Control of electric motor

Abstract

A method for controlling an electric machine (EM) during a synchronization procedure of a first shaft and a second shaft, whereby said first shaft is in drive connection with an output shaft of said electric machine (EM) and said first shaft and said second shaft are connectable over a synchronization mechanism, comprising: controlling the output shaft to a speed (na) close to a target speed (nt) of said second shaft by using speed control; continuously controlling an electrical torque of said electrical machine (EM), such that an output torque (Tout) of said electric machine (EM) becomes essentially equal to zero; and controlling said synchronization mechanism to synchronize the speed of the first shaft and the second shaft.

Claims

1. A method performed by an electronic control unit in a vehicle for controlling an electric machine during a synchronisation procedure of a first shaft and a second shaft, whereby said first shaft is in drive connection with an output shaft of said electric machine and said first shaft and said second shaft are connectable over a synchronisation mechanism, comprising: controlling, by the electronic control unit, the output shaft to an actual speed close to a target speed of said second shaft by using speed control; continuously controlling, by the electronic control unit, an electrical torque of said electric machine, such that a torque on said output shaft becomes essentially equal to zero during the synchronisation procedure of the synchronisation mechanism; and controlling, by the electronic control unit, said synchronisation mechanism to synchronise the speed of the first shaft and the second shaft.

2. The method according to claim 1, further comprising: continuously measuring an actual speed of the first shaft, wherein controlling the electrical torque of said electrical machine is performed dependent on any changes of said actual speed of said first shaft.

3. The method according to claim 1, further comprising: continuously measuring a position of said synchronising mechanism, an actual speed of said first shaft, and an actual speed of said second shaft; and controlling the output torque of said electrical machine when said synchronisation mechanism reaches a predetermined position, wherein said output torque of said electrical machine is dependent on a difference between said actual speed of said first shaft and an actual speed of said second shaft.

4. The method according to claim 3, wherein said output torque is based on said difference in actual speed between the first and the second shaft.

5. A vehicle comprising: a transmission having an input shaft and a second shaft, wherein the input shaft and the second shaft are connected by a synchronisation mechanism; an electrical machine having an output shaft, wherein said input shaft of the transmission is connected to said output shaft of said electrical machine; at least one gear allocated to said input shaft, wherein said gear is synchronised with the synchronising mechanism; and an electronic control unit for controlling the electrical machine during a synchronising procedure of the input shaft and the second shaft, wherein the electrical control unit is configured to: control the output shaft to an actual speed close to a target speed of said second shaft by using speed control; continuously control an electrical torque of said electrical machine, such that a torque on said output shaft of said electrical machine becomes essentially equal to zero during the synchronisation procedure of the synchronisation mechanism; and control said synchronisation mechanism to synchronise the speed of the input shaft and the second shaft.

6. The vehicle according to claim 5, wherein said transmission is a dual-clutch multi speed transmission and said input shaft is one of a first and a second input shaft and a plurality of gears are allocated to said input shaft.

7. A non-transitory computer readable medium storing a computer program comprising program code for controlling an electric machine during a synchronisation procedure of a first shaft and a second shaft, whereby said first shaft is in drive connection with an output shaft of said electric machine and said first shaft and said second shaft are connectable over a synchronisation mechanism, the program code, when executed by at least one processor of a device, causes the device to: control the output shaft to an actual speed close to a target speed of said second shaft by using speed control; continuously control an electrical torque of said electric machine, such that a torque on said output shaft becomes essentially equal to zero during the synchronisation procedure of the synchronisation mechanism; and control said synchronisation mechanism to synchronise the speed of the first shaft and the second shaft.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) All drawings in the figures are schematic.

(2) FIG. 1 discloses a vehicle.

(3) FIG. 2 discloses a dual-clutch transmission provided with an electrical machine.

(4) FIGS. 3a and 3b discloses two embodiments of the invention.

(5) FIG. 4a-c disclose diagrams showing a fork position, an e-machine speed and a shaft torque during a shifting procedure.

(6) FIG. 5 discloses a flowchart of the method of the invention.

DETAILED DESCRIPTION

(7) FIG. 1 discloses a vehicle V, in which the transmission 10 disclosed in FIG. 2 can be provided and which transmission 2, can benefit from the method for controlling an electric machine EM.

(8) Now FIG. 3 discloses an electrical machine EM with an output shaft 10 connected to a first shaft 11. The first shaft can be connected to a second shaft 12 via a synchronisation mechanism 13. A first speed sensor 14 continuously measures the speed of the first shaft 11. A second speed sensor 16 continuously measures the speed of the second shaft 12. A position sensor 15 measures the position of the synchronisation mechanism 13. The position of the synchronisation mechanism 13 is preferably measured as the position of a control fork (not disclosed), however any position of a moveable part indicating the engagement state of the synchronisation mechanism 13 could be measured.

(9) The signals from the sensors 14, 15, 16 are sent to the electronic control unit (ECU) ECU, which can control the electrical machine EM based on the input from the sensors 14, 15, 16. In one embodiment of the method, only the signal from the first speed sensor 14 is used, whereby the ECU controls the electric machine with a feedback control, such that a change in speed of the first shaft 11 (and consequently of the output shaft 10 of the electric machine) met by a torque control of the electric machine EM to counteract the torque from the inertia of the rotor of the electric machine EM caused by the change in speed.

(10) In another embodiment of the method, signals from all three sensors 14, 15, 16 are used by the ECU to control the electric machine EM. When the signals from all three sensors 14, 15, 16 are used a feed forward control of the output torque of the electric machine EM can be achieved. A difference between the speed of the first shaft 11 and the speed of the second shaft 12 can be calculated by the ECU. Further, the speed difference together with a continuously monitoring of the position of the synchronisation mechanism 13, the ECU can predict the speed change of the first shaft 11 when it is synchronising with the speed of the second shaft 12, whereby the output torque of the electric machine EM can be controlled to 0 with essentially no delay. When the synchronisation mechanism 13 passes a predefined position (e.g. the position when the synchronisation mechanism 13 starts to transmit torque), the ECU can start controlling the electric machine, such that the torque caused by the inertia of the rotor at a speed change of the output shaft 10 can be counteracted. The output torque from the electrical machine EM can thereby continue to be zero during the whole synchronisation procedure.

(11) In FIG. 3b, an alternative design of how the electrical machine EM is connected to the first shaft 11 is disclosed. The output shaft 10 is connected to the first shaft 11 over a gear step 17, 18, whereby a gear ratio different from 1:1 can be achieved. When the gear ratio is such that the output torque of the electrical machine EM is increased over the gear step the benefits of the method is even greater, since the reduction in torque load upon the synchronisation mechanism 13 becomes higher. The method is however applied correspondently, with the only modification that the speed of the output shaft 10 must be derived from the speed of the first shaft 11 with consideration of the gear ratio in the gear step 17, 18 between the output shaft 10 and the first shaft 11. Further gear steps of or other gear ratio changing means (e.g. chain, CVT) could be provided in between the electrical motor and the synchronisation mechanism 13, without effecting the scope of the invention.

(12) In the dual-clutch transmission 100 disclosed in FIG. 2 the output shaft 110 of an electrical machine EM is connected to the first input shaft 111 of the dual-clutch transmission 100. The transmission 100 is further provided with a second input shaft 150 and a first and a second input clutch C1, C2 are allocated to the first and the second input shaft 111, 150 respectively. The input clutches C1, C2 connects the transmission 100 to an internal combustion engine CE. The transmission 100 is provided with two output shafts 151, 152, which are connected to a differential 153, which distribute the torque to the drive wheels 154, 155 of the vehicle V. The schematically disclosed dual-clutch transmission 100 in FIG. 2 is provided with 7 forward and one backward speed, I, II, III, IV, V, VI, VII, R, which are marked with roman letters in the figure. The general function of a dual-clutch transmission 100 is known and won't be described in further detail.

(13) The output shaft 110 of the electrical machine EM is connected over a transfer transmission, such as the gear step 17, 18 disclosed in FIG. 3b, to the first input shaft 111. When any of the second, fourth, sixth or reverse gear (II, IV, VI, R) are synchronised, the rotor of the electrical machine EM are synchronised to. The disclosed method is used in order to minimise the load contribution from the inertia of the rotor of the electrical machine EM, on the synchronisation mechanisms 113a, 113b, during a synchronisation procedure of the any of the second, fourth, sixth or reverse gears II, IV, VI, R. It is understood that the electrical machine EM can be arranged elsewhere in the dual-clutch transmission 100 without departing from the scope of the invention, just as the method can be applied on other types of transmissions or for synchronising other gears.

(14) Now the method will be described in conjunction with FIGS. 4a-c and 5. In FIG. 4 a diagram disclosing a fork position FP (FIG. 4a), speed n_110 of the output shaft 110 of electrical machine EM (FIG. 4b) and the torque T on the output shaft 110 of the electrical machine EM (FIG. 4c) is disclosed. In FIG. 5 the method steps of the method are disclosed. The method could for example be applied in the transmission 100 disclosed in FIG. 2, whereby references will be made to the transmission 100 in FIG. 2. However, diagrams for the corresponding values of the embodiments disclosed in FIGS. 3a and 3b, would have correspondent values.

(15) In FIG. 4a the fork position FP, during shifting from a second gear II to a fourth gear IV, via a neutral position N is disclosed. Until the time t1 the synchronisation mechanism 113b is engaged with the second gear II, at which point it disengages. As can be seen in the diagram in FIG. 4c, the electrical machine EM has delivered torque to the drive line before the time t1. At t1, the output torque T110 has been decreased to zero.

(16) Now, the transmission 100 is to engage the fourth gear IV, whereby the method starts at the time t2. The speed of the output shaft 110 of the electrical machine EM is thereby decreased to a speed na, close to a target speed nt, n110.fwdarw.nt. A more accurate speed is not possible to achieve with speed control of the electrical motor EM. The target speed nt of the output shaft 110 is the speed that is equal a synchronised speed for the gear to be activated. The speed control is performed during the time t2-t3, whereby the output shaft 110 of the electrical machine EM is subjected to a negative torque T110, induced by the electrical motor EM in order to reduce the speed. Between the target speed nt and the actual speed na is a speed difference nd. It is this speed difference that causes the inertia torque load upon the synchronisation mechanism 113a, 113b, during synchronisation of the gears. The speed difference nd is only schematically disclosed and varies from time to time and may also be lower than the target speed.

(17) As can be seen in FIG. 4a, showing the fork positions, at t3, the synchronisation mechanism 113a starts to move to synchronise the fourth gear IV. Whereby during half the time between t3 and t4 the synchronisation mechanism 113a starts to transfer torque, whereby the output torque T110 of the electrical motor EM is controlled to be zero, i.e. to counteract the inertia torque on the output shaft 110, T110=0. The electrical motor EM is controlled using any of the disclosed embodiments to achieve the torque control T110=0 as long as the synchronisation of the fourth gear IV is performed. When a synchronised speed is achieved such that the fourth gear can be/is engaged and the speed of the output shaft 110 has reached the target speed nt, the method is ended at the time t4 and the electrical motor EM can start delivering torque to the drive train again.

(18) In FIG. 4c disclosing the torque of the output shat 110, the torque T is disclosed to be both positive and negative over a time period just before the time t6. This symbolises the torque caused by the change in speed caused by the synchronisation of a gear and the counteracting torque caused by the electrical motor control, these two opposite directed torques counteracts each other, so that the resulting torque upon the output shaft 110 is zero.