GB2075467A - Slewing device, especially for excavating implement - Google Patents

Abstract

A slewing system for an excavating implement (6) has, in addition to two symmetrically arranged lateral pivot cylinders (8, 9), an additional pivot cylinder (16) located in a plane of symmetry therebetween and lying on a different level from the lateral cylinders (8, 9) and the pivot shaft (5) of the excavating implement (6). The centre cylinder (16) is jointed to a point of attachment (19) on the excavating implement (6) located on its centre line. The lever arm of the centre cylinder (16) about the axis of rotation (5) of the implement (6) is thus zero when the implement is in its centre position (as shown) and increases with increasing slewing angle. When the implement is swung out 90 DEG , the centre cylinder (16) has a maximum slewing effect. Flow limitors (33, 35) in the feeder lines (31, 32) of the centre cylinder, cause the centre cylinder to be used at the same time as a brake for automatically reducing the speed of slewing as the excavating implement approaches its end positions. <IMAGE>

Description

SPECIFICATION Swing device, especially for an excavating implement The present invention relates to a device for swinging a body, especially an excavating implement.

A swing device is disclosed in U.S. patent specification 3 343 686. By virtue of the fact that the lever arm of the central auxiliary cylinder increases as the lever arms of the lateral pivot cylinders decrease and by virtue of the fact that said lever arm of the auxiliary cylinder increases as the pivot angle of the body from the center position increases, it is possible to have an essentially constant resultant effective lever arm to the body within its entire range of swing.

However, the known design has the disadvantage that if the operator is not cautious in the swing movement and swings with maximum speed, the body can strike its end abutment with great force at the end position of the swing movement. Attempts have been made to reduce this undesirable impact by placing one-way restrictions in the lines to the auxiliary cylinder, but this measure has not produced a satisfactory solution to the problem.

The purpose of the present invention is to prevent the velocity of the body from exceeding a predetermined value when it reaches its end position, even if the operator sets the controls for maximum speed of swing. At the same time the body should be able to be swung at high speed as it passes its centre position and within the major portion of its range of swing.

According to the invention there is provided a device for swinging a body, especially an excavating implement, about an axis of rotation in either direction from a centre position, comprising two pivot piston-cylinder devices arranged symmetrically on either side of a plane of symmetry formed by the centre plane of the body when in its centre position and passing through the axis of rotation, one end of each pivot piston cylinder device being pivotally joined to an individual stationary point of attachment, said points of attachment being situated on either side of and spaced from the plane of symmetry, each of the other ends of the pivot cylinder devices being pivotally joined to an individual point of attachment on the body, and spaced from the centre plane of said body, an auxiliary piston cylinder device being arranged between a stationary auxiliary cylinder point of attachment which is located in the plane of symmetry between the two lateral cylinders and an associated auxiliary pivot point of attachment on the body, said point of attachment being located in the centre plane of the body and spaced from the axis of rotation, a flow reversing device being included in the pressure medium connection of the auxiliary cylinder device and being disposed to reverse the cylinder connections when the body is swung past its centre position, the pressure medium lines connected to the auxiliary cylinder device being provided with means for preventing excessively high angular velocity of the body at the ends of its swing movement, characterized in that said means consist of a flow-limiting arrangement, which encompasses on the one hand a pressure-limiting valve in the cylinder-side line of the auxiliary cylinder and which is pilotcontrolled by means of the pressure in the piston rod side of the auxiliary cylinder, and on the other hand a pressure-compensated flow rate regulator in the line connected to the piston rod side of the auxiliary cylinder.

The invention is based on the insight that at constant angular velocity the flow rate increases in the auxiliary cylinder towards the end positions of the swing movement. By flow rate regulation, permitting unthrottled flow up to a certain rate which cannot be exceeded, the swing movement is unimpeded within the major portion of its range of swing. Only when the body approaches its end positions is the speed reduced by the flow rate not being permitted to exceed a maximum value. The invention enables the speed of swing to be limited even if the body is acted on by external forces not stemming from the hydraulic system, for example gravitational forces or wind.

This type of speed limitation cannot be achieved with simple restriction chokes according to the known device. It is true that fixed restriction chokes can be installed so as to limit the maximum highest swing speed at the end positions. However, since a fixed restriction choke is always in effect, it will reduce the speed within other portions of the swing range as well, which is a disadvantage. Nor is it able to react if the body is affected by external forces; it can allow higher speeds than the maximum intended.

An embodiment of the invention will be described below in more details with reference to the accompanying drawing, of which Fig. 1 shows from above a pivot joint, equipped with a swing device embodying the invention, for the digging implement on an excavator with said implement in its centre position. The associates hydraulic system is shown schematically; Fig. 2 shows the device with the implement swung 900 in one direction from its centre position.

A frame 1 and a support 6 are pivotally jointed to each other by means of a vertical axle 5. The frame 1 can be rigidly joined to a vehicle frame and the support 6 can carry the boom of a digging implement.

The swinging of the support 6 in the horizontal plane about the axis 5 is accomplished with the aid of three hydraulic piston cylinder devices. Two of these 8, 9 are arranged in the same horizontal plane with the cylinder ends pivotally joined to the frame 1 at points 10 and 11 respectively. The associated piston rods 1 2 and 1 3 respectively are pivotally jointed to the support 6 at points 1 4 and 1 5 respectively. Fig. 1 shows the support 6 in its centre position in which a vertical plane through the centre line of the support forms a plane of symmetry S. The two piston cylinder devices 8, 9 are located symmetrically on either side of the plane of symmetry S.As can be seen from Fig. 1, the two cylinders 8, 9 can swing the support 6 with maximum force when it is in the centre position since the lever arms of the cylinders, i.e.

the perpendicular distance from the piston rod 1 2 or 13 to the axis of rotation 5, are at a maximum when the support 6 is in the centre position shown in Fig. 1. The lever arms of the cylinders 8, 9, and thereby the force on the support 6, decrease with increasing pivot angle from the centre position until an angle of 900 has been reached, which is shown in Fig. 2. In this position, as in the corresponding position in the other direction, the cylinders 8, 9 have no lever arm to act on the support 6.

This is compensated for by a third piston cylinder arrangement 1 6, the cylinder of which is pivotally joined to the frame 1 via a point of attachment 1 7 located in the plane of symmetry S, and the piston rod 1 8 of which is pivotally joined to the support 6 at a point 1 9 located on the side of the pivot axle 5 away from the cylinder 1 6. In order to make this arrangement possible, the piston cylinder device 1 6 is placed lower than the lateral piston cylinder devices 8, 9.

To reduce the angular velocity near the end positions and thus produce a soft braking of the support 6 and the implement mounted thereon, the centre cylinder 1 6 is supplied with hydraulic fluid according to the hydraulic system shown in Fig. 1. A manual operating valve 20 is used to connect a fluid line 22 from a pump 21 and a return line 24 leading to a hydraulic tank 23 to two system feeder lines 25 and 26. The feeder line 25 is connected to a fluid line 27 to the cylinder side of the cylinder 8 and a line 28 to the piston rod side of the cylinder 9. The feeder line 26 is connected to a line 29 to the piston rod side of the cylinder 8 and a line 30 leading to the cylinder side of the cylinder 9.Feeder lines 25, 26 are also connected to an electromagnetically controlled 4/2 directional control valve 40, from which a line 31 goes to the cylinder side of the cylinder 1 6 and a line 32 goes to the piston rod side of the cylinder 1 6. The cylinder side line 31 has a pilot-controlled pressure-limiting valve 33, which is bridged by a nonreturn valve 34 opening in the direction to the cylinder side. The line 32 includes a pressure compensated flow rate regulator 35 acting in the direction towards the piston rod side. A pilot line 36 which is connected to the portion of the line 32 leading to the piston rod side, supplies the prevailing pressure in the piston rod side as a pilot pressure to the pressure-limiting valve 33.

The device functions in the following manner.

If, for example, one wishes to swing the support 6 to the left from its centre position shown in Fig. 1, the 4/3 operating valve 20 is moved to its position I in which the feeder line 26 is connected to the pump pressure line 22 and the feeder line 25 is connected to the return line 24. Via lines 29 and 30, the piston rod side of the cylinder 8 and the cylinder side of the cylinder 9 will be supplied with fluid, thus swinging the support 6 to the left. In the centre position, the cylinder 1 6 has no effect on the pivot movement since it has no lever arm in relation to the support 6. With the aid of a position sensor (not shown), arranged between the support 6 and the frame 1, for example, the reversing valve 40 is switched to its position II when the support 6 is in a swing position to the left of the plane of symmetry S.Fluid will thus be fed through the line 32 to the piston rod side of the cylinder 1 6 via the flow rate regulator 35. The return flow from the cylinder side of this cylinder passes through the pressure-limiting valve 33 and is directed to the feeder line 25. The pressure-limiting valve 33 sees to it that the flow from the cylinder side of the cylinder 1 6 does not exceed a predetermined value. The cylinders 8 and 9 strive to increase the speed of swing as the pivot angle from the centre position increases. With the aid of the pressurelimiting valve 33, however, the piston speed in the cylinder 1 6 is limited to a value corresponding to the just mentioned predetermined flow through the valve 33.In the event that the support 6 is made to move, by the cylinders 8, 9 or by other means, at a greater speed than that corresponding to the predetermined flow, the pressure in the piston rod side of the cylinder 1 6 will drop since the flow thereto is limited by the flow rate regulator 35. The pilot pressure in line 36 to the pilot-controlled pressure-limiting valve 33 will thereby drop, causing the valve 33 to throttle further and thereby brake the speed of swing.

At constant flow through the pressure-limiting valve 33 at the predetermined value, the angular velocity of the support 6 decreases the closer the support comes to its end position 90 from the centre position, which is dependent on the fact that the lever arm of the cylinder 1 6 in relation to the axis of rotation 5 of the support 6 increases with increasing angle of swing. This reduction of the speed of swing with movement towards the end positions is desirable since this eliminates the need for separate braking means and the support 6 can be permitted to strike the end abutments directly.

When the support 6 is to be swung back from its left-hand end position to the centre position, the operating valve 20 is shifted to its position II thereby pressure-feeding the feeder line 25. This feeds the line 27 to the cylinder side of the cylinder 8 and the line 28 to the piston rod side of the cylinder 9. The valve 40 remains in its position II and the fluid flows through line 31 and can bypass the pressure-limiting valve 33 through the check valve 34. The cylinder side of the cylinder 1 6 is supplied with fluid, thereby extending the piston rod 1 8 from the position shown in Fig. 2 and swinging the support 6 towards its centre position. The hydraulic fluid in the piston rod side of the cylinder 1 6 flows through the line 32 to the flow rate regulator 35, which is designed so that it does not restrict the flow in the direction towards the valve 40. This is indicated by a check valve 37, parallel with the valve 35 and indicated with dashed lines, which opens in the direction towards the valve 40. Thus when the piston of the cylinder 1 6 is pushed out to swing the support 6 towards its centre position, there is no limiting of the flow in the fluid circuit of the cylinder, and therefore the angular velocity of the support is only limited by the maximum flow of the pump 21 and unavoidable restrictions in valves and pipes. When the support 6 reaches its centre position, the valve 40 automatically switches to its position I.This valve switching occurs without any jerking in the system since the flow to the cylinder 1 6 is zero when the support 6 passes its centre position. As the support continues to swing to the right, the piston rod side of the cylinder 1 6 is now fed with fluid via the line 32, i.e. the middle cylinder 1 6 pulls once again as the support 6 swings away from its centre position. When swinging to the right from the centre position, the sequence described above for swinging to the left is repeated. The support 6 is braked as it moves towards its end position. When it is to be swung back towards the centre, the operating valve 20 is switched to its position I. The valve 40 remains in its position I and the swing back sequence described above is repeated.

The operation of the reversing valve 40 may be accomplished in many ways, but it must cause the valve to reverse the flow directions in the lines 31 and 32 when the support 6 passes its centre position. Suitably its operation can be automatic by sensing the angular position of the support 6 or of one of the cylinders 8, 9 or 1 6, or by sensing the piston rod position in one of the cylinders 8 or 9.

Claims (3)

1. Device for swinging a body, especially an excavating implement, about an axis of rotation in either direction from a centre position, comprising two pivot piston-cylinder devices arranged symmetrically on either side of a plane of symmetry formed by the centre plane of the body when in its centre position and passing through the axis of rotation, one end of each pivot piston cylinder device being pivotally joined to an individual stationary point of attachment, said points of attachment being situated on either side of and spaced from the plane of symmetry, each of the other ends of the pivot cylinder devices being pivotally joined to an individual point of attachment on the body, and spaced from the centre plane of said body, an auxiliary piston cylinder device being arranged between a stationary auxiliary cylinder point of attachment which is located in the plane of symmetry between the two lateral cylinders and an associated auxiliary pivot point of attachment on the body, said point of attachment being located in the centre plane of the body and spaced from the axis of rotation, a flow reversing device being included in the pressure medium connection of the auxiliary cylinder device and being disposed to reverse the cylinder connections when the body is swung past its centre position, the pressure medium lines connected to the auxiliary cylinder device being provided with means for preventing excessively high angular velocity of the body at the ends of its swing movement, characterized in that said means consist of a flow-limiting arrangement, which encompasses on the one hand a pressure-limiting valve in the cylinder-side line of the auxiliary cylinder and which is pilotcontrolled by means of the pressure in the piston rod side of the auxiliary cylinder, and on the other hand a pressure-compensated flow rate regulator in the line connected to the piston rod side of the auxiliary cylinder.

2. Device according to claim 1, characterized in that the pressure-limiting valve and the flow rate regulator are each by-passed by an individual check valve, which opens the flow direction which results in extension of the piston rod of the auxiliary cylinder.

3. Device for swinging a body substantially as hereinbefore described with reference to and as shown in the accompanying drawing.