A dumper vehicle

Abstract: A dumper (10) comprising a chassis (12, 14) on which there is mounted a load-carrying skip (26) and two fluid operable rams (40, 42) for slewing the skip, the rams being arranged in a fluid circuit which delivers fluid under pressure to the rams, the fluid circuit including valve means (58) for permitting fluid under pressure in one part of the said fluid circuit to escape to another part of the circuit in the event of the fluid in a line leading to one of the rams exceeding a given pressure due to that ram being subjected to a sudden increase in load.

Description: The invention relates to a fluid circuit for a dumper vehicle having the features as set forth in the preamble of claim 1 (see, for example, GB-A-847 238.) The invention also relates to a dumper vehicle and is particularly concerned with a dumper comprising a chassis on which there is mounted a load-carrying skip and two fluid-operable rams for slewing the skip, eg in a substantially horizontal plane, as set forth in the preamble of claim 2 (see, for example, the a.m. GB-A-847 238.) For some time, Thwaites Ltd has been manufacturing and selling dumpers of the foregoing kind which have proved to be extremely successful in use. The two fluid-operable rams for rotating the skip comprise two cylinders which are mounted at one end on the chassis and have piston rods extending from their other ends. The piston rods are pivotally connected to a turntable at positions one each side of the rotational axis of the turntable and in front of the axis with the skip in its central straight-ahead position. In order to slew the skip, fluid from a fluid circuit is fed under pressure to the rams so as to extend one ram and retract the other. Rotation of the turntable in the opposite direction can be effected by reversing the operation of the rams. Such a ram arrangement for slewing the skip provides a very positive action with minimum backlash and has proved to be extremely effective. Dumpers are typically used on very uneven terrain which can cause a dumper to be tilted sideways on an incline at a steep angle when carrying heavy loads in the skip. Such sideways tilting creates a large rotational force which would, if a heavily loaded skip were freely rotatable, cause the skip to turn until it pointed fully down the incline. The action of the rams is designed to inhibit such movement. However, the rams can be put under particularly severe loads if the loaded skip is, say, deliberately rotated in the direction it would naturally want to turn when the dumper is tilted on an incline and then suddenly stopped using a control valve in the fluid circuit before the skip points fully down the incline. GB-A-847238 discloses a system whereby hydraulic rams are operable to move a chain and thereby drive a slewing pulley. The fluid circuit to the rams is provided with a relief valve to prevent damage to rams in the event of external loading to the bucket or the like. BE-A-534 537 discloses a system similar to the above-mentioned one, in which the relief valve comprises first and second pressure release means connected directly to the hydraulic rams respectively. An object of the present invention is to provide an improved dumper which will enable the rams to cope with than type of loading situation particularly well. According to the invention there is provided a fluid circuit for a dumper, the circuit including two fluid operable rams, a fluid communication line to each ram and valve means for permitting fluid under pressure in one part of the said fluid circuit to escape to another part of the circuit in the event of the fluid in a communication line leading to one of the rams exceeding a given pressure due to that ram being subjected to a sudden increase in load, characterised in that the valve means comprise first and second pressure release means provided between the fluid communication lines to each ram. The invention further provides a dumper comprising a chassis on which there is mounted a load-carrying skip and two fluid operable rams for slewing the skip, the rams being arranged in a fluid circuit which delivers fluid under pressure to the rams, the fluid circuit including fluid communication means (lines) to each ram and valve means for permitting fluid under pressure in one part of the said fluid circuit to escape to another part of the circuit in the event of the fluid in a communication means leading to one of the rams exceeding a given pressure due to that ram being subjected to a sudden increase in load, characterised in that the rams are pivotally connected between the chassis and the skip, and the valve means comprise pressure release means provided between the fluid communication means to each ram. If, during slewing movement, the skip is suddenly stopped as described above, any resulting increase in pressure can be relieved via the valve means. In that way, the ram can withstand more effectively the load which results when that ram is used to stop deliberate downward slewing of the skip when the dumper is tilted on an incline. Preferably, fluid in the circuit is fed to both of the rams simultaneously so as to apply high pressure to one end of one ram and high pressure to the opposite end of the other ram, fluid at low pressure simultaneously leaving the other ends of the rams. Preferably a loaded skip is brought to a halt by preventing flow of fluid from the rams (which results in an increase in pressure in a line through which the fluid would normally flow) and relieving the high pressure formerly applied to slew the skip. The valve means in such a case may then operate to permit fluid to flow from the line subjected to the increase in pressure. Accordingly, the fluid circuit is preferably arranged to feed fluid to both of the rams simultaneously so as to enable the application of high pressure to one end of one ram and to the opposite end of the other ram. Also, the fluid circuit can be arranged to drain fluid from both rams simultaneously so as to enable the drainage of low pressure fluid from one end of one ram and the opposite end of the other ram. Preferably the rams each comprise one end and an opposite end and the fluid circuit comprises a first means for communicating fluid to the one end of a first ram and the opposite end of a second ram, and a second means for communicating fluid to the one end of the second ram and the opposite end of the first ram. The valve means comprise a first pressure release means for allowing communication of fluid from the first to the second fluid communication means in order to relieve fluid pressure above a predetermined level. Also, the valve means comprises a second pressure release means for allowing communication of fluid from the second to the first fluid communication means in order to relieve pressure above a predetermined level. Preferably, the fluid communication in the opposite direction through each of the pressure release means in inhibited respectively by said first or second pressure release means. Another aspect of the invention provides a method of halting the slewing of a dumper according to claim 9 and comprising the steps of applying an increase in fluid pressure to selected opposite ends of the rams so as to prevent fluid release therefrom and to counter the direction of movement of the skip; allowing release of excess fluid pressure above a predetermined level in the fluid circuit; and allowing fluid communication from a first fluid communication means connecting opposite ends of the two rams along a first release means to a second fluid communication means or allowing fluid communication from the second fluid communication means connecting different opposite ends of the two rams along a second release means to the first fluid communication means. A dumper in accordance with the invention will now be described by way of example with reference to the accompanying drawings in which Fig 1 is an elevation of a dumper in accordance with the invention: Fig 2 is a plan view of a front chassis section of the dumper of Fig 2 showing a turntable and an arrangement of rams for rotating the turntable, Fig 3 is a cross section through the turntable shown in Fig 2 on the line III III in Fig 2, Fig 4 illustrates a fluid circuit for rotating the turntable and for operating various other rams on the dumper and Figs 5a to 5e are diagrammatic views showing the way in which the rams are operated to rotate the turntable and hence slew the skip. Referring to Fig 1, a dumper 10 comprises front and rear chassis sections 12, 14 interconnected by a centre pivot 16 which will allow relative movement between the chassis sections for steering and also permit relative rolling movement therebetween. The chassis sections 12, 14 can be slewed by means of a steering ram 18. The front and rear chassis sections 12, 14 are supported by respective axles 11 having wheels 20 thereon. The front chassis section 12 has a turntable 22 thereon, the turntable 22 having a pair of upwardly extending arms 24 which pivotally support a load carrying skip 26. The skip 26 can be raised for tipping and lowered by pivoting the skip forwardly on the arms 24 by means of a tipping ram 27 (see Fig 4). The rear chassis section 14 carries an engine 28 and the normal seat 30 and controls 32 for a driver. Referring now to Figs 2 and 3, the front chassis section 12 has two mounting bearings 34 which pivotally support respective cylinders 36, 38 of first and second rams 40, 42 respectively. The rams, 40, 42 have respective piston rods 44, 46 extending therefrom and pivotally connected to bearings 48 on a bracket 50 connected to the underside of the turntable 22. The turntable 22 has an axis of pivoting X and, with the rams 40, 42 in the position shown in Fig 2 (corresponding to the straight ahead central position of the skip as shown in Fig 1), the bearings 48 lie evenly one each side and forwardly of the axis X. Referring to Fig 4, a hydraulic circuit for controlling the rams 18, 27, 40 and 42 is illustrated. A pump 50 draws hydraulic fluid from a tank 52 and pumps the fluid to a main control valve 54 which is controlled by means of a suitable lever 55 (see Fig 1) operated by the driver. Operation of the control valve 54 will cause fluid to be pumped either to the tipping ram 27 to raise and lower the skip 26 or to the rams 40,42 to effect slewing of the skip 26. Fluid can be fed to the steering ram 18 via a valve 57 operated by a steering wheel 59. By feeding fluid under high pressure Ph (Fig 5b) through a line 56 it will be noted from Fig 4 that the fluid will be fed to one end of the steering ram 40 and to the opposite end of the steering ram 42. Therefore, the piston rod 44 of ram 40 will begin to retract into the cylinder 36 and the piston rod 46 of the ram 42 will begin to extend from the cylinder 38. Fluid under low pressure (Pl) will leave the cylinders 40, 42 through a line 60 and flow towards the tank 52 via the control valve 54. Various stages of the retraction and extension of the piston rods 44, 46 are shown in Figs 5a to 5e. Arrow A in Figs 5a -5e indicates the position of axis A in Fig 2 which is always at right angles to an axis of tipping T for the skip 26 defined by the arms 24. Therefore, from those figures, it can be seen that the contraction/extension of the rams 40, 42 causes the turntable 22 to slew the skip 26. Once the Fig 5c position is reached, the fluid feed to the rams 40, 42 is reversed so that the piston rods 40, 44 are moved in opposite directions to those shown in Figs 5a to 5c if it is desired to rotate the skip further into the Figs 5d and 5e positions. To slew the skip 26 in the opposite direction, the sequence of fluid feed to the rams 40, 42 is reversed. In accordance with the present invention, a relief valve 58 is positioned between the two lines 56, 60. A suitable relief valve is obtainable from Oil Control UK Ltd of Coventry under reference no.05.16.03-03-02-35. The relief valve 58 has two ports 1, 2 connected to the line 56 and two ports 3, 4 connected to the line 60. Assuming that the dumper 10 is tilted on an incline with the rams 40, 42 in the Fig 5b position and assuming that the loaded skip 26 would naturally want to rotate in the direction of Arrow F, the rams 40, 42 will resist the natural tendency of the skip to rotate. If, with fluid pressures Ph and Pl as shown in Fig 5b, the ram 42 is extended and the ram 40 contracted so as deliberately to slew the skip 26 about its axis X in direction F, the driver can operate the control valve 54 to bring the skip suddenly to a stop by connecting line 60 to high pressure Ph and connecting line 56 to low pressure Pl. The braking of the skip 26 in that way brings about a suddenly applied force which tries to contract the piston rod 44 and extend the piston rod 46 against the high pressure fluid in line 60 thereby tending to increase the pressure in that line. However, in accordance with the invention as defined in the claims, the valve 58 relieves the pressure in the line 60 by allowing fluid in line 60 to pass through port 3 and through to port 2 thereby connecting the fluid at high pressure in line 60 to the fluid at low pressure Pl in line 56. The valve 58 is set to allow fluid to flow from port 3 to port 2 when the pressure in line 60 exceeds a given pressure. The pressure relief provided by the valve 58 provides a cushioning effect which relieves the load suddenly applied to the rams and enables the rams to withstand particularly well the effect of bringing the moving skip 26 to a sudden halt. When the high pressure feed to the rams 40, 42 is reversed so that fluid at high pressure Ph is fed to the cylinders through line 60 and fluid at low pressure Pl escapes through line 56 the valve 58 operates in a reverse manner to connect the line 56 to line 60 via ports 1 and 4 to relieve excess pressure when the fluid in line 56 is switched to high pressure to brake the skip 26 and the line 60 is connected to low pressure. Fluid is unable to flow from port 4 to port 1 and from port 2 to port 3 due to a one way flow valve arrangement within the valve 58. It has been found on test that, surprisingly, the operation of the valve 58 does not result in any perceptible over running of the skip 26 from the position at which the driver requires the skip to be positioned when it is brought to a stop. In that respect, the invention does not affect the accuracy of positioning of the skip by the driver.

Claims: A fluid circuit for a dumper, the circuit including two fluid operable rams (40,42), a fluid communication line (56,60) to each ram and valve means (58) for permitting fluid under pressure in one part of the said fluid circuit to escape to another part of the circuit in the event of the fluid in a communication line (56, 60) leading to one of the rams (40,42) exceeding a given pressure due to that ram (40,42) being subjected to a sudden increase in load, characterised in that the valve means (58) comprise first and second pressure release means provided between the fluid communication lines (56,60) to each ram (40,42), said first pressure release means allowing communication of fluid from a first to a second of said fluid communication lines (56,60), said second pressure release means allowing communication of fluid from the second to the first fluid communication line (60,56), and fluid communication in the opposite direction through each pressure release means is inhibited. A dumper (10) comprising a chassis (12, 14) on which there is mounted a load-carrying skip (26) and two fluid operable rams (40, 42) for slewing the skip (26), the rams (40, 42) heing arranged in a fluid circuit (56, 60) which delivers fluid under pressure to the rams (40, 42), the fluid circuit including fluid communication means (56, 60) to each ram (40, 42), and valve means (58) for permitting fluid under pressure in one part of the said fluid circuit to escape to another part of the circuit in the event of the fluid in a communication means (56, 60) leading to one of the rams (40, 42) exceeding a given pressure due to that ram (40, 42) being subjected to a sudden increase in load, characterised in that the rams (40, 42) are pivotally connected between the chassis (12, 14) and the skip (26), and the valve means (58) comprise pressure release means provided between the fluid communication means (56, 60) to each ram (40, 42). A dumper (10), according to claim 2 wherein the fluid circuit is arranged to feed fluid to the rams (40, 42) simultaneously so as to enable the application of high pressure to one end of the one ram and to the opposite end of the other ram. A dumper (10), according to claim 2 or 3 wherein the fluid circuit is arranged to drain fluid from both rams (40, 42) simultaneously so as to enable the drainage of low pressure fluid from one end of one ram and the opposite end of the other ram. A dumper (10), according to claim 3 and 4 wherein the rams (40, 42) each comprise one end and an opposite end and the fluid circuit comprises a first means for communicating fluid to the one end of a first ram and the opposite end of a second ram, and a second means for communicating fluid to the one end of the second ram and the opposite end of the first ram. A dumper (10), according to claim 5 wherein the valve means (58) comprises a first pressure release means for allowing communication of fluid from the first to the second fluid communication means (56, 60) in order to relieve fluid pressure above a predetermined level. A dumper (10) according to claim 5 or 6 wherein the valve means (58) comprises a second pressure release means for allowing communication of fluid from the second to the first fluid communication means (56, 60) in order to relieve fluid pressure above a predetermined level. A dumper (10) according to claim 6 or 7 wherein fluid communication through each of the pressure release means in the opposite direction to the pressure release direction is inhibited respectively by said first or second pressure release means. A method of halting the slewing of a dumper (10) according to any of claims 2 to 8 comprising the steps of: applying an increase in fluid pressure to selected opposite ends of the rams (40, 42) so as to prevent fluid release therefrom and to counter the direction of movement of the skip (26); allowing release of excess fluid pressure above a predetermined level in the fluid circuit; and allowing fluid communication from a first fluid communication means (56) connecting opposite ends of the two rams (40, 42) along a first release means to a second fluid communication means (60), or allowing fluid communication from the second fluid communication means (60) connecting different opposite ends of the two rams along a second release means to the first fluid communication means (56).

Inventors: WILLIAMS PETER, WILLIAMS, PETER
Applicants: THWAITES LIMITED
Application year: 1995
Main classification: B60P1
IPC codes: E02F9, B60P1