TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to a running gear for a rail vehicle, provided with a passive hydraulic wheel set steering system.

BACKGROUND ART

[0002] A two-axle bogie for a rail vehicle described in DE 31 23 858 C2 is provided with a passive hydraulic wheel set steering system comprising: a pair of front left hydraulic cylinders for moving the left wheel of the front wheel set towards and away from a median transverse vertical plane of the bogie, a pair of front right hydraulic cylinders for moving the right wheel of the front wheel set towards and away from the median transverse vertical plane, a pair of rear left hydraulic cylinders for moving the left wheel of the rear wheel set towards and away from the median transverse vertical plane, a pair of rear right hydraulic cylinders for moving the left wheel of the rear wheel set towards and away from the median transverse vertical plane, and hydraulic connection to ensure that movements of the left, respectively right wheels of the front wheel set towards, respectively away from the median transverse vertical plane result in movements of the left, respectively right wheels of the front wheel set towards, respectively away from the median transverse vertical plane. In other words, the steering of the front and rear wheel sets is coordinated to negotiate tight curves of the track. This system, however, has no substantial benefit on wide curve or straight tracks, where it is rather considered as detrimental because of its tendency to increase wear and lateral acceleration.

[0003] EP2762377A1 discloses a running gear for a rail vehicle, comprising: a pair of wheel sets comprising a front wheel set and a rear wheel set respectively on a front side and a rear side of a median transverse vertical plane of the running gear, each of the front wheel set and rear wheel set having a left wheel and a right wheel, respectively on a left side and a right side of a median longitudinal vertical plane of the running gear, and a passive hydraulic wheel set steering system comprising: a front left hydro-mechanical converter assembly for converting motion of the left

wheel of the front wheel set towards and away from the median transverse vertical plane into hydraulic energy and vice versa, a front right hydro-mechanical converter assembly for converting motion of the right wheel of the front wheel set towards and away from the median transverse vertical plane into hydraulic energy and vice versa, a rear left hydro-mechanical converter assembly for converting motion of the left wheel of the rear wheel set towards and away from the median transverse vertical plane into hydraulic energy and vice versa, a rear right hydro-mechanical converter assembly for converting motion of the right wheel of the rear wheel set towards and away from the median transverse vertical plane into hydraulic energy and vice versa, and a control valve assembly hydraulically connected to the front left, front right, rear left and rear right hydro-mechanical converter assemblies. The control valve assembly is movable between a first position, a second and a third position, each corresponding to an operating mode. In the first operating mode, each front converter one side of the running gear is connected to the rear converter on the opposite side of the running gear, so that the two wheel sets pivot in opposite directions about their respective vertical axes. In the second operating mode, each front converter on one side of the running gear is connected to the converter on the same side of the running gear so that the two wheel sets pivot in the same direction about their respective vertical axes. In the third operating mode, each converter is completely isolated, which means that no pivot motion of the wheel sets is possible.

[0004] Other, more sophisticated active wheel set steering systems are known, which can provide different steering behaviours depending on a series of parameters such as vehicle speed or angle of curvature of the track. However, such active systems, which involve pumps or motors for delivering power to steer the wheel sets, are more costly both in terms of initial cost and maintenance, in particular when taking into account the high standards of reliability and availability required from the rolling stock in public transportation.

SUMMARY OF THE INVENTION

[0005] The invention aims to provide a running gear with improved wheel set steering capabilities, which remains simple and at a low cost.

[0006] According to a first aspect of the invention, there is provided a running gear for a rail vehicle, comprising:

- at least a pair of wheel sets comprising a front wheel set and a rear wheel set respectively on a front side and a rear side of a median transverse vertical plane of the running gear, each of the front wheel set and rear wheel set having a left wheel and a right wheel, respectively on a left side and a right side of a median longitudinal vertical plane of the running gear, and

- a passive hydraulic wheel set steering system comprising:

- a front left hydro-mechanical converter assembly for converting motion of the left wheel of the front wheel set towards and away from the median transverse vertical plane into hydraulic energy and vice versa, a front right hydro-mechanical converter assembly for converting motion of the right wheel of the front wheel set towards and away from the median transverse vertical plane into hydraulic energy and vice versa, a rear left hydro-mechanical converter assembly for converting motion of the left wheel of the rear wheel set towards and away from the median transverse vertical plane into hydraulic energy and vice versa, a rear right hydro-mechanical converter assembly for converting motion of the right wheel of the rear wheel set towards and away from the median transverse vertical plane into hydraulic energy and vice versa, and

- a control valve assembly hydraulically connected to the front left, front right, rear left and rear right hydro-mechanical converter assemblies, the control valve assembly being movable between at least a first position and a second position, the passive hydraulic wheel set steering system being such that in the first position of the control valve assembly the front left and right hydro- mechanical converter assemblies are disconnected from the rear

left and right hydro-mechanical converter assemblies so as to allow movements of the left and right wheels of the front wheel set towards or away from the median transverse vertical plane and movements of the left and right wheels of the rear wheel set towards or away from the median transverse vertical plane that are independent from the movements of the left and right wheels of the front wheel set, and wherein in the second position of the control valve assembly, each of the front left and right hydro- mechanical converter assemblies is connected to at least a respective one of the rear left and right hydro-mechanical converter assemblies.

[0007] In the first position of the control valve assembly, there is no hydraulic connection, i.e. no transfer of hydraulic fluid or pressure, between the front hydro-mechanical converter assembly and the rear hydro-mechanical converter assembly. Accordingly, movements of the left and right wheels of the front wheel set towards or away from the median transverse vertical plane are independent of movements of the left and right wheels of the rear wheel set towards or away from the median transverse vertical plane. This first operation modus is particularly adapted to straight tracks and wide curves. In the second position of the control valve assembly, there is a transfer of pressure or hydraulic fluid between the hydro-mechanical converter assemblies of the front wheel set and the hydro-mechanical converter assemblies of the rear wheel set. This second operation modus is dedicated to tight curves. The structure of the hydraulic steering system is kept simple because it is passive, i.e. no pump or motor is involved in the motion of the hydro-mechanical converter assemblies, which are moved as a result of the external forces applied by the track on the wheels.

[0008] Preferably, the passive hydraulic wheel set steering system is such that at least in the first position of the control valve assembly, a motion of one of the left and right wheels of the front wheel set towards the median transverse vertical plane results in a motion of the other of the left and right wheels of the front wheel set away from the median transverse vertical plane, and a motion of one of the left and right wheels of the rear wheel set towards the median transverse vertical plane results in a motion of the other of the left and right wheels of the rear wheel set away from the median transverse vertical plane. Preferably, the passive hydraulic wheel set steering system is such that in the first position of the control valve assembly, the motion of one of the front wheels towards the median transverse vertical plane has the same magnitude as the motion of the other front wheel away from the median transverse vertical plane and the motion of one of the rear wheels towards the median transverse vertical plane has the same magnitude as the motion of the other rear wheel away from the median transverse vertical plane.

[0009] According to a preferred embodiment, the passive hydraulic wheel set steering system is such that at in the second position of the control valve assembly, a motion of one of the left and right wheels of the front wheel set towards the median transverse vertical plane results in a motion of the other of the left and right wheels of the front wheel set away from the median transverse vertical plane, and a motion of one of the left and right wheels of the rear wheel set towards the median transverse vertical plane results in a motion of the other of the left and right wheels of the rear wheel set away from the median transverse vertical plane. The passive hydraulic wheel set steering system is preferably such that in the second position of the control valve assembly, the motion of one of the front wheels towards the median transverse vertical plane has the same magnitude as the motion of the other front wheel away from the median transverse vertical plane and the motion of one of the rear wheels towards the median transverse vertical plane has the same magnitude as the motion of the other rear wheel away from the median transverse vertical plane.

[0010] Preferably, the passive hydraulic wheel set steering system is such that in the second position of the control valve assembly movements of the left, respectively right wheel of the front wheel set towards, respectively away from the median transverse vertical plane result in movements of the left, respectively right wheel of the rear wheel set towards, respectively away from the median transverse vertical plane. Preferably, the passive hydraulic wheel set steering system is such that in the second position of the control valve assembly movements of the left, respectively right wheels of the front wheel set towards, respectively away from the median

transverse vertical plane result in movements of the same magnitude of the left, respectively right wheels of the front wheel set towards, respectively away from the median transverse vertical plane.

[0011] According to a preferred embodiment, the passive hydraulic wheel set steering system is such that in the first position of the control valve assembly, the front left and right hydro-mechanical converter assemblies are connected to one another and the rear left and right hydro-mechanical converter assemblies are connected to one another.

[0012] According to one embodiment, the passive hydraulic wheel set steering system is such that in the second position of the control valve assembly, the front left and right hydro-mechanical converter assemblies are disconnected from one another and the rear left and right hydro-mechanical converter assemblies are disconnected from one another. Preferably, .

[0013] According to an alternative embodiment, the passive hydraulic wheel set steering system is such that in the second position of the control valve assembly, the front left and right hydro-mechanical converter assemblies are connected with one another and the rear left and right hydro-mechanical converter assemblies are connected with one another.

[0014] Preferably, the passive hydraulic wheel set steering system is such that in the second position of the control valve assembly, the front left and rear left hydro-mechanical converter assemblies are connected to one another and the front right and rear right hydro-mechanical converter assemblies are connected to one another.

[0015] According to one embodiment, the passive hydraulic wheel set steering system is such that in the second position of the control valve assembly, the front left and rear right hydro-mechanical converter assemblies are connected to one another and the front right and rear left hydro-mechanical converter assemblies are connected to one another.

[0016] Each hydro-mechanical converter assembly is able to convert a mechanical energy resulting from a motion of the associated wheel towards or away

from the median transverse vertical plane into hydraulic energy and to convert hydraulic energy back into mechanical energy for moving the associated wheel towards or away from the median transverse vertical plane. Each hydro-mechanical converter assembly may comprise one or more double acting hydro-mechanical converters s e.g. cylinders and/or one or more single acting hydro-mechanical converters e.g. cylinders. According to a preferred embodiment, each hydro-mechanical converter assembly consists of a single double acting hydraulic cylinder. According to another preferred embodiment, each hydro-mechanical converter assembly consists of two single acting hydraulic cylinders, one for hydraulically converting movements of the associated wheel towards the median transverse vertical plane and the other for hydraulically converting movements of the associated wheel away from the median transverse vertical plane.

[0017] According to one embodiment, the control valve assembly may consist in single two-position control valve. However, alternative with more than one valve are also possible. The control valve assembly may be actuated by any know electric, mechanic, pneumatic or hydraulic control means, in function of a signal which can be representative e.g. of the vehicle speed, lateral acceleration, radius of curvature of the track, position of the running gear with respect to the car body or can be a function of one or more of these variables.

[0018] According to a preferred embodiment, the left and right wheels of the front wheel set are supported on a common front wheel axle and the left and right wheels of the rear wheel set are supported on a common rear wheel axle. The wheel axles may have a fixed vertical pivot axis materialised by a pivot or an imaginary vertical pivot axis. Alternatively, each wheel set can consist of individual left and right wheels without a common axle, as disclosed e.g. in US 2010/0294163.

[0019] According to a preferred embodiment, the running gear is a bogie with at least two wheel sets, and comprises a bogie frame supported on the pair of wheel sets by means of a primary suspension.

[0020] According to one embodiment, at least one of the front wheel axle and rear wheel axle is pivotally connected to the frame of the running gear via a mechanical

pivot for pivoting the said one of the front wheel axle and rear wheel axle about a fixed vertical rotation axis. Alternatively, the frame of the running gear is pivotally connected to the frame of the running gear without a mechanical pivot for pivoting the said one of the front wheel axle and rear wheel axle about a fixed vertical rotation axis.

[0021] According to another aspect of the invention, there is provided rail vehicle comprising a plurality of running gears as described hereinbefore.

BRIEF DESCRIPTION OF THE FIGURES

[0022] 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:

- figure 1 is a diagrammatic illustration of a running gear of a rail vehicle according to a first embodiment of the invention, in a first operating mode;

- figure 2 is a diagrammatic illustration of the running gear according to the first embodiment of the invention, in a second operating mode;

- figure 3 is a diagrammatic illustration of a running gear of a rail vehicle according to a second embodiment of the invention, in a first operating mode;

- figure 4 is a diagrammatic illustration of the running gear according to the second embodiment of the invention, in a second operating mode.

[0023] Corresponding reference numerals refer to the same or corresponding parts in each of the figures.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0024] With reference to Figures 1 and 2, a running gear 10, more specifically a bogie, of a rail vehicle comprises a bogie frame 12 supported on a pair of front and rear wheel sets 14, 16 by means of a primary suspension (not shown). The front

wheel set 14 and the rear wheel set 16 are located respectively on a front side and a rear side of a median transverse vertical plane 100 of the running gear 10. Each of the front wheel set 14 and rear wheel set 16 comprises a left wheel 18L, 20L and a right wheel 18R, 20R, respectively on a left side and a right side of a median longitudinal vertical plane 200 of the running gear 10, and an axle 22, resp. 24 on which the left and right wheels 18L, 18R, resp. 20L, 20R are mounted (or which can be integral with the left and right wheels). Each axle 22, 24 can be a drive axle or a dead axle.

[0025] The bogie 10 is further provided with a passive hydraulic wheel set steering system 26 comprising: a front left hydro-mechanical converter assembly 28L consisting of a single double-acting cylinder for converting motion of the left wheel 18L of the front wheel set 14 towards and away from the median transverse vertical plane 100 into hydraulic energy and vice versa, a front right hydro-mechanical converter assembly 28R consisting of a single double-acting cylinder for converting motion of the right wheel 18R of the front wheel set 14 towards and away from the median transverse vertical plane 100 into hydraulic energy and vice versa, a rear left hydro-mechanical converter assembly 30L consisting of a single double-acting cylinder for converting motion of the left wheel 20L of the rear wheel set 16 towards and away from the median transverse vertical plane 100 into hydraulic energy and vice versa, and a rear right hydro-mechanical converter assembly 30R consisting of a single double-acting cylinder for converting motion of the right wheel 20R of the rear wheel set 16 towards and away from the median transverse vertical plane 100 into hydraulic energy and vice versa.

[0026] The passive hydraulic wheel set steering system 26 further comprises control valve assembly 32 which is depicted as a single twelve-port two-position control valve 32 hydraulically connected to the front left, front right, rear left and rear right hydraulic cylinders by means of hydraulic lines. More specifically, each hydraulic cylinder comprises a front and a rear chamber and each chamber is connected by a direct line to one or two of the ports of the control valve 32.

[0027] The control valve 32 is movable between a first position depicted in Figure 1 and a second position depicted in Figure 2.

CLAIMS

A running gear (10) for a rail vehicle, comprising:

at least a pair of wheel sets (14, 16) comprising a front wheel set (14) and a rear wheel set (16) respectively on a front side and a rear side of a median transverse vertical plane (100) of the running gear (10), each of the front wheel set (14) and rear wheel set (16) having a left wheel (18L, 20L) and a right wheel (18R, 20R), respectively on a left side and a right side of a median longitudinal vertical plane (200) of the running gear (10), and

a passive hydraulic wheel set steering system (26) comprising: a front left hydro-mechanical converter assembly (28L) for converting motion of the left wheel (18L) of the front wheel set (14) towards and away from the median transverse vertical plane (100) into hydraulic energy and vice versa, a front right hydro-mechanical converter assembly (28R) for converting motion of the right wheel (18R) of the front wheel set (14) towards and away from the median transverse vertical plane (100) into hydraulic energy and vice versa, a rear left hydro-mechanical converter assembly (30L) for converting motion of the left wheel (20L) of the rear wheel set (16) towards and away from the median transverse vertical plane (100) into hydraulic energy and vice versa, a rear right hydro-mechanical converter assembly (30R) for converting motion of the right wheel (20R) of the rear wheel set (16) towards and away from the median transverse vertical plane (100) into hydraulic energy and vice versa,

caracterised in that the passive hydraulic wheel set steering system (26) further comprises control valve assembly (32) hydraulically connected to the front left, front right, rear left and rear right hydro-mechanical converter assemblies, the control valve assembly (32) being movable between at least a first position and a second position, the passive hydraulic wheel set steering system (26) being such that in the first position of the control valve assembly (32) the front left and right hydro-mechanical converter assemblies are disconnected from the

rear left and right hydro-mechanical converter assemblies so as to allow movements of the left and right wheels of the front wheel set towards or away from the median transverse vertical plane and movements of the left and right wheels of the rear wheel set towards or away from the median transverse vertical plane that are independent from the movements of the left and right wheels of the front wheel set, and wherein in the second position of the control valve assembly (32), each of the front left and right hydro-mechanical converter assemblies is connected to at least a respective one of the rear left and right hydro-mechanical converter assemblies.

2. The running gear (10) of claim 1, wherein the passive hydraulic wheel set steering system (26) is such that at least in the first position of the control valve assembly (32), a motion of one of the left and right wheels (18L, 18R) of the front wheel set (14) towards the median transverse vertical plane (100) results in a motion of the other of the left and right wheels (18L, 18R) of the front wheel set (14) away from the median transverse vertical plane (100), and a motion of one of the left and right wheels (20L, 20R) of the rear wheel set (16) towards the median transverse vertical plane (100) results in a motion of the other of the left and right wheels (20L, 20R) of the rear wheel set (16) away from the median transverse vertical plane (100).

3. The running gear (10) of claim 2, wherein the passive hydraulic wheel set steering system (26) is such that at in the second position of the control valve assembly (32), a motion of one of the left and right wheels (18L, 18R) of the front wheel set (14) towards the median transverse vertical plane (100) results in a motion of the other of the left and right wheels (18L, 18R) of the front wheel set (14) away from the median transverse vertical plane (100), and a motion of one of the left and right wheels (20L, 20R) of the rear wheel set (16) towards the median transverse vertical plane (100) results in a motion of the other of the left and right wheels (20L, 20R) of the rear wheel set (16) away from the median transverse vertical plane (100).

4. The running gear (10) of any one of the preceding claims, wherein the passive hydraulic wheel set steering system (26) is such that in the second position of the control valve assembly (32) movements of the left, respectively right wheel of the front wheel set (14) towards, respectively away from the median transverse vertical plane (100) result in movements of the left, respectively right wheel of the rear wheel set (16) towards, respectively away from the median transverse vertical plane (100).

5. The running gear (10) of any one of the preceding claims, wherein the passive hydraulic wheel set steering system (26) is such that in the first position of the control valve assembly (32), the front left and right hydro-mechanical converter assemblies are connected to one another and the rear left and right hydro- mechanical converter assemblies are connected to one another.

6. The running gear (10) of any one of claims 1 to 5, wherein the passive hydraulic wheel set steering system (26) is such that in the second position of the control valve assembly (32), the front left and right hydro-mechanical converter assemblies are disconnected from one another and the rear left and right hydro- mechanical converter assemblies are disconnected from one another.

7. The running gear (10) of any one of the claims 1 to 5, wherein the passive hydraulic wheel set steering system (26) is such that in the second position of the control valve assembly (32), the front left and right hydro-mechanical converter assemblies are connected with one another and the rear left and right hydro-mechanical converter assemblies are connected with one another.

8. The running gear (10) of any one of the preceding claims, wherein the passive hydraulic wheel set steering system (26) is such that in the second position of the control valve assembly (32), the front left and rear left hydro-mechanical converter assemblies are connected to one another and the front right and rear right hydro-mechanical converter assemblies are connected to one another.

9. The running gear (10) of any one of the preceding claims, wherein the passive hydraulic wheel set steering system (26) is such that in the second position of the control valve assembly (32), the front left and rear right hydro-mechanical converter assemblies are connected to one another and the front right and rear left hydro-mechanical converter assemblies are connected to one another.

10. The running gear (10) of any one of the preceding claims, wherein the left and right wheels (18L, 18R) of the front wheel set (14) are supported on a common front wheel axle (22) and the left and right wheels (20L, 20R) of the rear wheel set (16) are supported on a common rear wheel axle (24).

1 1 . The running gear (10) of any one of the preceding claims, further comprising a bogie frame (12) supported on the pair of wheel sets (14, 16) by means of a primary suspension.

1 2. The running gear (10) of claim 10 and claim 11, wherein at least one of the front wheel axle (22) and rear wheel axle (24) is pivotally connected to the frame (12) of the running gear (10) via a mechanical pivot for pivoting the said one of the front wheel axle (22) and rear wheel axle (24) about a fixed vertical rotation axis.

13. The running gear (10) of claim 10 and claim 11, wherein the frame (12) of the running gear (10) is pivotally connected to the frame (12) of the running gear (10) without a mechanical pivot for pivoting the said one of the front wheel axle (22) and rear wheel axle (24) about a fixed vertical rotation axis.

14. A rail vehicle comprising a plurality of running gears (10) according to any one of the preceding claims.