Lever mechanisms

Technical Field

This invention relates to lever mechanisms and particularly, though not exclusively, to lever mechanisms for use in the control of tractor draft links from a location remote from the tractor operators station in order to facilitate, for example, the coupling of an implement to the draft links.

Whilst numerous lever mechanisms have been proposed in the past for other applications, for example the lever mechanism of GB-A--1478099 for the manual control of a hydraulic control system, none of the prior proposals have been particularly suitable for the control of tractor draft links from a location remote from the tractor operator's station where safety considerations are paramount.

Disclosure of the Invention

It is an object of the present invention to provide a lever mechanism which is suitable for use in the remote control of tractor draft links as referred to above.

Thus in accordance with the present invention there is provided a lever mechanism having an operating member, a support relative to which said operating member is displaceable, a lever pivotally mounted on the support about a pivot axis, a first formation on the lever, and a second formation on the operating member and engageable with the first formation to displace the operating member, the mechanism being characterised in that the pivot axis of the lever is translationally movable and a bias means acts to translationally move the lever on its axis away from the second formation to hold the first and second formations disengaged when the lever is released, the operating member being displaceable in a given direction relative to the support by translational movement of the lever on its movable axis against the bias to bring the first and second formations into engagement followed by pivotting of the lever relative to the support with the first and second formations engaged to displace the operation member.

A lever mechanism in accordance with the preceding paragraph is particularly suitable for use in the control of tractor draft links from a position remote from the tractor operators station.

Thus the present invention also provides a tractor draft link control system comprising means for operating tractor draft links characterised by the inclusion of a lever mechanism in accordance with the next but one preceding paragraph, the operating member of the lever mechanism being connected with said means of the control system so that operation of the lever to displace the operating member in said given direction is arranged to initiate raising or lowering of the tractor draft links.

The invention also provides a tractor with vertically pivotable draft links, the tractor being characterised in that the vertical position of the draft links is controlled by a control system according to the preceding paragraph and in which the lever mechanism is mounted on a rearward portion of the tractor to allow operation of the lever by an operator standing to the rear of the tractor at a location outside the draft links.

Using the above lever mechanism the coupling of an implement to the draft-links of the tractor becomes a one man operation which can be accomplished by an operator standing to the rear of the tractor at a location outside the draft links. The operator simply raises/lowers the draft links using the lever to bring the implement and draft-link attachment means into vertical alignment.

As will be evident from the description below the lever mechanism includes a number of safety features. For example, each full pivotting sweep of the lever with the first and second formations in engagement can be arranged to result in only a small raising/lowering of the draft-links so that the operator is protected against sudden and excessive raising and lowering which might lead to him becoming trapped.

Additionally, when the lever is released the bias ensures that the first and second formations disengage thus preventing further movement of the draft-links and ensuring that when the operator returns to control the draft links from his normal station (for example inside a cab) any previous use of the remotely mounted lever mechanism will not interfere with the subsequent ability to control the links from the normal draft link control lever or levers mounted adjacent to the operators station.

Returning to the details of the lever mechanism, conveniently the first formation may comprise a pin carried by the lever and the second formation may comprise a rack cut in or carried by the displaceable operating member.

The bias means may be a spring which acts between the pivot axis and the support, the pivot axis being translationally movable within a slot in the support which extends substantially at right angles to the intended direction of displacement of the operating member.

Conveniently, when the lever mechanism is intended for use in the control of tractor draft links, the mechanism is installed so that the lever is pulled generally downwardly against the bias to engage the second formation and pivoted about a generally horizontal axis.

It will be appreciated that the arc through which the lever can be pivoted with the first and second formations in engagement can be limited to control the total possible displacement of the operating member in said given direction for each full pivotting sweep of the lever. This gives the additional safety feature discussed above when the lever mechanism is applied to the control of tractor draft links. Clearly, if more movement of the operating member is required than can be obtained by one full pivotting sweep of the lever, the lever must first be released and then pulled again against the biassed to re-engage the first and second formations for a second pivotting sweep.

Description of Drawings

One embodiment of the present invention, as applied to the control of tractor draft links, will now be described, by way of example only, with reference to the accompanying drawings in which:-

• Figure 1 is a diagrammatic view of a lever mechanism embodying the present invention used in the control of tractor draft links;
• Figure 2 is a side view on a larger scale of the lever mechanism of Figure 1, and
• Figure 3 is an end view of the lever mechanism of Figure 2.

Best Mode of Carrying Out Invention

Referring to Figure 1, this shows part of the rear portion of a tractor in which a lever mechanism 10 in accordance with the present invention is secured on the inside of the right hand rear wheel fender 11 of the tractor. Part of the right hand wheel is indicated at 13 and the tractor cab is indicated at 14 with its rear wall shown at 15.

The tractor has a rear axle housing, parts of which are indicated at 18. A cross-shaft 17 is pivotally mounted on the housing 18 and carries a pair of lift arms 19 each of which is connected to a lift rod 20 whose lower end is connected at 21 with a draft-link 22 of a three point hitch pivoted on another part of the rear axle housing at 23.

A draft link control system is provided which includes a draft link actuating means in the form of a piston and cylinder assembly 16, 24 which is supplied, via conduit 36, with pressurised fluid from a pump (not shown). Fluid can also be exhausted from piston and cylinder assembly 16, 24 via conduit 36. Thus axial displacement of piston 16 within cylinder 24 causes raising/ lowering of the draft links 22 in a conventional manner.

The basic draft link control system may be of any conventional form. For example, a system of the type described and claimed in UK Patent 1101775 is suitable and will therefore be described to facilitate a full understanding of the present invention.

Thus two control levers 25 and 26 operating in adjacent control quadrants 27 and 28 are provided. The levers 25 and 26 pivot about aligned axes 28, lever 25 controlling the power lift in the so-called "position control" or "pressure-control" modes dependent on the position of lever 25 on quadrant 27, and lever 26 controlling the power lift in the so-called "draft-control" mode.

Lever 25 is connected via a control linkage 31 with a rotatable sleeve 29 surrounding a shaft 30 supported in the side of housing 18. Sleeve 29 is then connected within housing 18 via a further control linkage, shown schematically by dotted link 32, with the remainder of the control system shown schematically by box 33 and which includes further linkages, the fluid pump, and a control valve for controlling the supply of fluid to and exhausting fluid from the piston and cylinder assembly 16, 24 via conduit 36.

In a similar fashion lever 26 is connected via control linkage 34 with shaft 30 which is in turn connected within housing 18, via a further control linkage shown schematically at 35, with the remainder of the control system 33.

Thus in the known manner lever 25 is operated to set the desired operating value of 'position' or 'pressure' when the power lift is being controlled in the "position control" or "pressure control" modes and lever 26 sets the desired level of 'draft force' when the system is operating in the "draft control" mode. The control system also receives feedback signals of the actual hitch position, system fluid pressure, or draft force as indicated schematically by allows 'PO', 'PR', and 'DR' in, Figure 1. The appropriate feedback signal is compared by the control system with the desired value signal set by control lever 25 or 26 to produce an error signal which is used to control the control valve which supplies or exhausts hydraulic fluid from piston and cylinder 16, 24 via conduit 36 so that the desired operating condition of the hitch is attained.

Thus far described the draft link control system is of the general type described in the previously referred to UK Patent 1101775 to which the reader is directed if requiring a fuller description of a practical embodiment of such a control system.

The draft link control system also incorporates the lever mechanism 10 of the present invention which includes a lever 42 which can be pivoted (as indicated by arrow Y) to displace an operating member 40 backwards or forwards (as indicated by arrow Z). Operating member 40 is connected with an arm 31 a which forms part of the control linkage 31. Thus, as will be described in greater detail below, with the control lever 25 set to control the power lift in the "position control" mode pivotting of lever 42 gives a signal input to the control system 33 via member 40, arm 31a, sleeve 29 and linkage 32 which causes the draft-links to either rise or fall depending on the direction of pivotting of lever 42. This, for example, enables the tractor operator to raise/ lower the draft-links whilst standing to the rear of the tractor at a location outside the draft-links so that coupling up of an implement to the tractor becomes a simple one man operation.

Turning now to Figures 2 and 3 for a more detailed description of the lever mechanism 10, it will be seen that the upper part of the lever 42 is of U-shaped cross-section and is pivotally mounted on a support 43 of U-shaped cross-section by a pin 44 which slides in slots 45 in the two arms 43a of the U-shaped support. The support 43 is secured to fender 11 by two bolts 46 and 47 which extend through spacing pieces 48, 49 and 50, 51 respectively. A grooved bobbin 52 is rotatably mounted on spacing piece 50 and provides a guide for the displacement of operating member 40.

A spring 53 acts between the support 43 and the pin 44 to bias the pin 44 and hence the lever 42 upwardly in slots 45 so that, when lever 42 is released the lever occupies a stable central position with its upper end 42a against the inside of support 43. As can be seen from Figure 2, one end 53a of spring 53 acts on pin 44, the central portion 53b is wrapped around a stabilizing core 54 which floats between the arms of the support 43 and the other end 53c of the spring passes through holes 55 in the support.

The lever42 carries a first operating formation in the form of a further pin 56 which is engageable with a second operating formation in the form of rack 57 provided on operating member 40.

From the above description it will be evident that, if the lever 42 is pulled downwardly in the direction of arrow X againstthe action of spring 53, pin 56 will engage rack 57 and on pivotting of lever 42 about pin 44 in the direction of arrow Y the operating member 40 will be moved backwards or forwards as indicated by arrow Z.

As described previously, when the lever 42 is released the pin 56 automatically disengages the rack 57 under the action of spring 53 and the lever returns to the centre stable position 42a. As discussed above this is a significant feature.

The permitted arc of movement of lever 42 is defined by the positioning of spacing pieces 48 and 50 through which bolts 46 and 47 extend. Typically the leverarrangement and its connection with the control linkage 31 is arranged such that an angular movement of a of lever 42 produces approximately 100 mm of alteration in the height of the outer ends of the associated draft links of the tractor.

It will be understood that the operator can in fact achieve a total angular movement of the lever 42 whilst enmeshed with rack 57 equal to 2a by engaging the pin 56 with the rack when the lever is in one extreme of its travel and moving the lever throughout its full permitted range of travel.

It should be noted that the control lever arrangement of the present invention will still operate to adjust the height of the draft-links even if the control lever 25 is set in the "pressure control" portion of the quadrant 27 provided that the movement of the lever 25 into the "position control" portion of the quadrant 27 is not obstructed by any stop. Thus if the lever 25 is in the pressure control portion of the quadrant the initial movements of the lever 42 will simply move the control lever into the pressure control portion of the quadrant and will not cause any adjustment of the height of the draft-links. Once the lever 25 has moved into the position control portion of the quadrant further movements of the lever 42 continue to move lever 25 and also cause adjustment in the height of the draft-links.

The present invention thus provides a lever mechanism which is particularly suited for the control of the height of tractor draft-links from a location remote from the normal operators station.

Although the lever mechanism of the present invention has been described above solely in relation to the control of a tractor draft links it is not limited to such an application nor is it limited to use with the particular basic tractor draft link control system lift described. Clearly the lever mechanism could be used with a wide range of tractor draft link control systems by connecting the e operating member 40 with that part of the control system which sets the desired draft-link position signal.