EP3414153A1

EP3414153A1 - Unit for measuring the torque generated on the primary shaft of a bicycle

Info

Publication number: EP3414153A1
Application number: EP17714274.2A
Authority: EP
Inventors: Adolfo Pace
Original assignee: SME SpA
Current assignee: Dana TM4 Italia SRL
Priority date: 2016-02-11
Filing date: 2017-02-10
Publication date: 2018-12-19
Also published as: WO2017137940A1; ITUB20160667A1

Abstract

A unit (1) for mechanical transmission of the motion generated by a primary shaft (2) towards an output shaft (3) for measuring the torque generated on the primary shaft (2), comprising a first measuring wheel (9) mechanically connected to the primary shaft (2), a second measuring wheel (12) arranged alongside the first wheel (9) and mechanically connectable to an output shaft (3) for rotationally driving the latter. Furthermore, the transmission unit (1) comprises elastically deformable constraint means (13) arranged between the first measuring wheel (9) and the second measuring wheel (12) and measuring means (23) for measuring the angular phase shift between the first measuring wheel (9) and the second measuring wheel (12) configured to measure an angular phase shift value between the two wheels.

Description

UNIT FOR MEASURING THE TORQUE GENERATED ON THE PRIMARY

SHAFT OF A BICYCLE

*******

DESCRIPTION

The present invention relates to a unit for mechanical transmission of the motion generated by a primary shaft for measuring the torque generated on the primary shaft and a pedal assist bicycle comprising such transmission unit.

In particular the present invention relates to a mechanical transmission unit for a bicycle with a measuring element for measuring the motor torque transmitted by a pedalboard of a bicycle to an output shaft usually connected to a ring gear of the bicycle's pull wheel. However, it is to be noted that the transmission unit according to the present invention is applicable to any system (not only means of transport) that envisages the transmission of motion between two shafts and the measurement of torque.

In the state of the art, there are bicycles equipped with an electric motor with the aim of helping the user while pedalling.

Generally, such pedal assist bicycle technology comprises an electric motor, a rechargeable battery and an electronic management system, through which the auxiliary torque contribution provided by the electric motor is managed. In this way, the latter provides auxiliary torque to the cyclist while they are pedalling in order to reduce the physical effort.

According to the prior art, there are bicycles equipped with a more advanced electronic management system comprising an apparatus for measuring the torque exercised by the user on the pedal shaft in a bicycle transmission.

Measuring and monitoring the torque value generated on the pedal shaft generally allows the intervention of the electric motor while pedalling to be optimised. In fact, the electronic management system which equips electric bicycles processes the information received by the apparatus that measures the torque generated on the pedal shaft and activates/deactivates or divides the work of the electric motor according to requirements.

Therefore, while pedalling, the cyclist will benefit from the intervention of the electric motor which will in part replace the user reducing their physical effort; as soon as the pedalling load is reduced, the apparatus that measures the new motor torque value sends the information to the management system which will also make the torque dispensed by the electric motor decrease. Simultaneously to the intervention of the electric motor on the bicycle transmission, the user must see to managing the transmission ratio acting on the transmission itself.

According to the prior art, the apparatus that measures the motor torque value comprises a motor torque sensor.

In a first case shown, for example, in document EP1325241 , such torque sensor is provided by a body rotating on the bicycle's primary shaft (the one of the pedal cranks) movable axially along such shaft as a function of the torque that is imparted by the user.

In this way, by measuring the axial position of such rotating body with respect to a reference point, the torque applied to the pedals can be derived.

Such prior art implies some drawbacks mainly connected with the fact that the structure is complex, there are significant dimensions connected with the axial sliding of the rotating body and the measurement of the torque is assigned to "ratchets" that push the rotating body differently as a function of the effort applied on the primary shaft.

Other known solutions, for example, in document EP2783972, envisage the use of torque sensors generally installed on the central movement of the bicycle, i.e. on the axle of the pedal cranks, which comprise strain gauges or magnetoelastic sensors. This type of sensor often requires high implementation costs and times, also shifting the final cost of the electric bicycle from a certain type of market. Furthermore, the torque sensor thus designed is rather complicated in terms of assembly, fine tuning (calibration) and maintenance during the useful life of the transmission.

In detail, the realisation of the strain gauge could be rather bulky and heavy on the primary shaft. In detail, if using magnetoelastic sensors, the system is more mechanically complex and bulky, whereas using strain gauges, sliding contacts (not very reliable) or "wireless" connections are necessary, which must be powered by a battery which needs replacing periodically.

In this scope, the technical task of the present invention is providing a mechanical transmission unit free from the drawbacks cited above.

In particular, it is an object of the present invention to provide a mechanical transmission unit that allows the measurement of the transmitted torque to be improved in terms of precision.

It is also an object of the invention to provide a mechanical transmission unit for a bicycle that allows the dimensions of the torque sensor on the bicycle transmission to be reduced so as to obtain a more compact mechanical transmission unit.

The above-indicated objects are substantially attained by a mechanical transmission unit for a bicycle according to what is described in the appended claims.

Further characteristics and advantages of the present invention will more greatly emerge from the detailed description that follows of some preferred but not exclusive embodiments of a mechanical transmission unit illustrated in the appended drawings, in which:

- figure 1 shows an axonometric view of a schematic illustration of a pedal assist bicycle comprising the transmission unit according to the present invention;

- figure 2 shows a lateral view of a section of the transmission unit shown in figure 1 according to a section plane containing the axis of the pedal cranks;

- figures 3a, 3b and 3c show, according to different views, the first measuring wheel of the transmission unit according to the present invention;

- figures 4a, 4b and 4c show, according to different views, the second measuring wheel of the transmission unit according to the present invention; and

- figures 5a, and 5b show, according to different views, the measuring means for measuring the angular phase shift between the two measuring wheels of the transmission unit according to the present invention;

With reference to the mentioned figures, reference number 1 indicates overall a unit 1 for mechanical transmission of the motion generated by a primary shaft 2 for a pedal assist bicycle 100, according to the present invention.

In particular, the transmission unit 1 is preferably directed to a transmission system of a pedal assist bicycle 100 (hereinafter more simply known as "electric bicycle 100"), but could also be used for measuring the torque on the primary shaft in any transmission system that envisages the measurement of the torque between two shafts (coaxial as explained below) such as, for example, electric, thermal, hydraulic, pneumatic motors, ...

In the preferred case of the electric bicycle 100, the primary shaft 2 coincides with the shaft on which the pedal cranks 4 (and consequently the pedals 27) of the bicycle 100 are mounted.

In other words, the primary shaft 2 extends between two opposite ends at which respective pedal cranks 4 are connected, so as to generate primary motion on said primary shaft 2 through the effort of a user (cyclist).

The output shaft 3 is connected to a pull wheel of the bicycle 100 (usually the rear wheel) to transmit the motion to the latter. Preferably, such transmission of the motion takes place by means of a gear change system 5 and by means of a chain.

In other words, at least one ring gear 5 is connected (preferably keyed) at a final end 6 of the output shaft 3, for transmitting motion to the pull wheel of the bicycle 100 (in the event of numerous ring gears 5 they define the gear change system).

In the preferred case of a pedal assist bicycle 100, the latter comprises an electric assist motor 7 configured to generate auxiliary motion and operatively connected to the output shaft 3 for transmitting said auxiliary motion to the output shaft 3 itself. Preferably, the electric assist motor 7 is directly engaged or through intermediate stages on a toothed ring gear 8 of the output shaft 3 for transmitting the auxiliary motion to the latter.

In practice, the primary motion generated by the user is transmitted by the primary shaft 2, while the auxiliary motion is transmitted by the electric motor 7 towards the output shaft 3; the transmission unit 1 mechanically connects the primary shaft 2 with the output shaft 3.

In practice, the transmission unit 1 comprises a first measuring wheel 9 (fig. 3a, 3b, 3c) mechanically connected to the primary shaft 2 (directly or through interposed members) to be rotationally driven by the latter. Such first measuring wheel 9 is rotatable about a main axis of rotation 10.

In figure 2 it can be seen that such main axis of rotation 10 coincides with the axis of rotation of the primary shaft 2.

Furthermore, the first measuring wheel 9 is preferably assembled on the primary shaft 2.

It is to be noted that the mechanical connection between the primary shaft 2 and the first wheel 9 envisages two alternatives:

- in the preferred case (illustrated in figure 2) the transmission unit 1 comprises an upstream free wheel 11 operatively interposed between the primary shaft 2 and the first measuring wheel 9 so as to transmit the motion from the primary shaft 2 to the first measuring wheel 9;

- in an alternative embodiment not shown in the appended figures, the first measuring wheel 9 is solidly constrained to the primary shaft 2 and turns therewith.

As will be explained more clearly below, the latter case is advantageous since it is always possible to measure the rotation speed of the primary shaft 2 through the measuring means described below.

Furthermore, it is to be noted that in the preferred case (first case), the first wheel 9 and the primary shaft 2 can comprise respective torque transmission portions at least partially overlapping according to a radial direction to the primary shaft 2 so as to reduce the dimensions along the latter. The upstream free wheel 11 is interposed between such overlapping portions. For example, the primary shaft 2 may have a substantially bell- shaped transmission portion within which the transmission portion of the upstream free wheel 11 is interposed or vice versa.

Furthermore, the transmission unit 1 comprises a second measuring wheel 12 (fig. 4a, 4b, 4c) preferably arranged alongside the first measuring wheel 9 and rotatable about the main axis of rotation 10. In other words, the first measuring wheel 9 and the second measuring wheel 12 turn about the same axis.

As can be seen from figure 2, the second measuring wheel 12 is arranged alongside the first measuring wheel 9. Furthermore, the two measuring wheels turn (e.g. externally) about the primary shaft 2.

Furthermore, the second measuring wheel 12 is mechanically connected (directly or through interposed members) to the output shaft 3 to rotationally drive the latter so as to bring the motion to it.

Also in relation to the mechanical connection between the second wheel 2 and the output shaft 3, there are two alternatives:

- in the preferred case (illustrated in figure 2) the second wheel 12 is solidly constrained to the output shaft 3;

- in an alternative embodiment not shown in the appended figures, the transmission unit 1 comprises a downstream free wheel operatively interposed between the second measuring wheel 12 and the output shaft 3 so as to transmit the motion from the second measuring wheel 12 to the output shaft 3.

Furthermore, it is to be noted that preferably the second wheel 12 and the output shaft 3 comprise respective torque transmission portions at least partially overlapping according to a radial direction to the output shaft 3 so as to reduce the dimensions along the latter. In particular, in the second case the downstream free wheel is interposed between such overlapping portions. For example, the output shaft 3 may have a substantially bell- shaped transmission portion within which the transmission portion of the downstream free wheel is interposed or vice versa.

Summarising, in the preferred case illustrated in figure 2 between the primary shaft 2 and the first measuring wheel 9 there is the downstream free wheel rotating operatively so as to transmit motion from the primary shaft 2 to the first measuring wheel 9; while the second wheel 2 is solidly constrained to the output shaft 3.

Alternatively, the first measuring wheel 9 is solidly constrained to the primary shaft 2 and turns with it and the downstream free wheel is interposed between the second measuring wheel 12 and the output shaft 3 so as to transmit motion from the second measuring wheel 12 to the output shaft 3.

Furthermore, the transmission unit 1 according to the present invention comprises an elastically deformable constraint means 13, which are arranged between the first measuring wheel 9 and the second measuring wheel 12 and configured to transfer the motion torque from the first measuring wheel 9 to the second measuring wheel 12.

Such constraint means 13 is movable, by elastic deformation, between a condition of minimum angular phase shift between the measuring wheels and a condition of predetermined maximum angular phase shift, as a function of the torque transmitted.

In particular, the constraint means 13 is deformable having its axis of deformation 14 arranged according to a direction parallel to a straight line tangent to a measuring wheel. Preferably, the first measuring wheel 9 and the second measuring wheel 12 are coaxial to the primary shaft 2 so that the axis of deformation 14 of the constraint means 13 is positioned according to a direction parallel to a straight line tangent to the primary shaft 2.

In practice, the deformation axis 14 of the constraint means 13 is tangential with respect to the primary shaft 2 and to the output shaft 3 in order to minimise the friction and hysteresis in the system.

In the preferred embodiment, the constraint means 13 is defined by at least one spring 15 which is elastically deformable by compression so that during the condition of minimum angular phase shift, the spring 15 is in the minimum loading position (corresponding to a rest or preloaded position of the spring), while during the condition of predetermined maximum phase shift, the spring 15 is compressed (maximum loading position).

Preferably, each elastically deformable spring 15 is a Belleville spring 15. In this way, the forces generated by the springs 15 generate in turn a torque which gives a null resultant force so as to minimise friction and hysteresis in the system.

In an alternative embodiment not illustrated in the appended figures, the constraint means 13 is defined by at least one spring 15 that is elastically deformable by extension. In other words, the springs 15 could work by compression (as previously described) or by extension.

Furthermore, at least one of the measuring wheels comprises a seat 16 for inserting the constraint means 13. Preferably, the seat 16 is arranged between the respective axis of rotation and the periphery of the wheel itself (as represented in the appended figures). Alternatively, the periphery of the wheel could be in a more internal position with respect to the seat 16 (and therefore the seat 16 could be more external with respect to the periphery of the wheel).

As can be seen in figure 3b, the seats 16 are afforded on the first wheel 9 and. there are preferably two of them. Each seat 16 is afforded in the body of the wheel. Furthermore, the wheel comprises a pin 17 extending along a substantially parallel direction to a tangent to the wheel, in which pin 17 the spring 15 is inserted. Preferably, such pin 17 projects outwards with respect to a lying plane of the wheel itself. In other words, such pin 17 projects towards the other wheel alongside it.

In practice, the constraint means 13 is connected to another wheel, and projects towards the other wheel to come into contact with the latter.

Preferably, the constraint means 13 is connected to the first wheel 9 (as represented in figures 3a, 3b and 3c), and abuts against the second wheel 12.

The second wheel 12 has respective recesses 18 (through or not) arranged at the constraint means 13 for partially housing it. Such recesses 18 are arranged on the body of the second wheel 12 and extend in depth according to a parallel direction to the output shaft 3; while they extend in length according to a substantially parallel direction to a tangent to the wheel itself.

Therefore, under conditions of use, the constraint means 13 enters into the recesses 18 of the second wheel 12 transmitting the motion torque from the first wheel 9 to the second wheel 12.

Finally, the measuring wheels comprise limit stop means 19 interposed between the two so as to determine the maximum stroke between the minimum angular phase shift and the maximum angular phase shift.

Such limit stop means 19 is represented in figures 3b and 4b in which it can be seen that the first wheel 9 has holes 20 at the respective limit stop constraints 21 of the second wheel 12 projecting from the second wheel 12 with respect to the axis in which they lie. Such holes 20 have an elongated conformation in a substantially parallel direction to a tangent to the wheel. Alternatively, the configuration of the constraint means 13 with respect to the two wheels may be opposite (holes 20 on the second wheel 12 and constraints 21 projecting on the first).

It is to be noted that, as can be seen in figure 4b, the second wheel 12 is connected to the output shaft 3. In particular, the output shaft 3 comprises a toothed ring gear 8 of the auxiliary motion having a larger diameter than the second wheel 12 and extending to the outside thereof. In particular, in the preferred embodiment, the toothed ring gear 8 has an internal cavity 22 in which the second wheel 12 is inserted so as to optimise the dimensions. In other words, the teeth of the toothed ring gear 8 surround the second wheel 12. The toothed ring gear 8 and the second wheel 12 are coaxial.

In particular, the seats 18 described above may be afforded on the second wheel 12 or on the toothed wheel 8 (as represented in the appended figures) which acts as a support for the second wheel 12.

The toothed ring gear 8 is mechanically connected (directly or through an interposed stage) with a transmission mechanism 5 for transmitting the auxiliary motion deriving from the electric assist motor 7. Preferably, such toothed ring gear 8 is a toothed wheel.

Furthermore, the transmission unit 1 comprises a measuring means 23 for measuring the angular phase shift arranged between the first measuring wheel 9 and the second measuring wheel 12 configured to measure a angular phase shift value between the two wheels and to derive a motion torque value relative to the primary shaft 2 as a function of said angular phase shift value.

Preferably, such measuring means 23 is connected to a fixed point 24 with respect to the measuring wheels.

In the preferred embodiment illustrated in the appended figures, each measuring wheel comprises a respective phonic wheel.

Each phonic wheel has alternating projections and recesses (teeth or holes) according to a predefined pitch.

The measuring means 23 comprises at least one sensor 25 configured to generate an output signal having a sinusoidal component during the rotation of a respective phonic wheel as a function of the magnetic field that the sensor 25 itself measures. Such signal has a frequency or period as a function of the pitch of the phonic wheel.

In detail, the sensor 25 is of the magnetic type and, when the phonic wheel is rotating, it generates an electric signal having a continuous component and a sinusoidal component depending on the conformation of the teeth of the phonic wheel.

In particular, the measuring means 23 (in detail the control unit 26 described below) is configured to compare the sinusoidal component of the signals generated by each sensor 25 and to calculate the angular phase shift between the two phonic wheels. In other words, the sensor 25 of each phonic wheel generates respective signals having a sinusoidal component. In detail, the sensors 25 of each wheel 9, 12 generate respective signals having a sinusoidal component that is shifted as a function of the deformation of the constraint means 13 (springs).

The comparison of the sinusoidal waves gives the angular phase shift of the two wheels and therefore the deformation value of the constraint means (compression of the springs 15).

In figure 5a it is possible to see that the sensor or sensors 25 relative to a measuring wheel project to different extents with respect to the sensor or sensors 25 relative to the other measuring wheel so that each sensor 25 or sensors 25 are arranged at the respective wheel (preferably at the perimeter).

It is to be noted that the measuring means 23 comprises, as well as the sensors 25, a control unit 26 connected to the sensors 25 and configured to receive the detected sinusoidal signals. Further, the control unit 26 is configured so as to:

- compare the trend of the sinusoidal signals relative to the respective wheels and calculate the angular phase shift between the two;

- calculate the torque applied to the primary shaft 2 as a function of the phase shift calculated and the deformation of the constraint means 13. It is to be noted that each phonic wheel preferably has a fixed pitch (always the same as itself) along its circumference. In other embodiments each phonic wheel could have a variable pitch (at least one different from at least another) along its circumference.

In any case, the two phonic wheels have the same pitch when compared to one another and are circumferentially aligned so that the alternated sequence of teeth or holes is the same for both.

In the preferred embodiment, the measuring means 23 comprises two sensors 25 per phonic wheel. Such sensors 25 of each wheel are arranged in positions which are angularly offset from each other by a predetermined angle. The control unit 26 is configured to compare the sinusoidal signals generated by the sensors 25 of a respective wheel and to calculate the phasing of phonic wheel portions relative to the position of the sensors 25 themselves.

In particular, the present invention envisages two possible solutions for measuring the torque transmitted on the primary shaft 2; an analog solution and a digital solution.

In the analog solution, each sensor 25 is composed of a permanent magnet and an integrated circuit able to transduce the magnetic field into a voltage or current.

When the tooth of the phonic wheel passes in front of the sensor 25 it creates a magnetic field that varies between a minimum and a maximum corresponding to a gap and to a solid part in the wheel.

Such signal is periodically repeated as each tooth passes.

In this case the measuring means 23 comprises two sensors 25

(transducers) for each wheel offset by a mechanical angle f , relative to the angle of 2n which corresponds to the pitch of the teeth of the phonic wheel.

The output voltage of the two sensors 25 can therefore be expressed with:

V_x ( ) = V_]m + V_]Q x sin(a)

V₂ (o ) = V_2av + V_2o ^χ ύη(α + φ)

where a is equal to the phase shift of a tooth with respect to the first sensor 25. If the phase shift f between the 2 sensors 25 is: φ = ?L x n with "n" being whole and odd. Then the second equation is:

^V2 (^a) = ^V2a_V + ^V2₀ X COS(a)

Therefore, a can be calculated from the following operation:

V_x (a) - V a = arctg

^V2„

When the torque is null the phasing of the teeth of the wheel measured gives rise to a phase shift to rest between the two wheels equal to:

<!>„ = a, — a~.

When a torque is applied the phase shift between the two wheels will be equal to:

δ_τ = α_λτ - α_2τ

Therefore δ_τ - δ₀ will be a function of the torque applied.

If the maximum range falls within the angle corresponding to 2n the phase is only determined.

Advantageously, such calculations are valid both if the wheels are stationary and if they are turning.

Such information can be found if the phase shift between the two sensors

25 is different from— .

2

The same information can be obtained but rather than using phonic wheels and respective magnetic sensors 25, using a magnetised wheel with the same number of poles as the number of teeth on the wheel.

In the digital solution, each sensor 25 comprises a permanent magnet and an integrated circuit able to transduce the magnetic field into a voltage or a current. When the tooth of a wheel passes in front of the sensor 25 it creates a magnetic field that varies between a minimum and a maximum corresponding to a gap and to a solid part in the wheel.

Such signal is periodically repeated as each tooth passes. In this case one sensor 25 per wheel is sufficient.

The sensor 25 may generate an analog or digital output signal.

In the case of digital, the sensor 25 is calibrated to be triggered when it detects a variation in the magnetic field with respect to a predefined reference value which may be fixed or derived by interpolation.

In the event of an analog signal the signal is interpreted digitally by checking the moment of transit with respect to a reference value.

In the case of using two sensors 25 for each wheel, a second sensor 25, which is offset with respect to the first by an angle φ =— χ η with "n" whole and odd, may be used to discriminate the rotation direction and reduce the minimum operating speed.

When the primary shaft 2 turns at a certain angular speed ω, each sensor 25 generates a sinusoidal signal that switches from a logical value "L" to a logical value "H" or vice versa, at times ^ and t_{x ι} for the sensor 25 of the first wheel 9 and at times t₂ and t_{2n t} for the sensor 25 of the second wheel 12.

2π

The switching period is equal to T = (t, - t, ) = (t₂ - t₂ ) =

" "^"' (Nd x ώ) wherein "ω" represents the rotation speed of the primary shaft 2 and "Nd" the number of teeth on the phonic wheel.

Supposing that speed "ω" is constant when the applied torque is null, the phase shift between the two wheels is equal to δ₀ = ^¹"^{0 ~} ^"^{o )} = ^¹⁽"^{"1)o ~} ^²⁽"^"'^{)o )} where "T" indicates the switching period between the two switches.

When a torque T" is applied, the phase shift between the two wheels is equal to δ_Γ = K"-l⁾r t 2. (»-l)r )

where "T" is the switch

T T

period between the switches.

Such information can be obtained by shaping the teeth of the phonic wheels so as to generate any other periodic signal.

The same functionality can be obtained by using rather than the phonic wheel and sensor 25 with magnet, a magnetised wheel with magnets in place of teeth.

In the latter case the magnetic field generated will be a periodic function with mean value close to 0.

In any case, it is to be noted that each phonic wheel and the relative measuring means 23 may be of the inductive type or capacitive type or magnetic type or optical type or have eddy currents. In addition, the phonic wheel may be of the type with teeth or with slits. However, the various types of phonic wheels shall not be described in further detail since they are already known.

The subject matter of the present invention is also a pedal assist bicycle 100 comprising the primary shaft 2 extending between two opposite ends at which the pedal cranks 4 are connected so as to generate primary motion on said primary shaft 2.

Furthermore, the bicycle 100 comprises the transmission unit 1 previously described and connected between the primary shaft 2 and the output shaft 3. The latter is, in turn, connected to the pull wheel of the bicycle 100 to transmit motion to the latter.

In particular, the bicycle 100 comprises an electric assist motor 7 configured to generate auxiliary motion and operatively connected to the output shaft 3 for transmitting the auxiliary motion to the output shaft 3 itself.

Finally, the bicycle 100 comprises a battery (preferably rechargeable) for powering the electric motor 7 and connected to the latter for bringing the electrical energy to the motor. With regard to an operating example of the transmission unit 1 for the bicycle 100 it derives directly from what is described above which is referred to below.

In particular, the first wheel 9 receives the motion torque which comes from the primary shaft 2 of the pedals 27.

This torque generates a force on the springs 15 arranged between the measuring wheels which, in turn, transmit motion torque to the second wheel 12.

When the springs 15 are under strain their total length decreases. This generates the phase shift between the two measuring wheels, as a function of the torque acting on the shaft of the pedals 27.

The sensors 25 active on each measuring wheel generate two detection signals from which it is possible to calculate the phasing of the teeth of the wheel with respect to the position of the sensors 25 themselves. This phasing can be measured both when the wheels are stationary and moving. In the event of using two sensors 25 on the same wheel they are physically shifted with respect to the toothing by a predefined phase shift (as described above). This predefined phase shift between the sensors 25 of the same wheel also allows the rotation direction of the two wheels to be recognised.

From the difference in phasing of the teeth of the two wheels, the shift between the two wheels is obtained and therefore the measurement of the torque.

Advantageously, the sensors 25 chosen for the detection are of the analog type so as to allow continuous reading of the torque and also with the wheels stationary, which is very important for the delicate departure phase.

The present invention attains the set aims.

In the first place, the combination of an analog measuring system and a mechanical transmission system enables the continuous reading of the shift between the wheels and therefore greater readiness and precision in measuring the torque.

Furthermore, the system operates both with the measuring wheels moving and stationary so as to be able to control the departure of the bicycle 100 from standstill.

The forces developed on the springs 15 act in the tangential direction with respect to the axis of rotation of the primary shaft 2 of the pedals 27. This characteristic maximises the useful component and minimises the friction component and hysteresis of the system.

Furthermore, the system of forces generated by the springs 15 generates an equivalent torque to that to be measured, but gives a null resultant force. This characteristic also minimises the friction component and hysteresis of the system.

In addition, the measuring means 23 for measuring the phase shift (electric/electronic part) are fixed, whereas the rotating part is purely mechanical (the phonic wheels), so that for the transmission of the information of the torque measurement sensors 25 there is no need for sliding contacts or wireless data transmission. In this way, the system is simple and reliable.

Furthermore, in the configurations with the free wheel 11 downstream of the measuring wheels, the first measuring wheel 9 is solidly constrained to the shaft of the pedals 27. In this way, it is also possible to detect the rotation speed of the primary shaft 2 without adding other specific components to the system. This latter characteristic has two advantages: the first advantage consists of a more reactive system response; the second advantage consists of a high degree of safety (when the shaft of the pedals 27 is stationary the assistance of the electric motor 7 is interrupted regardless of the status of the rest of the system).

In the configurations with the free wheel 11 upstream of the measuring wheels, it is still possible to deduce the rotation speed of the output shaft 3 on which the "total" system torque is acting (from the physical effort and assistance of the motor).

Claims

1. A unit (1) for mechanical transmission of the motion generated by a primary shaft (2) towards an output shaft (3) for measuring the torque generated on the primary shaft (2), comprising:

a first measuring wheel (9) mechanically connected to the primary shaft (2) to be rotationally driven by the latter; the first measuring wheel (9) being rotatable about a main axis of rotation (10);

a second measuring wheel (12) positioned alongside the first measuring wheel (9) and rotatable about the main axis of rotation (10); said second measuring wheel (12) being mechanically connectable to an output shaft (3) to rotationally drive the latter so as to bring the motion to it; constraint means (13), which are elastically deformable according to predetermined deformation properties and are positioned between the first measuring wheel (9) and the second measuring wheel (12) and are configured to transfer the motion torque from the first measuring wheel (9) to the second measuring wheel (12); the constraint means (13) being movable, by elastic deformation, between a condition of minimum angular phase shift between the measuring wheels and a condition of predetermined maximum angular phase shift, as a function of the torque transmitted;

angular phase shift measuring means (23) positioned between the first measuring wheel (9) and the second measuring wheel (12), configured to measure an angular phase shift value between the two wheels and to derive a relative motion torque value of the primary shaft (2) as a function of the angular phase shift value and of the predetermined deformation properties of the constraint means (13);

characterised in that each measuring wheel comprises a respective phonic wheel having alternating projections and recesses according to a predefined pitch; said measuring means (23) comprising at least one sensor (25) for each phonic wheel configured to generate an output signal having a proportional period to said pitch of the phonic wheel; said measuring means (23) being configured to compare the signals generated by each sensor (25) of the respective phonic wheels and to calculate the angular phase shift between the two phonic wheels as a function of the deformation acting on the constraint means (13).

2. The mechanical transmission unit according to claim 1 , characterised in that the deformable constraint means (13) has its own axis of deformation (14) positioned according to a direction parallel to a straight line tangent to a measuring wheel.

3. The mechanical transmission unit (1 ) according to claim 2, characterised in that the first measuring wheel (9) and the second measuring wheel (12) are coaxial to the primary shaft (2) so that the axis of deformation (14) of the constraint means (13) is positioned according to a direction parallel to a straight line tangent to the primary shaft (2) in order to minimise the friction components and hysteresis of the transmission.

4. The mechanical transmission unit (1 ) according to any one of the preceding claims, characterised in that at least one of the measuring wheels comprises a seat (16) for inserting constraint means (13).

5. The mechanical transmission unit (1 ) according to any one of the preceding claims, characterised in that the constraint means (13) are defined by at least one spring (15) which is elastically deformable by compression or extension so that during the condition of minimum phase shift, the spring (15) is in the minimum loading position, while during the condition of predetermined maximum phase shift, the spring (15) is compressed or extended in maximum loading position.

6. The mechanical transmission unit (1 ) according to claim 5, characterised in that each elastically deformable spring (15) is a Belleville spring (15).

7. The mechanical transmission unit (1 ) according to any one of the preceding claims, characterised in that the sensor (25) of the measuring means (23) is configured to generate an output signal having a sinusoidal component during the rotation of the phonic wheel.

8. The mechanical transmission unit (1 ) according to claim 7, characterised in that the measuring means (23) are configured to compare the sinusoidal components of the signals generated by each sensor (25) and to calculate the angular phase shift between the two phonic wheels as a function of the deformation acting on the constraint means (13).

9. The mechanical transmission unit (1 ) according to claim 7 to 8, characterised in that the measuring means (23) comprise two phonic wheel sensors (25); the sensors (25) of each wheel being positioned in positions which are angularly offset from each other by a predetermined angle; the measuring means (23) being configured to compare the sinusoidal components of the signals generated by the sensors (25) of a respective wheel and to calculate the phasing of portions of phonic wheel relative to the position of the sensors (25) themselves, and the phasing of the two phonic wheels independently of the rotation.

10. The mechanical transmission unit (1 ) according to any one of claims 7 to 9, characterised in that each sensor (25) is configured to generate measuring signals having periodic sinusoid or different from sinusoid waveform components.

11. The mechanical transmission unit (1 ) according to claim 10, characterised in that each sensor (25) is configured to detect a variation of the magnetic field relating to the movement of the phonic wheel relative to a reference value which is fixed or interpolated so as to generate a digital output signal.

12. The mechanical transmission unit (1 ) according to any one of claims 7 to 1 1 , characterised in that each phonic wheel and the relative measuring means (23) are of the inductive type or capacitive type or magnetic type or optical type or have eddy currents.

13. The mechanical transmission unit (1 ) according to any one of the preceding claims characterised in that both of the phonic wheels have the same pitch.

14. The mechanical transmission unit (1 ) according to any one of the preceding claims characterised in that each phonic wheel has a fixed or variable pitch along the entire circumference.

15. The mechanical transmission unit (1) according to any one of the preceding claims characterised in that each sensor (25) is distanced from the respective phonic wheel so as to perform a contactless measurement.

16. The mechanical transmission unit (1 ) according to any one of the preceding claims characterised in that it comprises a toothed ring gear (8) keyed onto the output shaft (3) and configured to be engaged with a configured electric assist motor (7) which generates auxiliary motion.

17. The mechanical transmission unit (1 ) according to any one of the preceding claims characterised in that the toothed ring gear (8) has an internal cavity (22) in which the second wheel (12) is inserted so as to optimise the dimensions.

18. The mechanical transmission unit (1 ) according to any one of the preceding claims characterised in that each phonic wheel is of the nonmagnetic metal type and each sensor (25) is interposed between a fixed magnet and the respective phonic wheel so as to measure the magnetic field variation.

19. The mechanical transmission unit (1 ) according to any one of the preceding claims, characterised in that it comprises a rotating free wheel

(1 1) operatively interposed between the primary shaft (2) and the first measuring wheel (9) so as to transmit the motion from the primary shaft (2) to the first measuring wheel (9).

20. The mechanical transmission unit (1 ) according to any one of claims 1 to 19, characterised in that it comprises a rotating free wheel (1 1 ) operatively interposed between the second measuring wheel (12) and the output shaft (3) so as to transmit the motion from the second measuring wheel (12) to the output shaft (3).

21. A pedal assist bicycle (100) comprising:

a primary shaft (2) extending between two opposite ends;

pedal cranks (4) connected to the primary shaft (2) at respectively one end of the shaft so as to generate a primary motion on the primary shaft (2);

a transmission unit (1 ) according to any one of claims 1 to 7 connected to the primary shaft (2);

an output shaft (3) connected to a pull wheel of the bicycle (100) for transmitting the motion to the latter;

an electric assist motor (7) configured to generate an auxiliary motion and operatively connected to the output shaft (3) to transmit the auxiliary motion to the output shaft (3) itself.

22. The bicycle (100) according to claim 21 characterised in that the electric motor (7) is engaged with a toothed ring gear (8) keyed onto the output shaft (3) on the same side as the wheels (9, 12)