IES83408Y1 - Articulated forklift truck - Google Patents
Articulated forklift truckInfo
- Publication number
- IES83408Y1 IES83408Y1 IE2003/0493A IE20030493A IES83408Y1 IE S83408 Y1 IES83408 Y1 IE S83408Y1 IE 2003/0493 A IE2003/0493 A IE 2003/0493A IE 20030493 A IE20030493 A IE 20030493A IE S83408 Y1 IES83408 Y1 IE S83408Y1
- Authority
- IE
- Ireland
- Prior art keywords
- wheels
- chassis section
- motor
- forklift truck
- driving
- Prior art date
Links
- 230000002706 hydrostatic Effects 0.000 claims abstract description 8
- 238000011068 load Methods 0.000 description 9
- 239000012530 fluid Substances 0.000 description 3
- 238000006073 displacement reaction Methods 0.000 description 2
- 238000002485 combustion reaction Methods 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 239000010720 hydraulic oil Substances 0.000 description 1
Abstract
ABSTRACT An articulated forklift truck for use in narrow aisles comprises a front chassis section (10) having a first pair of ground—engaging wheels (20) and a rear chassis section (12) having a second pair of groundengaging wheels (22). The front chassis section (10) carries a mast (16) and lift forks (18) and is pivoted to the rear chassis section (12) about a substantially vertical axis (14) to allow the truck to be steered. Both front wheels (20), but only one of the rear wheels, (22) are driven by electric or hydrostatic motors (24,26).
Description
ARTICULATED FORKLIFT TRUCK
Field of the Invention
This invention relates to an articulated forklift
truck, especially of the kind designed for use in
narrow aisles.
Background to the Invention
A typical narrow—aisle articulated forklift truck
comprises front and rear chassis sections each having a
pair of wheels on a respective common axis. The rear
wheels are driven, while the front wheels are non-
driven. The chassis sections are pivoted together about
a vertical axis so that the front chassis section can
be turned at an angle at or approaching 90° relative to
the rear chassis section to allow the truck to insert
the face of the
loads into, and remove loads from,
aisle, i.e. normal to the length of the aisle.
Clearly, as the steering angle increases the inner rear
wheel, i.e. the wheel on the inside of the path taken
by the truck, will turn more slowly than the outer rear
wheel, and in fact may stop altogether or reverse if
the axis of the front wheels coincides with or lies
inside the ground contact point of the inner rear wheel
at large steering angles. In conventional narrow—aisle
articulated forklift trucks this leads to tyre wear and
difficulties in manoeuvring and controlling the truck.
At large steering angles,
too, the rear driving wheels
will tend to drive the forklift straight ahead (this is
known as "dozing on"), with the front wheels skidding
sideways.
It is an object of this invention to provide a
construction of forklift truck in which this problem is
avoided or mitigated.
Summary of the Invention
Accordingly to the present invention there is provided
an articulated forklift truck comprising a rear chassis
section having a rear pair of ground-engaging wheels on
a first substantially common axis, a front chassis
section pivoted to the rear chassis section about a
substantially vertical axis and having a front pair of
ground—engaging wheels on a second substantially common
axis, the front chassis section carrying a mast and
lift forks, and steering means for turning the front
chassis section relative to the rear chassis section,
the truck further including means for driving both
front wheels and one only of the rear wheels.
Brief Description of the Drawings
An embodiment of the invention will now be described,
by way of example, with reference to the accompanying
drawings, in which:
Fig. l is a schematic plan view of a narrow—aisle
articulated forklift truck according to the invention
in the straight—ahead position;
Fig. 2 is a schematic diagram of the hydraulic circuit
used to drive the hydrostatic motors associated with
the wheels of the truck of Fig. 1;
Fig. 3 is a plan View of the truck of Fig. 1 in the act
of manoeuvring goods into a loading bay; and
Fig. 4 is a perspective view of the truck of Fig. 1.
Detailed Description of the Preferred Embodiment
Referring to the drawings, an articulated forklift
truck 8 comprises front and rear chassis sections 10,
12 respectively. The rear chassis section 12 is
pivotable about a vertical shaft 14 fixed to the front
chassis section 10. The truck also includes a
conventional powered steering mechanism, not shown,
which allows the vehicle operator, who is seated on the
rear chassis section 12, to steer the truck by turning
the front chassis section 10 left or right through up
to 900 relative to the rear chassis section 12.
The front chassis section 10 carries a conventional
mast 16 and lift forks 18. The front chassis section
has a first pair of ground—engaging wheels 20 on a
common axis, and the rear chassis section 12 has a
second pair of ground—engaging wheels 22 on a common
axis. The axis of the front wheels 20 is tiltable in a
vertical plane containing said axis to accommodate
irregularities in the ground over which the truck
travels.
Each front wheel 20 is individually driven by a
respective hydrostatic motor 24, but one only of the
rear wheels 20 is individually driven by a hydrostatic
motor 26 (the other rear wheel 20 is allowed to
freewheel). As is well known, each motor 24, 26 has a
number of pistons which operates on a cam ring to drive
the respective wheel 20 or 22. A variable displacement
pump 28 powered by an internal combustion engine 30
supplies hydraulic fluid to the motors 24 and 26 in
known manner.
Referring to Fig. 2, under the control of the vehicle
operator the pump 28 can be selectively operated to
supply hydraulic fluid under pressure either via line A
to drive all three motors, and hence all three driven
wheels, simultaneously in a forward direction, or via
line B to drive all three motors, and hence all three
driven wheels, simultaneously in a reverse direction.
To manoeuvre a load 32, Fig. 3, into the loading bay
34, it is necessary to manoeuvre the forklift truck 8
such that the axis of the front wheels 20 is
substantially at 900 to the axis of the rear wheels 22
in order to position the load 32 in the loading bay 34
since the aisle 36 is relatively narrow when compared
with the width of the body 12.
The displacement and torque of the wheel motors 24, 26
is selected such that, when the truck is loading the
goods into the loading bay as shown in Fig. 3, the
supply of hydraulic fluid under pressure to line A is
sufficient to rotate the front wheels 20 in a forward
direction to move the load towards and into the loading
bay 34. Because of the geometry of the truck one of
the rear wheels, i.e. that on the inside of the path
taken by the truck, may actually rotate in the reverse
direction and if it
is the driven wheel, such rotation
will be against the force of the associated motor 26
tending to drive it forwardly.
The operation of the front and rear motors 24, 26
prevents the front wheels 20 from being forced sideways
in the direction of arrow A along the aisle and
increases the manoeuvrability of the forklift truck
enabling goods to be loaded and unloaded in confined
spaces such as narrow aisles or warehouses.
The front wheels 20 pull and steer the machine in the
required direction. As hydraulic oil takes the path of
least resistance it is much easier to drive the front
wheels in the required direction than the back wheel to
doze the front wheels forwards.
Variations of the above embodiment are possible. For
example, although the embodiment uses hydrostatic
motors, these could alternatively be electric motors.
Also, irrespective of whether hydrostatic or electric
motors are used, a single motor 24 could be used to
drive the front wheels 20. This could be achieved by,
for example, fitting the front wheels 20 at opposite
ends of a common axle. The axle may be fitted with a
differential and is driven by a motor. Then, a second
motor 26 would be used to individually drive the rear
driven wheel 22.
It may also be advantageous to remove the drive power
to the rear motor 26 when the angle between the front
and rear chassis sections 10, 12 exceeds a
predetermined angle relative to the straight ahead
when the front section 10 turns
position, for example,
through more than 450 relative to the rear section 12.
This could be achieved by fixing a switch (not shown)
to the rear chassis section, the switch being operated
by a member fixed to the front chassis section when the
latter turns more than the predetermined angle.
Operating the switch would remove electric or hydraulic
power, as the case may be, to the rear motor 26. This
feature could be used irrespective of whether the
motors are hydrostatic or electric, or whether the
front wheels 20 are driven in common by a single motor
or individually by separate motors.
The invention is not limited to the embodiment
described herein and may be modified or varied without
departing from the scope of the invention.
Claims (5)
1. An articulated forklift truck comprising a rear chassis section having a rear pair of ground—engaging wheels on a first substantially common axis, a front chassis section pivoted to the rear chassis section about a substantially vertical axis and having a front pair of ground-engaging wheels on a second the substantially common axis, front chassis section carrying a mast and lift forks, and steering means for turning the front chassis section relative to the rear chassis section, the truck further including means for driving both front wheels and one only of the rear wheels.
2. A forklift truck according to claim l, wherein the driving means comprises a respective motor for individually driving each of the three driven wheels, or the driving means comprises a single motor for driving the front wheels and a further motor for individually driving the rear driven wheel.
3. A forklift truck according to claim 2, wherein each motor is selected from a hydrostatic motor and an electric motor.
4. A forklift truck according to claim 2, wherein the driving means is selectively operable to drive all three driven wheels simultaneously in a forward direction or simultaneously in a reverse direction at the same time.
5. A forklift truck according to claim 4, including means to disengage the drive to the rear motor when the angle between the front and rear chassis sections exceeds a predetermined angle.
Publications (2)
Publication Number | Publication Date |
---|---|
IE20030493U1 IE20030493U1 (en) | 2004-04-21 |
IES83408Y1 true IES83408Y1 (en) | 2004-04-21 |
Family
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