GB2028265A

GB2028265A - Improvements in a parallel guide device for an attachment pivotally mounted on a link pivoted on a vehicle

Info

Publication number: GB2028265A
Application number: GB7909285A
Authority: GB
Original assignee: BAAS TECHNIK GmbH
Current assignee: BAAS TECHNIK GmbH
Priority date: 1978-08-05
Filing date: 1979-03-16
Publication date: 1980-03-05
Also published as: ATA105379A; FR2435437B1; FR2435437A1; DE2834480A1; AT380001B; GB2028265B; DE2834480C2

Abstract

Pivotal movement of the link relative to the vehicle is controlled by connecting one cylinder space 13 of a lifting cylinder 10 via a servo-valve 50 to a supply of hydraulic fluid under pressure or a reservoir therefor, and pivotal movement of the attachment relative to the link is controlled by connecting the cylinder spaces 33, 34 of a double- acting tilting cylinder 3 via a servo-valve 60 to a supply of fluid under pressure and exhaust. For parallel movement of the attachment, the other cylinder space 17 of the lifting cylinder 10, which is double-acting, is connected via a solenoid operating valve 40 to one of the spaces 33 of the tilting cylinder so that the tilting cylinder is extended and retracted in accordance with movements of the lifting cylinder. <IMAGE>

Description

SPECIFICATION Improvements in a parallel guide device for an attachment pivotally mounted on a vehicle.

The invention relates to a parallel guide device for an attachment, such as a front loader attachment, which is pivotally mounted on a vehicle.

Attachments, such as lifting platforms, working platforms, pallet forks and front loader attachments, which are generally pivotally mounted on a link pivotally mounted on the vehicle, should be able automatically and at any height to maintain a horizontal position or a predetermined angular position. Whilst the parallel guide device, required for this purpose, had been produced using purely mechanical means, such as rods, ropes or chains, the use of hydraulic parallel guide devices has recently gained increasing acceptance.

Such a device comprises at least one lifting cylinder with a first cylinder space for lifting or lowering the attachment, at least one double-acting tilting cylinder for tilting the attachment and one hydraulic servo-valve each for the tilting cylinder and the lifting cylinder.

It is known to provide such an hydraulic parallel guide device with a master cylinder which senses the angle of the front loader, but it is difficult to accommodate such a master cylinder in addition to the lifting cylinders, under the given space conditions and force conditions in conjunction with the extreme fluctuations of oil pressure which are common with front loader attachments. The space conditions are further constrained by the fact that the tilting cylinder, used for the parallel guide, must additionally, in any possible position of the front loader link, transmit tilting motions to the attachment, for example for dumping a load in or out.

According to the invention there is provided a parallel guide device for an attachment which is pivotally mounted on one end of a front loader link or the like, the other end of the link being pivotally connected to a vehicle, the device comprising at least one double-acting lifting cylinder providing first and second cylinder spaces and for lifting or lowering the attachment, at least one double-acting tilting cylinder providing first and second cylinder spaces and for tilting the attachment, one hydraulic servo-valve for each of the tilting cylinder and the lifting cylinder, a control valve having two positions and connected to the cylinders and servo-valves so that, in one position of the control valve, there is a first through-channel for connecting the second cylinder space of the lifting cylinder to the first cylinder space of the tilting cylinder and a second through-channel from the second cylinder space of the tilting cylinder to the lifting cylinder servo-valve and, in the other position of the control valve, there is a third through-channel from the second cylinder space of the lifting cylinder to the lifting cylinder servo-valve.

Since the lifting cylinder is a double-acting cylinder, a second cylinder space is available inside the lifting cylinder, which acts as a master cylinder for the tilting cylinder and is hydraulically connected, for this purpose, via the first through-channel to the first cylinder space of the tilting cylinder in order to displace the piston of the tiiting cylinder in such away that, during lifting or lowering of the front loader link, the attachment always assumes a horizontal position or a preset angular position relative to the horizontal, if the volumes of the cylinder spaces which are connected to one another by the first through-channel are correspondingly matched to one another. The second through-channel leads from the second cylinder space of the tilting cylinder to the servo-valve for the lifting cylinder.The space and force problems which have hitherto occurred can thus be solved in a simple manner by the fact that, in addition to the lifting cylinder and tilting cylinder, no further master cylinders are required, as a result of which the design of the device as a whole is simplified and less expensive. Aiready existing tilting cylinders can be included without difficulty in the above described parallel guide device as long as.

the cylinder space, which works as the master cylinder, of the lifting cylinder is correspondingly matched with respect to volume with the corresponding cylinder space of the tilting cylinder.

Afirst non-return valve is advantageously provided in the second through-channel, which valve opens when a preset inflow pressure into the first cylinder space of the tilting cylinder is exceeded, and allows hydraulic fluid to flow out of the second cylinder space of the tilting cylinder. As a result, it is possible to prevent the piston of the tilting cylinder being displaced in its first cylinder space without a corresponding control pressure, that is to say it is possible to prevent the angular position of the attachment relative to the horizontal being altered, for example on lifting the link, without a corresponding control pressure, only by its weight or obstacles in the path of the attachment.

Preferably, the first non-return valve is incorporated in the control valve, and is adapted to be unlocked hydraulically.

According to a preferred embodiment of the invention, a second non-retun valve is provided in the channel connected to the first cylinder space of the lifting cylinder, the valve opening at a preset inflow pressure into the second cylinder space of the lifting cylinder to allow hydraulic fluid to flow out of the first cylinder space of the lifting cylinder. Preferaby, this second non-return valve is also adapted to be unlocked hydraulically and has the effect that the piston of the lifting cylinder can only be shifted after the quantity of oil required for parallel guiding has also been displaced.

According to a particuiarly preferred embodiment of the invention the lifting cylinder comprises a barrel, a piston slidable therein and defining two spaces therewith, one on each side thereof, and a piston extending from one side of the piston, and the first cylinder space of the lifting cylinder is the space on the other side of the piston and the second cylinder space is the space on the one side of the piston. If the tilting cylinder is arranged in such a way that the motion of its piston rod is transmitted to the attachment without a reversal of direction above the pivot axis, the first cylinder space of the tilting cylinder may coincide with the cylinder space on the side of the piston opposite that connected to the piston rod and the second cylinder space of the tilting cylinder coincides with the cylinder space on the rod side of the piston.The first through-channel in the one position of the control valve then connects the cylinder space of the lifting cylinder on the piston rod side, which cylinder space acts as the master cylinder, to the cylinder space of the tilting cylinder on the side of the piston remote from the piston rod.

The cylinder space of the tilting cylinder on the piston rod side is connected via the second throughchannel to the lifting cylinder servo-valve. The supply and outflow of hydraulic fluid to or from the lifting cylinder then takes place between the lifting cylinder servo-valve and the cylinder space on the piston side.

Advantageously, the control valve is a solenoid valve which assumes its one position in a state of no current and which, on excitation, changes to its other state in which it establishes only the third throughchannel from the second cylinder space, for example that on the piston rod side, of the lifting cylinder to the lifting cylinder servo-valve. The hydraulic coupling between the second cylinder space of the lifting cylinder and the first cylinder space of the tilting cylinder, and hence the parallel guiding, is then interrupted.

A switch-over step of the control valve is arranged to take place when the attachment reaches its lower end position which can be preset or its upper end position which can be preset. For this purpose, the tilting cylinder is preferably associated with electric end-position contacts which, when contact is made, impose a voltage on the switching magnet of the solenoid valve and cause the solenoid valve to switch over from its one position to its other position and hence to interrupt the parallel guiding.

The invention will be more fully understood from the following description of an embodiment thereof, given by way of example only, with reference to the drawings, in which: Figure 1 is a schematic elevation of a front loader vehicle and attachment provided with an embodiment of a parallel guide device according to the invention; and Figure2 is a schematic electric/hydraulic circuit diagram of the parallel guide device of Figure 1.

The front loader vehicle 1, schematically shown in Figure 1,carries on its front part a front loader link 2 which can be pivoted up and down about an axis of rotation by means of a combined cylinder unit 10 which is described in detail below. An attachment 4 which as shown is a lifting fork is mounted for rotation about the axis of a bearing 3 fitted to the front end of the front loader link 2. The tiltable attachment may alternatively be, for example, a working platform, a trough or the like which replaces the lifting fork.

The attachment 4 is joined via a toggle or linkage 5 to the piston 35 of an hydraulic tilting cylinder 30, the cylinder barrel of which is pivotably connected to the front loader link. By displacing the tilting cylinder piston 35, the attachment 4 can be brought via the toggle 5 from a horizontal position B, to a tilted position A which is inclined upwards relative to the horizontal, to a downwardly tilted position C and into any desired intermediate position. Moreover, as exlained below, in a certain operating state of the hydraulic system, the attachment 4 can be moved parallel to itself in any selectable tilted position, when the front loader link 2 is raised or lowered.

In the hydraulic parallel guide device control circuit which is shown in Figure 2, both the lifting cylinder 10 and the tilting cylinder 30 are provided in duplicate, one for each side of the front loader link 2.

The schematic electric/hydraulic circuit diagram, shown in Figure 2, of the parallel guide device comprises a servo-valve 50, which is actuated manually, for controlling the lifting cylinders 10. A line 92 leads from the servo-valve 50 to the inlet/outlets 20 of first cylinder spaces 13 of the double-acting lifting cylinders 10. In the barrel 12 of each cylinder 10 a piston 14 with a piston rod 16 is displaceably guided.

The space 13 is provided on that side of the piston remote from the rod 16. On the piston rod side a second cylinder space 17 is provided within the barrel 12. Via the inlet/outlets 21, a line 90 and a control valve 40, designed as a solenoid valve, a first through-channel can be established from the cylinder spaces 17 to the inlet-outlets 36 of first cylinder spaces 33 on one side of the pistons of the doubleacting tilting cylinders 30, when the solenoid valve 40 is in its normal or zero position "0" A piston 31 with the piston rod 35 is displaceably mounted in each of the tilting cylinders 30, and the translational motion of the piston rods 35 is transmitted, as shown in Figure 1, via the toggle 5 to the attachment 4.

With the valve 40 in its normal position, a second through-channel extends from the inlet/outlets 37 of the second cylinder spaces 34 on the piston rod sides of the tilting cylinders 30 through the solenoid valve 40 to the line 91 of the servo-valve 50 for the lifting cylinders 10. In this second through-channel 37,97,91, a first non-return valve permits an outflow of hydraulic fluid from the cylinder spaces 34 only if a preset inflow pressure into the cylinder spaces 33 is already present, in order to ensure that the cylinders 30 are extended only at the present control pressure in the cylinder spaces 33 so that the cylinders 30 are prevented from being extended, and the attachment 4 is prevented from being pivoted downwardly by external influences, for example the , mere weight of obstacles in the path of motion. The unlocking of the non-return valve 70 is effected hydraulicallythrough an unlocking line 71 which leads, within the solenoid valve 40, from the first through-channel 21,90,96, 36 to the non-return valve 70.

A second non-return valve 80 is provided in the line 92, which non-return valve opens, on retracting the cylinders 10, only after a corresponding pressure of fluid from the cylinder spaces 33 of the tilting cylinders 30 has built up in the cylinder spaces 17 of the lifting cylinders 10, in order to ensure that the quantity of oil required for parallel guiding of the attachment 4 has in fact been displaced when the front loader link 2 is lowered and the cylinders 10 extended. Unlocking of the non-return valve 80 is effected hydraulically via an unlocking line 81.

An excitation voltage from a battery 48 can be applied to a switching magnet of the solenoid valve 40, for example manually by closing a contact 45, or by closing the end-position contacts 46, 47 provided on the piston rod 35, as a result of which the solenoid valve 40 moves from the zero position "0" to its other position "I". In this position, the first through-channel 21, 90, 96, 36 and the second through-channel 37,97,91 are interrupted and a third through-channel 21,90,91 is formed which leads from the second cylinder spaces 17 of the lifting cylinders 10 via the line 90 and the line 91 directly to the servo-valve 50. In this position of the solenoid valve 40, the hydraulic coupling of the lifting cylinders 10 and tilting cylinders 30 is interrupted and the hydraulic parallel guide is thus switched off.The hydraulic circuit then connects the servo-valve 50 via the line 92 to the inlet/outlets 20 of the cylinder spaces 13 and the cylinder spaces 17 via the inlet/outlets 21 and the third through-channel 90, 91 to the servo-valve 50, so that, depending on the direction of flow, only the pistons 14 of the lifting cylinders 10 are moved out or in.

Additionally, a servo-valve 60 for the tilting cylinders 30 is provided. One line 98 or 99 leads, respectively, from the servo-valve 60 to the inlet/ outlets 36 of the first cylinder spaces 33 or to the inlet/outlets 37 of the second cylinder spaces 34 in order to be able, alternatively or additionally to the parallel guide, to move the pistons 31 of the tilting cylinders 30 in or out manually and hence to set a desired position of the attachment 4.

The servo-valve 50 is connected via a pressure line to a hydraulic pump 100 and has a discharge line 102 in the direction of a reservoir 101 for hydraulic fluid.

This discharge line passes via the servo-valve 60 and is in fact switched through to the reservoir 101 only in the rest position b of valve 60. The two servovalves 50 and 60 have three working positions which can be set manually and which are marked a, band c and correspond to a lifting position, a rest position and a lowering position respectively. In the lifting position a of the servo-valve 50, the line 92 is pressurised and hydraulic fluid flows under pressure into the cylinder spaces 13 of the lifting cylinders 10.

If the solenoid valve 40 is in the zero position "0", the parallel guide is switched on and, so that as the spaces 13 are pressurised and the pistons 14 move to compress the cylinder spaces 17, the hydraulic fluid in the spaces 17 exerts pressure via the first through-channel 21,90,96,36 on the cylinder spaces 33 of the tilting cylinders 30, as a result of which the cylinders 30 are extended. From the cylinder spaces 34 of the tilting cylinders, the hydraulic fluid flows back via the second through-channel 37,97,91 through the servo-valve 50 via the line 102 into the reservoir 101 of hydraulic fluid, if the servo-valve 60 is in the rest position b.

In the rest positions b of the servo-valves 50 or 60, neither feed nor return of hydraulic fluid take place and the pump 100 delivers directly back into the reservoir 101 of hydraulic fluid via the line 102. The position c of the servo-valve 50 has the effect that, with the position of the solenoid valve 40 remaining the same, the direction of flow in the hydraulic system is reversed so that the second throughchannel 91 is now pressurised and the hydraulic fluid flows back via the line 92 from the cylinder spaces 13 ofthe lifting cylinders to the reservoir 101.

If the solenoid valve 40 is switched into its other position I, the tilting cylinders 30 are hydraulically separated from the lifting cylinders 10 and the hydraulic circuit now leads from the line 92 via the cylinder spaces 13 of the lifting cylinders 10, the cylinder spaces 17 and via the third through-channel 21, 90, 91 directly back to the servo-valve 50.

If the servo-valve 50 is in the rest position b, the pump 100 is switched to the servo-valve 60 for the tilting cylinders, and it is now possible separately to extend the tilting cylinders 30, the cylinder space 33 on the piston side then being pressurised via the line 98, or to retract them (position c), the cylinder spaces 34 then being pressurised via the line 99.

There is thus provided a parallel guide device which arranged in a particularly space-saving manner and, at the same time, is simplifed as a whole. It is consequently possible to reduce the manufacturing costs and the assembly effort while the possibility of being able to switch off the parallel guide at anytime is retained.

Claims

1. A parallel guide device for an attachment which is pivotally mounted on one end of a front loader link or the like, the other end of the link being pivotally connected to a vehicle, the device comprising at least one double-acting lifting cylinder providing first and second cylinder spaces and for tilting the attachment, one hydraulic servo-valve for each of the tilting cylinder and the lifting cylinder, a control valve having two positions and connected to the cylinders and servo-valves so that, in one position of the control valve, there is a first throughchannel for connecting the second cylinder space of the lifting cylinder to the first cylinder space of the tilting cylinder and a second through-channel from the second cylinder space of the tilting cylinder to the lifting cylinder servo-valve and, in the other position of the control valve, there is a third throughchannel from the second cylinder space of the lifting cylinder to the lifting cylinder servo-valve.

2. A device according to claim 1, wherein a first non-return valve is provided in the second throughchannel, the non-return valve being arranged to open when a preset inflow pressure in the first cylinder space of the tilting cylinder is exceeded, and allows hydraulic fluid to flow from the second cylinder space of the tilting cylinder.

3. A device according to claim 2, wherein the first non-return valve is contained in the control valve.

4. A device according to either claim 2 or claim 3, wherein the first non-return valve is adapted to be unlocked hydraulically.

5. A device according to one of the preceding claims, wherein a second non-return valve is provided in a channel connected to the first cylinder space of the lifting cylinder and is adapted to open at a preset inflow pressure into the second cylinder space of the lifting cylinder to allow hydraulic fluid to flow out of the first cylinder space of the lifting cylinder.

6. A device according to claim 5, wherein the second non-return valve is adapted to be unlocked hydraulically.

7. A device according to one of the preceding claims, wherein the lifting cylinder comprises a barrel, a piston slidable therein and defining two spaces therewith, one on each side thereof, and a piston extending from one side of the piston, and the first cylinder space of the lifting cylinder is the space on the other side of the piston and the second cylinder space is the space on the one side of the piston.

8. A device according to one of the preceding claims, wherein the tilting cylinder comprises a barrel, a piston slidabletherein and defining two spaces therewith, one on each side thereof, and a piston extending from one side of the piston, and the first cylinder space of the tilting cylinder is the space on the other side of the piston and the second cylinder space is the space on the one side of the piston.

9. A device according to one of the preceding claims, wherein the control valve is a solenoid valve which assumes its one position in the state of no current.

10. A device according to claim 9, wherein the tilting cylinder servo-valve has electric contacts for triggering the control valve.

11. A device according to one of the preceding claims, wherein the tilting cylinder is associated with electric end-position contacts for positioning the control valve.

12. A device according to claim 11, wherein at least one of the end-position contacts is adjustable in the direction of travel of the tilting cylinder.

13. A parallel guide device for an attachment pivotally mounted on a vehicle substantially as herein described with reference to the accompanying drawings.

14. A vehicle comprising an attachment pivotally mounted thereon and a parallel guide device as claimed in any one of the preceding claims.