METHOD FOR OPERATING A DRIVETRAIN AND VEHICLE DRIVETRAIN WITH ELECTROMOTIVE DRIVE

Description

State of the art

[0001] The invention relates to a method for operating a drive train according to the preamble of claim 1. Furthermore, the invention according to the preamble of claim 8 relates to a vehicle drive train with an electric motor drive.

[0002] DE 10 2016 211 394 A1 discloses a method and a device according to the preambles of claims 1 and 8.

[0003] DE 10 2015 119 167 A1 discloses a method and a system for compensating torque ripple of a traction motor of a battery electric vehicle that does not have a prime mover.

[0004] EP 2 007 005 A2 discloses a motor control device for performing vector control for a motor driving a load whose load torque fluctuates periodically. The motor is a three-phase synchronous motor with permanent magnets.

[0005] In electric vehicle drivetrains, unlike vehicles with combustion engines, the combustion engine is no longer a noise source, replaced by the significantly quieter electric motor. This means that noises that would not be noticeable in a combustion engine drivetrain because the combustion engine or its auxiliary components would have drowned them out are now also disturbing. This is especially true at low vehicle speeds, as tire noise and wind noise dominate at high speeds and mask any additional noise.

[0006] DE 10 2015 207 632 A1 relates to a device for reducing gear noise of a drive gear meshing with a driven gear, wherein forces from the gears can be introduced into a housing via a support, wherein the device has a sensor device, a control device, and an actuator, and wherein a dynamic vibration signal can be detected by means of the sensor device and the vibration signal can be fed to the control device, wherein a vibration reduction signal can be generated by means of the control device and fed to the actuator, wherein the actuator is arranged on or in the support such that forces from the gears can be transmitted into the housing via the actuator, wherein a relative displacement and / or a force application to a component carried by the support can be actively effected by means of the actuator. The device is also designed for use of the actuator as a sensor device. Disclosure of the invention

[0007] The object of the invention is to provide a method and to create a device which makes it possible to operate a drive train which is operated, in particular exclusively, by an electric motor.

[0008] The problem underlying the invention is solved by a method having the features of claim 1 and a vehicle drive train having the features of claim 8. Advantageous developments of the invention are specified in subclaims.

[0009] According to the invention, a method for operating a drive train with an electric motor drive provides that a speed and a drive torque of the drive can be converted via a toothed gear stage for an output, and the drive is controlled with a control signal.

[0010] A periodic torque change signal is superimposed on the control signal, which alternately reduces and increases the drive torque and is in phase with a change in the tooth stiffness of the toothed gear stage, whereby a signal strength of the torque change signal is lower when the tooth stiffness decreases than when the tooth stiffness increases.

[0011] Improved noise reduction is achieved by providing that the periodic torque change signal simulates the tooth stiffness and is stored in a table or described by a mathematical function that approximates the tooth stiffness.

[0012] One advantage of this process is that there is little or no disturbing noise due to the variable tooth stiffness when two gears roll. Such noise would be tonal and would increase with increasing torque transmitted through the gear stage. Tooth stiffness changes periodically across each individual tooth pair that is currently in mesh.

[0013] The frequency of this change is therefore, for simple spur gear stages, the speed of the gear multiplied by its number of teeth.

[0014] One advantage of the invention is that it entails neither additional costs nor additional weight and can be implemented purely via a software extension. The software can be implemented very late in the development process or even retrospectively, e.g., as a software update for vehicles in the field. The computing resource requirements on the control unit for this are low. The only signals required are the rotor position and the position of the gears, which are determined via the design, and an estimated torque. The torque of the electric machine can be estimated by the field-oriented control, and the rotor position is also measured or estimated for this. In principle, therefore, no additional sensors are required.

[0015] The method according to the invention can also be used in other drive trains with electrical machines that have a gearbox but no internal combustion engine. Such a drive train can, for example, be a drive train from industrial technology or even white goods. White goods include, among other things, refrigerators, freezers, etc., whose refrigerant compressor is driven by an electric motor. White goods also include washing machines and dishwashers, whose pump or drum is driven by an electric motor. Furthermore, the drive train according to the invention can also be used in power tools with a gearbox. Such power tools with a gearbox include, in particular, drills. However, electric saws and grinders, for example, can also have such drive trains, each with a gearbox.

[0016] According to a further development, the control signal is a torque control signal of a torque control system or an output voltage signal of a torque control system. Such control signals are advantageous in typical electric motor drives.

[0017] According to a further development, the output voltage signal or the torque control signal of the torque control is associated with a field-oriented torque control or current control. Field-oriented torque control or current control achieves an improvement in the speed and positioning accuracy of a frequency converter for the electric motor drive.

[0018] According to a further development, the periodic torque change signal is superimposed on the control signal depending on a torque setpoint or a rotor position of the drive. This dependence on the torque is particularly advantageous because the influence of the change in tooth stiffness changes with the transmitted torque of the gear unit. In this respect, the amplitude of the torque change signal can be adjusted according to any changes in the torque.

[0019] According to a further development, the periodic torque change signal has a sinusoidal shape. A sinusoidal signal is particularly easy to control.

[0020] Also for improved noise reduction, it may be provided that an equivalent value of the periodic torque change signal is equal to zero.

[0021] For a particularly good function of a field-oriented torque control over the entire speed range, it can be provided that in order to control the drive train via a suitable system model and a subtraction of its output signal from the measurement signal of the real system, an effect of noise damping on the real system can be masked out for a field-oriented torque control of the drive.

[0022] According to the invention, a vehicle drive train with electric motor drive comprises: a drive whose drive torque and speed are variable, a toothed gear stage which can be coupled to the drive to convert the speed and drive torque, a control unit for controlling the drive with a control signal.

[0023] The control unit is configured to superimpose a periodic torque change signal on the control signal, which alternately reduces and increases the drive torque and is in phase with a change in the tooth stiffness of the toothed gear stage. The signal strength of the torque change signal is lower when the tooth stiffness decreases than when the tooth stiffness increases. Improved noise reduction is achieved by providing that the periodic torque change signal simulates the tooth stiffness and is stored in a table or described by a mathematical function that approximates the tooth stiffness.

[0024] To further reduce disturbing noise, various additional design measures can be implemented. For example, the engagement of the gear teeth can be increased. Furthermore, the gearbox housing can be reinforced. The additional costs associated with housing reinforcement can be reduced by the design according to the invention.

[0025] The invention makes it possible to create a drive train that runs smoothly despite spur gearing, thus eliminating the additional costs of helical gearing. However, helical gearing can also be used in a drive train according to the invention. Compared to spur gearing, helical gearing achieves smoother running and lower noise levels because each pair of teeth engages and disengages with a continuous transition. Thus, torque is transmitted more evenly than with spur gearing.

[0026] Both the method and the device can be applied to a vehicle drivetrain that is exclusively powered by an electric motor. This means that the transmission stage cannot be coupled to an internal combustion engine.

[0027] Possible embodiments of the invention are explained below with reference to the drawings.

[0028] They show: Fig. 1 a vehicle powertrain having a drive and an associated control unit with noise dampening; Fig. 2 using a block diagram to illustrate the integration of noise damping into the vehicle drive train according to Fig. 1 , whereby a stationary torque change signal is simulated; Fig. 3 based on a block diagram, a further embodiment in which the integration of noise damping takes place as a superposition on the stator voltage setpoint for an inverter of the drive; Fig. 4 based on a block diagram, a further embodiment in which the integration of noise damping takes place as a superposition of a periodic torque change signal on the torque setpoint; and Fig. 5 based on a block diagram, a further embodiment in which the integration of noise damping takes place as an overlay on the voltage setpoint for a pulse inverter of the drive.

[0029] Figur 1 schematically shows a vehicle drive train 2 of an electric vehicle. The electric vehicle does not have an internal combustion engine drive and, to this extent, exclusively has an electric motor drive 4. The drive 4 is designed, in particular, as a converter-controlled synchronous motor. Depending on the motor vehicle type, the electric motor drive 4 can alternatively be designed as a DC motor or as a converter-controlled asynchronous motor. Another alternative for the drive 4 is a switched reluctance machine, also referred to as a "switched reluctance motor" (SRM for short). Furthermore, a transverse flux motor can be used as the drive 4.

[0030] The drive torque and the speed of the drive 4 can be varied by means of a control unit 6, which is provided for controlling the drive 4.

[0031] An output shaft 8 of the drive 4, rotatably mounted by means of a rolling bearing 7, is rotationally fixedly connected to a first gear 10 of a toothed gear stage 12 arranged within a gear housing 13. The first gear 10 meshes with a second gear 14 of the gear stage 12. The second gear 14 is coupled via a differential gear to two drive shafts 16, which are mounted in rolling bearings 17 and rotationally fixedly connected to vehicle wheels 18.

[0032] The first gear 10 is smaller in diameter than the second gear 14 and thus forms a pinion. A rotational speed and a drive torque of the drive 4 are converted via the toothed gear stage 12 to an output 19, which has the drive shafts 16. By means of the gear stage 12, the rotational speed of the drive 4 is translated into a lower transmission output speed, and the drive torque is translated into a higher transmission output torque. In this respect, a drive 4 can be used that has a relatively high maximum speed but too low a torque.

[0033] The second gear 14 contains the differential gear, which distributes the transmission output torque evenly to the two vehicle wheels 18.

[0034] Alternatively, the gear stage 12 can also be designed as a planetary gear and / or as a shiftable transmission with multiple stages, in particular two stages, which have different gear ratios. The vehicle drive train 2 can also be designed as a wheel hub motor that drives only a single vehicle wheel 18.

[0035] The gears 10, 12 are either straight-toothed or helical-toothed. The teeth 20, 22 of the gears 10, 12 mesh with each other. The system of the two meshing gears 10, 12 with variable tooth stiffness represents a dual-mass oscillator with a variable spring constant.

[0036] The first gear 10 has a first mass inertia, and the second gear 12 has a second mass inertia. Thus, the two gears 10, 12 form the dual-mass oscillator, which oscillates at a variable, rotation-path-dependent frequency, a tooth meshing frequency.

[0037] Due to the variable tooth stiffness of the teeth, vibrations are excited at the meshing gears 10, 12 during rotation. These vibrations are transmitted via the gears 10, 12, the shafts 8, 16, and the rolling bearings 7, 17 to the gear housing 13, where they are radiated as noise from a vibrating surface. In addition to the rotational vibrations, the gears 10, 12 also vibrate translationally with the bearings 7, 17 against the gear housing 13, causing the noise. Here, the gear housing 13 is excited to translational vibrations via the bearings 7, 17, causing sound waves to propagate in the air in the form of pressure and density fluctuations. The variable meshing force engages at the intersection point of the two gears 10, 12 and acts tangentially on the respective gear 10 or 12. This force must be supported by the respective bearing 7 or 17.

[0038] The control unit 6 has a control system which is based on the impression, i.e. superimposition of a periodic additive torque oscillation via the electric drive 4 for damping unwanted noise with the tooth meshing frequency during operation of the electric motor vehicle. For this purpose, a periodic torque change signal is superimposed on a control signal of the drive 4. The periodic torque change signal alternately reduces and increases the drive torque. The periodic torque change signal is in phase with the tooth stiffness of the gear stage 12 switched into the power flow. The control signal can in particular be a torque control signal or an output voltage signal of a torque control system. This torque control can in particular be field-oriented, i.e. a vector control.Field-oriented control is used to improve the speed and positioning accuracy with a frequency converter provided in control unit 6.

[0039] Ideally, this torque change signal has no DC component or a DC component of zero. The torque change signal increases or decreases a transmitted total torque, which is established based on the torque control signal and the drive control signal at drive 4. The tooth stiffness of the teeth 20, 22 currently in mesh determines whether the total torque is increased or reduced. On average, therefore, the output torque requested by the driver, which is set by the parallel torque control, remains unchanged. The periodic torque change signal can simulate the exact course of the torque fluctuation or, for example, be approximated by a sine signal of the same phase and frequency.

[0040] Since the influence of the tooth stiffness change changes with a transmission output torque requested by the driver, the amplitude, i.e. a signal strength, of the torque control signal must be adjusted accordingly with the requested transmission output torque.

[0041] In the following, the control by means of control unit 6 is explained in more detail using control-related variables.

[0042] By adding a periodic, steady-state torque setpoint or voltage setpoint signal to an output signal of, for example, a field-oriented torque or current controller, gear noise is dampened at the tooth meshing frequency. The change in stiffness over the rotational path acts like a vibration excitation for the dual-mass oscillator at constant torque. This means that the meshing teeth are excited to vibrate against each other. This excitation is counteracted by the modulation of the torque of drive 4. For this purpose, the signal strength of the drive control signal is slightly reduced when the tooth stiffness decreases. Conversely, the signal strength of the drive control signal is slightly increased when the tooth stiffness increases.

[0043] In Fig. 2 A first embodiment of the method is shown using a block diagram. The torque change signal 5 is simulated in a stationary manner. No controlled variable is fed back, so the example is a control system. The input variables are the torque 23 and the rotor position 24 of the drive. An offset position 26 is added to this rotor position 24. The number of teeth 30 of the gears is included in the control system. The torque 23 as an input variable can be represented in the model via a transfer function 32 of the rotational amplitude. The main determinant of the stationary torque change signal is a sine function 33. The output variable is the torque change signal 5 for damping the vibrations.

[0044] Fig. 3 shows, using a second embodiment, the integration of the noise damping 34 as a connection to the stator voltage setpoint 40 for a control unit of the drive 4 designed as an inverter. Instead of the sine function, a two-dimensional table is used, which outputs the appropriate torque setpoint 36 of the drive against the rotor position and the torque. Various periodic signals are conceivable for this purpose. For example, either a rectangular function or a tabularly stored sine function can be used. Sine and rectangular functions are each easy to implement. According to the invention, the tooth stiffness is simulated as precisely as possible and stored in the table. According to an alternative of the invention, the tooth stiffness is approximated using a function. Thus, in Fig. 3 possible integrations of the noise damping 34 in an existing field-oriented torque control 38 or current control are shown.

[0045] The field-oriented torque control 38 receives the torque setpoint 36 as an input variable. The field-oriented torque control 38 outputs the stator voltage setpoint 40 as the output variable, which in this respect represents the control signal of the drive 4. This stator voltage setpoint 40 is summed together with a torque change signal 5, which is the output value of the noise damping 34, at a summation node 41. The result of this summation is fed as an input value to the electric drive 4, which can be described for modeling purposes using a transfer function. The electric drive 4 has a drive torque 44. The gear meshing acts on this drive torque 44 as a disturbance variable 46. The frequency of the vibration excitation of the meshing gears of the gear stage can be described in the model by a transfer function 48.The output of the transfer function 48 is the output signal of the mechanical system, which can be, in particular, the speed 50 of the electric vehicle or the surface speed of the gear stage. This output signal of the mechanical system is also an input of the noise damping 34.

[0046] Out of Fig. 4 A third embodiment emerges, which represents a further development compared to the second embodiment. The noise damping 34 is integrated into the control unit by summing a periodic torque change signal 5 to the torque setpoint 36. The rotor position and the torque setpoint are used as input values. In contrast to the second embodiment according to Fig. 3 The torque change signal 5 output by the noise damping 34 is fed together with the torque setpoint 36 to a summation node 52, the output value of which forms the input value of the field-oriented torque control 38. This prevents the field-oriented torque control 38 from correcting the signal from the noise damping 34 again, since this oscillation of the speed or torque represents a disturbance for the field-oriented torque control 38. If the effect of the noise damping 34 on the speed signal is simulated with a model and subtracted from the measured value for the field-oriented torque control 38, the field-oriented torque control 38 will not view the noise damping 34 as a disturbance and will correct it. This correction occurs particularly at low speeds, since the dynamics of the field-oriented torque control 38 are sufficient for correction here.Furthermore, in contrast to the second embodiment, no summation node is provided between the field-oriented torque control 38 and the drive 4.

[0047] Fig. 5 shows a fourth embodiment, which also represents a further development compared to the second embodiment. The noise damping 34 is integrated into the control unit of the drive 4.

[0048] The noise damping 34 superimposes the torque change signal 5 on the stator voltage setpoint 40 for a pulse-controlled inverter 53. The rotor position and torque value of the field-oriented torque control 38 are again used as input variables.

[0049] In contrast to the second and third embodiments, an output signal of the field-oriented torque control 38 is fed directly to the noise dampening 34. Furthermore, in contrast to the second embodiment, the voltage 55 applied to the drive 4 is tapped and fed back to another summation node 54, where this voltage 55 is summed with the current setpoint 56 of the drive 4, with the result of this summation being fed as an input value to the field-oriented torque control 38. The pulse-controlled inverter 53 receives as an input value from the summation node 41 a summation of the stator voltage setpoint 40 and the torque change signal 5 of the noise dampening 34. The pulse-controlled inverter 53 controls the drive 4.

[0050] The method described above for operating a vehicle drive train can be implemented as part of the axle system or as a software option with a pulse inverter or control unit and can therefore represent a vehicle component.

Claims

1. Method for operating a drive train having an electromotive drive (4), wherein a rotational speed and a drive torque of the drive (4) can be converted via a toothed gear stage (12) for an output (19), and the drive (4) is controlled by a control signal (40), wherein a periodic torque change signal (5) is superimposed on the control signal (40), which periodic torque change signal alternately reduces and increases the drive torque and in the process is in phase with a change in tooth stiffness of the toothed gear stage (12), wherein a signal strength of the torque change signal (5) with a decreasing tooth stiffness is lower than with an increasing tooth stiffness, characterized in that the periodic torque change signal (5) simulates the tooth stiffness and is stored in a table or is described by a mathematical function with which the tooth stiffness is approximated.

2. Method according to Claim 1, characterized in that the control signal (40) is a torque control signal of a torque control operation (38) or an output voltage signal of a torque control operation (38).

3. Method according to Claim 2, characterized in that the output voltage signal or the torque control signal of the torque control operation is associated with a field-oriented torque control operation (38) or current control operation.

4. Method according to any of Claims 1 to 3, characterized in that the periodic torque change signal (5) is superimposed on the control signal (40) depending on a torque setpoint value (36) or a rotor position (24) of the drive (4).

5. Method according to any of the preceding claims, characterized in that the periodic torque change signal (5) has a sinusoidal form.

6. Method according to Claim 4 or a combination of Claims 4 and 5, characterized in that the torque change signal (5) together with the torque setpoint value (36) is passed to a summation node (52), which has an output value that forms an input value for the field-oriented torque control operation (38) in such a way that the field-oriented torque control operation (38) is prevented from re-adjusting the signal of a noise damping operation (34).

7. Method according to any of the preceding claims, characterized in that an equivalent value of the periodic torque change signal (5) is equal to zero.

8. Vehicle drive train having an electromotive drive, comprising: a drive (4), the drive torque and the rotational speed of which are variable, a toothed gear stage (12), which can be coupled to the drive (4) to convert the rotational speed and the drive torque, a controller (6) for controlling the drive (4) with a control signal (40), wherein the controller (6) is configured to superimpose a periodic torque change signal (5) on the control signal (40), which periodic torque change signal alternately reduces and increases the drive torque and in the process is in phase with a change in tooth stiffness of the toothed gear stage (12), and in that a signal strength of the torque change signal (5) with a decreasing tooth stiffness is lower than with an increasing tooth stiffness, characterized in that the periodic torque change signal (5) simulates the tooth stiffness and is stored in a table or is described by a mathematical function with which the tooth stiffness is approximated.

9. Vehicle drive train according to Claim 8, characterized in that the control signal (40) is a torque control signal of a torque control operation (38) or an output voltage signal of a torque control operation (38).