Method for controlling a traction drive motor of an electric motor vehicle drive

Abstract

Method for controlling an electric traction drive machine (1) of an electric motor vehicle drive, wherein a torque (M) and a speed (n) of the traction drive machine (1) are variably set by means of a drive inverter (2), the traction drive machine (1) is operated as a motor in a driving mode of the motor vehicle and generates a drive torque with which drive wheels (3) of the motor vehicle are driven, the traction drive machine (1) is operated as a generator in a braking mode of the motor vehicle via the drive wheels (3) of the motor vehicle and generates a braking torque with which the drive wheels (3) of the motor vehicle are braked;For the control of the speed (n) of the traction drive machine (1), the current speed (nakt) of the traction drive machine (1) is detected or calculated and supplied to the drive inverter (2) as actual speed (nist), wherein the actual speed (nist) is generated by smoothing the current speed (nakt), and in braking operation the braking torque is set as a function of the actual speed (nist) and / or the current vehicle speed (v); wherein in braking operation the braking torque is additionally set as a function of an at least indirectly detected current vehicle deceleration (a);characterized in that a torque reduction ramp (Msoll) is specified as a function of the brake torque to be set depending on the actual rotational speed (nist) or the current vehicle speed (v), wherein the torque reduction ramp (Msoll) is dynamically shifted to higher or lower actual rotational speeds (nist) or vehicle speeds (v) depending on the current vehicle deceleration (a), wherein a minimum torque reduction ramp (Mmin) and a maximum torque reduction ramp (Mmax) are specified as limit curves or limit lines between which the torque reduction ramp (Msoll) is specified, and wherein the torque reduction ramp (Msoll) is linearly interpolated between Mmin and Mmax depending on the current vehicle deceleration (a) and is shifted towards Mmin at lower vehicle decelerations (a) and towards Mmax at higher vehicle decelerations (a).

Description

[0001] The present invention relates to a method for controlling a traction drive machine of an electric motor vehicle drive, in particular a battery-electric motor vehicle drive, with the features according to the preamble of claim 1.

[0002] In the drive train of an electric motor vehicle drive, as described in the present invention, at least one electric traction drive motor is provided, which is controlled via a drive inverter. The drive inverter variably adjusts the torque and speed of the traction drive motor by applying corresponding electrical voltages to the individual phases of the electric traction drive motor.

[0003] The traction drive motor is powered by a motor in the vehicle's drive mode and generates a drive torque that drives the vehicle's drive wheels. A differential gear may be arranged in the drive connection between the traction drive motor and the vehicle's drive system.

[0004] Furthermore, in braking mode of the motor vehicle, the traction drive machine is operated as a generator by absorbing drive power from the drive wheels of the motor vehicle and generates a braking torque with which the drive wheels of the motor vehicle are braked.

[0005] Due to low damping in the electric drivetrain and especially mechanical play in the differential, the drivetrain is particularly susceptible to vibrations. To prevent these drivetrain vibrations from adversely affecting the control of the traction motor, relatively strong speed filtering is necessary when sensing and processing the traction motor's speed. Accordingly, for speed control of the traction motor, the current speed of the traction motor is measured and fed to the drive inverter as the actual speed, whereby the actual speed is generated by smoothing the current speed.

[0006] During braking, the braking torque generated by the traction drive motor is adjusted as a function of the actual rotational speed. Specifically, a torque reduction ramp is defined, meaning the torque curve as a function of the actual rotational speed. This torque is the braking torque to be set. In particular, as the vehicle decelerates to a standstill, the defined braking torque follows a torque reduction ramp that is initially steep and then flattens out. Therefore, plotted on a Cartesian coordinate system, the braking torque, with progressively lower actual rotational speed, essentially asymptotically approaches the x-axis, on which the actual rotational speed is plotted, and reaches the value 0 at a defined actual rotational speed slightly greater than 0.

[0007] This involves specifying exactly one torque reduction ramp, i.e., a unique curve of the torque versus the actual rotational speed in a two-dimensional coordinate system, where the actual rotational speed is plotted on the X-axis and the torque on the Y-axis.

[0008] The torque reduction ramp is set for the braking torque in such a way that, even during heavy braking, the braking torque applied by the traction drive motor, and thus the recuperation potential, is completely dissipated before the vehicle comes to a standstill. However, excessively rapid dissipation reduces the recuperation potential, leads to increased energy consumption during vehicle operation, and causes greater wear on the mechanical service brakes.

[0009] The present invention is based on the objective of providing a method for controlling an electric traction drive machine of an electric motor vehicle drive, in particular a battery-electric motor vehicle drive, for example a bus, with which safe braking of the motor vehicle is made possible with maximum utilization of the recuperation potential.

[0010] The problem according to the invention is solved by a method with the features of claim 1. The dependent claims describe advantageous and particularly expedient embodiments of the invention.

[0011] According to the inventive method for controlling an electric drive motor of an electric vehicle drive, in particular a battery-electric vehicle drive, for example a bus, a drive inverter is used to variably adjust the torque and speed of the traction drive motor. The traction drive motor is operated as a motor in drive mode of the vehicle and generates a drive torque. The drive wheels of the vehicle are driven by the traction drive motor by transmitting the drive torque of the traction drive motor to the drive wheels, in particular via a transmission and / or differential.

[0012] Furthermore, in braking mode of the motor vehicle, the traction drive machine is driven by the motor vehicle's drive wheels in a generator-like manner and produces a braking torque with which the motor vehicle's drive wheels are braked.

[0013] To control the speed of the traction drive machine, the current speed of the traction drive machine is at least indirectly detected or calculated and supplied to the drive inverter as actual speed, whereby the actual speed is generated by smoothing the current speed, and in braking operation the braking torque is adjusted as a function of the actual speed.

[0014] Alternatively, during braking operation, the braking torque can also be adjusted depending on the current vehicle speed, which usually correlates with the actual rotational speed of the traction drive motor.

[0015] According to the invention, during braking operation the braking torque is additionally adjusted depending on an at least indirectly detected current vehicle deceleration.

[0016] The invention enables the creation of a simple, real-time capable method for changing speed-dependent or velocity-dependent torque reduction ramps in the recuperation operation of the traction drive machine, i.e., braking operation of the motor vehicle.

[0017] According to an alternative embodiment, the generation of the actual rotational speed value can be intervened in real time to adjust the braking torque more precisely to the current vehicle deceleration, thereby improving the utilization of the recuperation potential. In particular, this effectively compensates for a time delay in the actual rotational speed signal resulting from the smoothing of the current rotational speed, which has a greater impact during rapid signal changes.

[0018] According to a preferred embodiment of the method according to the invention, the vehicle deceleration is directly detected as a linear vehicle deceleration using at least one deceleration sensor, or the vehicle deceleration is calculated as a linear vehicle deceleration. Thus, the total deceleration of the motor vehicle can be detected or calculated, whereby vehicle deceleration is understood to mean, in particular, the deceleration in the direction of travel, i.e., not perpendicular to it.

[0019] Alternatively, vehicle deceleration can also be measured as the angular deceleration of a wheel or shaft rotating within the vehicle as a function of vehicle speed. For example, the angular deceleration of the drive wheels and / or wheel drive shaft of the vehicle can be measured.

[0020] According to one embodiment of the invention, a torque reduction ramp is specified as a function of the braking torque to be set as a function of the actual rotational speed or the current vehicle speed for setting the torque of the traction drive motor, wherein the torque reduction ramp is dynamically shifted to larger or smaller actual rotational speeds or vehicle speeds as a function of the current vehicle deceleration.Thus, the braking torque to be set can be plotted against the actual rotational speed or the current vehicle speed in a two-dimensional Cartesian coordinate system, resulting in a straight line or curve extending from a starting point at a comparatively higher actual rotational speed or current vehicle speed to an endpoint at a comparatively lower actual rotational speed or current vehicle speed, where the braking torque to be set is zero at the endpoint. Accordingly, the actual rotational speed or current vehicle speed is plotted on the x-axis and the braking torque to be set on the y-axis.

[0021] Preferably, a minimum torque reduction ramp and a maximum torque reduction ramp are specified as boundary curves or boundary lines, between which the torque reduction ramp is defined. For actual engine speeds or vehicle speeds outside the range encompassed jointly by the minimum and maximum torque reduction ramps, either the minimum or the maximum torque reduction ramp is used for the braking torque to be set, depending on whether the actual engine speed or vehicle speed is less than that of the minimum torque reduction ramp, in which case the minimum ramp is used, or greater than that of the maximum torque reduction ramp, in which case the maximum ramp is used.

[0022] Preferably, especially as long as the limit curves or limit lines are not exceeded, the torque reduction ramp can be linearly interpolated between the minimum torque reduction ramp and the maximum torque reduction ramp as a function of the current vehicle deceleration in order to achieve a particularly suitable function of the braking torque to be set.

[0023] For example, at relatively low vehicle decelerations, the torque reduction ramp is shifted, particularly parallel, towards the minimum torque reduction ramp, and at relatively higher vehicle decelerations, the torque reduction ramp is shifted, particularly parallel, towards the maximum torque reduction ramp. This parallel shift advantageously occurs along the X-axis with the actual rotational speeds or vehicle speeds.

[0024] According to an alternative embodiment of the invention, which can also be combined with the aforementioned embodiment, the actual rotational speed is corrected by a vehicle deceleration-dependent differential value or correction factor. In this case, a comparatively larger correction of the actual rotational speed value can be applied in the case of comparatively larger vehicle decelerations.

[0025] This results in a comparatively smaller delay in the actual speed value during smoothing, particularly at relatively low current engine speeds, and a comparatively larger delay in providing the actual speed value during smoothing at relatively high current engine speeds. These different delays can be compensated for by correcting the actual engine speed value based on vehicle deceleration.

[0026] The invention ensures, on the one hand, that the reduction of braking torque is always completed before the vehicle comes to a standstill, despite the speed filtering. On the other hand, the recuperation potential can still be fully utilized at all times, either by shifting both the starting and ending points of the torque reduction ramp in real time towards lower actual speeds or vehicle speeds during light deceleration and towards higher actual speeds or vehicle speeds during heavy deceleration, or by making a correspondingly greater or lesser correction to the actual speed value in real time.

[0027] The invention will be described below by way of example with reference to embodiments and the figures.

[0028] They show: Fig. 1 a schematic representation of a battery-electric motor vehicle drive for the application of the method according to the invention; Fig. 2 an embodiment of the invention with a displacement of the torque reduction ramp; Fig. 3 an alternative embodiment of the invention with a vehicle deceleration-dependent correction of the actual rotational speed.

[0029] In the Fig. Figure 1 shows a battery-electric vehicle powertrain comprising a high-voltage electrical system 4 and a low-voltage electrical system 5. The high-voltage electrical system 4 contains HV components that together form an electrical intermediate circuit 6. High voltage is understood to mean, in particular, a voltage in accordance with Regulation No. 100 of the United Nations Economic Commission for Europe (UNECE), specifically an electrical voltage of more than 200 volts. The low-voltage electrical system 5 has, in particular, a maximum electrical voltage of 60 volts, specifically 36, 30, 24, or 12 volts.

[0030] The high-voltage electrical system 4 comprises a high-voltage battery 7, which can be electrically connected to and disconnected from the intermediate circuit 6 via a main contactor 8. The high-voltage battery 7 serves as an energy source for supplying the high-voltage components in the intermediate circuit 6, including the drive inverter 2. The electrical energy from the intermediate circuit 6 is fed into the traction motor 1, in particular via a three-phase connection, so that it drives the drive wheels 3 when the vehicle is in operation. The electrical power flow therefore proceeds from the intermediate circuit 6 towards the traction motor 1. The drive inverter 2 variably adjusts the torque and speed of the traction motor 1 depending on signals from a vehicle control system (not shown).

[0031] In contrast, during braking operation of the vehicle, the traction drive motor 1 is driven by the drive wheels 3 in a generator-like manner and feeds electrical power into the electrical DC link 6 via the drive inverter 2 to charge the HV battery 7 and / or supply power to the HV components. Here too, the torque and speed in the traction drive motor 1 are variably set by the drive inverter 2 depending on signals from the vehicle control system.

[0032] In this context, the torque during braking is referred to as braking torque.

[0033] The electrical intermediate circuit 6 includes, by way of example, an electric air conditioning compressor 9, an electric air compressor 10 of a vehicle compressed air system and an electric heater 11, as well as a voltage converter 12 for supplying the low-voltage electrical system 5. A low-voltage battery 13 and electrical consumers 14 are arranged in the low-voltage electrical system 5.

[0034] The interconnection of the various HV components in the electrical intermediate circuit 6 can be carried out using a power distribution unit 15.

[0035] To control the speed and torque of the traction drive machine 1, the current speed nakt is measured or calculated from other quantities and supplied to the drive inverter 2 as the actual speed nist. The inverter then regulates the torque M and the speed n of the traction drive machine 1 accordingly.

[0036] The current rotational speed nakt of the traction drive machine 1 can, for example, be fed to an electronic control device 16, which, by smoothing the current rotational speed nakt, generates the actual rotational speed nist and feeds it to the drive inverter 2. The control device 16 can also be integrated into the drive inverter 2.

[0037] The control device 16 is further supplied with the vehicle deceleration a, which can either be measured directly or determined from other measured quantities. Optionally, the vehicle speed v is also supplied to the control device 16, which in turn can be measured directly or determined from other quantities.

[0038] According to an embodiment of the invention, as described in the Fig. As shown in 2, the braking torque M is used in braking operation (see 2). Fig. 1) by the drive inverter 2 depending on the vehicle deceleration a (see the Fig. 1) is set by dynamically specifying a torque reduction ramp Mtarget for setting the torque M of the traction drive motor 1. The torque reduction ramp Mtarget is thereby set as in the Fig. As shown in Figure 2, the torque reduction ramp Mtarget is dynamically shifted between a minimum torque reduction ramp Mmin and a maximum torque reduction ramp Mmax parallel to the X-axis with the actual rotational speed ntarget, depending on the current vehicle deceleration. At a comparatively lower vehicle deceleration, the torque reduction ramp Mtarget is shifted towards the minimum torque reduction ramp Mmin, and at a comparatively higher vehicle deceleration, the torque reduction ramp Mtarget is shifted towards the maximum torque reduction ramp Mmax, without ever being shifted beyond the two torque reduction ramps Mmin and Mmax, which are defined as boundary lines, even if the current vehicle deceleration is correspondingly greater or lesser.

[0039] The curve's progression in the Fig. 2. To the right of the maximum torque reduction ramp Mmax, after which the torque (braking torque M) increases with decreasing actual speed nist and then remains constant up to the torque reduction ramp Msoll (maximum up to the minimum torque reduction ramp Mmin), corresponds to an initially moderate deceleration of the motor vehicle, which increases up to the maximum torque (braking torque M) in order to increase braking comfort, so that, for example, people in a bus are not thrown around when braking.

[0040] Instead of the actual rotational speed nist, the vehicle speed v could also be used to specify the torque reduction ramps Msoll, Mmin, Mmax.

[0041] In the Fig. 3 is the time delay Δt during the smoothing of the current rotational speed nakt of the traction drive motor 1 (see the Fig. 1) The actual rotational speed nist is shown. The higher the rotational speed nakt is, the greater the time delay Δt.

[0042] Accordingly, according to the invention, the filtered signal of the actual rotational speed nist can be corrected with a difference value or correction factor, which depends on the vehicle deceleration a (see the Fig. 1) is. For example, with a comparatively larger vehicle deceleration a, a larger difference value is added to or subtracted from the actual rotational speed nist, and with a comparatively smaller vehicle deceleration a, a correspondingly smaller difference value is added. Reference symbol list 1 traction drive machine 2 drive inverters 3 drive wheel 4 High-voltage electrical system 5 Low-voltage electrical system 6 electrical intermediate circuit 7 HV battery 8 Main gate 9 electric air conditioning compressor 10 electric air compressors 11 electric heaters 12 voltage converters 13 Low-voltage battery 14 electrical consumers 15 Power distribution unit 16 Control device a vehicle delay current RPM nist Actual speed Msoll torque reduction ramp Mmin minimum torque reduction ramp Mmax maximum torque reduction ramp v Vehicle speed Δt time delay

Claims

Method for controlling an electric traction drive machine (1) of an electric motor vehicle drive, wherein a torque (M) and a speed (n) of the traction drive machine (1) are variably set by means of a drive inverter (2), the traction drive machine (1) is operated as a motor in a driving mode of the motor vehicle and generates a drive torque with which drive wheels (3) of the motor vehicle are driven, the traction drive machine (1) is operated as a generator in a braking mode of the motor vehicle via the drive wheels (3) of the motor vehicle and generates a braking torque with which the drive wheels (3) of the motor vehicle are braked;For controlling the rotational speed (n) of the traction drive machine (1), the current rotational speed (nakt) of the traction drive machine (1) is detected or calculated and supplied to the drive inverter (2) as the actual rotational speed (nist), wherein the actual rotational speed (nist) is generated by smoothing the current rotational speed (nakt), and in braking operation the braking torque is adjusted as a function of the actual rotational speed (nist) and / or the current vehicle speed (v); characterized in that in braking operation the braking torque is additionally adjusted as a function of an at least indirectly detected current vehicle deceleration (a). Method according to claim 1, characterized in that the vehicle deceleration (a) is directly detected as linear vehicle deceleration (a) using a deceleration sensor or is calculated as linear vehicle deceleration (a). Method according to claim 1, characterized in that the vehicle deceleration (a) is detected as the angular deceleration of a shaft rotating in the motor vehicle as a function of the vehicle speed (v) and / or of a wheel rotating in the motor vehicle as a function of the vehicle speed (v). Method according to one of claims 1 to 3, characterized in that a torque reduction ramp (Msoll) is specified as a function of the braking torque to be set as a function of the actual rotational speed (nist) or the current vehicle speed (v) for setting the torque (M) of the traction drive machine (1), wherein the torque reduction ramp (Msoll) is dynamically shifted to larger or smaller actual rotational speeds (nist) or vehicle speeds (v) as a function of the current vehicle deceleration (a). Method according to claim 4, characterized in that a minimum torque reduction ramp (Mmin) and a maximum torque reduction ramp (Mmax) are specified as limit curves or limit lines, between which the torque reduction ramp (Msoll) is specified. Method according to claim 5, characterized in that the torque reduction ramp (Msoll) is interpolated linearly between the minimum torque reduction ramp (Mmin) and the maximum torque reduction ramp (Mmax) as a function of the current vehicle deceleration (a). Method according to one of claims 5 or 6, characterized in that at comparatively low vehicle decelerations (a) the torque reduction ramp (Msoll) is shifted, in particular parallel, in the direction of the minimum torque reduction ramp (Mmin), and at comparatively higher vehicle decelerations (a) the torque reduction ramp (Msoll) is shifted, in particular parallel, in the direction of the maximum torque reduction ramp (Mmax). Method according to one of claims 1 to 7, characterized in that the actual rotational speed (nist) is corrected with a vehicle deceleration-dependent difference value or correction factor. Method according to claim 8, characterized in that in the case of comparatively larger vehicle decelerations (a) a comparatively larger correction of the actual speed value (nist) is carried out.

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