GB2393696A

GB2393696A - Tensioning system for a tracked vehicle

Info

Publication number: GB2393696A
Application number: GB0223010A
Authority: GB
Inventors: Lathauwer Tom De; Carlos Verheye; Jean-Pierre Vandendriessche
Original assignee: CNH Belgium NV
Current assignee: CNH Industrial Belgium NV
Priority date: 2002-10-04
Filing date: 2002-10-04
Publication date: 2004-04-07
Also published as: GB0223010D0

Abstract

A track tensioning system suitable for a harvesting machine comprises a track chain 15. a front idler 11, a rear idler 12, track rollers 13 mounted on a track frame 10, and a drive sprocket 14. The track chain 15 extends around the sprocket 14, rollers 13 and idlers 11,12 and is tensioned by actuators 18,21 connected to the idlers 11,12. At least one of the actuators 18,21 is connected to an accumulator 24 or spring. Preferably, the other actuator 18 or 21 is also connected to the accumulator 24, a separate accumulator or a spring. The actuators typically comprise hydraulic cylinders. If two accumulators are used, they may be connected by at least one orifice (25 fig 5), which may be connected in series or parallel with check valves (26 fig 5). The idlers 11,12 are pivotally connected to the track frame by swing arms 16,17. The system reduces the risk of the chain 15 derailing in demanding situations such as during heavy braking or in a sudden change of direction.

Description

( - 1 TRACK TENSIONING SYSTEM FOR A TRACKED VEHICLE.

Field of the invention

5 The present invention relates to the tensioning of the endless track of a 'positive drive' vehicle track propulsion system. The term 'positive drive' refers to drives having drive sprockets that engage with a toothed belt or chain and do not merely rely on friction.

Background of the invention

Tracks are used on machines such as combine harvesters to operate on difficult ground conditions. It is known that 15 tracks have a better traction and higher flotation than Lyres. On combine harvesters, halfbacks are commonly used, that is to say that the front wheels, which are the main drive, are replaced by tracks. Conventional wheels with Lyres are used at the rear to steer the vehicle. This so steering may be assisted by braking the left or the right half-track, depending on the chosen direction.

The most common half-tracks used on combine harvesters have an elevated sprocket that fits on the wheel flange to 25 which the traction wheel is normally fitted. The teeth of this sprocket fit in an endless chain, which runs over front and rear idler wheels. Track rollers, which are mounted in between the idler wheels, distribute the weight of the vehicle to the tracks and then further to the ground. The 30 idler wheels and track rollers are mounted on a track frame, which can pivot around a pivot point that is fixed to the vehicle's main frame. This pivoting is necessary to let the half-track follow the contours of the field and to allow a

proper load distribution to the ground.

Thus, each half-track engages with the corresponding sprocket. Each sprocket is, in its turn, fixedly connected

( 2 to the corresponding wheel flange and thus, indirectly, to the vehicle's main frame. These wheel flanges provide traction to the halftracks. Each pivot point is fixed to the vehicle's main frame and allows the track frame to pivot 5 around this point.

The idlers and track rollers are equipped with flanges to prevent the chain from rolling off laterally. However, these flanges are only effective if the track is tensioned lo properly. This has been done in the past by movies one of the idlers outwards by means of a screw jack or grease cylinder in combination with a spring, or with a hydraulic cylinder in combination with an accumulator which acts like a spring.

This spring function is needed for three reasons, namely: 1. to keep the same tension on the chain when this chain lengthens due to temperature increase or wear; 20 2. to compensate for the change in pitch line length when the track frame rotates around its pivot point. This is only necessary when the pivot point is not co-axial with the centre of the sprocket; and 3. to avoid chain breakage when material, such as a stone, 25 gets trapped between the rollers and the chain.

As mentioned before, tensioning of the chain is normally done by moving the front or the rear idler outwardly. If tensioning is done by the front idler, then 30 during forward driving, a relatively small tensioning force is sufficient as there is no traction force in the front part of the chain. However, when the vehicle is braked during forward movement or when it is suddenly driven backwards, the front part of the chain is tensioned, causing 35 the front idler to move completely inwardly. As a result, the rear part of the chain becomes loose with only a relatively small tensioning force remaining in that part.

( - 3 This force is insufficient to resist the excessive braking or reverse traction forces. As a result, the rear part may slip off the rollers or cause the drive sprocket to skip over the chain links.

When, on the other hand, the tensioning is done by a rear idler, no problems occur during heavy braking or reverse driving. However, when the machine is suddenly driven forward, the rear idler needs a tension force that is 10 almost the double, depending on the relative position of the sprocket and both idlers, of the traction force in the chain to resist inward movement. Otherwise, the rear idler is pushed in by the chain, causing the front part of the chain to come loose. To ensure that the chain will not be derailed 15 (i.e. slip off the drive sprocket or idlers) and/or that the drive sprocket does not skip over the links, a tension force that corresponds with the maximum driving torque needs to be permanently applied. Such excessive tension reduces the lifetime of the track components and leads to a poor to efficiency due to the increased friction in the chain links.

One way to avoid this is to make the tension variable as a function of the driving torque. This is however a complex solution that does not work properly in all 25 situations, e.g. when the differential lock of the vehicle is engaged, or when the vehicle is heavily braked with its service brakes when it is driven in reverse.

Object of the invention The present invention therefore seeks to provide an improved tensioning system for tracks to avoid derailing of the tracks and to apply sufficient tension to the tracks under all circumstances.

- 4 Summary of the invention

According to the present invention, there is provided a track propulsion system for an agricultural harvesting I machine comprising a track frame; a front idler, a rear lo idler and track rollers, mounted on the track frame; a drive sprocket; a track chain extending around the drive sprocket, the front and rear idlers and the track rollers; and one actuator and accumulator connected to one of the front and lo rear idlers to tension said track chain, characterized by a second actuator connected to the other of the front and rear idlers. The present invention is based on the fact that a large 15 tensioning force is not needed, as long as the tensioning idler is not in the pulled part of the chain. The problem is however that the pulled part of the chain changes from the rear (when the torque is applied to drive forward) to the front (when the torque is inverted).

In the preferred embodiment of the present invention both the front and the rear idlers are acted upon by hydraulic cylinders. The cylinders are preferably hydraulically coupled to each other and to a hydraulic 25 accumulator. When the combine harvester is being driven forward, the rear idler moves completely in against a shoulder and thus becomes fixed. The front idler moves out and guides the loose part of the chain and prevents the chain from jumping off. A relatively low tensioning force is so needed to hold the weight of the chain, since there is no pulling force in this part of the chain. When the combine is driven in reverse(or braked during forward driving) the exact opposite occurs. The front idler moves completely in against its shoulder and thus becomes a fixed idler, while 35 the rear idler moves out and functions as the tensioning idler.

( Or f d_ cription of the drawings: The invention will now be described further, by way of example, with reference to the accompanying drawings, in 5 which: Figure 1 is a side view of a combine harvester, having halftracks at the front and steering wheels at the rear, Figure 2 is a detailed view of a half-track, showing lo the different components, Figure 3 is a view similar to that of Figure 2, showing the machine driving forward or braking while running backward, Figure 4 is a view similar to that of Figure 2 and 3, showing the machine driving in reverse or braking while running forward, Figure 5 is a diagram of a further improved hydraulic circuit. 20 Description of the preferred embodiment:

Figure 1 shows a combine harvester 1 fitted at the front with a track propulsion system 2 instead of the commonly used tires. As shown in Figure 2, the track <5 propulsion system 2 comprises a track frame 10 with a front idler 11, a rear idler 12 and track rollers or bogie wheels 13 connected to the track frame 10. A drive sprocket 14 is located above the track frame 10 and connected directly to the wheel flange of the combine harvester 1. The track chain so 15 is driven by the drive sprocket 14 by means of teeth 70 engaging into the track chain 15. The track chain 15 extends around the sprocket 14, the front idler 11, the rear idler 12 and the track rollers 13. The track rollers 13 are rotatably connected to the track frame 10 and this track s frame 10 is in its turn pivotally connected to the vehicle's main frame by a pivot 20.

( - 6 The front idler 11 and rear idler 12 can be moved by hydraulic cylinders 18 and 21 to provide sufficient tensioning into the track chain 15. The connection of the front and rear idlers 11 and 12, the cylinders 18 and 21, 5 the swing arms 16 and 17 to the track frame 10 are identical. A front swing-arm 16 is pivotally connected, at one end, to the front idler 11 and, at its other end, to the lo track frame 10. A hydraulic cylinder 18 is pivotally coupled at one end to the front swing-arm 16 and thus also to the front idler 11. At its other end, the hydraulic cylinder 18 is pivotally coupled to the track frame 10. This cylinder 18 enables the position of the front idler 11 to be changed 15 relative to the track frame 10. The inward stroke of the front hydraulic cylinder 18 and thus also the inward swing movement of the front swing-arm 16, is limited by a shoulder 19. This shoulder 19 is fixedly connected to the track frame 10. This shoulder 19 could be replaced by the normal 20 working of the cylinder 18. If the cylinder 18 is swung completely inwardly, then the cylinder 18 can not move in further. However, by using the cylinder 18 instead of the combination cylinder 18 with shoulder 19, a larger cylinder must be foreseen to be able to withstand the forces present.

Likewise, a rear swing-arm 17 is, at one end, pivotally connected to the rear idler 12 and, at the other end, to the track frame 10. A hydraulic cylinder 21 is, at one end, pivotally coupled to the rear swing-arm 17 and thus also to so the rear idler 12. The other end of the hydraulic cylinder 21 is pivotally coupled to the track frame 10. Similarly as with respect to the front idler 11, cylinder 21 is operable to change the position of the rear idler 12 relative to the track frame 10. The inward stroke of the rear hydraulic 35 cylinder 21 and thus also the inward swing movement of the rear swing-arm 17 is limited by a shoulder 22. This

- 7 shoulder 22 is, comparable with shoulder 19, also fixedly connected to the track frame 10.

The front cylinder 18 is coupled to the rear cylinder 5 21 by means of a hydraulic line 23. A hydraulic accumulator 24 is coupled to this line 23.

When the combine harvester 1 is driven forward (from right to left as viewed) or when it is braked when driving lo in reverse, as shown in Figure 3, the track chain 15 has a taut part 50 and a slack part 51. When driving forwards, the teeth 70 of the sprocket 14 pull on the track chain portion 50. This causes the rear idler 12 to move towards I pivot 20. The rear swing-arm 17 turns counter-clockwise, until it hits the rear shoulder 22. At the same time, the rear hydraulic cylinder 21 is pushed in, driving the hydraulic oil into the front hydraulic cylinder 18. This cylinder 18 is then pushed out, forcing the front swing-arm 16 to pivot counter-clockwise. The front idler 11, which is So mounted on this swingarm 16, is pushed against the track chain portion 51. The tension force delivered to the hydraulic cylinder 18 is determined by the pressure in the hydraulic accumulator 24. If the length of the chain increases, due to temperature increase, wear or simply 25 because the track frame 10 rotates clockwise around its pivot 20, then the accumulator 24 causes the front cylinder 18 and front idler 11 to move further out. Even when an object, such as a stone, gets trapped between the track chain 15 and the rollers 13 or idlers 11 and 12, the 30 function of the track is not endangered as the front cylinder 18 can move inwards, sending hydraulic fluid to the accumulator 24. Thereby, there is no overpressure in the system. 35 When the combine harvester 1 drives in reverse or when it is braked when driving forward, as shown in Figure 4, the track chain 15 has a taut part 55 and a slack part 56. When

( 8 driving in reverse, the teeth 70 of the sprocket 14 pull on the track chain part 55. This causes the front idler 11 to move towards pivot 20. The front swing-arm 6 turns clockwise, until it hits the front shoulder 19. At the same 5 time, the front hydraulic cylinder 18 is pushed in, driving the hydraulic oil into the rear hydraulic cylinder 21. This cylinder 21 is then pushed out, forcing the rear swing-arm 17 to turn clockwise. The rear idler 12, which is mounted on this swing-arm 17, is pushed against the track chain part lo 56. The tension force delivered to the hydraulic cylinder 21 is determined by the pressure in the hydraulic accumulator 24. If the length of the chain increases, due to temperature increase, wear or simply because the track frame 10 rotates clockwise around its pivot 20, then the accumulator 24 15 causes the rear cylinder 21 and rear idler 12 to move further out. As described before, if something gets trapped between the track chain 15 and the rollers 13 or idlers 11 and 12, the operation of the track is not endangered because the rear cylinder 21 can move inwards, sending hydraulic 20 fluid to the accumulator 24.

The same as described above, can be achieved by using telescoping cylinders, instead of swing-arms, for the idlers and/or by using recoil springs and mechanical jacks instead 25 of hydraulic cylinders and accumulators.

When using the hydraulic system as described above, it still is possible that the swing-arms 16 and 17 hit too abruptly against their respective shoulders 19 and 22. This So may cause serious damage to these shoulders. Therefore, an orifice or throttle 25 may be installed in the hydraulic line 23. However, when only this orifice 25 is included into the hydraulic circuit, this may jeopardise the proper operation of the hydraulic system. If a hydraulic cylinder as is pushed in, e.g. when the driving torque is inverted, the hydraulic oil would be driven into the accumulator first

( 9 -

instead of into the other cylinder. This would result in a momentary loose chain.

To solve this problem, in the embodiment of Figure 5, s the accumulator 24 is split in two hydraulic accumulators 24a and 24b, one accumulate. 24a acting on the front idler 11, and the other accumulator 24b on the rear idler 12.

These accumulators 24a and 24b are connected to the hydraulic line 23 and orifice 25, through orifices 25a and lo 25b and check valves 26a and 26b. The orifices 25a and 25b are used to prevent the oil from flowing into the accumulators 24a and 24b instead of into the other cylinder when the driving torque is inverted. The check valves 26a and 26b allow quick filling of the corresponding cylinder 18 15 or 21 when it needs to be pushed out to tension the track chain 15.

The tensioning of the track chain 15 does not require a separate hydraulic system, but may be coupled to the 20 existing hydraulic system 27 of the combine harvester 27.

Recoil springs 30 are used to centre the idlers 18 and 21 when the combine harvester 1 is not in motion.

Claims

- 10 CLAIMS

1. A track propulsion system for an agricultural harvesting machine (1) comprising: 5 - a track frame (10); - a front idler (11), a rear idler (12) and track rollers (13), mounted on the track frame (10); - a drive sprocket (14); - a track chain (15) extending around the drive sprocket lo (14), the front and rear idlers (11,12) and the track rollers (13); and one actuator (18,21) and accumulator (24) connected to one of the front and rear idlers (11,12) to tension said track chain (15), 15 characterized by a second actuator (21,18) connected to the other of the front and rear idlers (12,11).

2. A track propulsion system as claimed in Claim 1,

wherein the first and second actuators (18,21) are 20 associated with the same accumulator (24).

3. A track propulsion system as claimed in claim 1, wherein the second actuator is associated with a second accumulator and wherein a connection (23) is provided 25 between the two accumulators.

4. A track propulsion system as claimed in any preceding claim, characterized in that said actuators are hydraulic cylinders (18,21) and the or each accumulator (24; 30 24a, 24b) is a hydraulic accumulator.

5. A track propulsion system as claimed in claims 3 and 4, wherein the connection (23) between the two accumulators (24a, 24b) includes an orifice (25).

6. A track propulsion system as claimed in claim 5, characterized in that said accumulators (24a, 24b) are connected to the connection (23) and to said orifice (25) through supplementary orifices (25a,25b) and check valves 5 (26a,26b).

7. A track propulsion system as claimed in any one of claims 1 to 3, wherein the actuators are mechanical jacks and the or each accumulator is a spring.

8. A track propulsion system as claimed in any preceding claim, characterized in that each of the first and second actuators (18,21) extends between the track frame l (10) and a respective one of the front and rear idlers 15 (11, 12).

9. A track propulsion system as claimed in any preceding claim, wherein the front and rear idlers (11,12) are mounted on respective swing arms (16,17) which are 20 pivotally connected to the opposite ends of the track frame (10), and wherein the first and second actuators (18,21) extend between the track frame (10) and the respective swing arms (16,17) at locations spaced from the pivotal mountings of the swing arms (16,17) on said track frame (10).

10. A track propulsion system substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.