Abstract
A tracked vehicle, in particular a construction machine, more particularly a road construction machine, with at least one drive motor and a travel pump of a travel drive hydraulic circuit, which is driven by the drive motor, for generating a drive pressure; at least one track unit, said track unit comprising a drive wheel driven via the travel drive hydraulic circuit, at least one guide wheel, a track endlessly running around the drive wheel and the guide wheel, as well as a track tensioning apparatus for tensioning the track, and the track tensioning apparatus comprising an adjusting device with a track tensioning hydraulic cylinder with which the distance between two wheels of the track unit, in particular the drive wheel and the guide wheel, is adjustable for tensioning the track, the track tensioning hydraulic cylinder being connected via a hydraulic tensioning line to a hydraulic pretensioning source via which it can be loaded with an initial pretensioning pressure. The tensioning apparatus further has a damping device with a spring for damping pressure peaks in the adjusting device. A method for operating a tracked vehicle with a track unit.
Claims
1-13. (canceled)
14. A tracked vehicle comprising: at least one drive motor and a travel pump of a travel drive hydraulic circuit, which is driven by the drive motor, for generating a drive pressure; at least one track unit, the track unit comprising: a drive wheel driven via the travel drive hydraulic circuit, at least one guide wheel, a track endlessly running around the drive wheel and the guide wheel, as well as a track tensioning apparatus for tensioning the track, the track tensioning apparatus comprising: an adjusting device with a track tensioning hydraulic cylinder with which the distance between two wheels of the track unit is adjustable for tensioning the track, the track tensioning hydraulic cylinder being connected via a hydraulic tensioning line to a hydraulic pretensioning source via which it can be loaded with an initial pretensioning pressure; and a damping device with a spring for damping pressure peaks in the adjusting device, wherein the damping device includes an auxiliary tensioning device which is configured such that it varies the initial pretensioning pressure independently of the pretensioning source depending on the drive pressure in the travel drive hydraulic circuit towards a pretensioning pressure inside the track tensioning hydraulic cylinder which correlates with a change in the drive pressure, and that the auxiliary tensioning device comprises an auxiliary tensioning hydraulic cylinder with a hydraulic cylinder and a cylinder piston adjustably mounted therein, which divides the interior space of the auxiliary tensioning hydraulic cylinder into a piston space and a piston rod space, wherein the auxiliary tensioning hydraulic cylinder is loaded by the spring of the damping device with an adjusting force on the piston rod side.
15. The tracked vehicle according to claim 14, wherein the auxiliary tensioning device is configured such that it increases the actual pretensioning pressure inside the track tensioning hydraulic cylinder in relation to the initial pretensioning pressure during reverse travel.
16. The tracked vehicle according to claim 14, wherein the auxiliary tensioning device is configured as a hydraulic transmission unit such that it translates pressure changes in the drive pressure into smaller pressure changes inside the track tensioning hydraulic cylinder.
17. The tracked vehicle according to claim 14, wherein in addition to the piston rod space, the auxiliary tensioning hydraulic cylinder has a compression spring space separated from the piston rod space, into which the cylinder piston projects at the end and in which the compression spring of the damping device is completely arranged.
18. The tracked vehicle according to claim 14, wherein the auxiliary tensioning device is in fluid communication with the hydraulic tensioning line or directly with the track tensioning hydraulic cylinder via an auxiliary tensioning connection line.
19. The tracked vehicle according to claim 14, wherein a travel drive connection line from the travel drive hydraulic circuit, in particular its high-pressure side during reverse travel, to the auxiliary tensioning hydraulic cylinder is provided via which the auxiliary tensioning hydraulic cylinder is in fluid conducting connection with the travel drive circuit.
20. The tracked vehicle according to claim 18, wherein the auxiliary tensioning connection line and the travel drive connection line are arranged such that the auxiliary tensioning connection line is in fluid communication with a piston space and the travel drive connection line is in fluid communication with a piston rod space of the auxiliary tensioning hydraulic cylinder.
21. The tracked vehicle according to claim 14, wherein the damping device is arranged outside the track unit.
22. The tracked vehicle according to claim 14, wherein the damping device is centrally connected simultaneously to two or more track tensioning hydraulic cylinders of two or more track units.
23. The tracked vehicle according to claim 14, wherein it is a construction machine.
24. A method for operating a tracked vehicle according to claim 14, with a track tensioning apparatus comprising the steps of: a) Pretensioning a track of a track unit running around a drive wheel and a guide wheel with the aid of a track tensioning hydraulic cylinder with an initial pretensioning pressure, which is connected to a hydraulic pretensioning source; b) Damping pressure peaks occurring inside the track tensioning hydraulic cylinder using a compression spring of a damping device; c) Changing the initial pretensioning pressure towards a pretensioning pressure inside the track tensioning hydraulic cylinder correlating with a change in the drive pressure using an auxiliary tensioning device acting in dependence on the drive pressure in the travel drive hydraulic circuit.
25. The method according to claim 24, wherein step c) includes loading a cylinder piston of an auxiliary tensioning hydraulic cylinder on the input side with hydraulic fluid via a travel drive connection line which is in fluid communication with a travel drive hydraulic circuit, and that the auxiliary tensioning hydraulic cylinder is in fluid communication with the track tensioning hydraulic cylinder on the output side.
26. The method according to claim 24, wherein step c) includes performing a hydraulic transmission via the auxiliary tensioning device such that pressure peaks in the travel drive circuit are reduced towards the track tensioning hydraulic cylinder.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The invention will be explained in more detail below by reference to the embodiment examples shown in the figures. In the schematic figures:
[0021] FIG. 1 is a side view of a tracked vehicle of the construction machine type, more specifically a road milling machine;
[0022] FIG. 2 is a view of a track unit;
[0023] FIG. 3 shows a detail of a hydraulic circuit diagram;
[0024] FIG. 4 is a graphical comparison of the dependence of the track tension on the spring travel of the embodiment according to the invention with known prior art solutions;
[0025] FIG. 5. is a flowchart of a method according to the invention;
[0026] FIG. 6 is a side view of a construction machine of the road paver type;
[0027] FIG. 7 is a side view of a construction machine of the feeder type;
[0028] FIG. 8 shows a detail of a hydraulic circuit diagram of an alternative embodiment;
[0029] FIGS. 9A-9D show alternative embodiments of the spring tensioning cylinder;
[0030] FIG. 10 is a view of a track unit of the delta unit type;
[0031] FIG. 11 shows the drive pressure curve and the correlating adjustment of the pretensioning pressure inside the track tensioning hydraulic cylinder; and
[0032] FIGS. 12A-12E show further preferred types of tracked vehicles.
DETAILED DESCRIPTION OF THE DRAWINGS
[0033] Like or functionally like components are designated by like reference numerals in the figures, although designations of recurring components may be omitted in some figures.
[0034] FIG. 1 illustrates a construction machine 1 of the road milling machine type. Essential elements of the construction machine 1 include a machine frame 1, a drive motor (for example a combustion engine) 3, traveling devices in the form of track units 4, which in the present embodiment example are connected to the machine frame 2 via height-adjustable lifting columns 5, an operator platform 6, a working device 7 (in this case a milling drum arranged inside a milling drum box) as well as a loading conveyor belt 8. During working operation, the construction machine 1 moves in the working direction or forward direction A over the underlying ground to be processed. The construction machine 1 is driven via a travel pump of a travel drive hydraulic circuit, which is driven by the drive motor 3, said travel drive hydraulic circuit providing drive energy to one or more hydraulic motors for driving the track units 4. This can be seen in more detail, for example, in FIG. 2.
[0035] FIG. 2 illustrates one of the track units 4 of FIG. 1 and its drive. The travel pump 9 is operated via the drive motor 3, and further components such as a pump transfer gear, coupling devices, etc. may be interposed here, for example. The travel pump 9 is part of a travel drive hydraulic circuit 10 which further comprises a travel drive motor 11, for example a hydraulic motor. The travel drive motor 11 drives, in particular directly or via a toothed gearing, a drive wheel 12 of the track unit 4, thus setting a track 13 into an endless circulating motion that drives the drive wheel 12 and a guide wheel that is not directly driven by the travel drive motor, which ultimately enables the travel motion of the construction machine 1. It will be appreciated that the specific design of the track 13 may vary; the track 13 may, for example, comprise replaceable running pads etc. To enable reliable traveling operation, it is important to ensure that the track 13 will not slip off the drive wheel 12 and/or the guide wheel 14. To this end, the track is tensioned using a track tensioning apparatus 15 which can be used to adjust the horizontal distance between the drive wheel 12 and the guide wheel 14. For this, the track tensioning apparatus 15 according to FIG. 2 comprises, among other things, an adjusting device 16 with a track tensioning hydraulic cylinder 17 which is connected on the piston rod side to the guide wheel 14 and on the piston side to a machine frame not shown in more detail in FIG. 2, which also supports the drive wheel 12 in a manner known per se in the prior art. On the piston side, the track tensioning hydraulic cylinder 17 is connected to a hydraulic pretensioning source 19 via a hydraulic tensioning line 18. With the aid of this hydraulic pretensioning source 19, a hydraulic pretensioning pressure (initial pretensioning pressure) is built up inside the track tensioning hydraulic cylinder 17 when the construction machine 1 is started, for example, to achieve a desired initial tension of the track 13. This initial pretensioning pressure may, for example, be preset at the factory, for example in a suitable machine control system. Via a switching valve 20, the fluid connection between the track tensioning hydraulic cylinder 17 and the pretensioning source can be interrupted when the pretensioning pressure in the track tensioning hydraulic cylinder is reached, for example when the construction machine starts moving.
[0036] The track tensioning apparatus further comprises a damping device 21. The latter provides a certain degree of elasticity to the track tensioning apparatus 15, for example for damping or compensating for pressure peaks occurring at the track 13 and the track tensioning hydraulic cylinder, respectively, during traveling operation. Further details on the structure and mode of operation of the damping device 21 are given in particular in FIG. 3. However, what is important in the present embodiment example is that the damping device 21 is in fluid communication with both the travel drive hydraulic circuit 10 and the hydraulic tensioning line 18 or the track tensioning hydraulic cylinder 17. This makes it possible to build up an auxiliary tension at the track tensioning hydraulic cylinder 17 correlating to a change in the drive pressure in the travel drive hydraulic circuit 10 in a traveling direction-dependent manner and bypassing the hydraulic pretensioning source 19. For this purpose, the damping device 21 comprises an auxiliary tensioning device 22.
[0037] An embodiment example of such a damping device 21 with an auxiliary tensioning device 22 is shown in more detail in FIG. 3. The area framed by dashed lines in FIG. 3 corresponds to the dashed box of FIG. 2. The damping device comprises a compression spring 23 for damping pressure peaks in the track tensioning hydraulic cylinder 17. Depending on the arrangement and type of suspension, it is also possible to use an extension spring, as will be shown in more detail below. The spring is arranged inside a hydraulic cylinder 24 of an auxiliary tensioning hydraulic cylinder 25 together with a cylinder piston 26 mounted in said hydraulic cylinder 24 so as to be adjustable or more specifically axially displaceable. Via an auxiliary tensioning connection line 27, the hydraulic cylinder is connected on the piston side to a hydraulic supply line extending from the pretension source 19 to at least one track tensioning hydraulic cylinder 17, so that the hydraulic cylinder is in fluid conducting connection with the track tensioning hydraulic cylinder on the piston side. Thus, if a pressure peak occurs in the track tensioning hydraulic cylinder 17, it will ultimately affect, via the line system described above, the cylinder piston 26, which changes such a pressure peak by shifting its position to the compression spring 23 and compresses the latter. In this manner, the pressure peak is damped accordingly.
[0038] It is now essential that the auxiliary tensioning hydraulic cylinder is simultaneously in fluid conducting connection with the travel drive hydraulic circuit 10, which is only partially shown in FIG. 3, via a travel drive connection line 28. In this particular embodiment example, the travel drive connection line 28 connects one side of the travel drive connection circuit to the piston rod space 22 of the auxiliary tensioning hydraulic cylinder 25 and thus to the side of the cylinder piston 26 located opposite the auxiliary tensioning connection line 27. If pressure changes occur in the travel drive hydraulic circuit 10, for example when the direction of travel is reversed, these changes thus affect the pressure conditions in the auxiliary tensioning connection line 27 or at the track tensioning hydraulic cylinder 17 via the travel drive connection line 28 and the damping device 21. Thus, if the pressure in the travel drive hydraulic circuit 10 increases, the pressure inside the track tensioning hydraulic cylinder 17 will also increase. The auxiliary tensioning hydraulic cylinder 25 in this case acts as a hydraulic transmission unit, so that pressure changes are transmitted in a correlating manner but not one-to-one. If the construction machine now changes its direction of travel, for example by reversing the delivery direction of the travel pump 9 in the travel drive hydraulic circuit 10 (when changing from forward travel to reverse travel), the high-pressure side and the low-pressure side in the travel drive hydraulic circuit also change, which, with the arrangement described above, without the interposition of sensors or other electronic control devices, has a direct effect on the hydraulic pretensioning pressure generated by the auxiliary tensioning device 22 on the at least one track tensioning hydraulic cylinder. Since the conventional arrangements of the guide wheel and the drive wheel in a track unit usually require an increased track tension during reverse travel, the auxiliary tensioning device 22 is therefore ideally connected to that line section of the travel drive hydraulic circuit which is the high-pressure side of the travel drive hydraulic circuit 10 between the travel pump 9 and the drive motor 11 during reverse travel.
[0039] A particular advantage of the arrangement described above now is that the transmission of the pressure changes from the travel drive hydraulic circuit has practically no effect on the damping characteristic obtained via the compression spring 23. The change in the pretension or the pretensioning pressure in the line system to the at least one track tensioning hydraulic cylinder 17 will not or only minimally affect the compression position of the compression spring 23. The track tension generated via the track tensioning apparatus 15 is thus essentially decoupled from the spring travel of the compression spring 23. As a result, even with greatly increased track tension, optimum damping properties of the damping device 21 are still possible, enabling particularly reliable operation. This is illustrated in FIG. 4, which shows the dependence of the track tension KS on the spring travel FW, or the current spring compression position of the compression spring 23, compared to the prior art arrangements used so far. Curves A (spring compressor) and B (diaphragm accumulator) are assigned to the prior art and curve C to the arrangement according to the invention as shown, for example, in the embodiment example according to FIGS. 2 and 3. D indicates the optimum track tension (constant pretension). It can be seen that the arrangement described above allows an almost complete decoupling of the spring travel from the track tension.
[0040] Another essential advantage of the described arrangement is that a central damping device 21 can be provided for multiple track units. For example, several track tensioning hydraulic cylinders 17 (for example four of a total of four track units, or ideally all track units of the construction machine 1) can be simultaneously connected to said one damping device 21 and damped. This is illustrated in more detail, for example, in FIG. 8.
[0041] In the case of multiple track tensioning hydraulic cylinders at the same time, the connection of the damping device 21 to the respective track tensioning hydraulic cylinder may be made exclusively via the auxiliary tensioning connection line 27 instead of, for example, mechanical elements such as bearings. The damping device 21 can thus be arranged far away from the respective track unit. An arrangement in the dirty area of the track unit is not necessary.
[0042] FIG. 5 illustrates a method according to the invention for operating a construction machine as described above in the form of a flow chart. Step 29 comprises initially pretensioning a track of a track unit running around a drive wheel and a guide wheel with the aid of a track tensioning hydraulic cylinder with an initial pretensioning pressure, which is connected to a hydraulic pretensioning source. This can be done, for example, when starting the drive motor of the construction machine 1. The construction machine 1 does not move at this point. Step 30 now comprises damping pressure peaks occurring inside the track tensioning hydraulic cylinder with the aid of a compression spring of a damping device, for example as described above. This is done in particular during traveling operation of the construction machine. Independently of step 30, step 31 further comprises changing the initial pretensioning pressure towards a pretensioning pressure inside the track tensioning hydraulic cylinder correlating with a change in the drive pressure using an auxiliary tensioning device acting in dependence on the drive pressure in the travel drive hydraulic circuit.
[0043] FIGS. 6 and 7 schematically show examples of further construction machines, in particular road construction machines, for which a damping device of the type described above is suitable, and reference is made to the above discussion for the further details of the damping device. FIG. 6 shows a road paver, and FIG. 7 shows a feeder.
[0044] FIG. 8 shows an embodiment example which constitutes an alternative to the detail of the hydraulic circuit diagram of FIG. 3, and reference is essentially made to the above discussion, in particular of FIG. 3, with regard to the structure and the mode of operation. The main difference here is the simultaneous connection of the travel drive connection line 28 to multiple drive motors 11, or their hydraulic circuits. Specifically, each of the drive wheels 12 (not shown in FIG. 8) of the tracked vehicle 1 has its own drive motor 11. The provided drive motors 11 (in this case four) are connected in parallel and integrated into a common hydraulic circuit formed by the travel pump 9. Pressure changes are thus evenly distributed to all four of the provided track tensioning hydraulic cylinders, i.e. to all four provided track units of the tracked vehicle 1, in the entire travel drive hydraulic circuit. Furthermore, in contrast to the embodiment example of FIG. 3, there is also an adjustable pressure relief valve 32 which branches off from the auxiliary tensioning connection line 27 towards the fluid reservoir. With the aid of this valve 32, it is possible to set an adjustable upper pressure limit in the hydraulic tensioning line 18, for example to prevent excessive track tension.
[0045] FIGS. 9A to 9D illustrate alternative configurations of the spring tensioning cylinder of the auxiliary tensioning device 25 of the damping device 21. FIG. 9A shows the auxiliary tensioning device as used in FIGS. 3 and 8. It can further be seen that the spring 23 (compression spring) arranged on the piston rod side is arranged in an interior space that is ventilated to the outside environment. In the embodiment example according to FIG. 9B, on the other hand, the spring 23, which is again configured as a compression spring and is arranged on the piston side, is located in the hydraulic fluid towards the track tensioning hydraulic cylinder 17. The variants according to FIGS. 9C and 9D, on the other hand, relate to embodiments in which the spring 23 is configured as an extension spring. The spring 23 is in each case arranged on the piston side. In the embodiment example according to FIG. 9C, the spring 23 is again arranged in the hydraulic fluid, whereas in the embodiment example according to FIG. 9D, there is a separate interior space, sealed to the hydraulic piston 26 and ventilated to the outside environment, in which the spring 23 is positioned.
[0046] FIG. 10 shows an embodiment example of a so-called delta unit according to the invention. In this regard, reference is essentially made to the above discussion of FIG. 2. The difference now is that the drive wheel 12 is arranged opposite two guide wheels 14 which are offset downwards in vertical direction, the drive wheel 12 being located in horizontal direction between the two guide wheels 14. Provision may be made for each of the two guide wheels 14, or only one of them, to have its own track tensioning hydraulic cylinder 17.
[0047] The graph of FIG. 11 shows the curves of the changes of the travel drive hydraulic pressure in the travel drive hydraulic circuit 10, or in the travel drive connection line 28 (curve II: i.e. when the high-pressure side is on this side of the hydraulic circuit between the pump and the motor during reverse travel), the pressure curve in that part of the hydraulic circuit between the pump and the motor that has no connection to the travel drive connection line 28 and is the high-pressure side during forward travel (curve I), and the resulting pressure changes in the auxiliary tensioning connection line 27, or the track tensioning hydraulic cylinders 17 (curve III). Thus the change of the initial pretensioning pressure depending on the drive pressure is shown. FIG. 11 illustrates that with the auxiliary tensioning device 22 of the damping device 21, a hydraulic pressure transmission occurs such that large pressure changes in the travel drive hydraulic circuit (curve II) are translated into correlating smaller pressure changes of the pretensioning pressure currently existing at the track tensioning hydraulic cylinders 17 (curve III). In the present case, the transmission ratio is approx. 3:1. FIG. 11 further shows a change of the direction of travel from forward travel (phase P1) to reverse travel (phase P2) as a function of time t. As can be seen, the travel drive connection line 28 is connected to the travel drive hydraulic circuit such that it is connected to the high-pressure side of the travel drive hydraulic circuit during reverse travel. This ensures that the tensioning pressure built up by the auxiliary tensioning hydraulic cylinder 25 at the track tensioning hydraulic cylinders 17 during reverse travel is significantly higher than during forward travel (phase I).
[0048] FIGS. 12A to 12E finally show further tracked vehicles which are particularly suitable for the use of the damping device 21 according to the invention with auxiliary tensioning device 22 as described above. FIG. 12A shows an excavator, FIG. 12B shows a dozer or tracked loader, FIG. 12C shows a snow groomer, FIG. 12D shows an agricultural harvesting vehicle, more particularly a combine harvester, and FIG. 12E shows a hauler, in particular for use in agriculture and/or forestry. All vehicles shown in FIGS. 12A to 12E have in common that they have a drive motor, a travel pump and at least one track unit with a damping device 21 according to the invention with an auxiliary tensioning device 22. Differences consist in particular in the respective work tool provided and the field of application.
