GB2054338A - Device for controlling the hydraulic power-lift for an implement linkage of an agricultural tractor - Google Patents

Abstract

The implement linkage of an agricultural tractor (1) has a pair of lower links (2) attached adjacent respective ends of a flexible bar (5) which is connected to a hydraulic power-lift (7, 8) operable in response to flexural deformation of the bar (5) caused by the draft load of an implement hitched to the links (2). The flexural rigidity of the bar (5), and therefore the draft load necessary to operate the power-lift (7, 8), is varied by sliding each link (2) axially on its respective end of the flexible bar (5) and altering the distance between the adjacent bar support (6) and the attachment end (9) of the link (2), a spacer ring (14) retaining the link in its chosen position. The larger the spacing, the lower the rigidity of the bar and the lower the draft load necessary to operate the power-lift. <IMAGE>

Description

SPECIFICATION Device for controlling the hydraulic power-lift of an implement linkage of an agricultural tractor The present invention relates to a device for controlling the hydraulic power-lift of the implement lin kage an agricultural tractor, of the type comprising a flexible bar which is supported by the tractor to extend transversely thereof, and is pivoted adjacent each end to a respective link of the implement linkage, the flexible bar being connected to an hydraulic distributor which controls the hydraulic power-lift in such a way that the latter is activated when flexural deformation of the bar, due to a reaction force transmitted from the ground to the links by the implement, exceeds a predetermined value.

A device of the aforesaid type permits the operation of a hydraulic power-lift to be strictly controlled so that the agricultural implement carried by the tractor is automatically raised relative to the ground whenever the reaction force, that is, the "drag" or draft load, transmitted by the ground to the implement, exceeds a predetermined threshold value.

A considerable limitation to the use of such devices is the fact that the "sensitivity" of the flexible bar is constant, depending on its rigidity. This is disadvantageous insofar as the draft load transmitted to the flexible bar varies with different agriculture implements so that, if the rigidity of the bar is adjusted for one type of implement, it is no longer adjusted for other types of implement. When the flexible bar is wrongly adjusted for the implement being used, the automatic raising and lowering of the implement in response to varying working conditions of the ground will take place too soon or too late.

The object of the present invention is to provide a control device of the aforesaid type which can be adapted easily for use with different types of implement so that the hydraulic power-lift of the tractor can be operated correctly with any type of implement.

Accordingly, the present invention provides a control device of the aforesaid type, characterised in that each of the links is axially slidable on the flexible bar between respective first and second positions delimited respectively by a support of the flexible bar on the tractor and a locking sleeve mounted at each end of the flexible bar, and in that means are provided for retaining each link in one or other of said positions.

In a control device according to the present invention it is possible to vary, at each end of the flexible bar, the distance between the support of the bar on the tractor and the respective link of the implement linkage. This allows the flexural rigidity of the barto be varied. When the links are in respective positions towards the middle of the flexible bar, the rigidity of this bar is higher than when the links are in respective positions adjacent each end of the bar. These positions of each link are used respectively with agricultural implements which exert a high draft load and require a relatively high traction force, and implements exerting a low draft load and requiring low traction force.

In a preferred embodiment, each retaining means comprise a respective spacer ring which in the first position is interposed between the bar support and the link, and in the second position is interposed between the link and the adjacent locking sleeve.

One embodiment of the present invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a partially cut-away perspective view of the rear of a tractor having an implement towing linkage provided with a control device according to the present invention; Figure 2 is a side elevational view of a detail of the control device of Figure 1 on an enlarged scale and in a first operating condition, and Figure 3 is a longitudinal sectional view of the detail of Figure 2 in a second operating condition.

Referring now to Figure 1 of the drawings, there is shown, generally indicated 1, the rear of an agricultural tractor provided with a three-point linkage of known type, including a pair of lower or draft links 2 and an upper link 3. The upper link 3 is pivoted at one end to the rigid structure 4 of the tractor 1, and is provided at its other end with a coupling 3a for an agricultural implement. Each lower link 2 is pivotally connected at one end to a respective end of a flexible bar 5 which is supported on opposite sides of the rigid structure 4 of the tractor by respective supports 6, one of which is shown in Figures 2 and 3. Each support 6 includes a swivel bearing permitting limited angular movement of the supported part of the bar 5, as shown in Figure 3.In use of the linkage, the other end of each link 2 is hitched to the agricultural implement which is to be towed by the tractor 1.

The lower links 2 are raised and lowered by means of a hydraulic power-lift 7 which includes a pair of lift links 8. Each lift link 8 is connected at its lower end to a respective lower link 2, and at its upper end to a respective lift-arm of the power-lift 7.

The flexible bar 5 is operatively connected, by a conventional mechanical transmission (shown diagrammatically in Figure 2), to a known hydraulic dis tributor7a (Figure 2)which controls the operation of the hydraulic power-lift 7. When, during working conditions, the flexural deformation of the bar 5, due to the reaction force, that is, the "drag" or draft load transmitted from the ground to the lower links 2 by the implement, exceeds a predetermined value, the bar 5 operates the hydraulic distributorthrough the mechanical transmission, causing actuation of the power-lift 7. An example of this type of device is described in British Patent Application No. 7919709 by the same Applicants.

Figures 2 and 3 show the pivotal attachment of one of the lower links 2 to the flexible bar 5, and as can be seen, the end 9 of the lower link 2 engages a spheroidal coupling 10 which is axially slidably mounted on the bar 5. The coupling 10 is retained on the bar 5 by a locking sleeve 11 which is secured to the end of the flexible bar 5 by a bolt 12 engaged in a cooperating hole 13 through the bar 5.

A spacer ring 14 is mounted on the flexible bar and has a first position of use, shown in Figure 2, bet ween the support 6 of the flexible bar 5 and the attachment end 9 of the link 2, and a second position of use, shown in Figure 3, between the attachment end 9 of the link 2 and the locking sleeve 11.

The flexural rigidity of the bar 5 is less when the spacer ring 14 is in its first position than when it is in its second position (Figure 3), since in the latter position the points of attachment of the flexible bar 5 to the tractor, and the of lower link 2 to the bar 5, are closerthan in the first position. Therefore, with the same force being transmitted from the implement to the lowers links 2, the flexural deformation of the bar 5 is greater in the first position than the second position.

Thus, when agricultural implements which transmit relatively low reaction forces are being used, the spacer ring 14 is mounted in the first position (Figure 2), and when implements which transmit relatively high reaction forces are being used, the spacer ring 14 is mounted in the second position (Figure 3).

Claims (3)

1. A device for controlling the hydraulic powerlift of an implement linkage of an agricultural tractor, comprising a flexible bar which is supported by the tractorto extend transversely thereof, and is pivoted adjacent each end to a respective link of the implement linkage, the flexible bar being connected to an hydraulic distributor which controls the hydraulic power-lift in such a way that the latter is activated when flexural deformation of the bar, due to a reaction force transmitted from the ground to the links by the implement, exceeds a predetermined value, in which each of the links is axially slidable on the flexible bar between respective first and second positions delimited respectively by a support of the flexible bar on the tractor and a locking sleeve mounted at each end of the flexible bar, and in which means are provided for retaining each link in one or other of said positions.

2. A control device as claimed in Claim 1, in which each retaining means comprise a respective spacer ring which in the first position is interposed between the bar support and the link, and in the second position is interposed between the link and the adjacent locking sleeve.

3. A device for controlling the hydraulic powerlift of an implement linkage of an agricultural tractor, substantially as herein described with reference to, and as shown in, the accompanying drawings.