GB2293394A - Speed control for trenchers - Google Patents

Abstract

A trenching machine has a rotary trenching wheel 10 driven by a hydraulic motor 13, the wheel being mounted on a frame 12 pivoted to a support 16. A hydraulic actuator 17 connects the frame 12 to the support 16 to perform relative pivoting movement of the frame 12 in a retreating sense having regard to cutting movement of the wheel 10. On advancing the support 16 to perform trenching, the loading on the hydraulic motor 13 driving the wheel 10 is sensed, and the actuator 17 is controlled to cause retreating movement of the frame 12 dependent upon the sensed loading. <IMAGE>

Description

SPEED CONTROL FOR TRENCHERS This invention relates to methods of and apparatus for the control of the speed of advancement of a rotary trenching wheel mounted on a frame. The invention is particularly (but not exclusively) applicable to a trench cutting attachment detachably mounted on a prime moving machine for advancement of the attachment.

Machines which use cutters fitted to a rotating wheel to dig trenches in various types of ground, roads and concrete surfaces are well known. Such machines when digging a trench have to move forward very slowly and steadily often at as little as ten metres an hour. This usually requires a special machine or one with an adapted transmission. In many applications it would be beneficial to mount trench cutting attachments onto prime moving machines such as industrial or agricultural tractors, skid steer loaders or backhoe excavators, which do not have the necessary adaption to give a slow steady forward speed.

The disadvantage in mounting a trench cutting attachment onto such unadapted prime moving machines is that the operator must try to use the controls of the prime moving machine to advance the rotary trenching wheel steadily at the right speed.

Frequently this will not be achieved and over fast movements will stall the rotary trenching wheel or worse cause it to lurch forward so that a single cutting tip becomes hooked under the surface layer being cut or under a particularly tough element such as a reinforcing rod. Alternatively the operator may not advance the rotary trenching wheel as fast as it is capable of working and thus lose production.

When the prime moving machine is a backhoe excavator the trench cutting attachment may conveniently be mounted on the backhoe arms where normally the digging bucket would be mounted. This not only gives the advantage of a readily available prime mover but also allows the trench cutting attachment to be used in otherwise inaccessible places. A disadvantage is that it requires considerable skill and concentration for the operator to pull the trench cutting attachment forward smoothly and continuously and it is very difficult for him to judge the correct forward speed to optimise the rate of work and he must usually err on the side of caution.

A principal aim of this invention is to provide for the rotary trenching wheel, for example of a trench cutting attachment, an efficient compensating movement for over fast or erratic forward movement produced by the prime moving machine.

According to one aspect of the present invention there is provided a method of controlling the speed of advancement of a rotary trenching wheel mounted on a frame and driven by a hydraulic motor, the frame being movably mounted on a support arranged for advancing movement over the ground and there being a hydraulic actuator linking the frame to the support to effect relative retreating movement of the frame with respect to the support, in which method the retreating movement of the frame effected by the hydraulic actuator is controlled dependent upon the loading on the hydraulic motor.

An advantage of the method of the present invention is that it can be performed so that in many circumstances there is an actual forward movement of the rotary trenching wheel with respect to the medium being cut despite the relative retreating movement with respect to the support (which might itself be advancing faster), which assists to optimise the cutting action of the rotary trenching wheel.

According to a second aspect of this invention,there is provided a trenching apparatus comprising a rotary trenching wheel mounted on a frame and driven by a hydraulic motor, a support on which the frame is movably mounted and which is arranged for advancing movement over the ground, a hydraulic actuator linking the frame to the support to effect retreating movement of the frame with respect to the support, and control means to sense the loading on the hydraulic motor and to control the operation of the actuator dependent thereon.

An advantage of this aspect of the present invention is that the equipment can be configured as an attachment for use with a backhoe excavator.Then, the relative retreating movement may pivot the frame in such a way that it compensates for unwanted rotation about an axis perpendicular to the direction of movement.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows a trench cutting attachment mounted on a speed control and support assembly of this invention mounted on the arm of a backhoe excavator, with the arm pulled in; Figure 2 shows the arrangement of Figure 1 but with the arm extended; Figure 3 shows a trench cutting attachment mounted on a speed control and support assembly of this invention with the speed control and support assembly in the forward position; Figure 4 shows the arrangement of Figure 3 but with the speed control and support assembly in the retreated position; Figure 5 is a diagrammatic view of the hydraulic control with the double acting ram and spool valve shown in section; Figure 6 shows the arrangement of figure 5 but with two double acting rams; and Figure 7 shows the arrangement of figure 5 but with single acting rams.

Referring to Figures 1, 2, 3 and 4, a trench cutting attachment which includes a rotary trenching wheel 10, a support frame 12, a hydraulic motor 13, a control valve 46 and a wheel 18 is movably attached to a speed control and support assembly which includes a double acting hydraulic ram 17 and a pivot frame 16. The pivot frame 16 is detachably mounted on an hydraulically operated arm 14 of a backhoe excavator. The rotary trenching wheel 10 is rotatably driven using the hydraulic supply of the backhoe excavator supplied through pipe 25 and returned through pipe 39. The arms 14 and 15 are used to lower the trench cutting attachment to cut a trench to the depth set by wheel 18 and to provide forward motion by pulling the trench cutting attachment towards the backhoe excavator.

The pivot frame 16 is rotatably connected to the support frame 12 by a pivot pin 19. Double acting hydraulic ram 17 is rotatably supported by pivot pins 20 and 21 respectively connected to the pivot frame 16 and the support frame 12 so that when the double acting hydraulic ram 17 extends, the support frame 12 with the rotary trenching wheel 10 is rotated upwards and away from the arm 14 of the backhoe excavator, that is in a retreating direction with respect to the arm 14 and pivot frame 16. When it contracts the reverse movement takes place.

This movement is controlled by valve 46 which senses an hydraulic pressure in the hydraulic supply from the supply pipe 25 to the hydraulic motor 13 and when this first hydraulic pressure is less than a certain first pre-set figure causes the double acting hydraulic ram 17 to contract and when this hydraulic pressure exceeds a second pre-set figure causes it to extend. When the hydraulic pressure is between these two pre-set figures, which are separated by about twenty bar, the double acting hydraulic ram 17 will neither contract nor extend. The second pre-set figure for the hydraulic pressure is set at the level where the hydraulic motor 13 will work at its optimum and below the figure at which it will stall.Thus if the arm 14 is moved too quickly so that the rotary trenching wheel 10 is pulled towards the medium 1 1A to be cut too fast, the load on the hydraulic motor 13 will increase to the point that the hydraulic pressure needed to drive it exceeds the second pre-set figure where the valve actuates the double acting hydraulic ram 17 to produce the retreating movement and consequent reduction of the load on the hydraulic motor 13. This reduces the hydraulic pressure to below the second pre-set figure and thus cessation of the retreating movement.When the hydraulic pressure is between the first and second pre-set figures the double acting hydraulic ram 17 is static and unless the operator moves the arm 14 forward to increase the load on the hydraulic motor 13 the hydraulic pressure will decline further to below the first pre-set figure causing the double acting hydraulic ram 17 to contract and move the rotary trenching wheel 10 forward. The retreating movement as described above may only be relative to the pivot frame 16 and arm 14 but not to the medium 11A to be cut so that during the whole cycle the rotary trenching wheel continues digging with near its optimum working hydraulic pressure.If, however, the hydraulic pressure remains above the second pre-set figure even when the arm 14 of the backhoe excavator is not being moved forward too quickly and this can happen if the rotary trenching wheel is choked with an excess of cut debris or has become hooked into a tough element in the medium 11A to be cut, such as a steel reinforcing rod, the double acting ram 17 will continue to extend producing sufficient retreating action so that the rotary trenching wheel 10 retreats with respect to the medium 11A to be cut thus clearing or unhooking itself, reducing the load on the hydraulic motor 13, triggering contraction of the double acting ram 17 and the recommencement of forward movement.

Referring now also to figure 5, the shaft end port 27 of the double acting hydraulic ram 17 is connected to the valve port 45 of control valve 46 and to the hydraulic motor 13 pressure port by pipe 26 and is also connected by pipe 25 to the hydraulic supply from the backhoe excavator.

When hydraulic pressure is applied to the hydraulic motor 13 to turn the rotary trenching wheel 10 it is thus also applied through the valve port 45 to the nose 43 of the spool 37 in the control valve 46 and to the double acting hydraulic ram spring 35 hydraulic oil at valve port 45 is blocked by the spool 37. Spool 37 has a cylindrical shape with various diameters but is parallel at 42 and 42A and an accurate sliding fit in the circular hole 44 in the control valve 46. In this condition the double acting ram 17 contracts to pull the support frame 12 forward and downward increasing the cutting load on the rotary trenching wheel 10.The oil from the head end of the double acting hydraulic ram 17 passes through port 28 and by pipe 24 to valve port 48 and then past the annular ring channel 41 created between the reduced diameter section 41A on spool 37 and the accurate hole 44 and so to port 40 and by pipe 39 to the hydraulic tank of the backhoe excavator.

When the double acting hydraulic ram 17 has contracted to its minimum length or when the bottom edge 22 of the support frame 12 is approximately parallel with the surface 11 the operator uses the backhoe excavator controls to move the arms 14 and 15 so as to move the trench cutting attachment forward. This has the effect of increasing the load on the rotary trenching wheel 10 and hence the pressure in the hydraulic circuit feeding the hydraulic motor 13, the hydraulic ram port 27 and valve port 45. When the hydraulic pressure at valve port 45 equals the first pre-set figure controlled by spring 35 the spool 37 is pushed against the spring 35 until the parallel section 42 of the spool 37 closes off the orifice 38 stopping the double acting hydraulic ram 17 from further contraction.If the hydraulic pressure at valve port 45 exceeds this first pre-set figure the spool 37 is pushed further against the spring 35 until the second pre-set figure is reached and orifice 47 is opened allowing oil to pass to valve port 48 and through pipe 24 to the double acting hydraulic ram 17 at port 28.

Both ends of the double acting hydraulic ram 17 are now seeing the same hydraulic pressure and it will extend with the hydraulic pressure working on an effective area equal to the cross sectional area of the ram shaft 23. This rotates the support frame 12 around pivot pin 19 moving the rotary trenching wheel 10 backwards and upwards that is retreating from the pivot frame 16 and reducing the rate of movement towards the medium 1 lA to be cut. This reduces the load on the rotary trenching wheel 10 and hence the hydraulic pressure to the motor 13 and the spool 37 allowing spool 37 to close off the orifice 47 and when the pressure drops below the first pre-set figure to open the orifice 38 so that the double acting ram 17 again starts to contract and move the rotary trenching wheel 10 towards the medium I lA to be cut.

In this way jerky movements by the backhoe excavator are smoothed out and provided the operator pulls the trench cutting attachment forward when the double acting hydraulic ram 17 is at its fully contracted position or when the bottom edge 22 of the support frame 12 is approximately parallel to the surface 11 the pressure applied to the hydraulic motor 13 is controlled to near to the optimum figure controlled by the spring 35 and hence the rotary trenching wheel works to near its maximum effect. When the speed control and support assembly is used in this way the rotation of the trench cutting attachment automatically produced when the backhoe excavator arms 14 and 15 are pulled in is compensated for without continuous adjustment by the operator.Occasional adjustments to the angular position of pivot frame 16 using the backhoe excavator ram 31 are all that is necessary to keep the double acting hydraulic ram 17 in an appropriate working range.

The spool 37 is prevented from over rapid movement by a dashpot formed by the spring chamber 32 which is filled with oil and the spool collar 36 which is a close fit in the spring chamber 32. The spool end shaft 33 is an accurate fit in the circular hole 34 which is the same diameter as hole 44. Pipe 29 connects valve port 30 to pipe 39 hence ensuring that the hydraulic pressure sensed by the valve 46 is referenced to the tank pressure of the backhoe excavator.

Figure 6 shows a second embodiment of the speed control for trench cutting attachments in which two double acting hydraulic rams 17A and 17B are connected in parallel. Each hydraulic ram must be rotatably connected to the pivot frame 16 and the support frame 12 but in other respects the assembly is similar to that described with reference to figures 3, 4, and 5. Any number of double acting hydraulic rams may be so connected in parallel.

Figure 7 shows a third embodiment of the speed control for trench cutting attachments in which two single acting rams 49 and 50 are used to provide the rotation between the pivot frame 16 and support frame 12 and both rams are each rotatably connected to these two frames. Single acting ram 50 serves to move the rotary trenching wheel 10 towards the medium 1 lA to be cut and single acting ram 49 to move the rotary trenching wheel 10 away from the medium 1 lA to be cut. The moment of ram 50 acting about pivot 19 must be less than the moment of ram 49 acting about pivot 19. In other respects the assembly is similar to that described with reference to figures 3, 4, and 5. Any number of single acting hydraulic rams or combination of double acting and single acting rams may be so connected provided that the aggregate moment of the rams provided to move the rotary trenching wheel 10 towards the medium 11A to be cut is less than the aggregate moment of the rams provided to move the rotary trenching wheel 10 away from the medium 11A to be cut.

Claims (15)

1. A method of controlling the speed of advancement of a rotary trenching wheel mounted on a frame and driven by a hydraulic motor, the frame being movably mounted on a support arranged for advancing movement over the ground and there being a hydraulic actuator linking the frame to the support to effect relative retreating movement of the frame with respect to the support, in which method the retreating movement of the frame effected by the hydraulic actuator is controlled dependent upon the loading on the hydraulic motor.

2. A method as claimed in claim 1, wherein a control valve senses the pressure in a hydraulic line supplying hydraulic fluid under pressure to the hydraulic motor, said control valve controlling the operation of the hydraulic actuator dependent thereon.

3. A method as claimed in claim 2, wherein when the sensed pressure rises above a predetermined value, the actuator is operated to effect retreating movement of the frame.

4. A method as claimed in any of the preceding claims, wherein the frame is pivoted to the support such that operation of the actuator pivots the frame to effect retreating movement of the frame.

5. A method as claimed in any of the preceding claims, wherein at least one double-acting hydraulic ram serves as said hydraulic actuator.

6. A method as claimed in any of claims 1 to 4, wherein at least one pair of single-acting hydraulic rams, connected to drive in opposite senses, serves as said hydraulic actuator.

7. A method of controlling the speed of advancement of a trencher having a rotary trenching wheel mounted on a frame and driven by a hydraulic motor, and substantially as hereinbefore described with reference to the accompanying drawings.

8. Trenching apparatus comprising a rotary trenching wheel mounted on a frame and driven by a hydraulic motor, a support on which the frame is movably mounted and which is arranged for advancing movement over the ground, a hydraulic actuator linking the frame to the support to effect retreating movement of the frame with respect to the support, and control means to sense the loading on the hydraulic motor and to control the operation of the actuator dependent thereon.

9. Trenching apparatus as claimed in claim 8, wherein the frame is pivotally mounted on the support and the actuator is arranged to effect pivotal movement of the frame with respect to the support, which pivotal movement is in a retreating sense of the rotary trenching wheel.

10. Trenching apparatus as claimed in claim 8 or claim 9, wherein the hydraulic actuator comprises at least one double acting ram, or at least one pair of single-acting rams arranged to drive in opposite senses.

11. Trenching apparatus as claimed in any of claims 8 to 10, wherein the support is pivoted to an arm which arm is itself arranged for pivoting movement to move the support over the ground, there being a compensating ram to effect pivoting movement of the support to maintain substantially constant the angular position of the support relative to the ground despite pivoting of the arm.

12. Trenching apparatus as claimed in claim 11, wherein there is a lever pivoted to the arm, the compensating ram being arranged to effect pivoting movement of the lever and the lever being linked to the support to effect pivoting movement thereof.

13. Trenching apparatus as claimed in claim 11 or claim 12, wherein the arm is pivoted to a further arm articulated to a prime moving machine, whereby the support may be moved over the ground by a combined motion of said arm, said further arm and said compensating ram.

14. Trenching apparatus having a rotary trenching wheel mounted on a frame and driven by a hydraulic motor, and substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

15. A trenching machine comprising a tractor-mounted backhoe assembly together with trenching apparatus as claimed in any of claims 8 to 14.