FR2689476A1 - Railway vehicle transverse suspension - has pneumatic absorbers supplied by electro-valves responding to signals derived from force signals resulting from bogie displacements - Google Patents

Abstract

The suspension includes pneumatic absorbers whose supply is controlled by electro-valves in response to control signals (SCD,SCG) issued from a regulator. The regulator (50) produces a force signal (CP) corresponding to the displacement of the bogie relative to the vehicle. The regulator functions as a slow servo-control when an estimate of displacement (X + kV) is within a predetermined interval, centred on a displacement value corresponding to alignment of body and bogie. The regulator functions as a fast servo-control when the displacement estimate (X + kV) is outside the interval. Units (52,53) forming the signal (SCD,SCG), are selectively activated as a function of the sign of the force signal (CP). A unit (59) determines the absorber pressure and a further unit (56) subtracts this pressure from a value corresponding to the force signal (CP). A unit (57) then determines the control signal (SCG,SCD) for transmission to the electro-valves. ADVANTAGE - Provides optimum travel comfort with moderate energy consumption.

Description

 The present invention relates to a transverse suspension for railway vehicle.

 Such a suspension usually comprises one or more actuators mounted between a bogie and the body of the vehicle. These actuators apply a transverse force in one direction or the other between these parts of the vehicle to ensure its lateral stability.

 Suspensions of this type equipped with pneumatic actuators are known to which regulated pressures are applied as a function of the lateral displacement between the body of the vehicle and the bogie.

 The suspension described in US-A-3,695,186 thus comprises a mechanical connection between the bogie, the body of the vehicle and a control rod of a valve controlling the differential pressures in two pneumatic cushions mounted in opposition. Due to this connection, a relative displacement between the bogie and the body of the vehicle modifies the conditions of supply of the cushions. According to this document, the sum of the pressures in the two cushions remains substantially constant. This results in a relative stiffness of the suspension when the vehicle is traveling in a straight line and at a high speed.

As train trains nowadays run at higher and higher speeds and in a straight line on the majority of the route, this type of suspension does not ensure the optimal comfort of the passengers.

 US-A-4,715,289 describes an electronic pressure regulation applied to a double-acting pneumatic cylinder mounted transversely between the bogie and the body of the vehicle. This regulation also takes into account the acceleration of the vehicle along the railway to apply pressures to dampen vibrations. The arrangement described in this document has the disadvantage of being relatively complex.

In addition, this arrangement also does not ensure the optimum comfort of travelers because the pressure regulation occurs continuously, including when the vehicle is traveling in a straight line.

 Permanent pressure regulation, as in the above embodiments, also has the disadvantage of a high energy consumption (pressurized air).

 A main object of the present invention is to overcome the disadvantages of known embodiments by providing a transverse suspension ensuring optimum comfort for travelers.

 Another object of the invention is that the suspension acts with a moderate energy consumption.

 The invention thus proposes a transverse suspension for railway vehicle, the vehicle comprising a body supported by bogies, the transverse suspension comprising actuating means arranged between the body and a bogie so as to be able to apply a lateral force between the body and the bogie, active control means associated with the actuating means for modifying the lateral force applied by the actuating means in response to control signals, detection means responsive to the movement of the body relative to the bogie, and control means connected to the detection means and to the active control means, these regulation means determining the control signals addressed to the active control means as a function of the detected displacement, characterized in that the regulation means comprise a regulator producing a setpoint of effort to be applied by the actuating means as a function of the displacement of u body relative to the bogie, this regulator having a fast servocontrol regime in which it can vary relatively quickly the force reference as a function of the displacement and a slow servocontrol in which it varies substantially more slowly the setpoint displacement-dependent force, in that the controller is adapted to operate in the slow servo regime when a displacement estimate is within a predetermined range centered on a displacement value corresponding to the alignment of the body with respect to the bogie, and in that the regulator is adapted to operate according to the fast servocontrol regime when the displacement estimate is outside said interval.

 When the vehicle is traveling in a straight line, the lateral displacement of the body remains in the predetermined interval, and the applied effort setpoint does not vary substantially, except possibly slowly.

The suspension then behaves flexibly and its action is practically not felt by travelers. If a lateral impulse occurs, for example because of a small punctual obstacle on the track or a connection between rails, this impulse is damped very gradually in slow servo mode, unless it causes a drift of beyond the predetermined range, in which case the damping of the pulse comprises a fast servocontrol step to prevent the displacement from reaching excessive values.

 When the vehicle is traveling in a curve, the body of the vehicle is subjected to sustained centrifugal acceleration relative to the bogie. As soon as the displacement estimate comes out of the predetermined interval, the regulator operates according to the fast servocontrol regime to increase the force applied in the opposite direction by the actuating means. After this effort exceeds that which balances the centrifugal acceleration, the displacement begins to decrease until it returns to within the predetermined range. The regulator then operates in slow servocontrol mode and maintains practically unchanged the applied force at a value lower than that which balances the centrifugal acceleration. The displacement then tends to increase again and the effort setpoint begins to fluctuate with a smaller and smaller amplitude until it converges towards the value that balances the centrifugal acceleration. A similar process takes place when the vehicle exits the curve to travel again in a straight line.

 This mode of effort control has the advantage of ensuring excellent comfort for travelers because the applied force variations are only low or negligible, when the body of the vehicle is close to the alignment with respect to the bogie , that is most often. This result is obtained while reducing the energy consumption of the suspension, because it is often the variations in the applied force that consume energy and not the maintenance of a given effort, particularly when the actuating means are pneumatic or hydraulic type.

 A preferred version of the suspension according to the invention comprises means for calculating the displacement estimate according to the expression X + kV, in which X denotes the displacement detected by the detection means, k denotes a predetermined constant and V denotes the time derivative of the detected displacement, and means for determining whether this displacement estimate is within said predetermined range.

 The displacement estimate used to determine the servo regime applied is then an extrapolation of the displacement taking into account the relative lateral speed between the body and the bogie. One can thus anticipate the displacement to exert the effort required at the appropriate time despite a certain control delay related to the response time of the actuating means. This delay is taken into account in the choice of the constant k.

Other features and advantages of the present invention will appear in the following detailed description of a preferred and nonlimiting exemplary embodiment, read in conjunction with the appended drawings, in which:
FIG. 1 is a diagram in axial view of a railway vehicle equipped with a transverse suspension according to the invention;
FIG. 2 is a diagram illustrating a transverse suspension according to the invention
FIG. 3 is a block diagram of a control circuit included in the suspension of FIG. 2; and
FIG. 4 represents timing diagrams that illustrate the operation of the regulation circuit of FIG. 3.

 Referring to Figure 1, a rail vehicle 1 comprises, in a conventional manner, a body or box 2 supported by bogies 3 on which are mounted the wheels 4 of the vehicle. In the example shown, the vertical suspension of the body 2 relative to the bogie 3 is constituted by pneumatic cushions 6 arranged between horizontal surfaces vis-à-vis the body and the bogie, and allowing a certain lateral displacement between the body and the bogie.

This lateral displacement is limited by limit stops indicated schematically by reference 5 in FIG.

 A transverse suspension according to the invention is provided to act on these lateral movements while ensuring satisfactory comfort for travelers.

 The transverse suspension comprises actuating means constituted, in the example shown in Figures 1 and 2, by two pneumatic cushions 7, 8 mounted transversely and in opposition between the bogie 3 and the body 2 of the vehicle 1. These two cushions 7 , 8 each comprise a flange fixed on a central support 9 carried by the bogie 3 and an opposite flange fixed on a respective lateral support 11, 12 carried by the body 2, the different flanges being all perpendicular to the direction D, horizontal and transverse to vehicle 1 and the railway. Thus, when compressed air is injected into one of the pneumatic cushions 7, 8, it exerts a lateral force between the body 2 and the bogie 3.

 The transverse suspension further comprises detection means responsive to the displacement of the body 2 relative to the bogie 3. In the example shown in FIGS. 1 and 2, these detection means comprise a linear displacement sensor 13 installed between the central support 9 carried by the bogie and one of the lateral supports 12 carried by the body 2. This sensor 13 may be a known differential transformer whose windings are fixed relative to the lateral support 12, and comprising a plunger connected to the central support 9 and slidable between the windings parallel to the transverse direction D of the vehicle 1. The sensor 13 delivers an output signal representing the lateral displacement X between the body 2 and the bogie 3 relative to an alignment position in which the body 2 is centered on the bogie 3 (X = 0) .The accuracy of the measurement and its linearity with respect to the variable X are optimized by feeding the winding p the sensor 13 by a sinusoidal voltage forming a carrier wave and connecting the secondary winding to a synchronous demodulator. The response time of the sensor 13 may be less than 2 ms.

The compressed air supply of the actuating cushions 7, 8 is illustrated in FIG. 2. Each cushion 7, 8 is connected by a pipe 16, 17 to respective active control means installed on the body of the vehicle. These active control means comprise, for each cushion 7, 8, an arrangement of solenoid valves 18, 19 with three states. The arrangements of solenoid valves 18, 19 are identical for the two cushions 7, 8. They each comprise a first solenoid valve 21 mounted between the pipe 16, 17 and a supply pipe 22, 23, and a second solenoid valve 24 mounted between the 16, 17 and the atmosphere.The three states of the arrangement of solenoid valves 18, 19 are: a state of closure of the cushion (solenoid valves 21 and 24 closed); a cushion supply state (21 open and 24 closed); and a purge state of the cushion (21 closed and 24 open), the two solenoid valves 21, 24 never being open simultaneously. The state of the solenoid valve arrangement 18, 19 is controlled by a tri-state control signal
SCG, SCD, from regulation means 26 which will be described later. The electromagnets of the solenoid valves 21, 24 are arranged so that the arrangement of solenoid valves 18, 19 is in the supply state of the cushion when the state of the control signal SCG, SCD corresponds to a zero voltage. The solenoid valves 21, 24 may be two separate elements or be integrated in a single component forming the arrangement of solenoid valves 18, 19.

 The supply lines 22, 23 of the cushions 7, 8 are connected to the main pipe 28 of the vehicle 1 via a circuit 27. The main pipe 28 is connected to a source of pressurized air 29, such as a tank or a compressor, and serves to supply other pneumatic components of the vehicle.

 The circuit 27 is constituted by a parallel assembly of an expander 31 and a pipe element 32, this parallel assembly being connected upstream to the main pipe 28, and downstream to the supply pipes 22, 23 of the cushions via a switching solenoid valve 33.

 The expander 31 constitutes the passive control means of the transverse suspension. It is set to deliver downstream a predetermined constant pressure, for example about 0.3 MPa (3 bar).

The pipe element 32 may also comprise a not shown expander delivering downstream a higher pressure, for example about 1 MPa (10 bar).

 The solenoid valve 33 constitutes the two-state switching means of the transverse suspension.

It comprises two inputs respectively connected to the pipe element 32 and the expander 31, and an outlet communicating with the supply lines 22, 23 of the cushions 7, 8.

 In a first state, the solenoid valve 33 closes its inlet connected to the expander 31 and makes its outlet communicate with its inlet connected to the duct element 32 to allow the cushions 7, 8 to communicate with the pressurized air source 32 when the arrangement of corresponding solenoid valves 18, 19 is in the supply state.

 In its second state, the solenoid valve 33 closes its inlet connected to the pipe element 32 and communicates its output with its input connected to the expander 31 to commission the expander 31. The state of the switching solenoid valve 33 is controlled by a signal from the control means 26. The solenoid electromagnet 33 is arranged so that, when its supply voltage is zero, the solenoid valve 33 is in the second state of commissioning of the regulator 31 .

When the switching solenoid valve 33 is in this second state (zero voltage), the supply voltage of the solenoid valve arrangements 18, 19 is also zero, so that the solenoid valve arrangements 18, 19 are in the state power.

 The regulation means consist of an electric regulation circuit 26 installed inside the vehicle 1. This regulation circuit 26 is connected to the displacement sensor 13, to the solenoid valve arrangements 18, 19 and to the switching solenoid valve. 33. When powered from the positive terminal 36 of a battery 35 of the vehicle 1, the circuit 26 is adapted to determine the control signals SCG, SCD addressed to the arrangements of solenoid valves 18, 19 and thus modify the effort lateral control applied by the cushions 7, 8. The control signals SCG, SCD are determined as a function of the displacement X detected by the heading Leur 13 according to a predetermined servo law, the switching solenoid valve 33 then being in its first state ( regulator 31 out of service). It is thus possible to regulate the pressures of the cushions 7, 8 to optimize the comfort of the persons traveling in the vehicle 1.

 The electrical supply path 37 of the regulation circuit 26, the switching solenoid valve 33 and the solenoid valve arrangements 18, 19, extending between the positive terminal 36 of the battery 35 and the regulation circuit 26, comprises two electrical contacts 38. Each of these contacts 38 is part of a displacement limit sensor 39 disposed at the end stops 5 of the body 2 relative to the bogie 3 (Figures 1 and 2). The sensor 39 further comprises a spring 41 which urges the contact 38 towards its closed position, and a rod 42 connected to the contact 38 and arranged to receive the body 2 when it reaches the limit value of displacement corresponding to the end position. , so as to actuate the contact 38 to its open position.Thus, the contacts 38 are always closed except when the displacement of the body 2 relative to the bogie reaches a limit value. In this circumstance, the opening of one of the contacts 38 interrupts the power supply of the components 26, 33, 18, 19.

 When the displacement of the body 2 reaches a limit value (for example X = + 65 mm), it is considered that the operation of the pressure regulation is abnormal, without having to identify which fault is at the origin of this abnormal operation. The interruption of the power supply by one of the contacts 38 then makes the switching solenoid valve 33 go into the commissioning state of the expander 31 and the arrangements of solenoid valves 18, 19 in the state of supply of the cushions 7, 8. The pneumatic cushions 7, 8 are therefore passively controlled via the expander 31 which supplies the cushions 7, 8 constantly and independently of the regulating means 26. The cushions 7, 8 then apply between the body 2 and the bogie 3 a substantially constant lateral force corresponding to the nominal pressure delivered by the expander 31. The vehicle can thus continue to circulate, despite the existence of the defect of the regulation, in acceptable comfort conditions and without risking to damage the end stops 5 or to engage the template imposed on the vehicle.

 The passive control by the expander 31 is also put into service during a failure of the battery 35, which would of course interfere with the normal operation of the control circuit 26.

 It is also possible to provide in the circuit 26 means for detecting faults of this circuit or of the sensor 13, and consequently to control the state of the switching solenoid valve 33. These means then perform a direct or intrinsic fault detection. , as opposed to the indirect or extrinsic detection performed by the displacement limit sensors 39.

The regulating circuit 26 is shown in more detail in the diagram of FIG. 3. It comprises a PID regulator 50 which receives a shaped signal representing the displacement X measured by the sensor 13 and delivers a setpoint of effort CP in displacement function X. PID controllers (Proportional
Integral-Derivative) are well known to those skilled in the art.

The force reference is a pressure value assigned a sign. The pressure value corresponds to that which results in the desired effort in one of the cushions. For example, the force reference is positive (CP> 0) when it is necessary to apply the pressure value CP in the right cushion 8 to compensate for a shift to the right X> 0, and negative (CP <0 ) when it is necessary to apply the pressure value CP in the left cushion 7 to compensate for a leftward movement X <0.The regulator output
PID 50 is connected to a comparator 51 which, when the force setpoint CP is positive, transmits this instruction to means 52 for forming the control signal SCD addressed to the arrangement of solenoid valves 19 relative to the right cushion 8, and which, when the force reference CP is negative, transmits the absolute value -CP of this setpoint to means 53 for forming the control signal SCG addressed to the arrangement of solenoid valves 18 relative to the left cushion 7. The means 52 The control signal formation means CP are thus selectively activated according to the sign of the force command CP. When the means 52 for forming the control signal SCD are activated (CP> 0), the means 53 for forming the signal control SCG are deactivated, so that the signal SCG corresponds to a zero supply voltage of the solenoid valves 21, 24 of the arrangement 18 relative to the left cushion 7, and that this arrangement 18 is in the purge state of the cushion 7. When the means The means 52 for forming the control signal SCD are deactivated, so that the signal SCD corresponds to a zero supply voltage of the solenoid valves 21, 24 of the solenoid valves 21, 24. the arrangement 19 relating to the right cushion 8, and that this arrangement 19 is in the purge state of the cushion 8.Thus, the control signals SCG,
SCD produced by the control circuit 26 are such that there is always at least one of the arrangements of solenoid valves 18, 19 in the purge state.

In the example shown, the means 52, 53 for forming the control signals are identical for the two control signals SCG, SCD. These means 52 or 53 comprise a subtracter 56 whose positive input receives the CP or -CP signal from the comparator 51, and whose negative input receives a signal MP corresponding to a determination of the pressure prevailing in the respective pad. The output of the subtracter 56 is connected to an element 57 which determines the control signal SCG or SCD to be addressed to the arrangement of solenoid valves 18 or 19 as a function of the result DP of the subtraction effected by the subtractor 56. The output of the element 57 is connected to a stage 58 which includes the solenoid valve control transistors 21, 24 and which formats the SCG or SCD signals. The control signal SCG or SCD determined by the element 57 corresponds to the state of closure of the cushion (F) when the result
DP of the subtraction is, in absolute value, lower than a predetermined threshold, the supply state of the cushion (A) when the result DP of the subtraction is positive and greater than said threshold, and the purge state of the cushion (P) when the result DP of the subtraction is negative and greater than said threshold.

The output of the element 57 is furthermore connected to an integrator 59 which determines the pressure prevailing in the cushion 7 or 8. This integrator 59 produces the signal
MP addressed to the negative input of the subtracter 56.

The integrator 59 calculates the pressure in the cushion by numerical integration on the basis of the state (A, F or P) of the solenoid valve arrangement controlled by the signal SCG or SCD determined by the element 57. To perform this integration, it is necessary to provide the integrator 59 with parameters such as the pressure rise rates in the cushion in the supply state or the pressure drop rates in the cushion in the purge state. . These parameters are substantially fixed and can be determined experimentally. Based on these parameters, the integrator 59 integrates the feed and purge times to determine in real time the pressure MP prevailing in the cushion. Integrator 59 simulates a pressure sensor that would be installed to measure the pressure in the cushion.

 The PID regulator 50 has two servo control regimes: a fast servocontrol regime in which it can vary relatively quickly the effort setpoint CP as a function of the displacement X, and a slow servo regime in which it varies substantially more slowly the load setpoint CP as a function of the displacement X. In order to be able to implement these two speeds, the regulator 50 comprises two sets of distinct PID coefficients. The first game, used in rapid control mode, is composed of coefficients chosen, conventionally, according to the dynamic parameters of the suspension and the body 2.

In the second set, used in slow servo mode, the coefficient of the derivative term is zero, so that this derivative term (which normally serves to accelerate the transient oscillations) is zero, and the coefficient of the integral term is very low compared to the corresponding coefficient of the first game. Thus, in slow servo mode, the term of integral (dominating) varies very slowly, so that the CP effort setpoint also varies very slowly.

 In order to select the servocontrol speed of the PID regulator 50, an estimation of displacement X + kV is calculated at each cycle of the regulator by calculation means 60 receiving the signal representing the displacement X detected by the sensor 13. The calculation means 60 comprise a differentiator, a multiplier and an adder arranged to calculate the displacement estimate according to the expression X + kV, wherein k denotes a predetermined constant and V denotes the time derivative of the displacement X, that is to say the relative lateral velocity of the body 2 with respect to the bogie 3. The displacement estimate X + kV is supplied to a comparator 61 which determines whether its absolute value IX + kVt is greater or less than a predetermined value XM.Si IX + kVI < XM, that is, if the displacement estimate X + kV is within a predetermined interval [-XM, XM] centered on the displacement value X = 0 corresponding to the ali 2 of the body 2 relative to the bogie 3, the comparator 61 controls the PID regulator 50 to operate with its second set of coefficients corresponding to the slow servo regime. In the opposite case, if the displacement estimate X + kV is outside the interval [-XM, XM] (IX + kVI> XM), the comparator 61 commands the regulator 50 to operate with its first set of coefficients corresponding to the fast servo regime. The predetermined value XM may for example be of the order of 15 mm.

 The displacement estimate X + kM is an extrapolation of the actual displacement. The constant k can be chosen from the order of the response times of the cushions 7, 8 when they are powered or purged, so that these response times do not lead to a systematic delay of the forces applied.

 The control circuit 26 may be implemented in the form of a digital processing circuit, except for the amplifier stages 58 and the means for shaping the displacement signal X. The control signals SCG, SCD may be each constituted by a single three-state signal or by the combination of two separate two-state signals transmitted separately to the two solenoid valves 21, 24 by respective lines.

 The operation of the PID regulator 50 is illustrated by the timing diagrams of FIG. 4. These chronograms show an example of an evolution as a function of the time t of the lateral acceleration AL between the body 2 and the bogie 3, of the displacement X, of the estimation of displacement X + kV, and of the effort setpoint CP delivered by the PID regulator 50.

 In the first part of the timing diagrams, until time t0, the vehicle 1 is traveling in a straight line. Small perturbations can cause minor fluctuations in the X displacement around the 0 value. These fluctuations practically do not affect the effort setpoint which remains substantially zero as long as the estimate X + kV remains within the interval [-XM, XM] (slow servo regime).

The two cushions 7, 8 are kept purged
At the instant t0, the vehicle 1 approaches a curve of its course, corresponding to a lateral acceleration to the right ALO of the body 2 with respect to the bogie 3. The displacement X then begins to increase and the estimate X + kV still increases faster. At time tl, the displacement estimate X + kV reaches the value
XM, and the regulator 50 goes into a fast servocontrol mode and quickly increases the effort setpoint
CP to apply by the right cushion 8, the left cushion 7 remaining purged.

 After the force set point CP has exceeded the value PO which balances the lateral acceleration ALO, the displacement X and the estimate X + kV decrease until the estimate X + kV comes back inside the the interval (-XM, XM) at time t2 At this instant, the regulator 50 goes into a slow servocontrol regime and the effort setpoint CP stabilizes while the displacement X continues to decrease. At time t3, the estimate X + kV reaches the value -XM and leaves the interval (-XM, XM) The effort setpoint CP decreases and then stabilizes at a value less than PO.

 After some oscillations of the CP force setpoint, it converges and becomes substantially equal to PO. The displacement estimate X + kV then remains within the interval E-xM, XM and the effort setpoint CP varies only slightly and slowly (slow servo regime) to progressively reduce the displacement X around the value 0. After the transient oscillations, since the CP effort setpoint only varies slightly, the right cushion 8 remains closed and no longer consumes compressed air, while the left cushion 7 remains completely purged.

 When the vehicle leaves the curve to return in a straight line, the effort setpoint stabilizes around the zero value after a few oscillations of the same type.

 Although the invention has been described with reference to a preferred embodiment, it will be understood that this example is not limiting and that various modifications can be made to it without departing from the scope of the invention.

Claims (13)

 1. A transverse suspension for a railway vehicle (1), the vehicle comprising a body (2) supported by bogies (3), the transverse suspension comprising actuating means (7, 8) arranged between the body (2) and a bogie (3) so as to be able to apply a lateral force between the body and the bogie, active control means (18, 19) associated with the actuating means (7, 8) for modifying the lateral force applied by the means actuating in response to control signals (SCG, SCD), detecting means (13) responsive to movement (X) of the body relative to the bogie, and regulating means (26) connected to the detecting means ( 13) and the active control means (18, 19), these control means (26) determining the control signals (SCG, SCD) addressed to the active control means (18, 19) as a function of the detected displacement (X). characterized in that the regulating means (26) comprises a regulator (50) producing a force reference (CP) to be applied by the actuating means (7, 8) as a function of the displacement (X) of the body (2) with respect to the bogie (3), this regulator (50) having a speed of rapid control in which it can vary relatively quickly the force reference (CP) as a function of the displacement (X) and a slow servocontrol regime in which it varies substantially more slowly the effort setpoint (CP) in displacement function (X), in that the controller (50) is adapted to operate in the slow servo regime when a displacement estimate (X + kV) is within a predetermined range centered on a displacement value corresponding to the alignment of the body (2) with respect to the bogie (3), and in that the regulator (50) is adapted to operate according to the fast servocontrol regime when the displacement estimate (X + kV) is outside said range.  2. Suspension according to claim 1, characterized in that the actuating means comprise two pneumatic cushions (7, 8) mounted transversely and in opposition between the bogie (3) and the body (2) of the vehicle.  3. Suspension according to claim 2, characterized in that the active control means comprise, for each airbag (7, 8), an arrangement of solenoid valves (18, 19) having three states, namely a closed state. of the cushion, a state of supply of the cushion in which the cushion (7, 8) communicates with a source of pressurized air (29), and a state of purge of the cushion, in which the cushion (7, 8) communicates with the atmosphere, the state of the arrangement of solenoid valves being controlled by a control signal (SCG, SCD) from the control means (26).  4. Suspension according to claim 3, characterized in that the regulating means (26) are arranged to produce control signals (SCG, SCD) such that there is always at least one arrangement of solenoid valves (18, 19) in the purge state.  5. Suspension according to one of claims 3 or 4, characterized in that the regulating means (26) comprise, for each arrangement of solenoid valves (18, 19), means (52, 53) for forming the signal. control means, these training means of the control signals being selectively activated according to the sign of the effort setpoint (CP).  6. Suspension according to claim 5, characterized in that the means (52, 53) for forming the control signal (SCG, SCD) addressed to the arrangement of solenoid valves (18, 19) relating to a pneumatic cushion ( 7, 8) comprise means (59) for determining the pressure in this cushion, means (56) for subtracting the pressure thus determined from a pressure value corresponding to the force reference (CP), and a means (57) to determine the control signal (SCG, SCD) to be addressed to the arrangement of solenoid valves (18, 19) depending on the result (DP) of the subtraction.  7. Suspension according to claim 6, characterized in that the means (59) for determining the pressure in the cushion (7, 8) is adapted to calculate said pressure by integration on the basis of the state of the arrangement. of solenoid valves (18, 19) controlled by the control signal (SCG, SCD).  8. Suspension according to one of claims 1 to 7, characterized in that it comprises means (60) for calculating the displacement estimate according to the expression X + kV, wherein X denotes the displacement detected by the means. detecting (13), k is a predetermined constant and V is the time derivative of the detected displacement (X), and means (61) for determining whether said displacement estimate is within said predetermined range.  9. Suspension according to one of claims 1 to 8, characterized in that the controller (50) is a PID controller having two sets of separate coefficients.  10. Suspension according to one of claims 1 to 9, characterized in that it further comprises passive control means (31) selectively operated and can supply the actuating means (7, 8) so as to constant and independently of the control means (26), and two-state switching means (33) activating the passive control means (31) in one of these two states.  11. Suspension according to claim 10, characterized in that the switching means (33) are electrically controlled and are in the commissioning state of the passive control means (31) when they are not electrically powered. .  12. Suspension according to one of claims 10 or 11, characterized in that it comprises at least one displacement limit sensor (39) changing state when the displacement (X) of the body (2) relative to the bogie (3) reaches a limit value, and in that each displacement limit sensor (39) is mounted to switch the switching means (33) to the commissioning state of the passive control means ( 31) when the displacement of the body with respect to the bogie reaches the limit value.  13. Suspension according to claim 12, characterized in that each displacement limit sensor (39) comprises an electrical contact (38) which is closed when the displacement of the body (2) relative to the bogie (3) is less than the limit value and open when said displacement reaches the limit value, this electrical contact (38) being mounted on a supply path (37) of the switching means (33).