GB2271339A

GB2271339A - Control system for load-handling vehicle

Info

Publication number: GB2271339A
Application number: GB9221304A
Authority: GB
Inventors: Sir Neville Bowman-Shaw; Murray Boss Turner
Original assignee: BOSS TRUCKS Ltd
Current assignee: BOSS TRUCKS Ltd
Priority date: 1992-10-09
Filing date: 1992-10-09
Publication date: 1994-04-13
Anticipated expiration: 2012-10-09
Also published as: GB9221304D0; DE69324642T2; EP0592235A3; EP0592235A2; GB2271339B; ES2132195T3; EP0592235B1; DE69324642D1

Description

CONTROL SYSTEM FOR LOAD-HANDLING VEHICLE This invention relates to load

handling vehicles of the kind comprising a lifting mast, and a lifting carriage having means for engaging a load moveable up and down the mast; and more particularly to control systems for such vehicles.

The lifting mast in vehicles of this kind is commonly formed from two or more telescopic sections which are extended to increase the height to which the load can be lifted. In the case of vehicles which are designed to handle freight containers and similar standardised loads which can be stored in a stack, the required maximum lifting height has increased substantially over recent years and very tall extended masts are now needed to meet the demands of operators in this field. For example, empty freight containers are frequently stored in stacks of up to seven containers high, giving a required lifting height of more than 15 metres for the top container in the stack.

These very substantial lifting heights mean that the time taken to raise and lower the carriage during loading or unloading becomes a significant factor in the overall time required to complete a given operation. The speed of raising the mast assembly is within the control of the manufacturer of the vehicle, but the lowering speed of the lifting carriage is limited by safety legislation in most countries which restricts (2) the lowering speed of the carriage in a loaded condition to a specific maximum value. In general, the speed limitation imposed by this legislation has been regarded by manufacturers as limiting the lowering speed of the vehicle in both loaded and unloaded conditions.

The present invention provides a control system for a load-handling vehicle which enables the lowering speed of the carriage in an unladen condition to exceed the lowering speed of the carriage when laden. This is within the ambit of current legislation and can significantly reduce the time taken to complete a given loading or unloading operation.

According to the present invention, there is provided a control system for a load handling vehicle of the kind comprising a lifting mast and a carriage having means for engaging a load which is moveably up and down the mast, said control system comprising drive means for driving the carriage up the mast, and control means for controlling the rate of descent of the carriage down the mast; the control means being operable to limit the rate of de scent of the carriage to a first predetermined value when a load is being carried, and to a second, greater value when the carriage is in an unloaded condition.

Preferably the control means is operable to change the permitted rate of descent of the carriage from one value to another automatically in response to the presence of a load thereon. This is suitably achieved by load sensing means on the carriage. The higher rate of descent is thus. selected (3) automatically in the unloaded condition of the vehicle. Alternatively, the control means may be manually operable to change the permitted rate of descent of the load engaging means from one value to another. This arrangement enables the rate of descent to be selected by the driver of the vehicle depending on whether it is in an unloaded or loaded condition.

In one particular embodiment of the invention, the control means is operable selectively to vary the permitted rate of descent of the carriage in the unloaded condition. This enables the operator of the vehicle to select the rate of descent depending on local working conditions.

In order that the invention may be more fully- understood, an embodiment thereof will now be described by way of example only with reference to the accompanying schematic drawing which shows a hydraulic circuit for a container-handling vehicle fitted with a control system according to the invention.

The hydraulic circuit shown in the drawing is intended for controlling the operation of a container-handling vehicle fitted with a telescopic mast assembly. Various operating elements are illustrated including a cylinder 25 and associated pump 9 for operating the vehicle steering; lift cylinders 18 and 19 for raising and lowering the telescopic mast (which in known manner entrains the lifting carriage along it); tilt cylinders 7 for tilting the mast assembly between lifting and travelling positions; reach cylinders 6 and side-shift cylinder 5, with their associated control (4) manifold 4; and hydraulic valve 3 for the braking circuit. These components are all conventional and most of these will not be described in further detail.

The main components associated with the control system of the invention are hydraulic pumps 10 and 11, lift valve 14, lifting cylinders 18 and 19, auxiliary lowering valve 21, auxiliary lift and lowering valve 24, and joystick controller 30. The circuit described is intended for a containerhandling vehicle and the carriage in this case supports a gantry having twist locks 28 operable to engage the corner fittings of a container. However, it will be appreciated that the control system of the invention can be applied to any load-handling vehicle, for example one in which the carriage comprises forks, or other means for engaging a load such as a "piggy-back" attachment.

Lift valve 14, auxiliary lowering valve 21 and auxiliary lift and lowering valve 24 are all operated by servos controlled remotely by joystick controller 30 located in the driver's cab. In the embodiment shown the servos are operated hydraulically but they could be operated by other means, such as electrically. The position of these valves determines whether or not hydraulic f luid is fed to, held in, or drawn from lift cylinders 18 and 19. An additional electrical interlock is connected between the servos controlling valves 21 and 24 and the twistlocks 28.

Hydraulic pump 10 is dedicated to lift cylinders 18 and 19 and supplies fluid under pressure to lift valve 14 via line (5) 12. In the position of this valve which is shown in the drawing, the cylinders are inactive and fluid from pump 10 is diverted back to fluid reservoir 16 via return line 17. Operation of joystick controller 30 to call for lifting of the mast and carriage assembly causes valve 14 to move to the right in the drawing, directing fluid from line 12 into line 20 and operating lift cylinders 18 and 19. Movement of joystick controller 30 into the lift position also operates supplementary lift and lower valve 24. The servos are designed such that initial movement of the joystick controller operates valve 24 to provide slow-speed lift under fine control. Further operation of the joystick causes valve 14 to operate, giving full lift flow to cylinders 18 and 19.

Additional lift can also be supplied by pump 11 if fluid pressure is not being used for steering. Pump 11 supplies steering f low to steer cylinder 25 via lines 26 and 27 but if some or all of this flow is not required, load sensing flow divider 22 sends fluid via line 23 to auxiliary lift and lower valve 24 where it is directed via lines 31 and lines 32 and 33 to cylinders 18 and 19 to supplement the flow supplied through line 20.

Lowering of lift cylinders 18 and 19 takes place in this embodiment under gravity (i.e. not under power) and is accomplished at two different rates, as follows.

In a loaded condition of the vehicle, the twist-locks 28 will be engaged with the corner fittings of the container being carried and the electrical interlock will automatically (6) prevent the servos controlling auxiliary lowering valve 21 and auxiliary lift and lowering valve 24 from moving these valves into a lowering position. In this condition, operation of the joystick control 30 to call for lowering of the load will cause valve 14 to move to the left in the drawing, connecting line 20 to return line 36 and thereby returning the fluid from cylinders 18 and 19 to reservoir 16. The rate of retraction of cylinders 18 and 19 will be determined by the size of the load and the restrictions 34 built into line 20, but under current legislation this will not exceed 0.6 m/sec with a fully-loaded container.

A higher lowering speed is achieved where no load is being carried by the vehicle. In this condition, the twist locks 28 are in the disengaged position and the electrical interlock allows operation of both lift valve 14 and auxiliary valves 21 and 24. On operation of the joystick control to lower the carriage, lift valve 14 moves to the left as before, and auxiliary valves 21 and 24 are moved upwardly in the drawing into a lowering position. This connects lines 32 and 33, via lines 31 and 35, with return line 36 leading to reservoir 16. Since additional return lines are open, lift cylinders 18 and 19 void at a faster rate, and lowering of the mast and carriage assembly is achieved more rapidly. The lowering speed is determined by restrictions 37 in lines 32 and 33 but this will be significantly higher than in the loaded condition, for example between 0.8 and 1.4 m/sec and preferably about 1.2 m/sec. At high rates of descent, it may (7) be desirable to cushion the impact caused by stopping the carriage instantaneously. This can be achieved either hydraulically, with suitable valving, or electrically.

Instead of an electrical interlock controlling the circuit automatically, a manual control can be substituted. This allows the operator to select the rate of descent as required, and as permitted by current legislation.

It will be appreciated that the control circuit described herein represents only one possible solution to the control system of the invention. For example, it is possible to both raise and- lower the load under power; in this case the carriage and mast assembly would be driven downwards at a higher rater unladen than laden. It is also possible selectively to vary the rate at which the load is lowered; for example the rate of lower in both laden and unladen conditions could be controlled automatically by a micro processor under the command either of the driver or of factory programmed instructions contained on a data carrier such as a magnetic card. This would enable standard vehicles to be readily adapted for different purposes or for different markets in which different legislation might prevail.

(8)

Claims

CLAIMS:

& 1 A control system for a load handling vehicle of the kind comprising a lifting mast and a carriage having means for engaging a load moveable up and down the mast; said control system comprising drive means for driving the carriage up the mast, and control means for controlling the rate of descent of said carriage down the mast; said control means being operable to limit the rate of descent of the carriage to a first pre-determined value when a load is being carried thereby, and to a second, greater value when the carriage is in an unloaded condition.
2. A control system as claimed in Claim 1, wherein the control means is operable to change the permitted rate of descent of the carriage automatically in response to the presence of a load thereon.
3. A control system as claimed in Claim 2, wherein said carriage comprises load sensing means and said control means are operable to change the permitted rate of descent of said carriage from one value to another in response to said load sensing means.
4. A control system as claimed in Claim 1, wherein the control means is manually operable to change the permitted rate of descent of the carriage.

(9)
5. A control system as claimed in any of Claims 1 to 4, wherein the control means is operable selectively to vary the permitted rate of descent of the carriage in the unloaded condition.
6. A control system as claimed in any of Claims 1 to 5, wherein said lifting mast comprises a plurality of telescopic mast sections and said control means is operable to control the rate of descent of said carriage by controlling the rate of retraction of said mast sections.
7. A control system as claimed in Claim 6, wherein said drive means comprises one or more hydraulic jacks adapted to extend and retract the mast sections; and said control means is operable to control the rate of descent of said carriage by controlling the rate at which hydraulic fluid is expelled from said jack or jacks.
8. A control system as claimed in Claim 7, wherein said mast sections and said carriage are adapted to descend under gravity, and said control means comprises first hydraulic valve means operable to control fluid flow from said jack or jacks when the vehicle is in a loaded condition; and second, supplementary, valve means through which hydraulic fluid from said jack or jacks can be directed when the carriage is in an unloaded condition.

(10)
9. A control system as claimed in Claim 8, wherein the vehicle is adapted for handling f reight containers and other unitary load such as swop bodies and semi-trailers, and said load engaging means are provided with a locking device operable to engage a load; and the supplementary valve means are operable when the locking device is in the unlocked condition.
10. A control system for a load handling vehicle, substantially as herein described with reference to the accompanying drawings.