Motor vehicles – Steering gear – Each wheel steerable
Reexamination Certificate
2000-05-05
2002-03-12
Johnson, Brian L. (Department: 3618)
Motor vehicles
Steering gear
Each wheel steerable
C180S408000, C180S411000, C280S771000
Reexamination Certificate
active
06354394
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a steering gear for pivotal wheels on a vehicle or carriage, wherein the steering gear is adapted to steer the pivotal wheels so that the centre lines in the rotational axes for the pivotal and possible non-pivotal wheels meet in a common point which is the pivot point of the carriage, and wherein the vertical pivot axle of each of the pivotal wheels is provided with at least one chain wheel or belt pulley, each of said chain wheels/belt pulleys being connected with a chain wheel/belt pulley assigned to the pivot axle of another laterally positioned pivotal wheel by means of a chain or a belt, so that the pivot angle swing is transferred between the pivotal wheels.
The vehicle or the carriage, respectively, comprises in each single case a set of travelling wheels including at least two, preferably four or more, pivotal, steerable travelling wheels.
The steering gear is intended used on a vehicle/carriage having a plurality of steerable wheels, for the conveyance of long, heavy objects, such as loaded 40 feet containers. When driving on small quay and dock plants as well as within buildings, it is necessary that the carriage has several steerable wheels with a minimum pivot radius (90° to either side).
In a set of travelling wheels of a vehicle/carriage comprising in all six travelling wheels: two steerable front wheels, two steerable intermediate wheels and two non-steerable rear wheels, the mutually differing angular deflections of the individual travelling wheels upon turning of the vehicle may be illustrated as follows: The fixed rotational axis of the rear wheels is extended imaginarily, and an imaginary line is drawn from the rotational axis of one of the steerable wheels (e.g. the right hand front wheel) until it crosses the rotational axis extension of the rear wheels. Thus, a crossing point is created, the location thereof on said rotational axis extension is dependent on the radius of the turn; the more sudden turn, the closer to the rear wheels is the crossing point situated. This crossing point constitutes the turning centre of all pivotable, steerable wheels, and this pre-supposes, of course, that all four steerable travelling wheels in the present exemplary embodiment each exhibits an angular deflection differing from the angular deflection of each of the remaining three travelling wheels.
The angle between an imaginary line parallel to the rotational axis of the rear wheels and the rotational axis of the various steerable wheels will differ from wheel to wheel in any turning position of the vehicle/carriage. (In one case, said angles were: right hand front wheel: &agr;
1
26 75°; left hand front wheel: &agr;
2
≈67°; right hand intermediate wheel: &agr;
3
≈60°; left hand intermediate wheel: &agr;
4
≈53°)
When following the road ahead, all angles &agr;
1
-&agr;
4
are each equal to 90° (the wheels are parallel).
The above-mentioned case where the turning radius through the mid point of respective wheels of all pivotable, steerable travelling wheels passes through a common point, represents the ideal case.
In order to secure correct angular deflection at each single pivotable, steerable wheel upon turning of the vehicle/carriage, the steering angles (&agr;) are synchronised by means of a steering gear always securing correct angle of the wheel axes in relation to the rolling direction of the wheels.
Correct angular deflection/steering angle for all pivotable, steerable travelling wheels is characterized in that all centre lines for the wheel rotation have said common crossing point or are parallel (upon driving ahead/reversing).
Today, on loading and passenger vehicles, a synchronising mechanism comprising steering-gear levers and lateral struts is used for synchronising the turning movements of the steerable travelling wheels. A disadvantage of this prior art synchronising mechanism is that the inaccuracy adjacent maximum angular deflections is all too large.
Moreover, it does not allow full swing-out of the steering wheels. Thus, said swing-out will never approach 90° to either side. For vehicles and carriages having a need for approximately 90° turning possibility to either side, e.g. the above-mentioned construction where the set of travelling wheels comprises two steerable front wheels, two or more steerable intermediate wheels, as well as two rear wheels having a fixed rotational axis, this known synchronising mechanism is less fit.
In a vehicle having a 90° turning possibility to either side, the pivotable, steerable wheels must be driven; preferably hydraulic or electric operation. This has become more and more usual, e.g. in special vehicles within agriculture and industry.
Moreover, prior art comprises in the field concerned, e.g. those mechanisms disclosed in Swedish Laying-Out publication No. 343,254, British patent specification No. 1,155,469 as well as British patent applications Nos. 2,116,131 and 2,155,870.
The Swedish Laying-out publication No. 343,254 deals with a steering gear which is intended to be used on steerable portal cranes. Here, the steering movement is transferred to the wheels from a rack through a toothed segment. The racks are displaced by means of cam grooves (called slideways). The shape of the cam grooves (the slideways) is configurated such that the racks, through the toothed segments, allot to the guide wheels differing steering angles in relation to the driving direction of the vehicle. The critical point of this known steering gear is the shape of the two cam grooves (the slideways). The shape of cam grooves cannot be calculated mathematically, and must be adapted by tests. This known steering gear is likely to be too inaccurate, especially in connection with large turning angles, e.g. up to 90° deflection to either side. The steering mechanism has many mechanical parts which will probably be difficult and expensive to produce.
Moreover, the mechanism would not be usable in connection with two or more steerable intermediate wheels.
British patent specification No. 1,155,469 deals with a camera carriage which, in one embodiment, has four pair of wheels each allotted a vertical shaft for turning around the axis thereof in the horizontal plane. On each of the various vertical shafts, a chain wheel is mounted, two chain wheels being interconnected with an outer, driven chain wheel through a first chain, while the two chain wheels are interconnected with another chain which, through guides, likewise engages said outer, driven chain wheel.
In this known transmission mechanism, each chain wheel is circular, and it is, therefore, unfit for use in a set of wheels wherein the steerable wheels have to be allotted mutually differing angular deflections upon turning of the vehicle/carriage. With the known transmission mechanism, each wheel's angular deflection would be equal to the remaining deflections. Therefore, upon turning it will arise lateral sliding between the wheels.
British patent application No. 2,116,131 deals with a steerable platform for a lawn mower. In this known device, the vertical shaft of each wheel is provided with pulley. The pulleys are motion-transmittingly interconnected by means of a belt driven by means of an outer, driven pulley. The pulleys have the same size and will, thus, not be usable for a is set of wheels comprising two steerable front wheels and at least one steerable intermediate wheel, spaced from the front wheels in the longitudinal direction of the vehicle and, possibly, a pair of rear wheels without turnability.
British patent application No. 2,155,870 which is intended to be used for fork truck or harvesting vehicle for agricultural purposes, deals with two different mechanisms for the provision of differing rotational movement for two wheels of a pair, each wheel's vertical shaft being provided with a noncircular, rounded body which is comma-shaped or consists of two rounded bodies consisting of upright cones, the one with the smallest base lowermost, and the other in an opposite position. Both the comma mechanism and
Andrus Sceales Starke & Sawall LLP
Draper Deanna
Johnson Brian L.
LandOfFree
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