TENSILE FORCE-LIMITING DEVICE FOR A WORKING MACHINE

Abstract

A traction force limiting device for a working machine with a continuously variable transmission that comprises a variator for adjusting the rotational speed ratio of the transmission independently of the torque ratio of the transmission. The traction force limiting device has a traction force interface for providing information to determine a traction force of the working machine, a limit value interface for setting a traction force limit value of the working machine and a control interface for emitting a control signal to the variator. Additionally, the traction force limiting device has a computer unit designed, on a basis of information provided via the traction force interface, to determine the traction force, to compare the traction force determined with the traction force limit value set via the limit value interface, and to control the variator in such manner that the traction force does not exceed the traction force limit value.

Claims

1-12. (canceled)

13. A traction force limiting device (22) for a working machine (1) having a continuously variable transmission (18), wherein the transmission (18) comprises a controllable variator (19) in order to adjust a torque ratio of the transmission (18) independently of a rotational speed ratio of the transmission (18), and the traction force limiting device comprising: a traction force interface (24) for providing information to determine a traction force (F) of the working machine (1); a limit value interface (25) for setting a traction force limit value (F.sub.max) of the working machine (1); a control interface (27) for emitting a control signal to the variator (19) of the transmission (18) of the working machine (1); a computer unit (23) designed to determine the traction force (F) of the working machine (1) on a basis of the information provided by the traction force interface (24), to compare the traction force (F) of the working machine (1) with the traction force limit value (F.sub.max) set by the limit value interface (25), and, on a basis of the comparison, to control the variator (19) of the transmission (18), via the control interface (27), in such manner that the traction force of the working machine (1) does not exceed the traction force limit value (F.sub.max); and the computer unit (23) is designed to control the variator (19) in such manner that the rotational speed ratio of the transmission (18) is increased without thereby changing drive output torque of the transmission (18) when a continuous change of the transmission ratio of the transmission (18) to a higher rotational speed ratio is required and the traction force determined corresponds to the traction force limit value (F.sub.max).

14. The traction force limiting device (22) according to claim 13, further comprising an adjustment device (26) for setting the traction force limit value (F.sub.max), wherein the adjustment device is connected to the limit value interface (25).

15. The traction force limiting device (22) according to claim 13, wherein the computer unit (23) is designed to control the variator (19) in such manner that the rotational speed ratio of the transmission (18) is reduced without thereby changing the drive output torque of the transmission (18) when an acceleration of the vehicle with the transmission (18) by continuously varying the transmission ratio to a lower rotational speed ratio is required and the traction force determined corresponds to the traction force limit value (F.sub.max).

16. The traction force limiting device (22) according to claim 13, further comprising a display interface (28) for emitting a display signal to a display device (29); wherein the computer unit (23) is designed to emit a display signal via the display interface (28) to the display device (29) when the variator (19) is controlled, via the control interface (27), in such manner that a change of the rotational speed ratio of the transmission (18) takes place without thereby changing the drive output torque of the transmission (18).

17. A continuously variable transmission (18) for a working machine (1), the transmission comprising: a sensor device (20; 21) for determining a drive output torque of the transmission (18); a controllable variator (19) for adjusting a torque ratio of the transmission (18) independently of a rotational speed ratio of the transmission (18); and a traction force limiting device (22) having a traction force interface (24) for providing information for determining a traction force (F) of the working machine (1), a limit value interface (25) for setting a traction force limit value (F.sub.max) of the working machine (1), a control interface (27) for emitting a control signal to the variator (19) of the transmission (18) of the working machine (1), a computer unit (23) designed to determine the traction force (F) of the working machine (1) on a basis of the information provided by the traction force interface (24), to compare the traction force (F) of the working machine (1) with the traction force limit value (F.sub.max) set by the limit value interface (25), and, on a basis of the comparison, to control the variator (19) of the transmission (18), via the control interface (27), in such manner that the traction force of the working machine (1) does not exceed the traction force limit value (F.sub.max), and the computer unit (23) is designed to control the variator (19) in such manner that the rotational speed ratio of the transmission (18) is increased without thereby changing drive output torque of the transmission (18) when a continuous change of the transmission ratio of the transmission (18) to a higher rotational speed ratio is required and the traction force determined corresponds to the traction force limit value (F.sub.max); and the sensor device (20; 21) is connected to the traction force interface (24) and the variator (19) is connected to the control interface (27).

18. The continuously variable transmission (18) according to claim 17 wherein the sensor device (20; 21) is a device provided during manufacture of the transmission (18), which is required for proper functioning of the transmission (18).

19. The continuously variable transmission (18) according to claim 17, wherein the transmission is a hydrostatic-mechanical power-split transmission (18).

20. The continuously variable transmission (18) according to claim 19, wherein the sensor device (20; 21) comprises a rotational speed sensor (20) and a pressure sensor (21).

21. A working machine (1) having the continuously variable transmission according to claim 17.

22. The working machine according to claim 21, wherein the working machine (1) is a grader.

23. A method for limiting traction force of a working machine (1) having the continuously variable transmission (18) including a sensor device (20; 21) for determining a drive output torque of the transmission (18); a controllable variator (19) for adjusting a torque ratio of the transmission (18) independently of a rotational speed ratio of the transmission (18); and a traction force limiting device (22) having a traction force interface (24) for providing information for determining a traction force (F) of the working machine (1), a limit value interface (25) for setting a traction force limit value (F.sub.max) of the working machine (1), a control interface (27) for emitting a control signal to the variator (19) of the transmission (18) of the working machine (1), a computer unit (23) designed to determine the traction force (F) of the working machine (1) on a basis of the information provided by the traction force interface (24), to compare the traction force (F) of the working machine (1) with the traction force limit value (F.sub.max) set by the limit value interface (25), and, on a basis of the comparison, to control the variator (19) of the transmission (18), via the control interface (27), in such manner that the traction force of the working machine (1) does not exceed the traction force limit value (F.sub.max), and the computer unit (23) is designed to control the variator (19) in such manner that the rotational speed ratio of the transmission (18) is increased without thereby changing drive output torque of the transmission (18) when a continuous change of the transmission ratio of the transmission (18) to a higher rotational speed ratio is required and the traction force determined corresponds to the traction force limit value (F.sub.max); and the sensor device (20; 21) is connected to the traction force interface (24) and the variator (19) is connected to the control interface (27), the variator (19) enabling the adjustment of the torque ratio of the transmission (18) independently of the rotational speed ratio of the transmission (18), the method comprising: setting (I) the traction force limit value (F.sub.max); determining (II) an existing traction force of the working machine; comparing the existing traction force with the traction force limit value (F.sub.max); and adjusting (IV) the variator (19) of the continuously variable transmission (18) on the basis of the comparison, in such manner that the traction force of the working machine does not exceed the traction force limit value (F.sub.max).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG. 1 shows schematically the structure of a grader, according to an embodiment of the present invention.

[0021] FIG. 2 shows the drive-train of the grader in FIG. 1.

[0022] FIG. 3 shows the traction force variation of the drive-train in FIG. 2 as a function of the speed of the grader.

[0023] FIG. 4 shows a method for limiting the traction force of a grader in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Below, an embodiment of a working machine 1 according to the present invention is described with reference to the drawings. The working machine 1 of this embodiment is a grader.

[0025] The grader 1 has a front section 2 and a rear section 3. The rear section 3 comprises a drive-train 4 with two rear axles 5, 6, to which in each case two wheels 7a, 7b and 8a, 8b respectively are fitted. Furthermore the rear section 3 comprises a driver's cabin 3a. The front section 2 comprises an elongated frame 9 which connects the rear section 3 to an axle section 10, on which a front axle with front wheels 11 are fitted.

[0026] In addition the grader 1 comprises a tie beam 12 mounted rotatably on the axle section 10, which is located under the frame 9. A blade 13 is mounted on the tie beam 12 so that it can rotate about a vertical axis V of the grader 1. The tie beam 12 with the blade 13 attached thereto can be adjusted in the vertical direction V of the grader 1 by means of a tie beam cylinder 14 mounted on the frame 9. Furthermore, by means of a rotational cylinder 15 the blade 13 can be rotated about the vertical axis V of the grader 1 in order to position the blade 13 obliquely relative to the travel direction of the grader 1.

[0027] As can be seen in FIG. 2, the drive-train 4 of the grader 1 comprises a drive machine 16 which in this embodiment is in the form of a diesel engine. The drive machine 16 is connected to a continuously variable transmission 18. The transmission is in the form of a so-termed Geared Neutral transmission, so that without a starting clutch 17 the vehicle can only can start off from rest by adjusting the variator 19. If the transmission is not in the form of a Geared Neutral transmission, then in addition to the continuously variable transmission a starter clutch 17 can be provided. As a rule, however, this starter clutch 17 is omitted and the vehicle is set in motion exclusively by means of the continuously variable transmission. In this embodiment the transmission is in the form of a hydrostatic-mechanical power-split transmission. The transmission 18 comprises a variator 19 which is realized by virtue of a combination of a hydraulic pump and a hydraulic motor. The power-split transmission 18 is connected to the rear axles 5, 6, so that via the drive-train 4 drive power of the drive machine 16 can be transmitted to the wheels 7a, 7b and 8a, 8b. The power-split transmission 18 comprises at least one rotational speed sensor 20 and at least one pressure sensor 21 provided in the variator 19.

[0028] Moreover, the drive-train 4 comprises a traction force limiting device 22. The traction force limiting device 22 comprises a computer unit 23 in the form of a microprocessor. The traction force limiting device 22 comprises a traction force interface 24 to which the rotational speed sensor 20 and the pressure sensor 21 are connected. Likewise, the traction force limiting device 22 comprises a limit-value interface 25 which is connected to an adjustment device 26. In this embodiment the adjustment device 26 is located in the driver's cabin 3a of the grader 1 and enables a driver of the vehicle to set a limit value for the traction force of the drive-train 4. Furthermore, the traction force limiting device 22 comprises a control interface 27 by way of which the variator 19 of the power-split transmission 18 can be controlled.

[0029] The computer unit 23 of the traction force limiting device 22 is designed to carry out the method described below with reference to FIGS. 3 and 4.

[0030] In a first step I a traction force limit value F.sub.max is set by means of the adjustment device 26. In the representation shown in FIG. 3, the limit value F.sub.max amounts to 70% of the maximum possible traction force.

[0031] In a subsequent step II, with reference to the rotational speed and the pressure provided by means of the traction force limiting device 22 via the traction force interface 24, for example the pressure in the variator, the drive output torque of the transmission 18 is determined by way of a computation model. From the drive output torque, the traction force applied at the wheels 7a, 7b and 8a, 8b respectively is determined.

[0032] In the next step III the traction force is compared with the traction force limit value F.sub.max. If the traction force is lower than the limit value, the method reverts to step II. But if the traction force determined reaches the traction force limit value F.sub.max, the variator 19 of the transmission 18 is controlled by the computer device 23 via the control interface 27 in a subsequent step IV, in such manner that the traction force limit value F.sub.max is not exceeded. Then, the process reverts to step II.

[0033] For example, if the grader is in a driving condition 1 shown in FIG. 3 and is traveling at a speed v.sub.1 with a traction force F.sub.1 and if the driving resistance then increases, in the transmission 18 the transmission ratio is adjusted continuously in order to prevent stalling of the engine. Thereby the transmission ratio is increased, which results in a driving condition 2 with lower speed v.sub.2 and higher traction force F.sub.2. If a further increase of the transmission ratio is required, the grader reaches a driving condition F.sub.3 with traction force F.sub.max and speed v.sub.3. If the transmission ratio is increased still further by adjusting the variator 19 of the transmission 18, the speed of the grader falls to a value v.sub.4 at which the increase of the rotational speed ratio does not entail an increase of the traction force F. Instead, the traction force is limited to the limit value F.sub.max by appropriate control of the variator 19 by means of the traction force limiting device 22. If a reduction of the rotational speed ratio of the transmission 18 and thereby an acceleration of the vehicle is required, this also takes place without changing the traction force F until a speed v.sub.3 is reached. At a higher speed v the transmission ratio change and therefore the acceleration of the vehicle again brings about a reduction of the traction force F. In that way, by virtue of the traction force limiting device 22 the traction force does not rise above the limit value F.sub.max at any operating point of the transmission 18.

INDEXES

[0034] 1 Grader [0035] 2 Front section [0036] 3 Rear section [0037] 3a Driver's cabin [0038] 4 Drive-train [0039] 5, 6 Rear axles [0040] 7a, 7b, 8a, 8b Rear wheels [0041] 9 Frame [0042] 10 Axle section [0043] 11 Front wheels [0044] 12 Tie beam [0045] 13 Blade [0046] 14 Tie beam cylinder [0047] 15 Rotational cylinder [0048] 16 Drive machine [0049] 17 Starter clutch [0050] 18 Continuously variable transmission [0051] 19 Variator [0052] 20 Rotational speed sensor [0053] 21 Pressure sensor [0054] 22 Traction force limiting device [0055] 23 Computer unit [0056] 24 Traction force interface [0057] 25 Limit value interface [0058] 26 Adjustment device [0059] 27 Control interface [0060] 28 Display interface [0061] 29 Display device [0062] F.sub.max Traction force limit value [0063] I Set traction force limit value [0064] II Determine existing traction force [0065] III Compare existing traction force with traction force limit value [0066] IV Adjust variator