Wheel Axle Guiding Assembly With Longitudinal Hydro-Mechanical Converters and Associated Running Gear

Abstract

The invention relates to a wheel axle guiding assembly comprising an axle box carrier, an axle box located longitudinally between a front part and a rear part of the axle box carrier; a front longitudinal hydro-mechanical converter between a front part of an axle box carrier and a rear longitudinal hydro-mechanical converter between the axle box and a rear part of the axle box carrier to allow a fore-and-aft movement of the axle box relative to the axle box carrier parallel to a longitudinal direction. Each of the front and rear longitudinal hydro-mechanical converters includes a housing, a plunger and an elastomeric body fixed to the housing and to the plunger so as to allow a fore-and-aft relative movement parallel to the longitudinal direction between the plunger and the housing, a single variable volume hydraulic chamber being formed between the housing, the plunger and the elastomeric body.

Claims

1. A wheel axle guiding assembly comprising: an axle box defining a horizontal revolution axis and a longitudinal horizontal direction perpendicular to the revolution axis; an axle box carrier; and a front longitudinal hydro-mechanical converter fixed to a front interface of the axle box and a front interface of the axle box carrier and a rear longitudinal hydro-mechanical converter fixed to a rear interface of the axle box and a rear interface of the axle box carrier to allow a fore-and-aft movement of the axle box relative to the axle box carrier parallel to the longitudinal direction; wherein each of the front and rear longitudinal hydro-mechanical converters includes a housing, a plunger and an elastomeric body fixed to the housing and to the plunger so as to allow a fore-and-aft relative movement parallel to the longitudinal direction between the plunger and the housing, a single variable volume hydraulic chamber being formed between the housing, the plunger and the elastomeric body, each of the front and rear longitudinal hydro-mechanical converters further including a hydraulic port for connecting the variable volume hydraulic chamber to an external hydraulic circuit.

2. The wheel axle guiding assembly of claim 1, wherein the axle box houses a bearing having an inner diameter defining a cross-sectional area A.sub. of an end of a wheel axle to be received in the bearing and the plunger has an effective area A.sub.e measured in a plane perpendicular to the longitudinal direction, which is greater than half the cross-sectional area A.sub..

3. The wheel axle guiding assembly of claim 1, wherein each of the front and rear longitudinal hydro-mechanical converters has a longitudinal stiffness, which increases with a frequency of the fore-and-aft movement of the axle box relative to the axle box carrier from a quasistatic stiffness value to a dynamic stiffness value, wherein the plunger and the elastomeric body have dimensions such that a ratio R of the dynamic stiffness value to the quasistatic stiffness value is greater than 10.

4. The wheel axle guiding assembly of claim 1, further comprising a vertical suspension unit provided between the axle box and an upper part of the axle box carrier.

5. The wheel axle guiding assembly of claim 1, wherein each of the front and rear longitudinal hydro-mechanical converters further comprises a decoupling spring with a longitudinal stiffness at least ten times greater than a longitudinal stiffness of the elastomeric body, a lateral stiffness less than a two times the lateral stiffness of the elastomeric body and a vertical stiffness less than two times the vertical stiffness of the elastomeric body.

6. The wheel axle guiding assembly of claim 1, wherein the front interface of the axle box faces the front interface of the axle box carrier and the rear interface of the axle box faces the rear interface of the axle box carrier.

7. The wheel axle guiding assembly of claim 1, wherein the front interface and the rear interface of the axle box carrier are located between the front interface and the rear interface of the axle box.

8. The wheel axle guiding assembly of claim 1, wherein the horizontal revolution axis is located longitudinally between the front interface and a rear interface of the axle box carrier.

9. The wheel axle guiding assembly of claim 8, wherein the axle box carrier forms a ring around the axle box.

10. The wheel axle guiding assembly of claim 1, further comprising a vertical suspension assembly for connecting the axle box carrier to a running gear frame.

11. The wheel axle guiding assembly of claim 1, wherein the axle box carrier is a constituent portion of a running gear frame of a running gear.

12. The wheel axle guiding assembly of claim 11, wherein the running gear frame is flexible.

13. The wheel axle guiding assembly of claim 1, further comprising a hydraulic reservoir hydraulically connected to the hydraulic chamber.

14. A running gear for a rail vehicle, comprising at least a pair of wheel axle guiding assemblies according to claim 1, a first hydraulic circuit for establishing a hydraulic connection between a first variable volume hydraulic chamber and a second variable volume hydraulic chamber, and a second hydraulic circuit for establishing a hydraulic connection between a third variable volume hydraulic chamber and a fourth variable volume hydraulic chamber, the first, second, third and fourth variable volume hydraulic chambers being all different chambers and each of the first, second, third and fourth variable volume hydraulic chambers being the variable volume hydraulic chamber of one of the front and rear longitudinal hydro-mechanical converters of one of the wheel axle guiding assemblies of the pair of wheel axle guiding assemblies.

15. The running gear of claim 14, wherein the first hydraulic circuit establishes a hydraulic connection between the variable volume hydraulic chamber of the front longitudinal hydro-mechanical converter of one of the wheel axle guiding assemblies of the pair of the wheel axle guiding assemblies and the variable volume hydraulic chamber of the front longitudinal hydro-mechanical converter of the other of the wheel axle guiding assemblies of the pair of the wheel axle guiding assemblies and second hydraulic circuit establishes a hydraulic connection between the variable volume hydraulic chamber of the rear longitudinal hydro-mechanical converter of one of the wheel axle guiding assemblies of the pair of the wheel axle guiding assemblies and the variable volume hydraulic chamber of the rear longitudinal hydro-mechanical converter of the other of the wheel axle guiding assemblies of the pair of the wheel axle guiding assemblies.

16. The running gear of claim 14, further comprising at least a front wheel set and a rear wheel set, wherein an end of the front wheel set is supported by the axle box of a front wheel axle guiding assembly of the pair of wheel axle guiding assemblies, and an end of the rear wheel set is supported by the axle box of a rear wheel axle guiding assembly of the pair of wheel axle guiding assemblies.

17. The running gear of claim 14, further comprising at least one wheel set, wherein a left end of the wheel set is supported by the axle box of a left wheel axle guiding assembly of the pair of wheel axle guiding assemblies, and a right end of the wheel set is supported by the axle box of a right wheel axle guiding assembly of the pair of wheel axle guiding assemblies.

18. The running gear of claim 14, wherein the running gear does not include any hydraulic connection between the chamber of the front longitudinal hydro-mechanical converter and the chamber of the rear longitudinal hydro-mechanical converter of the same wheel axle guiding assembly.

19. The wheel axle guiding assembly of claim 13, wherein a check valve allows a flow of a fluid only from the hydraulic reservoir to the hydraulic chamber, wherein the hydraulic reservoir volume is at least twice the volume of the hydraulic chamber.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0036] Other advantages and features of the invention will then become more clearly apparent from the following description of a specific embodiment of the invention given as non-restrictive examples only and represented in the accompanying drawings in which:

[0037] FIG. 1 illustrates a longitudinal section of a wheel axle guiding assembly for a running gear of a rail vehicle according to a first embodiment of the invention by a longitudinal vertical plane along section line I-I of FIG. 3;

[0038] FIG. 2 illustrates a section of the wheel axle guiding assembly of FIG. 1 by a horizontal plane along section line II-II of FIG. 1;

[0039] FIG. 3 is a vertical section of the wheel axle guiding assembly of FIG. 1, along section line III-III of FIG. 1;

[0040] FIG. 4 is a vertical section along section line IV-IV of FIG. 1;

[0041] FIG. 5 is a longitudinal section of a wheel axle guiding assembly according to a second embodiment of the invention;

[0042] FIG. 6 is a longitudinal section of a wheel axle guiding assembly according to a third embodiment of the invention;

[0043] FIG. 7 illustrates a section of the wheel axle guiding assembly of FIG. 6 by a horizontal plane;

[0044] FIG. 8 is a longitudinal section of a wheel axle guiding assembly according to a fourth embodiment of the invention;

[0045] FIG. 9 is a longitudinal section of a wheel axle guiding assembly according to a fifth embodiment of the invention;

[0046] FIG. 10 is a longitudinal section of a wheel axle guiding assembly according to a sixth embodiment of the invention;

[0047] FIG. 11 is a longitudinal section of a wheel axle guiding assembly according to a seventh embodiment of the invention;

[0048] FIG. 12 is an exploded view o the wheel axle guiding assembly of FIG. 10;

[0049] FIG. 13 is a schematic view of a first embodiment of a running gear provided with sets of the wheel axle guiding assemblies according to any one of the previous embodiments of the invention;

[0050] FIG. 14 is a schematic view of a second embodiment of a running gear provided with sets of the wheel axle guiding assemblies according to any one of the previous embodiments of the invention;

[0051] FIG. 15 is a schematic view of a third embodiment of a running gear provided with sets of the wheel axle guiding assemblies according to any one of the previous embodiments of the invention;

[0052] FIG. 16 is a schematic view of a fourth embodiment of a running gear provided with sets of the wheel axle guiding assemblies according to any one of the previous embodiments of the invention;

[0053] FIG. 17 is a schematic view of a fifth embodiment of a running gear provided with sets of the wheel axle guiding assemblies according to any one of the previous embodiments of the invention;

[0054] FIG. 18 is a schematic view of running gear of FIG. 17, operating in a fail-safe mode of operation.

[0055] Corresponding reference numerals refer to the same or corresponding parts in each of the figures.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0056] A wheel axle guiding assembly 10 for a running gear 12 of a rail vehicle is illustrated in FIGS. 1 to 4. This wheel axle guiding assembly 10 comprises an axle box 14 located longitudinally between a front part 16 and a rear part 18 of an axle box carrier 20 formed by a C-shaped end portion of a frame 22 of the running gear 12. The axle box carrier 20 is supported on the axle box 14 by way of a vertical primary suspension unit 24, which comprises a chevron spring 26 having a V-shaped cross-section in a vertical transversal plane parallel to a revolution axis 100 defined by the axle box 14. As is well known in the art, the axle box 14 houses a bearing 28, usually a roller bearing, for guiding an end portion of a wheel axle 30.

[0057] A front longitudinal hydro-mechanical converter 32 is fixed to a front interface 14A of the axle box 14 and to a front interface 16A of the axle box carrier 20 formed by the front part 16 of the axle box carrier 20 and a rear longitudinal hydro-mechanical converter 34 is fixed to a rear interface 14B of the axle box 14 and to a front interface 18B of the axle box carrier 20 formed by the rear part 18 of the axle box carrier 20 to allow a fore-and-aft movement of the axle box 14 relative to the axle box carrier 20 parallel to a longitudinal direction 200. The longitudinal direction 200 in this context and in the whole application is the horizontal direction perpendicular to the horizontal revolution axis 100 defined by the axle box in a reference position. Each of the front and rear longitudinal hydro-mechanical converters 32, 34 includes a housing 36 fixed to the axle box 14 or integral with the axle box 14, a plunger 38 fixed to or integral with the axle box carrier 20 and an annular elastomeric body 40 adhered by vulcanisation or otherwise fixed in a sealed manner to the housing 36 and to the plunger 38 so as to form a single variable volume hydraulic chamber 42 between the housing 36, the plunger 38 and the elastomeric body 40. A hydraulic inlet and outlet port 44 (see FIG. 2) is provided for connecting the variable volume hydraulic chamber 42 to a hydraulic circuit, as will be discussed later on in connection with FIGS. 9 to 13.

[0058] In this preferred embodiment, the interface 46 between the annular elastomeric body 40 and the housing 36 and the interface 48 between the annular body 40 and the plunger 38 are cylindrical and coaxial. This ensures that the annular elastomeric body 40 is only subjected to shear stress when the plunger 38 and housing 36 move relative to one another in the longitudinal direction 200. The radial dimension of the annular body 40, i.e. the distance between the two interfaces 46, 48 is preferably greater than its longitudinal dimension.

[0059] This arrangement result in a low stiffness of each longitudinal hydro-mechanical converter 32, 34 in the longitudinal direction 200 while the stiffness is much higher in the radial directions, notably in the vertical and transverse directions. The chevron spring 26 has a stiffness which is higher than the hydro-mechanical converters 32, 34 in the vertical and transverse directions but lower in the longitudinal direction 200. As a result, the vertical primary suspension unit 24 is the main path for vertical loads and shares the transverse load with the hydro-mechanical converters 32, 34, which form the main path for longitudinal loads.

[0060] Due to its geometry, and in particular to their large pumping area, the hydro-mechanical converters 32, 34 have a stiffness, which significantly increases with the frequency of the applied load, as become more apparent from the discussion below.

[0061] When the axial load varies at a very low frequency, the hydraulic fluid moves in and out of the variable volume hydraulic chamber 42 through the hydraulic port 44 in phase with the motion of the plunger 38 relative to the housing 36. The static stiffness C.sub.static of the hydro-mechanical converter depends mainly on the geometry of the elastomeric body 40 and decreases when the ratio of the radial dimension to the longitudinal dimension of the elastomeric body 40 increases.

[0062] When the frequency of the longitudinal movement of the axle boxes 14 increases, the motion of the hydraulic fluid in and out of the hydraulic chambers 42 is increasingly out of phase with the relative motion between the plunger 38 and the housing 36. When the frequency is sufficiently high the hydraulic chambers 42 can be almost considered as closed chambers, since the movement of the fluid in and out of the chambers becomes insignificant. The behaviour is dependent on the viscosity of the fluid and the hydraulic circuit connecting the chambers, in particular the length and diameter of the connecting pipes. Relative fore and aft movement between the plunger and the housing is still possible despite the incompressible fluid in the hydraulic chamber thanks to a dynamic swell deformation of the elastomeric body 40. The elastomeric body 40 is therefore characterised by a dynamic swell stiffness C.sub.swell which is added to the static stiffness C.sub.static at higher frequencies. This dynamic swell stiffness increases approximately linearly with the effective pumping area A of the hydro-mechanical converter, which is the ratio of the elementary variation of volume V of the chamber to the corresponding elementary longitudinal relative movement Lx between the plunger and the housing:

[00001]$C_{\mathrm{swell}}K.Math.A=K.Math..Math.\frac{.Math..Math.V}{.Math..Math.x}$

[0063] In practice, the pumping area A is greater than or equal to the effective area A.sub.e of the plunger, i.e. the area of the geometric projection of the surface of the plunger within the housing on a plane P perpendicular to the longitudinal direction. In other words, the greater the effective area A.sub.e of the plunger, the greater the pumping area A, the dynamic swell stiffness S.sub.swell and the ratio R of the dynamic stiffness to the static stiffness of the longitudinal hydro-mechanical converter 32, 34. As a rule of thumb, the effective area A.sub.e of the plunger should preferably be greater than half the area of the cross-section A.sub. of the wheel axle measured in a plane perpendicular to the rotation axis of the wheel axle passing through a roller bearing of the axle box:

[00002]$A{A}_e\frac{A_{}}{2}$

[0064] Thanks to the geometry of the arrangement of the hydro-mechanical converters on each side of the wheel axle, the effective pumping area A can be large, and the dynamic stiffness, will also be very large. Concurrently, the static stiffness can be kept low, which leads to a high ratio of the dynamic stiffness to the static stiffness, preferably of more than 10, preferably of more than 20, and preferably more than 50.

[0065] Due to this high ratio of the dynamic stiffness to the static stiffness, the wheel axle guiding assembly provides a smooth response to the various longitudinal loads at low frequency and a stiffer response at higher frequency, which is particularly advantageous. The wheel axle guiding assembly will respond with a very low stiffness C.sub.static to quasistatic longitudinal loads so that the wheel axle 30 will naturally rotate about a vertical axis and find their position in a curve. The stroke of the longitudinal hydro-mechanical converters 32, 34 is greater than with conventional elastomeric or hydro-elastic bushings, which ensures a sufficient deflection of the wheel axle 30 in curves. In response to high frequency longitudinal vibrations, on the other hand, the system will provide a high dynamic stiffness that includes the component C.sub.swell so as to efficiently counteract hunting oscillations and provide an excellent stability.

[0066] The cutoff frequency in the frequency response of the system depends not only on the characteristic of the hydro-mechanical converters 32, 34 but also on the characteristics of the hydraulic circuit. Preferably, the cutoff frequency should be less than 4 Hz, ideally between 0.5 Hz and 1.5 Hz.

[0067] A wheel axle guiding assembly 10 for a running gear 12 of a rail vehicle according to a second embodiment of the invention is illustrated in FIG. 5. This wheel axle guiding assembly 10 comprises an axle box 14 located longitudinally between a front part 16 and a rear part 18 of a ring-shaped axle box carrier 20 formed by a C-shaped end portion of a frame 22 of the running gear and a C-shaped lower bracket 120. The axle box carrier 20 is supported on the axle box 14 by way of a vertical primary suspension unit 24, which comprises a sandwich spring 126 having a set of planar elastomeric elements extending in a horizontal plane.

[0068] A front longitudinal hydro-mechanical converter 32 is fixed to the axle box 14 and to the front part 16 of the axle box carrier 20 and a rear longitudinal hydro-mechanical converter 34 fixed to the axle box 14 and to the rear part 18 of the axle box carrier 20 to allow a fore-and-aft movement of the axle box 14 relative to the axle box carrier 20 parallel to the longitudinal direction 200 of the running gear 12. Each of the front and rear longitudinal hydro-mechanical converters 32, 34 includes a housing 36 fixed to or integral with the axle box 14, a plunger 38 fixed to or integral with the axle box carrier 20 and an annular elastomeric body 40 adhered by vulcanisation or otherwise fixed in a sealed manner to the housing 36 and to the plunger 38 so as to form a single variable volume hydraulic chamber 42 between the housing 36, the plunger 38 and the elastomeric body 40. In this embodiment, the interface between the annular elastomeric body and the plunger is frustum-shaped and coaxial with the interface between the annular body and the housing.

[0069] This arrangement results in a low stiffness of each longitudinal hydro-mechanical converter 32, 34 in the longitudinal direction while the stiffness is much higher in the radial directions, notably in the vertical and transverse directions. The sandwich spring 126 has a static stiffness, which is higher than the hydro-mechanical converters 32, 34 in the vertical directions but lower in the longitudinal and transverse directions. As a result, the sandwich spring 126 is the main path for vertical loads while the hydro-mechanical converters 32, 34 form the main path for longitudinal and transverse loads. The response of the wheel axle guiding assembly 10 of FIG. 5 to static and dynamic longitudinal loads is essentially similar to that of the first embodiment.

[0070] A wheel axle guiding assembly 10 for a running gear 12 of a rail vehicle according to a third embodiment of the invention is illustrated in FIGS. 6 and 7. This wheel axle guiding assembly 10 comprises an axle box 14 located longitudinally between a front part 16 and a rear part 18 of an axle box carrier 20 formed by a ring-shaped frame element fixed to the frame 22 of the running gear 12. The axle box carrier 20 is supported on the axle box 14 by way of a vertical primary suspension unit 24, which comprises an upper elastomeric pad 226 and a lower elastomeric pad 227. A front longitudinal hydro-mechanical converter 32 is provided between the axle box 14 and the front part 16 of the axle box carrier 20 and a rear longitudinal hydro-mechanical converter 34 is provided between the axle box 14 and the rear part 18 of the axle box carrier 20 to allow a fore-and-aft movement of the axle box 14 relative to the axle box carrier 20 parallel to the longitudinal direction 200 of the running gear 12. Each of the front and rear longitudinal hydro-mechanical converters 32, 34 includes a housing 36 fixed to the axle box carrier 20 or integral with the axle box carrier 20, a plunger 38 integral with the axle box 14 and an annular elastomeric body 40 adhered by vulcanisation or otherwise fixed in a sealed manner to the housing 36 and to the plunger 38 so as to form a single variable volume hydraulic chamber 42 between the housing 36, the plunger 38 and the elastomeric body 40. In this embodiment, the interface 46, 48 between the annular elastomeric body 40 and the housing 36 and between the annular body 40 and the plunger 38 are tapered. An elastomeric buffer 338 forms an abutment between the plunger 38 and the housing 36 for limiting a contraction movement of the hydro-mechanical converter 32, 34. The response of the wheel axle guiding assembly of FIGS. 6 and 7 to static and dynamic longitudinal loads is essentially similar to that of the previous embodiments.

[0071] The axle guiding assemblies of the various embodiments of FIGS. 1 to 7 are particularly adapted to a running gear with a flexible running gear frame that will undergo deformation to respond to vertical load. The embodiment of FIG. 8 is more adapted to a rigid running gear frame, which remains substantially without deformation under the usual operative conditions. The axle guiding assembly 10 of FIG. 8 differs from the axle guiding assembly of FIGS. 6 and 7 essentially in that the ring-shaped axle box carrier 20 is not rigidly fixed to the running gear frame 22. Instead, the running gear frame 22 bears on a pair of vertical primary suspension units 426, which consist in rubber springs that allow a substantial relative vertical movement between the running gear frame 22 and the axle box carrier 20 and transmit the longitudinal and lateral loads without substantial deformations. The upper and lower elastomeric pads 226, 227 between the axle box carrier 20 and the axle box 14 can be kept very stiff to substantially reduce the relative vertical and transverse motion between the axle box carrier 20 and the axle box 14 and limit the deformation of the elastomeric body 40 of each of the front and read hydro-mechanical converters 32, 34 in directions perpendicular to the longitudinal direction 200. The response of the wheel axle guiding assembly 10 of FIG. 8 to static and dynamic longitudinal loads is essentially similar to that of the previous embodiments.

[0072] The axle box guiding assembly of FIG. 9 derives from the embodiment of FIGS. 1 to 4 and differs from that embodiment in that an additional spring 526 is interposed between the axle box 14 and each of the longitudinal hydro-mechanical converter 32, 34. This additional decoupling spring 526 has vertical stiffness less than two times the vertical stiffness of the hydro-mechanical converter 32, 34, a longitudinal stiffness at least ten times greater than the longitudinal stiffness of the hydro-mechanical converter 32, 34 and a lateral stiffness less than two times than the lateral stiffness of the hydro-mechanical converter 32, 34. The decoupling spring 526 can be an elastomer ring around a fixed volume hydraulic chamber 527 filled with hydraulic fluid.

[0073] The axle box guiding assembly of FIG. 10 derives from the embodiment of FIG. 9 and differs from that embodiment merely in that no fixed volume hydraulic chamber is provided.

[0074] A wheel axle guiding assembly 10 for a running gear 12 of a rail vehicle according to a seventh embodiment of the invention is illustrated in FIGS. 11 to 12. This wheel axle guiding assembly 10 comprises an axle box 14 and an axle box carrier 20 formed by an end portion of a frame 22 of the running gear 12, supported on the axle box 14 by means of a primary suspension 24, which comprises a front vertical primary suspension unit 726A and a rear a vertical primary suspension unit 726B. The axle box 14 is located longitudinally between the front and rear suspension units 726A, 726B, which comprise each a chevron spring having a V-shaped cross-section in a vertical transversal plane parallel to a revolution axis 100 defined by the axle box 14.

[0075] The axle box guiding assembly of FIG. 11 and FIG. 12 is provided with a front longitudinal hydro-mechanical converter 32, which is fixed to a front interface 14A of the axle box 14 and to a front interface 16A of the axle box carrier 20 formed by a front face of a front pillar 722A that is integral with the frame 22 of the running gear 12 and extends between the inclined portions of the front chevron spring 726A. The axle box guiding assembly of FIG. 11 and FIG. 12 is further provided with a rear longitudinal hydro-mechanical converter 34, which is fixed to a rear interface 14B of the axle box 14 and to a rear interface 16B of the axle box carrier 20 formed by a rear face of the front pillar 722A. Unlike the previous embodiments, the front interface 14A and rear interface 14B of the axle box 14 face each other and the front interface 16B and rear interface 16B of the axle box carrier are located between the front interface 14A and rear interface 14B of the axle box 14. This embodiment is particularly suitable for retrofitting a running gear 12, when little space is available between the axle box 14 and the rear vertical primary suspension unit 726B.

[0076] Obviously, if there is more space between the axle box 14 and the rear vertical primary suspension unit 726B than between the axle box 14 and the front vertical primary suspension unit 726A, the front and rear longitudinal hydro-mechanical converter 32, 34 can be located on both longitudinal sides of the rear pillar 722B of the rear vertical primary suspension unit 726B.

[0077] It is also possible to provide the front longitudinal hydro-mechanical converter 32 and the rear longitudinal hydro-mechanical converter 34 at both longitudinal ends of axle box 14 such that the front pillar 722A and the rear pillar 722B are located between the front and rear longitudinal hydro-mechanical converters 32, 34. This variant is particularly advantageous if there is more room available in front of the front pillar 722A (i.e. left from the front pillar in FIG. 11) and behind the rear pillar 722B (i.e. right from the rear pillar in FIG. 11) than between each of the front and rear pillars 722A, 722B and the central ring-shaped part of the axle box 14.

[0078] According to another embodiment, it is also possible to provide the front longitudinal hydro-mechanical converter 32 between the front pillar 722A and the revolution axis 100 and rear pillar 722B between the revolution axis 100 and the rear longitudinal hydro-mechanical converter 34. Alternatively, it is also possible to provide the rear longitudinal hydro-mechanical converter 34 between the rear pillar 722B and the revolution axis 100 and front pillar 722A between the revolution axis 100 and the front longitudinal hydro-mechanical converter 32.

[0079] A running gear 12 including two pairs of wheel axle guiding assemblies according to the invention is illustrated in FIG. 13. In FIG. 13, the vertical primary suspension units have been left out for simplicity. The running gear 12 of FIG. 13 is a bogie with a two-wheel sets 50, each comprising left and right wheels 51 at opposite ends 52 of a wheel axle 30. Each end 52 of each wheel axle 30 is guided for rotation in an axle box 14 of a wheel axle guiding assembly 10. The two wheel axle guiding assemblies 10 on the same left or right side of the running gear 12 are hydraulically connected with one another via four independent hydraulic circuits 54, 56. More specifically, the variable volume hydraulic chamber 42 of the front hydro-mechanic converters 32 of the front and rear wheel axle guiding assemblies 10 on the left side are connected with one another via a hydraulic circuit 54 and the variable volume hydraulic chamber 42 of the rear hydro-mechanic converters 34 of the front and rear wheel axle guiding assemblies 10 on the left side are connected with one another via a hydraulic circuit 56. Similar hydraulic connections are provided between the axle guiding assemblies 10 on the right side of the running gear 10. A hydraulic reservoir 58 is connected via a check valve 60 to each of the hydraulic circuits to provide a temperature and leakage compensation. Preferably, each hydraulic reservoir 58, or more generally each hydraulic circuit 52, 54, is provided with a leakage detector 63. This type of hydraulic link between the front and rear axle will result in passive steering of the front and rear axles 30 in opposite directions.

[0080] An alternative connection between the individual variable volume hydraulic chambers 42 is shown in FIG. 14. The variable volume hydraulic chamber 42 of the front hydro-mechanic converters 32 of the front wheel axle guiding assembly 10 on each side is connected with the variable volume hydraulic chamber 42 of the rear hydro-mechanic converters 34 of the rear wheel axle guiding assembly 10 on the same side of the running gear 12 via a hydraulic circuit 64, while the variable volume hydraulic chamber 42 of the rear hydro-mechanic converters 34 of the front wheel axle guiding assembly 10 on each side is connected with the variable volume hydraulic chamber 42 of the front hydro-mechanic converters 32 of the rear wheel axle guiding assembly 10 on the same side of the running gear via a hydraulic circuit 66. This type of hydraulic link between the front and rear axle will result in passive steering of the front and rear axles in the same direction.

[0081] An alternative connection between the individual variable volume hydraulic chambers 42 is shown in FIG. 15. The variable volume hydraulic chamber 42 of the front hydro-mechanic converters 32 of the front wheel axle guiding assembly 10 on each side is connected with the variable volume hydraulic chamber 42 of the rear hydro-mechanic converters 34 of the rear wheel axle guiding assembly 10 on the other side of the running gear 12 via a hydraulic circuit 154, while the variable volume hydraulic chamber 42 of the rear hydro-mechanic converters 34 of the front wheel axle guiding assembly 10 on each side is connected with the variable volume hydraulic chamber 42 of the front hydro-mechanic converters 32 of the rear wheel axle guiding assembly 10 on the other side of the running gear via a hydraulic circuit 156. This type of hydraulic link between the front and rear axle will result in passive steering of the front and rear axles in opposite directions.

[0082] It may be appropriate to provide the running gear with additional distribution valves so as to switch configurations between two types of hydraulic circuits depending on the revolution speed of one of the wheel axles, e.g. with the configuration of FIG. 13 or FIG. 15 at low speed and the configuration of FIG. 14 at higher speed.

[0083] A wheel set 50 provided with two wheel axle guiding assemblies 10 according to the invention for guiding the two opposite ends 52 of a wheel axle 30 is illustrated in FIG. 16. Two independent hydraulic circuits 68, 70 are formed, each to connect the variable volume hydraulic chamber 42 of the front hydro-mechanic converters 32 of one wheel axle guiding assembly 10 with the variable volume hydraulic chamber 42 of the rear hydro-mechanic converters 34 of the same wheel axle guiding assembly 10. A hydraulic reservoir 58 is provided in each of the hydraulic circuits 68, 70. This embodiment can be implemented in a one-axle running gear or in a two-axle bogie.

[0084] An alternative connection between the individual variable volume hydraulic chambers 42 is shown in FIG. 17. Two independent hydraulic circuits 72, 74 are formed, one to connect the variable volume hydraulic chambers 42 of the front hydro-mechanic converters 32 of the left and right wheel axle guiding assemblies 10 with one another and another one to connect the variable volume hydraulic chamber 42 of the rear hydro-mechanic converters 32 of the left and right wheel axle guiding assemblies. A hydraulic reservoir 58 is provided in each of the hydraulic circuits 72, 74. This embodiment can be implemented in a one-axle running gear or in a two-axle bogie. This embodiment is particularly advantageous as it combines a very low static stiffness for rotation about the vertical axis with a limitation of translation movement of the axle parallel to the longitudinal axis. This is particularly helpful to preserve the steerability when the vehicle brakes or accelerates, the longitudinal forces being transmitted with minimal longitudinal translation of the axle.

[0085] Moreover, this embodiment provides a fail-safe operating mode illustrated in FIG. 18. If one of the hydraulic circuits leaks (in FIG. 18, the hydraulic circuit 72) and there is not enough hydraulic fluid left in that circuit, the reservoir 58 of the other hydraulic circuit will provide additional fluid in that circuit to force the wheel axle 30 towards the abutment position illustrated in FIG. 18. In this position, the wheel set 50 will not be able to rotate about the vertical axis, but will remain in a stable position. To this end, each reservoir 58 should preferably have a capacity superior to the volume of the respective hydraulic circuit, i.e. in practice at least twice and preferably more than twice the volume of the hydraulic chambers 42.

[0086] While the above examples illustrate preferred embodiments of the present invention it is noted that various other arrangements can also be considered, in particular combinations of features from different embodiments.