Patent Description:
Prior art patent document published <CIT>, which shows the preamble of claim <NUM>, discloses a drive assembly for bicycle, configured to be mounted on the bicycle frame and supporting the pedal arms. The drive assembly comprises a central input shaft supporting the pedal arms, a coaxial output shaft supporting a chain sprocket. The power transmission between the input shaft and the output shaft comprises a series of planetary gear units operatively connected to each other and whose ring gear, planetary gear carrier or sun gear can be selectively stopped by frictional braking units, so as to provide different transmission ratios. The use of frictional braking units is advantageous for smooth speed shifting, however lowers the mechanical efficiency of the transmission due to the frictional losses during shifting and the energy required for operating the shifting. The drive assembly also comprises an electric motor that is operatively permanently coupled to the input shaft, which is not favourable when using the drive assembly without power input of the electric motor. Also, the electric motor is positioned radially laterally relative to the central input and output shafts and operatively coupled to the power transmission via a reducing gearing. This increases the volume of the drive system and potentially raises the gravity centre of the bicycle.

Prior art patent document published <CIT> discloses a drive assembly for bicycles, configured to be mounted on the bicycle frame and supporting pedal arms. The drive assembly comprises a central input shaft supporting the pedal arms, a coaxial output shaft supporting a chain sprocket. The power transmission between the input shaft and the output shaft comprises a series of planetary gear units operatively connected to each other. The central input shaft comprises ratchet pawls pivotally mounted in recesses formed in the central input shaft. A tubular transmission shaft extends around the central input shaft and comprises pawl operation holes which allow, by rotation of the transmission shaft to selectively activate torque transmission to a specific sun gear while disactivate torque transmission to the other sun gears and thereby achieved different gear ratios. This construction has for advantage to be very compact; however, it has for disadvantage that gear shifting under load is difficult.

Also, it does not provide any input from an auxiliary electric motor.

The invention has for technical problem to overcome at least one drawback of the above-mentioned prior art. More specifically, the invention has for technical problem to provide a transmission unit for a vehicle equipped with propulsion pedals, like a bicycle, that is compact, has a high number of gear ratios, has a large transmission range, couples to an electric motor and provides a smooth great shifting under load.

The invention is directed to transmission unit for a vehicle equipped with propulsion pedals, comprising: a central shaft with two opposite ends configured, each, for supporting a pedal crank; a transmission output shaft coaxial with the central shaft and configured for outputting mechanical power; a planetary gear unit carried by the central shaft and configured for transmitting mechanical power from an input shaft of said planetary gear unit to the transmission output shaft, according to several selectable transmission ratios; an electric motor unit operatively coupled to the planetary gear unit in order to transmit mechanical power to the transmission output shaft; a housing carrying the central shaft, the transmission output shaft and the planetary gear unit; wherein the electric motor unit is coaxial with the central shaft and comprises an output shaft fixedly coupled to the input shaft of the planetary gear unit, and the central shaft is coupled to said output shaft of the electric motor and said input shaft of the planetary gear unit by a freewheel.

According to a preferred embodiment, the electric motor unit comprises an electric motor coaxial with the central shaft, and a planetary gear reduction unit coaxial with the central shaft and coupled to said electric motor.

According to a preferred embodiment, the planetary gear reduction unit comprises: a first planetary gear set with a sun gear coupled to the electric motor, a fixed ring gear, and a planetary gear carrier; a second planetary gear set with a sun gear fixedly coupled to the planetary gear carrier of the first planetary gear set, a fixed ring gear, and a planetary gear carrier coupled to the output shaft of the electric motor unit.

According to a preferred embodiment, the planetary gear reduction unit further comprises: a third planetary gear set with a sun gear fixedly coupled to the planetary gear carrier of the second planetary gear set, a fixed ring gear, and a planetary gear carrier fixedly coupled to the output shaft of the electric motor unit.

According to a preferred embodiment, the electric motor unit is located on an end portion of the central shaft.

Advantageously, the transmission unit comprises an annular cavity surrounding the electric motor and configured for containing a liquid for cooling the electric motor. The cavity can be formed on a portion of the housing that receives a stator of the electric motor. The annular cavity is formed by metallic material that contacts directly the stator of the electric motor.

According to a preferred embodiment, the planetary gear unit comprises a double planetary gear set comprising a ring gear, a first sun gear, first planetary gears meshing with the first sun gear and with the ring gear, a second sun gear, second planetary gears meshing with the second sun gear and with the ring gear, a carrier of the first and second planetary gears, a carrier brake and a ring gear brake, the first sun gear being formed on the input shaft of the planetary gear unit and the second sun gear being formed on an output shaft of the double planetary gear set.

According to a preferred embodiment, the freewheel is a first freewheel, the input shaft of the planetary gear unit being coupled to the output shaft of the double planetary gear set by a second freewheel, in order to bypass said double planetary gear set when the ring gear brake is released and the carrier brake is released.

Advantageously, the electric motor unit is coupled to the input shaft of the planetary gear unit by a freewheel so that rotation of the electric motor drives said input shaft, whereas said input shaft can be driven without driving said electric motor. That freewheel can be provided operatively between the electric motor and the input shaft of the planetary gear unit.

According to a preferred embodiment, the planetary gear unit further comprises an additional double planetary gear set comprising a ring gear, a first sun gear, first planetary gears meshing with the first sun gear and with the ring gear, a second sun gear, second planetary gears meshing with the second sun gear and with the ring gear, a carrier of the first and second planetary gears, a carrier brake and a ring gear brake, the first sun gear being formed on the output shaft of the double planetary gear set and the second sun gear being coupled to the transmission output shaft.

According to a preferred embodiment, the planetary gear unit comprises an output planetary gear set comprising an input shaft, a ring gear, a sun gear formed on the transmission output shaft, planetary gears meshing with the ring gear and the sun gear, a carrier of the planetary gears, fixedly coupled to the input shaft, a ring brake, the input shaft being coupled with the transmission output shaft by a freewheel, so as to by-pass the output planetary gear set when the ring brake is released.

According to a preferred embodiment, the input shaft of the output planetary gear set is the output shaft of the double planetary gear set or, if present, of the additional double planetary gear set.

According to a preferred embodiment, the double planetary gear set and, if present, the additional double planetary gear set provide(s), by selectively activating the carrier brake(s) and ring gear brake(s) of said double planetary gear set and, if present, said additional double planetary gear set, at least three transmission ratios comprising a maximum ratio and a minimum ratio, and the output planetary gear set provides, by selectively activating the ring brake of said output planetary gear set, two range transmission ratios with a difference between said range transmission ratios that is greater than a difference between said at least three transmission ratios.

According to a preferred embodiment, the ring gear brake and the carrier brake or each of the ring gear brakes and carrier brakes is of the dog type.

According to a preferred embodiment, the ring gear brake or each of the ring gear brakes comprises stops distributed along a periphery of the corresponding ring gear and a movable dog configured for selectively engaging in one of the stops for blocking said corresponding ring gear.

According to a preferred embodiment, the movable dog or each of the movable dogs is pivotable and actuatable by a rotatable cam.

According to a preferred embodiment, the movable dog or each of the movable dogs comprises a cam follower and a finger with a tooth extending laterally and configured for engaging the corresponding recess.

According to a preferred embodiment, the finger or each finger is configured so that the corresponding tooth is movable along said finger against an elastic force. That movement is advantageously a translation movement, e. g a sliding movement.

According to a preferred embodiment, the movable dog or each of the movable dogs comprises a bore and the finger or each finger is slidingly received in said bore, said finger carrying the corresponding tooth and delimiting with said bore a chamber containing a medium providing the elastic force.

According to a preferred embodiment, the medium is a spring, a gas, or a liquid in communication with an auxiliary chamber delimited by an elastic element such as a spring-piston assembly.

Advantageously, the communication between the chamber and the auxiliary chamber comprises a check-valve with a flow restriction when the liquid medium flows from the chamber to the auxiliary chamber and without restriction in the opposite direction.

According to a preferred embodiment, the movable dog or each of the movable dogs comprises an engagement controller configured for allowing engagement of the movable dog with the stop or one of the stops only when the movable dog is at a distance from the stop.

According to a preferred embodiment, the engagement controller or each of the engagement controllers comprises a contact member configured for sliding along the periphery of the corresponding ring gear and carrier and pivotally mounted on the movable dog between an extended position preventing engagement and a retracted position allowing engagement, and a spring urging the contact member in the extended position. The contact member is positioned for contacting the periphery of the corresponding ring gear and carrier before, in the sense of rotation of said corresponding ring gear and carrier, a portion of the movable dog engaging with a stop, said portion being for instance the tooth of the finger of the movable dog.

Advantageously, the planetary gear unit and the electric motor unit are concentric with the central axis and supported by the central axis.

The invention is also directed to a vehicle equipped with propulsion pedals and comprising a transmission unit carrying said propulsion pedals and configured for driving at least one wheel of said vehicle upon activation of the pedal; wherein the transmission unit is accord to the invention.

The invention can also be directed to a brake assembly for one or more planetary gear sets, comprising: a body, a pivoting shaft, one or more dog elements pivotally mounted on said pivoting shaft, a cam shaft with one or more cams cooperating with the one or more dog elements, respectively, a shifting unit operatively coupled to the cam shaft for selectively pivoting the one or more dog elements.

Advantageously, each dog element comprises a finger with a tooth extending essentially transversally from the finger, for engaging with a stop at the periphery of a ring or carrier of the one or more planetary gear sets.

Advantageously, for each dog element, the finger is slidably mounted in a bore formed in a body of the dog element, the finger delimiting with the bore a chamber containing a medium providing an elastic force.

Advantageously, the medium is a spring, a gas, or a liquid communication with an auxiliary chamber delimited by an elastic element such as a spring-piston assembly.

The invention is particularly interesting in that it provides a compact transmission unit including an electric motor. The latter is centred on the central shaft and thereby is optimally integrated to the transmission unit.

The planetary gear unit can provide a high number of transmission ratios with a large range while remaining compact. The construction of the double planetary gear set and any additional double planetary gear set is particularly interesting that respect. Also, the planetary gear unit provides a useful range splitter, participating in providing a large transmission range.

The planetary gear reduction unit of the electric motor unit provides a high transmission reduction ratio while remaining compact and fully integrated by being coaxial and lateral with the planetary gear unit.

Also, the different freewheels provides interesting functionalities to the transmission unit.

Further, the brake assembly of the dog type achieves a rapid gear shifting without losses inherent of frictional brake assemblies and very low activation forces compared to frictional brakes.

In the following description, several freewheels are mentioned with reference to the drawings, for instance the freewheels <NUM>, <NUM>, <NUM> and <NUM>, which are represented in [<FIG>] in a schematic way by a diode symbol as in electric wiring plans. This is for the sake of clarity and conciseness. It is to be understood that the direction represented by the arrow corresponds to direction in which the rotational movement is transmitted. The freewheel(s) can be formed by rachet pawls carried by a first rotating element and resiliently urged towards a notched surface of second directly neighbouring rotating element, so that in one rotating direction, the pawls engage with the notches and rotation of the first element is transmitted to the second element, whereas in the opposite rotating direction, the pawls slide on the notches and there is no rotation transmission. Other constructions can be considered.

<FIG> illustrate a transmission unit according to the invention. [<FIG>] is a schematic functional layout whereas [<FIG>] is a sectional view.

The transmission unit <NUM> comprises a central shaft <NUM> with two opposite ends configured, each, for supporting a pedal crank <NUM>, a transmission output shaft <NUM> coaxial with the central shaft <NUM> and configured outputting mechanical power via a chain sprocket <NUM> attached to said transmission output shaft <NUM>. The transmission unit <NUM> further comprises a planetary gear unit <NUM> carried by the central shaft <NUM> and configured for transmitting mechanical power from an input shaft <NUM> of said planetary gear unit <NUM> to the transmission output shaft <NUM>, according to several selectable transmission ratios, and an electric motor unit <NUM> operatively coupled to the planetary gear unit <NUM> in order to transmit mechanical power to the transmission output shaft <NUM>. The transmission unit <NUM> further comprises a housing <NUM> carrying the central shaft <NUM>, the transmission output shaft <NUM>, the planetary gear unit <NUM> and the electric motor unit <NUM>. As this is apparent, the planetary gear unit <NUM> comprises several planetary gear sets, for instance three planetary gear sets <NUM>, <NUM> and <NUM>, arranged operatively one after the other. Each of the planetary gear sets <NUM>, <NUM> and <NUM> comprises one or several brakes of different components of said planetary gear sets, said brakes being carried by the housing <NUM>. The planetary gear sets <NUM> and <NUM> advantageously have the same construction principle, whereas they can have different dimensions, i.e. different teeth modules and/or different numbers of teeth one each gear.

The electric motor unit <NUM> is coaxial with the central shaft and arranged laterally to the planetary gear unit <NUM>. It comprises an output shaft <NUM> fixedly coupled to the input shaft <NUM> of the planetary gear unit <NUM>. The central shaft <NUM> is coupled to the output shaft <NUM> of the electric motor unit <NUM> and the input shaft <NUM> of the planetary gear unit <NUM> by a freewheel <NUM>. This arrangement provides a direct coupling between the electric motor unit <NUM> and the planetary gear unit <NUM> while the coupling of the central shaft <NUM> which is driven by the user allows the output shaft <NUM> of the electric motor unit <NUM> and the input shaft <NUM> of the planetary gear unit <NUM> to rotate at a higher rotational speed than the central shaft <NUM>, by virtue of the freewheel <NUM>.

The electric motor unit <NUM> comprises an electric motor <NUM> which comprises, essentially, a stator <NUM>. <NUM> and a rotor <NUM>. <NUM>, the latter being carried by a shaft rotatably mounted on the central shaft <NUM>. The electric motor unit <NUM> further comprises a planetary gear reduction unit <NUM> coaxial with the central shaft <NUM> and coupled to the electric motor <NUM>. The planetary gear reduction unit <NUM> comprises a first planetary gear set <NUM>. <NUM> with a sun gear <NUM>. <NUM> coupled to the electric motor <NUM> via the shaft carrying the rotor <NUM>. <NUM>, a fixed ring gear <NUM>. <NUM>, and a planetary gear carrier <NUM>. <NUM>; a second planetary gear set <NUM>. <NUM> with a sun gear <NUM>. <NUM> fixedly coupled to the planetary gear carrier <NUM>. <NUM> of the first planetary gear set <NUM>. <NUM>, a fixed ring gear <NUM>. <NUM>, and a planetary gear carrier <NUM>. <NUM>, and a third planetary gear set <NUM>. <NUM> with a sun gear <NUM>. <NUM> fixedly coupled to the planetary gear carrier <NUM>. <NUM> of the second planetary gear set <NUM>. <NUM>, a fixed ring gear <NUM>. <NUM>, and a planetary gear carrier <NUM>. <NUM> fixedly coupled to the output shaft <NUM> of the electric motor unit <NUM>. Advantageously, the fixed ring gears <NUM>. <NUM> and <NUM>. <NUM> of the second and third planetary gear sets <NUM>. <NUM> and <NUM>. <NUM> are common, i.e. form a single ring gear, for constructional simplicity and manufacturing cost reduction.

As illustrated in [<FIG>], the electric motor unit <NUM> can comprise a freewheel such as the freewheel <NUM>, such that rotation of the central shaft <NUM> can drive the transmission output shaft <NUM> without having to drive the electric motor <NUM>, for instance its rotor <NUM>. <NUM> which shows inertia and generates a resisting cogging torque when not supplied with electrical energy. The freewheel <NUM> is for instance provided between the rotor <NUM>. <NUM> and the sun gear <NUM>. <NUM> of the first planetary gear set <NUM>. <NUM>, being however understood that the freewheel could be provided at other places in the planetary gear reduction unit <NUM>.

The above constructions of planetary gear reduction unit <NUM> achieves a high reduction ratio while taking about less than half of the useful length of the central shaft <NUM>, and remaining compact radially, as this more apparent in [<FIG>].

The planetary gear unit <NUM> comprises a first planetary gear set <NUM> being for instance a double planetary gear set comprising a ring gear <NUM>. <NUM>, a first sun gear <NUM>. <NUM>, first planetary gears <NUM>. <NUM> meshing with the first sun gear <NUM>. <NUM> and with the ring gear <NUM>. <NUM>, a second sun gear <NUM>. <NUM>, second planetary gears <NUM>. <NUM> meshing with the second sun gear <NUM>. <NUM> and with the ring gear <NUM>. <NUM>, a carrier <NUM>. <NUM> of the first and second planetary gears <NUM>. <NUM> and <NUM>. <NUM>, a carrier brake <NUM>. <NUM> and a ring gear brake <NUM>. <NUM>, the first sun gear <NUM>. <NUM> being formed on the input shaft <NUM> of the planetary gear unit <NUM> and the second sun gear <NUM>. <NUM> being formed on an output shaft <NUM>. <NUM> of the double planetary gear set <NUM>.

As this is apparent, the input shaft <NUM> of the planetary gear unit <NUM> is coupled to the output shaft <NUM>. <NUM> of the double planetary gear set <NUM> by a freewheel <NUM>, in order to bypass the double planetary gear set <NUM> when both the ring gear brake <NUM>. <NUM> and the carrier brake <NUM>. <NUM> are released.

The planetary gear unit <NUM> can further comprise a second planetary gear set <NUM> being for instance an additional double planetary gear set comprising a ring gear <NUM>. <NUM>, a first sun gear <NUM>. <NUM>, first planetary gears <NUM>. <NUM> meshing with the first sun gear <NUM>. <NUM> and with the ring gear <NUM>. <NUM>, a second sun gear <NUM>. <NUM>, second planetary gears <NUM>. <NUM> meshing with the second sun gear <NUM>. <NUM> and with the ring gear <NUM>. <NUM>, a carrier <NUM>. <NUM> of the first and second planetary gears <NUM>. <NUM> and <NUM>. <NUM>, a carrier brake <NUM>. <NUM> and a ring gear brake <NUM>. <NUM>, the first sun gear <NUM>. <NUM> being formed on the output shaft <NUM>. <NUM> of the double planetary gear set <NUM>. The second sun gear <NUM>. <NUM> is rigidly carried by an output shaft <NUM>. <NUM> of the additional double planetary gear set <NUM>.

In the above additional double planetary gear set <NUM>, it is possible to provide a freewheel (not represented) between the first sun gear <NUM>. <NUM> and the second sun gear <NUM>. <NUM>, similarly the freewheel <NUM> of the double planetary gear set <NUM>. This provides at least one additional speed or gear ratio, for instance when each of the carrier brake <NUM>. <NUM> and the ring brake <NUM>. <NUM> are not activated.

The planetary gear unit <NUM> further comprises a third planetary gear set <NUM> being for instance an output planetary gear set comprising a ring gear <NUM>. <NUM>, a sun gear <NUM>. <NUM> formed on the transmission output shaft <NUM>, planetary gears <NUM>. <NUM> meshing with the ring gear <NUM>. <NUM> and the sun gear <NUM>. <NUM>, a carrier <NUM>. <NUM> of the planetary gears <NUM>. <NUM>, fixedly coupled to the output shaft <NUM>. <NUM> of the additional double planetary gear set <NUM>, a ring brake <NUM>. <NUM>, the output shaft <NUM>. <NUM> being coupled with the transmission output shaft <NUM> by a freewheel <NUM>, so as to by-pass the output planetary gear set <NUM> when the ring brake <NUM>. <NUM> is released.

The above-described planetary gear unit <NUM> provides <NUM> different gear ratios that will be detailed here after in connection with the below table <NUM>. In that table, the sign # corresponds to the different gear or speed number, whose transmission ratio progressively diminishes with the speed number. In other words, the speed number #<NUM> is for starting the vehicle or bicycle at low speed whereas the speed number #<NUM> is for driving or riding at maximum speed. The symbol "x" means that the brake or freewheel is activated, being understood that for the brake the activation is active whereas for the freewheel it is passive, i.e. results of the activation and non-activation of the brakes.

In the speed number #<NUM>, none of the brakes of the <NUM>st planetary gear set <NUM> is activated, meaning that the freewheel <NUM> is active. The power is then transmitted directly, i.e. without any change of rotational speed, from the input shaft <NUM> of the transmission unit <NUM> to the output shaft <NUM>. <NUM> of the <NUM>st planetary gear set <NUM>. In the <NUM> nd planetary gear set <NUM>, the brake <NUM>. <NUM> of the ring gear <NUM>. <NUM> is activated, meaning that the power is transmitted through rotation of the planetary gears <NUM>. <NUM> and <NUM>. <NUM> and of their carrier <NUM>. <NUM>, from the first sun gear <NUM>. <NUM> to the second sun gear <NUM>. <NUM> rigidly carried by the output shaft <NUM>. <NUM> of the <NUM>nd planetary gear set <NUM>. In the <NUM>rd planetary gear set <NUM>, the brake <NUM>. <NUM> of the ring gear <NUM>. <NUM> is deactivated, meaning that the power is transmitted through the freewheel <NUM> to the output shaft <NUM>.

In the speed number #<NUM>, the configuration of the <NUM>nd planetary gear set <NUM> is changed by deactivating the brake <NUM>. <NUM> of the ring gear <NUM>. <NUM> and activating the brake <NUM>. <NUM> of planetary gears carrier <NUM>. The power is therefore transmitted from the first sun gear <NUM>. <NUM> to the second sun gear <NUM>. <NUM> via the planetary gears <NUM>. <NUM> and <NUM>. <NUM> free to rotate while their carrier <NUM>. <NUM> is blocked.

In the speed number #<NUM>, the <NUM>nd planetary gear set <NUM> and <NUM>rd planetary gear set <NUM> are as in the speed number #<NUM>, whereas in the <NUM>st planetary gear set <NUM>, the brake <NUM>. <NUM> of ring gear <NUM>. <NUM> is activated, meaning that the power is transmitted through rotation of the planetary gears <NUM>. <NUM> and <NUM>. <NUM> and of their carrier <NUM>. <NUM>, from the first sun gear <NUM>. <NUM> to the second sun gear <NUM>. <NUM> rigidly carried by the output shaft <NUM>. <NUM> of the <NUM>st planetary gear set <NUM>.

In the speed number #<NUM>, compared with the speed number #<NUM>, the configuration of the <NUM>nd planetary gear set <NUM> is changed by deactivating the brake <NUM>. <NUM> of the ring gear <NUM>. <NUM> and activating the brake <NUM>. <NUM> of planetary gears carrier <NUM>. <NUM>, similarly to the speed number #<NUM>.

In the speed number #<NUM>, compared with the speed number #<NUM>, the configuration of the <NUM>st planetary gear set <NUM> is changed by deactivating the brake <NUM>. <NUM> of the ring gear <NUM>. <NUM> and activating the brake <NUM>. <NUM> of planetary gears carrier <NUM>. <NUM>, meaning that the power is transmitted from the first sun gear <NUM>. <NUM> to the second sun gear <NUM>. <NUM> via the planetary gears <NUM>. <NUM> and <NUM>. <NUM> free to rotate while their carrier <NUM>. <NUM> is blocked.

In the speed number #<NUM>, compared with the speed number #<NUM>, on the <NUM>rd planetary gear set <NUM>, the brake <NUM>. <NUM> of the ring gear <NUM>. <NUM> is activated, meaning that the power is transmitted through rotation of carrier <NUM>. <NUM> and the planetary gears <NUM>. <NUM> to the sun gear <NUM>. <NUM> rigidly carried by the transmission output shaft <NUM>.

The speed number #<NUM> is similar to the speed number #<NUM> while the <NUM>rd planetary gear set <NUM> is as in the speed number #<NUM>.

The speed number #<NUM> is similar to the speed number #<NUM> while the <NUM>rd planetary gear set <NUM> is as in the speed numbers #<NUM> and #<NUM>.

The speed number #<NUM> is similar to the speed number #<NUM> while the <NUM>rd planetary gear set <NUM> is as in the speed numbers #<NUM>, #<NUM> and #<NUM>.

The speed number #<NUM> is similar to the speed number #<NUM> while the <NUM>rd planetary gear set <NUM> is as in the speed numbers #<NUM>, #<NUM>, #<NUM> and #<NUM>.

In the case of the presence an additional freewheel (not represented) between the first sun gear <NUM>. <NUM> and the second sun gear <NUM>. <NUM>, an additional speed is obtained where none of the ring and carrier brakes is activated, meaning that the freewheels <NUM> and <NUM> are activated and the additional one mentioned here above also, corresponding to the <NUM>:<NUM> transmission ratio between the central shaft <NUM> and the transmission output shaft <NUM>. With reference to the above table <NUM>, that additional speed could be named speed number #<NUM>.

As this more visible in [<FIG>], the brakes, i.e. the carrier brake <NUM>. <NUM> and ring brake <NUM>. <NUM> of the <NUM>st planetary gear set <NUM>, the carrier brake <NUM>. <NUM> and the ring brake <NUM>. <NUM> of the <NUM>nd planetary gear set <NUM>, and the ring brake <NUM>. <NUM> of the <NUM>rd planetary gear set <NUM> are advantageously of the dog type, i.e. with a movable dog configured for selectively engaging with a stop formed on an external surface of the carrier or ring to be braked. That type of brake has the advantage to avoid frictional movements between the carrier or ring to be braked and the movable element of the brake interacting with said carrier or ring.

All brakes <NUM>. <NUM>, <NUM>. <NUM>, <NUM>. <NUM>, <NUM>. <NUM> and <NUM>. <NUM> are for instance formed by a brake assembly <NUM> attached to the housing <NUM> of the transmission unit <NUM>.

Still in [<FIG>], we can observe that the housing <NUM> houses the electric motor, for instance the stator <NUM>. <NUM> thereof and that a cavity <NUM> is formed with the housing around the stator <NUM>. <NUM>, the cavity <NUM> being specifically designed for containing a liquid for cooling the stator. For instance, that cavity <NUM> forms a recess on the outer circular surface for the housing <NUM>, that is closed in a liquid tight fashion by a ring placed around said housing and recess. It is understood that annular cavity <NUM> can be constructed differently while still achieving a useful cooling of the electric motor.

<FIG> are different views of the brake assembly <NUM> of [<FIG>].

[<FIG>] shows in perspective the brake assembly <NUM> cooperating with the ring-shaped planetary gears carriers and the rings of the planetary gear sets <NUM>, <NUM> and <NUM> of the transmission unit <NUM>. As this is apparent, the brake assembly <NUM> comprises a series of, for instance five, pivoting dog elements cooperating with the stops formed at the outer periphery of the corresponding ring-shaped planetary gears carriers and rings.

[<FIG>] is a perspective view of the brake assembly <NUM> alone, seen from an opposite point of view as in [<FIG>].

The brake assembly <NUM> comprises a body <NUM> and a pivot axis <NUM> mounted on the body <NUM> and supporting the dog elements <NUM>, <NUM>, <NUM>, <NUM> and <NUM>. The dog elements <NUM>, <NUM>, <NUM>, <NUM> and <NUM> are moved by virtue of the cam shaft <NUM> that is rotated by the shift unit <NUM> comprising an electric motor and gearing coupling the electric motor with the cam shaft <NUM>. The latter comprises a series of, for instance five, cams each interacting with one of the dog elements <NUM>, <NUM>, <NUM>, <NUM> and <NUM> so as to pivot them in a selective manner.

[<FIG>] is section view of the one of the dog elements <NUM>, <NUM>, <NUM>, <NUM> and <NUM>, being understood that they are all identical or at least similar in their principle.

Each dog elements <NUM>, <NUM>, <NUM>, <NUM> and <NUM> comprises a body <NUM> with a central hole <NUM> for receiving the pivoting axis <NUM> ([<FIG>]), a cam follower <NUM>, a first bore <NUM> slidably receiving a finger <NUM> with a tooth <NUM> extending laterally and configured for engaging one stop on the corresponding ring-shaped planetary gears carrier or ring, a second bore <NUM> slidably receiving a piston and spring assembly <NUM>, and a fluid passage <NUM> interconnecting the first bore <NUM> with the second bore <NUM>.

As this is apparent, the body <NUM> is provided with a retaining means <NUM> preventing the finger <NUM> from separating of the body <NUM> while allowing said finger <NUM> to be slidable in the first bore <NUM>. The retaining means <NUM> is for instance a protrusion rigidly attached to or formed with the body <NUM>, and showing an oblong hole into which a screw slidingly engages and rigidly engages with the finger <NUM>. As this is apparent the cylindrical portion of the finger <NUM> that engages in the first bore <NUM> is provided with a gasket so as to delimit in said first bore <NUM> a first chamber that communicates via the passage <NUM> with a second chamber delimited in the second bore <NUM> by the piston of the piston-spring assembly <NUM> mounted on the body <NUM>. In the configuration as illustrated in [<FIG>], the second chamber shows a minimum volume, being for instance null, whereas the first chamber shows a maximum volume. The first chamber, the passage <NUM> and the second chamber are filled by a fluid, preferably a fluid that is incompressible, i.e. a liquid like oil. At rest, the finger <NUM> is urged in the illustrated extended position by the spring pushing the piston of the spring-piston assembly <NUM> towards the bottom of the second bore <NUM>, thereby pushing, via the passage <NUM>, the fluid towards the first chamber.

During operation of the transmission unit <NUM>, when the brake assembly <NUM> is operated to as to rotate the cam shaft <NUM> ([<FIG>]) and thereby pivot one of the dog elements <NUM>, <NUM>, <NUM>, <NUM> and <NUM> via the cam follower <NUM> so that its tooth <NUM> engages with one of the stops formed at the outer periphery of the corresponding ring-shaped planetary gears carrier or ring. The engagement of the tooth with one of the recesses occurs while the corresponding ring-shaped planetary gears carrier or ring is rotating, meaning that said carrier or ring is abruptly decelerated while important forces are generated between the tooth and the stop. These forces can be lowered by the sliding movement of the finger <NUM> relative to the body <NUM>. Upon engagement of the tooth with the stop, an important force is transmitted from the rotating carrier or ring to the finger <NUM> causing movement thereof towards the bottom of the first chamber in the first bore <NUM> and movement of the fluid towards the second chamber in the second bore <NUM> via the passage <NUM>, against the resilient force of the spring that progressively increases while the fluid fills the second chamber and moves the piston away from the bottom of the second chamber. This movement dampens the braking action of the dog element engaging with one of the recesses.

The passage <NUM> can comprise a check-valve with a flow restriction, configured so as to create a flow restriction when the fluid flows from the first chamber in the first body <NUM> towards the second chamber in the second body <NUM> while allowing the fluid to flow without such restriction in the reverse direction.

[<FIG>] is another perspective view of the brake assembly <NUM>, illustrating the potentially complex profiles of the cams on the cam shaft <NUM>, as well as the presence of springs <NUM> urging each dog element <NUM>, <NUM>, <NUM>, <NUM> and <NUM> towards engagement of their tooth with the corresponding the ring-shaped carriers or rings.

[<FIG>] is a perspective view of one of the ring and carrier brakes, for instance the dog element <NUM>, <NUM>, <NUM>, <NUM> and <NUM>, provided with an optional engagement controller <NUM>. The latter is provided at the distal end of the body <NUM>, for instance on the finger <NUM>. It is configured for allowing engagement of the finger with the stop on the ring-shaped carriers or rings only when the tooth of the finger is at a distance from the stop, so as to avoid a later engagement that can damage the contact surfaces on the finger and the stop.

As this is apparent, the engagement controller <NUM> comprises a clevis <NUM> fixedly mounted or attached to the body <NUM> of the dog element <NUM>, <NUM>, <NUM>, <NUM> and <NUM>, a contact member <NUM> pivotally mounted on the clevis <NUM>, a spring exerting a resilient force on the contact member <NUM> to as to urge it to the extended position illustrated in [<FIG>], an a stop pin <NUM> mounted on the contact member <NUM>, parallel to its pivoting axis and configured for abutting against the clevis <NUM> when the contact member <NUM> is in the extended position.

<FIG> are sectional views of the brake assembly <NUM> equipped with the engagement controller <NUM> and of a portion of one of the ring-shaped carriers or rings <NUM>. <NUM>, <NUM>. <NUM>, <NUM>. <NUM>, <NUM>. <NUM> and <NUM>. <NUM>, in three different engagement configurations.

In [<FIG>], the tooth <NUM> of the finger <NUM> is in position relative to the ring-shaped carrier or ring <NUM>. <NUM>, <NUM>. <NUM>, <NUM>. <NUM>, <NUM>. <NUM> or <NUM>. <NUM> where it can engage with the stop, however at a late stage where the tooth will engage only partially with the stop, leading to damages of the respective contact surface. The partial engagement is essentially due to the fact the pivoting movement of the dog element <NUM>, <NUM>, <NUM>, <NUM> or <NUM>, although rapid, occurs while the ring-shaped carrier or ring <NUM>. <NUM>, <NUM>. <NUM>, <NUM>. <NUM>, <NUM>. <NUM> or <NUM>. <NUM> is still rotating.

In the configuration of [<FIG>], the engagement controller <NUM> prevents engagement of the dog element <NUM>, <NUM>, <NUM>, <NUM> or <NUM> despite the rotation of the cam shaft <NUM> presenting a recess of the cam profile to the cam follower <NUM>. The contact member <NUM> slides along the outer periphery of the stop of the ring-shaped carrier or ring <NUM>. <NUM>, <NUM>. <NUM>, <NUM>. <NUM>, <NUM>. <NUM> or <NUM>. <NUM>, while remaining in the extended position by virtue of the force of the spring <NUM>.

In the configuration of [<FIG>], the engagement controller <NUM> prevents full engagement of the dog element <NUM>, <NUM>, <NUM>, <NUM> or <NUM> despite the rotation of the cam shaft <NUM> presenting a recess of the cam profile to the cam follower <NUM>. The contact member <NUM> slides along the outer periphery of the ring-shaped carrier or ring <NUM>. <NUM>, <NUM>. <NUM>, <NUM>. <NUM>, <NUM>. <NUM> or <NUM>. <NUM>, before the spot thereof, while remaining in the extended position by virtue of the force of the spring <NUM>.

In the configuration of [<FIG>], corresponding to a further step of the configuration of <NUM>, the contact member <NUM> further to being contacted by the stop has pivoted to a retracted position allowing the dog element to further <NUM>, <NUM>, <NUM>, <NUM> or <NUM> in the engagement direction until the tooth <NUM> fully engages with the stop.

The above-described brake assembly is particularly advantageous by its robustness and efficiency. By being mounted on the outside of the housing, its maintenance is greatly facilitated. More importantly, the mechanical engagement between the dog elements and the ring-shaped carriers and rings occurs at about the maximum radial distance of the central shaft, meaning that the forces generated by these engagements are minimum for a given torque. It also provides an efficient shifting of the transmission unit in that the transmission energy losses substantially reduced compared with friction brakes while still providing smooth operation thanks to the engagement controller <NUM>.

Claim 1:
Transmission unit (<NUM>) for a vehicle equipped with propulsion pedals, comprising:
a central shaft (<NUM>) with two opposite ends configured, each, for supporting a pedal crank (<NUM>);
a transmission output shaft (<NUM>) coaxial with the central shaft (<NUM>) and configured for outputting mechanical power;
a planetary gear unit (<NUM>) carried by the central shaft (<NUM>) and configured for transmitting mechanical power from an input shaft (<NUM>) of said planetary gear unit (<NUM>) to the transmission output shaft (<NUM>), according to several selectable transmission ratios;
an electric motor unit (<NUM>) operatively coupled to the planetary gear unit (<NUM>) in order to transmit mechanical power to the transmission output shaft (<NUM>);
a housing (<NUM>) carrying the central shaft (<NUM>), the transmission output shaft (<NUM>) and the planetary gear unit (<NUM>);
characterized in that
the electric motor unit (<NUM>) is coaxial with the central shaft (<NUM>) and comprises an output shaft (<NUM>) fixedly coupled to the input shaft (<NUM>) of the planetary gear unit (<NUM>), and
the central shaft (<NUM>) is coupled to said output shaft (<NUM>) of the electric motor unit (<NUM>) and said input shaft (<NUM>) of the planetary gear unit (<NUM>) by a freewheel (<NUM>).