EP0689981A1

EP0689981A1 - Running gear for low-floor rail vehicles

Info

Publication number: EP0689981A1
Application number: EP94830526A
Authority: EP
Inventors: Enrico Valfre'; Paolo Giraudo; Alberto Magnino; Roberto Lovaldi; Alberto Magnani
Original assignee: Fiat Ferroviaria SpA
Current assignee: Fiat Ferroviaria SpA
Priority date: 1994-06-30
Filing date: 1994-11-04
Publication date: 1996-01-03
Also published as: IT1268087B1; ITTO940537A0; ITTO940537A1

Abstract

A running gear for low-floor (4) rail vehicles comprising at least two bodies (1, 2) each having two independent steering respectively outer and inner axles (5, 6), and a tow bar (3) pivotally interconnecting the two bodies (1, 2). Drive means (14, 15) are provided for operating curve-steering of the inner axle (5) of each body (1, 2) through the relative angular displacement between the tow bar (3) and the bodies (1, 2), and as a function of such angular displacement. Transmission means (19) transmit opposite steering from the inner axles (5) to the outer axles (6) of the two bodies (1, 2).
The drive means may include two trapezoid-linkage mechanisms (14, 15) or a flying lever mechanism (28), and the vehicle may comprise three or more bodies.

Description

The present invention is related to running gears for rail vehicles, and more particularly for tramway vehicles.
The present manufacture trend in the field of tramway vehicles is directed towards an entirely lowered floor or platform, for a better convenience of passenger getting on and off. In order to achieve this object it is practically necessary to employ different bogies than the traditional ones, for instance provided with independently steering axles. Steering axles solve to a relevant extent the problem of the curve wheel-rail wear, since these axles can be radially adjusted following the curve radius of the track.
Axle steering is performed in some cases spontaneously, but more frequently it is driven by means of suitable mechanical systems, to the aim of ensuring the necessary intrinsic safety and also to warrant that the wheel set assembly be statically determined and, therefore, be not negatively affected by any track imperfections.
The invention is thus more particularly related to a running gear for low-floor rail vehicles, comprising at least two bodies having each two independent respectively outer and inner steering axles, with respect to the vehicle configuration, including respective axle structures rotatably connected to the body around respective central vertical axis and each carrying a wheel pair, a tow bar pivotally interconnecting at its ends the two bodies, and drive means for operating curve steering of the axles of the two bodies.
A running gear of the above-referenced type is known for instance from US-A-5,277,127, according to which the axle steering angle is transmitted from one body to the adjacent body via a longitudinal steering rod, a toggle lever centrally articulated on the inner axle bridge, a connecting rod and an extension present on one side of the wheel bridge. Steering is transmitted to the outer axles via a pair of longitudinal drawbars lying on opposite sides of the longitudinal center line of the vehicle and connected to each other with a connecting rod, or by an oblique connecting rod, or still by means of a swing lever supported on one side of the body central area and connected, via two connecting rods, to corresponding articulation points of the two axle frames.
As far as steering of the inner axles of the two bodies is concerned, the presently known systems are not adapted to enable achievement of low curve-radiality errors of the axles, particularly in the case of tramway vehicles having two bodies and, therefore, with only two available reference signals.
The object of the present invention is to provide a running gear for low-floor rail vehicles of the above-referenced type, which enables to combine high efficiency and relative simplicity, so as to obtain the lowest possible curve-radiality error of the axles, particularly in the case of a two-body tramway.
According to the invention, this object is achieved by virtue of a running gear of the type set forth at the beginning, essentially characterized in that said drive means operate steering of the axles of each body through the relative angular displacement between the tow bar and the bodies, and as a function of the rotation between said tow bar and the respective body.
The steering system according to the present invention originates from an analytical study of the running gear geometry, so as to obtain a steering law upon which the rotation of the inner axles is driven - and transmitted to the outer axles - following a unique linear relationship, independent from the curve radius, which shall be disclosed in detail herebelow. Following simple geometrical evaluations, the system may be simplified so as to reduce it to a single lever which transmits to the inner axles the rotation of the tow bar, and a simple rotation reversing member then transmits the same amount of angle of rotation to the vehicle outer axles.
The same system can be applied to three-body rail vehicles, suppressing the reversing member as far as the axles of the central body are concerned, and directly delivering the steering signal from the closer tow bar of the central body, so as to achieve extremely reduced radiality errors during curve entry and exit.
The same system may also be applied to tramway vehicles having a plurality of intermediate bodies, wherein only the two end bodies are equipped with the rotation reversing member between the respective axles, while the axles of the intermediate bodies receive the steering drive from the respective closest tow bars.
According to a preferred constructive embodiment of the invention, said drive means comprise two substantially coplanar trapezoid-linkage mechanisms interconnecting, on opposite sides, the tow bar and the inner axles of the two bodies and each of which includes;

a first angled lever arm rigidly connected at one end thereof to the corresponding articulated end of the tow bar to the respective body,
a second angled lever arm having a greater length than the first lever arm and rigidly connected at one end to the axle structure in a spaced relationship from the respective vertical rotation central axis thereof,
an oblique bar pivotally connected to the free ends of said first and second lever arms,
and wherein the ratio between the length of the first and second lever arms is equal to a predetermined value.

The invention contemplates alternative embodiments in connection with said drive means, among which a solution employing a flying lever mechanism applied to the ends of the tow bar.
The running gear according to the invention affords, in comparison to similar known solutions, the following advantages:

achievement of a perfect radiality of the axles when running along a curve, independently of the radius of the curve itself;
minimization of the maximum radiality error of the axles upon curve entry and exit phases;
remarkable efficiency and simplicity of the steering system;
complete bi-directionality, in the sense that the steering system identically operates in both advancement directions of the vehicle.

The invention will now be disclosed in detail with reference to the annexed drawings, purely provided by way of non limiting example, in which:

figure 1 is a partial and simplified perspective view of a low-floor two-body tramway vehicle provided with a running gear according to the invention,
figure 2 is a simplified top plan view of figure 1,
figure 3 is a partial lateral elevational view in an enlarged scale according to arrow III of figure 1,
figure 4 is a geometrical diagram of figure 2,
figure 5 is a diagram similar to figure 4 of a first variant of the invention,
figure 6 is a partial geometrical diagram showing a second variant of figure 4,
figure 7 is a view similar to figure 4 showing a tramway vehicle having three bodies, and
figure 8 is a view similar to figure 7 of a tramway vehicle having a plurality of bodies.

The example shown in figures 1 through 3 is related to a tramway vehicle formed by two bodies generally designated as 1, 2 and interconnected by an intermediate tow bar 3.
Each body 1, 2 has a low floor 4 and two respectively inner and outer, with respect to the vehicle configuration, independent steering axles 5, 6. Assuming that in the advancing condition of the vehicle the body 1 is placed forwardly and the body 2 is placed rearwardly with respect to the travel direction, the outer axle 6 and the inner axle 5 of the body 1 shall be the front axle and the rear axle, respectively, while the inner axle 5 and the outer axle 6 of the body 2 shall be the front axle and the rear axle, respectively.
Each of the inner and outer axles 5, 6 comprises conventionally an axle support structure or bridge, diagrammatically shown as 7 and carrying a respective coaxial wheel pair 8.
Each support structure 7 is centrally connected rotatably to the respective body 1, 2 around a respective vertical axis, so as to enable curve steering of the corresponding axle 5, 6. In the case of the shown example each rotation vertical axis is defined by a respective journal 9 centrally carried by a rocker lever 10 the opposite ends of which are connected to the axle structure 7 through a pair of longitudinal arms 11. This arrangement is however to be considered as purely given by way of example.
The tow bar 3 is connected to the facing ends of the two bodies 1, 2 around respective central articulated joints 12, 13.
In order to perform steering of the axles 5, 6, the invention provides a mechanical drive system which, on one side, guarantees that the complex of the wheels 8 be statically determined, so as to afford intrinsic safety against negative effects deriving from any possible track imperfections, and on the other hand enables to obtain a perfect radial steering of the axles along full curve, independently of the radius of the curve itself. This steering system has been conceived starting from an analytical study of the running gear geometry, the explanation of which will now be given with reference to figure 4, showing the simplified geometrical diagram of the vehicle depicted in figures 1 through 3.
In the geometrical diagram of figure 4 the following references have been used:
A = trace of the vertical rotation axis 9 of the outer axle 6 relative to the body 1.
B = trace of the vertical rotation axis 9 of the inner axle 5 relative to the body 1.
C = trace of the articulated joint 12 between the tow bar 3 and the body 1.
D = trace of the articulated joint 13 between the tow bar 3 and the body 2.
E = trace of the vertical rotation axis 9 of the inner axle 5 relative to the body 2.
F = trace of the vertical rotation axis 9 of the outer axle 6 relative to the body 2.
In the same diagram the following dimensions are also indicated:
a = distance between the vertical rotation axis A, B of the axles 5, 6 of the body 1 and between the vertical rotation axis E, F of the axles 5, 6 of the body 2.
b = distance between the articulated joint C of the tow bar 3 and the vertical rotation axis B of the inner axle 5 of the body 1, and also distance between the articulated joint D of the tow bar 3 and the vertical rotation axis E of the inner axle 5 of the body 2.
c = length of the tow bar 3.
$\underset{̲}{d} = \underset{̲}{b} + \underset{̲}{c} + \underset{̲}{b} .$
Lengths a and b are same for both bodies 1, 2.
Further, the following angles are indicated in the geometrical diagram of figure 4.
δ_A, δ_F = steering angles of the outer axles 6 of the two bodies 1, 2, respectively, measured with reference to the longitudinal axis thereof.
δ_B, δ_E = steering angles of the inner axles 5 of the two bodies 1, 2, respectively, measured with reference to the longitudinal axis thereof.
σ₁, σ₂ = relative angles between the tow bar 3 and the two bodies 1, 2, respectively, with reference to the longitudinal axis thereof.
From the analytical study of the theoretical laws of the steering angles δ_A, δ_B, δ_E, δ_F of the axles 5, 6 as a function of the advancement of the vehicle along a curve, the constant steering angle to be maintained in full curve, i.e. when $σ_{1} {=σ}_{2} = σ$
is defined by the following expression: $δ_{A} {= -δ}_{B} {= δ}_{E} {= -δ}_{F} = arcsen (a/2R) ≅ a/2R$
wherein R is the curve radius.
The angle σ is as follows: $σ = arcsen (a/2R) + arcsen (d/2R) ≅ (a+d)/2R$
thus, independently of the curve radius R: $δ_{A} ≅ [a/(a+d)] σ (conditions of radiality in full curve).$
In view of the above relation, the idea upon which the invention is based consists of operating steering of the inner axles 5 of each body 1, 2 by means of the relative angular displacement between the tow bar 3 and the bodies 1, 2, and more particularly of causing these inner axles 5 to rotate proportionally to the corresponding rotation between the tow bar 3 and the respective bodies 1, 2, and then transmitting same but opposite rotation to the outer axles 6 of the two bodies.
The steering angle of the axles is thus expressed as a function of the rotation angle of the tow bar 3 by the following linear relations: $\begin{matrix} \begin{matrix} δ_{A} {= - δ}_{B} {=Mσ}_{1} {= [a/(a+d)]σ}_{1} \\ δ_{E} {= - δ}_{F} {=Mσ}_{2} {= [a/(a+d)]σ}_{2} \end{matrix} \end{matrix}$
Once having fixed the geometrical characteristics a and d, the preceding law satisfies radiality in full curve of the axles 5, 6 independently of the radius R of the curve.
It is then necessary providing a means to minimize the maximum radiality error of the axles 5, 6 during the entry and exit phases thereof relative to the curve. Once having fixed the values a and d (i.e. the distance between the inner axle 5 and the outer axle 6 of each body 1, 2 and the distance between the inner axles 5 of the two bodies 1, 2), a geometrical entity to act upon so as to minimize said maximum error for the four axles still subsists: it is the magnitude b, i.e. the distance between the ends of the tow bar 3 corresponding to the articulated joint C, D, and the vertical rotation axis B, E of the inner axle 5 of each body 1, 2.
Following a numerical simulation of entry into a curve having a radius R = 15 m, once having fixed a and d, one and only one value of b was identified which minimizes the maximum error for all four axles 5, 6. It has been found that the minimum error value which can be achieved is only function of a and d. If one or both these values are decreased, the error can be correspondingly reduced.
In order to operate steering of the inner axles 5 according to the above law $\begin{matrix} \begin{matrix} δ_{A} {= - δ}_{B} {=Mσ}_{1} {= [a/(a+d)]σ}_{1} \\ δ_{E} {= - δ}_{F} {=Mσ}_{2} {= [a/(a+d)]σ}_{2} \end{matrix} \end{matrix}$
i.e. a control which is proportional to the rotation between the tow bar 3 and each body 1, 2, the invention is providing, in the case of the embodiment shown in figures 1 through 4, two simple trapezoid-linkage mechanisms referenced as 14, 15 for the body 1 and for the body 2, respectively.
The two trapezoid- linkages 14, 15 are substantially coplanar to each other and are placed, in the case of the shown example, on opposite sides with respect to the longitudinal center line of the vehicle. However an arrangement (not shown in the drawings) is also contemplated, according to which the two trapezoid linkages are situated on the same side with respect to the longitudinal center line of the vehicle.
Specifically referring to the geometric diagram shown in figure 4, the trapezoid linkage 14 associated to the body 1 comprises a first angled lever arm 16 rigidly connected to the articulated end C of the tow bar 3, and a second angled lever arm 17 rigidly connected to the inner axle 5 of the body 1, at a distance from the respective vertical central rotation axis B, and having a greater length than the first lever arm 16.
The two lever arms 16, 17, which in the condition of straightward motion of the vehicle shown in the drawings are parallel to each other, are pivotally connected at the respective free ends G, H to an oblique bar 18.
The ratio between the length of the lever arm 16 (CG) and the length of the first lever arm 17 (BH) is such that $CG/BH = M = a/a+d$
In the condition of straightward travel shown in the drawings, the oblique bar 18 is arranged perpendicularly to the two lever arms 16, 17: this permits ensuring a kinematic behaviour which is most close to the linear one, so as to minimize the non-linearity errors due to the different lengths of the lever arms 16, 17.
The arrangement of the trapezoid linkage 15 associated to the body 2 is almost identical to that of the trapezoid linkage 14, but for the fact that the former is placed on the opposite side relative to the longitudinal vehicle axis. Thus the trapezoid linkage 15 also comprises a first lever arm 16 rigid with the articulated end D of the tow bar 3 to the body 2, a second lever arm 17 rigidly connected to the inner axle 5 of the body 2 at a distance from the respective central vertical rotation axis E, and an oblique bar 18 pivotally connected at I and L, respectively, to the free ends of the angled lever arms 16 and 17.
Even in this case the ratio between the length of the arm 16 (DI) and the length of the arm 17 (EL) is such that: $DI/EL = M = a/a+d$
Actually, in accordance with the structural arrangement shown in figures 1 through 3, the second angled lever arms 17 are not physically present, since the articulations H and L of the oblique bars 18 of the two trapezoid linkages 14, 15 are directly carried by the ends, opposite to each other, of the support structures 7 of the inner axle 5 of the body 1 and of the body 2, respectively. Therefore, the second lever arms 17, which are materially depicted in the geometrical diagram of figure 4, simply correspond to the distance between the articulations H, L and the central vertical rotation axis B, E of the two inner axles 5.
For operating steering of the outer axles 6 of the two bodies 1, 2, that as previously pointed out shall be of the same but opposite entity with respect to that of the inner axles 5, two oblique rods 19 are provided which interconnect, for each body 1, 2, respective points of the support structures 7 of the inner axle 5 and of the outer axle 6 placed on opposite sides with respect to the longitudinal axis of the vehicle. As shown in the structural arrangement of figures 1 through 3, each rod 19 is articulated respectively to one end 20 and to the opposite end 21 of the respective rocker levers 10 associated to the two axles 5, 6.
In operation, the two trapezoid linkages 14, 15 and the two oblique rods 19 operate and, respectively, transmit curve steering of the axles 5, 6 of the two bodies 1, 2 proportionally to the rotation between the tow bar 3 and these bodies 1, 2, according to the above specified linear relationship, which enables to achieve almost perfect radiality of the axles 5, 6 in full curve independently of the radius of the curve itself, while minimizing the maximum radiality error of the axles during the entry and exit phases relative to the curve.
As a matter of fact the above linear relationship $\begin{matrix} \begin{matrix} δ_{A} {= - δ}_{B} {=Mσ}_{1} {= [a/(a+d)]σ}_{1} \\ δ_{E} {= - δ}_{F} {=Mσ}_{2} {= [a/(a+d)]σ}_{2} \end{matrix} \end{matrix}$
Is a particular case of the following more general law: $\begin{matrix} \begin{matrix} δ_{A} {= - δ}_{B} {=Mσ}_{1} {+Nσ}_{2} \\ δ_{E} {= - δ}_{F} {=Mσ}_{2} {+Nσ}_{1} \end{matrix} \end{matrix}$
wherein the distance b is selected at will and the following relationship is anyhow valid: $M + N = a/a+d$
It is thus a matter of determining one or the other of the two variables M, N through a normal method of optimization of the resulting radiality errors.
The embodiment of the invention such as previously disclosed, simply employing the two trapezoid linkages 14, 15, accomplishes the particular condition wherein the length b is optimized so as to annul the coefficient N.
However, selecting different values of the length b, i.e. not annulling the coefficient N, the invention contemplates the possibility of carrying out a kinematic configuration such as shown in figure 5, or even of employing a so called "flying lever" mechanism such as diagrammatically depicted in figure 6.
The embodiment according to figure 5, wherein parts which are identical or similar to those disclosed with reference to figure 4 are designated by the same reference numerals, differs therefrom in that each trapezoid linkage 14, 15 further comprises a second oblique bar 22 pivotally interconnecting the articulation point G, or respectively I, between the first arm 16 and the oblique bar 18 of the respective trapezoid linkage 14, 15, with a third angled arm 23.
The third arm 23 associated to the trapezoid linkage 14 of the body 1 is connected to the other body 2 behind the articulation end D of the tow bar 3 to the body 2, while the third arm 23 associated to the trapezoid linkage 15 of the body 2 is connected to the body 1 in front of the corresponding articulation point C of the tow bar 3 to the body 1.
The "flying lever" mechanism is purely depicted in the form of a geometrical diagram in figure 6, in which only the tow bar 3 is shown with the articulation ends C and D thereof to the bodies 1 and 2 of the vehicle.
This mechanism comprises a first lever 24 and a second lever 25 of which the first one is articulated to the articulation end C of the tow bar 3 to the body 1, and the second one is articulated to the articulation end D of the tow bar 3 to the body 2, and these levers 24 and 25 are placed on opposite sides of the tow bar 3. The levers 24 and 25 are therefore freely rotatable and are connected to the inner axles 5 of the respective bodies 1, 2 via respective rigid square arms 26, 27, which in turn are connected to the inner axles 5 of the two bodies.
Reference numeral 28 designates a flying lever which is oriented generally transversely to the tow bar 3, and which is articulated at one end 29 thereof to a connecting rod 30 which is in turn articulated to the end 31 of the lever 25. A second connecting rod 32 pivotally connects the end 33 of the lever 24 with a point 35 of the flying lever 28 which is spaced apart from the opposite end 36 thereof. A third lever 37, also articulated in correspondence of the articulation end C of the tow bar 3 to the body 1, is pivotally connected at the end 38 thereof to the end 36 of the flying lever 28 via a third connecting rod 39.
In figure 6, a, b, c and d designate the length of the first lever 24, of the second lever 25, of the third lever 37 and of the flying lever 28, respectively.
In operation, the displacements of the points 28 and 35 due to rotations α and β of the levers 24 and 25 cause a rotation of the flying lever 28. Since, as previously pointed out, the latter is also connected via the connecting rod 39 to the third lever 37, the final effect is thus a rotation γ of such lever 37 with respect to the tow bar 3.
Once having set the values a, b, c, d, corresponding as explained in the above to the lengths of the various mechanism components, the following relationships are deriving from geometrical studies: $\begin{matrix} \begin{matrix} {γ = γ}_{α} {+ γ}_{β} \\ γ_{α} = [a(b+c)/c(a+b)] α = Aα \\ γ_{β} = [b(c-a)/c(a+b)] β = Bβ \end{matrix} \end{matrix}$
The above relationships are valid if the flying lever 28 is dimensioned so as the length thereof is corresponding to the sum of the lengths of the third lever 37 and of the second lever 25, i.e. if $d = c + b$
whereby $A + B = 1$
A law of more general character may be obtained varying the length d of the flying lever 28.
Reverting now to the preceding general law of axle steering as a function of the tow bar 3 rotation: $\begin{matrix} \begin{matrix} δ_{A} {= - δ}_{B} {=Mσ}_{1} {+Nσ}_{2} \\ δ_{E} {= - δ}_{F} {=Mσ}_{2} {+Nσ}_{1} \end{matrix} \end{matrix}$
it is to be pointed out that, according to the above law, the steering angles δ of the axles were referred to the longitudinal axis of the bodies 1 and 2.
In the case of the flying lever mechanism, the same law is accomplished referring the axle steering not to the bodies, but relative to the tow bar 3. For instance, in the case of the body 1, since the relative rotation between this body and the tow bar 3 is σ₁, it is: ${δ'}_{A} {= σ}_{1} {- δ}_{A} {= (1-M) σ}_{1} {-Nσ}_{2}$
Wherein δ'_A is in fact the steering angle referred to the tow bar 3.
It is sufficient to select the lengths a, b, c, d so as to obtain $γ = δ'$
The flying lever mechanism shown in figure 6 may be simplified, with equivalent functional effects, suppressing the first connecting rod 32 and the second connecting rod 39, and in such a case the flying lever 28 shall be articulated at 35 and 36 directly to the first lever 34 and to the third lever 37, respectively.
According to a further simplification, corresponding to the case where the coefficient N = 0, also the second connecting rod 30 may be suppressed, whereby the end 29 of the flying lever 28 shall be directly articulated to the second lever 25.
The invention is applicable not only to tramway vehicles having two bodies, but also to vehicles provided of three or more bodies.
Figure 7 shows the embodiment according to figure 4 applied to a tramway vehicle having three bodies, i.e. with an intermediate body 2a interposed between the bodies 1 and 2, and also having a pair of independent steering axles 5a, 5b. The intermediate body 2a is connected at one end to the body 1 via a tow bar 3a, and at the other end to the body 2 via a tow bar 3b, both identical to the tow bar 3 as previously disclosed.
A trapezoid linkage 14 placed on the side of the body 1, and a trapezoid linkage 15a situated on the side of the intermediate body 2a, are operatively associated to the tow bar 3a. Likewise, a trapezoid linkage 14a placed on the side of the intermediate body 2a and a trapezoid linkage 15 situated on the side of the body 2 are operatively associated to the tow bar 3b.
The trapezoid linkages 14, 15a, 14a, 15 are exactly same as those previously disclosed with reference to the trapezoid linkages 14 and 15.
The axles 5 and 6 of the bodies 1, 2 are interconnected through the reversing bars 19, while no such bar is provided for the intermediate body 2a.
According to this arrangement, also steering of each of the axles 5a, 5b of the intermediate body 2a is operated through the angular displacement of the tow bar 3a, 3b which is closest, and as a function of the rotation thereof, thus achieving extremely reduced radiality errors during curve entry and exit.
A similar arrangement is applicable to the case of a vehicle comprising, between the bodies 1 and 2, a plurality of intermediate bodies 2a.....2n with respective pairs of independent steering axles 5a, 5b and connected to the adjacent bodies via respective tow bars 3a.....3n. In such a case each intermediate body 2a......2n is equipped with respective trapezoid linkages 15a, 14a.......15n,14n, while the reversing bars 19 are even in this case only applied to the end bodies 1 and 2. In practice, therefore, all of the axles 5a, 5b of the intermediate bodies 2a......2n receive the steering drive from the tow bar 3a.......3n which is closest thereto.
Obviously, the arrangement of the steering drive system disclosed with reference to figure 5 as well as the flying lever system of figure 6 can also be applied to the case of tramway vehicle having three or more bodies.
Lastly it is to be pointed out that, in any case, it will be necessary to prevent negative effects and fouling of the axle steering signals deriving from the movements of the body relative to the axles in the horizontal plane, due to yielding of the vehicle lateral suspension. To such effect the vehicle lateral suspension shall normally be interposed between the body structure and the low floor 4.
Naturally the details of construction and the embodiments may be widely varied with respect to what has been disclosed and illustrated, without thereby departing from the scope of the invention such as defined by the appended claims.

Claims

A running gear for low-floor (4) rail vehicles comprising at least two bodies (1, 2) each having two independent respectively outer (6) and inner (5) steering axles, with respect to the vehicle configuration, including respective axle structures (7) rotatably connected to the body (1, 2) around respective central vertical axis (9; A, B, E, F) and each carrying a wheel pair (8), a tow bar (3) pivotally interconnecting at its ends (12, 13; C, D) the two bodies (1, 2), and drive means (14, 15; 24-39; 19) for operating curve steering of the axles (5, 6) of the two bodies (1, 2), characterized in that said drive means (14, 15; 24-39) operate steering of the axles (5) of each body (1, 2) through the relative angular displacement between the tow bar (3) and the bodies, and as a function of the rotation between said tow bar (3) and the respective body (1, 2).
A running gear according to claim 1, characterized in that steering of the inner axles (5) is operated, and transmitted to the outer axles (6), in accordance to the following linear relationship: $\begin{matrix} \begin{matrix} δ_{A} {= - δ}_{B} {= Mσ}_{1} {+ Nσ}_{2} \\ δ_{E} {= - δ}_{F} {= Mσ}_{2} {+ Nσ}_{1} \end{matrix} \end{matrix}$
wherein $M + N = a/a+d$
and wherein:
δ_B, δ_E: steering angles of the inner axles (5) of the two bodies (1, 2) relative thereto,
δ_A, δ_F: steering angles of the outer axles (6) of the two bodies (1, 2) relative thereto,
σ₁, σ₂: relative angles between the tow bar (3) and the two bodies (1, 2),
a = distance between the central rotation axis (A-B; E-F) of the inner axle (5) and of the outer axle (6) of each body (1, 2),
d = sum of the length (c) of the tow bar (3) and the distance (b) between each articulation end (C, D) of the tow bar (3) and the central rotation axis (B, E) of the inner axle (5) of the respective body (1, 2).
A running gear according to claim 2, characterized in that the distance (b) between each articulation end (C, D) of the tow bar (3) and the central rotation axis (B, E) of the inner axle (5) of the respective body (1, 2) is selected and optimized so that N = 0, and said linear relationship is approximated as follows: $\begin{matrix} \begin{matrix} δ_{A} {= - δ}_{B} {= Mσ}_{1} {= (a/a+d) σ}_{1} \\ δ_{E} {= - δ}_{F} {= Mσ}_{2} {= (a/a+d) σ}_{2} \end{matrix} \end{matrix}$
whereby the axles (5, 6) of each body (1, 2) are solely operated through a control which is proportional to the rotation between the body and the tow bar (3).
A running gear according to claim 3, characterized in that said drive means comprise two substantially coplanar trapezoid linkages (14, 15) interconnecting the tow bar (3) and the inner axles (5) of the two bodies (1, 2) and each including:
- a first angled lever arm (16) rigidly connected at one end thereof to the corresponding articulation end (C, D) of the tow bar (3) to the respective body (1, 2),

- a second angled lever arm (17) having a greater length than the first lever arm (16) and carried by the support structure (7) of the axle (5) at a distance from the respective central vertical rotation axis (B, E) thereof,

- an oblique bar (18) pivotally connected to said first and second lever arms (16, 17),
wherein the ratio between the lengths of the first arm (16) and of the second arm (17) is equal to M.
A running gear according to claim 4, characterized in that, in the non steered condition of the axles (5, 6), said first and said second angled lever arms (16, 17) are parallel to each other and are oriented perpendicularly to the oblique bar (18).
A running gear according to claim 2, characterized in that said drive means comprise two substantially coplanar trapezoid linkages (14, 15) interconnecting the tow bar (3) and the inner axles (5) of the two bodies (1) and each including:
- a first angled lever arm (16) rigidly connected at one end thereof to the corresponding articulation end (C, D) of the tow bar (3) to the respective body (1, 2),

- second angled lever arm (17) having a greater length than the first lever arm (16) and carried by the support structure (7) of the axle (5) at a distance from the respective central vertical rotation axis (B, E) thereof,

- an oblique bar (18) pivotally connected to said first and second lever arms (16, 17)
wherein the ratio between the lengths of the first arm (16) and of the second arm (17) is equal to M,
- a pair of oblique rods (22) each pivotally interconnecting the free end of the first lever arm (16) of the trapezoid linkage (14, 15) associated to one body (1, 2) and a third angled arm (23) connected to the other body (2, 1) in proximity of the corresponding articulation end (D, C) of the tow bar (3).
A running gear according to claim 2, characterized in that said drive means comprise a flying lever mechanism applied to the ends of the tow bar (3) and including:
- a first and a second lever (24, 25) each articulated in correspondence of a respective articulation end (C, D) of the tow bar (3) to the respective body (1, 2), said first and second lever (24, 25) being arranged on opposite sides of said tow bar (3) and being connected to the inner axles (5) of the respective bodies (1, 2) via respective rigid square arms (26, 27),

- a flying lever (28) oriented generally transversally to the tow bar (3),

- a first and a second connecting rod (32, 30) pivotally connecting the first and, respectively, the second lever (24, 25) with said flying lever (28) at one end (29) thereof and, respectively, at a point (35) thereof spaced apart from the other end (36) thereof,

- a third lever (37) articulated in correspondence of one of the articulation ends (C) of the tow bar (3) to one of the bodies,

- a third connecting rod (39) pivotally connecting said third lever (37) to the other end (36) of the flying lever (28).
A running gear according to claim 7, characterized in that the flying lever (28) has a length (d) which is equal to the sum of the lengths (b + c) of said second and third levers (25, 24).
A running gear according to claim 7, characterized in that the first connecting rod (32) and the third connecting rod (39) are suppressed, whereby said flying lever (38) is directly articulated to said first and third levers (24, 37).
A running gear according to claim 9, characterized in that also the second connecting rod (30) is suppressed, whereby said flying lever (28) is directly articulated to the second lever (25).
A running gear according to claim 1, characterized in that said drive means comprise transmission means (19) for transmitting reversed steering from the inner axles (5) to the outer axles (6) of the two bodies (1, 2), said transmission means comprising an oblique reversing rod (19) pivotally connecting the outer and inner axles (5, 6) of each body (1, 2).
A running gear according to claim 11, wherein the vehicle comprises a third body (2a) interposed between said bodies (1, 2), having a pair of independent steering axles (5a, 5b) and connected to said two bodies (1, 2) via a pair of tow bars (3a, 3b), characterized in that said drive means (14, 14a, 15, 15a) are associated to both said tow bars (3a, 3b) and said transmission means (19) are only associated to said two bodies (1, 2).
A running gear according to claim 11, wherein the vehicle comprises a number of bodies (2a.....2n) interposed between said two bodies (1, 2), each having a pair of independent steering axles (5a, 5b) and each of which is connected to the adjacent bodies via respective tow bars (3a....3n), characterized in that said drive means (14, 14a.....14n, 15, 15a......15n) are associated to each tow bar (3a.....3n) and said transmission means (19) are only associated to said two bodies (1, 2).