This invention relates to guards for Power Take-Off (PTO) shafts used on tractors or similar vehicles.

It is known to have PTO guards which can be moved between an extended position in which the guard provides protection from injury from an associated PTO shaft and a retracted position when such protection is not required. It is also known to have removeable PTO guards which are detached when the protection is not required but these moveable guards the impose a storage problem.

It is an object of the present invention to provide an improved form of PTO guard.

Thus according to the present invention there is provided a PTO shaft guard arrangement in which a guard member is pivotally mounted on a support structure and is pivotable between a non-operative retracted position and an operative extended position, the guard member having an over-centre spring means for holding the guard member in both the retracted and extended positions.

Such an arrangement holds the guard member in either the retracted or extended positions thus preventing rattling and can be easily pivoted between the positions by movement initially against the action of the spring means which, in the second part of such movement, is subsequently assisted by the spring means.

The support structure may comprise a pair of generally vertically extending plates located on opposite sides of the associated PTO shaft, the guard member being of inverted general U- shaped form with each side of the inverted U- shape guard pivotally mounted on a respective generally vertically extending plate.

Each side of the guard member may be mounted on its respective generally vertically extending plate via a support arm one end portion of which is pivoted on the plate, the other end portion of the arm being connected with the respective side of the guard. The spring means may comprise a pair of bow springs, one end of each bow spring being mounted on the adjacent generally vertically extending plate and the other end being mounted on the adjacent support arm.

Each generally vertically extending plate may include a generally vertically extending slot, a towing hitch being vertically slidable between the plates in the slots and lockable relative to the plates at various heights.

In such an arrangement as the hitch is moved vertically into the vicinity of the PTO shaft, if the guard member is in the extended position, the hitch contacts the guard and moves the guard towards the retracted position.

Fixed side protection plates may extend between the vertically extending plates and the tractor chassis on which the vertically extending plates are mounted, each support arm moving in a slot provided in its respective side protection plate.

A fixed top protection plate may extend between the tractor chassis and an inner edge of the top of the guard member when the guard member is in its extended position.

The invention will now be described, by way of example only, with reference to the accompanying drawings in which: -

Figures 1 , 2 and 3 show side, end and plan views respectively of a PTO shaft guard arrangement in accordance with the present invention in its retracted position, and

Figures 4, 5 and 6 show side, end and plan views respectively of the guard arrangement of Figures 1 to 3 in its extended position, and

Figures 7, 8, 9, 10 and 11 show perspective views of PTO guards in accordance with the present invention.

According to figures 1 to 6, the rear of a tractor chassis 10 is provided with a PTO shaft 11 which emerges from the chassis between two vertical hitch support plates 12, each provided with a vertically extending slot 13 in which a vertically moveable hitch (not shown) is slideable.

A PTO guard member 14 is pivotally mounted on the plates 12 by two arms 15 which are screwed to the guard at 15a and which pivot about pins 16 screwed into the plates 12. Each vertical plate 12 has a cut-out 17 to save weight which is covered by a side protection plate 18 secured to the adjacent vertical plate 12 by bolts 19. Each protection plate 18 has a slot 20 through which the respective support arm 15 for the PTO shaft cover 14 extends.

A bow spring 21 acts between a pin 22 on the support arm 15 and a pin 23 mounted on the adjacent vertical plate 12.

A top protection plate 24 is bolted on the rear of the chassis at 25 and extends between the edge portion 14a of the guard and the chassis when the guard is in its extended position shown in Figure 4.

With the PTO shaft guard 14 in its retracted position shown in Figure 1, the bow spring 21 applies force to the guard 14 in the direction of the arrow A resulting in a turning moment on the guard in an anti-clockwise sense as shown by the arrow R thus holding the guard in its fully retracted position shown in Figure 1. The lower end of the slot 20 in each protection plate 18 provides a stop for the downward movement of arm 15.

Figure 4 shows the PTO shaft guard in its fully extended position which the bow spring 21 applies a force B to the guard which generates a clockwise turning moment about the axis 16 thus tending to hold the guard in its fully extended position. The clockwise movement of the arm 15 is limited by the edge 12a of the plate 12.

The guard 14 has a tab 14b allowing the operator to easily grip the guard for moving the guard between its retracted and extended position. As will be appreciated, the bow springs 21 initially oppose the movement of the guard from its current retracted or extended position, but when the pins 21 cross the lines 26 between the pivots 16 and the pins 23, the spring go "over centre" and assist in moving the guard towards its new position. As can be seen from Figure 4, the front edge of the guard 14 has cam surfaces 27 which extends across the vertical slots 13 in the vertical plates 12. If a vertically moveable hitch is mounted in the slots 12 and is moved upwardly it will contact this cam surfaces 27 and move the PTO guard towards its retracted position. Initially this movement will be opposed by the bow springs 21 but after the mounting pins 22 move "over centre" this spring force will assist in retracting the PTO guard.

Figures 7 to 11 show different arrangements of the shaft guard 14 according to the invention. The PTO shaft and hitch support plates 12 are not shown in these drawings. All other features, where present are indicated using the same reference numbers as in figures 1 to 6.

Figure 7 shows a perspective view of the guard 14 from the front as it would be viewed if attached to a vehicle having a PTO shaft. The guard 14 has two side portions 40 and a central portion 41 which form a generally flat bottomed inverted U-shape. Figure 8 shows a perspective view of the guard in which side portions 40 are fitted with releasably attachable adapter side members 42. The adapter side members 42 protrude inwards towards each other and are attached to side portions 40 by fastening means such as bolts, or screws. The attachment means can be seen in figure 9 which show a perspective view of the back of the guard of figure 8. The adapter side members decrease the distance of the side portions 40 of the guard from the PTO shaft . By fitting the adapter side members 42 greater space either side of the shaft is protected.

Figures 10 and 11 show front and rear perspective views of the guard 14 in which both side 40 portions and the central portion 41 of the guard 14 are provided with releasably attachable side adapter members 42 and a central portion adapter member 43. The central portion adapter member 43 protrudes downwards towards a PTO shaft (not shown) and provides greater protection of the space between the central portion 41 and the PTO shaft. The central portion adapter member 43 is attached to the guard 14, for example by bolts, or screws as can be seen from figure 11 which is a rear perspective view of figure 10. The central portion adapted 43 and side portion members 42 may be individual parts, or a single piece. The adapter side members 42 and central potion adapter member 43 alter the size of the guard which may be necessary to comply with certain rules and regulations in various countries.