Control method of a powertrain unit of an assisted pedal bicycle and related assisted pedal bicycle

An assisted pedal electrical bicycle including an electronic control unit, being adapted and configured to carry out a control method of a powertrain unit of a pedal assisted electrical bicycle, wherein the powertrain unit includes an electrical machine having a stator and a permanent magnet rotor, being rotatable around a driving axis, the stator including a three-phase stator winding adapted to be supplied in order to cause the rotation of the rotor, a DC/AC converter controllable in order to supply the stator winding, a crank spindle, defining a crank axis and a pair of pedals mechanically fastened to the crank spindle, transmission means adapted to transmit the movement from the rotor to the crank spindle;

• the control method including the steps of a) starting the electrical machine in order to rotate the rotor, b) estimating a back electromotive force produced by the electrical machine, c) estimating the angular position of the rotor with respect to the stator winding starting from the estimation of the back electromotive force, and d) controlling the DC/AC converter based on said estimated angular position in order to make it supply the stator winding so that said electrical machine delivers a torque;
• wherein the electronic control unit is adapted and configured to carry out the control method wherein said transmission means include at least one free wheel (112, 116) in order to be adapted to selectively take the engaged state or the disengaged state and where in the control method said transmission means are adapted to selectively take an engaged state wherein said means allow transmitting the movement from the rotor to the crank spindle or a disengaged state wherein said means prevent transmitting the movement from the rotor to the crank spindle and wherein the control method also includes an initial synchronization step wherein the steps b), c) and d) are carried out sequentially one or more times after starting the electrical machine in the step a), in a condition where said transmission means are in the disengaged state.