Method of operating a hydraulic system for wheeled loader

Abstract: A method of operating a hydraulic system of a wheeled loader, having a loader arm assembly movable between raised and lowered positions by means of a hydraulic ram means (20) of the hydraulic system, the hydraulic system further including a ride improvement means including a hydraulic accumulator (30) and a check valve (39) which is normally closed the method including operating a selection valve means (40) to raise or lower the loader arm assembly (16), and when the selection valve means (40) is operated to raise the loader arm assembly (16), permitting the passage of hydraulic fluid between a first chamber (25) of the hydraulic ram means (20) and the accumulator (30), whilst permitting the passage of hydraulic fluid from a second chamber (26) to a low pressure region (35).

Description: Description of Invention This invention relates to a hydraulic system for a wheeled loader having a loader arm assembly which carries a working implement and in which the loader arm assembly is connected to the body and which is movable between raised and lowered positions by means of a hydraulic ram means. It is known to improve the ride of such a wheeled loader by connecting an hydraulic accumulator into the hydraulic hose which feeds hydraulic fluid into said ram means to raise the loader arm assembly. As a result when the wheeled loader is travelling across a site, or when travelling along a road, at speed the loader arm assembly is suspended in spring manner by the accumulator and so the wheeled loader is able to travel with less pitch and bounce than would otherwise have been the case. Such a deflection reduction system is disclosed in the document US-A-4 658 970, which corresponds to the preamble of claim 1. However, such a ride improvement system has not been provided hitherto in a loader vehicle comprising a loader arm assembly connected at, or adjacent to, the rear end of the assembly to the body at, or adjacent to, the rear end of the body so that the loader arm assembly extends forwardly whereby, in a lowered position of the arm assembly, the working implement is disposed in front of the body. Such a vehicle is provided with a hose burst check valve. According to the present we provide method of operating a hydraulic system for a wheeled loader according to claim 1. The selection valve may be manually operable. The control valves may be electrically operated solenoid valves to which current is supplied by a manually operable switch means to cause operation of said ride improvement means when said valves are positioned to permit passage of hydraulic fluid. The selection valve may be provided with a switch means to sense the position of the selection valve to close said second control valve when the boom is lowered and said control valves are open. The accumulator and the control valves and the check valves may be mounted directly on the ram. At least one of said accumulator, solenoid valves, check valves and connecting pipework may be made in metal, preferably steel. Said check valve may be a hose burst check valve. Said one chamber may be disposed on the opposite side of the valve to the piston rod and said other chamber may be an annular chamber surrounding said piston rod. An example of the invention will now be described with reference to the accompanying drawings wherein: Figure 1 is a side view of a vehicle according to the invention, Figure 2 is a diagrammatic circuit diagram showing the flow of hydraulic fluid and valve positions in normal operation of the vehicle during lifting of the arm, Figure 3 is a view similar to that of Figure 2 but showing normal operation during lowering of the arm, Figure 4 is a view similar to that of Figure 2 but showing a travel position of the vehicle with the ride improvement means engaged, Figure 5 is a view similar to that of Figure 4 but showing a boom lift position and ride improvement means engaged. Figure 6 is a view similar to that of Figure 4 but showing flow of fluid in a boom lower position with the ride improvement means engaged. Referring to the drawings, a wheeled loader vehicle comprises a body 10 supported, in conventional manner, on two pairs of front and rear wheels 11, 12 each of which is steerable and each of which is driven by a suitable transmission and differential means from an engine which may be disposed as desired on the vehicle. The body 10 has a rear end 13 and a front end 14. A loader arm assembly 16, at a position adjacent its rear end, is pivotally mounted to the body 10 adjacent the rear end 13 of the body, about an axis 15. The loader arm assembly 16 in the present example, is a two part boom having an outer part 16 a , within which is telescoped an inner part 16 b and which parts are slidable relative to each other by hydraulic ram means so as to provide an extendible loader arm assembly. If desired the vehicle may have a two or more part boom or an un-extendible single part boom. At the front end of the boom assembly 16 is a downwardly extending nose part 17 by which a working implement 18 is releasably carried in conventional manner. If desired, the working implement 18 may be a pair of lifting tines as shown or may be a bucket or any other suitable working implement. The loader arm assembly may be connected to the body at or adjacent the rear thereof, by any suitable pivot means disposed at or adjacent the rear of the loader arm assembly. The loader arm assembly 16 is pivotable about the axis 15 between raised and lowered positions. In the lowered position working implement 18 is disposed in front of the vehicle front end 14. The loader arm assembly 16 is movable between said raised and lowered positions by a ram assembly 20, which in the present example comprises a single ram. The ram assembly 20, in conventional manner, comprises a cylinder part 21 and a piston rod 22. The piston rod 22 is connected at one end to a bracket 23 depending downwardly from the underside of the part 16 a of the lowered arm assembly by means of a pivot pin 24 a whilst the cylinder 21 is connected, at its lower end, by a pivot pin 24 b to a part of the body 10. Obviously extension and retraction of the piston rod 22 from the cylinder 21 causes pivotal raising and lowering of the arm assembly 16. Within the cylinder 21 is a first chamber 25, on one side of the piston 27, which is of cylindrical configuration and a second chamber 26 on the opposite side of the piston 27, see Figures 2 to 5, to the first chamber 25 and which is of annular configuration in cross section. Mounted on the cylinder 21 is a conventional accumulator means 30 made of, in the present example, steel and connected by a pipe 31 to a first control valve 32. A second control valve 33 is connected by a line 34 comprising flexible hoses and/or rigid pipes to an hydraulic reservoir or other low pressure area 35. Each control valve 32, 33 is an electrically operated solenoid valve and which is movable between a first or "at rest" position in which passage of fluid is prevented in one direction of the valve 32 and in both directions in the valve 33 and a second position in which passage of fluid is permitted. Both control valves 32, 33 are normally spring biased by a spring means 36 to the position in which flow of fluid is prevented as illustrated in Figure 2 and Figure 3. A line 38, comprising a rigid pipe 38 a and a flexible line 38 b , connects the first chamber 25 of the ram 20 to a first port 40 a of a selection valve 40 via a hose burst check valve 39. The first control valve 32 is connected by a line 37, comprising a rigid pipe, to the line 38 between ram chamber 25 and the hose burst check valve 39. The hose burst check valve 39 is a pilot valve that is normally maintained closed in the direction to prevent flow of fluid under pressure from the chamber 25 to the valve 40 but it may be opened by supply of pilot pressure on line 41, comprising a rigid pipe, from a line 42, comprising a rigid pipe 42 a and flexible hoses 42 b which extends between a second port 40 b of the selection valve 40 and the chamber 26 of the ram 20. The line 42 is connected by a line 43 to the second control valve 33. In use, as best shown in Figure 2, during normal operation, when it is desired to lift the arm, fluid under pressure is fed from the first port 40a of the selection valve 40 along the line 38 through the one-way check valve within the hose burst check valve 39. As boom suspension has not been selected there is no electrical supply to valves 32 and 33 and they remain in the normally closed position. As the telescopic boom 16 is raised, by the supply of fluid to the chamber 25, fluid under lower pressure is fed from the chamber 26 along line 42 into a port 40 b of the selection valve 40. The valve 33, of course, being, like the valve 32, maintained in the position shown in Figure 2 to prevent flow of fluid therethrough by virtue of no electrical supply being supplied to the solenoid thereof. Referring now to Figure 3, when it is desired to lower the loader arm assembly the valve 40 is actuated to feed fluid under pressure through port 40 b along line 42 into the chamber 26 and thus fluid under lower pressure is fed from chamber 25 along line 38 through hose burst check valve 39 which is maintained in an open position by virtue of supply of pilot pressure on line 41 which extends from line 42. Referring now to Figure 4, when it is desired to operate the ride improvement means i.e. boom suspension means the system is activated by operation of a suitable electric control so that electrical supply is provided to the valves 32, 33 to move them from the positions shown Figures 2 and 3 to the positions shown in Figures 4 to 6 in which passage of hydraulic fluid is permitted. In this position fluid can flow both to the accumulator 30 and also to the reservoir 35 in accordance with the external forces imposed on the piston 27 to displace fluid to or from chambers 25, 26. Such a condition is shown in Figure 4. As a result the loader arm is supported by the action of the accumulator on the hydraulic fluid and it is, in effect, sprung. Referring now to Figure 5, when it is desired to raise the loader arm assembly whilst the ride improvement means is engaged, the valve 40 is actuated to feed fluid from port 40 a under pressure along line 38 into the chamber 25 whilst fluid from the chamber 26 passes along the line 42 back to the valve 40. At the same time the suspension of the arm assembly is suspended by the accumulator 30 as described hereinbefore in connection with the Figure 4. Referring now to Figure 6, when it is desired to lower the boom whilst the ride improvement means is engaged, the actuation of the valve 40 to raise pressure at port 40 b , by virtue of switch 44, has the effect of collapsing the electrical signal to valve 33 which becomes closed and so allows pressure to be raised in line 42 which feeds fluid under pressure to chamber 26, whilst fluid in chamber 25 is fed via line 38 through the hose burst check valve 39 to the port 40 a of the valve 40. The hose burst check valve 39 is maintained open by pilot pressure fluid on line 41 which extends from line 42. Whilst in this example the accumulator 30, valves 32, 33 and check valve 39 are all disposed on the cylinder 21, if desired one or more of these components may be positioned as desired and made of material as desired where permitted by local regulations. In the present specification "comprise" means "includes or consists of' and "comprising" means "including or consisting of".

Claims: A method of operating a hydraulic system of a wheeled loader, the loader having a loader arm assembly (16) connected to a body (10) so that in a lowered position of the loader arm assembly (16), a working implement (18) carried at an outer end of the loader arm assembly (16) is disposed in front of the body (10), and which loader arm assembly (16) is movable between raised and lowered positions by means of a hydraulic ram means (20) of the hydraulic system, the hydraulic system further including a ride improvement means including a hydraulic accumulator (30) which is connected to the hydraulic ram means (20), and a selection valve means (40) connected to each of a first and second chamber of the hydraulic ram means (20), and a check valve (39) connected between the first chamber (25) and the selection valve means (40) such that the check valve (39) is normally closed to prevent fluid under pressure passing from the first chamber (25) to the selection valve means (40), and the check valve (39) having hydraulic fluid responsive means responsive to hydraulic fluid pressure in the second chamber (26) to open the check valve (39) and there being means (41) to connect said hydraulic fluid pressure to said second chamber (26), the method including operating the selection valve means (40) to feed fluid under pressure to one chamber (25) of the ram means (20) and to receive fluid at a lower pressure from the other chamber (26) of the ram means (20) in order to raise the loader arm assembly (16) or to feed fluid under pressure to said other chamber (26) of the ram means (20) and receive fluid at a lower pressure from said one chamber (25) of the ram means (20) to lower the loader arm assembly (16), characterised in that the method includes operating the selection valve means (40) to raise or lower the loader arm assembly (16), and when the selection valve means (40) is operated to raise the loader arm assembly (16), permitting the passage of hydraulic fluid between the first chamber (25) of the hydraulic ram means (20) and the accumulator (30), and whilst permitting the passage of hydraulic fluid from the second chamber (26) to a low pressure region (35). A method according to claim 1 characterised in that when the selection valve means (40) is operated to lower the loader arm assembly (16), the passage of hydraulic fluid from the second chamber (26) to a low pressure region (35) is prevented. A method according to claim 1 or claim 2 characterised in that the method includes moving a first control valve which is connected between the first chamber (25) of the hydraulic ram means (20) and the hydraulic accumulator (30), between a first position in which the passage of hydraulic fluid between the first chamber (25) of the hydraulic ram means (20) and the accumulator (30) is permitted and a second position in which passage of hydraulic fluid to the accumulator is prevented. A method according to claim 1 or claim 2 or claim 3 characterised in that the method includes moving a second control valve (33) which is connected between the second chamber and the low pressure region (35) between a first position in which passage of hydraulic fluid therethrough to the low pressure region (35) is permitted, and a second position in which the flow of hydraulic fluid to the low pressure region (35) is prevented. A method according to claim 4 wherein the selection valve means (40) is provided with a switch means (44) to sense when the selection valve means (4) is operated to lower the loader arm assembly (16), characterised in that the method includes sensing operation of the selection valve means (40) to lower the loader arm assembly (16), and moving at least the second control valve (33) to the second position in response.

Inventors: COOK DAVID, COVELL BEN, COOK, DAVID, COVELL, BEN
Applicants: BAMFORD EXCAVATORS LTD, J.C. BAMFORD EXCAVATORS LTD.
Application year: 2001
Main classification: B66F9
IPC codes: E02F9, B66F9