooth) acts as the sun gear of an epicyclic gear set which has been slid onto the cassette hub of a rear wheel of a bicycle to replace an existing sprocket cassette.

A 52t chainring is used as a ring gear. In this example the planet gears are 20t to mesh correctly with sun and ring gears. The planet gears are roller gears as previously described, mounted on a 24t sprocket gear as planet carrier.

The chainring at the bottom bracket is connected to the pedals and driving the 24t sprocket of the planet carrier. In this example this is a 24t chainring giving a 1 :1 gear ratio to start with.

With the ring gear locked top gear will be the result of the sun and ring gear and the described method of use. That is with planet gear input (from planet carrier), sun gear output and ring gear locked. Top gear will thus be (52t +12t)/12t, i.e. 5.3:1 . Then the ring gear is unlocked. With nothing to restrain it, the ring gear will be carried around by the planet gears as they react against the sun gear which will be no longer rotating.

With the sun gear, and therefore the pedal cycle, stationary but the cyclist still pedalling, the gear ratio at this point will be 0:1 and the speed of the ring gear will be given by (52t+12t)/52t or 1 .23 times the cadence, input pedalling rate.

So in this case a continuously variable gear from top gear 5.3:1 down to 0:1 is offered.

With regard to the chainring at the bottom bracket which is 24t, if that is now made a 48t chainring driving the 24t planet carrier sprocket we will be starting with an initial 2:1 step up. Top gear will then be 5.3 times 2, i.e. 10.6:1 but still going down to a bottom gear of 0:1 .

The next step as previously described is restraining the ring gear and controlling its rotational speed. As already stated, in examples the mechanism for controlling the speed of the ring gear comprises a one-way transmission system. This gives the planet gears something to react against to drive the sun gear.

As described above, a low powered electric motor controlling the speed of the ring gear through a worm drive can be used, or an escapement mechanism can be used.

In practice, the gear system 100 offers 100% non-slip, non-jam positive transmission, with no or negligible power loss. This contrasts with conventional derailleur gear systems where for every gear change that is made the chain is no longer transmitting power, no matter how brief, with the ever-present possibility of slipping and jamming.

In some examples the gear system 100 may be incorporated inside a rear wheel hub. Power to the electric speed controller may be provided to the gear system via a hollow rear axle.

As also described (e.g. with respect to Figure 2), the gear system 100 may be incorporated within the bottom bracket, with the rear wheel being driven via a chain connected to, for example, a 12 tooth sprocket at the rear wheel. It will be understood that the present disclosure pertains not only to the gear system 100 itself, but also to a pedal cycle 150 incorporating such a gear system. In some examples the pedal cycle comprises a bicycle.

In some examples, the gear system 100 may be retrofitted to an existing pedal cycle. For example, the gear system 100 may be retrofitted to a conventional derailleur geared bicycle. The method of retrofitting may comprise removing at least part of an existing gear system of the pedal cycle and replacing with the novel gear system 100. For example, the retrofitting may include removal of an existing rear cassette of a bicycle, with the connecting portion 118 of the gear system then slid into the rearwheel hub instead. Alternatively, where the gear system is bottom-bracket mounted, this may require removal of existing front chainring and pedal cranks, retrofitting of the gear system 150 to the bottom bracket (for example sliding connecting portion 118 into the bottom bracket), and then re-fitting of the pedal cranks (for example to the planet carrier 110). The chain or belt 116 will also need removal and re-fitting. Specialist skills are not required for the retrofitting, and a detailed instruction manual will be provided with the gear system 100. The required skills will be within those of a hobby cyclist who is accustomed to changing wheels, tyres, inner tubes, pedals etc. The skills required will certainly be within those of any bike mechanic, and the retrofitting will take minimal labour time. For example, a proficient bike mechanic should be able to perform the retrofitting within half an hour or so.

It will of course be understood that the gear system 150 can also be directly attached to a pedal cycle frame before any other gear system has been put in place, and thus no retrofitting is required.

It will be understood that the description is given by way of example only to assist in understanding the invention and is not intended to limit the scope of the invention defined in the appended claims.

Claims

1 . A gear system for a pedal cycle comprising: an epicyclic gear set having a sun gear, one or more planet gears meshed with the sun gear, and a ring gear meshed with the one or more planet gears; each of the planet gears connected to a planet carrier; the sun gear having a connecting portion for connecting to a component of the pedal cycle; the gear system comprising a control arrangement that is arranged to control a speed of rotation of the ring gear, so as to provide a variable gear ratio to the gear system.

2. A gear system according to claim 1 , wherein the control arrangement is arranged to restrain rotation of the ring gear.

3. A gear system according to claim 1 or claim 2, wherein the control arrangement comprises an electric motor for controlling the speed of rotation of the ring gear.

4. A gear system according to claim 3, the control arrangement comprising a oneway transmission between the electric motor and the ring gear.

5. A gear system according to claim 1 or claim 2, wherein the control arrangement comprises an escapement mechanism for controlling the speed of rotation of the ring gear.

6. A gear system according to claim 5, comprising a solenoid that is arranged to control the escapement mechanism.

7. A gear system according to claim 6, the control arrangement comprising a disc connected to the ring gear, the disc having a plurality of holes around a periphery of the disc, a peg of the solenoid arranged to selectively engage with the holes of the disc to control rotation of the disc and to consequently control rotation of the ring gear.

8. A gear system according to claim 1 , wherein pedal input is provided to the gear system via the planet carrier, and output from the gear system is via the sun gear.

9. The gear system according to any of claims 1 to 8, wherein the connecting portion of the sun gear is constructed and arranged to engage with and provide drive to a wheel-hub, and the planet carrier comprises a sprocket arranged to be driven by a belt or chain.

10. The gear system according to any of claims 1 to 8, wherein the planet carrier is constructed and arranged to be connected to a pedal crank of the pedal cycle, and a sprocket being located on the connecting portion of the sun gear, the sprocket arranged to provide drive to a belt or chain.

11. The gear system according to any of claims 1 to 10, wherein the control arrangement is configured to selectively enable any one of: restrained rotation of the ring gear in a forward direction; locking of the ring gear.

12. The gear system according to claim 11 , the control arrangement having a sprint setting, wherein when the sprint setting is invoked the ring gear is locked.

13. The gear system according to any of claims 1 to 12, wherein the control arrangement is configured to control rotation of the ring gear at a speed that provides a gear ratio of 3:1 or higher.

14. The gear system according to any of claims 1 to 13, wherein the control arrangement is configured to control rotation of the ring gear at a speed that provides a gear ratio lower than 1 :1.

15. The gear system according to any of claims 1 to 14, comprising an electricity generator for recharging a battery of the control arrangement.

16. The gear system according to claim 15, wherein the electricity generator comprises a brushless, ironless generator.

17. The gear system according to claim 15 or claim 16, wherein the gear system comprise a pitch sensor for sensing whether the pedal cycle is going uphill, downhill or is on flat terrain, the electricity generator configured to generate electricity only when it is detected that the pedal cycle is travelling downhill.

18. The gear system according to any of claims 1 to 17, wherein the gear system comprises an automatic gear mode and when in the automatic gear mode the control arrangement is configured to control the speed of rotation of the ring gear so as to cause a constant or near-constant pedalling cadence of the pedal cycle.

19. The gear system according to any of claims 1 to 18, wherein the gear system is configured to be retrofitted to the pedal cycle.

20. A pedal cycle comprising the gear system according to any of claims 1 to 19.

21 . The pedal cycle of claim 20, comprising a bicycle.

22. A method comprising removing at least part of an existing gear system of a bicycle and retrofitting the gear system of any of claims 1 to 19 to the bicycle.