METHOD FOR CONTROLLING AN OPERATING CHARACTERISTIC OF A VEHICLE, SUCH AS THE GROUND CLEARANCE

Abstract

The invention relates to a method for controlling an operating characteristic (for example ground clearance or acceleration) of a vehicle (100) resting on a contact surface (200) by means of at least one landing gear (150) comprising means of actuating (160) adapted to vary a behaviour of the landing gear when the latter is in contact with the contact surface, whereby the said method makes the operating characteristic of the vehicle dependent upon a given set-point by generating a command intended for the means of actuating as a function of a difference (ε) between the operating characteristic and the set-point. According to the invention, the control system comprises the use of an estimation (P.sub.est) of a load (P) seen by the landing gear to generate a modification of the command so as to minimise a variation in the deviation caused by a variation in the load.

Claims

1. A method for controlling an operating characteristic (for example, ground clearance or acceleration) of a vehicle (100) resting on a contact surface (200) by means of at least one landing gear (150) comprising means of actuating (160) adapted to vary a behaviour of the landing gear when the latter is in contact with the contact surface, whereby the said method makes the operating characteristic of the vehicle (h) dependent upon a given set-point (hc) by generating a command (u) intended for the means of actuating as a function of a difference (ε) between the operating characteristic and the set-point, characterized in that the control system comprises the use of an estimation (P.sub.est) of a load (P) seen by the landing gear in order to generate a modification of the command (u) so as to minimise a variation in the deviation (c) caused by a variation in the load.

2. A method for controlling the landing gear according to claim 1, wherein the command (u) is modified by adding to it a corrective command (u.sub.corr) determined as a function of the estimation (P.sub.est) of the load seen by the landing gear

3. A method according to claim 2, wherein the corrective control (u.sub.corr) is determined by a predictive algorithm implementing a model of the behaviour of the landing gear (150) and anticipating the reaction of the landing gear to a variation in the load (P) seen by the landing gear.

4. A method according to claim 1, wherein the command (u) is determined by a controller (401) having characteristics dependent upon the estimation (P.sub.est) of the load seen by the landing gear.

5. A method according to claim 4, wherein the controller is of the PID type characterised by gains (k.sub.P,k.sub.I,k.sub.D) which are determined as a function of the estimation (P.sub.est) of the load (P) seen by the landing gear.

6. A method according to claim 5, wherein the gains (k.sub.P,k.sub.I,k.sub.D)are determined by means of a parametric function of the estimation of the load (P.sub.est), or a table of values.

7. A method according to claim 1, wherein the controlled operating characteristic is a ground clearance (h) of the vehicle.

8. A method according to claim 1, wherein the command (u) is intended for an electric motor (160) of the landing gear adapted to vary a load/sinkage characteristic of the landing gear capable of modifying the behaviour of the landing gear.

9. A method according to claim 8, applied to a vehicle whose landing gear comprises a shock-absorber cylinder whose motor (160) enables a no-load length to be varied.

10. A magnetically levitated vehicle comprising a landing gear associated with means of actuating arranged to implement a control system according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The invention will be better understood upon reading the following description of specific embodiments of the method of the invention, while referring to the appended figures, wherein:

[0015] FIG. 1A is a schematic view of a vehicle in the form of a train of magnetically levitated cars travelling in a tunnel under partial vacuum straddling a central rail and bearing on a contact surface by means of landing gear;

[0016] FIG. 1B is a front view of the device in FIG. 1A;

[0017] FIG. 2 is a schematic view of one of the landing gears fitted to one of the cars of the vehicle in FIG. 1, illustrating the means of actuating adapted to modify the load/sinkage characteristic of the landing gear;

[0018] FIG. 3 is a block diagram of a control system for the ground clearance of the vehicle in FIG. 1 according to a first particular mode of implementation of the method of the invention;

[0019] FIG. 4 is a block diagram of a control system for the ground clearance of the vehicle in FIG. 1 according to a first particular mode of implementation of the method of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0020] The invention is described here in application to a magnetically levitated vehicle as illustrated in FIGS. 1A and 1B in the form of a train 100 of cars 101 and 102.

[0021] The train 100 travels in a tunnel 103 partially evacuated of air in order to minimise aerodynamic drag, straddling a central rail 104 capable of generating a magnetic field suitable for levitating the train 100. The means of magnetic levitation are not detailed here, as they do not constitute the core of the invention.

[0022] For low speeds, where the levitating force is not great enough to fully support the train 100, each car rests on a contact surface 200 by means of landing gear 150 together forming a landing gear of the vehicle, each landing gear being deployable between a retracted position (as shown for car 101) in which the landing gear is remote from the contact surface 200, and a deployed position (as shown for car 102) in which the landing gear units 150 are in contact with the contact surface 200 and capable of transmitting, to the ground, a portion of the weight of the car that is not compensated for by the levitating forces (hereinafter the load).

[0023] As can be seen in FIG. 2, each landing gear 150 here comprises a swing arm 151 articulated onto the associated car and carrying at its free end, an axle 152, accommodating a wheel or wheels 153 for rotation. Each wheel 153 is equipped with a brake and a tyre 154 for driving on the contact surface 200. A shock-absorber cylinder 155 is coupled between the car and the swing arm 151. The shock-absorber cylinder 155 has a body 156 articulated onto the car, and in which a cylinder 158 of a damper 159 is slidably mounted and can be moved in the body 156 by means of an electric motor 160, here by means of a screw 161 driven in rotation by the electric motor 160.

[0024] A rod 162 is slidably mounted in the cylinder 158 of the damper 159. In a manner known per se, the damper 159 can be compressed under load to both suspend the car and dampen its vertical movements. The end of the sliding rod 162 is directly articulated onto the swing arm 151.

[0025] For a given position of the damper 159 in the body 156, the sinkage of the landing gear, and therefore the ground clearance h (measured here between the contact surface 200 and the lower part of the car body represented in dotted lines) depends on the load P transmitted to the ground by the wheel, which represents the part of the weight of the car not compensated for by the means of levitation, increased or decreased by the transfers of loads due in particular to the acceleration or braking of the vehicle. If the motor 160 pushes the damper 159 towards the ground, the no-load length of the shock-absorber cylinder 155 will be increased, which will lead to a lower sinkage of the landing gear, and therefore a higher ground clearance for the same load P. The electric motor 160 (as well as the means for transforming the rotary movement of the motor shaft into a displacement of the cylinder 158 of the damper 159, comprising the screw 161) therefore constitute means of actuating capable of modifying the load/sinking characteristic of the landing gear, and therefore the behaviour of the landing gear when the latter is in contact with the contact surface.

[0026] Note that the motor 160 can also be used to retract the landing gear to the retracted position, by fully retracting the damper 159 into the body 156.

[0027] In the modes of implementation detailed below, the invention aims to implement a control system in order to, when the landing gear is in the deployed position and the car is resting on the contact surface via the landing gear, generate a command u for the electric motor 160 of the landing gear so that the ground clearance h of the car remains as close as possible to a ground clearance set-point hc, with the invention consisting in modifying the command u for the motor as a function of an estimation of the load P seen by the landing gear.

[0028] According to a first embodiment of the invention, illustrated in FIG. 3, a feedback-loop control system 300 is implemented in which a command u intended for the motor 160 is generated by a PID type controller 301 from a deviation ε between the ground clearance set-point hc and an estimation h.sub.est of the ground clearance h, obtained using an estimator 302. The estimator 302 estimates the ground clearance by using data such as damper sinking, or by using a sensor to measure ground clearance directly.

[0029] Before the command u is sent to the motor 160 to adjust the position of the damper 159 in the body 156, the command u according to the invention is modified by adding a corrective command u.sub.corr which is determined with the help of a corrector 303 (implementing a transfer function) which receives as an input an estimation Pest of the load P seen by the landing gear, obtained with the help of an estimator 304. The estimator 304 estimates the ground load by exploiting data such as the internal pressure of the damper 159, or by measuring a force or stress seen by the landing gear 150 using, for example, a force sensor or strain gauges. The corrective command u.sub.corr makes it possible to modify the command u by anticipating a predictable increase in the deviation ε due to a sudden variation in load P. Thus, the command u can be changed quickly to compensate for a certain slowness in the reaction of the landing gear to this sudden variation in load P, so as to minimise variations in the deviation ε, and thus minimise variations in ground clearance.

[0030] The corrective control is preferably determined by the corrector 303 by means of a predictive algorithm implementing a behavioural model of the landing gear and anticipating the reaction of the landing gear to a change in the load P.

[0031] According to a second mode of implementation of the method of the invention illustrated in FIG. 4, and in which the elements common to the previous mode of implementation have a reference increased by one hundred, the control system 400 is still of the feedback-loop type and also implements a PID controller 401 to determine a command u from a deviation ε between a ground clearance set-point he and an estimation of the ground clearance h.sub.est. Unlike the first implementation mode, the estimation Pest of the load P seen by the landing gear is now used not to develop a corrective control, but to modify the gains k.sub.P, k.sub.I, k.sub.D used by the PID corrector 401 (respectively the gains of the proportional, integral and differential components of the PID). To this end, an adapter 403 is used which, on the basis of the load estimation P.sub.est, adapts the gains k.sub.P, k.sub.I, k.sub.D in order to change the command u according to the invention in the direction of minimising variations in the deviation ε, and thus minimising variations in ground clearance.

[0032] The gains k.sub.P, k.sub.I, k.sub.D are preferably calculated in real time from the load estimation P.sub.est, by using parametric functions, or tables of values, or by implementing sliding mode control.

[0033] The invention is not limited to what has just been described but encompasses every alternative solution within the scope of the claims.

[0034] In particular, although the invention has been described in application to a magnetically levitated vehicle moving in a tunnel under partial vacuum, the invention is applicable to other types of vehicles, including air-cushioned vehicles, or helicopters or gyroplanes where the rotor(s) can compensate for some of the weight of the aircraft while the aircraft is resting on the ground by its landing gear.

[0035] Although the means of actuating for modifying the load/sinkage characteristic of the landing gear takes the form of an electric motor capable of modifying the no-load length of a shock-absorber cylinder, the means of actuating may take other forms, such as means adapted to change the inflation pressure of the damper, or means of fluid transfer adapted to admit or, on the contrary, drain hydraulic fluid into, or from, the damper, or any other means capable of modifying the load/sinkage characteristic of the landing gear, and more generally the behaviour of the landing gear when it is in contact with the ground.

[0036] Although the controller illustrated in the two embodiments of the invention is a PID, the invention is not limited to the use of this type of controller, and any other type of controller may be used, for example a bang-bang controller or even a H∞ controller.

[0037] Although the methods detailed herein make the ground clearance dependent upon a ground-clearance set-point, the method of the invention can be used to control other vehicle operating characteristics, such as acceleration.