CA2695931A1 - A forklift truck - Google Patents
A forklift truck Download PDFInfo
- Publication number
- CA2695931A1 CA2695931A1 CA2695931A CA2695931A CA2695931A1 CA 2695931 A1 CA2695931 A1 CA 2695931A1 CA 2695931 A CA2695931 A CA 2695931A CA 2695931 A CA2695931 A CA 2695931A CA 2695931 A1 CA2695931 A1 CA 2695931A1
- Authority
- CA
- Canada
- Prior art keywords
- ram
- forklift truck
- mast
- supply line
- fluid supply
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B66—HOISTING; LIFTING; HAULING
- B66F—HOISTING, LIFTING, HAULING OR PUSHING, NOT OTHERWISE PROVIDED FOR, e.g. DEVICES WHICH APPLY A LIFTING OR PUSHING FORCE DIRECTLY TO THE SURFACE OF A LOAD
- B66F9/00—Devices for lifting or lowering bulky or heavy goods for loading or unloading purposes
- B66F9/06—Devices for lifting or lowering bulky or heavy goods for loading or unloading purposes movable, with their loads, on wheels or the like, e.g. fork-lift trucks
- B66F9/075—Constructional features or details
- B66F9/07559—Stabilizing means
Abstract
This invention relates to forklift truck adapted for mounting on a carrying vehicle comprising a U-shaped chassis and an upright mast carrying forks mounted the chassis. The forklift is supplied with load rest supports to facilitate loading of goods onto and unloading of goods off of a raised platform, such as a trailer bed, at or near maximum extension of the forks. The load rest supports include an upright and a fluid actuated ram to move the upright to and from an operating position in which a contact surface of the upright is forward of a leading surface of the mast and a stowed position in which the contact surface of the upright is rearward of a leading surface of the mast. A pressure limiting means is provided to limit the pressure of the fluid supply to the ram of the load rest support thereby obviating the possibility of damage to the load rest supports and/or the platform.
Description
"A Forklift Truck"
Introduction This invention relates to a forklift truck and in particular to a forklift truck adapted to be transported on a carrying vehicle.
Forklift trucks that are adapted to be transported on a carrying vehicle, commonly referred to as piggy-back forklift trucks, are of necessity very lightweight machines.
This is due to the fact that the heavier the piggy-back forklift truck, the lower the available load carrying capacity of the carrying vehicle. As a consequence of their relatively light weight, there is a tendency for the piggy-back forklift trucks to tip forwards, particularly when picking up a load off a raised platform when the forks are at their maximum or near maximum extension. If the forklift tips forward against the platform, there is a danger that the mast of the forklift will become damaged from the impact. This is highly undesirable.
Various apparatus have been devised to prevent the mast being damaged through the forklift tipping forward against a platform. One such device is so-called load rest support, described in the Applicant's own European Patent Nos. EP 1 457 456 and EP 1 792 869. The load rest supports comprise an upright bar pivotable to and from a position forward of the mast where it can engage a substantially vertical, external surface of the platform and rearward of the mast where it is stowed out of the way.
These devices have proven to be very successful in obviating damage to the mast of the piggy-back forklift. There is however an issue with the known load rest supports.
The upright bar is moved by a fluid actuated ram which is supplied from the hydraulic supply of the piggy-back forklift and therefore it is quite common for the load rest support to exert an excessive force on the platform such that the forklift is pushed away from the trailer, or the trailer is pushed away from the forklift. This can result in damage to either the platform or the load rest supports.
Furthermore, in the case of the platform being the bed of an articulated chassis trailer, the side of the trailer adjacent the load rest supports can be raised relative to the opposite side of the trailer, thereby placing the trailer bed at an angle offset to the
Introduction This invention relates to a forklift truck and in particular to a forklift truck adapted to be transported on a carrying vehicle.
Forklift trucks that are adapted to be transported on a carrying vehicle, commonly referred to as piggy-back forklift trucks, are of necessity very lightweight machines.
This is due to the fact that the heavier the piggy-back forklift truck, the lower the available load carrying capacity of the carrying vehicle. As a consequence of their relatively light weight, there is a tendency for the piggy-back forklift trucks to tip forwards, particularly when picking up a load off a raised platform when the forks are at their maximum or near maximum extension. If the forklift tips forward against the platform, there is a danger that the mast of the forklift will become damaged from the impact. This is highly undesirable.
Various apparatus have been devised to prevent the mast being damaged through the forklift tipping forward against a platform. One such device is so-called load rest support, described in the Applicant's own European Patent Nos. EP 1 457 456 and EP 1 792 869. The load rest supports comprise an upright bar pivotable to and from a position forward of the mast where it can engage a substantially vertical, external surface of the platform and rearward of the mast where it is stowed out of the way.
These devices have proven to be very successful in obviating damage to the mast of the piggy-back forklift. There is however an issue with the known load rest supports.
The upright bar is moved by a fluid actuated ram which is supplied from the hydraulic supply of the piggy-back forklift and therefore it is quite common for the load rest support to exert an excessive force on the platform such that the forklift is pushed away from the trailer, or the trailer is pushed away from the forklift. This can result in damage to either the platform or the load rest supports.
Furthermore, in the case of the platform being the bed of an articulated chassis trailer, the side of the trailer adjacent the load rest supports can be raised relative to the opposite side of the trailer, thereby placing the trailer bed at an angle offset to the
-2-substantially horizontal plane of the forks. This can cause difficulties engaging a load on the trailer bed with the forks.
It is an object of the present invention to provide an improved forklift with load rest supports.
Statements of Invention According to the invention there is provided a forklift truck of the type adapted to be transported on a carrying vehicle comprising a wheeled U-shaped chassis, a vertical mast carrying forks mounted on the chassis and means to extend the reach of the forks relative to the mast to remove loads from and place loads on a raised platform, a platform engaging load rest support comprising a substantially upright bar having a contact surface for engagement against a substantially vertical, external facing surface of the platform, the upright bar being pivotably mounted on the forklift truck pivotable to and from a platform engaging position with the contact surface forward of a leading surface of the mast and a stowed position with the contact surface rearward of a leading surface of the mast and means to pivot the upright bar to and from a platform engaging position and a stowed position including a fluid actuated ram and in which there is provided a pressure limiting means to limit the pressure of the fluid supplied to the fluid actuated ram.
By having a pressure limiting means, there is no longer a tendency for the load rest support to exert an excessive force on the trailer and cause damage to either the trailer or the load rest supports. Furthermore, the side of the trailer adjacent the load rest supports will not be raised upwards which previously caused difficulties for the operator of the forklift engaging loads on the trailer bed with the forks.
In one embodiment of the invention the pressure limiting means comprises a relief valve in a fluid supply line to the fluid actuated ram. The relief valve is seen as a particularly useful way of limiting the pressure as it is cost effective, reliable and compact.
In one embodiment of the invention the fluid actuated ram is a double-acting ram
It is an object of the present invention to provide an improved forklift with load rest supports.
Statements of Invention According to the invention there is provided a forklift truck of the type adapted to be transported on a carrying vehicle comprising a wheeled U-shaped chassis, a vertical mast carrying forks mounted on the chassis and means to extend the reach of the forks relative to the mast to remove loads from and place loads on a raised platform, a platform engaging load rest support comprising a substantially upright bar having a contact surface for engagement against a substantially vertical, external facing surface of the platform, the upright bar being pivotably mounted on the forklift truck pivotable to and from a platform engaging position with the contact surface forward of a leading surface of the mast and a stowed position with the contact surface rearward of a leading surface of the mast and means to pivot the upright bar to and from a platform engaging position and a stowed position including a fluid actuated ram and in which there is provided a pressure limiting means to limit the pressure of the fluid supplied to the fluid actuated ram.
By having a pressure limiting means, there is no longer a tendency for the load rest support to exert an excessive force on the trailer and cause damage to either the trailer or the load rest supports. Furthermore, the side of the trailer adjacent the load rest supports will not be raised upwards which previously caused difficulties for the operator of the forklift engaging loads on the trailer bed with the forks.
In one embodiment of the invention the pressure limiting means comprises a relief valve in a fluid supply line to the fluid actuated ram. The relief valve is seen as a particularly useful way of limiting the pressure as it is cost effective, reliable and compact.
In one embodiment of the invention the fluid actuated ram is a double-acting ram
-3-having a ram extension fluid supply line and a ram contraction fluid supply line.
In one embodiment of the invention the relief valve is connected between the ram extension fluid supply line and the ram contraction fluid supply line.
In one embodiment of the invention the relief valve is connected between the fluid supply line and an independent tank line.
In one embodiment of the invention the relief valve limit is of the order of 20 bar pressure.
In one embodiment of the invention the pressure limiting means comprises a pressure sensor and a cylinder feed block valve.
Detailed Description of the Invention The invention will be more clearly understood by the following description of some embodiments thereof, given by way of example only with reference to the accompanying drawings, in which:
Figure 1 is a rear perspective view of a forklift truck having a load rest support;
and Figure 2 is a schematic diagram of the hydraulic circuit supplying the load rest supports.
Referring to Figure 1, there is shown a piggy-back forklift truck, indicated generally by the reference numeral 1, comprising a U-shaped chassis 3 having a rear cross-bar 5 and a pair of side bars 7 projecting forwardly therefrom. A mast carriage 9 is mounted on the chassis between the side bars 7 and slidable forwards and backwards along the chassis towards and away from the rear cross-bar 5. A mast carrying a pair of forks 13 is mounted on the mast carriage 9 and there is provided means to extend the reach of the forks 13 relative to the mast to remove loads from and place loads on a raised platform (not shown). The means to extend the reach of
In one embodiment of the invention the relief valve is connected between the ram extension fluid supply line and the ram contraction fluid supply line.
In one embodiment of the invention the relief valve is connected between the fluid supply line and an independent tank line.
In one embodiment of the invention the relief valve limit is of the order of 20 bar pressure.
In one embodiment of the invention the pressure limiting means comprises a pressure sensor and a cylinder feed block valve.
Detailed Description of the Invention The invention will be more clearly understood by the following description of some embodiments thereof, given by way of example only with reference to the accompanying drawings, in which:
Figure 1 is a rear perspective view of a forklift truck having a load rest support;
and Figure 2 is a schematic diagram of the hydraulic circuit supplying the load rest supports.
Referring to Figure 1, there is shown a piggy-back forklift truck, indicated generally by the reference numeral 1, comprising a U-shaped chassis 3 having a rear cross-bar 5 and a pair of side bars 7 projecting forwardly therefrom. A mast carriage 9 is mounted on the chassis between the side bars 7 and slidable forwards and backwards along the chassis towards and away from the rear cross-bar 5. A mast carrying a pair of forks 13 is mounted on the mast carriage 9 and there is provided means to extend the reach of the forks 13 relative to the mast to remove loads from and place loads on a raised platform (not shown). The means to extend the reach of
-4-the forks relative to the mast is provided by way of a pantograph linkage 15 however other means to extend the reach of the forks could be used such as extensible forks.
A platform engaging load rest support 17 (shown circled) comprising a substantially upright bar 19 having a contact surface 21 for engagement against a substantially vertical external facing surface of the platform is pivotably mounted on the mast carriage 9. A fluid actuated ram 23 is provided to pivot the upright bar 19 to and from a platform engaging position in which the contact surface is forward of a leading surface of the mast and a stowed position with the contact surface rearward of the leading surface of the mast. In the embodiment shown, there is provided a pair of upright bars 19 mounted on either side of the upright mast on the mast carriage.
The operation of the load rest supports is known in the art. A thorough description of the operation of the load rest supports and the steps taken to remove or place a load on the raised platform may be found in the Applicant's own European Patent Nos. EP
1 457 456 and EP 1 792 869, the entire disclosures of which are incorporated herein by way of reference and in particular the description contained therein relating to the operation of the load rest supports and the various embodiments and features of the load rest supports.
Referring now to Figure 2, there is shown a circuit schematic of the hydraulic supply to the load rest supports. The load rest supports each comprise a load rest support ram, 23, one ram 23 is provided for each load rest support. The fluid actuated rams each comprise a cylinder 24 and a piston 25. The fluid supply, indicated generally by the reference numeral 27, supplies fluid to each of the rams 23 as required.
The rams 23 are double-acting rams each comprising a ram extension fluid supply line 29 and a ram contraction fluid supply line 31. There is provided a pressure limiting means, in this case a relief valve 33 connected between the ram extension fluid supply line 29 and the ram contracting fluid supply line 31. In the embodiment shown, the relief valve limit is set to 20bar. However, it is envisaged that the relief valve limit could be set to a lower or higher pressure as desired although 20bar is preferred.
In use, when fluid is being delivered through the ram extension fluid supply line 29 to cause the pistons 25 to move outward of the cylinders 24, the fluid will continue to be
A platform engaging load rest support 17 (shown circled) comprising a substantially upright bar 19 having a contact surface 21 for engagement against a substantially vertical external facing surface of the platform is pivotably mounted on the mast carriage 9. A fluid actuated ram 23 is provided to pivot the upright bar 19 to and from a platform engaging position in which the contact surface is forward of a leading surface of the mast and a stowed position with the contact surface rearward of the leading surface of the mast. In the embodiment shown, there is provided a pair of upright bars 19 mounted on either side of the upright mast on the mast carriage.
The operation of the load rest supports is known in the art. A thorough description of the operation of the load rest supports and the steps taken to remove or place a load on the raised platform may be found in the Applicant's own European Patent Nos. EP
1 457 456 and EP 1 792 869, the entire disclosures of which are incorporated herein by way of reference and in particular the description contained therein relating to the operation of the load rest supports and the various embodiments and features of the load rest supports.
Referring now to Figure 2, there is shown a circuit schematic of the hydraulic supply to the load rest supports. The load rest supports each comprise a load rest support ram, 23, one ram 23 is provided for each load rest support. The fluid actuated rams each comprise a cylinder 24 and a piston 25. The fluid supply, indicated generally by the reference numeral 27, supplies fluid to each of the rams 23 as required.
The rams 23 are double-acting rams each comprising a ram extension fluid supply line 29 and a ram contraction fluid supply line 31. There is provided a pressure limiting means, in this case a relief valve 33 connected between the ram extension fluid supply line 29 and the ram contracting fluid supply line 31. In the embodiment shown, the relief valve limit is set to 20bar. However, it is envisaged that the relief valve limit could be set to a lower or higher pressure as desired although 20bar is preferred.
In use, when fluid is being delivered through the ram extension fluid supply line 29 to cause the pistons 25 to move outward of the cylinders 24, the fluid will continue to be
-5-delivered to the cylinder 24 through the ram extension fluid supply line 29 until such time as the ram reaches its maximum stroke and/or the pressure of the fluid in the ram extension fluid supply line reaches 20 bar. If the contact surface 21 of the load rest support 17 comes into engagement with the platform before the ram 23 reaches its maximum stroke, pressure will begin to build up in the ram extension fluid supply line 29 and in the cylinders 24. When the pressure reaches 20 bar, the relief valve 33 will allow fluid to escape from the ram extension fluid supply line 29 to the ram contraction fluid supply line 31, thereby preventing further movement of the load rest supports. In this way, damage to the load rest supports and/or the platform is avoided. Furthermore, the side of the trailer will not be raised at an angle offset to the horizontal plane of the forks preventing simple engagement of a load by the forks.
In addition to the above, a check valve 34 is incorporated into the same manifold block as the pressure relief valve. The check valve is added to ensure that the cylinders lock forward and don't retract due to leakage. The check valve typically consists of a small valve containing a spherical ball and cone shaped seat.
When oil is fed against the ball, it in turn is pushed against the cone face creating a seal thus prevent oil getting through. When oil is fed in the opposite direction, the ball is unseated from the cone and the oil can pass normally. When it is desired to have oil flow travel past the ball, a separate source of oil pressure, known as signal pressure, (normally from the opposite feed line) is fed into the valve forcing the ball to unseat, therefore allowing oil to transfer.
Various other modifications could be incorporated into the forklift truck.
First of all, instead of using a pressure relief valve, it is possible to provide a pressure sensor monitoring the pressure of the fluid in the load rest support cylinder and a cylinder feed block valve. The cylinder feed block valve would be operated to prevent further flow of fluid into the cylinder in response to the pressure sensor determining that a predetermined pressure limit had been reached. A controller responsive to the pressure sensor to operate the cylinder feed block valve would be provided to interface between the sensor and the block valve. Secondly, instead of providing a pressure relief valve intermediate the ram extension fluid supply line and the ram contraction fluid supply line, it would be possible to provide a relief valve connected between the fluid supply line and an independent tank line.
In addition to the above, a check valve 34 is incorporated into the same manifold block as the pressure relief valve. The check valve is added to ensure that the cylinders lock forward and don't retract due to leakage. The check valve typically consists of a small valve containing a spherical ball and cone shaped seat.
When oil is fed against the ball, it in turn is pushed against the cone face creating a seal thus prevent oil getting through. When oil is fed in the opposite direction, the ball is unseated from the cone and the oil can pass normally. When it is desired to have oil flow travel past the ball, a separate source of oil pressure, known as signal pressure, (normally from the opposite feed line) is fed into the valve forcing the ball to unseat, therefore allowing oil to transfer.
Various other modifications could be incorporated into the forklift truck.
First of all, instead of using a pressure relief valve, it is possible to provide a pressure sensor monitoring the pressure of the fluid in the load rest support cylinder and a cylinder feed block valve. The cylinder feed block valve would be operated to prevent further flow of fluid into the cylinder in response to the pressure sensor determining that a predetermined pressure limit had been reached. A controller responsive to the pressure sensor to operate the cylinder feed block valve would be provided to interface between the sensor and the block valve. Secondly, instead of providing a pressure relief valve intermediate the ram extension fluid supply line and the ram contraction fluid supply line, it would be possible to provide a relief valve connected between the fluid supply line and an independent tank line.
-6-In the specification the terms "comprise, comprises, comprised and comprising"
and the terms "include, includes, included and including" are deemed to be totally interchangeable and should be afforded the widest possible interpretation.
The invention is in no way limited to the embodiments hereinbefore described, but may be varied in both construction and detail within the scope of the claims.
and the terms "include, includes, included and including" are deemed to be totally interchangeable and should be afforded the widest possible interpretation.
The invention is in no way limited to the embodiments hereinbefore described, but may be varied in both construction and detail within the scope of the claims.
Claims (8)
1. A forklift truck of the type adapted to be transported on a carrying vehicle comprising a wheeled U-shaped chassis, a vertical mast carrying forks mounted on the chassis and means to extend the reach of the forks relative to the mast to remove loads from and place loads on a raised platform, a platform engaging load rest support comprising a substantially upright bar having a contact surface for engagement against a substantially vertical, external facing surface of the platform, the upright bar being pivotably mounted on the forklift truck pivotable to and from a platform engaging position with the contact surface forward of a leading surface of the mast and a stowed position with the contact surface rearward of a leading surface of the mast and means to pivot the upright bar to and from a platform engaging position and a stowed position including a fluid actuated ram, and in which there is provided a pressure limiting means to limit the pressure of the fluid supplied to the fluid actuated ram.
2. A forklift truck as claimed in claim 1 in which the pressure limiting means comprises a relief valve in a fluid supply line to the fluid actuated ram.
3. A forklift truck as claimed in claim 2 in which the fluid actuated ram is a double-acting ram having a ram extension fluid supply line and a ram contraction fluid supply line.
4. A forklift truck as claimed in claim 3 in which the relief valve is connected between the ram extension fluid supply line and the ram contraction fluid supply line.
5. A forklift truck as claimed in claim 2 or 3 in which the relief valve is connected between the fluid supply line and an independent tank line.
6. A forklift truck as claimed in claims 2 to 4 in which the relief valve limit is of the order of 20 bar pressure.
7. A forklift truck as claimed in claim 1 in which the pressure limiting means comprises a pressure sensor and a cylinder feed block valve.
8. A forklift truck substantially as hereinbefore described with reference to and as illustrated by the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA2695931A CA2695931C (en) | 2010-03-05 | 2010-03-05 | A forklift truck |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA2695931A CA2695931C (en) | 2010-03-05 | 2010-03-05 | A forklift truck |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2695931A1 true CA2695931A1 (en) | 2011-09-05 |
| CA2695931C CA2695931C (en) | 2017-10-03 |
Family
ID=44561321
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA2695931A Active CA2695931C (en) | 2010-03-05 | 2010-03-05 | A forklift truck |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2695931C (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104310278A (en) * | 2014-09-23 | 2015-01-28 | 合肥工业大学 | Special mechanical loading, unloading and transporting device for multifunctional forklift truck |
-
2010
- 2010-03-05 CA CA2695931A patent/CA2695931C/en active Active
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104310278A (en) * | 2014-09-23 | 2015-01-28 | 合肥工业大学 | Special mechanical loading, unloading and transporting device for multifunctional forklift truck |
Also Published As
| Publication number | Publication date |
|---|---|
| CA2695931C (en) | 2017-10-03 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request |
Effective date: 20150305 |