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EP-4572967-B1 - VEHICLE WITH CONTROLLABLE CLUTCH BETWEEN FRONT AND REAR AXLE AND METHOD FOR CONTROLLING VARIABLE CLUTCH ENGAGEMENT RATIO OF THE CLUTCH

EP4572967B1EP 4572967 B1EP4572967 B1EP 4572967B1EP-4572967-B1

Inventors

  • ABEL, Manuel
  • HEINDL, RICHARD
  • GEIGER, MARKUS

Dates

Publication Date
20260513
Application Date
20230714

Claims (19)

  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); with a controllable clutch (30) arranged between the front axle drive output shaft (25) and the rear axle drive output shaft (29) 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 a rotational speed of the front axle drive output shaft (25); a second speed sensor (47) for determining a rotational speed of the rear axle drive output shaft (29); and a control unit (5) configured to determine a speed difference (V_d) between the rotational speed of the front axle drive output shaft (25) and the rotational speed of the rear axle drive output shaft (29); characterized by a measuring unit (35) for determining a pull force; wherein the control unit (5) is further configured to determine a first threshold value (V_t1) based on the pull force; to set the first threshold value (V_t1) as an active threshold value (V_ta); and to control the clutch engagement ratio of the controllable clutch (30) in dependence on the speed difference (V_d) and the active threshold value (V_ta).
  2. The vehicle (1) of claim 1, wherein the control unit (5) is configured to normalize the rotational speed of the front or the rear axle drive output shaft (25, 29) in respect of a lead ratio, a steering angle (α) of steerable wheels (13a, 13b) and/or dimensions of front and rear wheels (13a, 13b, 15a, 15b).
  3. The vehicle (1) of claim 1 or 2, wherein the higher the pull force is, the lower the value of the first threshold value (V_t1) is determined by the control unit (5), and vice versa.
  4. The vehicle (1) of 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 rotational speed of the front axle drive output shaft (25) or the rear axle drive output shaft (29).
  5. The vehicle (1) of any one of claims 1 to 4, wherein the control unit (5) is configured to determine at least one additional threshold value (V_t2, V_t3); and to set the additional threshold value as the active threshold value (V_ta) if the first threshold value (V_t1) is below the additional threshold value (V_t2, V_t3).
  6. The vehicle (1) of claim 5, wherein the control unit (5) is configured to determine a lead ratio; and to determine a second threshold value (V_t2) as one of the at least one additional threshold value if the determination of the lead ratio is void; wherein the second threshold value (V_t2) is based on the rotational speed of the front axle drive output shaft (25) or the rear axle drive output shaft (29).
  7. The vehicle (1) of claim 6, comprising a brake unit (55a, 55b, 56a, 56b); a steerable wheel (13a, 13b); and a steering sensor (61) for determining a steering angle (α) of the steerable wheel (13a, 13b), wherein the control unit (5) determines the lead ratio if the pull force is below a first parameter, the steering angle (α) is below a second parameter, the brake unit (55a, 55b, 56a, 56b) is released, and/or the clutch engagement ratio of the controllable clutch (30) is below a third parameter.
  8. The vehicle (1) of claim 6 or 7, wherein the control unit (5) is configured to determine the second threshold value (V_t2) as a constant value after a valid determination of the lead ratio.
  9. The vehicle (1) of any one of claims 5 to 8, wherein the control unit (5) is configured to detect a brake steering action; and to determine a third threshold value (V_3) as one of the at least one additional threshold value in dependence on a detection of a brake steering action.
  10. The vehicle (1) of any one of claims 5 to 9, wherein the control unit (5) is configured to determine a maximum threshold value out of the first threshold value (V_t1) and the at least one additional threshold value (V_t2, V_t3); and to set the maximum threshold value as the active threshold value (V_ta).
  11. The vehicle (1) of any one of claims 1 to 10, wherein the control unit (5) is configured to compare the speed difference (V_d) with the active threshold value (V_ta); and to adjust the clutch engagement ratio of the controllable clutch (30) to reduce the speed difference (V_d).
  12. The vehicle (1) of claim 11, wherein the control unit (5) is configured to reduce the speed difference (V_d) if the speed difference (V_d) exceeds the active threshold value (V_ta).
  13. The vehicle (1) of claim 11 or 12, wherein the control unit (5) is configured to reduce the clutch engagement ratio if the speed difference (V_d) is below the active threshold value (V_ta).
  14. The vehicle (1) of any one of claims 1 to 13, wherein the control unit (5) is configured to determine a lead ratio; to detect a brake steering action; and to set the first threshold value (V_t1) as the active threshold value (V_ta) only if the lead ratio has been validly determined and an absence of a brake steering action has been detected.
  15. The vehicle (1) of any one of claims 2 to 14, wherein the first threshold value (V_t1) is equal or below 5% of the normalized rotational speed of the front or rear axle drive output shaft (25, 29).
  16. The vehicle (1) of 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 or rear axle drive output shaft (25, 29).
  17. The vehicle (1) of any one of the proceeding 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. Method for controlling a variable clutch engagement ratio of a first controllable clutch (30) of a vehicle (1), comprising the steps: Determining a rotational speed value of a front axle drive output shaft (25) connected with the first controllable clutch (30); determining a rotational speed value of a rear axle drive output shaft (29) connected with the first controllable clutch (30); determining a normalized rotational 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); characterized by determining a pull force of the vehicle (1); determining a first threshold value (V_t1) based on the normalized rotational speed value (V_29) of the rear axle drive output shaft (29) and the pull force; comparing the speed difference (V_d) with the first threshold value (V_t1); and increasing the clutch engagement ratio if the speed difference (V_d) exceeds the first threshold value (V_t1) to reduce the speed difference (V_d).
  19. The method of claim 18 comprising the steps: Determining a second threshold value in dependence on a determination of a lead ratio; determining a third threshold value in dependence on a brake steering action; determining a maximum threshold value out of the first, second and third threshold values and setting the maximum threshold value as the active threshold value.

Description

FIELD The present invention relates generally to a vehicle with a controllable clutch between front and rear axle having a variable clutch engagement ratio and a method for controlling the variable clutch engagement ratio of the clutch. BACKGROUND Vehicles with an all-wheel drive may have a common drive shaft for transmitting a drive torque provided by an engine to the drive front and rear wheels of the vehicle. Depending on the conditions of the ground the wheels are rolling on, a different torque may be transferrable by the wheels. For example, low torque may be transferrable on icy ground only instead of a higher torque if the ground is rough. Thus, it may be useful to distribute the drive torque between the front and rear wheels if front wheels are on a ground having a different condition than the rear wheels so that the wheels rolling on the ground with the better condition can transfer higher torque. The torque distribution may be provided by a controllable clutch integrated in the drive shaft between the front and rear wheels. EP 3 720 076 B1 discloses a drive system for a utility vehicle such as a tractor with 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 vary the distribution of delivered torque between the front and rear axles. The clutch may be engaged if a speed difference between the front axle and the rear axle exceeds a threshold value having a fixed value. Thus, skidding of the wheels may be prevented. BRIEF SUMMARY It is an objective to improve 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. According to an aspect of the invention there is provided a 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 with a controllable clutch 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 a pull force, and a control unit 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 pull force, to set the first threshold value as an active threshold value, and to control the clutch engagement ratio of the controllable clutch in dependence on the speed difference and the active threshold value. The active threshold value defines a threshold value for the speed difference. When the first threshold value is set as the active 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 active threshold value, which may be the first threshold value, and may detect if the speed difference exceeds or undercuts the active threshold value. The clutch engagement ratio defines the level of engagement of the controllable clutch that may continuously vary from fully released (also disengaged) to fully engaged. When the controllable clutch is fully released, the front axle drive output shaft and the rear axle drive output shaft may rotate independently from each other such as two disconnected axles. When the controllable clutch is fully engaged, the front axle drive output shaft and the rear axle drive output shaft may rotate together such as an one-piece axle. In case of any intermediate clutch engagement ratio, drive torque is distributed between both axles accordingly. The vehicle may be any utility vehicle or agricultural machine such as a tractor, a harvester or a combine, for example. The vehicle may be used to pull a tool or an implement over a ground, e. g. an agricultural field, to perform a task as for example ploughing the agricultural field or transport an object. Depending on the task to be performed a different pull force may be required to be provided by the vehicle to overcome with the load caused by resistance forces. For example, ploughing a field may require much more pull force to be provided by the vehicle as driving on a road because of the much higher resistance forces cause by the field operation increasing the load accordingly. The pull force provided by the vehicle may be determined by the control unit processing appropriate sensor values. The sensor values may be determined by the measuring unit for determining a pull force. For example, the pull force may depend on a pressure value of a fluid in a