Method and device for controlling a drive torque in a motor vehicle and motor vehicle

Abstract

Method for controlling a drive torque in a motor vehicle (1), comprising: - detecting a wheel speed on a front axle (200) of the motor vehicle (1); - detecting a wheel speed on a rear axle (300) of the motor vehicle (1); - detecting a differential speed based on the wheel speed of the front axle (200) and the wheel speed of the rear axle (300); - if the differential speed exceeds an amount of a predetermined value: reading a torque distribution factor from a map based on the differential speed; and - Controlling the drive torque based on the torque distribution factor read from the map.

Description

[0001] The invention relates to a method and a device for controlling a drive torque in a motor vehicle and to a motor vehicle with such a device.

[0002] To avoid overloading the axles of a motor vehicle, especially an all-wheel drive vehicle, it is necessary to know the respective torques acting on each axle. However, torque sensors are complex and expensive.

[0003] Document DE 10 2014 007 235 A1 discloses a control device for vehicle drive force distribution. Document DE 10 2010 036 860 A1 discloses a method for determining an actual torque distribution of an all-wheel clutch device of a four-wheel drive motor vehicle. Document DE 101 53 758 A1 discloses a method and system for determining an acceptable torque level. Document US 2002 / 0 179 357 A1 discloses an automatic axle traction control.

[0004] It is therefore an object of the present invention to provide an improved method and an improved device for controlling a drive torque in a motor vehicle.

[0005] This problem is solved by the independent claims. Advantageous further developments are specified in the dependent claims.

[0006] According to a first aspect, a method for controlling a drive torque in a motor vehicle is provided.

[0007] The method comprises the steps of detecting a wheel speed on a front axle of the motor vehicle, detecting a wheel speed on a rear axle of the motor vehicle, detecting a differential speed based on the wheel speed of the front axle and the wheel speed of the rear axle, if the differential speed exceeds an amount of a predetermined value, reading out a torque distribution factor from a characteristic map based on the differential speed and controlling the drive torque based on the read-out torque distribution factor from the characteristic map.

[0008] The motor vehicle is, in particular, a vehicle in which two axles, in particular the front and rear axles, are driven by one or more engines. In particular, the motor vehicle is a four- or all-wheel drive motor vehicle.

[0009] Likewise, in particular, the torque generated for driving the axles is applied to a single shaft, for example by connecting in series an internal combustion engine and an electric machine, which drives a so-called center differential, which can also be referred to as a Torsen, via a gearbox or provides it with a single drive torque, and from where the torque is distributed to the front and rear axles in accordance with the design and, in particular, usually unchangeable parameters or framework conditions of the Torsen.

[0010] The method according to the invention serves in particular to particularly accurately determine or determine a torque distribution factor which is present between a front axle and a rear axle and which in particular comprises a quotient of the application of torque to the front and rear axle by the engine, but without providing one or more torque sensors on the respective axles.

[0011] First, a wheel speed is measured on the front and rear axles. This can be done, for example, using one or more suitable speed sensors located on the front and rear axles. In particular, the wheel speed is measured or recorded periodically, in particular every 100 ms, 50 ms, 10 ms, or 5 ms, or continuously on each of the two axles. The procedure is performed with a similar or identical repetition frequency, or the respective state and, in particular, the basis for the torque distribution factor is recalculated.

[0012] Based on these wheel speeds, a difference is calculated, which represents the differential speed. The absolute value is then taken from this differential speed. This absolute value serves as the basis for a comparison. If the absolute value is greater than a predetermined value, a different action is taken than if the absolute value is less than a predetermined value.

[0013] If this speed difference is greater than a predetermined or predefined threshold, a characteristic map is used to control the drive torque. For example, the characteristic map is used for control if the speed difference is greater than 0.5, 1, 5, 10, or 100 revolutions per minute. This speed difference, or the effect underlying this value, can also be referred to as slip.

[0014] If, however, the amount of the differential speed is smaller than the predetermined threshold value, the characteristic map cannot be used as a basis for the control, but rather other values ​​or bases, as will be described later.

[0015] In this case, a characteristic map comprises a point cloud that plots a torque distribution factor across two dimensions. In particular, this is a characteristic map in which different torque distribution factors are used for different differential speeds. Thus, a specific torque distribution factor is read out for a specific determined differential speed.

[0016] The characteristic map may in particular be a characteristic map that was previously determined on a test bench for the specific model of the Torsen, the drive type, the vehicle type, the tire type and / or the wheel-tire combination, in particular using one or more torque sensors arranged on one or more axles.

[0017] In this case, the torque distribution factor represents the ratio of the torque applied to the front axle to the torque applied to the rear axle. In other words, the torque distribution factor is a quotient of front axle / rear axle, where front axle represents the torque at the front axle and rear axle represents the torque at the rear axle. Specifically, the torque distribution factor is defined such that it is not greater than 1, meaning the larger value is recorded in the denominator and the smaller value in the numerator.

[0018] The torque distribution factor is noted in such a way that it is defined in relation to a main drive axle, which in this case is the rear axle. For example, a force of 20% on the front axle and 80% on the rear axle, i.e., a ratio of 20 / 80, results in a torque distribution factor of 0.8. A force distribution of 50 / 50 would therefore result in a torque distribution factor of 0.5.

[0019] This torque distribution factor, read from the map, is then used to control the drive torque. Controlling, in this case, means supplying and / or, in particular, limiting the torque delivered to the center differential and thus to the front and rear axles.

[0020] The control can be carried out in particular by controlling the engine, for example by increasing or decreasing the speed, the transmission, for example by changing gear, and / or by actuating one or more brakes on the respective axles.

[0021] In particular, the torque is limited in such a way that a maximum or minimum torque distribution factor based on the map is not reached. For example, the torque is limited in such a way that a torque distribution factor is not less than 0.5, 0.4, 0.3, or 0.2, depending on the direction of travel, as will be explained later.

[0022] This operation, or rather, this mode, can be described as limiting operation, in which wheel slip typically occurs. In particular, a characteristic map is used to determine the torque distribution factor exclusively in this mode, i.e., only when the differential speed deviates by a predetermined threshold.

[0023] The method according to the invention makes it possible to determine a torque distribution factor particularly precisely, but without providing one or more torque sensors on the respective axles.

[0024] In particular, the method according to the invention is based on the finding that once a certain value of the differential speed between the front and rear axles is exceeded, a Torsen torque no longer necessarily behaves linearly, and it can be difficult to estimate the torque occurring at the front and rear axles. This nonlinear behavior of the Torsen torque is particularly well taken into account by the present invention.

[0025] According to a further development, the method further comprises the steps of: if the wheel speed on the rear axle is greater than the wheel speed on the front axle: reading out the torque distribution factor from a first area of ​​the characteristic map and if the wheel speed on the rear axle is less than the wheel speed on the front axle: reading out the torque distribution factor from a second area of ​​the characteristic map.

[0026] According to this further development, two different ranges or two different characteristic maps are used to determine the torque distribution factor, depending on which wheel speed of the front axle or the rear axle is higher.

[0027] In particular, if the wheel speed of the rear axle is higher than the wheel speed of the front axle, it can be concluded that the motor vehicle is currently in coasting mode, particularly when driving forward. If, however, the wheel speed of the front axle is higher than the wheel speed of the rear axle, it can be concluded that the motor vehicle is in traction mode, particularly when driving backward.

[0028] Based on the determined operation of the vehicle, a different characteristic map is used, and thus a different torque distribution factor is usually determined. In particular, the drive torque is limited to a different maximum or minimum torque distribution factor depending on the direction of travel or operation.

[0029] For example, in overrun mode, the drive torque can be limited in such a way that a minimum ratio of 20 / 80 between front and rear axle torque and thus a torque distribution factor of 0.8 is not exceeded, whereas in traction mode, the drive torque is limited in such a way that a maximum ratio of 70 / 30 between front and rear axle torque and thus a torque distribution factor of 0.3 is not undercut.

[0030] This further development enables a particularly precise determination of the torque distribution factor and thus a particularly precise control of the drive torque.

[0031] According to a further development, the method further comprises the steps of, if the differential speed does not exceed an amount of the predetermined value: detecting a speed of the motor vehicle, and, if the speed does not exceed a predetermined value: controlling the drive torque based on a torque distribution factor of 0.5.

[0032] According to this further development, a torque distribution factor of 0.5, i.e. a distribution of 50 / 50, is assumed for certain, in particular low speeds, close to standstill or when the motor vehicle is at a standstill, which is to be used for those operating conditions in which the determined differential speed does not exceed the predetermined threshold value.

[0033] For this purpose, the speed of the vehicle is determined continuously or periodically, as previously described in connection with the engine speeds. This can also be done via the engine speed sensors or derived from the engine speed. One or more speed sensors can also be provided.

[0034] This operating state or mode is a special case of a starting process, which usually occurs from a standstill. In particular, in this mode, the speed of the vehicle is less than 10 m / s, 5 m / s, or 2.5 m / s.

[0035] This further development enables a particularly simple determination of the torque distribution factor for a starting mode.

[0036] This refinement is based, in particular, on the realization that a torque distribution factor of 0.5 can be assumed for particularly low speeds. In other words, in this condition, a locking effect of the Torsen actuator occurs, resulting in this torque distribution factor of 0.5, or torque equilibrium.

[0037] According to a further development, the method further comprises the steps of, if the speed is above a predetermined value: detecting an acceleration of the motor vehicle, if the acceleration is below a predetermined value: controlling the drive torque based on a first predetermined torque distribution factor, and if the acceleration is above a predetermined value: controlling the drive torque based on a second predetermined torque distribution factor which is different from the first torque distribution factor.

[0038] For this purpose, the acceleration of the vehicle is determined continuously or periodically, as previously described in connection with the engine speed. This can also be done via the engine speed sensors or derived from the engine speed or speed. One or more acceleration sensors can also be provided.

[0039] In particular, this further development is also used exclusively when the differential speed does not exceed an amount of the predetermined value, as described in connection with the previous further development, or in particular this further development develops the previous one.

[0040] According to this further development, no characteristic map is used, but only a fixed torque distribution factor, which only differs based on an acceleration or which is different for smaller accelerations from one for larger accelerations.

[0041] The first predetermined torque distribution factor is used for accelerations below a predetermined value, and the second torque distribution factor for accelerations above the predetermined value. This threshold acceleration value can, in particular, be an acceleration of 5 m / s. 2 , 10 m / s 2 or 15 m / s 2 act.

[0042] In particular, both the first and the second torque distribution factors are different from 0.5, in particular less than 0.5. The first torque distribution factor can be assumed, for example, to be 0.45, 0.40, or 0.35, and the second torque distribution factor to be 0.50, 0.45, or 0.40. In particular, the second torque distribution factor is greater than the first torque distribution factor.

[0043] This operation can also be referred to as normal mode, which is outside the limit range, but in which acceleration can be increased to a greater or lesser extent without leaving the normal range.

[0044] This further development enables a particularly simple determination of the torque distribution factor in normal operation.

[0045] According to a further development, the detection of the acceleration includes detecting a moving average of the acceleration.

[0046] In particular, this advanced version uses a moving average of past acceleration measurements. For example, an average is calculated from the last 2, 5, 10, or 20 measurements.

[0047] This enables particularly smooth control and, in particular, ignores measurement outliers.

[0048] According to a further development, the method further comprises the steps of detecting an axle load distribution, wherein the control of the drive torque is additionally carried out based on the axle load distribution.

[0049] An axle load distribution takes into account the actual center of gravity in the direction of travel, which can shift, especially due to a particularly heavy payload. For example, the axle load distribution is normally 0.5, meaning the front and rear axles are equally loaded. Due to a particularly heavy payload or a trailer, this axle load distribution can then shift, typically backward, i.e., to the rear axle, and then has a value between 0 and 1, which differs from 0.5.

[0050] This axle load distribution can then be taken into account when determining the torque distribution factor and thus also when controlling the drive torque. In particular, a characteristic curve can be stored for different axle loads, based on which the torque distribution factor is then determined or the drive torque is controlled.

[0051] The axle load distribution can be determined in various ways, as will be described later.

[0052] This further development enables particularly precise determination of the torque distribution factor and thus of the drive torque control.

[0053] According to a further development, the detection of the axle load distribution includes detecting a wheel contact force and / or an inclination of the motor vehicle.

[0054] In particular, a wheel contact force can be measured for each axle, especially for each wheel. This can be done using suitable sensors, such as force sensors. Likewise, an inclination can be measured using suitable sensors, such as position sensors or gyroscopes. Both values ​​can be included in the calculation or determination of the axle load distribution.

[0055] Additionally or alternatively, acceleration sensors, in particular lateral and / or longitudinal acceleration sensors, can also be used to determine the axle load distribution.

[0056] The axle load distribution can be taken into account in particular for the first mode, in which a characteristic map is used to determine the torque distribution factor, and for the third mode, in which an acceleration threshold is used as a basis.

[0057] This also results in a particularly precise determination of the torque distribution factor.

[0058] For use cases or application situations that may arise during the method and which are not explicitly described here, it may be provided that, in accordance with the method, an error message and / or a request to enter user feedback is issued and / or a default setting and / or a predetermined initial state is set.

[0059] According to a further aspect, a device is provided. The device may comprise a data processing device or a processor device configured to carry out an embodiment of the method according to the invention.

[0060] In particular, the device is configured to communicate and / or cooperate with the user terminal, as described above, to carry out or at least effect the above-described embodiments of the method. In particular, the device can also comprise the user terminal, thereby forming a system for carrying out embodiments of the method according to the invention.

[0061] For this purpose, the processor device can have at least one microprocessor and / or at least one microcontroller and / or at least one FPGA (Field Programmable Gate Array) and / or at least one DSP (Digital Signal Processor). In particular, a CPU (Central Processing Unit), a GPU (Graphical Processing Unit) or an NPU (Neural Processing Unit) can be used as the microprocessor. Furthermore, the processor device can have program code which, when executed by the processor device, is configured to carry out the embodiment of the method according to the invention. The program code can be stored in a data memory of the processor device. The processor device can, for example, be based on at least one circuit board and / or on at least one SoC (System on Chip).

[0062] According to a further aspect, a motor vehicle is provided which comprises such a device.

[0063] The motor vehicle according to the invention is preferably designed as a motor vehicle, in particular as a passenger car or truck, or as a passenger bus or motorcycle.

[0064] As a further solution, the invention also encompasses a computer-readable storage medium comprising program code which, when executed by a computer or computer network, causes the computer to carry out an embodiment of the method according to the invention. The storage medium can be provided at least partially as a non-volatile data memory (e.g. as a flash memory and / or as an SSD - solid state drive) and / or at least partially as a volatile data memory (e.g. as a RAM - random access memory). The storage medium can be arranged in the computer or computer network. However, the storage medium can also be operated on the Internet, for example, as a so-called app store server and / or cloud server. The computer or computer network can provide a processor circuit with, for example, at least one microprocessor.The program code may be provided as binary code and / or as assembly code and / or as source code of a programming language (e.g. C) and / or as a program script (e.g. Python).

[0065] The invention also encompasses combinations of the features of the described embodiments. The invention therefore also encompasses implementations that each comprise a combination of the features of several of the described embodiments, unless the embodiments are described as mutually exclusive.

[0066] With regard to the embodiments of the device, the motor vehicle and the storage medium as well as the associated advantages, reference is made to the previously described embodiments of the method and the associated advantages.

[0067] Exemplary embodiments of the invention are described below. Shown are: Fig. 1 a schematic view of an embodiment of a method and a device for controlling a drive torque in a motor vehicle.

[0068] The exemplary embodiments explained below are preferred embodiments of the invention. In the exemplary embodiments, the described components of the embodiments each represent individual features of the invention that can be considered independently of one another, each of which also develops the invention independently of one another. Therefore, the disclosure is intended to encompass combinations of the features of the embodiments other than those shown. Furthermore, the described embodiments can also be supplemented by further features of the invention already described.

[0069] In the figures, the same reference symbols designate elements with the same function.

[0070] Fig.1 shows a schematic view of an embodiment of a method and a device 100 for controlling a drive torque in a motor vehicle 1.

[0071] The device 100 is comprised by the motor vehicle 1 and is designed to carry out the steps described below.

[0072] The motor vehicle 1 comprises an internal combustion engine 10 and an electric motor 20, which are connected in series and drive a transmission 30 through a single shaft with drive torque. The output shaft of the transmission 30 feeds a center differential 40, which can also be referred to as a Torsen differential, which, due to its structural characteristics, distributes the drive torque to the front axle 200 and the rear axle 300.

[0073] The device 100 is designed to detect a wheel speed on the front axle 200 and on a rear axle 300 and to form a differential speed therefrom.

[0074] When the differential speed exceeds an amount of a predetermined value, the device is designed to read out a torque distribution factor of the torque between the front axle and the rear axle from a map based on the differential speed and to control the drive torque based on the read-out torque distribution factor from the map.

[0075] The device 100 is designed in particular to read out the torque distribution factor from a first area of ​​the characteristic map when the wheel speed on the rear axle 300 is greater than the wheel speed on the front axle 200, and to read out the torque distribution factor from a second area of ​​the characteristic map when the wheel speed on the rear axle 300 is less than the wheel speed on the front axle 200, and to use this as a basis for the control.

[0076] The device 100 is also designed to detect a speed of the motor vehicle 1 when the differential speed does not exceed an amount of the predetermined value and, when the speed does not exceed a predetermined value, to control the drive torque based on a torque distribution factor of 1.

[0077] The device 100 is also designed to detect an acceleration of the motor vehicle when the speed is above a predetermined value and to control the drive torque based on a first predetermined torque distribution factor when the acceleration is below a predetermined value and to control the drive torque based on a second predetermined torque distribution factor that is different from the first torque distribution factor when the acceleration is above a predetermined value, wherein the second torque distribution factor is greater than the first torque distribution factor.

[0078] The recording of the acceleration involves recording a moving average of the acceleration.

[0079] The device 100 is also designed to detect an axle load distribution, wherein the control of the drive torque is additionally carried out based on the axle load distribution.

[0080] The recording of the axle load distribution includes recording a wheel contact force and an inclination of the motor vehicle 1.

[0081] Overall, the examples show how a motor vehicle control system can be provided based on a Torsen model.

Claims

[1] Method for controlling a drive torque in a motor vehicle (1), comprising: - Detecting the wheel speed on a front axle (200) of the motor vehicle (1); - Detecting the wheel speed on a rear axle (300) of the motor vehicle (1); - Capturing a differential speed based on the wheel speed of the front axle (200) and the wheel speed of the rear axle (300); - if the differential speed exceeds a predetermined value: reading a torque distribution factor from a characteristic map based on the differential speed; and - Controlling the drive torque based on the torque distribution factor read from the characteristic map. [2] Method according to claim 1, further comprising: - if the wheel speed at the rear axle (300) is greater than the wheel speed at the front axle (200): reading the torque distribution factor from a first section of the map; and - if the wheel speed on the rear axle (300) is lower than the wheel speed on the front axle (200): Reading the torque distribution factor from a second area of ​​the map. [3] Method according to any one of the preceding claims, further comprising: - if the differential rotational speed does not exceed a predetermined value: Detecting the speed of the motor vehicle (1); - if the speed does not exceed a predetermined value: Control of the drive torque based on a torque distribution factor of 0.

5. [4] Method according to any one of the preceding claims, further comprising: - if the speed exceeds a predetermined value: Detecting the acceleration of the motor vehicle; - if the acceleration is below a predetermined value: Controlling the drive torque based on a first predetermined torque distribution factor; and - if the acceleration exceeds a predetermined value: Controlling the drive torque based on a second predetermined torque distribution factor that is different from the first torque distribution factor. [5] Method according to claim 4, wherein the second torque distribution factor is larger than the first torque distribution factor. [6] Method according to one of claims 5 or 4 wherein the acceleration detection comprises detection of a moving average of the acceleration. [7] Method according to any one of the preceding claims, further comprising: - Detecting axle load distribution; whereby the control of the drive torque is additionally based on the axle load distribution. [8] Method according to claim 7, wherein the detection of the axle load distribution comprises the detection of a wheel contact force and / or an inclination of the motor vehicle (1). [9] Device (100) for controlling a drive torque in a motor vehicle (1), wherein the device is configured to carry out a method according to one of the preceding claims. [10] Motor vehicle (1) comprising a device (100) according to claim 9.

Images