Methods for operating a motor vehicle, in particular an electric vehicle

Abstract

Method for operating a motor vehicle (10) in which the motor vehicle (10) has at least one vehicle wheel (24) and a drive train with at least one electric machine (32) by means of which the vehicle wheel (24) can be driven, characterized in that: - during a journey of the motor vehicle, at least one motor vehicle acceleration value is determined by means of an electronic computing device (36), which characterizes a condition of a roadway (28) for the motor vehicle (10); and - the electric machine (32) is decoupled from the vehicle wheel (24) when the vehicle acceleration value is greater than a predetermined threshold value, and when a braking process of the vehicle (10) is detected.

Description

[0001] The invention relates to a method for operating a motor vehicle, in particular an electric vehicle, according to the preamble of claim 1.

[0002] DE 10 2020 205 497 A1 discloses a transmission arrangement for a motor vehicle. DE 10 2018 204 384 A1 discloses a method for operating electric motors designed as asynchronous machines. DE 10 2004 045 268 A1 discloses a device for determining control signals from at least one headlight. Furthermore, DE 43 40 735 A1 discloses a drive system for propelling a self-driving vehicle.

[0003] The object of the present invention is to create a method for operating a motor vehicle, in particular an electric vehicle, in such a way that a particularly advantageous operation can be realized.

[0004] This problem is solved by a method with the features of claim 1. Advantageous embodiments with expedient further developments of the invention are specified in the remaining claims.

[0005] The invention relates to a method for operating a motor vehicle, also referred to simply as a vehicle, whose interior, also referred to as the passenger compartment or passenger space, can be formed, for example, by a body structure of the motor vehicle, particularly a self-supporting body. Preferably, the motor vehicle, also referred to simply as a vehicle, is a motor car, particularly a passenger car. Most preferably, the motor vehicle is an electric vehicle, particularly a battery electric vehicle (BEV). During each journey of the motor vehicle, persons such as the driver of the motor vehicle can be present in the interior of the motor vehicle.

[0006] In this method, the motor vehicle has at least one wheel, also referred to simply as a wheel, and a drive train comprising at least one electric machine. The electric machine can drive the wheel. In particular, the electric machine can drive the wheel, especially purely electrically. For example, by driving the wheel, the motor vehicle can be driven, especially electrically and most especially purely electrically. For example, the motor vehicle has at least or exactly two axles arranged consecutively in the longitudinal direction of the vehicle, which are also referred to simply as axles. The aforementioned wheel is also referred to as the first wheel.When the vehicle wheel is mentioned before and below, unless otherwise stated, this refers to the first vehicle wheel.

[0007] For example, each vehicle axle has at least or exactly two vehicle wheels, which are also simply referred to as wheels. For example, the respective vehicle wheels of each vehicle axle are arranged on opposite sides of the vehicle in the transverse direction of the vehicle. One of the vehicle wheels is the aforementioned first vehicle wheel, which is driven by the electric motor. The vehicle wheels, and thus the first vehicle wheel, are ground contact elements of the vehicle, which can be supported or is supported downwards by the ground contact elements in the vehicle's vertical direction. If the vehicle is driven along the ground while supported downwards by the ground contact elements in the vehicle's vertical direction, the ground contact elements roll along the ground, particularly directly.For example, the vehicle wheels of at least one of the vehicle axles can be driven, in particular electrically and especially purely electrically, by means of the electric machine. This allows the motor vehicle to be driven, in particular electrically and especially purely electrically. In particular, it is provided that during the process, the vehicle wheel is driven, at least for a first period of time, by means of the electric machine, in particular electrically and especially purely electrically, wherein, for example, the motor vehicle is driven, at least for the first period of time, by means of the electric machine, in particular electrically and especially purely electrically. In particular, the vehicle wheel rolls, for example, directly on the ground during the process, that is, during the process.

[0008] In order to achieve a particularly advantageous operation, especially one that places minimal stress on the drivetrain, the invention provides that, during a journey of the motor vehicle, i.e., during driving operation of the motor vehicle, at least one, and in particular characteristic, motor vehicle acceleration value is determined by means of an electronic computing device, in particular of the motor vehicle, which characterizes a road surface condition for the motor vehicle. In particular, the road surface is the aforementioned ground.Thus, it is provided, for example, that the motor vehicle travels on and along the roadway during the procedure, in particular while the motor vehicle is supported downwards on the roadway by the vehicle wheel, which is designed as a ground contact element, so that, for example, the vehicle wheel rolls on the roadway at least during the initial period, and in particular directly. For example, the motor vehicle acceleration value characterizes at least one acceleration of the motor vehicle, that is, at least one acceleration acting on the motor vehicle, whereby, for example, this acceleration is used as a measure of the roadway condition.

[0009] In this process, the electric machine is decoupled from the vehicle wheel when the vehicle's acceleration value, particularly its characteristic value, exceeds a predetermined and thus defined threshold, and when a braking process of the vehicle is detected, particularly by means of the electronic computing device. The braking process is designed or intended to decelerate the vehicle, that is, to reduce its speed as it travels along the road, particularly forwards, at the speed also referred to as vehicle speed.

[0010] This method prevents excessive stress on the drivetrain, thus enabling particularly low-wear operation of the vehicle, especially over its entire lifespan. The electronic computing unit is also referred to as a control unit or is designed as a control unit.

[0011] The braking process of the motor vehicle is detected, for example, by the electronic computing device, by means of which the electronic computing device detects, for example, the activation of a control element of the motor vehicle by a person. The braking process, i.e., the braking of the motor vehicle (also referred to as deceleration), can be initiated or is initiated by means of the control element. The activation of the control element is detected, for example, by means of at least one control sensor. For example, the activation of the control element closes a switch, and the closing of the switch is detected and thus the braking process can be recognized. Thus, the control sensor is, for example, the aforementioned switch. The control element is, for example, located in the interior of the vehicle.For example, the control element is a pedal, also known as a brake pedal, by which the braking of the motor vehicle can be effected by depressing the pedal, thus making the motor vehicle capable of being slowed down. In particular, a service brake of the motor vehicle can be actuated by depressing the control element, whereby the braking process can be carried out or is carried out by means of the service brake. Preferably, the service brake is a friction brake. If, for example, an actuation of the control element by a person, such as the driver of the motor vehicle, is detected by means of the control sensor, also known as an actuation sensor, then the braking process is detected, for example. For example, the control sensor provides an actuation signal, also known as an actuation signal, in particular an electrical signal, which is received, for example, by the electronic computing device.For example, the control signal characterizes the actuation of the control element as detected by the control sensor. Depending on the received actuation signal (control signal), the electronic control unit can recognize the braking process and, for example, subsequently decouple the electric motor from the vehicle wheel.

[0012] For example, to decouple the electric motor from the vehicle wheel, the electronic control unit activates a coupling device, specifically in such a way that the coupling device is switched from a coupled state to a decoupling state. By switching the coupling device from the coupled state to the decoupling state, the vehicle wheel is decoupled from the electric motor, or vice versa.

[0013] For example, the aforementioned switch is a brake switch. When the closing of the brake switch is detected, the actuation of the control element is also detected, thus recognizing the braking process. The detection of the braking process, particularly the closing of the switch, causes, for example, the rear brake lights of the vehicle to be activated and thus emit light.

[0014] For example, at least during the initial period, the electric machine is coupled to the vehicle wheel in a torque-transmitting manner, particularly in a rotationally fixed manner, so that, for example, during the initial period, a respective torque that can be provided or is provided by the electric machine can be transmitted to the vehicle wheel, particularly via the coupling device, in particular to drive the vehicle wheel. As a result of the electric machine being decoupled from the vehicle wheel, no more torque can be transmitted to the vehicle wheel of the electric machine.

[0015] The electric machine, for example, has a stator and a rotor, which can be driven by means of the stator and is thus rotatable about a machine axis of rotation relative to the stator. For example, the electric machine can provide drive torques via its rotor, by means of which the vehicle wheel can be driven, particularly electrically and especially purely electrically. It is provided, for example, that at least during the initial period, the stator drives the rotor and thus rotates it about the machine axis of rotation relative to the stator, so that, for example, at least during the initial period, the electric machine provides at least one drive torque via its rotor, by means of which the vehicle wheel can be driven or is driven.

[0016] In particular, it is provided that, at least during the initial period, the rotor is coupled to the vehicle wheel in a torque-transmitting manner, specifically via the coupling device, and in a rotationally fixed manner, so that, at least during the initial period, a respective torque can be transmitted between the rotor and the vehicle wheel, specifically via the coupling device. By decoupling the electric machine from the vehicle wheel, a torque transmission path, through which torques can be transmitted between the rotor and the vehicle wheel (where, for example, the coupling device is located in the torque transmission path), is interrupted, i.e., opened, so that no more torque can be transmitted between the rotor and the vehicle wheel via the coupling device.

[0017] Thus, it is provided, for example, that the electric machine coupled to the vehicle wheel, in particular initially in a torque-transmitting manner and in particular in a rotationally fixed manner, i.e., for example, the rotor coupled to the vehicle wheel, in particular initially in a torque-transmitting manner and in particular in a rotationally fixed manner, is decoupled from the vehicle wheel when the vehicle acceleration value is greater than the threshold value and when the braking process of the vehicle is detected.The characteristic that the electric machine or rotor is initially and / or during the first period of time coupled to the vehicle wheel in a torque-transmitting manner means that the electric machine, in particular the rotor, is connected to the vehicle wheel in such a way that torques, such as the aforementioned drive torques, can be transmitted between the vehicle wheel and the electric machine, or from the electric machine to the vehicle wheel, particularly via the coupling device. The decoupling of the electric machine from the vehicle wheel, also referred to as disconnection, means that the electric machine, in particular the rotor, is decoupled from the vehicle wheel, i.e., separated, so that no (further) torques can be transmitted between the electric machine and the vehicle wheel, particularly via the coupling device.Decoupling the electric machine from the vehicle wheel can in particular include decoupling the rotor, which is initially coupled to the vehicle wheel in a torque-transmitting manner and / or during the first period of time, from the vehicle wheel so that no torques can (or can no longer) be transmitted between the rotor and the vehicle wheel.

[0018] In particular, the motor vehicle has the aforementioned coupling device, also referred to as a clutch or designed as a clutch, which can be switched between the aforementioned coupled and uncoupled states. For example, the electric machine, in particular the rotor, is coupled to the vehicle wheel via the coupling device, especially during the first period and / or initially, thus transmitting torque, so that the torque transmission path is closed and torques can be transmitted between the electric machine, in particular the rotor, and the vehicle wheel via the coupling device. For this purpose, the coupling device is in the coupled state, especially initially and / or during the first period.To decouple the electric machine, particularly the rotor, from the vehicle wheel, the coupling device is switched from the coupled state to the decoupling state, so that no more torque can be transmitted between the electric machine, particularly the rotor, and the vehicle wheel via the coupling device. The coupling device thus acts as a disconnect unit, also known as a decoupling device or disconnect unit (DCU). In particular, the coupling device can be switched between the coupled and decoupling states by, for example, electrical control. This control can be carried out, for instance, by means of an electronic computer.To control the coupling device, for example, the electronic processing unit provides a control signal, particularly an electrical one, which is received by the coupling device. This control signal switches the coupling device from the coupled state to the decoupled state. To switch the coupling device back into the coupled state after the vehicle wheel has been decoupled from the electric motor, or vice versa, the electronic processing unit provides a second control signal, particularly an electrical one, which is received by the coupling device. This signal controls the coupling device, switching it from the decoupled state to the coupled state.Thus, for example, a second time period follows directly after the first, during which the coupling device is in a decoupling state, particularly as a result of the decoupling of the electric machine from the vehicle wheel, so that, particularly during the second time period, the electric machine, particularly the rotor, is continuously and thus without interruption decoupled from the vehicle wheel. During the first time period, for example, the coupling device is continuously and thus without interruption in a coupled state, so that, particularly during the first time period, the electric machine, particularly the rotor, is continuously and thus without interruption coupled to the vehicle wheel in a torque-transmitting manner.Switching the coupling device from the coupled state to the uncoupled state is also referred to as opening the coupling device, and switching the coupling device from the uncoupled state to the coupled state is also referred to as closing the coupling device. In particular, the vehicle acceleration value characterizes at least one road surface irregularity, that is, for example, the degree of road surface irregularity. Thus, for example, the vehicle acceleration value characterizes a number of road surface irregularities and / or the height of the road surface irregularities, especially relative to a reference plane.

[0019] The invention is based in particular on the following findings and considerations: In motor vehicles, especially electric vehicles and, most especially, battery electric vehicles (BEVs), braking on uneven road surfaces, also known as rough roads, can cause a torsional vibration, also referred to as a drivetrain-chassis assembly, comprising the respective powertrain and chassis of the respective motor vehicle. This torsional vibration can lead to enormous stress on all components located in the load path where the vibration occurs. One cause of this torsional vibration, also simply referred to as vibration, can be an unfavorable frequency ratio between the wheel natural frequency and the torsional natural frequency of the electric drivetrain.The torsional natural frequency of the drivetrain is primarily determined by the rotational inertia of the electric motor's rotor and the stiffness of the drive shafts. When driving over an excessively uneven road surface, the wheel is excited to vertical vibrations at its natural frequency. During braking on an uneven surface, a longitudinal force can be generated, determined by the applied braking torque. The longitudinal force in the tire contact patch fluctuates with the wheel's vertical frequency, and consequently, the braking torque also fluctuates with this frequency. Due to the unfavorable relationship between the two frequencies, the longitudinal forces in the tire contact patch induce a dynamic amplification of the torsional vibration in the drivetrain (resonance case). Due to the dynamic wheel load distribution during braking, this amplification of the torsional vibration is particularly pronounced at the front axle and in the front of the vehicle.The invention enables the decoupling of the electric machine, in particular the electric drive train, from the vehicle wheel, especially during braking on an uneven road surface, for example. In the method according to the invention, the electric machine is decoupled, i.e., disconnected, depending on the vehicle acceleration value. Specifically, the electric machine, in particular the rotor, is decoupled, i.e., disconnected, from the vehicle wheel when the characteristic vehicle acceleration value is higher than, i.e., greater than, the threshold value, and thus higher than the threshold value, particularly with the proviso that the higher the vehicle acceleration value, the more uneven the road surface. Determining the vehicle acceleration value thus serves, for example, as a rough road surface detection method.The invention thus enables the decoupling of the electric machine, in particular the rotor, and therefore, for example, the electric drive train, from the vehicle wheel, especially during braking on an uneven road surface, by utilizing rough road detection. This prevents excessive, road-induced vibration of the vehicle's front end, also known as front-end vibration. As a result, excessive stress on the vehicle, particularly the front end, can be avoided, enabling particularly low-wear operation of the vehicle.

[0020] Conventionally, excessive torsional vibrations are avoided and / or dampened by using side shafts with specific stiffnesses, which drive or can drive the vehicle wheels. However, this solution generally only reduces, but does not prevent, the aforementioned torsional vibration. In particular, depending on other design parameters in the vehicle, the desired side shaft stiffness cannot always be achieved. Since the method according to the invention provides for decoupling the electric machine, especially the rotor, from the vehicle wheel, excessive torsional vibrations can be advantageously avoided, particularly in the aforementioned assembly.This prevents, for example, excessive stress and thus excessive dimensioning of components located in a load path where torsional vibrations would propagate, since road-induced torsional vibrations can no longer occur in the aforementioned assembly. Consequently, the components can be designed to be lighter and more cost-effective. Damage and failures caused by braking on uneven road surfaces, especially rough roads, can be prevented. Complex, costly, and potentially site-specific measures for damping front-end vibrations can also be avoided.

[0021] For example, in the coupled state, the coupling device forms a positive-locking connection between the electric machine, in particular the rotor, and the vehicle wheel, such that torques can be positively transmitted between the electric machine, in particular the rotor, and the vehicle wheel via the coupling device, whereas, for example, in the decoupling state, the positive-locking connection is released, i.e., interrupted or separated. This ensures particularly efficient operation.

[0022] In an advantageous embodiment of the invention, the characteristic acceleration value of the motor vehicle is determined, in particular, by means of an electronic computing device, from the longitudinal acceleration of the motor vehicle in the longitudinal direction of the vehicle. This allows the condition of the road surface to be advantageously determined. In other words, it has been found that the longitudinal acceleration can be used particularly advantageously as an indicator or measure of the condition, in particular of unevenness, of the road surface, thereby enabling particularly advantageous operation.

[0023] It has proven particularly advantageous to detect, or measure, the longitudinal acceleration using a sensor in the vehicle, also known as the first sensor. Specifically, the first sensor is an acceleration sensor in the vehicle. More specifically, the first sensor is an ESP sensor. By detecting the longitudinal acceleration using the first sensor, it can be measured with exceptional precision, allowing for a particularly useful and meaningful determination of the vehicle's acceleration value in relation to the road surface conditions.

[0024] For example, the first sensor provides a sensor signal, particularly an electrical one, that characterizes the detected longitudinal acceleration. Based on this sensor signal, that is, depending on the sensor signal, the electronic computing unit can advantageously determine the longitudinal acceleration and, consequently, the vehicle acceleration value.

[0025] Preferably, the sensor signal is filtered using a bandpass filter with a frequency range, which is also referred to as a bandpass filter. The electronic computing device can, for example, receive the filtered sensor signal, thereby advantageously determining the longitudinal acceleration and, in particular, the vehicle acceleration value as a function of the longitudinal acceleration. For this purpose, the sensor signal is evaluated in the frequency range of the bandpass filter, for example, by means of the electronic computing device, thereby advantageously determining the vehicle acceleration value and, consequently, allowing particularly meaningful conclusions to be drawn about the condition of the road surface.

[0026] In order to determine the vehicle acceleration value particularly advantageously and, consequently, to be able to draw particularly meaningful conclusions about the condition of the road surface, a further embodiment of the invention provides that the vehicle acceleration value, in particular its characteristic value, is determined from a moving average of the magnitude of the sensor signal, especially by means of the electronic computing device. Specifically, the magnitude of the sensor signal is to be understood as the absolute value, also referred to as the absolute magnitude or absolute value.

[0027] In a further, particularly advantageous embodiment of the invention, it is provided that the, in particular characteristic, vehicle acceleration value is determined from a gradient of acceleration values ​​recorded over a defined period of time, particularly by means of the electronic computing device. The respective acceleration value characterizes, for example, the vehicle acceleration, also simply referred to as acceleration, wherein the vehicle acceleration, for example, runs in the longitudinal direction of the vehicle and is thus, for example, the aforementioned longitudinal acceleration. Thus, the vehicle acceleration is measured, for example, by means of the first sensor.For example, a gradient is understood to be a gradient of a temporal profile exhibiting acceleration values, such that, for instance, the vehicle acceleration value is determined, and in particular calculated, from the gradient of the profile, especially by means of the electronic computing device. This allows for a particularly advantageous inference about the condition of the road surface, depending on the vehicle acceleration value, thus avoiding unnecessary opening of the coupling device and enabling the coupling device to be opened whenever this is necessary and / or advantageous, particularly due to the poor condition of the road surface on which the vehicle is driven, in order to prevent excessive stress on the vehicle.

[0028] In order to determine the vehicle acceleration value particularly advantageously and thus be able to draw particularly meaningful conclusions about the condition of the road, it is provided in a further embodiment of the invention that the particularly characteristic vehicle acceleration value is determined, in particular calculated, from a pitch rate of the vehicle, in particular by means of the electronic computing device.

[0029] It has proven particularly advantageous to detect the pitch rate using at least one sensor of the vehicle, also referred to as a second sensor. For example, the second sensor could be the first sensor, or the second sensor could be an additional sensor provided by the vehicle. By detecting the pitch rate with the second sensor, the vehicle acceleration value can be determined particularly effectively, making it especially informative regarding the current road surface conditions. Consequently, advantageous operation can be demonstrated.

[0030] A further embodiment of the invention is characterized in that the particularly characteristic vehicle acceleration value is determined from the vehicle's roll rate. This makes the vehicle acceleration value particularly meaningful for the current road surface conditions, thus ensuring advantageous operation.

[0031] To achieve particularly advantageous operation and to be able to draw particularly accurate, i.e., highly informative, conclusions about the current condition of the road surface, a further embodiment of the invention provides that the roll rate is detected, i.e., measured, by means of at least one sensor of the vehicle, also referred to as a third sensor. For example, the third sensor is the first sensor and / or the second sensor. Furthermore, it is conceivable that the third sensor is provided in addition to the first sensor and / or in addition to the second sensor.

[0032] Finally, it has proven particularly advantageous for achieving optimal operation if the electric machine is decoupled when the speed of the motor vehicle, which is currently traveling along the road, particularly forwards, is greater than a first limit value that is greater than zero and less than a second limit value that is greater than both the first and zero. Preferably, the first limit value is greater than 20 kilometers per hour. More specifically, the first limit value is 30 kilometers per hour. Preferably, the second limit value is greater than 50 kilometers per hour. More preferably, the second limit value is 60 kilometers per hour. This avoids the unnecessary opening of the coupling device.Furthermore, it can be ensured that the coupling device is opened when and, in particular, whenever this is advantageous, especially due to pronounced unevenness of the road surface, in order to avoid excessive vibrations of the motor vehicle, especially of the drive train.

[0033] The second sensor is also known as the pitch rate sensor, and the third sensor is also known as the roll rate sensor.

[0034] The pitch rate is the rate of a vehicle's pitching motion around its lateral direction. This design is based on the understanding that the pitch rate is a useful parameter for determining the unevenness or degree of unevenness of the road surface, allowing the vehicle's acceleration value to be precisely calculated. Consequently, the electric motor can be decoupled as needed, specifically when and only when the road surface unevenness is so severe that it could lead to torsional vibration in the vehicle assembly.

[0035] The roll rate is the rate of a vehicle's rolling motion around its longitudinal direction. This definition is based on the understanding that the roll rate is a particularly informative parameter for road surface irregularities, allowing for a highly precise determination of the vehicle's acceleration value.

[0036] This allows the electric machine to be decoupled as needed, so that excessive torsional vibrations in the assembly can be reliably avoided.

[0037] For example, each sensor provides a signal, particularly an electrical one, that characterizes the detected acceleration, pitch rate, or roll rate. Depending on this signal, the electronic computer can determine the acceleration, pitch rate, or roll rate, specifically by receiving the signal.

[0038] Preferably, the electric machine is also decoupled depending on the speed of the motor vehicle, which is also referred to as the driving speed. This speed is, for example, currently traveling along the road, particularly forwards. The speed is determined, for example, by means of an electronic computing device. The speed is detected, for example, by means of a sensor, also referred to as a speed sensor. The speed sensor provides, for example, a signal, particularly an electrical one, also referred to as a speed signal, whereby, for example, the electronic computing device can receive the speed signal and determine the speed based on the speed signal.For example, the electronic control unit can control the coupling device depending on the speed, thereby switching from the coupled state to the decoupling state. This design thus takes speed into account when decoupling the electric motor. The underlying reason for this is that unfavorable torsional vibrations in the drivetrain or the aforementioned assembly only occur, or can only occur, within a certain speed range. If the current speed of the vehicle lies outside this speed range—for example, if the speed is less than or equal to the first limit and greater than or equal to the second limit—then decoupling of the electric motor from the vehicle wheel may be omitted, even if the vehicle's acceleration exceeds the threshold.Thus, the electric machine, and in particular the rotor, can remain coupled to the vehicle wheel. However, if the speed, especially the current speed, lies within the specified speed range—which is particularly the case when the speed is greater than the first limit and less than the second limit—and, in particular, if the vehicle acceleration value also exceeds the threshold, the electric machine is decoupled from the vehicle wheel. This prevents unfavorable torsional vibrations in the drivetrain or the assembly. Therefore, it has proven particularly advantageous if the electric machine is decoupled, and preferably only decoupled, when the vehicle speed is greater than, for example, the first limit (which can be predefined or predetermined) and less than, for example, the second limit (which can be predefined or predetermined).

[0039] For example, the aforementioned signals are transmitted via a data bus such as a CAN bus in a motor vehicle, so the signals are also referred to as CAN signals.

[0040] Furthermore, it is conceivable to determine the level of a vehicle's chassis, also referred to as the ride height, particularly by detecting the ride height using at least one sensor, also referred to as a ride height sensor. For example, it is envisaged that the electric motor is decoupled depending on the determined ride height. For this purpose, the ride height sensor provides a signal, particularly an electrical one, also referred to as a ride height signal, which characterizes the detected ride height. Depending on the ride height, the electronic control unit can, for example, control the coupling device and thereby switch from the coupled state to the decoupled state. For this purpose, the electronic control unit receives the ride height signal.The rationale behind this design is, in particular, that the vehicle's ride height can be a meaningful parameter regarding road surface irregularities, allowing conclusions to be drawn, for example, about excessive road surface irregularities based on the ride height. Specifically, it is conceivable that the vehicle's acceleration value could be determined based on the measured ride height.

[0041] Further advantages, features, and details of the invention will become apparent from the following description of a preferred embodiment and from the drawing. The features and combinations of features mentioned above in the description, as well as those mentioned below in the figure description and / or shown in the figures alone, can be used not only in the combinations specified, but also in other combinations or individually, without departing from the scope of the invention.

[0042] The drawing shows in: Fig. 1. A schematic side view of a motor vehicle designed as a passenger car and also simply referred to as a vehicle; and Fig. 2. A flowchart to illustrate a procedure for operating the motor vehicle.

[0043] In the figures, identical or functionally equivalent elements are provided with the same reference symbols.

[0044] Fig. Figure 1 shows a schematic side view of a motor vehicle 10, also simply referred to as a vehicle, which is located at the site described in Fig. In the embodiment shown in Figure 1, the vehicle is designed as a passenger car, the interior space 12 of which is also referred to as the passenger compartment or passenger cell and is formed, i.e., bounded, by a body 14 of the vehicle 10, for example, a self-supporting body. The vehicle 10 has, in particular, two axles 16 and 18, which are arranged one behind the other in the longitudinal direction of the vehicle 10. The longitudinal direction of the vehicle 10 is illustrated by a double arrow 20. Each axle 16, 18 has, in particular, two wheels, which are also referred to simply as wheels, with the wheels of axle 16 being designated 22 and the wheels of axle 18 being designated 24.The respective vehicle wheels 22, 24 of the respective vehicle axle 16, 18 are arranged on opposite sides of the vehicle 10 in the transverse direction of the vehicle 10, the transverse direction of the vehicle being illustrated by a double arrow 26 and perpendicular to the plane of the image. Fig. 1 runs. Of the vehicle wheels 22 of the vehicle axle 16, in Fig. 1 the vehicle wheel 22 arranged on the left side of the motor vehicle 10 is recognizable, and consequently, of the vehicle wheels 24 of the vehicle axle 18, Fig. 1. The left wheel 24 of the vehicle axle 18 is visible. The wheels 22 of the vehicle axle 16 and the wheels 24 of the vehicle axle 18 are ground contact elements of the motor vehicle 10, which, in the vertical direction of the motor vehicle 10, can be supported or are supported downwards by the ground contact elements against a ground 28. The vertical direction of the motor vehicle 10 is illustrated by a double arrow 30. The ground 28 is, for example, a roadway or is also referred to as the road surface. If the motor vehicle 10 is driven along the roadway (ground 28) while, in the vertical direction of the motor vehicle 10, it is supported downwards by the ground contact elements (wheels 22 and 24) against the ground 28, the wheels 22 and 24 roll, in particular directly, along the roadway (ground 28).

[0045] The preceding and following explanations regarding vehicle axle 18 and the vehicle wheels 24 of vehicle axle 18 can readily be applied to vehicle axle 16 and the vehicle wheels 22 of vehicle axle 16, and vice versa. In the case of the Fig. In the embodiment shown in 1, the vehicle axle 18 has a Fig. 1. A particularly schematically represented electric machine 32, by means of which the vehicle wheels 22, in particular purely, can be driven electrically, thereby enabling the motor vehicle 10, in particular purely, to be driven electrically. In the case of the Fig. In the embodiment shown in Figure 1, the motor vehicle 10 is an electric vehicle, in particular a battery electric vehicle (BEV). For example, the electric machine 32 is an electric powertrain, or the electric machine 32 is also referred to as an electric powertrain, or the electric machine 32 is a component of an electric powertrain. In particular, the electric machine 32 is designed as a high-voltage component whose electrical voltage, in particular its operating or nominal voltage, is preferably greater than 50 volts, in particular greater than 60 volts, and most preferably several hundred volts.

[0046] The vehicle axle 18 also has a Fig. Figure 1 shows a coupling device 34, which is also referred to as a disconnect unit (DCU). The coupling device 34 is switchable between a coupled state and a decoupling state. In the coupled state, the electric machine 32, in particular a rotor of the electric machine 32, is coupled to the vehicle wheels 24 via the coupling device 34 in a torque-transmitting manner, so that drive torques provided or available by the electric machine 32 via its rotor and intended for driving the vehicle wheels 24, which are also referred to as torques, can be transmitted to the vehicle wheels 24 via the coupling device 34. Thus, in the decoupling state of the coupling device 34, the electric machine 32, in particular via its rotor, can drive the vehicle wheels 24, in particular purely electrically, via the coupling device 34.In the decoupling state of the coupling device 34, the electric machine 32, in particular the rotor of the electric machine 32, is decoupled from the vehicle wheels 24, so that no torques can be transmitted between the electric machine 32, in particular the rotor, and the respective vehicle wheel 24. Thus, if, for example, the coupling device 34 is in its decoupling state while the motor vehicle 10 is rolling on and along the ground 28, so that the vehicle wheels 24, in particular directly, roll on or against the ground 28 and rotate relative to the body 14, then the vehicle wheels 24 do not drag the rotor of the electric machine 32; consequently, the rotor of the electric machine 32 is not driven by the vehicle wheels 24. This ensures particularly efficient operation.

[0047] Fig. Figure 2 shows a flowchart to illustrate a procedure for operating the motor vehicle 10.

[0048] In particular, the vehicle wheels 22, 24 are components of the chassis of the motor vehicle 10. The chassis comprises a wheel suspension via which the vehicle wheels 22 and 24 are connected to the body 14. A system comprising the drivetrain and the chassis is also referred to as a drivetrain-chassis system.

[0049] In order to avoid excessive stress on the aforementioned assembly and thus achieve particularly low-wear and advantageous operation of the motor vehicle 10, especially over its service life, the method provides that an electronic computing device 36, also referred to as a control unit, is used ( Fig. 2) in particular of the motor vehicle 10, at least one characteristic motor vehicle acceleration value is determined, in particular calculated, wherein the motor vehicle acceleration value characterizes a particularly current state of the roadway (ground 28) along which the motor vehicle 10 is currently traveling. Thus, in the method, it is provided that the characteristic motor vehicle acceleration value is determined, in particular calculated, by means of the electronic computing device 36 during a journey of the motor vehicle 10, which travels along the roadway and is supported downwards in the vehicle's upward direction by the ground contact elements on the roadway, so that during the journey the ground contact elements roll, in particular directly, along the roadway.Thus, for example, the vehicle acceleration value is determined by means of the electronic computing device 36, in particular calculated, while the vehicle 10 is driving on and along the roadway. Specifically, the condition of the roadway is or includes an unevenness, so that, for example, the vehicle acceleration value indicates or characterizes an unevenness of the roadway. If, for example, the vehicle acceleration value exceeds a predetermined threshold, the roadway exhibits excessive, that is, excessively pronounced unevenness, so that, for example, the unevenness of the roadway is determined to be more pronounced or greater the higher the vehicle acceleration value.

[0050] Furthermore, the method provides that the electric machine 32, in particular the rotor, which is initially coupled to the vehicle wheels 24 via the coupling device 34 to transmit torque, is decoupled from the vehicle wheels 24 when the characteristic vehicle acceleration value is greater than the predetermined threshold value, and also when a braking process of the vehicle 10 is detected, in particular by means of the electronic computing device 36. This is achieved, in particular, by switching the coupling device 34, which is initially in the coupled state, from the coupled state to the decoupling state. For example, the vehicle acceleration value is compared with the threshold value by means of the electronic computing device 36.This means that, for example, a comparison is performed using the electronic computing device 36, in which the vehicle acceleration value is compared with the threshold value. If the comparison of the vehicle acceleration value with the threshold value shows that the vehicle acceleration value exceeds the threshold value and is therefore greater or higher than the threshold value, and in particular if a braking process of the vehicle 10 is also detected by the electronic computing device, then, for example, the electronic computing device 36 controls the coupling device 34, thereby switching the coupling device 34 from the coupled state to the decoupling state. This decouples the vehicle wheels 24 from the electric machine 32, in particular from the rotor.The electronic computing device 36 thus performs a preventive switching of the coupling device 34, such that the coupling device 34 is opened by means of the preventive switching, and thus switched from the coupled state to the decoupling state. For example, this is illustrated in . Fig.Blocks 40, 42, and 44 describe measures which, as illustrated in particular by arrows 38, are effected by the electronic computing device 36 when the characteristic vehicle acceleration value is greater than the threshold value and, in particular, when the aforementioned braking process of the vehicle 10 is simultaneously detected. A first measure is illustrated by block 40. This first measure includes, for example, a so-called torque shedding, which, for example, causes the electric machine 32 to no longer provide any torque via its rotor. A second measure is illustrated by block 42. This second measure includes, for example, a circuit without feedback as to whether the torque provided by the electric machine 32 via its rotor is zero. A third measure is illustrated by block 44.The third measure includes, for example, opening the coupling device 34, thus switching the coupling device 34 from the coupled state to the decoupling state and therefore decoupling the electric machine 32, in particular the rotor, from the vehicle wheels 24. The aforementioned drive train, which is an electric drive train, is illustrated by a block 46.

[0051] The aforementioned threshold is illustrated, for example, by block 48 and is, for example, such a threshold which, if exceeded by the vehicle acceleration value, could lead to critical frequencies and / or frequency ranges and possibly damaging amplitudes if no appropriate countermeasures are taken, such as decoupling the electric machine 32 from the vehicle wheels 24.

[0052] In this method, the characteristic acceleration value of the vehicle 10 is determined by means of an electronic computing device from the longitudinal acceleration of the vehicle 10 in the longitudinal direction. For this purpose, as illustrated by block 50, the longitudinal acceleration of the vehicle 10 is detected by means of at least one sensor, also referred to as an acceleration sensor or designed as an acceleration sensor. For example, the acceleration sensor provides a sensor signal, in particular an electrical one, which characterizes, that is, indicates, the longitudinal acceleration of the vehicle 10 detected by the acceleration sensor. For example, the sensor signal comprises several acceleration values ​​characterizing the detected longitudinal acceleration, which are or were detected sequentially by the acceleration sensor.Thus, the sensor signal is, or characterizes, a temporal profile of the longitudinal acceleration detected, i.e., measured, by the accelerometer. In other words, the acceleration values, for example, represent a temporal profile of the longitudinal acceleration of the motor vehicle 10 detected by the accelerometer, where, for example, the temporal profile of the longitudinal acceleration formed by the acceleration values ​​is the aforementioned sensor signal.

[0053] Block 52 illustrates that, for example, the sensor signal is filtered using a bandpass filter, which in particular has a frequency range. Alternatively or additionally, a gradient of the unfiltered or filtered sensor signal or its waveform is calculated. The vehicle acceleration value is determined, in particular calculated, by the electronic computing device 36 as a function of the waveform and / or as a function of the filtered sensor signal and / or as a function of the gradient.

[0054] Block 54 illustrates averaging. In averaging, for example, an average value is calculated from the acceleration values ​​of the unfiltered or filtered sensor signal or curve, where the value is expressed as an absolute value. Alternatively or additionally, a moving average of the curve and / or the filtered sensor signal and / or the unfiltered sensor signal is determined. For example, the vehicle acceleration value is calculated from the moving average using the electronic computing device 36. Consequently, the vehicle acceleration value is a particularly useful indicator of the current condition of the road surface.

[0055] Block 56 illustrates that the detection of the braking process is also taken into account for decoupling the electric machine 32 from the vehicle wheels 24. In other words, block 56 illustrates, for example, the detection of the braking process. Furthermore, block 58 illustrates that the current driving speed of the motor vehicle 10, also referred to simply as speed, is taken into account for decoupling the electric machine 32 from the vehicle wheels 24. The vehicle speed is, for example, currently traveling at the current driving speed along the road, particularly forwards.Thus, for example, the method provides that the electric machine 32, i.e., the rotor, is decoupled from the vehicle wheels 24 when the characteristic vehicle acceleration value is greater than the predetermined threshold value, when the braking process of the vehicle 10 is detected, and when, in particular, the current speed of the vehicle 10 is greater than a first limit value and less than a second limit value that is higher than the first limit value. In the embodiment shown in the figures, 30 kilometers per hour is used as the first limit value, and 60 kilometers per hour is used as the second limit value.

[0056] It is evident that blocks 52 and 54 illustrate specific frequency filtering processes. These processes include, for example, bandpass filtering, where the sensor signal is filtered using the aforementioned bandpass filter. Thus, blocks 52 and 54 illustrate signal processing through frequency filtering, specifically bandpass filtering. The bandpass filter has a frequency range within which the sensor signal is allowed to pass. This frequency range extends, for example, from 5 Hz to 16 Hz, and the frequencies within this range are particularly relevant for detecting significant road surface irregularities and thus poor road conditions.In particular, poor road conditions such as potholes and uneven road surfaces can be advantageously detected. For example, in blocks 52 and 54, the absolute value of the filtered sensor signal is calculated. This means, for instance, that after filtering the sensor signal using the bandpass filter, the value, specifically the absolute value, of the sensor signal is calculated. This is advantageous for creating a uniform basis for analysis and for taking both positive and negative signal peaks of the sensor signal into account. Furthermore, the moving average is calculated, for example. Here, the moving average is calculated from the absolute values ​​of the filtered sensor signal. This is done, for example, by regularly adding new data and removing the oldest data points to ensure continuous adaptation to current road conditions.The vehicle acceleration value is determined primarily from the moving average. The threshold value is determined, for example, through driving tests. Above the threshold value, that is, when the vehicle acceleration value is greater than the threshold, road surface excitation can lead to critical vibration excitations in the drivetrain, especially when other conditions are met, such as during braking, and when the speed is within a certain speed range.If the vehicle acceleration value exceeds the threshold and, for example, the vehicle 10 brakes simultaneously when its current speed is greater than the first threshold and less than the second, the coupling device 34 opens, thus switching from the coupled state to the decoupling state, in order to prevent the transmission of shocks and vibrations to the coupling device 34 and to protect it from damage. If, for example, the vehicle acceleration value falls below the threshold, the coupling device 34 closes again, that is, switches from the decoupling state to the coupled state.

[0057] The longitudinal acceleration of the vehicle 10 is measured, for example, by means of an acceleration sensor, which is, for instance, an ESP sensor. Longitudinal acceleration, or longitudinal acceleration data, characterizes the dynamic movements of the vehicle along its longitudinal axis. For example, an acceleration gradient of the longitudinal acceleration is determined. By determining the acceleration gradient, a jerk, for instance, is calculated. The jerk can be a measure of the rate of change of the longitudinal acceleration and can indicate an abrupt change in the vehicle's movement. The gradient, or the jerk, is characterized, for example, by a jerk signal. This jerk signal, particularly an electrical one, is filtered, for instance, to reduce noise and extract relevant information for vehicle dynamics.The filtering focuses, for example, on specific frequency ranges that are important for analyzing the movements of the vehicle 10. The jerk signal, or at least a jerk value characterizing the jerk signal, is compared with a level value. If the jerk value exceeds the level value and further conditions are met, in particular that the current speed of the vehicle 10 is greater than the first limit and less than the second limit value, and that the braking process is detected, then the coupling device 34 is activated, thereby switching from the coupled state to the coupled state. If the jerk value is high, such that it exceeds the level value, this indicates a strong and abrupt change in the vehicle dynamics of the vehicle 10.In this case, it is advisable to open the coupling device 34, particularly when the vehicle 10 is braking and the speed is greater than the first limit value and less than the second limit value. This prevents the transmission of excessively high forces to the coupling device 34, thus avoiding damage to the coupling device 34. If, for example, the jerk value is so low that it is less than or equal to the level value, this indicates smoother movements, which suggest stable driving conditions. In this case, the coupling device 34 can then be closed, or it can be left open.

[0058] For example, if it has been determined that the coupling device 34 should be opened, a redistribution of the drive and / or recuperation torques from the front axle to the rear axle or vice versa first takes place. This redistribution is delayed, for example, by a gradient limiter, so that a smooth and imperceptible redistribution of torques occurs. As soon as, for example, the actual torque of the front axle is low enough, the coupling device 34 is opened. In this case, a normal opening speed is requested, so that, for example, an actuator of the coupling device 34 is energized at normal speed to open the coupling device 34.To ensure an immediate response, such as the immediate opening of the coupling device 34, particularly for component protection reasons, the drive or recuperation torques are not redistributed from the front to the rear axle. Instead, the target torque of the front axle is directly set to 0 Newton meters, meaning all filtering is digitally deactivated. The system does not wait for the actual torque of the front axle to be low enough; instead, the coupling device 34 is opened immediately. In this case, rapid opening is requested, so the actuator receives maximum current to open the coupling device 34 as quickly as possible.Strong road excitation results in a strong introduction of vibrations into the structure 14, which at least largely masks any loss of comfort due to the immediate opening of the coupling device 34 and the lack of prior torque redistribution to the rear axle. Reference symbol list 10 motor vehicle 12 Interior 14 Structure 16 vehicle axle 18 vehicle axle 20 Double Arrow 22 vehicle wheel 24-inch vehicle wheel 26 Double Arrow 28 Floor 30 Double Arrow 32 electric machine 34 Coupling device 36 electronic computing equipment 38 arrows 40 blocks 42 Block 44 Block 46 Block 48 blocks 50 blocks 52 Block Block 54 Block 56 58 Block

Claims

[1] Method for operating a motor vehicle (10) in which the motor vehicle (10) has at least one vehicle wheel (24) and a drive train with at least one electric machine (32) by means of which the vehicle wheel (24) can be driven, characterized by , that: - during a journey of the motor vehicle, at least one motor vehicle acceleration value is determined by means of an electronic computing device (36), which characterizes a condition of a roadway (28) for the motor vehicle (10); and - the electric machine (32) is decoupled from the vehicle wheel (24) when the vehicle acceleration value is greater than a predetermined threshold value, and when a braking process of the vehicle (10) is detected. [2] Method according to claim 1, characterized by, that the motor vehicle acceleration value is determined from a longitudinal acceleration of the motor vehicle (10) running in the longitudinal direction (30) of the vehicle. [3] Method according to claim 2, characterized by , that the longitudinal acceleration is detected by means of at least one sensor of the motor vehicle (10), wherein the sensor provides a sensor signal characterizing the detected longitudinal acceleration, which is filtered by a bandpass filter having a frequency range and evaluated in the frequency range of the bandpass filter. [4] Method according to claim 3, characterized by , that the vehicle acceleration value is determined from a moving average of the magnitude of the sensor signal. [5] Method according to any one of the preceding claims, characterized by that the vehicle acceleration value is determined from a gradient of acceleration values ​​recorded over a defined period of time. [6] Method according to any one of the preceding claims, characterized by , that the motor vehicle acceleration value is determined from a pitch rate of the motor vehicle (10). [7] Method according to claim 6, characterized by , that the pitch rate is detected by means of at least one sensor of the motor vehicle (10). [8] Method according to any one of the preceding claims, characterized by , that the motor vehicle acceleration value is determined from a roll rate of the motor vehicle (10). [9] Method according to claim 8, characterized by , that the roll rate is detected by means of at least one sensor of the motor vehicle (10). [10] Method according to any of the preceding claims, characterized by , that the electric machine (32) is decoupled when the speed of the motor vehicle (10) is greater than a first limit value and less than a second limit value which is greater than the first limit value.

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