Automatically cross-guided vehicle, especially for the public local passenger traffic

A steerable vehicle adapted to be driven on roads, especially for the public local passenger traffic, which has a steerable axle with deflectable wheels and at least one axle with wheels immovable relative to the axle which is pivotally secured at the vehicle in a bogey-like manner, and with cross-guide rollers mounted on both sides of the vehicle within the area of the vehicle axles and carried at least indirectly by the respective axle bodies. The pivotal axle is elastically centered in a straight driving position, out of which it is pivotal by the steering forces produced by the cross-guide rollers against the force of centering springs, whereby the centering springs and the prestress are chosen so strong that brake force differences of one vehicle side compared to the other side do not effect an automatic axle deflection.

The present invention relates to an automatically cross-guided vehicle, 
especially for the public local passenger traffic, which includes a 
steerable axle with deflectable wheels and with at least one axle having 
wheels immovable relative to the axle which is pivotally secured at the 
vehicle in a bogey-like manner, and with cross-guide rollers mounted on 
both sides of the vehicle within the area of the vehicle axles and carried 
at least indirectly by the respective axle bodies. 
With cross-guided vehicles, which are positively guided on a track by means 
of lateral cross-guide rollers between cross-guide webs of the road, it is 
necessary that the rear axle is able to adjust itself during curve drives 
at least approximately radially to the curve predetermined by the 
cross-guide webs for purposes of avoiding or at least reducing an 
excessive tire wear. Prior proposals of the assignee of the present 
application provided in that connection that the axle for a 
non-track-guided drive of the vehicle on normal roads is form-lockingly 
locked in an exact cross-position and in that this locking action is 
lifted for a track-tied drive between cross-guide webs. Such a 
form-locking locking system is not only relatively costly from a 
constructive and manufacturing point of view but also requires a certain 
length of time for the engagement of the locking system. It is thereby 
necessary that at first the exact cross-position of the axle is 
established. If one desires to undertake this locking action during the 
drive, then a certain drive without cross guidance and without mechanical 
locking of the rear axle in its cross-position is unavoidable. 
It is the aim of the present invention to simplify the constructive and 
manufacturing expenditures for such a locking system as well as to shorten 
timewise and to simplify also the transition from a track-tied drive to a 
track-non-tied-drive and vice-versa. 
The underlying problems are solved according to the present invention in 
that the pivotal axle is elastically centered in a straight driving 
direction, out of which it is pivotal by the steering forces produced by 
the cross-guide rollers against the force of the centering springs, 
whereby the centering springs and the prestress thereof are selected so 
strong that brake force differences of one vehicle side with respect to 
the other side cannot effect an automatic axle pivoting. 
Owing to the elastic centering of the axle which is nonsteerable as such, 
in the straight driving direction, a mechanical locking of the axle can be 
dispensed with. Nonetheless, by reason of a correspondingly hard selection 
of the springs, a sufficiently accurate straight guidance of the axle is 
assured in case of a track non-tied drive, i.e., when driving in the 
customary manner on normal roads. 
The pivotability of the axle can be brought about by a pair of triangular 
guide members engaging in the pivot center on the side of the axle, which 
preferably engage centrally at a relatively high point of the axle body. 
The centering springs may engage at a relatively low point of the axle body 
in the manner of longitudinal guide members and may take over the function 
of longitudinal guide members which maintain the cross-position of the 
axle as well as absorb the braking and acceleration moments which act on 
the axle. The centering springs may be prestressed more strongly during 
the braking and/or during the acceleration than normally, as a result of 
which they are able to better assume the task of the axle support against 
braking and acceleration moments. 
Undoubtedly, the pivoting of the axle with respect to the vehicle body will 
be connected with certain friction moments which oppose a rapid and exact 
return of the rear axle into the cross-position. A certain return 
hysteresis might result therefrom. In order to preclude such a hysteresis, 
the centering springs may be equipped with a constraint in such a manner 
that with oppositely acting springs, only one of the oppositely operating 
springs is always effective during a deflection and the two mutually 
oppositely operating springs just contact one another only in an exact 
cross-position. 
The centering springs may also be formed by several coaxial nested coil 
springs or by air-spring-bellows. Instead of such spring elements 
extending in the vehicle longitudinal direction, also a packet of leaf 
springs extending transversely to the vehicle longitudinal direction may 
be provided. 
Accordingly, it is an object of the present invention to provide an 
automatically cross-guided vehicle, especially for the public local 
passenger traffic which avoids by simple means the aforementioned 
shortcomings and drawbacks encountered in the prior art. 
Another object of the present invention resides in an automatically 
cross-guided vehicle, especially for the public local passenger traffic, 
which is simple in construction and relatively low in manufacturing costs. 
A further object of the present invention resides in an automatically 
cross-guided vehicle of the type described above which greatly increases 
the safety of the vehicle, especially when passing from a track-tied drive 
to a track-non-tied-drive and vice-versa. 
A still further object of the present invention resides in an automatically 
cross-guided vehicle which eliminates a certain time lapse previously 
required for engaging the locking mechanism of the rear axle when passing 
from a track-tied drive to a normal road traffic. 
Another object of the present invention resides in an automatically 
cross-guided vehicle, especially for the public local passenger traffic, 
which completely dispenses with the need of a mechanical locking mechanism 
for the axle.

Referring now to the drawing wherein like reference numerals are used 
throughout the various views to designate like parts, the illustrated 
vehicle generally designated by reference numeral 1 includes a front axle 
generally designated by reference numeral 2 which is steerable as such and 
includes deflectable or steerable wheels 3, and a rear axle generally 
designated by reference numeral 4 which is non-steerable and includes 
wheels 5 immovable relative to the rear axle body. One cross guide roller 
6 is provided on each vehicle side within the area of the front axle 2, 
which is at least indirectly rigidly connected with the axle body 7 of the 
front axle 2 and which are track-determinative for the front part of the 
vehicle within the area of track guidances on both sides--the cross guide 
webs 8 mounted along the sides of the road serve for this purpose. The 
front cross-guide rollers 6 may be combined with the vehicle steering 
system. In addition to the front cross-guide rollers 6, switch guide 
rollers 9 adapted to be alternately extended are provided which extend 
over a switch guide web and take over in an auxiliary manner the 
cross-guidance function of the mutually oppositely disposed, temporarily 
non-actuated rollers 6. 
Two cross-guide rollers 10 are provided on each vehicle side within the 
area of the bogey-like movable rear axle 4, which are supported in front, 
respectively, to the rear of the wheels 5 on fork-shaped support arms 11 
and are rigidly coupled to the rear axle body 12. The pairwise roller 
arrangement for each vehicle side within the area of the rear axle makes 
it possible to exert directional moments on the rotary axle 4 by way of 
the cross-guide rollers 10 and to deflect the rear axle 4 in the sense of 
a track-true rolling-off along the mechanically predetermined track. An 
unnecessary width requirement of the vehicle is avoided thereby since with 
an immovable rear axle the vehicle has the tendency within the area of the 
rear axle to deflect toward the inside of the curve. As to the rest, an 
unnecessary tire wear on the rear wheels is avoided by the pivotability. 
The pivot center 12a of the rear axle body 12 is predetermined by a pair 
of triangular guide members 13 (FIGS. 2 and 3) engaging centrally at the 
axle body 12. The point of engagement of this pair of triangular guide 
members 13 at the axle body 12 is located relatively high. Four centering 
springs 14 to 17 extending in the longitudinal direction engage at 
relatively low points of engagement, which are arranged pairwise coaxially 
disposed one behind the other and which take over the function of 
longitudinal guide members and additionally have the task to support the 
rear axle body against braking and accelerating moments. On the side of 
the frame, these centering springs 14 to 17 are supported by way of spring 
abutments 21 (FIG. 3). The springs 14-17 are constructed so hard and 
prestressed so strongly that brake force differences on one vehicle side 
with respect to the other side do not lead to an automatic inclined 
running of the rear axle with a trake-non-tied drive. In order to be able 
to utilize still better this elastic centering effect also during stronger 
braking actions, provision is made that the centering springs are still 
more strongly prestressed during braking actions. For that purpose, the 
spring abutments 21 are coupled to eccentric shafts 22 (FIG. 3) which can 
be pivoted or rotated by way of levers 23. The pivoting of the shafts 22 
can be controlled by the brake-actuating installation 19 which also acts 
upon the brakes 18 of the rear axle and which, in its turn, is controlled 
by the brake pedal 20. In lieu of an eccentric shaft, the levers 23 may 
also be equipped with eccentric bushes which during pivoting effect a 
cross displacement of the shaft and of the spring abutments. The spring 
abutment as the frame should thereby be so constructed (preferably 
tiltable or pivotal) that the lateral inclined deflection of the springs 
14 to 17 which results from a spring inward movement of the axle relative 
to the frame, can be absorbed by these springs without transversely 
loading or stressing the same. 
The centering springs 14-17 may be formed, as shown in FIG. 4, by at least 
two coaxially nested coil springs 14, 14', 15, 15', etc. Additionally, 
unlaterally effective restraint means such as, for example, a tie rod 24, 
may be provided for preventing a spring expansion of each of the centering 
springs 14-17 so as to limit the spring length to an expansion condition 
corresponding to the normal position of the pivotal axle 4. 
As shown in FIGS. 5 and 6, the centering springs may be formed by at least 
one set of leaf springs 25 disposed parallel to the pivotal axle 4 and 
connected centrally of the frame or be constructed as spring bellows 26. 
While I have shown and described several embodiments in accordance with the 
present invention, it is understood that the same is not limited thereto 
but is susceptible of numerous changes and modifications as known to those 
skilled in the art, and I therefore do not wish to be limited to the 
details shown and described herein but intend to cover all such changes 
and modifications as are encompassed by the scope of the appended claims.