Track tensioning system of a closed-loop track chain and method thereof

Abstract

A track tensioning system (50) and a method for adjustably controlling tension in a closed-loop track chain (71) entrained about an idler wheel (72) of a track undercarriage (70) comprising a first hydraulic actuator (30) connected with the idler wheel (72) and comprising a first hydraulic cylinder (31) with a variable-volume first interior chamber (34); a second hydraulic actuator (40) comprising a second hydraulic cylinder (45) comprising non-communicating balancing interior chamber (46) and receiving interior chamber (47); a source (20) of pressurized hydraulic fluid coupled / uncoupled to / from a first supply flow line (24) in communication with the first hydraulic actuator (30), the source (20) being configured to be coupled / uncoupled to / from a second supply flow line (25) in communication with the receiving interior chamber (47), the first supply flow line (24) communicates with a bridge flow line (21) connecting the first interior chamber (34) with the balancing interior chamber (46).

Description

[0001] Track tensioning system of a closed-loop track chain and method thereof

[0002] The present invention concerns a system and a method for adjusting the tension of a closed-loop track chain of a tracked undercarriage.

[0003] Tracked undercarriages of tracked vehicles, such as earthmoving machines, mining machines, demolition machines and the like, typically comprise a pair of chain assemblies spaced apart and arranged parallel to each other and configured to receive a drive torque and transfer it to the ground.

[0004] The chain assembly is an endless or closed-loop chain assembly comprising a plurality of articulated interconnected links and shoes mounted to the chain for engagement with the ground. The closed-loop chain is entrained on an idler wheel (idler) and on a drive sprocket for driving the track chain. Between the drive sprocket and the idler, the undercarriage comprises a plurality of rollers configured to guide the chain during its motion.

[0005] Since during operation of the vehicle the track chain should be maintained at a proper level of tension, the idler is usually connected to a tensioner that acts on the idler to apply a tension to the chain. If the chain too loosely tensioned, the chain becomes slack and sags excessively. As a result, the chain may slip out of the guide of the undercarriage components (rollers, drive sprocket and / or idler), thereby causing damage to the undercarriage. A chain too tightly tensioned can significantly increase the wear of parts of the links, e.g. pins and bushings, and requires a higher drive power for the movement of the vehicle and an associated increase in fuel consumption.

[0006] The tension of the chain is often represented as a degree of sag of the chain.

[0007] Figure 1 is a side view, partly in cross-section, of an exemplary track undercarriage 10. Figure 1A is an enlargement of a portion of FIG. 1 to show some details. The track undercarriage 10 comprises a closed-loop track chain 16 comprising a plurality of articulated interconnected links 11 and shoes 18 secured to track links, for example by bolts and nuts (not shown). The closed-loop chain 16 is entrained on an idler wheel 14 and on a drive sprocket 15 for the driving of the undercarriage. Between the drive sprocket and the idler wheel 14, the undercarriage 10 comprises a plurality of lower rollers 12 configured to guide the chain during movement and one or two carrier rollers 17. The track chain 16 wraps around the drive sprocket 15, the carrier rollers 17, the idler wheel 14, and then under the lower rollers 12 where the track chain contacts the ground. An undercarriage rigid frame 13, typically made of steel, supports the drive sprocket 15 and the idler wheel 14. The frame 13 is partly shown in a cross-sectional view to show some elements described here below. The lower rollers 12 and the upper rollers 17 are mechanically coupled to the undercarriage frame 13. The idler wheel 14 is configured to rotate passively during operation of the undercarriage 10. The idler wheel 14 has a sliding attachment mechanism to the frame 13 through a slidable element 14a, in particular a shaft moving with the rotation of the idler wheel.

[0008] In most cases, for a proper functioning of the track undercarriage, the chain should exhibit a certain amount of sag. A correct or required sag is often a value comprised within a relatively narrow range of values, although the relevant values may vary for different track-type machines and, generally, each machine has a specific range of values.

[0009] Conventionally, adjustments of the tension of the chain employs a tensioning system 9 using a grease-filled hydraulic cylinder 19, which is fastened on one side to a bulkhead 8 of the undercarriage frame 13 and on the opposite side to the idler wheel 14 in particular to the slidable element 14a. Typically, the grease-filled cylinder 19 has a piston with a screwed-in grease nipple 7 which protrudes from the bulkhead 8. A device for overload protection of the system is often used, such as a coil spring 9.

[0010] From time to time, the chain must be retightened to take into account the wear. In addition, when the chain needs to be replaced, the grease must be drained from the hydraulic cylinder 19 by unscrewing the grease nipple 7. The grease drained out must be then removed manually, often from areas with difficult access, thus making the operations particularly burdensome.

[0011] Independently of whether the hydraulic cylinder uses grease or hydraulic oil, the chain is typically tensioned by increasing the fluid volume in the hydraulic cylinder. The chain tension may change with the ground conditions, e.g. level of contamination of the soil or with the speed of the vehicle. The chain tension is usually controlled either by measuring the sag of the chain or by measuring the pressure inside the tensioning cylinder. Measuring the sag and in particular adjusting the sag to a correct working point typically requires the manual intervention of a skilled technician.

[0012] The Applicant has noted that a control of the working point of the hydraulic cylinder as a function of pressure inside the cylinder, which takes into account the variability of the operating conditions, often needs complex control systems employing a large number of sensors and, in some cases, an ideal chain pre-tension under any operating condition remains difficult to achieve.

[0013] The Applicant has perceived that a control of the stroke of the tension hydraulic cylinder for the adjustment of the tension (instead of a control of the working pressure) of the hydraulic cylinder would allow to generate a certain chain pre-tension while minimizing the operations that require an active control of the system.

[0014] The Applicant has realized that the provision of an additional hydraulic actuator in fluid communication with the tension hydraulic cylinder actuator and having two different surface areas may allow an adjustment of the idler wheel position corresponding to an associated chain preload. According to an aspect of the present invention, a track tensioning system for adjustably controlling tension in a closed-loop track chain entrained about an idler wheel of a track undercarriage is provided. The system comprises:

[0015] - a first hydraulic actuator operatively connected, at a first side, with the idler wheel of the track undercarriage and comprising a first hydraulic cylinder comprising a first interior chamber of variable volume, and

[0016] - a second hydraulic actuator comprising a second hydraulic cylinder comprising a balancing interior chamber having a first cross sectional area and a receiving interior chamber having a second cross sectional area larger than the first cross sectional area, the balancing interior chamber and the receiving interior chamber being non-communicating contiguous chambers.

[0017] Preferably, the tension controlling system further comprises a source of pressurized hydraulic fluid configured to be fluidly coupled and uncoupled to / from a first supply flow line in fluid communication with the first hydraulic actuator, wherein the source is further configured to be fluidly coupled and uncoupled to / from a second supply flow line in fluid communication with the receiving interior chamber of the second hydraulic actuator, wherein the first supply flow line is in fluid communication with a bridge flow line fluidly connecting the first interior chamber with the balancing interior chamber.

[0018] According to a main feature of the disclosed system, it is possible to set the sag of the chain without the need of an active control of the tension of the first hydraulic actuator.

[0019] In particular, as the pressure decreases in the receiving chamber, the second piston moves in a direction where the pressure is smaller, thus towards the receiving chamber until the balancing chamber is filled with pressurised hydraulic fluid.

[0020] Preferably, the first hydraulic actuator comprises a first piston. Preferably, the first cylinder and the first piston are configured to move reciprocally to define the first interior chamber.

[0021] Preferably, the movement of the first piston within the first hydraulic cylinder is in a first main direction corresponding to the direction of movement of the idler wheel.

[0022] Preferably, the second hydraulic actuator comprises a second piston being slideably movable within the balancing chamber and the receiving chamber.

[0023] Preferably, the second hydraulic cylinder extends in a second longitudinal axis defining a working direction of the second piston, which makes a linear movement across the balancing and the receiving chamber.

[0024] Preferably, the second piston has, at one side, a first surface area and, at an opposite side, a second surface area. The first surface area of the second piston corresponds to the cross sectional area of the balancing chamber and the second surface area corresponds to the cross sectional area of the receiving chamber.

[0025] Preferably, the first hydraulic actuator comprises a first inlet-outlet port in fluid communication with the first interior chamber.

[0026] Preferably, the second hydraulic actuator comprises a second inlet-outlet port in fluid communication with the receiving chamber and a third inletoutlet port in fluid communication with the balancing chamber.

[0027] Preferably, the system for adjustably controlling tension is configured to operate in a first operative condition and in a second operative condition. Preferably, in the first operative condition, the first supply flow line and the second supply flow line are fluidly coupled to the source, the first supply flow line is fluidly connected to the first interior chamber to receive hydraulic fluid and the second supply flow line is fluidly connected to the receiving interior chamber to receive hydraulic fluid.

[0028] Preferably, the second operative condition is subsequent to the first operative condition.

[0029] Preferably, in the second operative condition, each of the first supply flow line and the second supply flow line are uncoupled from the source and the receiving chamber is connected to a discharge flow line to discharge the hydraulic fluid received during the first operative condition.

[0030] In the second operative condition, once there is no pressure in the receiving chamber, namely the receiving chamber is empty, the pressure built-up in the first hydraulic actuator causes the second hydraulic actuator to move in a direction towards a chamber with larger surface area, thus towards the receiving chamber. In particular, if the fluid pressure is released from the receiving chamber by discharging the fluid, the piston moves in the direction where there is no longer pressure exerted.

[0031] Preferably, both the receiving chamber and the balancing chamber of the second hydraulic cylinder are provided with a hydraulic fluid substantially at the same pressure, when the system is in the first operative condition. Preferably, in the second operative condition, the first supply flow line is closed upstream of the bridge flow line.

[0032] Preferably, the bridge flow line is fluidly connected to an exhaust line provided with an exhaust valve configured to move between an open position and a closed position.

[0033] Preferably, in both the first and the second operative conditions, the exhaust valve is in the closed position.

[0034] During maintenance of the undercarriage or in case of replacement of a new chain, the exhaust valve can be set in the open position in order to depressurize the track tensioning system.

[0035] Preferably, the system comprises a control valve device arranged to intercept the first and the second supply flow lines. The control valve device is configured to be selectively operated to move between two operative positions: a first operative position when the system is in the first operative condition and a second operative position when the system is in the second operative condition. Preferably, in the first operative position, the control valve device is configured to be connected to the first supply flow line to enable a fluid communication between the source of hydraulic fluid and the first interior chamber and to be connected to the second supply flow line to enable a fluid communication between the source and the receiving interior chamber.

[0036] Preferably, in the second operative position, the control valve device is configured to: disconnect the first supply flow line and the second supply flow line from the source so as to halt the flow of pressurized oil to the first interior chamber and to the receiving interior chamber, and connect the receiving interior chamber to the discharge flow line to empty the receiving chamber.

[0037] In some embodiments, the control valve device is a multiway directional valve.

[0038] An overload protection device may be provided to prevent the components from being overloaded if the chain tension is too high.

[0039] In an embodiment, the overload protection device comprises a coil spring axially aligned with the first hydraulic actuator and being operatively connected at a one side with the idler wheel.

[0040] In another embodiment, the overload protection device comprises a pressure relief valve arranged in an exhaust flow line fluidly connected to the first supply flow line and configured to change the state from a closed state to an open state, the open state being triggered by an internal pressure in the first supply flow line or in the second supply flow line higher than a threshold pressure value.

[0041] In a further embodiment, the overload protection device comprises a bladder accumulator comprising a cylinder having an inner cavity, the first hydraulic cylinder being configured to be slideably mounted within the inner cavity of the cylinder and a bladder comprising a fluid section apt to contain a hydraulic fluid and a gas section apt to contain pressurized gas, wherein the cylinder comprises an inlet-outlet port connected to the fluid section of the bladder through a connecting flow line.

[0042] Preferably, the second hydraulic actuator comprises a volume adjusting element configured to change the volume of the receiving chamber. According to a further aspect of the present invention, a method for adjusting the track tension of a closed-loop track chain entrained about an idler wheel of a track undercarriage is provided. The method comprises: providing a first hydraulic actuator operatively connected, at a first side, with an idler wheel of a track undercarriage and comprising a first hydraulic cylinder comprising a first interior chamber of variable volume, and providing a second hydraulic actuator comprising a second hydraulic cylinder comprising a balancing interior chamber having a first cross- sectional area and a receiving interior chamber having a second cross- sectional area larger than the first cross-sectional area, the balancing interior chamber and the receiving interior chamber being noncommunicating contiguous chambers, the balancing interior chamber being in fluid communication with the first interior chamber via a bridge flow line,

[0043] Preferably, the method operates in a first operative condition and in a second operative condition.

[0044] Preferably, in the first operative condition, the method comprises supplying pressurized hydraulic fluid to the first interior chamber via a first supply flow line and to the receiving chamber via a second supply flow line.

[0045] Preferably, in the second operative condition, the method comprises interrupting the flow of pressurized hydraulic fluid through the first and second supply flow lines, and discharging the fluid flow from the receiving chamber so as to enable a transfer of the hydraulic fluid from the first interior chamber to the balancing chamber.

[0046] Preferably, in the second operative condition, upon interrupting the flow of pressurized hydraulic fluid through the first and second supply flow lines, the method comprises closing the first supply flow line upstream of the bridge flow line.

[0047] Preferably, in the first operative condition, supplying pressurized hydraulic fluid to the first interior chamber via a first supply flow line and to the receiving chamber via a second supply flow line comprises coupling the first supply flow line and the second supply flow line to a source of pressurized hydraulic fluid. Preferably, the method further comprises, when in the second operative condition, discharging the hydraulic fluid flow from the receiving chamber comprises uncoupling the second supply flow line from a source of pressurized hydraulic fluid and coupling the second supply flow line to a discharge flow line.

[0048] Brief description of the drawings

[0049] The present disclosure will be now described more in detail hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the disclosure are shown. Drawings illustrating the embodiments are not-to-scale schematic representations.

[0050] For the purpose of the present description and of the appended claims, all ranges include the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein.

[0051] FIG. 1 is a side view, partly in cross-section, of an exemplary track undercarriage with some parts shown in cross-sectional view.

[0052] FIG. 1A is an enlargement of a portion of FIG. 1 to show some details.

[0053] FIG. 2 is a side view of a track undercarriage to schematically illustrate a tightly tensioned chain.

[0054] FIG. 3 is a side view the track undercarriage of FIG. 2 to schematically illustrate the presence of a sag in the chain.

[0055] FIG. 4 shows a front view of a track tensioning system according to an embodiment consistent with the present invention in a first operative condition. Some parts of the system are shown in cross-sectional view.

[0056] FIG. 4A is an enlarged view of FIG. 4 showing in some more details the second hydraulic actuator and the control valve device.

[0057] FIG. 5 shows the track tensioning system of FIG. 4 in a second operative condition.

[0058] FIG.5A is an enlarged view of FIG. 5 showing in some more details the second hydraulic actuator and the control valve device.

[0059] FIG. 6 shows a front view of a track tensioning system according to a further embodiment of the invention.

[0060] FIG. 7 illustrates the track tensioning system of Figs. 4 and 5, in a configuration adapted to replace the undercarriage chain. FIG. 8 illustrates a track tensioning system according to a further embodiment of the invention.

[0061] FIG. 9 illustrates a track tensioning system according to a further embodiment of the invention.

[0062] In general, the same reference numeral will be used for possible variant embodiments of similar elements.

[0063] Detailed description

[0064] For a proper functioning of the track undercarriage, typically, the chain should exhibit a certain amount of sag. The required sag is often a value comprised within a relatively narrow range of values, although the relevant values may vary for different track-type machines and, generally, each machine has a specific nominal value and a tolerance. Sag is often measured at the center of the upper side of the undercarriage.

[0065] Figure 2 shows a track undercarriage 70, which typically comprises the elements described with reference to Fig. 1, in particular a closed-loop chain 71 and an idler wheel 72. The sag of the chain is taken at the center of an upper side portion of the chain 71. The upper side portion is substantially straight and roughly corresponding to a chain section between the two arrows 3. In the example illustrated in Fig. 2, the track chain 71 is shown tightly tensioned, i.e. no sag, as represented by straight line 6.

[0066] Figure 3 shows the track undercarriage 70 of Fig. 2 in a condition where the chain 71 exhibits a sag 5 (indicated by the vertical arrows), which is defined with respect the tightly tensioned chain 6 of Fig. 2 over a length of the upper side portion of chain 71. For example, a suitable range of values for the chain sag of an undercarriage may be 2-3 cm over a length of the chain of 1.0-1.5 m. It is however noted that suitable values of the sag may depend on the different types of undercarriage or vehicles.

[0067] Figure 4 illustrates a track tensioning system 50 for adjusting the tension of the undercarriage chain, according to an embodiment of the present invention. The track tensioning system 50 comprises a first hydraulic actuator 30 operatively connected, at a first side, with an idler wheel 72 of an undercarriage 70. At an opposite second side, the first hydraulic actuator 30 is connected integrally to a frame of the undercarriage, such as with a frame element 51, which can be a bulkhead or a steel beam. In ways per se known, the idler wheel 72 is rotationally connected to the first hydraulic actuator 30 via a coupling element 39 (not shown in detail), such as an articulated arm or a yoke. For example, an end of the coupling element 39 is operatively coupled to the first hydraulic actuator 30. Both the coupling element 39 and the first hydraulic actuator 30 are connected to one another at a rigid connecting element 56.

[0068] The first hydraulic actuator 30 comprises a first hydraulic cylinder 31. The first hydraulic cylinder 31 extends in a first main extension axis along a first longitudinal direction X. The first longitudinal direction X corresponds to a main direction of movement of the idler wheel 72.

[0069] The first hydraulic cylinder is configured to house a first piston 32 slideably mounted within the first cylinder 31, the first cylinder 31 and the first piston 32 being configured to move reciprocally in the first longitudinal direction X or in a direction parallel to the same. The cylinder 31 and the first piston 32 define a first interior chamber 34 of variable volume. The volume of the interior chamber 34 varies with the relative movement of the first cylinder 31 and the first piston 32.

[0070] In embodiments, the first main direction X is the working direction of the reciprocal movement of the first piston 32 and the first cylinder 31 of the first hydraulic actuator.

[0071] The first hydraulic actuator 30 has a first inlet-outlet port 33 communicating with the first interior chamber 34.

[0072] In an embodiment, the first hydraulic cylinder 31 is a single-acting cylinder with the first interior chamber 34 having a uniform cross sectional area.

[0073] In the non-limiting example of the figures, the first piston 32 is a piston rod and the first hydraulic cylinder 31 is configured to move back and forth in the first longitudinal direction X through the movement of a telescopic linear actuator 57.

[0074] In the embodiment of Fig. 4, a spring 55 is fastened to the connecting element 56 of the idler unit 72 to act as an overload protection device, as discussed in more detail in the following.

[0075] The first inlet-outlet port 33 of the first cylinder 30 is formed within the piston rod 32 to be in fluid communication with the first interior chamber 34. The frame element 51 may be provided with guideways (not shown) to allow a linear movement of first cylinder 31 in the X direction. The track tensioning system 50 comprises a second hydraulic actuator 40. The second hydraulic actuator 40 comprises a second hydraulic cylinder 45 extending in a second main extension axis.

[0076] As described more in detail in the following, the second hydraulic actuator 40 is in fluid communication with the first hydraulic actuator 30.

[0077] The second hydraulic cylinder 45 comprises two chambers, a balancing interior chamber 46 and a receiving interior chamber 47. Within the present description and claims, the interior chambers of the second hydraulic cylinder 45 will be referred also to as "balancing chamber" and "receiving chamber".

[0078] The second hydraulic cylinder 45 comprises a second piston 48. The second main extension axis is defined by the working direction of the second piston 48, in particular by the linear movement of the second piston 48 across the balancing and receiving chambers 46, 47.

[0079] The second piston 48 is slideably movable therein in two opposite directions 44, 49 (indicated in Figs. 4A and 5A) along the second main extension axis of the second hydraulic cylinder 45.

[0080] In the non-limiting example of the figures, the second main extension axis is a direction parallel to a second longitudinal direction Z transversal, e.g. perpendicular, to the first longitudinal direction X of the first hydraulic actuator 30. However, this configuration is not intended to be limitative, as the second longitudinal direction may extend in any direction, including a direction parallel to the X direction.

[0081] The balancing chamber 46 and the receiving chamber 47 have different cross sectional areas, the cross sectional area of each chamber being defined in a direction perpendicular to the second main extension axis of the second hydraulic cylinder 45. The balancing chamber 46 has a first cross sectional area and the receiving chamber has a second cross sectional area, the first cross sectional area being smaller than the second cross sectional area.

[0082] The second piston 48 has two surface areas on its opposite sides with respect to the working direction of the second hydraulic cylinder (Z): a first surface area Al having the first cross sectional area of the balancing chamber 46 and a second surface area A2 having the second cross sectional area of the receiving chamber 47 (indicated in Fig. 5A). In particular, the first surface area Al correspond to the cross section of the balancing chamber 48 and the second surface area A2 corresponds to the cross section of the receiving chamber 47. The second surface area A2 is larger than the first surface area Al.

[0083] In the embodiment of the figures, the second piston 48 has an inverted T-shape in section.

[0084] In view of the different and opposite surface areas with respect the working direction of the second piston 48, the second piston 48 prevents the fluid communication between the two chambers 46, 47.

[0085] Therefore, the balancing chamber and the receiving chamber 46, 47 are non-communicating contiguous chambers.

[0086] The second cylinder 45 comprises a second inlet-outlet port 42 in fluid communication with the receiving chamber 47 and a third inlet-outlet port 43 in fluid communication with the balancing chamber 46.

[0087] In the example of the figures, the second inlet-outlet port 42 is positioned opposite to the third inlet-outlet port 43 with respect to the second main extension axis of the second hydraulic cylinder 45. However, the illustrated configuration should not be considered limitative as the second port 42 and / or third port 43 may be differently arranged, for example in a respective section of a lateral wall of the second cylinder 45 corresponding to the balancing chamber or to the receiving chamber.

[0088] The track tensioning system 50 comprises a source 20 of pressurized hydraulic fluid, e.g. pressurized hydraulic oil, configured to be in fluid communication with both the first and the second hydraulic actuators 30, 40. The source 20 comprises a container 29 for containing the hydraulic fluid and a hydraulic pump 22 configured to pump the hydraulic fluid from the container 29. For example, the hydraulic fluid is oil at a pressure of about 200 bar.

[0089] In an example, the source 20 is a hydraulic system of a tracked vehicle (not shown) comprising the track undercarriage 70.

[0090] The source 20 of pressurized hydraulic fluid is configured to be fluidly coupled and uncoupled to / from a first supply flow line 24 and to / from a second supply flow line 25.

[0091] In the embodiment illustrated in the figures, a main supply line 23 is fluidly coupled with the source 20, in particular with hydraulic pump 22, the main supply line 23 being fluidly coupled to the first and second supply flow lines 24, 25. In particular, each of the first supply flow line 24 and the second supply flow line 25 is configured to be in fluid communication with the source 20 through the main supply line 23. In particular, the main supply line 23 is configured to be fluidly uncoupled to / from the first supply flow line 24 and to / from the second supply flow line 25.

[0092] Figure 4 shows the track tensioning system 50 in a first operative condition. In the first operative condition, the hydraulic pump 22 and the source 20 provides the pressurized fluid to each of the first and second hydraulic actuator 30, 40. In particular, the receiving chamber 47 of larger cross-sectional area A2 of the second hydraulic cylinder 45 and the first interior chamber 34 of the first hydraulic cylinder 30 are supplied with pressurized fluid through the respective and separate supply flow lines 24, 25.

[0093] The first supply flow line 24 is configured to connect the source 20 with the first hydraulic actuator 30, in particular with the first interior chamber 34. Specifically, the first supply flow line 24 connects the source 20 to the first fluid inlet-outlet port 33 of the first hydraulic cylinder 30.

[0094] The second supply flow line 25 is configured to fluidly connect the receiving chamber 47 of the second hydraulic cylinder 40 to the source 20. Specifically, the second supply flow line 25 is configured to connect the source 20 to the second inlet-outlet port 42 of the receiving chamber 47.

[0095] The first hydraulic cylinder 30 is fluidly connected with the balancing chamber 46 of smaller cross sectional area Al of the second hydraulic cylinder 45. To this end, a bridge flow line 21 fluidly connects the balancing chamber 46 with the first chamber 34 of the first cylinder 31. In particular, the bridge flow line 21 connects the first inlet / outlet port 33 of the first chamber 34 to the third inlet-outlet port 43 of the balancing chamber 46.

[0096] In the example of the figures, the bridge fluid line 21 connects the third inlet / outlet port 43 of the balancing chamber 46 to the first supply flow line 24, in turn connected to the first inlet / outlet port 33. In particular, the bridge flow line 21 is in fluid communication with the first supply flow line 24.

[0097] In this way, the receiving chamber 47 of larger cross-sectional area A2 of the second hydraulic cylinder 45 and the first interior chamber 34 of the first cylinder 30 are supplied with pressurized fluid through separate supply lines.

[0098] In the first operative condition shown in Fig. 4, a first fluid circuit of pressurized oil is formed, the first fluid circuit comprising the source 20 fluidly connected to the first supply flow line 24 and thus to the bridge flow line 21.

[0099] A second fluid circuit of pressurized oil includes the source 20 connected to the second supply flow line 25, which is in turn connected to the receiving chamber 47. Therefore, the second fluid circuit is a separate non-communicating fluid circuit from the first fluid circuit.

[0100] The bridge flow line 21 is fluidly connected to an exhaust flow line 27 provided with an exhaust valve 28 configured to move between an open position and a closed position. In the first operative condition of Fig. 4, the exhaust valve 28 is in a closed position.

[0101] The hydraulic oil flowing through the supply flow lines 24, 25 is at a pressure that approximately corresponds to the pressure being delivered by pump 22. In particular, the first supply flow line 24 and the second supply flow line 25 are at about the same pressure. The bridge flow line 21 connected to the first chamber 34, is also at about the same pressure. By pumping the pressurized oil to the first chamber 34, the variable volume of the first interior chamber 34 of the first hydraulic actuator 30 increases.

[0102] Due to the different surface areas of the receiving chamber 47 and the balancing chamber 46, the pressurized oil from the second supply flow line 25 moves the second piston 48 of surface area A2 in the direction of arrow 44 (indicated in Fig. 4A), namely towards the balancing chamber 46 of smaller surface area Al so as to fill the receiving chamber 47 with hydraulic oil, which is then pressed against the second piston 48 moving towards the contiguous balancing chamber 46.

[0103] In this first operative condition, the balancing chamber 46 is fluidly connected to the first hydraulic cylinder 31. However, since the first surface area Al of the balancing chamber 46 is smaller than the second surface area A2 of the receiving chamber 47, no fluid enters in the balancing chamber 46.

[0104] Once the receiving chamber 47 is filled, the first chamber 34 of the first hydraulic cylinder 31 reaches a maximum volume allowed by the track adjusting system. The value of the maximum volume of the first cylinder 31 is set to correspond to a tightly tensioned chain (i.e. without slack) at any level of tension caused by the wear, as exemplified in Fig. 2.

[0105] Arrows 52 of Fig. 4 schematically illustrate the direction of the tension force applied to the idler wheel 72, when the system is in the first operative condition.

[0106] The operations to set the track tensioning system 50 at the first operative condition may take place relatively fast, such as within some seconds, corresponding approximately to the time needed to fill the receiving chamber 47 with hydraulic oil.

[0107] Figure 5 illustrates the track tensioning system 50 of Fig. 4 in a second operative condition subsequent to the first operative condition. In the second operative condition, the chain tension is at least partially released for the sag adjustment.

[0108] In the second operative condition, the supply of pressurized hydraulic oil into the first and second hydraulic actuators 30, 40 is interrupted. The first supply flow line 24 is closed upstream of the first hydraulic cylinder 31, in particular upstream of both the first inlet / outlet port 33 and the third inlet / outlet port 43.

[0109] During the second operative condition, the exhaust valve 28 remains closed.

[0110] Once the supply of hydraulic oil is interrupted, the receiving chamber 47 is opened so that the hydraulic oil can flow out from the chamber with no pressure. In particular, the oil in the receiving chamber 47 flows out from the second inlet-outlet port 42 to the oil container 29. In the example illustrated in the figure, the oil flowing out from the receiving chamber 47 is discharged back to the oil container 29 through a discharge flow line 36 in fluid communication the second inlet-outlet port 42 of the second cylinder 45. The discharge flow line 36 is connected to a main discharge line 26.

[0111] Once there is no pressure in the receiving chamber 47, the pressure built- up in the first cylinder 31 causes the second piston 48 of the second cylinder 45 to move in a direction towards the receiving chamber 47 with larger surface area A2, as represented by arrow 49 (Figs. 5 and 5A).

[0112] Due to the fact that the balancing chamber 46 has a direct fluid connection with the first cylinder 31, an oil transfer takes place from the first chamber 34 to the balancing chamber 46. During this transfer, the fluid volume in the first chamber 34 decreases while the fluid volume in the balancing chamber 46 increases until the balancing chamber 46 is filled with oil. At this point, the first chamber 34 of the first hydraulic cylinder 30 has a fluid volume, which is herein referred to as a target fluid volume.

[0113] This mechanism provides for a decrease of the fluid volume in the first chamber 34 of the first hydraulic actuator 30 operatively connected to the idler wheel 72. The target fluid volume is generally smaller than the fluid volume of the first chamber 34 at the end of the first operating condition.

[0114] Due to the presence of a chain tension that takes into account also the chain weight, the hydraulic cylinder 30 and the idler 72 are pushed back in a direction indicated in Fig. 5 by arrow 53 as far as the displaced fluid volume within the first chamber 34 allows it. The target fluid volume corresponds to a desired amount of chain slack.

[0115] In particular, the chain slack corresponding to the target fluid volume can be set to be the same after each run of the second operative condition following the first operative condition. This procedure can be carried out with no adjustments of the first or of the second hydraulic actuator 30, 40 being necessary.

[0116] The degree of sag of the chain is related to the volume of the balancing chamber 46 at the end of the second operative condition, and thus to the position of the second piston 48 within the balancing chamber 46. The larger the volume of hydraulic oil in the balancing chamber 46, the larger the degree of sag of the chain.

[0117] The target fluid volume of the hydraulic oil in the balancing chamber 46, when the tension adjusting system 50 is in the second operative condition, can either be a fixed volume or a variable volume, which can be set before operating the track tensioning system.

[0118] To this end and according to an embodiment, the second hydraulic actuator 40 comprises a volume adjusting element 38 (indicated in Figs. 4A and 5A) configured to change the volume of the receiving chamber 47 and thus also the volume of the balancing chamber 46. The volume adjusting element 38 can be a set screw, which is configured to adjust the maximum fluid volume of the receiving chamber 47. This can be achieved for example by adjusting the end position of the second surface area A2 of the second piston 48. Instead of a set screw, in order to change the fluid volume of the balancing chamber 46, a servomechanism controlled electronically by a servo drive (not shown in the figures) may be used.

[0119] Adjusting the volume of the balancing chamber 46 would result in an adjustment of the return stroke of the first hydraulic actuator 30 and thus of the sag of the chain.

[0120] In the embodiment of Figs. 4 and 5, the track tensioning system 50 comprises an overload protection device 54 to prevent overloading of the components of the track tensioning system if the chain tension is too high, e.g. above a certain threshold value. The overload protection device 54 comprises a coil spring 55 constrained at one end to the connecting element 56 and, at an opposite end, to frame element 51. The coil spring 55, which may be pre-loaded, is axially aligned with the first hydraulic actuator 30 (i.e. along the X-axis).

[0121] In an embodiment shown in the figures, the hydraulic circuit of the track tensioning system 50 uses a control valve device 58 configured to control the flow of the hydraulic oil to / from the first hydraulic cylinder 31 and to / from the second hydraulic cylinder 45.

[0122] The control valve device 58 is arranged upstream of the first and second hydraulic actuators 30, 40, specifically upstream of the inlet / outlet fluid ports 33, 42, 43 of the first and second hydraulic actuators 30, 40. The control valve device 58 is placed to intercept the first and second supply flow lines 24, 25.

[0123] The control valve device 58 is configured to be selectively operated to move between two operative positions: a first operative position in the first operative configuration and a second operative position in the second operative configuration.

[0124] In the first operative position, the control valve device 58 is configured to be connected with the first supply flow line 24 for enabling a fluid communication between the source 20 and the first hydraulic actuator 30 and to be connected with the second supply flow line 25 for enabling the fluid communication between the source 20 the second hydraulic actuator 40.

[0125] In particular, in the first operative position, the control valve device 58 is configured to connect the source 20 of pressurized hydraulic oil to the first chamber 34 of the first hydraulic cylinder 31 through the first supply flow line 24, and to connect the receiving chamber 47 of the second hydraulic cylinder 45 to the second supply flow line 25.

[0126] In the second operative position, the control valve device 58 is configured to disconnect both the first supply flow line 24 and the second supply flow line 25 from the source 20 so as to halt the flow of pressurized oil to the first and to the second hydraulic cylinders 31, 45, and is configured to connect the receiving chamber 47 to the discharge line 36.

[0127] Following the disconnection, the first chamber 34 keeps a fluid communication with the balancing chamber 46 through the bridge flow line 21.

[0128] As described in the foregoing, the presence of pressurized oil in the first supply flow line 24 and in the bridge flow line 21 combined with the discharge of the pressurized oil from the receiving chamber 47 allows a transfer of the oil from the first chamber 34 to the balancing chamber 46 until a target fluid volume in the first chamber 34 is reached.

[0129] In the embodiment shown in the figures, the control valve device 58 is a multiway valve configured to be selectively operated to move between the two operative positions. In the example of the figures, the control valve device 58 is a 5 / 2 way directional valve, such as a 5 / 2 ways solenoid valve, having three ports.

[0130] In ways known in the art, the control valve device 58 may be connected to an electronic control system (not shown) configured to electronically control the valve actuation, in particular to control the switching between the two operative positions. In other embodiments, the control valve device 58 can be operated in manually or mechanically to switch between the two operative positions.

[0131] In the first operative condition of the track tensioning system 50, the control valve device 58 is in the first operative position (Figs. 4 and 4A). The control valve device 58 is configured to be coupled with the first and second flow supply lines 24, 25 directed upstream with respect to the source 20. In particular, first and second ports 01, 02 (indicated in Figs. 4A and 5A) of the control valve device 58 allow the passage of pressurized oil to be fed to the receiving chamber 47 of the second cylinder 45 and to the first chamber 34 of the first cylinder 31.

[0132] In the second operative condition of the track tensioning system 50, the multiway valve 58 moves to the second operative position in the direction of arrow 59 (Fig. 5A). In the second operative position, the control valve device 58 is configured to:

[0133] - disconnect the first and second supply lines 24, 25 from the source 20 by disconnecting the supply lines from the first and second ports 01 and 02, and

[0134] - to couple the second supply line 25 to discharge flow line 36, via a third port (03) directed downstream with respect to the control valve device 58.

[0135] In this way, in the second operative condition, the first supply line 24 is closed upstream of the control valve device 58 so as to keep a flow of hydraulic oil in the line and a fluid communication between the first chamber 34 and the balancing chamber 46 via the bridge flow line 21 connected to the first supply line 24.

[0136] The installation of a multiway valve and its connection with the flow lines of the hydraulic circuit may be implemented as a retrofit unit.

[0137] Figure 6 illustrates a track tensioning system 50a according to a further embodiment of the present invention. With respect to the previous embodiment of Figs. 4 and 5, the system 50a comprises a safety relief valve 63 as an additional overload protection mechanism to further reduce the risk of an overload of the chain or of other track components. Excessive chain tension may occur during machine operation, for example in case of the presence of jammed objects, such as stones or steel parts, in the drive mechanisms, e.g. the drive sprocket, idler or rollers when the machine is moving. The pressure relief valve 63 is configured to release the excess pressure from the first supply line 24 to the exhaust line 27.

[0138] The safety valve 63 is arranged on a flow line 27a connected to exhaust line 27. In a further embodiment (not shown in the figures), the safety valve 63 is arranged on the exhaust line 27.

[0139] In an example, the safety valve 63 is a pressure relief valve.

[0140] The pressure relief valve 63 is configured to change the state from a closed state to an open state in the event of an overload, i.e. if the chain tension is too high. The open state is triggered by an internal pressure in the flow lines higher than a predetermined threshold pressure value. If the pressure exceeds the threshold pressure value, pressure is released from the tensioning system by releasing oil from the flow lines until the pressure threshold value is reached. When the oil is released, the first actuator 30 and the idler wheel 72 are pushed in, thereby preventing the components of the chain assembly and of the steel frame from being overloaded.

[0141] Figure 7 illustrates the track tensioning system 50 described with reference to Figs. 4 and 5, in a configuration adapted for the replacement of the undercarriage chain. To replace the chain, the first hydraulic actuator 30 is placed in a fully retracted position. To this end, the exhaust valve 28 in the exhaust line 27 is opened in order to depressurize the track tensioning system 50. Any oil contained in the first chamber 34 of the first hydraulic cylinder 31 is discharged to the oil container 29. The idler wheel 72 moves backwards, the chain (not shown) loosens and it can then be replaced.

[0142] Preferably, the depressurization is carried out with the track tensioning system 50 in the second operative condition. Once a new chain has been mounted on the undercarriage, the exhaust valve 28 is moved to the closed position. The track tensioning system 50 is set in the first operative condition and then in the second operative condition to reach the target fluid volume in the first hydraulic actuator 30.

[0143] Figure 8 illustrates a track tensioning system according to a further embodiment of the present invention. Same reference numbers in different figures indicate similar or identical elements as described with reference to the previous figures. With respect to the embodiment of figures 4 to 7, a track tensioning system 50b comprises, as overload protection device, a pressure relief valve 63 described with reference to the embodiment of Fig. 6. In this embodiment, no coil spring is provided. The pressure relief valve 63 may have a pre-established value of pressure triggering its open state, which can be electronically or manually adjustable.

[0144] After the pressure relief valve 63 is opened, the undercarriage chain needs to be tensioned again by executing the subsequent steps to configure the system to the first operative condition and to the second operative condition, as described in the foregoing with reference to figures 4 and 5.

[0145] Figure 9 illustrates a track tensioning system according to a further embodiment of the invention. The track tensioning system of Fig. 9 comprises a bladder accumulator 80 as overload protection device. The bladder accumulator 80 comprises a cylinder 76 and a bladder 66 acting as a spring. The cylinder 76 is constrained at one end to the connecting element 56 in turn connected to the idler wheel 72 via coupling element 39.

[0146] The cylinder 76 comprises an inner cavity 68.

[0147] The first hydraulic cylinder 31 is configured to be slideably mounted within the inner cavity 68 of the cylinder 76, the inner cavity forming a chamber of variable volume. The spring cylinder 76 comprises an inletoutlet port 77 which is connected to the bladder 66 through a connecting flow line 67. As generally known in the art, the bladder accumulator uses the difference in compressibility between a pressurized gas, e.g. N2 gas, and an incompressible fluid, e.g. hydraulic oil.

[0148] The bladder 66 comprises a fluid section 78 containing a fluid, e.g. hydraulic oil, and a gas section 79 containing pressurized gas. The fluid section 78 is in fluid communication with the inlet / outlet port 77 of the spring cylinder 76 by means of the connecting flow line 67. A spring effect is achieved by the expansion and contraction of the pressurized gas.

[0149] The bladder of bladder accumulators typically requires a relatively large space due to its large volume. However, the Applicant has noted that the connecting flow line 67 may be selected to have different lengths. In particular, the bladder 66 may be stored anywhere in the tracked vehicle. Instead of a bladder accumulator, the overload protection device may comprise a diaphragm accumulator or a piston accumulator (embodiments not illustrated).

[0150] Those skilled in the art will recognize that it is possible to combine the various features of the embodiments described above in order to obtain further embodiments, all of which are in any case encompassed by the present invention as defined by the following claims.

Claims

CLAIMS1. A track tensioning system (50; 50a; 50b; 50c) for adjustably controlling tension in a closed-loop track chain (71) entrained about an idler wheel (72) of a track undercarriage (70), the system comprising: a first hydraulic actuator (30) operatively connected, at a first side, with the idler wheel (72) of the track undercarriage (70) and comprising a first hydraulic cylinder (31) comprising a first interior chamber (34) of variable volume; a second hydraulic actuator (40) comprising a second hydraulic cylinder (45) comprising a balancing interior chamber (46) having a first cross sectional area (Al) and a receiving interior chamber (47) having a second cross sectional area (A2) larger than the first cross sectional area (Al), the balancing interior chamber (46) and the receiving interior chamber(47) being non-communicating contiguous chambers, and a source (20) of pressurized hydraulic fluid configured to be fluidly coupled and uncoupled to / from a first supply flow line (24) in fluid communication with the first hydraulic actuator (30), the source (20) being further configured to be fluidly coupled and uncoupled to / from a second supply flow line (25) in fluid communication with the receiving interior chamber (47) of the second hydraulic actuator (40), wherein the first supply flow line (24) is in fluid communication with a bridge flow line (21) fluidly connecting the first interior chamber (34) with the balancing interior chamber (46).

2. The track tensioning system (50; 50a; 50b; 50c) of claim 1, wherein the first hydraulic actuator (30) comprises a first piston (32), the first cylinder (31) and the first piston (32) being configured to move reciprocally to define the first interior chamber (34), the movement being in a first main direction corresponding to the direction of movement of the idler wheel (72).

3. The track tensioning system (50; 50a; 50b; 50c) of claim 1 or 2, wherein the second hydraulic actuator (40) comprises a second piston(48) being slideably movable within the balancing chamber (46) and the receiving chamber (47), the second piston (48) having a first surface area and a second surface area on its opposite sides, the first surface area(Al) corresponding to the cross sectional area of the balancing chamber (46) and a second surface area (A2) corresponding to the cross sectional area of the receiving chamber (47).

4. The track tensioning system (50; 50a; 50b; 50c) of any one of the preceding claims, wherein the first hydraulic actuator (30) comprises a first inlet-outlet port (33) in fluid communication with the first interior chamber (34), and the second hydraulic actuator (40) comprises a second inlet-outlet port (42) in fluid communication with the receiving chamber (47) and a third inlet-outlet port (43) in fluid communication with the balancing chamber (46).

5. The track tensioning system (50; 50a; 50b; 50c) of any one of the preceding claims, the system being configured to operate in a first operative condition and in a second operative condition, in which in the first operative condition, the first supply flow line (24) and the second supply flow line (25) are fluidly coupled to the source (20), the first supply flow line (24) is fluidly connected to the first interior chamber (34) to receive hydraulic fluid and the second supply flow line (25) is fluidly connected to the receiving interior chamber (47) to receive hydraulic fluid, and in the second operative condition, each of the first supply flow line (24) and the second supply flow line (25) are uncoupled from the source (20) and the receiving chamber (47) is connected to a discharge flow line (36) to discharge the received hydraulic fluid.

6. The track tensioning system (50; 50a; 50b; 50c) of claim 5, wherein, in the second operative condition, the first supply flow line (24) is closed upstream of the bridge flow line (21).

7. The track tensioning system (50; 50a; 50b; 50c) of any one of the preceding claims, wherein the bridge flow line (21) is fluidly connected to an exhaust line (27) provided with an exhaust valve (28) configured to move between an open position and a closed position.

8. The track tensioning system (50; 50a; 50b; 50c) of claim 7, when dependent on claim 5 or 6, wherein both in the first and in the second operative condition, the exhaust valve (28) is in the closed position.

9. The track tensioning system (50; 50a; 50b; 50c) of claim 5 or of any one of claims from 6 to 8 when dependent on claim 5, further comprising a control valve device (58) arranged to intercept the first and the second supply flow lines (24, 25), the control valve device (58) being configured to be selectively operated to move between two operative positions: a first operative position when the system (50) is in the first operative condition and in a second operative position when the system (50) is in the second operative condition.

10. The track tensioning system (50; 50a; 50b; 50c) of claim 9, wherein- in the first operative position, the control valve device (58) is configured to be connected to the first supply flow line (24) to enable a fluid communication between the source (20) and the first interior chamber (34) and to be connected to the second supply flow line (25) to enable a fluid communication between the source (20) and the receiving interior chamber (47), and- in the second operative position, the control valve device (58) is configured to: disconnect the first supply flow line (24) and the second supply flow line (25) from the source (20), and connect the receiving interior chamber (47) to the discharge flow line (36) to empty the receiving chamber (47).

11. The track tensioning system of claim 9 (50; 50a; 50b; 50c), wherein the control valve device (58) is a multiway directional valve.

12. The track tensioning system (50; 50a; 50b; 50c) of any one of the preceding claims, further comprising an overload protection device, the overload protection device being selected in the group consisting of:- a coil spring (55) axially aligned with the first hydraulic actuator (30) and being operatively connected at a one side with the idler wheel (72);- a pressure relief valve (63) arranged in an exhaust flow line (27) fluidly connected to the first supply flow line (24) and configured to change the state from a closed state to an open state, the open state being triggered by an internal pressure in the first supply flow line or in the second supply flow line higher than a threshold pressure value, and- a bladder accumulator (80) comprising a cylinder (76) having an inner cavity (68), the first hydraulic cylinder (31) being configured to be slideably mounted within the inner cavity (68) of the cylinder (76) and a bladder (66) comprising a fluid section (78) apt to contain a hydraulic fluid and a gas section apt to contain pressurized gas, wherein the cylinder (76) comprises an inlet-outlet port (77) connected to the fluid section (78) of the bladder (66) through a connecting flow line (67).

13. A method for adjusting the track tension of a closed loop track chain entrained about an idler wheel (72) of a track undercarriage (70), the method comprising: providing a first hydraulic actuator (30) operatively connected, at a first side, with an idler wheel (72) of a track undercarriage (70) and comprising a first hydraulic cylinder (31) comprising a first interior chamber (34) of variable volume, and providing a second hydraulic actuator (40) comprising a second hydraulic cylinder (45) comprising a balancing interior chamber (46) having a first cross-sectional area (Al) and a receiving interior chamber (47) having a second cross-sectional area (A2) larger than the first cross-sectional area (Al), the balancing interior chamber (45) and the receiving interior chamber (46) being non-communicating contiguous chambers , the balancing interior chamber (46) being in fluid communication with the first interior chamber (34) via a bridge flow line (21), wherein the method is configured to operate in a first operative condition and in a second operative condition, the method comprising: in the first operative condition, supplying pressurized hydraulic fluid to the first interior chamber (34) via a first supply flow line (24) and to the receiving chamber (47) via a second supply flow line (25), andin the second operative condition, interrupting the flow of pressurized hydraulic fluid through the first and second supply flow lines (24, 25), and discharging the fluid flow from the receiving chamber (47) so as to enable a transfer of the hydraulic fluid from the first interior chamber (34) to the balancing chamber (46).

14. The method of claim 13, comprising, in the second operative condition, upon interrupting the flow of pressurized hydraulic fluid through the first and second supply flow lines (24, 25), closing the first supply flow line (24) upstream of the bridge flow line (21).

15. The method of claim 13 or 14, wherein, in the first operative condition, supplying pressurized hydraulic fluid to the first interior chamber (34) via a first supply flow line (24) and to the receiving chamber (47) via a second supply flow line (25) comprises coupling the first supply flow line (24) and the second supply flow line (25) to a source (20) of pressurized hydraulic fluid.

16. The method of any one of claims 13 to 15, wherein, in the second operative condition, discharging the hydraulic fluid flow from the receiving chamber (47) comprises uncoupling the second supply flow line (25) from a source (20) of pressurized hydraulic fluid and coupling the second supply flow line (25) to a discharge flow line (36).

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