Land vehicles – Wheeled – Articulated vehicle
Reexamination Certificate
1999-01-22
2001-10-30
Boehler, Anne Marie (Department: 3618)
Land vehicles
Wheeled
Articulated vehicle
C280S426000, C280S442000, C280S098000
Reexamination Certificate
active
06308976
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to multiple axle trailers and in particular to automatic steering mechanism for such trailers.
BACKGROUND TO THE INVENTION
It is known that to reduce tire and road wear, it is advantageous to provide steering mechanisms for multiple axle trailers. One example of such a mechanism is shown in U.S. Pat. No. 5,207,443. This is an example of a true four wheel steering mechanism in which each of four wheels on the trailer is independently steerable (i.e. pivotable relative to its associated axle) and which therefore allows optimum steering geometry to be selected. Other more primitive mechanisms exist, in which the wheels on only one axle are independently steerable, but these systems whilst offering a reduced turning circle still suffer from tire wear on the wheels which are not independently steerable and consequently give rise to road damage.
The mechanism disclosed in U.S. Pat. No. 5,207,443 steers the wheels using a linkage mechanism for each pair of wheels, operated by relative movement of a sub-chassis on which the wheels are mounted and a draw bar which is articulated to a tractor unit. As the tractor unit rounds a corner, the draw bar follows it, but the sub-chassis initially does not. Thus, the draw bar moves relative to the sub-chassis, activating the steering allowing the trailer to follow the tractor unit. This mechanism, although highly satisfactory in achieving four wheel steering, is somewhat complicated. This stems from the need to be able to reverse the direction in which the trailer wheels steer depending upon whether the trailer is being drawn or backed up by a tractor unit. To achieve this, a hydraulically activated device is used for each linkage mechanism, i.e. for each pair of steerable wheels.
The present invention is designed to address the problems outlined above and to provide a simplified reversible steering mechanism for a trailer having four independently steerable wheels.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides a trailer comprising:
a main chassis adapted to be articulated to a tractor unit;
a sub-chassis relative to which the main chassis may rotate about a substantially vertical axis and including a laterally spaced pair of forward steerable wheels and a laterally spaced pair of rear steerable wheel, each such wheel being pivotable relative to the sub-chassis about a respective substantially vertical axis; and
a linkage mechanism coupling each of the steerable wheels to a steering mounting on the main chassis such that rotation of the main chassis relative to the sub-chassis causes the wheels to pivot about their respective axes and including at least one primary link coupled at one end to the steering mounting;
the steering mounting being movable relative to the main chassis between a first position and a second position such that the line of action joining the two ends of each primary link crosses the axis about which the main chassis rotates relative to the sub-chassis.
As will become clear from the later description, the present invention allow the direction in which each of the steerable wheel pivots in response to movement of the main chassis relative to the sub-chassis to be reversed in one movement of the steering mounting. For example, when the steering mounting is in its first position, the line of action of any one primary link lies to one side of the axis about which the main chassis rotates relative to the sub-chassis. Thus, rotation of the main chassis relative to the sub-chassis will either push or pull on the primary link.
However, when the steering mounting is moved to its second position, the line of action of the primary link crosses the axis about which the main chassis rotates relative to the sub-chassis so as to lie on the other side. Thus, any rotation of the main chassis which, before the steering mounting was moved, pushed on the primary link, now pulls on the primary link. This is because the motion which the end of the primary link coupled to the steering mounting undergoes relative to the sub-chassis, when resolved along the line of action of the primary link, is opposite to that which it underwent before the steering housing was moved. Similarly, any rotation of the main chassis which, before the steering mounting was moved, pulled on the primary link, now pushes on the primary link. Thus, the direction of steering of each of the four wheels is reversed.
The path taken by the trailer will of course depend on the geometry of the steering mechanism. However, it will be understood that all four wheels are actively brought into the optimum position for following the towing vehicle when the trailer is drawn, or leading it when it is backing up.
The trailer according to the invention may make use of standard steering and suspension components. Thus, each such steerable wheel may rotate on a stub axle assembly adapted to pivot relative to the sub-chassis, e.g. on a king pin carried by the sub-chassis.
Each of the steerable wheels may be associated with a steering arm which pivots with the wheel (e.g. a steering arm on its corresponding stub axle assembly), with the steering arms of each pair of wheels or stub axle assemblies being linked by a track rod. Thus, conventional technology may be used to seat and adjust the steering geometry.
There are a number of ways in which the steering mounting may be coupled, via the primary link or links to the steerable wheels. For example, at least one primary link may couple the steering mounting directly to a steering arm of a respective pair of wheels or stub axle assemblies. This steering arm may the same as that to which the track rod attaches or may be a supplementary steering arm.
Alternatively, at least one primary link may couple the steering mounting directly to an intermediate coupling of a respective pair of wheels or stub axle assemblies, with the track rod of that pair of wheels or stub axle assemblies being in two parts, each part connecting a respective steering arm to the intermediate coupling. The intermediate coupling may be a bell crank mounted on the sub-chassis at a pivot point, with the lines of action of the primary link and of the track rod parts offset from the pivot point.
The linkage mechanism may include one primary link and a secondary link coupling a steering arm or the intermediate coupling of the pair of wheels or stub axle assemblies to which the primary link is coupled to a steering arm or intermediate coupling of the other pair of wheels or stub axle assemblies. Alternatively, the linkage mechanism may include a primary link for each pair of wheels or stub axle assemblies.
The movement of the steering mounting between its first and second positions may be in a vertical plane or a horizontal plane. Substantially horizontal movement may be provided by a steering mounting comprising a swinging arm suspended from and securely fixed to the main chassis, each primary link being coupled to the swinging arm. For example, the steering mounting may comprise two swinging arms suspended from the main chassis, joined at their free ends by a horizontal tie to form a parallelogram, each primary link being coupled directly to the horizontal tie. In either case, for maximum effect with minimum movement, the movement of the steering mounting is preferably substantially perpendicular to the line of action of each primary link.
Alternatively, the movement of the steering mounting may be in a horizontal plane. e.g. rotary movement. For example, the steering mounting may comprise a crank mounted on the main chassis at a pivot point and to which each primary link is directly coupled.
Use of the single, common steering mounting allows its movement to be controlled by just a single telescopic ram, hydraulic or pneumatic.
To spread the load of the chassis and any superstructure and payload, it is preferred that the main chassis and the sub-chassis have cooperating arcuate bearing surfaces which permit their relative rotation. These arcuate bearing surfaces may, for example be comprised in two halves of a tur
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