Motor vehicles – Steering gear – Each wheel steerable
Patent
1994-07-14
1996-07-09
Boehler, Anne Marie
Motor vehicles
Steering gear
Each wheel steerable
180410, 180405, B62D 506
Patent
active
055335845
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a vehicle comprising front and rear steering mechanisms and a steering control system having a first mode in which both steering mechanisms operate and a second mode in which only one of the steering mechanisms operates. The invention is applicable primarily, but not exclusively, to wheeled vehicles, e.g. telescopic material handlers, fork lifters, off-road vehicles, etc.
A vehicle is known having steerable front wheels and optionally steerable rear wheels. The driver turns the steering wheel in the cab to align the rear wheels in the straight-ahead position before changing from four-wheel steering (compound steering) to two-wheel (front-wheel) steering (simple steering). This is a difficult operation, particularly if the rear wheels are not visible from the driver's normal position in the cab.
The present invention relates to an arrangement such that, when switching means is operated to switch the steering control system from the first mode to the second mode, the change to the second mode is prevented unless and until the other steering mechanism (which does not operate in the second mode) is in its straight-ahead condition or state. In other words, after operating the switching means, the driver only has to turn his steering wheel (or other steering device) through the straight-ahead position in order to cause the change to the second mode to occur automatically, leaving the said other steering mechanism in the straight-ahead condition.
Such an arrangement is described in GB-A-2 208 282, which discloses a materials handling vehicle having two pairs of wheels movable to effect steering of the vehicle, at least one pair of wheels being lockable in a position so that steering is effected solely by the other pair of wheels, wherein sensor means are provided associated with each of the two pairs of wheels to provide an electrical signal to a control means when the respective wheels are in an aligned position in which their axes of rotation are perpendicular to a longitudinal axis of the vehicle, the control means including a selector means comprising electrical switch means to enable an operator to select simple steering mode in which only one of the pairs of wheels are movable to effect steering, or a compound steering mode in which both of the pairs of wheels are movable to effect steering, the control means further comprising means to maintain the selected steering mode until an alternative steering mode is selected by operation of the selector means and the control means receives a signal from at least one of the sensor means associated with one of the pairs of wheels. In that vehicle, each of the front and rear steering mechanisms has its own alignment sensor which is permanently activated so long as the vehicle is in operation.
The present invention provides a vehicle comprising a front steering mechanism and a rear steering mechanism, each steering mechanism having an operating range including a straight-ahead condition, a steering control system operatively connected to the front and rear steering mechanisms, the control system having a first mode in which both steering mechanisms operate and a second mode in which only one of the steering mechanisms operates, and first switching means for switching the control system from one mode to the other, the arrangement being such that, when the switching means is operated to switch from the first mode to the second mode, the change to the second mode is prevented unless and until the other steering mechanism is in its straight-ahead condition.
The vehicle includes alignment sensing means for sensing whether the other steering mechanism is in its straight-ahead condition, and second switching means switchable between a first state for preventing the change from the first mode to the second mode and a second state for permitting the said change, the alignment sensing means being operatively connected to the second switching means so that, when the first-mentioned switching means is operated to switch the control system from the first
REFERENCES:
patent: 3813936 (1975-10-01), Thomas
patent: 4982799 (1991-01-01), Fujimoto et al.
patent: 4995472 (1991-02-01), Hayashi et al.
patent: 5076382 (1991-12-01), Vaughn et al.
Boehler Anne Marie
Caterpillar Inc.
White Claude F.
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