Method for operating a drive unit of a hub drive of an electric bicycle

Abstract

The invention relates to a method for operating a drive unit of a hub drive of an electric bicycle, the drive unit comprising a permanent-magnet synchronous motor, the method comprising the steps: actuating the drive unit by means of an actuation signal which comprises a PWM signal; modifying the PWM signal by means of high-frequency voltage injection; identifying at least two phase currents in different phases of the drive unit; and determining an electrical angle of the drive unit on the basis of the identified phase currents.

Description

[0001] Description

[0002] title

[0003] Method for operating a drive unit of a hub drive of an electric bicycle

[0004] State of the art

[0005] The present invention relates to a method for operating a drive unit of a hub drive of an electric bicycle, a drive arrangement of a hub drive of an electric bicycle, and an electric bicycle.

[0006] Electric bicycles with hub drives are known, with a drive unit mounted on the hub of a front or rear wheel. The drive unit is typically actuated based on a rider's input, particularly in the form of a detected pedaling moment. In addition, knowledge of the current rotor position of the drive unit is usually required to provide the actuating current used to operate the drive unit. The rotor position is often detected using angle sensors integrated into the drive unit.

[0007] Disclosure of the invention

[0008] The method according to the invention with the features of claim 1 is distinguished by the fact that it enables the current angle of the drive unit to be detected without the use of an angle sensor. In particular, this enables precise monitoring of the angular position in a particularly simple and cost-effective manner. This is achieved according to the invention by a method for operating a drive unit of a hub drive of an electric bicycle, wherein the drive unit comprises a permanent magnet synchronous motor. The method comprises the following steps:

[0009] - Actuating the drive unit by means of an actuation signal which comprises a PWM signal,

[0010] - Modifying the PWM signal using high-frequency voltage injection,

[0011] - Detecting at least two phase currents on different phases of the drive unit, and

[0012] - Determining an electrical angle of the drive unit based on the measured phase currents.

[0013] An actuation signal is considered to be, in particular, an electric current by means of which the drive unit can be actuated. The actuation signal is preferably provided by a control unit of the electric bicycle.

[0014] A PWM signal is considered a pulse-width modulated signal. In particular, a PWM signal is generated as a square wave, which preferably fluctuates between the value 0 and a predetermined constant value.

[0015] High-frequency voltage injection can alternatively be referred to as "high-frequency voltage signal injection." In particular, high-frequency voltage injection is a well-known method, which the person skilled in the art can learn about, for example, from the literature.

[0016] In particular, the permanent magnet synchronous motor comprises a total of three phases. The instantaneous phase current is measured in at least two of these three phases, preferably using a current sensor.

[0017] In other words, the method specifically modifies the actuation signal using high-frequency voltage injection. This results in different currents, particularly at the different phases of the permanent magnet synchronous motor, which can be determined. By monitoring at least two phase currents, the current electrical angle of the permanent magnet synchronous motor can be determined. The method offers the advantage of enabling the current angular position of the drive unit to be determined without the need for angle sensors. The only sensors required are current sensors for detecting the phase currents. Furthermore, the determination can be performed silently, particularly since a voltage injection that is imperceptible to humans can be used.A particularly advantageous feature is that the entire detection technology can be integrated into a control unit, which in particular generates the actuation signal and is preferably designed as a separate component from the drive unit. The control unit and drive unit can be connected to each other via cables.

[0018] Particularly in the case of hub drives, where the drive unit can be located on the hub of the front or rear wheel, simple cabling can be provided easily and cost-effectively, even with long cable lengths, without the need for separate sensor cables, for example. For example, the control unit can be mounted on the frame, or near the saddle, or similarly. This also makes the drive system more robust against defects.

[0019] The subclaims contain preferred developments of the invention.

[0020] Preferably, the method further comprises the step of adapting the actuation signal for actuating the drive unit based on the determined electrical angle in such a way as to generate a predetermined motor torque by means of the drive unit. This means that the electrical angle determined without an angle sensor is used in the method to specifically adapt the actuation signal provided for the targeted operation of the drive unit in order to provide the desired operation of the drive unit, namely to generate the predetermined motor torque. This allows the drive unit to be operated particularly simply, efficiently, and precisely.

[0021] Particularly preferably, the high-frequency voltage injection is performed by PWM shifting at least part of the PWM signal. Preferably, the PWM shift occurs between at least two partial signals of the PWM signal, with each partial signal being provided for exactly one separate phase of the permanent magnet synchronous motor. This allows the high-frequency voltage injection to be provided in a particularly simple and targeted manner, in order to easily and clearly obtain a current difference between the phases that can be detected by the current sensors in order to determine the electrical angle.

[0022] Preferably, detecting the at least two phase currents each involves measuring the current twice per phase of the permanent magnet synchronous motor during a single PWM period. This means that each current sensor detects the respective phase current exactly twice during each PWM period, in particular at different times. This allows the current difference to be determined in a particularly simple and unambiguous manner, based on which the electrical angle of the drive unit can be estimated.

[0023] Preferably, the current measurement is performed at the beginning and in the middle of each PWM period. In particular, the current measurements are always performed at constant intervals per phase. This allows for reliable detection of current differences and a particularly simple and cost-effective technical implementation of the measurement.

[0024] Preferably, the electrical angle of the drive unit is determined based on a detected current difference between the two current measurements during the individual PWM period. This means that during the detection step, a difference is calculated between the measured current of a first phase and a second phase of the permanent magnet synchronous motor. This enables a particularly simple, cost-effective, and reliable implementation of the measurement method.

[0025] More preferably, the PWM signal is generated at a preferably constant frequency of at least 10 kHz, preferably at least 14 kHz, particularly preferably 18 kHz. In particular, the high-frequency voltage injection also occurs at a corresponding frequency, preferably of at least 10 kHz, preferably at least 14 kHz, particularly preferably 18 kHz. This makes it easy to ensure that the signals are generated in a range that is acoustically imperceptible to humans, which, for example, can also enable a particularly high level of user comfort for the electric bicycle.

[0026] Particularly preferably, the high-frequency voltage injection is generated exclusively in a d-current direction of the permanent magnet synchronous motor. A d-current direction is considered to be, in particular, a direction of current generation such that it occurs in a non-torque-generating manner, preferably such that a stator magnetic field is aligned parallel to a rotor magnetic field. As a result, the stator magnetic field does not exert a magnetic force on the rotor that would generate a drive torque. In particular, instead, only a magnetic force is exerted on the rotor in the radial direction. This ensures that the high-frequency voltage injection has no influence on the torque generation of the drive unit. This allows for particularly effective operation of the electric bicycle.

[0027] Preferably, the method is only performed up to a certain maximum speed of the drive unit. This means that if the speed of the drive unit, preferably also determined using the method, reaches or exceeds the predetermined maximum speed, the method is deactivated. For example, an alternative method for determining the electrical angle can be performed starting at this maximum speed. This enables the electric bicycle to operate particularly efficiently at low speeds.

[0028] Preferably, a current rotor position and / or a rotational speed of the drive unit, in particular of the permanent magnet synchronous motor, is determined based on the determined electrical angle of the drive unit. This means that a physical variable that directly characterizes the operating state of the drive unit is calculated from the electrical angle, preferably corresponding to the control. This variable can be directly used, for example, for other components or operating modes of the electric bicycle.

[0029] Particularly preferably, the electrical angle of the drive unit is determined entirely without angle sensors. This means that the electrical angle is determined based on current measurements, for example, using current sensors, exclusively in software, with no hardware angle sensors present or used.

[0030] Furthermore, the invention leads to a drive assembly for a hub drive of an electric bicycle, comprising a drive unit, at least two current sensors, and a control unit. The control unit is configured to carry out the described method. In particular, the drive assembly is designed entirely without angle sensors.

[0031] Preferably, the current sensors are an integral part of the control unit. This means that the current sensors are geometrically arranged within the control unit, which is preferably designed as a structural unit. This enables a particularly simple and cost-effective design of the drive unit, which is preferably designed as a structural unit separate from the control unit.

[0032] Preferably, the drive unit and the control unit are connected by a cable. In particular, electrical currents and signals can be transmitted via the cable. Preferably, the cable can be provided exclusively for transmitting the actuation signal. This means that additional sensor cables between the control unit and the drive unit can be dispensed with, enabling a particularly simple, cost-effective, and compact design of the drive arrangement.

[0033] The invention further relates to an electric bicycle comprising the described drive assembly. The drive unit is arranged on a hub of a wheel of the electric bicycle, preferably a front wheel or a rear wheel. The control unit is preferably arranged remotely from the hub, for example, on a frame or on a saddle of the electric bicycle.

[0034] Short description of the drawings

[0035] The invention is described below using an exemplary embodiment in conjunction with the figures. In the figures, functionally identical components are identified by the same reference numerals. Figure 1 shows a simplified schematic view of an electric bicycle in which a method according to a preferred embodiment of the invention is implemented.

[0036] Figure 2 is a highly simplified schematic view of the method according to the invention, and

[0037] Figure 3 shows a simplified detailed view of a control of the drive unit of the electric bicycle of Figure 1 by means of the method according to the invention.

[0038] Preferred embodiments of the invention

[0039] Figure 1 shows a simplified schematic view of an electric bicycle 100 with a drive arrangement 20 in which a method 50 according to a preferred embodiment of the invention is carried out.

[0040] The drive arrangement 20 comprises a drive unit 1. The drive unit 1 can be supplied with electrical energy by means of an electrical energy storage device 109 of the electric bicycle 100.

[0041] The drive unit 1 of the drive assembly 20 is arranged on a hub of a rear wheel 110 of the vehicle 100. In particular, this is an electric bicycle 100 with a hub drive 10.

[0042] A motor torque generated by the drive unit 1 can provide motor assistance to the pedaling force generated by the muscular power of a rider of the electric bicycle 100. To generate the motor torque, the drive unit 1 comprises a permanent magnet synchronous motor.

[0043] The rider's muscle power can be applied via a crank mechanism comprising cranks 104. The crank mechanism is connected to the hub of the rear wheel 110 via a chain drive. During operation of the electric bicycle 100, the drive unit 1 is operated depending on the pedal force generated by the rider, which can be detected, for example, by means of a torque sensor, e.g., on the crank mechanism and / or on a pedal shaft.

[0044] The drive unit 1 is operated by providing an actuation signal from a control unit 3. In particular, an electric current is provided as the actuation signal, by means of which the permanent magnet synchronous motor of the drive unit 1 is supplied. The actuation signal is additionally generated based on a current electrical angle of the drive unit 1, based on which, in particular, a current rotor position and / or a current rotational speed of the permanent magnet synchronous motor is determined.

[0045] The method 50 according to the invention for operating the drive unit 1 of the hub drive 10 of the electric bicycle 100 comprises determining the electrical angle of the drive unit 1 without an angle sensor, which is described in detail below.

[0046] Figure 2 shows a highly simplified schematic representation of steps of method 50. Further details of the control of drive unit 1 and the sensor system of electric bicycle 100 are shown in Figure 3.

[0047] In the method 50, the actuation 51 of the drive unit 1 occurs by means of the actuation signal 11, wherein the actuation signal 11 comprises a PWM signal 12. In particular, the electrical current for actuating the permanent magnet synchronous motor is provided as the PWM signal 12.

[0048] The permanent magnet synchronous motor comprises a total of three different phases, each supplied with a separate phase current 31, 32, 33, which can be considered parts of the actuation signal 12. Fig. 3 above shows an example diagram of a temporal progression of the PWM signal 12 with the phase currents 31, 32, 33.

[0049] In method 50, the PWM signal is modified 52 by means of high-frequency voltage injection, which is generated by a PWM shift of parts of the PWM signal 12. In detail, two of the three supply voltages 41, 42, 43 (see Figure 3, center) are shifted in time relative to each other.

[0050] The PWM signal 12 is generated at a frequency of 18 kHz. This allows the actuation signal 11 and the high-frequency voltage injection to be generated in a range inaudible to humans. The rider of the electric bicycle 100 cannot perceive any noises specifically generated by the implementation of the method 50, thereby providing a particularly high level of user comfort.

[0051] The modification 52 of the actuation signal 11 is further performed such that the high-frequency voltage injection is generated exclusively in a, particularly non-torque-generating, d-current direction of the permanent magnet synchronous motor. As a result, the high-frequency voltage injection does not generate any torque that influences the overall generated motor torque.

[0052] Subsequently, at least the two phase currents 31, 32, 33 of the corresponding phases between which the PWM shift occurs are detected 53. Detection 53 is performed by measuring the current twice per phase during a single PWM period, specifically at the beginning and in the middle of each PWM period. The corresponding measuring points 35 are marked in Figure 3 above.

[0053] The determination 54 of the instantaneous electrical angle of the drive unit 1 is then performed based on a current difference between the two current measurements 35 during the individual PWM period. The high-frequency voltage injection generated by the PWM shift results in a current difference 37 (see Fig. 3 below) between the two mutually shifted phases that is easy and clearly detectable, and from which the instantaneous electrical angle can be easily and accurately calculated.

[0054] The detection 53 is carried out by means of current sensors, which are integrated into the control unit

[0055] 3 are integrated. In detail, exactly two current sensors are provided, which are designed to detect the respective phase currents 31, 32, 33, in particular the phases shifted relative to one another.

[0056] Based on the electrical angle of the drive unit 1 determined in step 54, the actuation signal is then adjusted 55 to provide an adjusted actuation of the drive unit 1. In detail, the actuation signal is adjusted 55 in such a way as to generate a predetermined motor torque by means of the drive unit 1. For example, the predetermined motor torque can be calculated by means of the control unit 3, preferably based on other factors, such as the pedaling torque, an assistance factor, or the like.

[0057] The control unit 3 can be arranged at a greater distance from the drive unit 1, for example, as shown in Figure 1 near the saddle 107. The control unit 3 and the drive unit 1 are connected to one another by a line 4. The fact that only the current sensors arranged in the control unit 3 are required for the measurement technology for detecting the angle of the drive unit 1 enables a particularly simple, cost-effective, and robust design. In particular, additional sensor lines between the drive unit 1 and the control unit 3 can be dispensed with. This also makes it possible to provide a drive arrangement 20 that is more robust against defects.

[0058] Method 50 offers the advantage that the current angular position of drive unit 1 can be detected simply and precisely, without angle sensors and without noise. Particularly in the case of hub drive 10 with large distances between control unit 3 and drive unit 1, a particularly advantageous, simple, cost-effective, and robust design can be achieved.

Claims

Claims 1 . A method for operating a drive unit (1) of a hub drive (10) of an electric bicycle (100), wherein the drive unit (1) comprises a permanent magnet synchronous motor, comprising the steps of: actuating (51) the drive unit (1) by means of an actuation signal (11) which comprises a PWM signal (12), Modifying (52) the PWM signal (12) by means of high-frequency voltage injection, detecting (53) at least two phase currents at different phases of the drive unit (1), and Determining (54) an electrical angle of the drive unit (1) based on the detected phase currents.

2. The method according to claim 1, further comprising the step of: adjusting (55) the actuation signal for actuating the drive unit (1) based on the determined electrical angle in such a way as to generate a predetermined motor torque by means of the drive unit (1).

3. Method according to one of the preceding claims, wherein the high-frequency voltage injection is carried out by means of PWM shifting of at least a part of the PWM signal.

4. The method according to any one of the preceding claims, wherein detecting the at least two phase currents comprises measuring the current twice per phase during a single PWM period.

5. The method according to claim 4, wherein the current measurement is carried out at the beginning and in the middle of each PWM period.

6. The method according to one of claims 4 or 5, wherein the determination of the electrical angle of the drive unit (1) is based on a detected current difference between the two current measurements during the individual PWM period.

7. Method according to one of the preceding claims, wherein the PWM signal is generated with a, in particular constant, frequency of at least 10 kHz, preferably at least 14 kHz, particularly preferably 18 kHz.

8. Method according to one of the preceding claims, wherein the high-frequency voltage injection is generated exclusively in a d-current direction of the permanent magnet synchronous motor.

9. Method according to one of the preceding claims, wherein the method is carried out only up to a predetermined maximum speed of the drive unit (1).

10. Method according to one of the preceding claims, wherein a rotor position and / or a rotational speed of the drive unit (1) is determined based on the determined electrical angle of the drive unit (1).

11. Method according to one of the preceding claims, wherein the determination of the electrical angle of the drive unit (1) is carried out completely without angle sensors.

12. Drive arrangement of a hub drive (10) of an electric bicycle (100), comprising: a drive unit (1), at least two current sensors (2) and a control unit (3) which is configured to carry out the method according to one of the preceding claims.

13. Drive arrangement according to claim 12, wherein the current sensors (2) are an integral part of the control unit (3).

14. Drive arrangement according to claim 12 or 13, wherein the drive unit (1) and the control unit (3) are connected by means of a line (4).

15. Electric bicycle, comprising a drive arrangement (20) according to one of claims 12 to 14, wherein the drive unit (1) is arranged on a hub (101) of a wheel (110), in particular a front wheel or rear wheel.

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