GB1583557A

GB1583557A - Fork lift trucks

Info

Publication number: GB1583557A
Application number: GB32261/77A
Authority: GB
Original assignee: JE LAU SA
Current assignee: JE LAU SA
Priority date: 1977-03-21
Filing date: 1977-08-01
Publication date: 1981-01-28
Also published as: ES457047A1; LU77624A1; BE856774A; FR2384706A1; IT1081270B

Description

(54) IMPROVEMENTS IN OR RELATING TO FORK LIFT TRUCKS (71) We, JE-LAU S.A., a Spanish Company, of 373 Calle C6rcega, Barcelona, Spain, 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 fork lift trucks.

According to one aspect of the invention there is provided a fork lift truck having a hydraulic drive system comprising a variable delivery hydraulic pump cooperating with a plurality of independent hydraulic motors associated with driven wheels of the truck, wherein the supply of fluid from the pump is controlled by valve means operable to produce both forward and reverse movement of the truck under the control of a single pedal, and pushbutton operated means- is provided to selectively enable drive or hydraulically lock the driven wheels, whilst in either case enabling operation of the truck fork.

In one embodiment of the invention each of the columns or uprights for the truck fork comprises a pair of members of U-shapedcross-section, of which one is fixed to the truck and the other slides with respect to the fixed member and carries the fork, a frusto-conical roller being provided at the upper end of the fixed member with its axis inclined to the lateral direction of the truck, while another frusto-conical roller is provided at the lower end of the sliding member with its axis inclined to the lateral direction of the truck in the opposite direction to the axis of the first-mentioned roller, the roller of the sliding member bearing against the inner side of one arm of the U-section of the fixed member, while the roller of the fixed member bears against a longitudinal rib provided on the sliding member, said rib being located between said roller of the fixed member and one of the arms of the U-section of the fixed member.

A fork lift truck in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a side elevation of the truck, Figure 2 is a plan view of the truck, Figure 3 is a plan view of the truck, on a larger scale, with the bodywork removed, Figure 4 is a schematic view showing the hydraulic drive system of the truck, Figure 5 is a top plan view showing one of the two columns or uprights supporting the truck fork, and Figure 6 is a sectional view of one of the frusto-conical rollers arranged in said column.

The hydraulic drive system for the truck comprises a two-way variable delivery axial plunger type of pump 1 and two independent hydraulic motors 2, also of axial plunger type, for operating the driving wheels of the truck by means of three planetary reducing gears. The pump is driven by an internal combustion engine, having incorporated therein a generating pump (not shown in Figure 4) for drawing oil through suitable check valves from a reservoir 3 through a filter 4. The pump 1 is coupled to the motors 2 by a system comprising respective flow and return lines associated with each motor 2. The oil unused by the system passes through an overload valve (not shown) and, together with the leakage oil from the pump 1, is used for washing and cooling the hydraulic motors 2, a conventional radiator 5 being provided in the circuit for oil cooling.

The supply of oil from pump 1 to the motors 2 is controlled by a three-way electrovalve and a servopiston (not shown), the oil delivery to the servopiston being regulated by throttling means and an overpressure valve (not shown).

Automatic operability of the truck is provided by the above briefly described elements, producing smooth acceleration and deceleration. Forward and reverse movement of the truck are produced in accordance with the direction of the supply of oil from the pump 1 to the motors 2 under control of the electrovalve which is operated using only one pedal 6, said pedal having a substantial amplitude or stroke and being carried on a rocker arm enabling the driver to carry out said opertions without having to lift his heel from the platform of the truck. The elimina tion of additional levers or pedals for drive engagement or reversing has the advantage that the truck can be driven with a much lower degree of fatique than is experienced when driving any other conventional truck.

In addition, the provision of two independent hydraulic motors has the advantage that the need for a conventional differential gear assembly is obviated.

In order to enable prevention of any accidental movement of the truck when loading or unloading operations are being affected by the fork, or when the truck is parked when the motor is running, a push button 7 is provided on the control panel which, when not acutated, closes the electro valve, enabling operation of the fork, while simultaneously blocking the vehicle wheels, so that loads can be lifted to considerable heights by the fork without any fear of the truck moving. When said pushbutton is actuated, the electrovalve in the above mentioned hydraulic system is opened, so that the truck can be driven in the forward or reverse directions and the fork operated at the same time if desired. The hydraulic system is also provided with a distributor simultaneously acting as a manual pump, allowing the truck to be operated when the engine is not running.

The members comprising the columns or uprights supporting the fork in conventional trucks are provided with suitably arranged rollers for resisting both frontal and lateral forces to which the sliding member of the fork column or upright is subjected, this requiring hitherto at least four rollers, of which two are for resisting the frontal forces and the other two are for resisting the lateral forces also acting on the fork.

In the embodiment described, the columns or uprights for the truck each comprise a pair of members 8 and 9 of U-shaped cross section, of which the member 8 is fixed to the truck and the member 9 is movable or slidable with respect to the member 8 and carries the fork. Frusto-conical rollers 10 are provided, one at the upper end of the fixed member 8 and another at the lower end of the sliding member 9, which rollers 10 are carried on axles 11 having axes inclined away from each other at a small angle either side of the lateral direction of the truck. The axles 11 are each integral with the respective member 8 or 9, disengagement of the rollers 10 from their associated axles 11 being prevented by a removable plate 12 screwed onto the free end of each axle 11, the removal of this plate 12 allowing a rapid change of roller in case of failure.

The roller 10 provided on the sliding member 9 bears against the inner side of one arm of the U-section of the fixed member 8, while the roller 10 of the fixed member bears against a longitudinal rib 13 formed integrally with the sliding member 9, the rib 13 being located between the latter roller 10 and said one arm of the fixed member 8.

Such an arrangement dispenses with two of the four rollers hitherto required for overcoming frontal and lateral forces, since both forces are resisted by the above described frusto-conical rollers 10, thus substantially simplifying truck maintenance and at the same time assuring better alignment and more accurate adjustment between the two members 8 and 9. As the number of points of contact between the two members has been reduced from four to two when compared with previous arrangements, the noise associated with conventional forks is largely eliminated.

Finally, it should be noted that the truck is provided with a single hydraulically operated double-acting cylinder 14, by means of which the rear wheels can be steered in a convenient direction. This is a highly significant development, since conventional trucks normally use a pair of cylinders for this purpose.

WHAT WE CLAIM IS:- 1. A fork lift truck having a hydraulic drive system comprising a variable delivery hydraulic pump cooperating with a plurality of independent hydraulic motors associated with driven wheels of the truck, wherein the supply of fluid from the pump is controlled by valve means operable to produce both forward and reverse movement of the truck under the control of a single pedal, and pushbutton operated means is provided to selectively enable drive or hydraulically lock the driven wheels, whilst in either case enabling operation of the truck fork.

2. A fork lift truck according to claim 1, wherein the valve means comprises a threeway electrovalve and a servopiston, throttling means and an overpressure valve being provided for regulating the pump delivery.

3. A fork lift truck according to claim 1 or 2, including a single double-acting cylinder by means of which, in use, one or more of the wheels of the truck may be rotated about a substantially vertical axis for steering purposes.

4. A fork lift truck according to claim 1, 2 or 3, wherein each of the columns or uprights for the truck fork comprises a pair of members of U-shaped cross-section, of which one is fixed to the truck and the other slides with respect to the fixed member and carries the fork, a frusto-conical roller being provided at the upper end of the fixed member with its axis inclined to the lateral

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Claims

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one pedal 6, said pedal having a substantial amplitude or stroke and being carried on a rocker arm enabling the driver to carry out said opertions without having to lift his heel from the platform of the truck. The elimina tion of additional levers or pedals for drive engagement or reversing has the advantage that the truck can be driven with a much lower degree of fatique than is experienced when driving any other conventional truck.

In addition, the provision of two independent hydraulic motors has the advantage that the need for a conventional differential gear assembly is obviated.

In order to enable prevention of any accidental movement of the truck when loading or unloading operations are being affected by the fork, or when the truck is parked when the motor is running, a push button 7 is provided on the control panel which, when not acutated, closes the electro valve, enabling operation of the fork, while simultaneously blocking the vehicle wheels, so that loads can be lifted to considerable heights by the fork without any fear of the truck moving. When said pushbutton is actuated, the electrovalve in the above mentioned hydraulic system is opened, so that the truck can be driven in the forward or reverse directions and the fork operated at the same time if desired. The hydraulic system is also provided with a distributor simultaneously acting as a manual pump, allowing the truck to be operated when the engine is not running.

The members comprising the columns or uprights supporting the fork in conventional trucks are provided with suitably arranged rollers for resisting both frontal and lateral forces to which the sliding member of the fork column or upright is subjected, this requiring hitherto at least four rollers, of which two are for resisting the frontal forces and the other two are for resisting the lateral forces also acting on the fork.

In the embodiment described, the columns or uprights for the truck each comprise a pair of members 8 and 9 of U-shaped cross section, of which the member 8 is fixed to the truck and the member 9 is movable or slidable with respect to the member 8 and carries the fork. Frusto-conical rollers 10 are provided, one at the upper end of the fixed member 8 and another at the lower end of the sliding member 9, which rollers 10 are carried on axles 11 having axes inclined away from each other at a small angle either side of the lateral direction of the truck. The axles

11 are each integral with the respective member 8 or 9, disengagement of the rollers

10 from their associated axles 11 being prevented by a removable plate 12 screwed onto the free end of each axle 11, the removal of this plate 12 allowing a rapid change of roller in case of failure.

The roller 10 provided on the sliding member 9 bears against the inner side of one arm of the U-section of the fixed member 8, while the roller 10 of the fixed member bears against a longitudinal rib 13 formed integrally with the sliding member 9, the rib 13 being located between the latter roller 10 and said one arm of the fixed member 8.

Such an arrangement dispenses with two of the four rollers hitherto required for overcoming frontal and lateral forces, since both forces are resisted by the above described frusto-conical rollers 10, thus substantially simplifying truck maintenance and at the same time assuring better alignment and more accurate adjustment between the two members 8 and 9. As the number of points of contact between the two members has been reduced from four to two when compared with previous arrangements, the noise associated with conventional forks is largely eliminated.

Finally, it should be noted that the truck is provided with a single hydraulically operated double-acting cylinder 14, by means of which the rear wheels can be steered in a convenient direction. This is a highly significant development, since conventional trucks normally use a pair of cylinders for this purpose.

WHAT WE CLAIM IS:- 1. A fork lift truck having a hydraulic drive system comprising a variable delivery hydraulic pump cooperating with a plurality of independent hydraulic motors associated with driven wheels of the truck, wherein the supply of fluid from the pump is controlled by valve means operable to produce both forward and reverse movement of the truck under the control of a single pedal, and pushbutton operated means is provided to selectively enable drive or hydraulically lock the driven wheels, whilst in either case enabling operation of the truck fork.
2. A fork lift truck according to claim 1, wherein the valve means comprises a threeway electrovalve and a servopiston, throttling means and an overpressure valve being provided for regulating the pump delivery.
3. A fork lift truck according to claim 1 or 2, including a single double-acting cylinder by means of which, in use, one or more of the wheels of the truck may be rotated about a substantially vertical axis for steering purposes.
4. A fork lift truck according to claim 1, 2 or 3, wherein each of the columns or uprights for the truck fork comprises a pair of members of U-shaped cross-section, of which one is fixed to the truck and the other slides with respect to the fixed member and carries the fork, a frusto-conical roller being provided at the upper end of the fixed member with its axis inclined to the lateral

direction of the truck, while another frustoconical roller is provided at the lower end of the sliding member with its axis inclined to the lateral direction of the truck in the opposite direction to the axis of the firstmentioned roller, the roller of the sliding member bearing against the inner side of one arm of the U-section of the fixed member, while the roller of the fixed member bears against a longitudinal rib provided on the sliding member, said rib being located between said roller of the fixed member and one of the arms of the U-section of the fixed member.
5. A fork lift truck substantially as hereinbefore described with reference to and as shown in the accompanying drawings.