GB1582754A

GB1582754A - Loadcarrying vehicles

Info

Publication number: GB1582754A
Application number: GB41220/77A
Authority: GB
Original assignee: Lancer Boss Ltd
Current assignee: Lancer Boss Ltd
Priority date: 1977-10-04
Filing date: 1977-10-04
Publication date: 1981-01-14
Also published as: DE7829571U1; IT7869288A0; DE2843205A1; FR2405171A1; JPS5459721A; SE7810399L

Description

(54) IMPROVEMENTS IN LOAD-CARRYING VEHICLES (71) We, LANCER Boss LIMITED, a British Company of Grovebury Road, Leighton Buzzard, Bedfordshire, England, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to load-carrying vehicles such as mobile cranes and fork lift trucks which are mounted on ground engaging road wheels and have load lifting mechanisms.

It is known to provide fork lift trucks with additional wheels which are mounted separately from the road wheels and which are maintained out of contact with the ground surface (or at least in a non load-carrying position when no load is carried on the load carrying means of the vehicle). During a load lifting operation, means are provided for lowering these wheels in response to the load carried so as to reduce the axle loading of the vehicle road wheels.

The means for lowering the additional wheels into contact with the ground surface in known constructions include hydraulic rams connected into a hydraulic circuit which includes the load lifting mechanism for the mast and fork carriage of the truck, this mechanism having the fork carriage and mast hydraulic lifting circuit and the rams for lowering the additional wheels interconnected such that the wheels are pressed downwardly against the ground surface with a force which increases in direct proportion to the load carried by the forks.

It is not always necessary or desirable to lower the additional wheels during a lifting operation. For example, the road wheels and axle assemblies of the truck may be adequate to support the maximum weight capable of being handled by the truck, and additional wheels may be required only when working for example over soft ground or on suspended floors such as ships decks where maximum permitted axle loadings are specified.

With a fork lift truck the load lifting mast is usually secured at its lower end close to the front road wheels or close to the vertical plane through the axis of the front road wheels. However, the forks project forwardly of the mast and the position of the centre of gravity of the load on the forks varies in practice both in the load position on the forks and the centre of gravity of the load itself. The horizontal distance from the vertical plane through the axle centre to the centre of gravity of the load on the forks is called the effective load centre. It has been found in practice that while the downward thrust of the load itself through the mast and the load lifting ram is one of the forces acting on the road wheels, the load multiplied by the effective load centre produces a substantial turning i.e. overturning moment about the axis of rotation of the front road wheels, and this turning movement is not countered by the fork and mast lifting ram. This is equally applicable in other load lifting vehicles for exampe of the crane type where the effective centre is the horizontal distance from the centre of gravity of the load to the vertical plane through the road wheel axles of the vehicle nearest to the road.

An object of the present invention is to provide an improved load carrying vehicle with an additional ground engaging wheel or wheels with means which can be operated automatically to lower or raise such wheel or wheels when the overturning moment about the axle of the road wheels respectively exceeds or falls below a predetermined value.

According to the present invention, there is provided a load-carrying vehicle movable on road wheels and provided with means for engaging and lifting a load, and one or more additional wheels which are capable of being moved between an operative position in which they are in contact with the ground surface and capable of supporting at least part of the laden weight of the vehicle, and an inoperative position in which the laden weight of the vehicle is carried entirely on the road wheels, and means for moving the additional wheel or wheels between said operative and inoperative positions in response to the overturning moment (as herein defined) on the road wheels.

The additional wheel or wheels is or are lowered only when the overturning moment and the road wheel axle loading of the vehicle exceed a predetermined value. This value may be varied by the operator of the vehicle by suitable control means so that when working for example on a suspended floor having a maximum permitted axle loading, the mechanism can be controlled such that the additional wheels may be lowered by the operator prior to the preset overturning movement being reached at which time the additional wheels would normally be automatically lowered.

Advantageously the means for moving the additional wheels between their operative and inoperative positions are capable of lifting the additional wheels into an inoperative position clear of the ground surface to prevent tyre wear and scuffing.

The additional wheels are suitably mounted on slides or pivoted brackets movable with respect to the vehicle chasis or body.

These slides or brackets may be controlled by any suitable means such as hydraulic or pneumatic rams, rack and pinion drives or electrically operated.

As the additional wheels are not part of the axles carrying the road wheels, known arrangements for lowering additional wheels which incorporate means, e.g. hydraulic circuits connected to the vehicle load lifting cylinder, suffer from the disadvantage that if the loaded vehicle drives over an obstruction such as a kerb or a ramp or when the vehicle is crossing rough ground or railway lines, a substantial proportion of the laden weight of the vehicle can pass temporarily onto one of the additional wheels, resulting in damage to the wheel or its stub axle assembly or its support structure.

In a preferred embodiment of the invention, this possibility is eliminated as the means for moving the additional wheel or wheels into the operative position are operable in response to the overturning moment about the road wheel axles and an hydraulic accumulator allows upward movement of the respective wheel when a predetermined loading is reached, thereby preventing damage to the wheel and its support.

In order that the invention may be more fully understood, embodiments in accordance therewith will now be described by way of example with reference to the accompanying drawings in which.

Figure 1 shows a side elevation of a loadcarrving assembly suitable for fitting to a vehicle chasis incorporating one or more additional wheels; Figure 2 shows an end elevation of a drive axle of a vehicle fitted with two additional wheels provided with raising and lowering devices operating on different principles; Figure 3 shows a side elevation of the additional wheel assembly shown in Figure 2 looking in direction of arrow B in Figure 2; Figure 4 shows a side elevation of the additional wheel assembly shown in Figure 2 looking in the direction of arrow A in Figure 2; and Figure 5 shows a suitable hydraulic operating circuit for a vehicle incorporating a load-carrying assembly as shown in Figure 1 and an additional wheel assembly as shown in Figures 2, 3 or 4.

Referring to the drawings, Figure 1 shows a load-carrying and lifting arrangement fitted to a vehicle incorporating the additional wheel arrangement according to the invention. The chassis 1 of the vehicle has a bracket 2 fitted to its upper surface to which is pivotally connected a cantilever arm 3.

A hydraulic elevation ram 4 is fitted between a bracket 5 (also fixed to the upper surface of the chassis) and the cantilever arm 3, and operation of this hydraulic ram raises and lowers the cantilever arm 3. The free end of the cantilever arm 3 is fitted with engagement means 6 for a load 7, the engagement means being for example in the form of a frame fitted with twist lock units at the corners and suitable for handling containers, lifting forks, or any other suitable arrangement.

While the raising and lowering means for the cantilever arm 3 is shown as a hydraulic ram, it will be appreciated that any other suitable means may be employed such as a pneumatically-operated ram, a rack and pinion assembly, a powered winch and cable arrangement, or an electrically-operated device.

A view of the front axles of the vehicles which as a front wheel device vehicle is shown in end elevation in Figure 2. The vehicle is steered from the driver's cab through the vehicle rear road wheels. The drive axle 10 is fitted with road wheels 11 which support the vehicle during its normal travelling and lifting movements. Addli- tional wheels 12 and 13 (shown in their operative position) are provided independently of the drive axle 10, and these wheels are raised and lowered by means of supporting assemblies 15 and 16 respectively. In the drawings, the assemblies 15 and 16 operate on different principles. In practice, it is likely that where a plurality of additional wheels are provided, the means for raising and lowering these additional wheels would be identical. Although the wheels 12 and 13 shown in the drawings are identical to the road wheels 11, it will be- appreciated that they may be designed for supporting a specific load range and as a result may be bigger or smaller and with or without pneumatic tyres.

Figures 3 and 4 illustrate respectively the arrangements for raising and lowering the wheels 12 and 13. Referring to Figure 3, in this case the additional wheel 12 is mounted on a hub carrier 19 which is slidably received within a vertical guide 20. One end of a hydraulic cylinder 21 is fixed to the chassis 1 at 22, and the piston rod 23 of this cylinder is attached to the hub carrier 19 at 24. Operation of the cylinder 21 in one direction causes the wheel 12 to be pushed downwardly into contact with the ground surface. Retraction of the piston rod 23 causes the wheel to be raised into its inoperative position out of contact with the ground surface, or into a non load-bearing position.

In Fig. 4 the hub carrier 30 of the additional wheel 13 is pivotally mounted at 31 to a bracket 32 secured to the vehicle chasis 1. A hydraulic cylinder 33 is mounted on the chassis 1 at 34 and its piston rod 35 is pivotally attached at 35 to the bracket 30.

Extension and retraction of the piston rod 35 causes the hub carrier 30 to be pivoted about the bracket 32 to move the wheel 13 between its operative position in contact with the ground surface, and its inoperative position clear of the ground or into a nonload bearing position where tyre wear and scuffing is prevented. An alternative location for the cylinder 3 is shown in broken lines in Figure 4.

Figure 5 shows the hydraulic operating circuit for the vehicle shown in Figures 1 to 4.

The circuit includes a reservoir 40 for hydraulic fluid and a pump 41, one side of which is connected to the reservoir and the other side of which is connected to a control valve 42. During a lifting operation, fluid passes from the control valve 42 to the lifting ram 4, thus elevating the cantilever arm 3.

The ram 4 is connected via a pilot line 44 and one-way valve 45 to a servo valve 46, which is also connected by line 50 to the control valve 42. Alternatively, the pilot line 44 and the valve 45 may be omitted and replaced by an electrical sensor device which senses the pressure in the ram 4 to initiate a signal which is transmitted to the servo valve 46 which would be electrically controlled by the signal. The ram 21 for raising and lowering the wheel 12 or 13 is connected to the servo valve 46 via line 47, and an accumulator or pressure relief valve 48 is connected to this line 47 between the servo valve 46 and the ram 21.

During a load handling operation initiated by actuation of the control valve 42 by the driver pressure fluid flows to the ram 4 which thus elevates the arm 3 with its load 7. Since the load is horizontally spaced from the axle 10 of the road wheels by the effective load centre the resultant overturning movement on the axle is the multiple of this effective load centre and the load.

The additional wheel raising ram 21 is fed with pressure fluid from the control valve 42 through the line 50 and the servo-valve 46 so that the pressure in the ram 21 is lower than is necessary to cause the ram 21 to lower the additional wheel or wheels.

This may be augmented by pressure fluid from the pressure vessel 48. Should the overturning moment exceed a predetermined value the pressure in the ram 4 will rise and the one-way valve 45 will open and bleed pressure fluid through the valve 46 to the top of the ram 21 which will then cause the ram 21 to lower the additional wheel or wheels. When the overturning moment falls below the aforesaid predetermined value the servo-valve will operate to permit pressure fluid to flow back from the top of the ram 21 to the reservoir 40 through the control valve 42 and thus the then high pressure in the bottom of the ram 21 will cause the additional wheel or wheels to rise into the inoperative position.

Where the line 44 and one-way valve 45 are replaced by a sensor device responsive to the pressure in the ram 4 to initiate a signal to the servo-valve 46, the mechanism will function as described above and the additional wheel or wheels will be lowered when said signal reaches a predetermined value. The lowered additional wheel or wheels will be forced against the ground surface at a constant pressure from the pump 41.

The pressure at which the servo valve 46 operates can be pre-set within wide limits so that the additional wheels are lowered at any desired overturning moment and axle loading. In addition, should the operator elect to control the movement of the additional wheels independently of the automatic system, he can override the servo valve 46 by a suitable control device. This manual control allows the systems to be overridden by the driver, enabling him to lower the supplementary wheels into contact with the ground when the vehicle is unladen or partly laden. This might be necessary when working on soft ground or on very light decks. Where more than one additional wheel is provided the hydraulic controls for raising and lowering these wheels may if desired be operated independently or together.

The same system as described for a cantilever arm load lifting truck may be used with a fork lift truck, in which case the ram 4 will be the tilt ram by which the fork lift mast, which is pivoted about a horizontal axis at its power end adjacent to or in vertical alignment with the front road wheel axles, is moved backwards or forwards through an angle usually of the order of + 15 . Thus the pressure sensed by line 44 or electrical sensor is representative of the overturning moment acting cn the machine.

In the known fork lift trucks provided with additional road wheels, when the wheels are lowered they are maintained permanently in contact with the ground under high pressure directly proportional to the load and hence the hydraulic pressure in the lifting hydraulic circuit. As a result, if the truck forks are supporting a raised load, and the truck is driven over rough ground or over an obstruction such as a kerb or a rail, a substantial proportion of the load can pass onto one of the additional wheels, causing severe damage to the wheel and its supporting mechanism. In order to prevent this, line 47 of this invention feeding the cylinder 21 is provided with the accumulator or pressure relief valve 48. This valve is set to operate at a predetermined pressure such that when the loading on the additional wheel exceeds a given maximum the relief valve is overcome and the piston rod 23 is allowed to retract into the cylinder 21 until the load on the wheel falls below the maximum value. Where an accumulator is provided, this is charged when the additional wheel runs over the obstruction, and when the obstacle is passed the ram returns to its normal position and pressure, thus maintaining a constant load on the wheel. The purpose of the one-way valve 45 is to allow pressure sensing in one direction only.

When the pressure in the pilot line 44 or the signal from the electrical sensor falls below the predetermined level (e.g. by the vehicle setting down its load), the servo valve 46 operates to release pressure in line 47 and place line 52 from the control valve 42 in communication with line 53 delivering to the return side of the ram 21. The piston rod 23 (or 35) is raised to lift wheel 12 or 13 clear of the ground surface into its inoperative position. This prevents scuffing of these wheels during movement of the vehicle at axle loadings below the preset level and reduces typre wear.

While two additional wheel assemblies are described in connection with the preferred embodiments one for each side of the vehicle, it will be understood that more than two wheels may be used, or even a single wheel may be fitted on the centre-line of the vehicle.

By means of the present invention the additional wheel or wheels are moved into and out of the ground engaging operative position by means, exemplified herein as an hydraulic circuit, responsive to the turning moment, engendered by the effective load centre multiplied by the value of the load lifted, about the front axles of the vehicle road wheels. This is so whatever the load lifting means of the vehicle is, such as the fork lift mast with its work carriage and forks or a cantilever arm lifting constructon. This turning moment is the main factor in the load or forces acting on the front axles of the vehicle over and above the constant load on these axles due to the weight of the vehicle itself when not carrying a load on its load lifting means. This mechanism enhances the safety of the vehicle as it senses the turning moment on the road wheel axle, and results in spreading the total load on the vehicle road wheel axles over a substantial area of the ground.

WHAT WE CLAIM IS: - 1. A load-carrying vehicle movable on road wheels provided with means for raising and lowering a load, and one or more additional wheels which are capable of being moved between an operative position in which they are in contact with the ground surface and capable of supporting at least part of the laden weight of the vehicle, and an inoperative position in which the laden weight of the vehicle is carried entirely on the road wheels, and means for moving the additional wheel or wheels between said operative and inoperative positions in response to the overturning moment (as herein defined) on the road wheels.

2. A load-carrying vehicle according to Claim 1 wherein the additional wheel or wheels is or are lowered only when the overturning moment and road wheel axle loading of the vehicle exceed a predetermined value.

3. A load-carrying vehicle according to Claim 1 or 2 wherein the means for moving the additional wheels between their operative and inoperative positions are capable of lifting the additional wheels into a non loadbearing situation or into an inoperative position clear of the ground surface to prevent tyre wear and scuffing.

4. A load-carrying vehicle according to any of Claims 1-3, wherein the additional wheels are mounted on slides or pivoted brackets movable with respect to the vehicle chassis or body.

5. A load-carrying vehicle according to Claim 4 wherein the slides or brackets are controlled by hydraulic or pneumatic rams, rack and pinion devices or electrically operated drive means responsive to the overturning moment on the vehicle road axles.

6. A load-carrying vehicle according to any one of Claims 1 to 5 wherein manual control means are provided operable by the operator and connected with the means for moving the additional wheel or wheels to override the actuation of said means in its response to the said overturning moment.

7. A load-carrying vehicle movable on

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. vertical alignment with the front road wheel axles, is moved backwards or forwards through an angle usually of the order of + 15 . Thus the pressure sensed by line 44 or electrical sensor is representative of the overturning moment acting cn the machine. In the known fork lift trucks provided with additional road wheels, when the wheels are lowered they are maintained permanently in contact with the ground under high pressure directly proportional to the load and hence the hydraulic pressure in the lifting hydraulic circuit. As a result, if the truck forks are supporting a raised load, and the truck is driven over rough ground or over an obstruction such as a kerb or a rail, a substantial proportion of the load can pass onto one of the additional wheels, causing severe damage to the wheel and its supporting mechanism. In order to prevent this, line 47 of this invention feeding the cylinder 21 is provided with the accumulator or pressure relief valve 48. This valve is set to operate at a predetermined pressure such that when the loading on the additional wheel exceeds a given maximum the relief valve is overcome and the piston rod 23 is allowed to retract into the cylinder 21 until the load on the wheel falls below the maximum value. Where an accumulator is provided, this is charged when the additional wheel runs over the obstruction, and when the obstacle is passed the ram returns to its normal position and pressure, thus maintaining a constant load on the wheel. The purpose of the one-way valve 45 is to allow pressure sensing in one direction only. When the pressure in the pilot line 44 or the signal from the electrical sensor falls below the predetermined level (e.g. by the vehicle setting down its load), the servo valve 46 operates to release pressure in line 47 and place line 52 from the control valve 42 in communication with line 53 delivering to the return side of the ram 21. The piston rod 23 (or 35) is raised to lift wheel 12 or 13 clear of the ground surface into its inoperative position. This prevents scuffing of these wheels during movement of the vehicle at axle loadings below the preset level and reduces typre wear. While two additional wheel assemblies are described in connection with the preferred embodiments one for each side of the vehicle, it will be understood that more than two wheels may be used, or even a single wheel may be fitted on the centre-line of the vehicle. By means of the present invention the additional wheel or wheels are moved into and out of the ground engaging operative position by means, exemplified herein as an hydraulic circuit, responsive to the turning moment, engendered by the effective load centre multiplied by the value of the load lifted, about the front axles of the vehicle road wheels. This is so whatever the load lifting means of the vehicle is, such as the fork lift mast with its work carriage and forks or a cantilever arm lifting constructon. This turning moment is the main factor in the load or forces acting on the front axles of the vehicle over and above the constant load on these axles due to the weight of the vehicle itself when not carrying a load on its load lifting means. This mechanism enhances the safety of the vehicle as it senses the turning moment on the road wheel axle, and results in spreading the total load on the vehicle road wheel axles over a substantial area of the ground. WHAT WE CLAIM IS: -

1. A load-carrying vehicle movable on road wheels provided with means for raising and lowering a load, and one or more additional wheels which are capable of being moved between an operative position in which they are in contact with the ground surface and capable of supporting at least part of the laden weight of the vehicle, and an inoperative position in which the laden weight of the vehicle is carried entirely on the road wheels, and means for moving the additional wheel or wheels between said operative and inoperative positions in response to the overturning moment (as herein defined) on the road wheels.

7. A load-carrying vehicle movable on

said wheels and provided with means for raising and lowering a load substantially as herein described with reference to the accompanying drawings including the constructions on the right and left hand sides of the vehicle in Figure 2.