"Rotarv Rockwheel Assemblies" This invention relates to rotary rockwheel assemblies which serve to cut a narrow trench in the ground when driven along the ground by a vehicle. It is known to use a rotary rockwheel assembly pulled by a tractor for cutting a narrow trench in the ground, for example for installation of television cables and other services beneath the surface of a road or pavement. The cutting wheel of such an assembly has a plurality of carbide teeth attached to its outer rim and is driven in a clockwise or anti-clockwise direction by the power take-off from the tractor. Furthermore the cutting wheel is supported by the tractor by way of a pivot linkage permitting the rotating cutting wheel to be lowered into the ground to commence cutting of the trench. The tractor may then be moved forward whilst rotating of the cutting wheel continues so as to continue cutting of the trench. However, there are certain disadvantages associated with such rockwheel assemblies in use. Because .the cutting wheel is directly carried by the pivot linkage shock and vibration are transmitted from the cutting wheel to the linkage and to the tractor, and there is a tendency for the depth of trench to vary uncontrollably. Furthermore when used for cutting through the surface of a tarmac road or pavement such assemblies produce trenches having ragged edges due to the fact that the cutting wheel has a tendency to break away stones at the edges of the trench. This means that, in many applications, it is

necessary to subsequently smooth the edges of the trench in a separate operation using an inclined saw. This significantly increases the trench cutting costs.

It is an object of the invention to provide an improved rotary rockwheel assembly which is capable of cutting a trench in a particularly efficient manner.

According to the present invention there is provided a rotary rockwheel assembly for cutting a narrow trench in the ground when driven along the ground by a vehicle, the assembly comprising a support .frame,- ground-engaging means on the support frame for ^' supporting the support frame on the ground and permitting the support frame to be moved in the direction in which the trench is to be cut, a rotary cutting wheel carried by the support frame, drive means for rotating the cutting wheel about a substantially horizontal axis, and lowering means on the support frame for lowering the cutting wheel relative to the support frame from a raised position in which substantially the whole of the cutting wheel is above the ground to a lowered position in which a substantial part of the cutting wheel is sunk into the ground in a trench cut by the cutting wheel.

Such an assembly is capable of cutting a trench in a particularly efficient manner by virtue of the fact that the reaction forces generated by the cutting action of the cutting wheel are transmitted by way of the ground- engaging means to the ground, rather than producing undesirable vibration of the assembly detrimental to the

tractor or the linkage coupling the rockwheel assembly to the tractor.

Preferably the ground-engaging means comprises ground-engaging members which are adapted to engage the ground along the opposing edges of the trench being cut. The ground-engaging members are advantageously constituted by two skids disposed one on each side of the cutting wheel, although they may also be constituted by ground- engaging wheels. The ground-engaging means may comprise a single skid which surrounds the wheel and is adapted to engage the ground on opposite sides of the trench being cut.

The lowering means may comprise a sub-frame carrying the cutting wheel and pivotally connected to the support frame, and pivoting means for pivoting the sub- frame relative to the support frame to move the cutting wheel between the raised position and the lowered position. The pivoting means may be constituted by at least one extensible and contractable ram pivotally connected between the support frame and the sub-frame.

Furthermore the assembly may include a linkage, such as a parallel arm linkage, for coupling the support frame to a vehicle and permitting vertical movement of the assembly relative to the vehicle and to the ground. In addition the assembly may include lifting means, such as at least one extensible and contractable ram, for lifting the assembly clear of the ground when it is to be transported by the vehicle.

The drive means may comprise a hydraulic motor which may be coupled to the cutting wheel by a chain drive mechanism.

In order that the invention may be more fully understood, a preferred embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a schematic side view of the assembly; Figure 2 is a front view of the assembly with the cutting wheel being shown in vertical section; and

Figures 3, 4 and 5 are diagrammatic side views of the assembly coupled to a tractor in three possible operational positions. Referring to Figures 1 and 2, the rotary rockwheel assembly 1 comprises a cutting wheel 2 mounted within a sub-frame 3 so as to be rotatable about a horizontal axis 4 parallel to the surface 5 of the ground. The cutting wheel 2 , which is shown in vertical section in Figure 2, has two rows of carbide teeth 6 attached to its outer rim 7, and .is driven clockwise or anti-clockwise by a hydraulic drive motor 8 coupled to the drive shaft of the cutting wheel 2 by a 2.5 : 1 chain drive mechanism 10.- The cutting wheel 2 and associated drive motor 8 are supported within the sub-frame 3 which is welded at its front (towards the right in Figure 1) to a transverse tube 11 (shown in Figure' 2) . Furthermore a pivot pin 12

extends through the tube 11 and through side cheeks 13 of a ground-engaging support frame 14 between which the sub- frame 3 is positioned so as to permit pivoting of the sub- frame 3 about the pivot pin 12 within the support frame 14. Each of the side cheeks 13 is welded to a respective upright 15 and ground-engaging skid 17 of the support frame 14 on the associated side of the cutting wheel 2, and the two skids 17 on opposite sides of the cutting wheel 2 are connected together by a cross-member 16 at the rear of the cutting wheel 2 and additionally by- a .cross- member (not illustrated) at the front of the wheel 2. In addition a respective pivot ram 18 on each side of the cutting wheel is pivotally connected at 19 to the associated upright 15 of the frame 14 and is pivotally connected at 20 to the sub-frame 3, and is extensible and contractable to pivot the sub-frame 3 between a raised position and a lowered position (shown in Figures 1 and 2).

The sub-frame 3 comprises, on each side of the cutting wheel 2, a respective side cheek 21, and the two side cheeks 21 are joined together .by an arcuate sheet 25 which extends between the side cheeks 21 over the top of the cutting wheel 2. Furthermore a crumber 26 extends through a clamp box constituting the cross-member 16 and is slidable within the clamp box so as to be adjustable in height in dependence on the depth of the trench 33 being cut. The crumber 26 serves to clear the soil from the bottom of the trench 33.

A respective aperture 50 is provided at the rear of each side cheek 21 of the sub-frame 3, and associated chutes 51, and chevrons (not illustrated) within the sub- frame 3, serve to discharge spoil outwardly of the sub- frame 3 and to deposit the spoil onto the ground, rather than into the trench. In addition rubber flaps 52 are provided on the side cheeks 13 of the support frame 14 to prevent the spoil thrown up by the cutting wheel 2 from flying forwardly of the assembly to present a hazard to operating personnel. A ■ spoil guidance system 53 is provided within the sub-frame 3 at the front of the cutting wheel 2 to divide the spoil thrown up by the wheel 2 and guide it towards the two sides of the sub-frame 3.

Each of the skids 17 is fitted with a plough member 31, and optionally also with a 45 degree two-way spoil plough 32 for use when cutting through tarmac.

Figures 3, 4 and 5 show highly diagrammatical side views of the ^" assembly 1 in three operational positions coupled to a tractor 40 by a pivot linkage 41. The pivot linkage 41 comprises a respective pair of parallel arms 42, 43 pivotally connected to each upright 15 of the frame 14 and pivotally connected to the tractor 40, and a respective lift ram 44 pivotally connected between- the tractor 40 and each arm 42. When a trench is to be cut, the assembly 1 is lowered by the lift rams 44 of the pivot linkage 41 into a ready-for-work position, shown in Figure 3, in which the skids 17 on the support frame 14 engage the surface 5 of

skids 17 on the support frame 14 engage the surface 5 of the ground. In this position the pivot rams 18 are fully extended so that the sub-frame 3 is in its raised position in which the cutting wheel 2 is held clear of the surface 5 of the ground.

After the cutting wheel 2 has been set in motion by the motor 8 which is driven from the power take¬ off of the tractor 40, the cutting wheel _. 2 is lowered into the ground to cut a trench 33 by contracting the pivot. rams 18 to pivot the sub-frame 3 within the support frame 14. The depth of the trench 33 to be cut is determined by the degree to which the pivot rams 18 are contracted. The tractor 40 may then be moved forward as the cutting wheel 2 continues to rotate to thereby cut a continuous trench. During cutting the skids 17 with the fitted plough members 31 travel along the two edges of the trench 33 being cut, as best shown in Figure 2.

After the required length of trench has been cut, the cutting"wheel 2 may be lifted out of the ground by expanding the pivot rams 18 so that the assembly again assumes the position shown in Figure 3. The lift rams 44 of the pivot linkage 41 may then be operated to lift the assembly l into a transport position clear of the surface 5 of the ground, as shown in Figure 5, in which the assembly may be transported to another location whilst being carried on the back of the tractor 40. It is to be noted that, in this transport position, the pivot rams 18 are contracted so that the sub-frame 3 is in its lower

pivotal position in order to lower the centre of gravity of the assembly during transport.

The above-described assembly is particularly advantageous in use for cutting a trench as the pivot rams 18 ^" absorb and transmit all the shock loads produced by the cutting action of the cutting wheel 2 through the support frame 14 into the ground. Thus substantially no vibration or forces detrimental to the tractor 40 or pivot linkage 41 are transmitted by the assembly. ' The pivot linkage 41 enables the assembly to move vertically up and down relative to the tractor 40 during cutting of the trench to accommodate uneveness in the ground. Furthermore the cutting depth may be varied by the pivot rams 18 without the skids 17 leaving the ground and without permitting substantial forces to be transmitted to the tractor.

The assembly may be used for cutting trenches of varying widths and depths through different media, from soil to solid rock. Furthermore the pivot linkage can easily be mounted on a cross-slide and steering device to enable the assembly to be steered independently of the tractor. Furthermore the assembly can be fitted to different types of vehicle and can be used in association with different types of coupling linkage.