Method of controlling a transport means and a transport means

A method of controlling a transport means (1) comprising a body (2) and wheels (3a to 3h) attached to the body (2) on both sides of its central line one after another in the longitudinal direction of the body, all the wheels (3a to 3h) being arranged to turn about vertical axes (4a to 4h) of turning to change the direction of travel of the transport means (1) so that rotation axes (11a to 11h) for all the wheels (3a to 3h) intersect substantially at the same vertical axis of turning (9) so that the position of the axis of turning in the longitudinal direction of the transport means (1) is shifted in proportion to the magnitude of the an angle of turning (.alpha.); and a transport means (1). To avoid an unexpected obstacle (10) the turning of the wheels (3a to 3h) is deviated from their normal path by shifting the axis of turning (9) in the longitudinal direction of the transport means (1) towards its forward end, so that the rear end moves with a larger curved movement than usually. When the driving conditions are normalized, the axis (9) of turning is returned to its normal position.

This invention relates to a method of controlling a transport means 
comprising a body and wheels attached to the body on both sides of its 
central line one after another in the longitudinal direction of the body, 
all the wheels being turned about vertical axes of turning at an angle to 
the longitudinal direction of the body to change the direction of travel 
of the transport means in such a way that rotation axes for all the wheels 
intersect substantially at the same vertical axis of turning, whereby the 
transport means turns about the axis of turning when it moves, and when 
the angle of turning of the transport means at least exceeds a 
predetermined value, the wheels are turned with respect to each other in 
such a way that the position of the axis of turning in the longitudinal 
direction of the transport means shifts in proportion to the magnitude of 
the angle of turning. 
The invention is also concerned with a transport means comprising a body; 
wheels attached to the body on both sides of its central line one after 
another in the longitudinal direction of the body, the wheels being 
arranged to turn about vertical axes of turning to change the direction of 
travel of the transport means; power means for turning the wheels; and 
control means comprising an adjusting device for controlling the power 
means in such a way that when the direction of travel is changed, rotation 
axes for the wheels intersect substantially at the same vertical axis of 
turning; and a control sensor detecting the angle of turning of the 
transport means, the sensor being arranged to control the adjusting device 
so that it controls the power means in such a way that at least when the 
angle of turning exceeds a predetermined value, the position of the axis 
of turning in the longitudinal direction of the transport means is shifted 
in proportion to the angle of turning. 
Heavy objects, such as containers and work machines are usually transported 
by means of trailers or vehicles provided with several wheels and shafts 
comprising several wheels. Wheels in such trailers are usually mounted in 
one end while the other end comprises coupling means by which the trailer 
is turnably coupled to a tractor. When transferring a load, the tractor 
draws or pushes the trailer, depending on the conditions, and the driver 
controls the movement of the trailer by turning the tractor in a suitable 
direction with respect to the trailer. There are prior art solutions in 
which the wheel assembly or a portion of it can in some way be turned with 
respect to the trailer in proportion to the angle of turning of the 
tractor, in order to improve the turnability and ease of movement of the 
vehicle. 
German Offenlegungsschrift 22 00 739 discloses a solution in which some of 
the wheels are turned in proportion to the angle of turning of the tractor 
in such a way that the axes of turning of all the wheels supporting the 
trailer intersect at the same centre of turning. In this publication the 
location of the centre of turning is constant in the longitudinal 
direction of the trailer. Correspondingly, the ratio of the angle of 
turning of the wheels to the angle of turning of the tractor is also 
constant. This causes problems with the handling of the trailer when the 
driving conditions or the path deviates for some reason from the 
originally designed, as a result of which it may be necessary to move the 
trailer back and forth to get it into the desired position. 
U.S. Pat. No. 3,733,084, in turn, discloses a solution in which the wheels 
of the trailer are able to turn relative to the trailer and the driver can 
position the wheels in parallel with each other at an angle to the trailer 
so that the trailer need not always be moved along a curved path. In the 
publication the position of the wheels is in no way dependent on the angle 
of turning of the tractor, being in most cases in no proportion to it. As 
the wheels are always positioned in parallel with each other when deviated 
as described above, no more than one wheel pair is able to turn about a 
turning point coinciding with the axis of turning of the tractor, whereas 
the other wheel pairs have to move in the transverse direction, being 
dragged along the surface of the road, which wears down the tires and 
strains the trailer. 
The object of the present invention is to provide a method of controlling a 
transport means in such a way that the axes of turning of all wheels, 
irrespective of the direction of travel and angle of turning of the 
equipment, always intersect at the same axis of turning, whereby all the 
wheels move along a curved path, which reduces the wear of the tires as 
well as the strains exerted on the equipment. This is achieved according 
to the invention by turning the wheels in such a way that the axis of 
turning moves along a predetermined curve relative to the body of the 
transport means. 
The basic idea of the invention is to control the wheels in such a way that 
they follow the turning movement of the tractor so that the axes of all 
the wheels always intersect at the same turning point and that when the 
driving conditions change, the control is, if necessary, modified in such 
a way that the turning point is shifted during normal drive towards the 
rear of the equipment so that the angle of turning is increased or, to 
avoid an unexpected obstacle, still further backwards or alternatively 
forwards, depending on the location of the obstacle to be avoided. The 
turning of the trailer end remote from the tractor is thereby controlled 
so that the obstacle can be avoided and the trailer can be positioned in 
the desired driving direction easily by a simple control movement. 
A further object of the invention is to provide a transport means in which 
all wheels can always be positioned so that their axes intersect at the 
same turning point, the location of which can be altered according to 
driving conditions to cause the trailer end remote from the tractor to 
move along a desired path. This is achieved according to the invention by 
means of a transport means in which the control means comprise an 
adjusting device which controls the turning of the wheels in such a way 
that the axis of turning moves along a predetermined curve with respect to 
the body of the transport means when the angle of turning changes. 
The basic idea of the transport means of the invention is that the angles 
of turning of the wheels of the trailer and, as a consequence, the path of 
the trailer, can be adjusted by means of the adjusting device comprised in 
the control means, e.g., to avoid an unexpected obstacle, so that the path 
deviates from the normal curved path while the axes of the wheels 
nevertheless always intersect at the same turning point as the axis of 
turning of the trailer when the trailer is turned relative to the ground. 
An advantage of the equipment of the invention is that it is easy to 
control in different situations and its wheels always move by rolling 
along the ground instead of being dragged, which involves a considerable 
reduction in wear as compared with prior art solutions.

FIG. 1 shows a trailer 1 comprising a body 2 and wheel pairs 3a to 3h at 
the rear end of the body. The wheel pairs are turnable about vertical axes 
4a to 4h. The other end of the body 2 is provided with a joint 5 by means 
of which a tractor 6 is coupled to the trailer 1 and about which the 
tractor 6 can be turned. The joint 5 is provided with a sensor 7 which 
detects the angle of turning .alpha. of the tractor 6 relative to the 
longitudinal axis of the body 2. The sensor 7 is connected to control 
means (not shown) which control the wheel pairs 3a to 3h on the basis of 
the angle of turning .alpha. detected by the sensor in such a way that 
rotation axes 11a to 11h for all the wheel pairs intersect at the same 
point. In normal drive, the position of the axis of turning 9 shifts in 
accordance with the turning angle .alpha. along a curve A so that the 
larger the angle .alpha. the farther back in the longitudinal direction 
of the body 2 the axis of turning 9 is positioned. The radius of turning 
of the joint 5 thereby shifts from a line S1 to a line S2. To control the 
transport means, it is also possible to select a curve A' which extends in 
a different way. The axis of turning 9' thereby shifts along the curve A' 
in accordance with the angle .alpha. and the turning radius of the joint 5 
shifts, e.g., from a line S'1 to a line S'2. Several such curves can be 
drawn, whereby one of them normally acts as a control curve. It is, of 
course, obvious that the same curves can be used on equal terms when 
turning in the opposite direction. 
If the path of the transport means has not been chosen properly for some 
reason, or an unexpected obstacle is observed in the path of the transport 
means, the turning of the transport means 1 is controlled in another way. 
In FIG. 2, the rear end of the trailer 1 would hit an obstacle 10 unless 
the position of the point of turning 9 is shifted closer to the tractor 6 
as compared with normal drive, so that it moves according to the curve A'. 
As compared with normal drive, the curved movement of the rear end of the 
trailer 1 is thereby larger so that the rear end is at a greater distance 
from the obstacle 10. This is illustrated in FIG. 2 with curves La, Lg and 
L'a and L'g indicating the curved movement of the wheels 3a and 3g, 
respectively. With normal movement along the curve A, the wheels 3a to 3h 
move along the curves La and Lg. When the axis of turning 9 is changed 
into the axis of turning 9' extending in accordance with the control curve 
A', the turning radius of the joint 5 changing by the length .DELTA. S, 
the wheels 3a and 3g turn so that they start to follow the curves L'a and 
L'g. Correspondingly, the other wheels are displaced so that they move 
along curves the axes of turning of which coincide with the axis 9' on the 
curve A'. 
After the transport means has been displaced relative to the obstacle 10 so 
that it is able to pass by it, the control of the wheels 3a to 3h is 
released and the normal control is restored, so that the wheels turn into 
a position originally proportional to the angle of turning .alpha. of the 
tractor and the axis of turning coincides with the axis 9 in accordance 
with the position proportional to said angle of turning on the curve A and 
in the longitudinal direction of the trailer at a corresponding point. 
The method of the invention can be applied in transport means in various 
ways. Normally, the axis of turning can be shifted along one predetermined 
curve relative to the body of the transport means. If need be, however, 
the wheels can be arranged to turn by means of the additional control 
member either in proportion to the additional control or always to a 
predetermined extent when the additional control is applied, so that the 
axis of turning is shifted from its position according to the normal 
control over a distance forwards in the longitudinal direction of the 
trailer. Further, the control can be realized by providing several 
different control curves for the control of the axis of turning, one of 
which is selected for normal control so that the axis of turning normally 
moves relative to the trailer along said curve but can, if need be, be 
arranged to follow one of the other control curves. Correspondingly, the 
control can be realized so that the axis of turning normally follows a 
predetermined curve the shape of which can be altered continuously by the 
additional control when the driving conditions are changed. The control 
can further be realized in such a way that the normal control will be 
restored automatically after the deviation control is no longer needed.