Steerable crawler track

Abstract

A steerable crawler track for an agricultural utility vehicle such as a tractor or a self-propelled harvesting machine has a left-side track roller unit, a right-side track roller unit, a differential having a transmission input driven by an engine, a first transmission output for driving the left track roller unit, and a second transmission output for driving the right track roller unit and a hydraulic transmission having a variable transmission ratio (i). The transmission outputs of the differential are coupled to one another via the hydraulic transmission such that the ratio of the rotational speeds (n.sub.l, n.sub.r) of the transmission outputs are influenced by changing the transmission ratio (i) of the hydraulic transmission.

Claims

1. A steerable crawler track for an agricultural utility vehicle, comprising: a left-side track roller unit; a right-side track roller unit; a differential having a transmission input, which is driven by an engine, a first transmission output coupled to the left-side track roller unit via a first coupling, for driving the left-side track roller unit and a second transmission output coupled to the right-side track roller unit via a second coupling, for driving the right-side track roller unit; a hydraulic transmission having a variable transmission ratio (i), wherein the first and the second transmission outputs of the differential are coupled to one another via the hydraulic transmission such that a ratio of the rotational speeds (n.sub.1, n.sub.r) of the first and the second transmission outputs is influenced by changing the transmission ratio (i) of the hydraulic transmission; and a control device for decoupling the transmission outputs from the hydraulic transmission; wherein the first coupling and the second coupling are friction clutches.

2. The crawler track according to claim 1, wherein the first friction clutch is disposed between the first transmission output and a first member of the hydraulic transmission and the second friction clutch is disposed between the second transmission output and a second member of the hydraulic transmission.

3. The crawler track according to claim 2, wherein the first member of the hydraulic transmission embodies a first hydrostatic unit, which can be brought into a drive connection with the first transmission output, and the second member of the hydrostatic transmission embodies a second hydrostatic unit, which can be brought into a drive connection with the second transmission output, and wherein the first and the second hydrostatic units are interconnected within a hydraulic circuit.

4. The crawler track according to claim 3, wherein at least one of the first and the second hydrostatic units has a variable intake volume and pump capacity.

5. The crawler track according to claim 4, wherein the first and the second hydrostatic units can be brought into a drive connection with the associated first and second transmission outputs via respective spur gear stages.

6. The crawler track according to claim 5, wherein each respective spur gear stage includes a first spur gear assigned to one of the first and the second hydrostatic units and a second spur gear, wherein the second spur gear meshes with the first spur gear and wherein the respective second spur gears are assigned to the first and the second transmission outputs, respectively.

7. The crawler track according to claim 6, wherein the second spur gears, which are assigned to the first and the second transmission outputs, respectively, are assigned a respective one of the first and the second couplings, and are used to disengage or engage a drive connection between the particular second spur gear and the first and second transmission outputs.

8. The crawler track according to claim 3, wherein the hydraulic circuit can be connected to a hydraulic pump that is driven by a drive motor.

9. A steerable crawler track for an agricultural utility vehicle, comprising: a left-side track roller unit; a right-side track roller unit; a differential having a transmission input, which is driven by an engine, a first transmission output, coupled to the left-side track roller unit via a first friction clutch, for driving the left-side track roller unit and a second transmission output coupled to the right-side track roller unit via a second friction clutch, for driving the right-side track roller unit; a hydraulic transmission having a variable transmission ratio (i), wherein the first and the second transmission outputs of the differential are coupled to one another via the hydraulic transmission such that a ratio of the rotational speeds (n.sub.1, n.sub.r) of the first and the second transmission outputs is influenced by changing the transmission ratio (i) of the hydraulic transmission; and a control device operable to decouple the first and the second transmission outputs, via the respective first and second friction clutches, from the hydraulic transmission depending on an operating parameter selected from the group consisting of: a ground speed of the crawler track, a rotational speed of the transmission input, a rotational speed (n.sub.1, n.sub.r) of one or both of the first and the second transmission outputs, and a rotational speed of one or both of the first and the second hydrostatic units.

10. The crawler track according to claim 9, wherein the control device is operated to actuate the first and the second friction clutches jointly using a control.

11. A steerable crawler track for an agricultural utility vehicle, comprising: a left-side track roller unit; a right-side track roller unit; a differential having a transmission input, which is driven by an engine, a first transmission output for driving the left-side track roller unit and a second transmission output for driving the right-side track roller unit; a hydraulic transmission having a variable transmission ratio (i), wherein the first and the second transmission outputs of the differential are coupled to one another via the hydraulic transmission such that a ratio of the rotational speeds (n.sub.1, n.sub.r) of the first and the second transmission outputs is influenced by changing the transmission ratio (i) of the hydraulic transmission; and a means for decoupling the transmission outputs from the hydraulic transmission; wherein the crawler track is configured to operate in one of first and second operating modes (M.sub.1, M.sub.2), wherein the first operating mode (M.sub.1) is a coupled operating mode in which the first and the second transmission outputs of the differential are coupled to one another via the hydraulic transmission such that the crawler track is steered by changing the transmission ratio (i) of the hydraulic transmission and via an associated change in the ratio of the rotational speeds of the left-side and the right-side track roller units, and wherein the second operating mode (M.sub.2) is a decoupled operating mode in which the first and the second transmission outputs of the differential are decoupled from the hydraulic transmission such that, in a forced driving state of the crawler track, the ratio of the rotational speeds (n.sub.1, n.sub.r) of the first and the second transmission outputs is adapted to the forced driving state.

12. The crawler track according to claim 11, further comprising a control device that is operated to select one of the first or the second operating modes (M.sub.1, M.sub.2) of the crawler track depending on one or multiple operating parameters selected from the group consisting of: the ground speed of the crawler track, a rotational speed of the transmission input, a rotational speed (n.sub.1, n.sub.r) of one of the first and the second transmission outputs, and a rotational speed of one or both of the first and the second hydrostatic units.

13. The crawler track according to claim 11, wherein the first operating mode (M.sub.1) is selected for ground speeds, for rotational speeds (n.sub.1, n.sub.r) or both, that are below a predefinable value and the second operating mode (M.sub.2) is selected for ground speeds, for rotational speeds (n.sub.1, n.sub.r) or both, above the predefinable value.

14. An agricultural utility vehicle having, a half-track design and a vehicle structure that is supported on the ground by a crawler track as defined by claim 11, and by an additional axle, wherein the additional axle is steerable to steer the utility vehicle at least in the second operating mode (M.sub.2).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is described in greater detail in the following with reference to an attached drawing. Therein:

(2) FIG. 1 shows a perspective view of an agricultural utility vehicle in the form of a combine harvester;

(3) FIG. 2 shows a schematic diagram of a steerable crawler track; and

(4) FIG. 3 shows a schematic diagram of a steerable crawler track, the hydraulic circuit of which can be connected to a hydraulic pump.

DETAILED DESCRIPTION OF THE INVENTION

(5) FIG. 2 shows a schematic diagram of a steerable crawler track 1 according to the invention. The crawler track 1 shown can be used, advantageously, to drive an agricultural utility vehicle, such as a combine harvester 50 shown in FIG. 1, for example.

(6) According to the illustration in FIG. 2, the crawler track 1 comprises, as essential elements, a left track roller unit 10, a right track roller unit 20, a differential 30, and a hydraulic transmission 40, which can be coupled and decoupled from this differential. A preferred direction of travel FR of the crawler track 1 is indicated by the arrow FR.

(7) The differential 30 is a differential, which is known per se and can be driven by means of a drive engine 2. A drive shaft 3, which can be driven by the drive engine 2, has a drive connection to a differential case 34 of the differential 30 via a spur gear stage, which includes a spur gear 4 and a spur gear 33 meshed therewith. The differential case 34 rotatably accommodates a plurality of bevel gears 35. Each of the bevel gears 35 is in meshed engagement with two opposing bevel gears 36, 37. The bevel gear 37 is assigned to a first transmission output 31 for driving the left track roller unit 10 and the bevel gear 36 is assigned to a second transmission output 32 for driving the right track roller unit 20. In a manner known per se, the differential 30 distributes the drive power entering via the drive shaft 3 to the transmission outputs 31, 32.

(8) Assigned to the first transmission output 31 is a spur gear 11, which meshes with a further spur gear 13 in order to establish a drive connection to a hydrostatic unit 15 via a shaft 14. The hydrostatic unit 15 has a variable intake volume and pump capacity (pivot angle ?).

(9) Assigned to the second transmission output 32 is a spur gear 21, which meshes with a further spur gear 23 in order to establish a drive connection to a hydrostatic unit 25 via a shaft 24. The hydrostatic unit 25 also has a variable intake volume and pump capacity (pivot angle ?). The pivot angles ? of the hydrostatic units 15, 25 can be controlled separately.

(10) The two hydrostatic units 15, 25 are drivably interconnected via a closed hydraulic circuit 41 (hydraulic medium 42) in order to form a hydraulic transmission 40. The transmission outputs 31, 32 of the differential 30 are therefore coupled via the hydraulic transmission 40 in a manner known per se. A variable transmission ratio i between the transmission outputs 31, 32 results depending on the pivot angle ? of the hydrostatic units 15, 25 that is selected.

(11) The closed hydraulic circuit 41 is supplied with hydraulic medium 42 via a feed circuit 43 in a manner known per se. The feed circuit includes a hydraulic pump 44, which functions as an external pressure source, a tank 47, an oil cooler 46, and an oil filter 45.

(12) According to the invention, the crawler track 1 shown comprises means, for example in the form of couplings, which are used to decouple the transmission outputs 31, 32 from the hydraulic transmission 40.

(13) To this end, a first coupling 12 is disposed between the first transmission output 31 and the hydrostatic unit 15 and a second coupling 22 is disposed between the second transmission output 32 and the hydrostatic unit 25. The couplings 12, 22 are each designed as friction clutches, by means of which the respectively assigned spur gear 11, 21 can be selectively connected to the respective transmission output 31, 32 in a rotationally locked manner, or can be disconnected therefrom.

(14) A central control device 5 has a signal connection to the two couplings 11, 21 and is operated so as to decouple the transmission outputs 31, 32 from the hydraulic transmission 40 depending on an operating parameter, in particular the ground speed of the crawler track 1, a rotational speed of the transmission input 34, a rotational speed n.sub.l, n.sub.r of a transmission output 31, 32, a rotational speed of a hydrostatic unit 15, 25 and/or the like. Preferably, this decoupling is carried out jointly by means of a corresponding control in each case.

(15) The crawler track can be operated in two operating modes M.sub.1, M.sub.2 with the aid of the control device 5. In a coupled operating mode M.sub.1, the transmission outputs 31, 32 of the differential 30 are coupled to one another via the hydraulic transmission 40 such that the crawler track 1 can be steered by changing the ratio i of the hydraulic transmission 40 and via an associated change in the ratio of the drive speeds n.sub.l, n.sub.r of the track roller units 10, 20 and, in a decoupled operating mode M.sub.2, the transmission outputs 31, 32 of the differential 30 are decoupled from the hydraulic transmission 40 such that, in a forced driving state of the crawler track, in particular during forced travel around a curve, the ratio of the rotational speeds n.sub.1, n.sub.2 of the transmission outputs 31, 32 can be adapted to this driving state.

(16) The control device 5 can be operated to select the operating mode M.sub.1, M.sub.2 of the crawler track 1 depending on one or multiple operating parameters, in particular depending on the ground speed of the crawler track 1, a rotational speed of the transmission input 34, a rotational speed n.sub.l, n.sub.r of a transmission output 31, 32, a rotational speed of an hydrostatic unit 15, 25 and/or the like. The control device 5 selects the coupled operating mode M.sub.1 for ground speeds and/or rotational speeds n.sub.l, n.sub.r which are below a predefinable value. The control device 5 selects the decoupled operating mode M.sub.2 for ground speeds and/or rotational speeds n.sub.l, n.sub.r which are above a predefinable value.

(17) FIG. 1 shows, by way of example, an agricultural utility vehicle in the form of a combine harvester 50 having a half-track design. The combine harvester 50 comprises a main drive engine 51, inter alia, for driving the drive engine 2, and comprises a vehicle structure 52, which is supported on the ground by means of a crawler track 1, which is described above with reference to FIG. 2, and by means of an additional axle 53. The additional axle 53 is designed to be steerable such that the combine harvester 50 can be steered via the additional axle 53 at least in the decoupled operating mode M.sub.2 of the crawler track 1.

(18) The combine harvester 50 comprising the crawler track 1 designed according to the invention provides the advantage that the crawler track 1 can be steered at relatively slow ground speeds by means of the coupled hydraulic transmission 40 with the aid of the hydraulic superimposed steering. Neither brake wear nor power losses associated therewith occur during steering. In addition, particularly sensitive steerability is achieved.

(19) At relatively high ground speeds, the crawler track 1 provided on the combine harvester 50 provides the advantage that the transmission outputs 31, 32 are decoupled from the hydraulic transmission 40 and, therefore, the hydrostatic units 15, 25 do not need to be operated at an excessive rotational speed. Therefore, a compact design is possible. In this case, the steerable rear axle 53 exclusively ensures the steerability of the combine harvester 50 when the hydraulic transmission 40 is decoupled.

(20) FIG. 3 shows a schematic diagram of a steerable crawler track 1, the hydraulic circuit 41 of which can be connected to a hydraulic pump 55 via a control valve 54. The hydraulic pump 55 is driven by an engine 56, for example the drive engine of an agricultural utility vehicle. When the hydraulic circuit 41 is connected to the hydraulic pump 55, power can be supplied via the hydraulic pump 55, whereby the utility vehicle can be steered when at a standstill and/or steering can be improved at a relatively slow speed.

LIST OF REFERENCE NUMBERS

(21) 1 crawler track

(22) 2 drive engine

(23) 3 drive shaft

(24) 4 spur gear

(25) 5 control device

(26) 10 left track roller unit

(27) 11 spur gear

(28) 12 friction clutch

(29) 13 spur gear

(30) 14 shaft

(31) 15 hydrostatic unit

(32) 20 right track roller unit

(33) 21 spur gear

(34) 22 friction clutch

(35) 23 spur gear

(36) 24 shaft

(37) 25 hydrostatic unit

(38) 30 differential

(39) 31 transmission output (left)

(40) 32 transmission output (right)

(41) 33 spur gear

(42) 34 differential case

(43) 35 bevel gear

(44) 36 bevel gear

(45) 37 bevel gear

(46) 40 hydraulic transmission

(47) 41 closed hydraulic circuit

(48) 42 hydraulic medium

(49) 43 feed circuit

(50) 44 hydraulic pump

(51) 45 oil filter

(52) 46 oil cooler

(53) 47 tank

(54) 50 combine harvester

(55) 51 main drive engine

(56) 52 vehicle structure

(57) 53 rear axle

(58) 54 control valve

(59) 55 hydraulic pump

(60) 56 engine

(61) FR direction of travel

(62) M.sub.1 coupled operating mode

(63) M.sub.2 decoupled operating mode

(64) n.sub.l rotational speed (left output)

(65) n.sub.r rotational speed (right output)

(66) ? pivot angle