Material or article handling – Elevator or hoist and loading or unloading means therefor – Elevator wherein means comprises guide mounted for relative...
Patent
1992-01-14
1994-05-17
Bucci, David A.
Material or article handling
Elevator or hoist and loading or unloading means therefor
Elevator wherein means comprises guide mounted for relative...
180 648, B66F 910, B62D 5302
Patent
active
053122194
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to narrow aisle lift trucks.
BACKGROUND OF THE INVENTION
When a fork lift truck is driven in other than a straight line, the wheels nearer the centre of turning travel a smaller distance than the outer wheels.
EP 0 303 413 shows a narrow aisle lift truck having a body and a mast structure which are pivoted together about a main vertical or king pin axis. The body has wheels on a first common axis and the mast structure has feet with wheels on a second common axis. When the axes are parallel the parts are pivotally related for straight ahead, or straight back, travel. The mast has a carriage for elevation of forks which are for insertion and retraction of a load to and from the stack in which the aisle extends. Steering is effected by driving the mast structure about the king pin by any suitable means. A truck having all of these mentioned features is herein called "of the kind referred to".
A truck of this kind may, in an extreme position, have the said axes at an angle of the order of 90 deg. to one another. This can result in skidding and tire wear.
DE 1049307B shows a truck having front wheels only driven by separate motors which can be controlled individually as to direction of speed. This provides a solution to the problem of the inner and outer wheels moving differently, but because those motors act as the only steering means, there are other problems introduced.
DE 1209450B uses two hydrostatic motors, one for each driven wheel, which can run at different speeds when the truck is in curvilinear motion, but this only goes some way towards solving the problem and does not cater for the possibilities of extreme movement of the steering such as those mentioned in the foregoing paragraphs.
GB 2 167 024 shows a vibratory trench roller with four rolls, which can be controlled by so-called tank steering in which two rolls on one side are driven in the same or the opposite direction as those on the other side. However, this does not give satisfactory steering possibilities for a wheeled forklift truck.
The object of the invention is to provide improvements.
SUMMARY OF INVENTION
According to the invention, a forklift truck comprises a rear section having a pair of driven wheels on a common axis, a front part pivoted to the rear part about a vertical axis, said front part being provided with a pair of non-driven wheels on a second common axis and also with a mast provided with the lift forks, and steering means for turning the second part relative to the first part, a pair of separate and individually controlled drive motors, one for each rear wheel and control means arranged to vary both the speed down to zero, and direction of drive of one motor, relative to the other according to the steering angle.
As the steering angle increases, the inner wheel may be driven at a slower speed then the outer one, and then disengaged from drive. Depending upon the geometry, it may then be driven in the opposite direction to the outer wheel.
For any one truck the choice depends upon the geometry; and at any one time it depends upon the steering angle.
Preferably the two motors are under the control of circuitry (software) with an input from the steering wheel position, or from micro-switches contacted by parts of the steering gear, according to the angle of turning. The arrangement is most desirably such that in the straight line position both wheels are driven synchronously, and drive to the inside wheel--whichever one is involved according to the direction of turning--is progressively reduced as the radius of turning is reduced, down to zero, or first down to zero then reversing of the inside wheel when the steering is near or is on full lock, according to the geometry and design of the truck.
It will be appreciated that when the truck turns and goes forward to the aisle side face the outer wheel is driven forwardly and the inner wheel is stopped or reversed; when the truck is reversed to withdraw from the aisle side face and straighten up, it is the outer wheel which is rever
REFERENCES:
patent: 2957533 (1960-10-01), Lewis et al.
patent: 2986295 (1961-05-01), Shaffer
patent: 3031024 (1962-04-01), Ulinski
patent: 3901339 (1975-08-01), Williamson
patent: 4301881 (1981-11-01), Griffin
patent: 4470475 (1984-09-01), Carlson
patent: 4621562 (1986-11-01), Carr et al.
patent: 4914592 (1990-04-01), Callahan et al.
Bucci David A.
Translift Material Handling Limited
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