Method for controlling the slip of a motor vehicle

Abstract

A method for controlling the slip of a motor vehicle, in which: - the motor vehicle has an electric machine (22), a first vehicle wheel (12), a second vehicle wheel (14), a differential gear (28) via which a drive torque emanating from the electric machine (22) can be transmitted to the vehicle wheels (12, 14), and a differential lock (32) designed as a friction clutch (30) for locking the differential gear (28); - the differential gear (28) has three differential shafts, namely a differential input shaft (34), a first differential output shaft (36) and a second differential output shaft (38); - the electric machine (22) is coupled to the differential input shaft (34) in such a way that the respective drive torque emanating from the electric machine (22) can be introduced into the differential gear (28) at the differential input shaft (34); - the first differential output shaft (36) is connected to the first vehicle wheel (12) in a torque-transmitting manner; - the second differential output shaft (38) is connected to the second vehicle wheel (14) in a torque-transmitting manner; - the friction clutch (30) is designed to couple two of the three differential shafts together; - provided that both torque output from the electric machine (22) occurs and wheel slip is detected on the first vehicle wheel (12) and / or on the second vehicle wheel (14), the slip control is carried out in such a way that the friction clutch (30) is at least partially closed and at the same time the torque output of the electric machine (22) is reduced, - the slip control is carried out in such a way that a clutch torque of the friction clutch (30) and the drive torque which is provided by the electric machine (22) during torque delivery are each adjusted depending on an accelerator pedal position of an accelerator pedal of the motor vehicle, - in a first phase (A) of the slip control, the drive torque is reduced from a first torque value (DW1) to a second torque value (DW2) and at the same time the clutch torque is increased from a first clutch torque value (KW1) to a second clutch torque value (KW2); - in a second phase (B) of the slip control following the first phase (A), the drive torque is increased to the first torque value (DW1) and at the same time the clutch torque is reduced to a third clutch torque value (KW3) that is larger than the first clutch torque value (KW1) and smaller than the second clutch torque value (KW2). - in a first part (T1) of the first phase (A) the drive torque is reduced from the first torque value (DW1) to the second torque value (DW2) and at the same time the clutch torque is increased from the first clutch torque value (KW1) to the second clutch torque value (KW2); and - in a second part (T2) of the first phase (A) following the first part (T1), the second torque value (DW2) and the second clutch torque value (KW2) are kept constant.

Description

[0001] The invention relates to a method for controlling the slip of a motor vehicle.

[0002] DE 101 20 221 A1 discloses a method for the automatic actuation of differential locks in all-wheel-drive vehicles by controlling load-shiftable locking clutches for each differential of the vehicle equipped with a transmission.

[0003] Documents DE 10 2013 202 836 A1, US 2021 / 0 009 129 A1, DE 10 2014 225 490 A1, DE 10 2005 049 396 A1, DE 10 2015 117 818 A1, and DE 10 2010 027 978 A1 disclose methods for slip control in which differential locks and drive motors are controlled in a coordinated manner. For example, a design of a locking differential using a friction clutch is known from Küçükay, Ferhat: Classification of Differential Systems and Locks; in: Fundamentals of Vehicle Technology; Wiesbaden; Springer, 2022. DE 10 2016 123 691 A1 describes a control and regulation of a differential motor in conjunction with friction brake devices. DE 10 2011 081 709 A1 describes the reduction of a drive torque of a drive motor when wheel slip occurs. DE 10 2020 109 720 A1 discloses a method for controlling a drive torque of a motor in conjunction with the braking force of a locking differential.

[0004] The object of the present invention is to create a method for slip control of a motor vehicle, so that advantageous propulsion of the motor vehicle can be achieved in a particularly comfortable manner.

[0005] 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.

[0006] The invention relates to a method for slip control of a motor vehicle, also referred to simply as a vehicle, which is preferably a car, in particular a passenger car. In the method, the motor vehicle has a first wheel and a second wheel. Preferably, the wheels are located on the same axle of the motor vehicle. The axle is also referred to as the first axle. When the term "axle" is used before and below, it refers to the first axle unless otherwise specified. For example, the motor vehicle has at least or exactly two axles, also referred to simply as axles, namely the first axle and a second axle. The axles are arranged consecutively in the longitudinal direction of the motor vehicle and thus one behind the other.The vehicle wheels of the axle are arranged on opposite sides of the vehicle in the transverse direction. The vehicle wheels are also simply referred to as wheels. The vehicle wheels of the motor vehicle are ground contact elements of the vehicle, which, in the vehicle's vertical direction, can be supported or are supported downwards by the ground contact elements on a roadway, also referred to as the ground or forming a ground. When the vehicle is driven along the ground while, in the vehicle's vertical direction, it is supported downwards by the ground contact elements on the ground (roadway), the ground contact elements roll, in particular directly, along the ground (roadway).The vehicle wheels are, in particular, assigned a common electric machine by means of which the vehicle wheels can be driven, especially via a differential gear of the motor vehicle, also referred to as a differential, and are driven, in particular, during the process. Thus, a respective drive torque emanating from the electric machine, i.e., available or provided, also referred to as drive torque, can be transmitted to the vehicle wheels via the differential gear, in particular to drive the vehicle wheels. In particular, it is provided that in the process the drive torque is transmitted from the electric machine to the vehicle wheels via the differential gear, thereby, for example, driving the vehicle wheels. In particular, the drive torque can assume different values ​​and thus be varied.

[0007] In this method, the differential gear has, in particular, three differential shafts: a differential input shaft, a first differential output shaft, and a second differential output shaft. The differential input shaft is also referred to as the input shaft. The first differential output shaft is also referred to as the first output shaft, and the second differential output shaft is also referred to as the second output shaft.

[0008] For example, the electric machine has a stator and a rotor, which can be driven by means of the stator and is therefore rotatable about a machine axis of rotation relative to the stator. In particular, the electric machine can provide the drive torque via the rotor, so that the drive torque originates from the rotor. Thus, the vehicle wheels can be driven by the rotor via the differential gear. The electric machine is coupled to the differential input shaft, in particular in a torque-transmitting manner, and most especially in a rotationally fixed manner, such that the respective drive torque originating from the electric machine, in particular from the rotor, i.e., provided or available from the electric machine, i.e., from the rotor, can be introduced into the differential gear at the differential input shaft.Along a given torque flow, the drive torque can be transmitted from the electric machine, i.e., from the rotor, via the differential input shaft to the respective differential output shaft. With respect to the respective torque flow, the differential input shaft is located downstream of the rotor and upstream of the respective differential output shaft, which is thus located downstream of the rotor and downstream of the differential input shaft. The first differential output shaft is connected to the first vehicle wheel for torque transmission, and the second differential output shaft is connected to the second vehicle wheel for torque transmission. Each differential output shaft is also referred to, for example, as a side shaft. Each differential output shaft can be a driveshaft, which may, for example, have at least or exactly two constant velocity joints.

[0009] The term "torque-transmitting connection" means that the respective differential output shaft is either rotationally fixed to the respective wheel or is connected via a gear transmission device in such a way that torques originating from the respective differential output shaft can be transmitted to the respective wheel.

[0010] The term "rotatably connected" means that two rotatably mounted elements are rotatably connected to each other if and only if they are arranged coaxially and connected in such a way that they rotate at the same angular velocity.

[0011] In this method, the motor vehicle, and in particular the differential gear, has a differential lock designed as a friction clutch for locking the differential gear. Since the differential lock is designed as a friction clutch, it is also referred to as a friction locking clutch. The friction clutch is designed to couple two of the three differential shafts, in particular in a rotationally fixed manner. The two differential shafts that can be coupled to each other by means of the friction clutch, in particular in a rotationally fixed manner, are also referred to as coupling shafts. In particular, the clutch torque of the friction clutch is adjustable, i.e., variable, so that the clutch torque can assume different values, i.e., so that different values ​​of the clutch torque can be set. Preferably, and in particular precisely, one of the values ​​of the clutch torque is zero.Preferably, several further values ​​of the clutch torque are different from each other and non-zero. The clutch torque can be transmitted between the coupling shafts via the friction clutch. For example, different states of the friction clutch can be set. In a first state, for example, the clutch torque has a first value. In a second state, for example, the clutch torque has a second value, and in a third state, for example, the clutch torque has a third value. For example, the first value is zero. The second value is greater than the first value, and the third value is greater than the second value. It is conceivable that, for example, in the second state, the second value is a non-zero value, but the coupling shafts are rotatable relative to each other.It is conceivable that in the third state, the third value is a non-zero value, and the coupling shafts are rotatable relative to each other, or that in the third state, the coupling shafts are rotationally fixed to each other by means of the friction coupling, so that the third value is a non-zero value and relative rotation between the coupling shafts is prevented by the friction coupling. For example, it is conceivable that the first value is zero, so that the coupling shafts are rotatable relative to each other. Furthermore, it is conceivable that the first value is a non-zero value, and, for example, the coupling shafts are rotatable relative to each other.

[0012] In this method, provided that both torque output from the electric machine occurs and wheel slip is detected at the first and / or second vehicle wheel, slip control is implemented, in particular by means of an electronic computing device, such that the friction clutch is at least partially engaged and the torque output of the electric machine is simultaneously reduced. The torque output of the electric machine is understood to mean that the electric machine provides the drive torque during torque output, which preferably has a value other than zero during torque output.Reducing the torque output means, for example, that the drive torque provided by the electric machine, particularly the rotor, is reduced from a first torque value (which is not zero) to a second torque value that is lower than the first, wherein the second torque value is zero or, preferably, other than zero, and in particular, greater than zero. At least partially closing the friction clutch means, for example, increasing the clutch torque (also referred to as the clutch torque) from the first value to a second value that is greater than the first, particularly with the proviso described above that the first value is zero or other than zero, and that the second value is greater than the first and other than zero.The method according to the invention ensures advantageous, and in particular maximum, propulsion of the motor vehicle when it is detected that the aforementioned wheel slip occurs at the first and / or second vehicle wheel, that is, when it is detected that the first and / or second vehicle wheel is slipping. This is especially true when the slipping and thus spinning vehicle wheel is very advantageously, and in particular ideally, controlled. Furthermore, compared to conventional solutions, the invention can achieve an improvement in comfort, particularly when controlling the slipping and thus spinning vehicle wheel.

[0013] For example, the method is designed to detect that one of the vehicle wheels is slipping, particularly while simultaneously detecting that the other vehicle wheel is not slipping. In other words, it is preferably designed to detect wheel slip of one vehicle wheel, particularly while simultaneously detecting that there is no wheel slip of the other vehicle wheel. The feature of detecting that one vehicle wheel is slipping includes, for example, the detection that the wheel slip of one vehicle wheel is greater than a threshold value, which can be specified or predetermined. Furthermore, the feature of detecting that the other vehicle wheel is not slipping, and thus that there is no wheel slip of the other vehicle wheel, includes, for example, the detection that the wheel slip of the other vehicle wheel is less than or equal to the threshold value.

[0014] The invention is based in particular on the following findings and considerations: During driving maneuvers in which one or both vehicle wheels begin to spin, i.e., slip, for example due to low friction coefficients and / or due to a dynamic wheel load distribution, the drive torque should be reduced to counteract the spinning, i.e., the slippage of the vehicle wheel(s). In this method, the friction clutch is used as a variable locking clutch to maintain a specific drive torque, i.e., a specific value of the drive torque, and simultaneously, for example, to precisely control a target slip at the spinning vehicle wheel(s).The aforementioned vehicle axle is an electric axle, since the electric motor drives the differential output shafts and thus the vehicle wheels via the differential gear. The method according to the invention makes it possible to set an advantageous, and in particular optimal, profile of the clutch torque (also referred to as friction clutch torque) and an advantageous, and in particular optimal, time profile of the drive torque for slip control. By at least partially closing the friction clutch (also referred to simply as a clutch), the side shafts are coupled to each other, in particular for torque transmission, i.e., coupled to each other in such a way that the clutch torque can be transmitted via the friction clutch with a value higher than or different from zero.

[0015] If, for example, the friction clutch were fully engaged, the entire drive torque would be transmitted to the non-slipping, i.e., non-rotating, vehicle wheel. However, when the friction clutch is fully engaged, the previously slipping vehicle wheel is also braked, which can result in the rotational energy stored in the previously slipping vehicle wheel being converted into additional torque acting on the non-slip vehicle wheel. This, in turn, causes the total torque acting on the non-slip vehicle wheel to be greater than the drive torque and thus a torque desired by the driver of the vehicle. This can now be avoided in the method according to the invention by engaging the friction clutch and simultaneously reducing the torque output, i.e., the drive torque.This compensates for the rotational energy of the slipping wheel. This prevents excessive torque from being applied to the wheel that is not slipping, or slipping less. Furthermore, it ensures efficient propulsion of the vehicle.

[0016] In order to ensure particularly advantageous propulsion of the motor vehicle in a particularly comfortable manner, it is further part of the invention that the slip control is carried out in such a way, that is, in such a way that the clutch torque of the friction clutch and the drive torque, which is provided by the electric machine during torque delivery and is transmitted, for example, via the differential gear to the differential output shafts and the vehicle wheels, in particular to drive the vehicle wheels, are each adjusted depending on a position of an accelerator pedal of the motor vehicle, which is also referred to as the accelerator pedal position.The accelerator pedal is a control element that the driver of the motor vehicle operates, in particular by means of their foot, and can thereby move into different positions, specifically to adjust the drive torque and request it from the electric motor. It is therefore preferably provided that the clutch torque and the drive torque, i.e., for example, a time-dependent profile of the clutch torque and a time-dependent profile of the drive torque, are each calculated as a function of the accelerator pedal position, i.e., adjusted as a function of the accelerator pedal position.

[0017] As a further component of the invention, it is provided that in a first phase of the slip control the drive torque is reduced from a first torque value to a second torque value and at the same time the clutch torque is increased from a first clutch torque value to a second clutch torque value.

[0018] Preferably, the first torque value is a non-zero value. Preferably, the second torque value is a non-zero value, or the second torque value is zero. The second torque value is less than the first torque value. Preferably, the first clutch torque value is a non-zero value, or the first clutch torque value is zero. Furthermore, it is preferably provided that the second clutch torque value, which is greater than the first clutch torque value, is a non-zero value.In a second phase of the slip control, which follows directly after the first phase, the drive torque is increased, in particular from the second torque value to the first torque value, and at the same time the clutch torque is reduced, in particular from the second clutch torque value, to a third clutch torque value that is larger than the first clutch torque value and smaller than the second clutch torque value.

[0019] Finally, in the method according to the invention, in a first part of the first phase, the drive torque is reduced from the first torque value to the second torque value, and simultaneously the clutch torque is increased from the first clutch torque value to the second clutch torque value. In a second part of the first phase, which follows directly after the first part, the second torque value and the second clutch torque value are kept constant. This allows for particularly comfortable slip control with advantageous propulsion of the vehicle.

[0020] A further development of the invention is characterized in that the slip control is implemented in such a way that the clutch torque and the drive torque are each adjusted as a function of a target speed profile of the vehicle wheel, particularly over time, for which wheel slip is detected, i.e., which wheel slip is recognized as occurring. This ensures advantageous and comfortable propulsion of the vehicle.

[0021] In order to realize a particularly advantageous feature of the motor vehicle in a particularly convenient way, it is further provided in the invention that the slip control is carried out in such a way, that is, in such a way that the clutch torque and the drive torque are each adjusted as a function of a torque, also referred to as transmission torque, which can be transmitted between the road surface and the vehicle wheel for which wheel slip is detected, i.e., which is recognized as slipping.

[0022] Another embodiment is characterized in that the slip control is implemented in such a way that the clutch torque and the drive torque are each adjusted as a function of a target speed profile of the vehicle wheel for which a non-slip state is detected. The slipping vehicle wheel is also referred to as a spinning vehicle wheel, and the non-slip vehicle wheel is also referred to as a non-spinning vehicle wheel. This allows for advantageous propulsion of the vehicle without causing excessive loss of comfort.

[0023] In a further development of the invention, it has proven particularly advantageous for realizing a particularly convenient slip control if, in a third phase of the slip control which follows the second phase, in particular directly, the first torque value and the third clutch torque value are kept constant.

[0024] It has proven particularly advantageous if the third phase follows directly after the second phase, so that the second phase ends at the same time as the third phase begins.

[0025] Finally, it has proven particularly advantageous for achieving a particularly beneficial, comfortable slip control with a particularly beneficial propulsion of the motor vehicle if the second phase directly follows the second part of the first phase and thus connects to the first phase.

[0026] For example, the target speed profile of the slipping wheel is, particularly for comfort reasons, an advantageous compromise between quickly ending the wheel spin and ensuring smooth acceleration or continued driving. In the first phase, the wheel speeds decrease, primarily due to the reduction in drive torque and the increase in clutch torque. Following predefined target wheel speed curves, for example, from approximately the middle of the first phase, the drive torque is then increased again and the clutch torque is slightly reduced. This further decreases the wheel speeds, thus reducing wheel slip. According to the target wheel speed curves, the second phase then transitions into the third phase.In the third phase, there may still be slight wheel slippage of the slipping wheel; however, even with this slight slippage or spinning, torque can still be transferred from the slipping wheel to the road surface. Thus, the third phase represents an advantageous compromise between wheel slippage and propulsion of the vehicle. In the third phase, the full drive torque is applied. However, the friction clutch is still slightly engaged—that is, not fully engaged, but also not fully disengaged—and the vehicle wheel(s) are still spinning slightly.

[0027] The first phase begins, for example, approximately 50 ms to 100 ms after wheel slip is detected. The first and second phases together last, for example, approximately 50 ms to 100 ms. The third phase lasts, for example, until none of the vehicle's wheels are slipping anymore, meaning they are no longer spinning freely.

[0028] The transmission torque that can be transmitted between the road surface and the slipping wheel depends on the wheel speed of the slipping wheel and the rotor speed of the non-slipping wheel, and can be determined from these two factors. The characteristic that two of the three differential shafts can be coupled to each other, particularly for torque transmission, by means of the friction clutch means, in particular, that the coupling shafts, when coupled by means of the friction clutch, are either rotationally fixed or, more specifically, almost rotationally fixed in such a way that a non-zero torque can be transmitted between the two differential shafts, but the differential shafts are rotatable relative to each other or rotate relative to each other and thus slip relative to each other.In particular, the two differential shafts can be directly coupled or connected to each other by means of the friction clutch.

[0029] 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.

[0030] The drawing shows in: Fig. 1 a schematic representation of a vehicle axle of a motor vehicle; Fig. 2 diagrams illustrating a procedure for controlling the slip of a motor vehicle.

[0031] In the figures, identical or functionally equivalent elements are provided with the same reference symbols.

[0032] Fig. Figure 1 shows a schematic view of a vehicle axle 10, also referred to as the first axle, of a motor vehicle, also referred to simply as a vehicle, which is preferably a motor car, in particular a passenger car. The motor vehicle has exactly two axles arranged consecutively in the longitudinal direction of the motor vehicle, namely the vehicle axle 10 as the first axle and a second axle. Each axle has exactly two wheels, the wheels of axle 10 being designated 12 and 14. The wheels of each axle are arranged on opposite sides of the motor vehicle in the transverse direction. Fig. Figure 1 illustrates the transverse direction of the motor vehicle by a double arrow 16. The vehicle wheels are ground contact elements by which the motor vehicle can be supported or is supported downwards against a roadway 18 in the vehicle's vertical direction. The vehicle's vertical direction is illustrated by a double arrow 20. The roadway 18 is or forms a ground for the motor vehicle. If the motor vehicle is driven along the roadway 18 while the vehicle is supported downwards in the vehicle's vertical direction by the ground contact elements against the ground, i.e., the roadway 18, the ground contact elements should, in particular, be directly attached to the roadway 18.

[0033] The vehicle axle 10 has exactly one electric machine 22, which has a stator 24 and a rotor 26. Preferably, the electric machine 22 is designed as a high-voltage component, the first voltage of which, in particular, the electrical operating or nominal voltage, is preferably greater than 50 volts, particularly greater than 60 volts, and most preferably several hundred volts. The vehicle axle 10 also has a differential gear 28, also simply referred to as a differential, via which the vehicle wheels 12 and 14 can be driven by the rotor 26 and thus by the electric machine 22. The electric machine 22 can provide a drive torque via its rotor 26, which, particularly when provided by the electric machine 22 via the rotor 26, originates from the rotor 26 and thus from the electric machine 22. The drive torque is a torque and is also referred to as drive torque.The drive torque can be adjusted, i.e., varied, and thus assume different values, these values ​​being referred to as torque values.

[0034] The vehicle axle 10 also has a differential lock 32 designed as a friction clutch 30, which is also referred to as a friction locking clutch. The differential lock 32, i.e., the friction clutch 30, allows the differential gear 28 to be locked, as will be explained in more detail below.

[0035] The differential gear 28 has, in particular, three differential shafts, namely a differential input shaft 34, a first differential output shaft 36, and a second differential output shaft 38. In the case of the Fig. In the embodiment shown in Figure 1, the differential gear 28 is designed as a planetary differential, which has a sun gear, a planet carrier, and a ring gear. The planetary differential also has planet gears 40, which are rotatably mounted on the planet carrier. Furthermore, each planet gear 40 meshes, in particular simultaneously, with the sun gear and the ring gear. In the embodiment shown in Figure 1, the differential gear 28 is designed as a planetary differential, which has a sun gear, a planet carrier, and a ring gear. Fig. In the embodiment shown in Figure 1, the sun gear is the second differential output shaft 38, and the planet carrier is the first differential output shaft 36. The ring gear is the differential input shaft 34. The electric machine 22, in particular the rotor 26, is coupled to the differential input shaft 34, in particular in a torque-transmitting manner and, more importantly, in a permanently torque-transmitting manner, such that the respective drive torque emanating from the electric machine 22, in particular from the rotor 26, and thus provided or makeable, can be introduced into the differential gear 28 via the differential input shaft 34. The respective differential output shafts 36 and 38 can be driven by the differential input shaft 34 and, via this, by the rotor 26, and thus by the electric machine 22.The first differential output shaft 36 is non-rotatably connected to the first vehicle wheel 12, in particular via a driveshaft which, for example, and especially, has two constant velocity joints. The second differential output shaft 38 is non-rotatably connected to the second vehicle wheel 14, in particular via a second driveshaft which, for example, and especially, has two constant velocity joints.

[0036] The friction clutch 30 is designed to couple two of the three differential shafts together in a torque-transmitting manner. The two differential shafts that can be coupled together by means of the friction clutch 30 are also referred to as coupling shafts. In the case of the Fig. In the embodiment shown in Figure 1, a first coupling shaft is the differential output shaft 36, and a second coupling shaft is the differential output shaft 38. The clutch torque of the friction clutch 30, also referred to as the clutch torque, is adjustable, meaning it can be varied so that the clutch torque can assume different values, also referred to as clutch torque values. In other words, the aforementioned different torque values ​​of the drive torque are adjustable, and the different clutch torque values ​​are also adjustable.The friction clutch 30 transmits the coupling torque between the two differential shafts that can be coupled to each other by means of the friction clutch 30, in particular such that at most the currently set coupling torque, i.e., at most the currently set coupling torque value, can be transmitted between the coupling shafts via the friction clutch 30. In other words, torques greater than or equal to the currently set coupling torque value can be transmitted between the coupling shafts via the friction clutch 30 without causing relative rotation, i.e., slippage, between the coupling shafts. A torque greater than the currently set coupling torque would lead to slippage, i.e., relative rotation, between the coupling shafts.For example, in particular, one of the torque values ​​is zero, wherein the other several remaining torque values ​​are different from each other and from zero. For example, in particular, one of the clutch torque values ​​is zero, wherein the other remaining clutch torque values ​​are different from each other and from zero.

[0037] The drive torque can be transmitted along a respective torque flow from the rotor 26 to the respective vehicle wheel 12, 14, in particular to drive the respective vehicle wheel 12, 14. With respect to the respective torque flow, the differential input shaft 34 is arranged downstream of the rotor 26 and upstream of the respective differential output shaft 36, 38. It may be provided that a respective transmission stage 42, 44 is arranged in the respective torque flow upstream of the respective vehicle wheel 12, 14 and downstream of the respective differential output shaft 36, 38, so that, for example, the respective vehicle wheel 12, 14 can be driven by the respective differential output shaft 36, 38 via the respective transmission stage 42, 44. The respective transmission stage 42, 44 is optional and can therefore be omitted.In an alternative embodiment, not shown in the figures, the differential gear 28 could be designed as a bevel gear differential, also known as a bevel differential. Furthermore, the differential gear 28 could be designed as a different type of differential gear. In an unlocked state, i.e., not locked by the differential lock 32, the differential gear 28 has the function, in particular, of allowing different rotational speeds of the vehicle wheels 12 and 14 when the vehicle is cornering, specifically such that the outer wheel rotates, or can rotate, at a higher speed than the inner wheel.

[0038] The following will be based on Fig. 1 and Fig. 2. A method for controlling the slip of a motor vehicle is described. The method is implemented, for example, by means of a Fig. The procedure is carried out using a particularly schematically represented electronic computing device 46, which is also referred to, for example, as a control unit or can comprise at least one or more control units. In particular, the electronic computing device 46 is a component of the motor vehicle. The procedure is described using diagrams in Fig. 2 illustrated. Fig. Figure 1 shows a first diagram D1, on whose abscissa 48 time is plotted. On the ordinate 50 of diagram D1, the respective rotational speed of the respective vehicle wheel 12, 14, also referred to as wheel speed, is plotted. A diagram D2 in Fig. Diagram 2 has an ordinate 52 on which a pedal value is plotted. The pedal value characterizes the position of the vehicle's accelerator pedal, also known as the accelerator pedal position. A driver can operate the accelerator pedal and thereby move it to different positions, thus varying the accelerator pedal value or position. A third diagram, D3, has an ordinate 54 on which the drive torque or its values ​​are plotted. Finally, a fourth diagram, D4, has an ordinate 56 on which the clutch torque, i.e., the clutch torque values, are plotted. The method determines, for example, and thus detects, that wheel slip occurs at vehicle wheel 12. In other words, the method detects that vehicle wheel 12 is slipping.In particular, the method detects that vehicle wheel 12 is slipping while vehicle wheel 14 is not slipping, i.e., it detects that there is no wheel slip at vehicle wheel 14. Furthermore, the method involves the electric machine 22 delivering torque, which provides the drive torque via its rotor 26. Provided that both the electric machine 22 delivers torque and wheel slip is detected at vehicle wheel 12, and, for example, it is detected that vehicle wheel 14 is not slipping, the slip control is implemented such that the friction clutch 30 is at least partially engaged and the torque output of the electric machine 22 is simultaneously reduced.In particular, the feature that the wheel slip of the vehicle wheel 12 is detected, i.e., that it is detected that the vehicle wheel 12 is slipping, is to be understood as the detection that the wheel slip of the vehicle wheel 12 exceeds a threshold value, which can be specified or predetermined. In particular, for example, the feature that it is detected that the vehicle wheel 14 is not slipping is to be understood as the detection that the wheel slip of the vehicle wheel 14 is less than or equal to the threshold value. The slipping vehicle wheel 12, i.e., the one detected as slipping, is also referred to as a spinning wheel or spinning vehicle wheel 12, and the vehicle wheel 14, detected or determined as not slipping, is also referred to as a non-spinning wheel or non-spinning vehicle wheel 14.

[0039] If the respective vehicle wheel 12, 14 is driven, it rotates about its respective wheel axis relative to a reference element, such as a wheel carrier, at a speed also referred to as wheel speed, which depends, for example, on the drive torque. A curve V represents an ideal speed profile over time for the respective wheel speed when the respective vehicle wheel 12, 14 does not slip, i.e., does not spin freely. This is also referred to as ω. L The curve V1 is an actual time-dependent rotational speed profile of the wheel speed of the slipping vehicle wheel 12, and is also represented by ω. R The curve labeled V2 is an actual time-dependent rotational speed profile of the wheel speed of the non-rotating vehicle wheel 14. Dashed curves labeled SL are target curves of the wheel speeds and also with Δω µL,traj or Δω µH,traj denoted by ω. L,limA speed limit for the vehicle wheel 12 is shown, and with ω R,lim A speed limit for the vehicle wheel 14 is illustrated, where the speed limits coincide. If the respective wheel speed exceeds the respective speed limit, the respective vehicle wheel 12, 14 will indeed spin freely, but a sufficiently large torque, also referred to as transmission torque, can still be transmitted between the respective vehicle wheel 12 and 14 and the road surface 18. With Δω µLow Δω denotes the difference between the curves V and V1, or between the curves V1 and V2. µHigh is a difference between the curve V and ω R,lim designated.

[0040] Out of Fig. 2. It is evident that, for example, the driver depresses the accelerator pedal, thereby moving it from a first accelerator pedal position to a second accelerator pedal position that differs from the first. This allows the driver to set the electric motor 22 to provide the drive torque with one of the first torque values. The first torque value is labelled DW1. This is evident from... Fig. In a first phase A of the slip control, the drive torque is reduced from the first torque value DW1 to a second torque value, and simultaneously the clutch torque is increased from a first clutch torque value to a second clutch torque value. The second torque value is denoted as DW2 and is smaller than the first torque value DW1, which in this case is a non-zero value and, in particular, a larger value than zero. The second torque value DW2 can be zero or a non-zero value. The first clutch torque value is denoted as KW1, and the second clutch torque value is denoted as KW2. The first clutch torque value KW1 can be zero or a non-zero value. The clutch torque value KW2 is larger than the clutch torque value KW1 and preferably a non-zero value.Recognizable from . Fig.Paragraph 2 states that in a first part T1 of the first phase A, the drive torque is reduced from the first torque value DW1 to the second torque value DW2, and simultaneously the clutch torque is increased from the first clutch torque value KW1 to the second clutch torque value KW2. In a second part T2 of the first phase A, which directly follows the first part T1, the second torque value DW2 and the second clutch torque value KW2 are kept constant. In a second phase B of the slip control, which directly follows the second part T2 and thus directly follows the first phase A, the drive torque, in particular from the second torque value DW2, is increased to the first torque value DW1, and simultaneously the clutch torque, in particular from the clutch torque value KW2, is reduced to a third clutch torque value, where the third clutch torque value is designated KW3.The clutch torque value KW3 is preferably a non-zero value, wherein the clutch torque value KW3 is greater than the clutch torque value KW1 and less than the clutch torque value KW2. In a third phase C of the slip control, which directly follows the second phase B, the first torque value DW1 and the third clutch torque value KW3 are kept constant.

[0041] The method is based, in particular, on the understanding that if, for example, the vehicle wheel 12 slips and the friction clutch 30 is fully engaged, the entire drive torque is transferred to the non-slipping and therefore non-rotating vehicle wheel 14. This causes the slipping vehicle wheel 12 to be braked, which results in the rotational energy stored in the rotating vehicle wheel 12 being converted into an additional torque acting on the non-rotating vehicle wheel 14. Consequently, the total torque acting on the non-slip, i.e., non-rotating, vehicle wheel 14 is greater than the drive torque. To prevent this, the friction clutch 30 is at least partially or fully engaged, in particular in such a way that slippage between the coupling shafts is permitted or occurs.Furthermore, in the first phase A, the drive torque or torque output is reduced. In phase B, the clutch torque is reduced to allow for a smooth transition of the wheel speed (also known as slip speed) of the slipping vehicle wheel 12 to a target value. The lower the clutch torque is or becomes, the higher the drive torque or torque output should be or become. The third phase C is a steady-state phase in which the friction clutch 30 only engages to the extent necessary to maintain the wheel slip at a target level. Dynamic torque is absent, and the electric motor 22 again provides the full drive torque as requested by the driver. Reference symbol list 10 vehicle axle 12 vehicle wheel 14 vehicle wheel 16 Double Arrow 18 lanes 20 Double Arrow 22 electric machine 24 Stator 26 Rotor 28 Differential gears 30 friction clutch 32 Differential lock 34 Differential input shaft 36 Differential output shaft 38 Differential output shaft 40 planetary gear 42 translation level 44 translation level 46 electronic computing equipment 48 Abscissa 50 ordinates 52 ordinates 54 ordinates 56 ordinates D1 diagram D2 diagram D3 diagram D4 diagram DW1 first torque value DW2 second torque value KW1 first clutch torque value KW2 second clutch torque value KW3 third clutch torque value A first phase B second phase C third phase T1 Part One T2 Part Two V Course V1 progress V2 progress SL runs

Claims

[1] A method for controlling the slip of a motor vehicle in which: - the motor vehicle has an electric machine (22), a first vehicle wheel (12), a second vehicle wheel (14), a differential gear (28) via which a drive torque emanating from the electric machine (22) can be transmitted to the vehicle wheels (12, 14), and a differential lock (32) designed as a friction clutch (30) for locking the differential gear (28); - the differential gear (28) has three differential shafts, namely a differential input shaft (34), a first differential output shaft (36) and a second differential output shaft (38); - the electric machine (22) is coupled to the differential input shaft (34) in such a way that the respective drive torque emanating from the electric machine (22) can be introduced into the differential gear (28) at the differential input shaft (34); - the first differential output shaft (36) is connected to the first vehicle wheel (12) in a torque-transmitting manner; - the second differential output shaft (38) is connected to the second vehicle wheel (14) in a torque-transmitting manner; - the friction clutch (30) is designed to couple two of the three differential shafts together; - provided that both torque output from the electric machine (22) occurs and wheel slip is detected on the first vehicle wheel (12) and / or on the second vehicle wheel (14), the slip control is carried out in such a way that the friction clutch (30) is at least partially closed and at the same time the torque output of the electric machine (22) is reduced, - the slip control is carried out in such a way that a clutch torque of the friction clutch (30) and the drive torque which is provided by the electric machine (22) during torque delivery are each adjusted depending on an accelerator pedal position of an accelerator pedal of the motor vehicle, - in a first phase (A) of the slip control, the drive torque is reduced from a first torque value (DW1) to a second torque value (DW2) and at the same time the clutch torque is increased from a first clutch torque value (KW1) to a second clutch torque value (KW2); - in a second phase (B) of the slip control following the first phase (A), the drive torque is increased to the first torque value (DW1) and at the same time the clutch torque is reduced to a third clutch torque value (KW3) that is larger than the first clutch torque value (KW1) and smaller than the second clutch torque value (KW2). - in a first part (T1) of the first phase (A) the drive torque is reduced from the first torque value (DW1) to the second torque value (DW2) and at the same time the clutch torque is increased from the first clutch torque value (KW1) to the second clutch torque value (KW2); and - in a second part (T2) of the first phase (A) following the first part (T1), the second torque value (DW2) and the second clutch torque value (KW2) are kept constant. [2] Method according to claim 1, characterized by, that the slip control is carried out in such a way that the clutch torque and the drive torque are each adjusted depending on a target speed profile of the vehicle wheel (12, 14) for which wheel slip is detected. [3] Method according to claim 1 or 2, characterized by , that the slip control is carried out in such a way that the clutch torque and the drive torque are each adjusted depending on a torque which can be transmitted between a road surface (18) and the vehicle wheel (12, 14) for which wheel slip is detected. [4] Method according to any one of the preceding claims, characterized by , that the slip control is carried out in such a way that the clutch torque and the drive torque are each adjusted depending on a target speed profile of the vehicle wheel (12, 14) for which a non-slip condition is detected. [5] Method according to any one of the preceding claims, characterized by, that in a third phase (C) of the slip control following the second phase (B), the first torque value (DW1) and the third clutch torque value (KW3) are kept constant. [6] Method according to claim 5, characterized by that the third phase (C) directly follows the second phase (B). [7] Method according to any one of the preceding claims, characterized by that the second phase (B) directly follows the second part (T2) and thus directly follows the first phase (A).

Images