Vehicle with controllable clutch between front axle and rear axle and method for controlling variable clutch engagement ratio of clutch

Abstract

A vehicle (1) includes a controllable clutch (30) having a variable clutch engagement ratio. A clutch (30) is arranged between a front axle drive output shaft (25) connected to a front axle (12) of a vehicle (1) and a rear axle drive output shaft (29) connected to a rear axle (14) of the vehicle. The control unit (5) may determine a speed difference (Vd) between the front axle drive output shaft (25) and the rear axle drive output shaft (29) and reduce the speed difference (V-d) if the speed difference (V-d) exceeds a threshold value. The threshold may depend on a traction of the vehicle (1) and a normalized rotational speed value of the rear axle drive output shaft (29).

Description

Technical Field

[0001] The present disclosure generally relates to a vehicle having a controllable clutch between a front axle and a rear axle, the controllable clutch having a variable clutch engagement ratio, and to a method for controlling the variable clutch engagement ratio of the clutch. Background Art

[0002] A vehicle equipped with all-wheel drive may have a common drive shaft for transferring the drive torque provided by the engine to the front and rear drive wheels of the vehicle. Depending on the condition of the ground on which the wheels are rolling, the wheels may be able to transfer different torques. For example, if the ground is rough, only low torque may be transferable on icy ground, rather than higher torque. Therefore, if the front wheels are on ground in a different condition to the ground on which the rear wheels are located, it may be useful to distribute the drive torque between the front and rear wheels so that the wheels rolling on the better ground can transfer a higher torque. The torque distribution may be provided by a controllable clutch integrated in the drive shaft between the front and rear wheels.

[0003] EP 3 720 076 B1 discloses a drive system for a utility vehicle, such as a tractor, having an engine and a transmission to drive a front axle and a rear axle. A clutch is arranged between the front axle and the rear axle to change the distribution of the torque transmitted between the front axle and the rear axle. If the speed difference between the front axle and the rear axle exceeds a threshold value having a fixed value, the clutch can be engaged. Thus, wheel slip can be prevented. Summary of the invention

[0004] The object is to improve the vehicle dynamics of a vehicle having a drive system with a controllable clutch between a front axle and a rear axle for varying the distribution of torque between the two axles.

[0005] According to one aspect of the present invention, a vehicle is provided, the vehicle comprising: a drive system for generating a drive torque and transmitting the drive torque to a front axle drive output shaft and a rear axle drive output shaft, wherein a controllable clutch is arranged between the front axle drive output shaft and the rear axle drive output shaft for distributing the drive torque between the front axle drive output shaft and the rear axle drive output shaft according to a clutch engagement ratio; a first speed sensor for determining a rotational speed of the front axle drive output shaft; a second speed sensor for determining a rotational speed of the rear axle drive output shaft; a measuring unit for determining traction; and a control unit, the control unit being configured to determine a speed difference between the rotational speed of the front axle drive output shaft and the rotational speed of the rear axle drive output shaft to determine a first threshold value based on the traction force, thereby setting the first threshold value as an effective threshold value, and controlling the clutch engagement ratio of the controllable clutch according to the speed difference and the effective threshold value.

[0006] The effective threshold value defines a threshold value for the speed difference. When the first threshold value is set as the effective threshold value, the value of the first threshold value defines the threshold value for the speed difference. The control unit may compare the speed difference with the effective threshold value, which may be the first threshold value, and may detect whether the speed difference exceeds or falls below the effective threshold value.

[0007] The clutch engagement ratio defines the engagement level of the controllable clutch, which can be continuously changed from fully released (also fully disengaged) to fully engaged. When the controllable clutch is fully released, the front axle drive output shaft and the rear axle drive output shaft can rotate independently of each other, for example, two disconnected axles. When the controllable clutch is fully engaged, the front axle drive output shaft and the rear axle drive output shaft can rotate together, for example, a one-piece axle. In the event of any intermediate clutch engagement ratio, the drive torque is distributed accordingly between the two axles.

[0008] The vehicle may be any utility vehicle or agricultural machinery, such as a tractor, harvester or combine. The vehicle may be used to pull tools or implements over the ground (e.g., a farm field) to perform tasks such as cultivating the farm field or transporting objects. Depending on the task to be performed, different traction forces may be required to be provided by the vehicle to overcome the load caused by resistance. For example, when the vehicle is traveling on a road, cultivating a field may require significantly more traction forces to be provided by the vehicle because the significantly higher resistance caused by field work increases the load accordingly.

[0009] The traction force provided by the vehicle can be determined by processing appropriate sensor values ​​by the control unit. The sensor values ​​can be determined by the measuring unit for determining the traction force. For example, the traction force may depend on the pressure value of a fluid in a hydraulic line of a component of the drive system. The measuring unit for determining the traction force may be a pressure sensor connected to the hydraulic line of the component of the drive system. The traction force can then be indirectly determined based on the pressure value provided by the pressure sensor. Based on the traction force, the first threshold value can be determined. Thus, the first threshold value depends on the traction force and, instead of being a constant or fixed threshold value, varies accordingly when the traction force increases or decreases. Due to the variability of the first threshold value, the engagement level of the controllable clutch can be adapted to the traction force, resulting in improved vehicle dynamics. Furthermore, stresses in the drive system caused by insufficient drive torque distribution caused by the controllable clutch can be reduced to extend the life of the vehicle components.

[0010] The control unit may be configured to normalize the rotation speed of the front axle drive output shaft or the rear axle drive output shaft with respect to a lead ratio, a steering angle of the steerable wheels and / or sizes of the front and rear wheels.

[0011] Since each wheel of the vehicle can rotate at an individual speed, the comparison of the speeds of the front and rear axles or the comparison of the speeds of the front and rear axle drive output shafts connected to the front and rear axles is not intuitive. The individual speeds may depend on several constraints, such as the lead ratio, the steering angle and the influence of the Ackerman steering geometry and the different sizes of the wheels (in terms of the outer diameter). However, the lead ratio, the steering angle and the different sizes of the wheels may be parameterizable and may be determined by the control unit. Therefore, the constraints may be compensated by the control unit for determining the normalized speeds of the front axle, the rear axle, the rear axle drive output shaft and the front axle drive output shaft. As a result, the deviations of the speeds of the front and rear axles or the speeds of the front and rear axle drive output shafts may be determined without being affected by the above constraints. Furthermore, if the difference between the normalized rotational speeds of the front axle and the rear axle or between the normalized rotational speeds of the front axle drive output shaft and the rear axle drive output shaft is too large, an abnormal driving situation may be determined by the control unit.

[0012] The higher the traction force, the lower the first threshold value that may be determined by the control unit, and vice versa.

[0013] In other words, the higher the traction force, the smaller the speed difference between the front axle and the rear axle may be sufficient for the control unit to engage the controllable clutch for adjusting the clutch engagement ratio. The first threshold value may be determined based on a characteristic from a set of different characteristics. The higher the traction force, the characteristic with the lower threshold value is selected from the set of characteristics for the first threshold value. Alternatively, the first threshold value may be determined by the control unit based on a lookup table stored in a memory of the control unit. Again, the first threshold value may be adjusted accordingly to the traction force. Therefore, since the traction force affects the traction force and the transferable torque of the vehicle, the first threshold value may be adapted to increase the traction force or the transferable torque of the wheel.

[0014] The control unit may be configured to determine the first threshold value based on a rotation speed of the front axle drive output shaft or the rear axle drive output shaft.

[0015] The rotational speed of the front axle drive output shaft and the rear axle drive output shaft depends on the vehicle speed, which has an impact on the driving behavior. If one of the axles rotates faster than the speed expected for the vehicle speed, the wheels driven by the axle drive output shaft will slip. Therefore, if the rotational speed of the front axle drive output shaft or the rear axle drive output shaft is taken into account, the first threshold value can be determined to improve the driving behavior. The control unit can take into account the rotational speed of one of the two axle drive output shafts or the rotational speed of both axle drive output shafts. If the variable clutch engagement ratio is too high, an excessive difference in the rotational speed of the front axle drive output shaft and the rear axle drive output shaft can also cause damage to the drive system. Therefore, if the rotational speed of one of the two axle drive output shafts or the rotational speed of both axle drive output shafts is taken into account for the first threshold value, damage can be prevented.

[0016] The driving behavior may have an impact on the driving stability of the vehicle. Therefore, the improvement of the driving behavior may be used to improve the driving stability of the vehicle.

[0017] The control unit may be configured to determine at least one additional threshold value, and if the first threshold value is lower than the additional threshold value, the control unit may be configured to set the additional threshold value as the effective threshold value.

[0018] The at least one additional threshold value may depend on other or additional parameters than the first threshold value. Thus, the controllable clutch may be controlled based on additional or other conditions than the rotational speed and traction of one of the axle drive output shafts as taken into account for the first threshold value. However, the control unit may take into account a threshold value other than the first threshold value if the at least one additional threshold value has a greater influence on the driving behavior than the first threshold value.

[0019] The control unit may be configured to determine an advance ratio, and if the determination of the advance ratio is invalid, the control unit may be configured to determine a second threshold as one of the at least one additional threshold, wherein the second threshold may be based on the rotational speed of the front axle drive output shaft or the rear axle drive output shaft.

[0020] Therefore, as long as the influence of the lead ratio on the vehicle dynamics is unknown, the control unit determines the second threshold value for taking into account the uncertainty due to unknown parameters. Similar to the first threshold value, but taking into account an additional tolerance range for improving the driving behavior, the second threshold value can be based on the rotational speed of the front axle drive output shaft or the rear axle drive output shaft. Similar to the first threshold value, the second threshold value will also depend on the traction force. If the traction force increases the traction force threshold value, the second threshold value can be set to zero.

[0021] The vehicle may comprise a braking unit, a steerable wheel and a steering sensor for determining a steering angle of the steerable wheel, wherein the control unit determines the leading ratio if the traction may be below a first parameter, the steering angle may be below a second parameter, the braking unit may be released and / or a clutch engagement ratio of the controllable clutch may be below a third parameter.

[0022] If the state of the vehicle is not applicable for the determination, the determination of the lead ratio may be falsified. For example, driving a bend or braking the vehicle may have a negative impact on the determination of the lead ratio. Thus, the determination of the lead ratio is favoured if the vehicle is travelling in a straight line, if the traction is not too high, if the vehicle is not decelerating and if the controllable clutch is disengaged. If the control unit detects the presence of such a vehicle state, the determination of the lead ratio is started.

[0023] The control unit may be configured to determine the second threshold value as a constant value after effectively determining the lead ratio.

[0024] In other words, after the lead ratio is effectively determined, the second threshold value can be independent of the rotational speed of the front axle drive output shaft or the rear axle drive output shaft or the traction force or any other parameter. For example, if the lead ratio has been determined, the second threshold value can be set to zero, so that the second threshold value is always lower than the first threshold value. Alternatively, if the lead ratio has not yet been determined, the control unit can determine the second threshold value that is higher than the first threshold value, so that the second threshold value can be set as the effective threshold value.

[0025] The control unit may be configured to detect a braking steering action and to determine the third threshold value as one of the at least one additional threshold value in dependence on the detection of the braking steering action.

[0026] Braking and steering action, i.e. braking and steering the vehicle simultaneously, can have a significant impact on the driving behavior. Therefore, the control unit can determine a separate threshold for this specific vehicle state. The third threshold can be higher than the first threshold, so that if there is a braking and steering action, the third threshold can be set as the effective threshold. The third threshold can also be higher than the second threshold, so that if there is a braking and steering action, the third threshold can be set as the effective threshold in any case. Therefore, with respect to braking and steering action, the variable clutch engagement ratio of the controllable clutch can be adjusted according to the third threshold to improve the driving behavior. The third threshold can also depend on the front axle drive output shaft or the rear axle drive output shaft. The third threshold can be determined based on a characteristic or a lookup table.

[0027] The control unit may be configured to determine a maximum threshold value from among the first threshold value and the at least one additional threshold value, and set the maximum threshold value as the effective threshold value.

[0028] Therefore, the control unit can select a threshold value that has the greatest influence on the driving behavior as the effective threshold value. The control unit can compare the first threshold value and all other additional threshold values ​​with each other to determine the threshold value with the highest value. The threshold value with the highest value can be set as the effective threshold value. The second threshold value and the third threshold value can be used as the additional threshold value.

[0029] The control unit may be configured to compare the speed difference with the effectiveness threshold value and to adjust a clutch engagement ratio of the controllable clutch to reduce the speed difference.

[0030] The control unit may increase the clutch engagement ratio to continuously engage the clutch. The more the clutch is engaged, the greater the torque distributed between the front axle drive output shaft and the rear axle drive output shaft, so that the rotation speed of the front axle drive output shaft and the rotation speed of the rear axle drive output shaft can be more and more balanced. The effective threshold is determined by the control unit, and the effective threshold may be a maximum threshold, for example, the first threshold, the second threshold or the third threshold.

[0031] If the speed difference exceeds the validity threshold, the control unit may be configured to reduce the speed difference.

[0032] In other words, as long as the speed difference is below the effective threshold, the control unit will not increase the clutch engagement ratio. However, if the speed difference would exceed the effective threshold, the clutch engagement ratio may be increased until the speed difference falls below the effective threshold again. Optionally, the clutch engagement ratio may be increased until the speed difference between the front axle drive output shaft and the rear axle drive output shaft is balanced.

[0033] If the speed difference is below the activation threshold, the control unit may be configured to reduce the clutch engagement ratio.

[0034] Thus, as long as the speed difference is below the effective threshold, the controllable clutch can be disengaged more and more. The more the clutch is disengaged, the less torque is distributed between the front axle drive output shaft and the rear axle drive output shaft. If the speed difference remains below the effective threshold, the controllable clutch can be completely disengaged. The front axle drive output shaft and the rear axle drive output shaft can then rotate completely independently of each other.

[0035] The control unit may be configured to determine a lead ratio and detect a braking steering action, and only if the lead ratio has been effectively determined and a lack of braking steering action has been detected, the control unit may be configured to set the first threshold to the effective threshold.

[0036] The lead ratio may be determined as described above. The lack of a braking steering action may be detected by the control unit if the signal of the steering sensor is below a threshold indicating straight ahead travel, or if the braking unit is not applied so that the vehicle is not decelerated. The braking unit may send a corresponding signal if the braking unit is not applied. That is, the control unit does not set the first threshold as the effective threshold as long as the control unit detects a braking steering action.

[0037] The first threshold may be equal to or lower than 5% of the normalized rotational speed of the front axle drive output shaft or the rear axle drive output shaft.

[0038] The lower the first threshold, the smaller the speed difference between the front axle drive output shaft and the rear axle drive output shaft required to exceed the first threshold. The first threshold can vary according to a set of characteristics as described above. For example, one characteristic in the set of characteristics can be limited to 5% of the normalized speed of the front axle drive output shaft or the rear axle drive output shaft. The second characteristic in the set of characteristics can be limited to 4% of the normalized speed of the front axle drive output shaft or the rear axle drive output shaft. The third characteristic in the set of characteristics can be limited to 3% of the normalized speed of the front axle drive output shaft or the rear axle drive output shaft, and so on. Optionally, the first threshold can be based only on the normalized speed of the rear axle drive output shaft.

[0039] The at least one additional threshold value may be higher than 5% of the normalized rotational speed of the front axle drive output shaft or the rear axle drive output shaft.

[0040] The higher the at least one threshold value, the greater the speed difference between the front axle drive output shaft and the rear axle drive output shaft required to exceed the at least one additional threshold value. The at least one additional threshold value may include the second threshold value or the third threshold value or both or any other additional threshold value. For example, the third threshold value may be between 15% and 20% of the normalized speed of the front axle drive output shaft or the rear axle drive output shaft. The second threshold value may, for example, be between 5% and the third threshold value. Optionally, the second threshold value and / or the third threshold value may be based only on the normalized speed of the rear axle drive output shaft.

[0041] According to another aspect of the present invention, a method for controlling a variable clutch engagement ratio of a first controllable clutch of a vehicle is provided, the method comprising the following steps: determining a rotational speed value of a front axle drive output shaft connected to the first controllable clutch; determining a rotational speed value of a rear axle drive output shaft connected to the first controllable clutch; determining a normalized rotational speed value of the rear axle drive output shaft; determining a speed difference between the rotational speed value of the front axle drive output shaft and the normalized rotational speed value of the rear axle drive output shaft; determining the traction of the vehicle; determining a first threshold value based on the normalized rotational speed value of the rear axle drive output shaft and the traction force; comparing the speed difference with the first threshold value; and, if the speed difference exceeds the first threshold value, increasing the clutch engagement ratio to reduce the speed difference.

[0042] As described above, the traction force may be determined indirectly by using a pressure sensor. Since the determination of the first threshold is based on the traction force, the driving behavior of the vehicle may be improved by avoiding slipping of the wheels. The higher the traction force, the lower the first threshold may be. The engagement level of the controllable clutch may vary depending on the clutch engagement ratio. If the clutch engagement ratio increases, the controllable clutch is increasingly engaged. Additionally, if the clutch engagement ratio decreases, the controllable clutch is increasingly released (disengaged).

[0043] The method may optionally include the following steps: determining a second threshold based on a determination of an advance ratio; determining a third threshold based on a braking steering action; determining a maximum threshold from among the first threshold, the second threshold and the third threshold; and setting the maximum threshold as the effective threshold.

[0044] Thus, the control unit may determine several thresholds and may set the one threshold that has the greatest influence on the driving behavior of the vehicle as the effective threshold. Each of the first threshold, the second threshold and the third threshold may depend on different conditions, such as the value of the traction force, the determination of the lead ratio and the determination of the brake steering action. Depending on which of these conditions causes the greatest influence, the control unit may set the first threshold, the second threshold or the third threshold as the maximum threshold and thus, respectively, as the effective threshold.

[0045] Within the scope of the present application, it should be understood that the various aspects, embodiments, examples and alternatives and their respective features set forth herein may be adopted independently or in any possible and compatible combination. Where features are described with reference to a single aspect or embodiment, it should be understood that such features are applicable to all aspects and embodiments unless otherwise specified or in the case where such features are not compatible. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Several aspects of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0047] Figure 1 A utility vehicle in the form of a tractor is shown.

[0048] Figure 2 yes Figure 1 A simplified view of a control unit of a vehicle is shown;

[0049] Figure 3 yes Figure 1 Schematic diagram of the drive system of the tractor;

[0050] Figure 4 A flow chart is shown.

[0051] Figure 5A A set of characteristics for a first threshold is shown.

[0052] Figure 5B The characteristics for the second threshold are shown.

[0053] Figure 5C The characteristics for the third threshold are shown. DETAILED DESCRIPTION

[0054] Reference Figure 1 , shows a utility vehicle 1 in the form of a tractor having a cab 3 and an engine compartment 2. A partially visible chassis 4 connects a front axle 12 (including suspension and steering components) and a rear axle 14. A left front wheel 13a and a left rear wheel 15a as well as a right front wheel 13b and a right rear wheel 15b (see Figure 3 ) are connected to the respective front axles 12 and rear axles 14. The drive system 11 drives the front wheels 13a, 13b and the rear wheels 15a and 15b. When the vehicle 1 moves on the ground 19 at a vehicle speed 20, the left front wheel 13a rotates at a rotation speed 9 or a wheel speed 16, and the left rear wheel 15a rotates at a rotation speed 10 or a wheel speed 17.

[0055] The control unit 5 is coupled to receive data from a plurality of sensors 6 and 7. Such data may include (but is not limited to):

[0056] the gross weight of the vehicle 1;

[0057] the amount of front and / or rear ballast carried by the vehicle 1;

[0058] Weighing information related to towed or carried equipment;

[0059] a measured degree of wheel slip for one or more wheels 13a, 13b, 15a, 15b of the vehicle 1;

[0060] tire pressure in one or more tires on respective wheels 13a, 13b, 15a, 15b of vehicle 1;

[0061] a turning angle indicated by a user of vehicle 1;

[0062] The current speed of vehicle 1 is 20;

[0063] Environmental conditions external to vehicle 1 .

[0064] Further inputs to the control unit 5 may come from a user operable human machine interface (HMI 18 ), such as a touch screen display and input devices located in the cab 3 , and a geo-positioning system 8 for the vehicle 1 .

[0065] Figure 2 A control unit 5 is shown, which comprises an interface 21, a controller 22 and a memory 23. The control unit 5 can receive and send signals or data via the interface 21, for example, signals determined by the sensors 6 and 7. The interface 21 can be a wireless interface or a connector. The controller 22 can store data or signals received by the control unit 5 in the memory 23. The memory 23 can contain additional data or an executable computer program product, for example, in terms of a computer-implemented method that can be retrieved, processed or executed by the controller 22. Data or signals resulting from the processing of data or signals or from the execution of the computer program product can be stored in the memory 23 or sent by the controller 22 to the interface 21.

[0066] Figure 3 A drive system 11 of a vehicle 1 is shown. Such a drive system is disclosed in European patent EP 3 720 760 B1, filed on October 26, 2018, entitled "Utility vehicle braking", the entire contents of which are incorporated herein by reference. The drive system 11 includes a prime mover, such as an internal combustion engine 31, which drives an input shaft 32 of a transmission 24 via a flywheel 33. The transmission 24 drives a front axle drive output shaft 25 and a rear axle drive output shaft 29 to provide propulsion drive to the respective front axle 12 and rear axle 14. In addition to providing propulsion drive, the transmission 24 also provides drive to a power output shaft 49.

[0067] The input shaft 32 is connected at its inboard end to a planetary gear assembly 37. The purpose of the planetary gear assembly 37 is to distribute the torque provided by the input shaft 32 between the mechanical branch 38 and the hydrostatic branch 36. On the side of the planetary gear assembly 37 opposite the input shaft 32 is a power take-off shaft 49.

[0068] The hydrostatic branch 36 drives the hydraulic pump 34. The mechanical branch 38 is connected to the front axle drive output shaft 25 and the rear axle drive output shaft 29 as follows. Torque is transmitted from the mechanical branch 38 of the planetary gear assembly 37 to the rear axle drive output shaft 29 via the rear axle drive gear 40. Mounted on the same shaft as the rear axle drive gear 40 is an intermediate gear 48, which in turn drives the front axle drive gear 39, which selectively drives the front axle drive output shaft 25. A first controllable clutch 30 is provided to selectively engage and disengage the front axle drive output shaft 25 from the rear axle drive output shaft 29, or to control the clutch engagement ratio of the torque distribution between the two shafts. This allows the wheel grip to be optimized depending on the ground conditions.

[0069] In addition to the mechanical drive path described above, the hydraulic pump 34, the first hydraulic motor 41 and the second hydraulic motor 42 are connected to each other by means of a hydraulic circuit so that the hydraulic fluid circulates from the pump 34 to the motors 41 and 42 and circulates from the motors 41 and 42 back to the pump 34 (or a reservoir connected to the pump 34). The hydraulic circuit includes a high-pressure line for transferring the fluid delivered by the pump 34 and a low-pressure line for transferring the fluid back to the pump 34. The hydraulic pump 34 is hydraulically connected to the first hydraulic motor 41, which is drivably connected to the rear axle drive output shaft 29 to provide hydraulic drive for the rear wheels 15a and 15b. The hydraulic pump 34 is connected in parallel with the second hydraulic motor 42 to provide hydraulic drive to the front axle drive output shaft 25 as follows. A measuring unit 35 is integrated in the high-pressure line of the hydraulic circuit to determine a pressure signal indicating the pressure value of the high-pressure line. The control unit 5 receives the pressure signal and stores it in the memory 23 of the control unit 5.

[0070] The second hydraulic motor 42 is drivably connected to the front axle drive output shaft 25 via the first hydraulic motor gear 44 and the second hydraulic motor gear 45. The second controllable clutch 43 allows the second hydraulic motor 42 to selectively engage and disengage with the front axle drive output shaft 25. In addition to or as an alternative to the drive delivered to the front axle drive output shaft 25 from the rear axle drive output shaft 29 via the intermediate gear 48 and the front axle drive gear 39, this allows hydraulic drive to be provided to the front axle drive output shaft 25 by the second hydraulic motor 42 depending on the degree of engagement of the first controllable clutch 30.

[0071] The first hydraulic motor gear 44 and the second hydraulic motor gear 45 have a high gear ratio. This allows the motor 42 to provide high torque at a limited lower range of vehicle speeds 20. Therefore, at higher vehicle speeds 20, the motor 42 can be disconnected from the driveline via the second controllable clutch 43. Due to this design, the first hydraulic motor 41 is configured to deliver lower torque over the entire range of vehicle speeds 20. However, both motors 41 and 42 in combination enable the transmission 24 to provide a full transmission output power with variable torque, variable vehicle speed and variable travel direction over the entire range of vehicle speeds 20.

[0072] The pump 34, the first motor 41 and the second motor 42 are each provided with an adjustment device operable by an actuator to vary the operating angles of the pump 34 and the first motor 41 and the second motor 42, respectively. Advantageously, the individual adjustment devices provided for each of the motors 41 and 42 allow the speed and torque output of the motors 41 and 42 to be independently and flexibly controlled. This provides significant advantages in terms of vehicle control and efficiency.

[0073] The rear axle drive output shaft 29 drives the left rear axle shaft 51a and the right rear axle shaft 51b via the rear axle differential 50. Please note that the names "front", "rear", "left" and "right" as used herein are derived from the perspective of the operator sitting in the cab 3 facing forward. The rear axle 14 also includes a left brake unit 55a and a right brake unit 55b, a left rear axle final reducer 52a and a right rear axle final reducer 52b, and a left rear wheel 15a and a right rear wheel 15b. As shown, the left brake unit 55a includes a service brake actuator 53a biased to an open position by a spring and a parking brake actuator 54a biased to a closed position by a spring. Similarly, the right brake unit 55b includes a service brake actuator 53b biased to an open position by a spring and a parking brake actuator 54b biased to a closed position by a spring. Such an arrangement is described in German utility model DE 92 04 417 U1, filed on April 1, 1992, entitled “Druckmittelbetätigte Lenkbremsanlage für Kraftfahrzeuge mit Anhänger”, the entire content of which is incorporated herein by reference.

[0074] In the same manner, the front axle drive output shaft 25 drives the left front axle shaft 28a and the right front axle shaft 28b via the universal joint shaft 26 and the front axle differential 27. The front axle 12 also includes left and right brake units 56a and 56b, left and right front axle final reducers 57a and 57b, and left and right front wheels 13a and 13b.

[0075] The vehicle 1 includes a steering unit 60 for steering the left front wheel 13a and the right front wheel 13b (which are also referred to as steerable wheels 13a, 13b) according to the steering demand of the operator controlling the HMI 18. The steering unit 60 includes a left steering joint 62a, a right steering joint 62b and a steering sensor 61. The left front wheel 13a can rotate around the left steering joint 62a, and the right front wheel 13b can rotate around the right steering joint 62b. The steering sensor 61 determines a steering angle signal indicating a steering angle α of the left front wheel 13a. The steering angle signal can be used to determine the steering angle of the right front wheel 13b. Optionally, the steering unit 60 includes an additional steering angle sensor to separately determine the steering angle of the right front wheel 13b. The control unit 5 receives the steering angle signal and can store it in the memory 23 of the control unit 5.

[0076] The first controllable clutch 30 and the second controllable clutch 43 are under the instruction of the control unit 5, as further described below, so that the drive to the front wheels 13a, 13b can be selectively engaged or disengaged, or engaged with a controllably variable degree of clutch slip according to the clutch engagement ratio, so that the engine output torque delivered to the front axle 12 and the rear axle 14 can be controllably varied.

[0077] A first controllable clutch 30 is also provided to control the wheel speed or rotational speed of the front axle 12 and the rear axle 14 to avoid failure of the transmission 24. The wheel speed is the speed of the wheel at the point of contact with the ground 19 and along the ground (radially). For example, referring to Figure 1 , wheel speed 16 is the speed of the left front wheel 13a at the point of contact with the ground 19. Similarly, wheel speed 17 is the speed of the left rear wheel 15a at the point of contact with the ground 19. Taking into account the known wheel diameter, the rotational speed of the wheel can be calculated. Based on this, the wheel speed can be determined by measuring the rotational speed at any shaft in the drive system 11, which is connected to one of the front axle 12 and the rear axle 14 via a fixed constant ratio. If the vehicle 1 is equipped with tires of different sizes (requiring an overall gear ratio between the front axle 12 and the rear axle 14), under ideal conditions, the wheel speeds for the front axle 12 and the rear axle 14 should be equal, while the rotational speeds of the front axle 12 and the rear axle 14 are different due to the divergent tire diameters. However, since the corresponding gear ratios from the transmission 24 to the corresponding front axle 12 or rear axle 14 in the drive system 11 are known, both the rotational speed and the wheel speed can be monitored by measuring the rotational speed at any shaft in the drive system 11 connected to the corresponding front axle 12 and rear axle 14.

[0078] The control unit 5 permanently monitors a rotational speed signal 58 from the speed sensor 46 and a rotational speed signal 59 from the speed sensor 47. The speed sensor 47 is connected to the rear axle drive output shaft 29 at a fixed ratio, so that the speed sensor 47 provides a rotational speed signal 59 indicating the rotational speed of the rear axle drive output shaft 29, the left rear axle shaft 51a and the right rear axle shaft 51b and thus the rotational speed of the left rear wheel 15a and the right rear wheel 15b. The speed sensor 46 is connected to the front axle drive output shaft 25 at a fixed ratio, so that the speed sensor 46 provides a rotational speed signal 58 indicating the rotational speed of the front axle drive output shaft 25, the left front axle shaft 28a and the right front axle shaft 28b and thus the rotational speed of the left front wheel 13a and the right front wheel 13b.

[0079] When the vehicle 1 is traveling at a constant vehicle speed 20 on the ground 19, if the wheel slip is equal for both axles (in simple terms, the ground 19 beneath the wheels 13a, 13b, 15a, 15b shows the same conditions), the wheel speeds for the front axle 12 and the rear axle 14 should be the same. A wheel slip of 10% (which is typical for soft-surface type tracks) means that the wheel speeds for the front axle 12 and the rear axle 14 are 10% higher than the vehicle speed 20.

[0080] Now observe the rotational speed of the front axle drive output shaft 25 and the rotational speed of the rear axle drive output shaft 29: When the vehicle 1 is traveling at the vehicle speed 20, the front axle drive output shaft 25 and the rear axle drive output shaft 29 rotate at different rotational speeds due to several constraints. For example, due to the different sizes of the front and rear wheels (in terms of outer diameter), the front wheels 13a and 13b rotate faster than the rear wheels 15a and 15b. The total gear ratio of the front axle 12 (including the front axle differential 27 and the front axle final drive 57a, 57b) can be different from the total gear ratio of the rear axle 14 (including the rear axle differential 50 and the rear axle final drive 52a, 52b). Other constraints, such as the lead ratio, the steering angle relative to the Ackerman steering geometry of the vehicle 1, and the high traction of the vehicle 1, all have an impact on the rotational speed of the front axle drive output shaft 25.

[0081] Since the rotation speeds of the front axle drive output shaft 25 and the rear axle drive output shaft 29 are different, the comparison of these rotation speeds is not intuitive. Therefore, the control unit 5 is configured to normalize the rotation speed of the front axle drive output shaft 25 or the rear axle drive output shaft 29 to compensate for the above-mentioned constraints that cause the different rotation speeds of the front axle drive output shaft 25 and the rear axle drive output shaft 29. Constraints such as tire size, total gear ratio and lead ratio can be parameters. Constraints as traction can be values ​​determined by corresponding sensors. That is, the control unit 5 determines the normalized rotation speed of the front axle drive output shaft 25 and / or the rear axle drive output shaft 29 based on the parameters of the constraints and the sensor values. As a result, when the vehicle 1 is traveling on the ground 19 under normal conditions, the normalized rotation speed of one of the two drive output shafts is equal to the rotation speed of the other drive output shaft. Therefore, if one of the two rotation speeds deviates from the other rotation speed, poor vehicle dynamics or abnormal driving situations, such as wheel slip caused by very uneven conditions of the ground 19, can be easily detected by the control unit 5.

[0082] Considering the use of normalized rotation speed, some operating conditions of the vehicle 1 are now described in detail:

[0083] Straight ahead driving on the same ground 19 with both axles 12, 14: When the vehicle 1 is driving straight ahead, the normalized rotational speeds and wheel speeds of the front axle drive output shaft 25 and the rear axle drive output shaft 29 should be equal if the front and rear wheels are driving on similar ground 19. In this condition, the first controllable clutch 30 is disengaged so that the first hydraulic motor 41 drives the rear axle 14 via the rear axle drive output shaft 29 without any connection to the front axle drive output shaft 25, which is driven by the second hydraulic motor 42 to drive the front axle 12 (when the second controllable clutch 43 is engaged). This condition is preferred as an independent drive for the axles 12, 14 to avoid torsional stresses in the drive train. However, in some cases, the engagement of the first controllable clutch 30 is advantageous.

[0084] Driving straight ahead on uneven (different) ground 19 with two axles 12 , 14 : If at least one wheel 13 a , 13 b of the front axle 12 is driven on sand or frozen ground (the wheels 15 a , 15 b of the rear axle 14 are still driven on hard ground) with the first controllable clutch 30 disengaged, the front axle 12 will start to rotate (as the torque provided cannot be transferred to the ground 19 ). In terms of wheel speed, this means that the wheel speed or rotation speed of the front axle 12 will increase significantly compared to the wheel speed / rotation speed of the rear axle 14 . In other words, the difference in wheel speed / rotation speed between the front axle 12 and the rear axle 14 (which is ideally zero) will increase. As a result, the fluid supplied by the pump 34 will be completely consumed by the second hydraulic motor 42 (due to the lack of resistance / torque support), so that the first hydraulic motor 41 will come to a standstill. In other words, when observing the pressure in the hydraulic circuit of the pump 34, the first motor 41 and the second motor 42, the fluid will flow at a minimum pressure level (almost no pressure) in the second motor 42 assigned to the front axle 12 due to the lack of torque support at the second motor 42 assigned to the front axle 12. Since both motors 41, 42 are connected (in parallel) in the same hydraulic circuit, the same minimum pressure level will impact the first motor 41 assigned to the rear axle 14. As a result, the first motor 41 cannot provide torque. In the case where the front axle 12 rotates on a sandy or icy ground 19 and the rear axle 14 is stationary, the vehicle 1 will simply slow down and stop. Changing the vehicle speed to adjust the speed and torque provided by the motors 41 and 42 will help to a certain extent, but it will not help on a glass-like frozen ground 19. In addition, reducing the speed during agricultural work (e.g., plowing or sowing) is disadvantageous because the work results will be affected.

[0085] In order to avoid that the vehicle 1 unexpectedly comes to a standstill on a sandy or icy ground 19, the control unit 5 permanently adjusts the variable clutch engagement ratio of the first controllable clutch 30. The higher the clutch engagement ratio, the more engaged the first controllable clutch 30. That is, if the clutch engagement ratio is 0%, the first controllable clutch 30 is completely disengaged, and if the clutch engagement ratio is 100%, the first controllable clutch 30 is completely engaged.

[0086] Figure 4A flow chart of a method for adjusting a variable clutch engagement ratio of a first controllable clutch 30 is shown. The method may be a computer-implemented method stored in a memory 23 of a control unit 5 as a computer program product. The method may be executed by a controller 22 of a control unit 5. The method is described by way of example with respect to several steps, without any limitation as to these steps. That is, the number or order of steps may be modified, for example, individual steps may be excluded and / or added, and executed earlier or later than described. The method further comprises a method module 63. The method module 63 may receive several signals or data, and provide the signals and data to all method steps contained in the method module 63, here for example method steps S108 to S111. The method starts with step S100 and proceeds to step S101.

[0087] The method proceeds to step S101, and the control unit 5 determines several signals and parameters as

[0088] The speed signal 58 (front axle drive output shaft 25) received from the speed sensor 46,

[0089] The speed signal 59 received from the speed sensor 47 (rear axle drive output shaft 29),

[0090] The pressure signal of the high pressure pipeline received from the measuring unit 35,

[0091] The steering angle signal α received from the steering sensor 61,

[0092] a brake activation signal received from the HMI 18 and / or the brake units 55a, 55b, 56a and 56b,

[0093] The tire sizes (outer diameters) of the front wheels 13a, 13b and the rear wheels 15a, 15b read from the memory 23,

[0094] The total gear ratio of the front axle 12 and the rear axle 14 read from the memory 23, and

[0095] The traction of vehicle 1.

[0096] The traction force can be calculated by the control unit 5 based on the pressure signal of the high pressure line. For example, the control unit 5 can use a procedure for calculating the traction force as disclosed in PCT patent application WO 2013 / 053564 A1, entitled “Method to determine vehicle weight”, filed on September 13, 2012, the entire contents of which are incorporated herein by reference.

[0097] Then, the method proceeds to step S102 and the control unit 5 determines whether the braking steering action is valid. This is the case if the vehicle 1 is steering and braking simultaneously, so that the control unit 5 receives the steering angle signal α and the brake activation signal simultaneously. If the braking steering action is valid, the control unit 5 sets a positive braking steering index, and if it is not a negative braking steering index, the control unit 5 forwards the braking steering index to the method module 63.

[0098] The method proceeds to step S103 and the control unit 5 determines a traction dependency factor. The traction dependency factor may be determined by a look-up table or characteristic stored in the memory 23 of the control unit 5. The higher the traction, the lower the traction dependency factor. The traction dependency factor may be set in relation to the maximum traction provided by the vehicle 1 and sent to the method module 63.

[0099] The method proceeds to step S104, and the control unit 5 checks whether the conditions for determining the leading ratio are met. The above conditions are met if the following items are achieved:

[0100] The traction force is lower than the first parameter p1,

[0101] The steering angle signal α is lower than the second parameter p2,

[0102] The speed signal 58 is between the third parameter p3 and the fourth parameter p4,

[0103] The speed signal 59 is between the fifth parameter p5 and the sixth parameter p6.

[0104] The brake units 55a, 55b, 56a and 56b are released, and / or

[0105] The variable clutch engagement ratio of the first controllable clutch 30 is lower than the seventh parameter p7.

[0106] If these conditions are met, the method proceeds to step S105 to determine the lead ratio of vehicle 1. In addition, a default value is assigned to the lead value, such as, for example, a value of 1, and the method proceeds to step S106.

[0107] At step S105, the control unit 5 determines the leading ratio of the vehicle 1. The leading ratio may be determined according to the following formula:

[0108]

[0109] The front axle mechanical ratio can be determined by one tenth of the number of front wheel rotations after the rear wheels rotate ten times. Alternatively, the lead ratio can be determined based on the rotation speeds of the front axle drive output shaft 25 and the rear axle drive output shaft 29. If the lead ratio has been determined, a positive index I_lr is sent to the method module 63 to indicate a valid determination event of the lead ratio. If not, the index I_lr is a negative value.

[0110] At step S106, the control unit 5 determines the normalized rotational speed (V_n25) of the front axle drive output shaft 25 and / or the normalized rotational speed (V_n29) of the rear axle drive output shaft 29 to compensate for the constraints as described above, such as the different sizes of the front and rear wheels (in terms of outer diameter), the total gear ratio of the front axle 12, the total gear ratio of the rear axle 14, the lead ratio, the steering angle associated with the Ackerman steering geometry, and high traction.

[0111] Then, the method proceeds to step S107, and the control unit 5 determines the speed difference V_d between the rotation speed of the front axle drive output shaft 25 and the rotation speed of the rear axle drive output shaft 29, for example, according to the following formula:

[0112]

[0113] Since the control unit 5 uses normalized rotation speed values ​​for determining the speed difference, the speed difference V_d itself is a normalized value.

[0114] The method proceeds to method module 63 comprising steps S108 to S111. Signals and data provided to method module 63 may be distributed to each of steps S108 to S111 contained in method module 63. Steps S108 to S110 may be processed simultaneously.

[0115] At step S108, the control unit 5 determines a first threshold value V_t1 for the speed difference V_d based on the traction force and the normalized speed (V_n29) of the rear axle drive output shaft 29. The first threshold value V_t1 can be obtained by a lookup table or by Figure 5A characteristics shown.

[0116] If you can Figure 5A67, the upper characteristic 64 defines an upper limit and the lower characteristic 65 defines a lower limit. Between the upper characteristic 64 and the lower characteristic 65, for example, an additional characteristic may be defined as indicated with characteristic 66. All characteristics collectively define a set of characteristics. Each characteristic of the set of characteristics is assigned to a traction force, wherein the upper characteristic 64 is assigned to very low traction forces and the lower characteristic 65 is assigned to very high traction forces. The gradient of each characteristic may depend on a traction force dependency factor, wherein the gradients of all characteristics of a set of characteristics may be below a gradient limit 67. For example, the grade limit 67 may be defined by a characteristic of 5% of the normalized rotational speed of the rear axle drive output shaft 29.

[0117] The control unit 5 selects a characteristic from the set of characteristics based on the traction force determined at step S101, for example, characteristic 66. Taking into account the selected characteristic, the control unit 5 determines a first threshold value V_t1 corresponding to the normalized rotational speed value (V_n29) of the rear axle drive output shaft 29 determined at step S106.

[0118] Since different characteristics are assigned to different tractions, the control unit 5 can adapt the first threshold value V_t1 to any changes in the traction of the vehicle 1. Thus, undesirable vehicle dynamics or abnormal driving situations of wheel slip can be mitigated and the driving experience of enhanced traction on uneven ground 19 can be improved.

[0119] At step S109, the control unit 5 determines a second threshold value V_t2 for the speed difference V_d. As long as the lead ratio has not been determined at step S105, the lead ratio is invalid. If the lead ratio is invalid, the control unit 5 determines the second threshold value V_t2 for the speed difference V_d by means of a lookup table or by means of Figure 5B The second threshold value V_t2 is determined by the characteristic shown. After the invalid determination of the lead ratio, the pending determination of the lead ratio can be indicated by the negative index I_lr set at step S105. The control unit 5 recognizes the negative index I_lr and checks whether the traction of the vehicle 1 is low or high. In the case of low traction, according to Figure 5B The second threshold value V_t2 is determined as a value corresponding to the normalized rotation speed of the rear axle drive output shaft 29 according to the characteristic 68. In addition, the control unit 5 sets the second threshold value V_t2 to zero. When the lead ratio has been determined, the control unit 5 identifies the positive index I_lr. Then, the control unit 5 also sets the second threshold value to zero.

[0120] At step S110, the control unit 5 determines a third threshold value V_t3 for the speed difference V_d. The control unit 5 checks whether the braking steering action is valid as indicated by the positive braking steering index set at step S102. As long as the braking steering action is valid, the control unit 5 determines the third threshold value V_t3 for the speed difference V_d. Figure 5CThe third threshold V_t3 is determined according to the characteristics shown in FIG. Figure 5C The third threshold value V_t3 is determined as a value corresponding to the normalized rotation speed of the rear axle drive output shaft 29. Figure 5C As can be seen in FIG. 1 , the third threshold value V_t3 has an absolute minimum value greater than zero for the entire range of the normalized rotational speed (V_n29) of the rear axle drive output shaft 29. If the control unit 5 identifies a negative brake steering index indicating that the brake steering action is not valid, the control unit 5 sets the third threshold value V_t3 to zero.

[0121] The third threshold value V_t3 according to the characteristic 69 can be higher than 5%, for example, between 15% and 20%, of the normalized rotational speed V_n29 of the rear axle drive output shaft 29. The second threshold value V_t2 according to the characteristic 68 can be higher than 5% of the normalized rotational speed V_n29 of the rear axle drive output shaft 29, but lower than 15% to 20% of the normalized rotational speed V_n29 of the rear axle drive output shaft 29.

[0122] Then, the method proceeds to step S111, and the control unit 5 checks which of the first threshold, the second threshold, and the third threshold (V_t1, V_t2, V-T3) has the highest value, and determines the maximum threshold of the three thresholds. Then, the control unit 5 sets the maximum threshold as the effective threshold V_ta. Therefore, the control unit 5 can set the first threshold V_t1, the second threshold V_t2, or the third threshold V_t3 as the effective threshold V_ta according to which of the three thresholds is higher than the other two thresholds. For example, if the lead ratio has been effectively determined (at step S105) and the lack of braking steering action has been detected (at step S102), the control unit 5 sets the first threshold V_t1 as the effective threshold V_ta.

[0123] The method proceeds to step S112, and the control unit 5 compares the speed difference V_d determined at step S107 with the effective threshold value V_ta determined at step S111. If the speed difference V_d exceeds the effective threshold value V_ta, the method proceeds to step S114. If not, the method proceeds to step S113. Depending on whether the speed difference V_d exceeds the effective threshold value V_ta, the control unit 5 controls the clutch engagement ratio accordingly, as will be described below.

[0124] At step S113, the control unit 5 adjusts the variable clutch engagement ratio of the first controllable clutch 30 to release the first controllable clutch 30. That is, the control unit 5 reduces the variable clutch engagement ratio until torque is not transmitted through the first controllable clutch 30 between the front axle drive output shaft 25 and the rear axle drive output shaft 29.

[0125] The method then proceeds to step S115 and ends.

[0126] At step S114, the control unit 5 adjusts the variable clutch engagement ratio of the first controllable clutch 30 to reduce the speed difference V_d. In doing so, the control unit 5 increases the variable clutch engagement ratio to improve the engagement level of the first controllable clutch 30 and increase the torque transmitted by the first controllable clutch 30. The variable clutch engagement ratio is increased to reduce the speed difference V_d. The variable clutch engagement ratio can be increased until the speed difference V_d drops below the effective speed threshold V_ta. Optionally, the variable clutch engagement ratio can be increased until the rotational speed of the front axle drive output shaft 25 is equal to the rotational speed of the rear axle drive output shaft 29, so that the speed difference V_d is reduced to (almost) zero.

[0127] Due to the three different threshold values ​​V_t1, V_t2 and V_t3 and the variability of the first threshold value V_t1, the control unit 5 can react to various driving situations that lead to poor vehicle dynamics or driving instability. Since the selection of the effective threshold value V_ta depends on the maximum of the three threshold values ​​V_t1, V_t2 and V_t3, the control unit 5 mitigates the driving situations that have the most negative impact on vehicle dynamics or driving behavior.

[0128] For example, in driving situations such as straight ahead driving, turning and steering braking, the control unit 5 can react individually as follows. For simplicity, it is assumed that the lead ratio has been determined by the control unit 5 at step S105. The rotation speed signals 58 and 59 of the speed sensor 46 and the speed sensor 47 are permanently monitored to determine the speed difference V_d.

[0129] Since no braking steering action occurs during straight forward driving, the control unit 5 sets the first threshold value V_t1 (rather than the third threshold value V_t3) as the effective threshold value V_ta according to step S108. If the speed difference V_d exceeds the first threshold value V_t1 during straight forward driving, the control unit 5 increases the clutch engagement ratio and controllably engages the first controllable clutch 30 until the first threshold value V_t1 is undercut again. If the front axle 12 rotates on a sandy surface, this will cause the first controllable clutch 30 to be further engaged, so that the second motor 42 is drivingly connected to the rear axle 14, which can support torque to avoid rotation. This will also keep the first motor 41 powered to drive the rear axle 14. Then, the vehicle 1 will not be forced to stand still. Therefore, the method maintains the two axles 12 and 14 driven independently most of the time to avoid torsional stress in the drive system 11.

[0130] The operator of the vehicle 1 can now control the steering unit 60 for turning the vehicle 1. During a driven turn (determined by the steering sensor 61) without any braking action, no braking steering action will occur either. However, the Ackermann steering geometry influences the driving situation. The steered front wheels 13a, 13b roll on a larger radius of curvature (path) than the rear wheels 15a, 15b, so that the front wheels 13a, 13b have to accelerate simultaneously to pass the curvature path. Therefore, the control unit 5 will take into account the steering angle for determining the normalized rotational speed V_n29 of the rear axle drive output shaft, wherein the adaptive normalized rotational speed V_n29 of the rear axle drive output shaft will cause an adaptation of the first threshold value V_t1, as can be seen in 5A.

[0131] Furthermore, the traction of the vehicle 1 can have an influence on the situation of driving in a bend. If high traction is acting (e.g. when the vehicle 1 is pulling heavy equipment), the front axle 12 becomes lighter, so that the vehicle 1 cannot follow the radius of curvature as expected by the steering angle. Therefore, according to step S108, the control unit 5 will take into account the traction for determining the appropriate characteristic 66 from the set of characteristics, wherein different characteristics will also cause an adaptation of the first threshold value V_t1, as can be seen in 5A.

[0132] Then, at step S107, the adapted threshold value V_t1 is set as a new effective threshold value V_ta and used for comparison with the speed difference. For example, the adaptability of the first threshold value V_t1 leads to improved vehicle dynamics for driving a turn and prevents the front axle from slipping. Therefore, in the case where the front wheels 13a, 13b are driving on an icy surface in a bend, the control unit 5 can still react to improve the driving behavior and further improve the traction capacity of the front wheels 13a and 13b supporting the turn.

[0133] When the operator can apply the brake units 55a, 55b, 56a, 56b during driving turns, according to step S102, there is a braking steering action detected by the control unit 5. Then, the control unit 5 sets the third threshold value V_t3 (instead of the first threshold value V_t1) as the effective threshold value V_ta according to step S108.

[0134] In the case of steering braking, the inner steering wheel is braked, while the outer steering wheel should support the steering braking action by accelerating to further pull the vehicle 1 into the curve. The third threshold value V_t3 enables the vehicle 1 to pass the curve and steering braking, but prevents slipping, so that in the case when the front wheels 13a, 13b are driving over an icy surface in a curve, the control unit 5 can still react to improve the driving behavior of the vehicle 1.

[0135] After step S114, the method proceeds to step S115 and ends.

[0136] After step S115, the method may start again at step S100. When the method starts again, the parameters, signals and data that have been determined and stored in the memory 23 may be reused. For example, if the lead ratio has been determined in a previous run of the method, the lead ratio may be used in a subsequent run of the method.

[0137] All references cited herein are incorporated herein in their entirety. If there is a conflict between a definition in this document and a definition in an incorporated reference, the definition in this document shall control. Reference numerals list

[0138] 1 Car

[0139] 2 Engine compartment

[0140] 3 Cab

[0141] 4 Chassis

[0142] 5 Control unit

[0143] 6 Sensors

[0144] 7 Sensors

[0145] 8 Geographic Positioning System

[0146] 9 Speed

[0147] 10 Speed

[0148] 11. Drive system

[0149] 12 Front axle

[0150] 13a Wheel

[0151] 13b Wheel

[0152] 14 Rear axle

[0153] 15a Wheel

[0154] 15b Wheel

[0155] 16 Wheel Speed

[0156] 17 Wheel Speed

[0157] 18 HMI

[0158] 19 Ground

[0159] 20 speed

[0160] 21 Interface

[0161] 22 Controller

[0162] 23 Memory

[0163] 24 Transmission

[0164] 25 Front axle drive output shaft

[0165] 26 Cardan shaft

[0166] 27 Front axle differential

[0167] 28a Front axle shaft

[0168] 28b Front axle shaft

[0169] 29 Rear axle drive output shaft

[0170] 30 First controllable clutch

[0171] 31 Engine

[0172] 32 Input shaft

[0173] 33 Flywheel

[0174] 34 Pumps

[0175] 35 measurement units

[0176] 36 Hydrostatic branch

[0177] 37 Planetary gear assembly

[0178] 38 Mechanical Branch

[0179] 39 Front axle drive gear

[0180] 40 Rear axle drive gear

[0181] 41 Motor

[0182] 42 Motor

[0183] 43 Second controllable clutch

[0184] 44 Hydraulic motor gear

[0185] 45 Hydraulic motor gear

[0186] 46 Speed ​​sensor

[0187] 47 Speed ​​sensor

[0188] 48 Intermediate gear

[0189] 49 Power output shaft

[0190] 50 Rear axle differential

[0191] 51a Rear axle shaft

[0192] 51b Rear axle shaft

[0193] 52a Rear axle final reducer

[0194] 52b Rear axle final reducer

[0195] 53a Service brake actuator

[0196] 53b Service brake actuator

[0197] 54a Parking brake actuator

[0198] 54b Parking brake actuator

[0199] 55a Braking unit

[0200] 55b Braking unit

[0201] 56a Braking unit

[0202] 56b Braking unit

[0203] 57a Front axle final reducer

[0204] 57b Front axle final reducer

[0205] 58 Speed ​​signal

[0206] 59 Speed ​​signal

[0207] 60 Steering unit

[0208] 61 Steering sensor

[0209] 62a Steering joint

[0210] 62b Steering joint

[0211] 63 Method Module

[0212] 64 Features

[0213] 65 Features

[0214] 66 Features

[0215] 67 Gradient Limit

[0216] 68 Features

[0217] 69 Features

Claims

1. A vehicle (1), comprising: A drive system (11) for generating a drive torque and transmitting the drive torque to a front axle drive output shaft (25) and a rear axle drive output shaft (29); and a controllable clutch (30) arranged between the front axle drive output shaft (25) and the rear axle drive output shaft (29) and used for distributing the drive torque between the front axle drive output shaft (25) and the rear axle drive output shaft (29) according to a clutch engagement ratio; a first speed sensor (46) for determining the rotational speed of the front axle drive output shaft (25); a second speed sensor (47) for determining the rotational speed of the rear axle drive output shaft (29); a measuring unit (35) for determining the traction force; and A control unit (5), the control unit being configured to Determining a speed difference (V_d) between a rotational speed of the front axle drive output shaft (25) and a rotational speed of the rear axle drive output shaft (29); determining a first threshold value (V_t1) based on the traction force; setting the first threshold value (V_t1) as an effective threshold value (V_ta); and A clutch engagement ratio of the controllable clutch (30) is controlled according to the speed difference (V_d) and the effective threshold value (V_ta).

2. The vehicle (1) according to claim 1, wherein: The control unit (5) is configured to normalize the rotation speed of the front axle drive output shaft or the rear axle drive output shaft (25, 29) relative to: Leading ratio, The steering angle (α) of the steerable wheels (13a, 13b) and / or The dimensions of the front and rear wheels (13a, 13b, 15a, 15b).

3. The vehicle (1) according to claim 1 or 2, wherein: The higher the traction force, the lower the value of the first threshold value (V_t1) determined by the control unit (5), and vice versa.

4. The vehicle (1) according to any one of claims 1 to 3, wherein: The control unit (5) is configured to determine the first threshold value (V_t1) based on the rotation speed of the front axle drive output shaft (25) or the rear axle drive output shaft (29).

5. The vehicle (1) according to any one of claims 1 to 4, wherein: The control unit (5) is configured to determining at least one additional threshold value (V_t2, V_t3); and If the first threshold value (V_t1) is lower than the additional threshold value (V_t2, V_t3), the additional threshold value is set as the effective threshold value (V_ta).

6. The vehicle (1) according to claim 5, wherein: The control unit (5) is configured to determining a lead ratio; and If the determination of the lead ratio is invalid, determining a second threshold value (V_t2) as one of the at least one additional threshold value; The second threshold value (V_t2) is based on the rotation speed of the front axle drive output shaft (25) or the rear axle drive output shaft (29).

7. The vehicle (1) according to claim 6, comprising: Braking unit (55a, 55b, 56a, 56b); Steerable wheels (13a, 13b); and a steering sensor (61) for determining a steering angle (α) of the steerable wheels (13a, 13b), Among them, if The traction force is lower than a first parameter, The steering angle (α) is lower than the second parameter, The brake unit (55a, 55b, 56a, 56b) is released, and / or The clutch engagement ratio of the controllable clutch (30) is lower than a third parameter, The control unit (5) then determines the lead ratio.

8. The vehicle (1) according to claim 6 or 7, wherein: The control unit (5) is configured to determine the second threshold value (V_t2) as a constant value after effectively determining the leading ratio.

9. The vehicle (1) according to any one of claims 5 to 8, wherein: The control unit (5) is configured to Detecting braking and steering movements; and A third threshold value (V_3) is determined as one of the at least one additional threshold value in dependence on the detection of a braking steering action.

10. The vehicle (1) according to any one of claims 5 to 9, wherein: The control unit (5) is configured to determining a maximum threshold value from among said first threshold value (V_t1) and said at least one additional threshold value (V_t2, V_t3); and The maximum threshold is set as the effective threshold (V_ta).

11. The vehicle (1) according to any one of claims 1 to 10, wherein: The control unit (5) is configured to comparing the speed difference (V_d) with the validity threshold (V_ta); and The clutch engagement ratio of the controllable clutch (30) is adjusted to reduce the speed difference (V_d).

12. The vehicle (1) according to claim 11, wherein: If the speed difference (V_d) exceeds the active threshold value (V_ta), the control unit (5) is configured to reduce the speed difference (V_d).

13. The vehicle (1) according to claim 11 or 12, wherein: If the speed difference (V_d) is below the effective threshold (V_ta), the control unit (5) is configured to reduce the clutch engagement ratio.

14. The vehicle (1) according to any one of claims 1 to 13, wherein: The control unit (5) is configured to Determine the lead ratio; Detecting braking and steering movements; and The first threshold value (V_t1) is set as the effective threshold value (V_ta) only in the case where the leading ratio has been effectively determined and the lack of braking steering action has been detected.

15. The vehicle (1) according to any one of claims 2 to 14, wherein: The first threshold value (V_t1) is equal to or lower than 5% of a normalized rotation speed of the front axle drive output shaft or the rear axle drive output shaft (25, 29).

16. The vehicle (1) according to any one of claims 5 to 14, wherein: The at least one additional threshold value (V_t2, V_t3) is higher than 5% of a normalized rotational speed of the front axle drive output shaft or the rear axle drive output shaft (25, 29).

17. The vehicle (1) according to any one of the preceding claims, wherein: The measuring unit (35) is a pressure sensor integrated in a pressure line of a hydraulic circuit of a component of the drive system (11).

18. A method for controlling a variable clutch engagement ratio of a first controllable clutch (30) of a vehicle (1), the method comprising the following steps: Determining a rotational speed value of a front axle drive output shaft (25) connected to the first controllable clutch (30); Determining a rotational speed value of a rear axle drive output shaft (29) connected to the first controllable clutch (30); Determining a normalized speed value (V_n29) of the rear axle drive output shaft (29); Determining a speed difference (V_d) between the rotational speed value of the front axle drive output shaft (25) and the normalized rotational speed value (V_n29) of the rear axle drive output shaft (29); determining the traction of the vehicle (1); determining a first threshold value (V_t1) based on the normalized rotation speed value (V_29) of the rear axle drive output shaft (29) and the traction force; comparing the speed difference (V_d) with the first threshold value (V_t1); and If the speed difference (V_d) exceeds the first threshold value (V_t1), the clutch engagement ratio is increased to reduce the speed difference (V_d).

19. The method according to claim 18, comprising the steps of: determining a second threshold value based on the determination of the lead ratio; determining a third threshold value according to the braking steering action; determining a maximum threshold value from among the first threshold value, the second threshold value and the third threshold value, and The maximum threshold is set as the effective threshold.

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