Hill start assistance for an electrically assisted bicycle

Abstract

The invention relates to a method for controlling the start-up of an electrically assisted bicycle, which method comprises the following steps, which are implemented when no rotation of a crankset is detected: measuring the torque (Cp) exerted on the crankset; if the torque exceeds a triggering threshold (Sd), triggering a time delay (Tstart); and upon expiration of the time delay, if the torque is greater than a holding threshold (Sm) at most equal to the triggering threshold, engaging electrical assistance proportional to the torque despite no rotation of the crankset being detected.

Description

Hill start assistance for an electrically assisted bicycle

[0001] The invention relates to electrically assisted bicycles and more particularly to the start of assistance when getting on the bicycle. Background

[0002] In e-bikes equipped with a torque sensor, a typical assistance law is to control the motor current proportional to the torque measured at the crankset, representing the effort provided by the cyclist. However, this assistance law is typically only implemented when a crankset rotation is detected. This can cause difficulties for the cyclist in certain situations. Summary

[0003] A method for controlling the start-up of an electrically assisted bicycle is generally provided, comprising the following steps implemented in the absence of detection of rotation of a crankset: measuring the torque exerted on the crankset; when the torque exceeds a trigger threshold, triggering a time delay; and upon expiry of the time delay, if the torque is greater than a maintenance threshold at most equal to the trigger threshold, engaging electrical assistance proportional to the torque despite the absence of detection of rotation of the crankset.

[0004] The method may comprise a step implemented in the absence of detection of rotation of the pedal assembly consisting of stopping the electric assistance when the torque falls below the maintenance threshold.

[0005] The method may comprise the step of stopping the electric assistance after a time interval during which no rotation of the pedals has been detected.

[0006] The method may comprise a step implemented in the absence of detection of rotation of the pedal assembly consisting of stopping the electric assistance when a rotation speed of a wheel driven by a motor is measured at a value greater than a threshold. Summary description of the drawings

[0007] Embodiments will be set out in the following description, given without limitation in relation to the attached figures among which:

[0008] This is a graph illustrating an example of the evolution of the torque exerted by a cyclist on a pedal assembly of a stationary bicycle, and various thresholds used to implement an assisted start process; and

[0009] This is a graph illustrating the evolution of an assistance control instruction generated in response to the evolution of the torque. Detailed description

[0010] As previously mentioned, e-bike assist laws typically require crank rotation to start. This can be difficult for the rider in starting situations requiring significant torque, such as on steep slopes, or if the bike is loaded or has a trailer. In such a situation, it can be difficult for the rider to generate an initial crank rotation at start-up.

[0011] To facilitate starting in such situations, the present application provides an assistance law which triggers assistance, not by detecting actual pedaling, but by detecting a desire to pedal. The desire to pedal is detected, in summary, when the cyclist presses a pedal of the stationary bicycle sufficiently hard and for a long time. The cyclist's pressure on the pedal is translated into a torque value returned by the crankset torque sensor.

[0012] This is a graph illustrating an example of the evolution of the torque Cp exerted by a cyclist on a pedal assembly of a stationary bicycle. Various thresholds and time intervals illustrated are parameters involved in a bicycle start-up process.

[0013] Laest is a graph illustrating the evolution of an ASSIST assistance control setpoint generated as a function of the torque evolution of laet and the parameters illustrated.

[0014] At time t0, with the bicycle stationary under difficult starting conditions, for example on a steep hill, the cyclist begins to press a pedal. The cyclist will have previously positioned the crank arms approximately horizontally to transmit maximum torque. The effort is insufficient to start the bicycle, and the pedal does not move. The torque Cp measured by the crank sensor increases as the cyclist presses harder.

[0015] At a time t1, the torque reaches a preconfigured start threshold Sd. This event starts a time delay of duration Tstart. From this time, the torque value is monitored and compared to a holding threshold Sm which could be the same as the threshold Sd. The threshold Sm is preferably lower than the threshold Sd to obtain a hysteresis effect which filters tolerated variations in the torque. In the example shown, the torque Cp oscillates above the first threshold Sd.

[0016] At a time t2, the time delay Tstart expires. If the torque Cp is above the holding threshold Sm, as in the case shown where it is also above the threshold Sd, the assistance proportional to the torque is engaged despite the absence of detection of pedal rotation. At the same time, another time delay of duration Tstop is started. The engagement of the assistance is illustrated by the transition from 0 to 1 of the ASSIST setpoint of the. This setpoint could be that of the pedal rotation detection, modified to be activated also when the conditions of a desire to pedal are detected.

[0017] Alternatively, which is not shown, if the torque Cp falls below the holding threshold Sm before the expiry of the time delay Tstart (before time t2), the system returns to the initial state and waits for a new event (the rotation of the pedal assembly or a new exceeding of the threshold Sd by the torque Cp).

[0018] From time t2, the harder the cyclist presses the pedal, the more the engine torque increases to help the bike move off. When the bike is finally started (which is not shown), the cyclist begins to turn the crankset, which initiates the normal assistance procedure. Activating the normal procedure takes over from the start-up assistance procedure.

[0019] Figures 1A and 1B illustrate two cases of cancellation of the start procedure.

[0020] At time t3, before the end of the time delay Tstop, no crank rotation is detected and the torque Cp falls below the holding threshold Sm. The cyclist releases the pressure and it is assumed that he no longer wishes to start. The assistance is stopped by setting the ASSIST setpoint to 0.

[0021] At time t3', corresponding to the expiration of the time delay Tstop, the torque Cp is still greater than the holding threshold Sm, but no rotation of the crankset has been detected. The cyclist is not pressing hard enough, and it is assumed that the pressure does not reflect a desire to pedal. The assistance is stopped by setting the ASSIST setpoint to 0.

[0022] Other conditions for stopping the start-up assistance procedure can be implemented for safety reasons, reflecting an abnormal situation caused by a power supply to the motor. For example, the procedure can be stopped when the drive wheel starts to rotate while no pedaling is detected. Indeed, this can indicate an obstruction of the pedal assembly while the drive wheel is not in contact with the ground, or in contact with low grip. To do this, the measurement of the wheel rotation speed is compared to a threshold value, and the assistance is stopped if the threshold is crossed in the absence of pedal rotation detection.

[0023] Examples of values ​​for the various parameters of the start-up assistance procedure are provided:

[0024] Starting threshold Sd: 30 Nm

[0025] Holding threshold Sm: 25 Nm

[0026] Hold time before Tstart assistance is engaged: 0.3 s.

[0027] Time limit to start rotation of the pedal Tstop: 5 s.

Claims

Method for controlling the start-up of an electrically assisted bicycle, comprising the following steps implemented in the absence of detection of rotation of a crankset: measuring the torque (Cp) exerted on the crankset; when the torque exceeds a trigger threshold (Sd), triggering a time delay (Tstart); and upon expiry of the time delay, if the torque is greater than a maintenance threshold (Sm) at most equal to the trigger threshold, engaging electrical assistance proportional to the torque despite the absence of detection of rotation of the crankset. Method according to claim 1, comprising the following step implemented in the absence of detection of rotation of the pedal assembly: stopping the electric assistance when the torque falls below the maintenance threshold (Sm). Method according to claim 1, comprising the following step: stopping the electric assistance after a time interval (Tstop) during which no rotation of the pedals has been detected. Method according to claim 1, comprising the following step implemented in the absence of detection of rotation of the pedal assembly: stopping the electric assistance when a rotation speed of a wheel driven by a motor is measured at a value greater than a threshold.

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