EP2483124A1

EP2483124A1 - Method of controlling a pneumatic suspension of a bogie of a rail vehicle, and bogie provided with a pneumatic suspension

Info

Publication number: EP2483124A1
Application number: EP10771513A
Authority: EP
Inventors: Frederik Allert
Original assignee: Bombardier Transportation GmbH
Current assignee: Alstom Transportation Germany GmbH
Priority date: 2009-09-29
Filing date: 2010-09-24
Publication date: 2012-08-08
Anticipated expiration: 2030-09-24
Also published as: EP2483124B1; WO2011039597A1; GB0917009D0; GB2473873A

Abstract

A bogie (10) comprises a frame (16), a set of wheels, and a pneumatic suspension for supporting a car body of a rail vehicle. The suspension includes a secondary suspension for vertically supporting a superstructure of the rail vehicle on the frame, the secondary suspension comprising at least one left secondary air spring (22L) and one right secondary air spring (22R) respectively located on a left and a right side of a median longitudinal vertical plane of the bogie. Left and right levelling valves (60L, 60R) independently connect each of the left and right secondary air springs (22L, 22R) to a pressure source (53) or to the atmosphere based on at least one height signal representative of a distance between a car body of the rail vehicle and one of the bogie frame and the set of wheels. Additional pneumatic means, e.g. a primary suspension or lateral actuators (18L, 18R; 118L, 118R) are provided for controlling relative motion between the frame and at least one of the superstructure and of the set of wheels. One or more control valves (58L1 58R) are used to connect the additional pneumatic means to the pressure source or to the atmosphere based on one or more pressure signals derived from the pressures of the left and/or right secondary air springs (22L, 22R).

Description

METHOD OF CONTROLLING A PNEUMATIC SUSPENSION OF A BOGIE OF A RAIL VEHICLE. AND BOGIE PROVIDED WITH A PNEUMATIC SUSPENSION

TECHNICAL FIELD OF THE INVENTION

[0001] The invention relates to a bogie for a rail vehicle, provided with a frame and a pneumatic suspension comprising at least a secondary suspension stage, and to a method of controlling such a pneumatic suspension. As is well-known in the art, the secondary suspension of a bogie is the suspension stage for supporting a superstructure of the rail vehicle, e.g. a car or coach body, on the frame of the bogie. This secondary suspension may or may not be complemented by a primary suspension stage between the wheels and frame of the bogie.

BACKGROUND ART

[0002] Pneumatic secondary suspension arrangements for controlling the tilt of the coach body are well known in the art. They usually involve at least two levelling valves located on each side of the bogie frame for controlling the left and right air springs of the secondary suspension. In order to better control the positioning of the coach body on the front and rear bogies, four-point secondary suspensions have been proposed, in which each of the four air springs supporting the car body on front and rear bogie frames is individually controlled. As a variant, three-point suspensions are also known in the art, as disclosed e.g. in US3738680.

[0003] The arrangement disclosed in US4693185 provides a control system for a vehicle secondary suspension system consisting of four fluid springs, which support the car body from two longitudinally-spaced trucks. Typically such a vehicle is a rail car employing air springs. The two air springs on each truck are disposed on opposite sides of the longitudinal centreline of the vehicle, corresponding to its direction of travel. Three of the springs are provided with levelling valves, which keep them at a constant height. A measuring device, either mechanical or electrical, measures the difference in internal spring pressure in the two springs on one truck that both have levelling valves; it also measures the difference in internal spring pressures in the two springs on the other truck and then adjusts the pressure in the spring without a levelling valve until the pressure difference is the same as for the two springs on the other truck. The arrangement avoids the establishment of unequal pressures diagonally of the vehicle that normally result from height adjustment errors in the levelling valve links and can seriously affect wheel loading and control of braking. However, the system does not provide a joint control of the height of the car body and of other components of the suspension of the vehicle, e.g. the primary suspension for controlling the movement of the frame of the truck or bogie with respect to the wheels, or lateral springs or actuators for controlling the lateral motion of the car body with respect to the bogie.

[0004] Prior art document DE3048516 discloses a bogie provided with a multi- stage pneumatic suspension comprising secondary suspension air springs as well as a primary suspension stage including a set of combined rubber springs and air springs. The chambers of the primary suspension air springs and secondary suspension air springs are all connected with one another. The rubber springs are chosen so as to support the weight of the frame of the bogie. Thanks to this arrangement, the height of the frame of the bogie does not substantially change with the load, if the effective area of the primary suspension air springs is equal or close to the effective area of the secondary suspension air springs. However, the height will not remain constant if the effective areas of the primary and secondary suspension stages differ substantially. Moreover, the response of the suspension to loads unequally distributed on each side of the bogie is not well controlled.

SUMMARY OF THE INVENTION

[0005] The foregoing shortcomings of the prior art are addressed by the present invention. According to one aspect of the invention, there is provided a bogie for a rail vehicle, comprising

- a frame,

- a set of wheels,

- a pneumatic suspension comprising:

- a secondary suspension for vertically supporting a superstructure of the rail vehicle on the frame, the secondary suspension comprising at least one left secondary air spring and one right secondary air spring respectively located on a left and a right side of a median longitudinal vertical plane of the bogie,

- levelling valve means independently connecting each of the left and right secondary air springs to a pressure source or to the atmosphere based on at least one height signal representative of a distance between a car body of the rail vehicle and one of the bogie frame and the set of wheels,

- additional pneumatic means for controlling relative motion between the frame and at least one of the superstructure and of the set of wheels,

- control valve means for connecting the additional pneumatic means to a pressure source or to the atmosphere based on one or more pressure signals derived from the pressures of the left and/or right secondary air springs.

[0006] Thanks to the control valve means, the additional pneumatic means can easily be controlled. Unlike the prior art, this control is based on a pressure information from the secondary suspension, which creates a control link between the secondary suspension and the additional pneumatic means, which can be used in order to fully compensate suspension deflection under load (i.e. the deflection of both the primary and secondary suspension) and/or to compensate roll motion or create an inclination control. [0007] The levelling valve means may include a left levelling valve for connecting the left secondary air spring to the pressure source or to the atmosphere and a right levelling valve for connecting the right secondary air spring to the pressure source or to the atmosphere. Preferably, the levelling valve means comprise sensor means for sensing a left distance and a right distance between the vehicle superstructure and one of the bogie frame and the set of wheels, respectively on the left and right sides of the median longitudinal plane. Any type of transducer can be used to measure the varying distance between the car body and the frame (or the car body and the axle boxes or wheels) e.g. mechanical transducers such as levers and telescopic transducers or optical sensors. [0008] The pressure signals for controlling the additional pneumatic means preferably include the pressures of the left and right secondary air springs. However, in certain circumstances, the pressure difference between the left and right secondary springs or the average of the pressures of the left and right secondary springs can be sufficient. [0009] Preferably, the control valve means are such as to vent or isolate the additional pneumatic means if a predetermined condition is met, e.g. if the pressure of the left or right secondary springs is below a predetermined threshold or if the average of the pressures of the left and right secondary springs is below a predetermined threshold. This is used in particular to avoid undesired application of the additional pneumatic means when the secondary suspension is under a tare pressure of the vehicle, e.g. during initial inflation of the pneumatic system.

[0010] According to a preferred embodiment, the additional pneumatic means include one or more first air chambers and one or more second air chambers, which are preferably variable volume chambers. Hence, the application of pressure to the additional pneumatic means may result in an increase of stiffness of the additional pneumatic means and/or the production of mechanical work (i.e. the product of the displacement of a wall or piston of the variable volume chamber by the force applied).

[0011] One option to implement the invention is to provide means for controlling the air chambers based on a signal, preferably a pneumatic signal, which itself is a function of the pressure difference between the first and secondary air springs. In one embodiment, the first and second air chambers are part of a double acting cylinder.

[0012] As a preferred alternative, however, each of the two air chambers is controlled with the pressure of a respective one of the two secondary air springs only. According to a preferred embodiment, the pressure of the one or more first air chambers is a function F1 of the pressure of the left secondary air spring and is independent from the pressure of the right secondary air spring, the pressure of the one or more second air chambers is a function F2 of the pressure of the right secondary air spring and is independent from the pressure of the left secondary air spring, wherein F1=F2. Preferably, the function F=F1=F2 is a positive increasing function (increasing meaning that it increases strictly or remains constant). Preferably, no action is taken if the pressure P_s of the secondary air spring and is below a predetermined tare pressure Pr■ Hence, the function F is such that

F{P_s) = 0 t P_S≤P_T where Ps the pressure of a secondary air spring and P_T is a tare pressure. The function F is preferably linear above the tare pressure, such that

F{P_s ) = K - {P_s - P_T) i1 P_S > P_T where is a positive constant.

[0013] The control valve means may include a first valve for feeding air to the one or more first air chambers and a second valve for feeding air to the one or more second air chamber, wherein the first valve is controlled by the pressure of the left secondary air spring and the second valve is controlled by the pressure of the right secondary air spring.

[0014] According to one embodiment, the control valve means are such that the difference of pressure between the one or more first air chambers and the one or more second air chambers is a function of a difference of pressure between the first secondary air spring and the second secondary air spring.

[0015] According to a preferred embodiment, the additional pneumatic means include left and right primary air springs located on the left and right sides of the median longitudinal vertical plane, respectively, for vertically supporting the frame on the set of wheels. The control valve means are preferably such as to increase and/or decrease the pressure of the left and right primary air springs to the effect that the overall resulting force applied by the left and right primary air springs on the frame is larger than or equal to the overall resulting force applied by the left and right secondary air springs to the frame, respectively. In this instance, the one or more first air chambers are part of the left primary air springs and the one or more second air chambers are part of the right primary air springs.

[0016] Alternatively or additionally, the additional pneumatic means may include means for controlling the lateral displacement of the frame relative to the superstructure perpendicular to the median longitudinal vertical plane of the frame. In this variant the means for feeding air to the additional pneumatic means are preferably such that the frame is deflected laterally towards the one of the left and right secondary air springs which encounters the lower pressure.

[0017] According to a further aspect of the invention, there is provided a pneumatic circuit for a pneumatic suspension of a rail vehicle, comprising

- left and right secondary branches provided with left and right secondary air springs respectively,

- levelling valve means for independently connecting each of the left and right secondary branches to a pressure source or to the atmosphere,

- additional pneumatic actuator means including at least a first and a second additional variable volume chambers,

- control valve means for feeding air to and releasing air from the first and second additional volume chambers as a function of the pressure in the left and right secondary branches, respectively.

[0018] In a preferred embodiment, the first and second primary air springs are mounted in parallel with first and second primary rubber springs.

[0019] Alternatively or additionally, the additional pneumatic means may include means for controlling the lateral displacement of the frame relative to the superstructure perpendicular to the median longitudinal vertical plane of the frame. The means for feeding air to the additional pneumatic means may be used to feed air to the additional pneumatic means such that the frame is deflected laterally towards the one of the first and second secondary air springs that encounters the greater pressure.

[0020]- According to another aspectof the invention, there is provided a method of controlling a pneumatic suspension of a bogie of a rail vehicle, the bogie being provided with a frame and a set of wheels, the pneumatic suspension comprising at least a secondary suspension for vertically supporting a superstructure of the rail vehicle on the frame and additional pneumatic means for controlling relative motion between the frame and at least one of the superstructure and of the set of wheels, the secondary suspension comprising at least a first secondary air spring located on a first side of a median longitudinal vertical plane of the frame and a second secondary air spring located on a second side of the median longitudinal vertical plane of the frame, the additional pneumatic means including at least a first air chamber and a second air chamber, wherein the method comprises feeding air to the additional pneumatic means such that the difference of pressure between the first air chamber and the second air chamber is a function of a difference of pressure between the first secondary air spring and the second secondary air spring.

[0021] Where the additional pneumatic means include a primary suspension for vertically supporting the frame on the set of wheels as disclosed above, the method may include feeding air to the first primary air spring and/or to the second primary air spring such that the difference of pressure between the first primary air spring and the second primary air spring is a positive increasing function, e.g. a linear function, of a difference of pressure between the first secondary air spring and the second secondary air spring.

[0022] Where the additional pneumatic means include means for controlling the lateral displacement of the frame relative to the superstructure perpendicular to the median longitudinal vertical plane of the frame, the method may include feeding air to the additional pneumatic means such that the frame is deflected laterally towards the one of the first and second secondary air springs which encounters the greater pressure.

BRIEF DESCRIPTION OF THE DRAWINGS [0023] Other advantages and features of the invention will become more clearly apparent from the following description of specific embodiments of the invention given as non-restrictive examples only and represented in the accompanying drawings in which:

- Figure 1 is a plan view of a bogie provided with a multi-stage pneumatic suspension according to one embodiment of the invention;

- Figure 2 is an enlarged vertical sectional view of a primary stage of the suspension taken on line A-A of figure 1 ;

- Figure 3 is an enlarged vertical sectional view of a secondary stage of the suspension taken on line C-C of figure 1 ;

- Figure 4 is a diagrammatic view of a pneumatic circuit of the multi-stage pneumatic suspension of figure 1 ;

- Figure 5A and 5B depict two alternative embodiment of a control valve for the pneumatic circuit of Figure 4;

- Figure 6 is a plan view of a bogie provided with a multi-stage pneumatic suspension according to another embodiment of the invention;

- Figure 7 is an enlarged vertical sectional view of a king pin of the suspension of figure 6;

- Figure 8 is a diagrammatic view of a pneumatic circuit of the multi-stage pneumatic suspension of figure 6.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

[0024] Referring to figures 1 to 3, a bogie 10 of a rail vehicle includes two wheelsets, each composed of a wheel axle received in two axle boxes 12L, 12R and provided with wheels at each end. Each of the four axle boxes 12L, 12R, one of which (12L) is illustrated in figure 2, supports one branch 14 of a H-shaped frame 16 via a primary suspension air spring 18L, 18R. Each end of the transverse beam 20 of the bogie frame 16 receives a secondary suspension element comprising at least one air spring 22L, 22R, which supports a corresponding end of a bolster 24 provided with a king pin or centre bearing 26 for supporting the car body of the rail vehicle. The structure of the bogie assembly and in particular of the primary and secondary suspension is symmetrical with respect to a longitudinal central plane P of the bogie (and of the rail vehicle 100).

[0025] As shown in Figure 2, each combined air and rubber spring 18L, 18R of the primary suspension (hereinbelow also referred to as air spring) includes a lower cup 28 attached to the axle box 12, an upper central tapered pin 30 attached to the bogie frame 16 and a multilayer tapered rubber and metal spring 38 attached at one end to the central pin 30 and at the other end to the lower cup 28. A closed air chamber 34L, 34R is defined by the pin 30, rubber spring 38 and lower cup 28. This primary suspension variable volume air chamber 34L, 34R is connected to a pneumatic circuit 36 as will be described below in order to feed the air chamber 34 with air under pressure.

[0026] As illustrated in Figure 3, each air spring 22L, 22R of the secondary suspension 22 comprises an inflatable air bag 40 defining a closed variable volume air chamber 42 with an upper cup 44 attached to the bolster 24 and a lower cup 46, which is linked to bogie frame 14 via a coil spring 48 and guided in translation with respect to the bogie frame 14.

[0027] In Figure 4, the pneumatic circuit 36 for controlling the secondary suspension of the two bogies 10 supporting the car body 100 of a rail coach is illustrated. The circuit 36 includes four identical sub-circuits, namely a left and a right sub-circuit 52L, 52R for each of the two bogies 0, fed by a common pressure source 50.

[0028] One of the left sub-circuits 52L. It will be understood that the other left and right sub-circuits 52L, 52R are identical. Hence, in the figures, the components which will be described with a suffix "L" below have counterparts with the suffix "R" on the right side of the bogie. The sub-circuit 52L includes a primary branch 54L and a secondary branch 56L. The primary branch connects the air chambers 34L of the four primary air springs 18L in parallel and is provided with a control valve to connect the air chambers 34L to the pressure source 50. Air pressure is applied to the deformable chamber 42L of the air spring 22L of the secondary suspension via the secondary branch 56L of the circuit, which may comprise an additional non- deformable chamber or reservoir 58L in series with the deformable chamber 42L, in order to increase the overall volume of air and decrease the corresponding pneumatic stiffness of the secondary air spring 22L. A levelling valve 60L is added to the secondary branch 56L of the circuit to control the pressure of the secondary branch 56L and secondary air spring 22L as a function of the height of the coach body with respect to the bogie frame. Each levelling valve 60L is operated by a lever attached to one end of a link, whose other end is fixed to the car body. Any vertical movement between the car body and the bogie is detected by the lever 61 L, which adjusts the levelling valve accordingly.

[0029] A differential valve 62L may be added between the secondary branch 56L of the left and right sub-circuits 52L of each bogie, such that the difference of pressure between the left and right secondary suspension elements remains within a predefined range.

[0030] One embodiment of the control valve 58L used to control the pressure of the primary suspension air springs 18L, 18R in each branch is illustrated in Figure 5A. The control valve 58L is shown in its intermediate position, in which the port leading to the primary branch 54L and to the chambers 34L of the primary air springs 18L is isolated. The position of the control valve 58L is controlled by an actuator 66, which moves according to the pressure differential between the primary and secondary air springs. More specifically, the pressure of the primary suspension chambers 34L and of the primary branch 54L is fed to one chamber 68B of a differential cylinder 68 of the actuator 66, while the other chamber 66A of the differential cylinder 68 is connected to the chamber 42L of the secondary suspension air spring 22L. Preferably, a differential valve 70 is connected between the secondary branch 56L and the chamber 68B, such that the control valve 58L remains in the intermediate position as long as the pressure of the secondary air spring 22L as not reached a pressure threshold. This pressure threshold is predetermined e.g. as a tare pressure P_T of the vehicle.

[0031] During initial inflation of the pneumatic system, the levelling valve 60L remains open so that air from the pressure source 53 is fed through the levelling valve 60L to the secondary air spring 22L until the deformable chamber 42L has raised the car body to its target position. At the beginning of this initial phase, the pressure in the secondary branch 56L of the circuit remains below the tare pressure and the primary branch 54L of the circuit remains isolated. At some stage during the raising phase, however, before the target position has been reached, the pressure in the secondary branch of the circuit reaches the tare pressure and pushes the piston rod 72 of the actuator 66 of the control valve 58L towards the right in Figure 5A. As a result, the pressure source 53 is connected to the primary branch 54L of the pneumatic circuit to inflate the primary air springs chambers 34L, until the increased primary air spring pressure moves the actuator 66 back to the neutral position to isolate the primary air springs 18L. When the car body has reached its target position, the levelling valve 60L isolates the secondary branch of the circuit. The same raising phase occurs simultaneously in the four sub-circuits 52L, 52R, each controlled by one of the levelling valves 60L, 60R.

[0032] After the initial inflation phase, the pressure and stiffness of the primary suspension is controlled as follows. Starting from a neutral position of the control valve 58L, 58R, if the load is increased on the left side of the bogie, e.g. in a curve, the pressure of the secondary suspension air spring 22L on that side of the bogie will increase proportionally. If this increase exceeds the threshold defined by the differential valve 70, the increased pressure is directed to the actuator 66 and pushes the piston rod 72 of the actuator towards the right in Figure 5A, such that the pressure source 53 becomes connected to the primary air springs 18L on the same side of the bogie to increase the pressure said primary air springs, until the increased primary air spring pressure moves the actuator 66 back to the neutral position to isolate the primary air springs 18L. If, on the other hand, the pressure of the secondary air spring 22L decreases, the actuator 66 is moved towards the left and air from the primary branch 54L is released to the atmosphere until the pressure of the primary air springs 18L reaches a lower value, which enables the actuator to return to the neutral position.

[0033] Hence, the control valves 58L, 58R selectively increase the pressure of the primary air springs 18L, 18R on the side of the bogie 10 which experiences an increased secondary air spring pressure. This increase of the primary air spring pressure results in an increased stiffness of the primary air springs and a lifting of the corresponding side of the bogie frame with respect to the wheels.

[0034] As an indirect result of the control of the primary suspension, the difference of pressure between the left and right air springs of the primary suspension is a function of the difference of pressure between the left and right air springs of the secondary suspension.

[0035] As an alternative to the pneumatically controlled control valve of Figure 5A, an electro-pneumatic control valve can be used, as shown in Figure 5B. The person skilled in the art will also see that the somewhat complex three-position control valves of Figures 5A and 5B can be replaced with a set of two two-position control valves.

[0036] In the embodiment of Figures 1 to 5A, the pressure of the left and right pneumatic suspension elements is used to selectively control the left and right elements of the primary suspension. By analogy, other components of the suspension can be controlled using as input the pressure of the left and right part of the secondary suspension. [0037] Figures 6 to 8 depict an example of a pneumatic circuit for controlling the lateral displacement of the coach body with respect to the bogie as a function of the pressures of the left and right elements of the secondary suspension. Identical reference numbers will be used to identify identical components of the first and second embodiments.

[0038] Remarkably, the king pin 126 of the bogie is allowed to move laterally with respect to the frame and its position is constrained and controlled by two lateral pneumatic actuators 1 18L, 1 18R, each very similar to the air and rubber springs 18L, 18R of the primary suspension of the first embodiment and each provided with a chamber 134L, 134R. The two pneumatic actuators 1 18L, 1 18R constitute lateral abutments for the king pin 126.

[0039] As illustrated in figure 8, each of the pneumatic actuators 1 18L, 1 18R is part of an additional branch 154L, 154R of the pneumatic circuit and connected to a control valve 58L, 58L in a manner similar to the primary suspension springs 18L, 18R of the first embodiment. Accordingly, each of the two lateral pneumatic actuators is individually controlled by the pressure in the corresponding secondary branch 56L, 56R of circuit on the same side of the bogie, such that an increase of the pressure of the secondary air springs 22L, 22R on one side of the bogie will result in an increased pressure of the lateral pneumatic actuator 1 18L, 1 18R on the same side. Accordingly, the lateral actuator will apply an increased force to the king pin towards the opposite side of the bogie and its stiffness will increase.

[0040] The invention is not limited to the embodiments described hereinbefore.

[0041 ] According tcr a÷ non-illustrated^ variant, the secondary suspension of the bogie can be provided with a lateral double acting cylinder, pivotally attached at one end to the bogie frame and at the other end to the bolster of the bogie. One of the chambers of double acting cylinder is connected to the right secondary air spring while the other chamber of the double acting cylinder is connected to the left secondary air spring. The connections are such that the piston of the double acting cylinder will move to push the frame of the bogie in the lateral direction of the secondary air spring with the lowest pressure.

[0042] Several components can be simultaneously controlled with the pressure on the left and right side of the secondary suspension, e.g. primary suspension elements and lateral actuators.

[0043] While the preferred embodiment includes two wheelsets, the invention is also applicable to a bogie provided with a set of four individual wheels, each supported from one of four journal boxes. According to still another variant, the bogie may include only one wheelset, composed of an axle with a bearing and wheels at each end.

[0044] While the bogie of the preferred embodiment is provided with a bolster, a similar control of the primary suspension elements based on the pressure applied to each side of secondary suspension can be advantageous for a bolsterless bogie.

Claims

1. A bogie (10) for a rail vehicle, comprising

- a frame (16),

- a set of wheels,

- a pneumatic suspension comprising:

- a secondary suspension for vertically supporting a superstructure of the rail vehicle on the frame, the secondary suspension comprising at least one left secondary air spring (22L) and one right secondary air spring (22R) respectively located on a left and a right side of a median longitudinal vertical plane of the bogie,

- levelling valve means (60L, 60R) independently connecting each of the left and right secondary air springs (22L, 22R) to a pressure source (53) or to the atmosphere based on at least one height signal representative of a distance between a car body of the rail vehicle and one of the bogie frame and the set of wheels,

- additional pneumatic means (18L, 18R; 118L, 1 18R) for controlling relative motion between the frame and at least one of the superstructure and of the set of wheels,

- control valve means (58L, 58R) for connecting the additional pneumatic means to a pressure source or to the atmosphere based on one or more pressure signals derived from the pressures of the left and/or right secondary air springs (22L, 22R).

2. The bogie of claim 1 , wherein the levelling means include a left levelling valve (60L) for connecting the left secondary air spring to the pressure source or to the atmosphere and a right levelling valve (60R) for connecting the right secondary air spring to the pressure source or to the atmosphere.

3. The bogie of claim 1 or claim 2, wherein the levelling valve means comprise sensor means for sensing a left distance and a right distance between the vehicle superstructure and one of the bogie frame and the set of wheels, respectively on the left and right sides of the median longitudinal plane.

4. The bogie of any one of the preceding claims, wherein the one or more pressure signals are selected from a group consisting of:

- the pressures of the left and right secondary air springs, - the pressure difference between the left and right secondary springs,

- the average of the pressures of the left and right secondary springs.

5. The bogie of any one of the preceding claim, wherein the control valve means are such as to vent or isolate the additional pneumatic means (18,

1 18) if a predetermined condition is met, said predetermined condition being selected from a group consisting of:

- the pressure of the left or right secondary springs is below a predetermined threshold; - the average of the pressures of the left and right secondary springs is below a predetermined threshold.

6. The bogie of any one of claims 1 to 5, wherein the additional pneumatic means (18L, 18R; 1 18L, 1 18R) include one or more first air chambers (34L, 134L) and one or more second air chambers (34R, 134R).

7. The bogie of claim 6, wherein the first and second air chambers are variable volume chambers.

8. The bogie of claim 6 or claim 7, wherein the control valve means (58L, 58R) are such that the pressure of the one or more first air chambers (34L, 134L) is a function F1 of the pressure of the left secondary air spring (18L) and is independent from the pressure of the right secondary air spring (18R), the pressure of the one or more second air chambers (34R, 134R) is a function F2 of the pressure of the right secondary air spring (18R) and is independent from the pressure of the left secondary air spring (18L), wherein F1=F2.

9. The bogie of claim 8, wherein the function F=F1=F2 is a positive increasing function.

10. The bogie of claim 9, wherein the function F is such that

F(P_s) - 0 if P_S≤P_T where P_s the pressure of a secondary air spring and P_T is a tare pressure.

1 1. The bogie of claim 10, wherein the function F is such that

F{P_S) = K - {P_S ~ P_T) if P_S > P_T where K is a positive constant.

12. The bogie of any one of claims 6 to 1 1 , wherein the control valve means include a first valve (58L) for feeding air to the one or more first air chambers and a second valve (58R) for feeding air to the one or more second air chamber, wherein the first valve is controlled by the pressure of the left secondary air spring and the second valve is controlled by the pressure of the right secondary air spring.

13. The bogie any one of the preceding claims, wherein the additional pneumatic means include left and right primary air springs (18L, 18R) located on the left and right sides of the median longitudinal vertical plane, respectively, for vertically supporting the frame on the set of wheels.

14. The bogie of claim 13, wherein the control valve means are such as to increase and/or decrease the pressure of the left and right primary air springs to the effect that the overall resulting force applied by the left and right primary air springs on the frame is larger than or equal to the overall resulting force applied by the left and right secondary air springs to the frame, respectively.

15. The bogie of any one of the preceding claims, wherein the additional pneumatic means include means (1 18) for controlling the lateral displacement of the frame relative to the superstructure perpendicular to the median longitudinal vertical plane of the frame.

16. The bogie of the preceding claim, wherein the means for feeding air to the additional pneumatic means are such that the frame is deflected laterally towards the one of the left and right secondary air springs which encounters the lower pressure.

17. A pneumatic circuit for a pneumatic suspension of a rail vehicle, comprising - left and right secondary branches (56L, 56R) provided with left and right secondary air springs (22L, 22R) respectively,

- levelling valve means (60L, 60R) for independently connecting each of the left and right secondary branches to a pressure source or to the atmosphere, - additional pneumatic actuator means (18L, 18R; 1 18L, 1 18R) including at least a first and a second additional variable volume chambers (34L, 34R; 134L, 134R),

- control valve means (58L, 58R) for feeding air to and releasing air from the first and second additional volume chambers as a function of the pressure in the left and right secondary branches, respectively.

18. A method of controlling a pneumatic suspension of a bogie of a rail vehicle, the bogie being provided with a frame and a set of wheels, the pneumatic suspension comprising at least a secondary suspension for vertically supporting a superstructure of the rail vehicle on the frame and additional pneumatic means for controlling relative motion between the frame and at least one of the superstructure and of the set of wheels, the secondary suspension comprising at least a first secondary air spring located on a first side of a median longitudinal vertical plane of the frame and a second secondary air spring located on a second side of the median longitudinal vertical plane of the frame, the additional pneumatic means including at least a first air chamber attached to the frame on the first side of a median longitudinal vertical plane of the frame and a second air chamber attached to the frame on the second side of the median longitudinal vertical plane of the frame, wherein the method comprises feeding air to and releasing air from the additional pneumatic means as a function of at least one or more pressure signals derived from the pressures of the left and/or right secondary air springs.

19. The method of claim 18 comprising:

- measuring a pressure difference between the first and second secondary air springs over time and feeding air to the additional pneumatic means based at least on the measured pressure difference over time.

20. The method of claim 18, comprising feeding air to the first air chamber as a function of the pressure of one of the first and second secondary air springs and feeding air to the second air chamber as a function of the pressure of the other one of the first and second secondary air springs.

21. The method of any one of claims 18 to 20, wherein the additional pneumatic means include a primary suspension for vertically supporting the frame on the set of wheels, the first air chamber being a first primary air spring located on the first side of a median longitudinal vertical plane of the frame and the second air chamber being a second primary air spring located on the second side of the median longitudinal vertical plane of the frame, wherein the method comprises feeding air to the first primary air spring and/or to the second primary air spring such that the difference of pressure between the first primary air spring and the second primary air spring is a positive increasing function of a difference of pressure between the first secondary air spring and the second secondary air spring.

22. The method of the preceding claim wherein the positive increasing function is a linear function.

23. The method of any one of the preceding claims, wherein the additional pneumatic means include means for controlling the lateral displacement of the frame relative to the superstructure perpendicular to the median longitudinal vertical plane of the frame, the method comprising feeding air to the additional pneumatic means such that the frame is deflected laterally towards the one of the first and second secondary air springs which encounters the greater pressure.