Railroad car body rotation control system

Abstract: A control system wherein an electronic control unit (14) generates a drive signal for a hydraulic device (13l, 13r, 15) for rotating the body (11) of a railroad car (3) about a longitudinal axis (G) of the car to reduce the non-compensated transverse acceleration to which the passengers are subjected. The control system presents a differentiating circuit (37) and a proportional circuit (31), which are supplied with an error signal (ϑe) equal to the difference between a reference signal (ϑc) and a feedback signal (ϑz) indicating the actual tilt angle of the body. The outputs of the differentiating circuit (37) and the proportional circuit (31) are added to generate a drive signal for driving the hydraulic device (13l, 13r, 15); and the differentiating circuit (37) presents a derivative gain (Gd) which is a function of the derivative in time (d|ϑe|/dt) of the error signal (ϑe) modulus.

Description: The present invention relates to a system for controlling rotation of a railroad car body. In particular, the present invention relates to a control system for rotating the body about a longitudinal axis of the car to reduce the acceleration to which the passengers are subjected. Variable-trim railroad cars are known which, when cornering, permit the body to rotate about a longitudinal axis of the car to compensate by gravitational acceleration the centrifugal transverse acceleration to which the passengers are subjected. When cornering, the passengers of a variable-trim railroad car are therefore subjected to a lateral force equal to the difference between the transverse centrifugal force and the transverse weight force. Known control systems comprise actuating devices (e.g. hydraulic) for regulating the tilt angle of the body on the basis of a drive signal. More specifically, control systems are known which comprise regulating circuits for generating the drive signal according to predetermined laws and on the basis of a number of input parameters measured on the car. Known regulating circuits comprise electronic circuits for generating a reference signal representing a reference body tilt angle pattern on the basis of a number of input parameters. The reference signal is compared with a signal indicating the actual tilt angle of the body, and the resulting error signal is used in closed-loop manner to calculate the drive signal. During the transient states at the start and end of the curve, known control systems fail to provide for accurate convergence of the reference and actual tilt angle signals, so that the actual tilt angle of the car often differs considerably from the reference angle, thus resulting in a lateral force sufficient to impair the comfort of the passengers. It is an object of the present invention to provide a control system designed to overcome the drawbacks typically associated with known systems. According to the present invention, there is provided a railroad car body rotation control system, as claimed in Claim 1. The present invention will be described with reference to the accompanying drawings, in which: Figure 1 shows a schematic cross section of a railroad car featuring the control system according to the present invention; Figure 2 shows a schematic diagram of an electronic circuit implementing the control system according to the present invention; Figures 3 and 4 show graphs of a number of quantities of the system according to the present invention; Figure 5 shows a schematic diagram of an electronic circuit implementing a known control system. Number 1 in Figure 1 indicates a control system applied to a variable-trim railroad car 3 substantially comprising two or more trucks 5, each connected elastically by a suspension 7 to axles 8 fitted with wheels 9 running along rails 10, and a body 11 tiltable by means of a hydraulic device 12 about a longitudinal axis (G) of car 3. Device 12 substantially comprises a right and left hydraulic actuator 13r, 13l interposed between body 11 and truck 5, and a servovalve 15 for supplying actuators 13r, 13l. When cornering, as shown schematically in Figure 1, the passengers (not shown) are subjected to non-compensated transverse acceleration Anc roughly according to the equation: Anc = V 2 /R - gϕ where V is the traveling speed of car 3, R the curve radius, g the gravitational acceleration, and  the angle between the supporting surface P of rail 10 and horizontal plane H. Non-compensated acceleration Anc may be reduced by rotating body 11 by angle ϑ about barycentric axis G, as shown in Figure 1, so that Anc equals: Anc = V 2 /R - g(ϕ+ϑ) which is obviously less than value [1]. System 1 comprises an electronic control unit 14 supplied with a number of parameters measured on car 3, and which generates a drive signal for servovalve 15 (shown schematically). Servovalve 15 presents an inlet 15a supplied with pressurized fluid 16, and at the outlet supplies hydraulic actuators 13r, 13l to regulate the tilt angle ϑ of body 11. More specifically, servovalve 15 presents a first outlet 15r communicating with actuator 13r via a conduit 17r; a second outlet 15l communicating with actuator 13l via a conduit 17l; and a recirculating outlet 18u. Servovalve 15 comprises a hollow outer casing (not shown) housing a central slide valve (not shown) movable axially in a straight direction X by a pressure difference as a function of a drive signal supplied to an electric driver 21. More specifically, servovalve 15 is an open-center type, i.e. when slide valve is positioned centrally (X=0) and driver 21 is not supplied, outlets 15r, 15l communicate with recirculating outlet 18u. The slide valve is also movable by driver 21 between a left limit position wherein inlet 15a communicates with outlet 15l and outlet 15r communicates with recirculating outlet 18u, and a right limit position wherein inlet 15a communicates with outlet 15r and outlet 15l communicates with recirculating outlet 18u. When servovalve 15 moves into the left limit position, pressurized fluid is supplied to actuator 13l, and actuator 13r is drained to rotate body 11 clockwise; and when servovalve 15 moves into the right limit position, pressurized fluid is supplied to actuator 13r, and actuator 13l is drained to rotate body 11 anticlockwise. Number 22 in Figure 2 indicates a regulating circuit of control unit 14, in accordance with the teachings of the present invention. Regulating circuit 22 comprises a first node 23 presenting an adding input 23a and a subtracting input 23b. Adding input 23a is supplied with a reference signal ϑc generated by a circuit 26 (e.g. an electronic map) supplied with a number of signals P1, P2, ..., Pn relative to parameters measured on car 3 (e.g. speed and acceleration of the car). Signal ϑc represents the ideal pattern (Ref) of angle ϑ as a function of time t, and as shown by the Ref curve in Figure 3, which presents a first portion A (between time t=0 and t=T1 ) in which angle ϑ increases steadily, and a second portion B in which angle ϑ assumes a constant value ϑlim (for t>T1). Subtracting input 23b is supplied with a feedback signal ϑz generated by a sensor 28 for measuring the instantaneous angle ϑ of body 11. Node 23 presents an output 23u communicating with the input 31a of a circuit 31 presenting a constant proportional gain Gp, and which generates a signal equal to the product of the input signal multiplied by proportional gain Gp. Output 23u presents an error signal ϑe = ϑc-ϑz representing the error between the angle ϑ requested by the control system (ϑc) and the actual angle (ϑz) of body 11 of car 3. Circuit 31 presents an output 31u communicating with a first adding input 34a of a node 34, which presents an output 34u presenting a signal I which, when amplified, forms the drive signal of driver 21. According to the present invention, regulating circuit 22 comprises a differentiating circuit 37 presenting an input 37a communicating with output 23u of node 23, and an output 37u communicating with a second adding input 34b of node 34. Circuit 37 generates a signal equal to the derivative of the input signal multiplied by a derivative gain term Gd. The derivative gain Gd of circuit 37 is a function of the derivative in time (d|ϑe|/dt) of the error signal ϑe modulus, as shown in Figure 4, which shows three portions: a first portion (K) between a first value (0) and a second value (e.g. 0.2 degrees/seconds) of the derivative of the error signal modulus (d|ϑe|/dt), and wherein derivative gain Gd is zero; a second portion (L) between a second value (e.g. 0.2 degrees/seconds) and a third value (e.g. 2.2 degrees/seconds) of the derivative of the error signal modulus (d|ϑe|/dt), and wherein derivative gain Gd increases steadily with a constant slope; and a third portion (M) wherein the derivative of the error signal modulus (d|ϑe|/dt) exceeds the third value (e.g. 2.2 degrees/seconds) and derivative gain Gd assumes a constant value (0.5 mA/°/second). Operation of circuit 22 will be described with reference to Figures 2 and 5, and commencing, for the sake of clarity, with a description of the operation of known control systems. A first known type of (proportional) control system comprises a node 23 (Figure 5) supplied with a reference signal ϑc indicating the ideal pattern of angle ϑ, and a feedback signal ϑz indicating the actual angle ϑ of the car body; node 23 supplies an error signal ϑe, equal to the difference between the reference and feedback signals, to a proportional circuit 31 presenting a constant proportional gain Gp; and circuit 31 generates a drive signal which, when converted and amplified, controls the solenoid valve supplying the hydraulic actuators to regulate the tilt angle ϑ of the body. The reference signal may be as shown by the Ref curve in Figure 3, and comprise a first portion A in which angle ϑ increases steadily, and a second portion B in which angle ϑ assumes a constant value ϑlim. During the transient states at the start and end of the curve, proportional control systems fail to provide for effectively "tracking" reference signal Ref, so that, for physical reasons not gone into here, the actual angle ϑ of the body differs considerably from the reference angle, as shown by the dot-and-dash curve Mis in Figure 3 indicating the actual pattern of angle in relation to time. As can be seen, at the start of the time scale (portion W), i.e. at the initial control stage, the Mis curve differs considerably from the Ref curve, and comes closer to it as reference signal Ref assumes a constant value (portion V). As a result, the non-compensated acceleration at the initial control stage is far from negligible, to the extent of impairing the comfort of the passengers. To overcome the above drawback, proportional-derivative control systems have been used, which feature a differentiating circuit D (shown by the dotted line in Figure 5) parallel to proportional circuit 31 and generating a signal proportional to the error signal derivative. Since this is positive at portion W and negative at portion V, the differentiating circuit reduces the error at portion W, but increases it at portion V, by adding to the Mis curve a positive term (error derivative greater than zero) at portion W, and a negative term (error derivative of less than zero) at portion V. The angle ϑ signal achieved using proportional-derivative systems is shown by the dotted-line curve Ref2, which shows a distinct error increase at portion V. The regulating circuit according to the present invention provides for effectively eliminating the drawbacks of both proportional and proportional-derivative systems. As shown in Figure 3 and the Figure 2 circuit: at portion W (in which the error signal derivative is positive), the gain Gd of circuit 37 increases alongside the error derivative, as shown in Figure 4, so that the positive signal produced by circuit 31 is added (at node 34) to the signal (Mis) generated by circuit 31, thus reducing the total error; at portion V (in which the error signal derivative is negative or barely positive), the gain Gd of circuit 37 is zero (or very small), as shown in Figure 4, so that to the signal (Mis) generated by circuit 31 is added (at node 34) a small (or zero) signal having very little effect on the Mis signal, and the error remains small. Regulator 22 therefore provides for effectively "tracking" the reference signal by maintaining a very small error between the reference and feedback signals at both portions W and V, so that the actual angle assumed by the car comes very close to the reference angle. Regulating circuit 22 also comprises an integrating circuit 40 presenting an input 40a connected to node 23 via the interposition of a threshold circuit 42, and an output 40u connected to an adding input 34c of node 34 via the interposition of a limiting circuit 44. Circuit 40 forms the integral of the input signal, and multiplies it by an integral gain term Gi; and circuit 42 is a threshold comparing circuit, which blocks any input signals with an absolute value below a threshold value ε. Operation of circuit 40 will now be described with reference to the physical operation of servovalve 15. The slide valve of an ideal servovalve is theoretically set to the central position (X=0; hydraulic zero) when no drive current is applied to driver 21 (electric zero), so that fluid is supplied at the same pressure to actuators 13r, 13l. In actual practice, however, for various physical reasons (e.g. variation in temperature of the servovalve components, acceleration of the servovalve, machining tolerances), the hydraulic zero does not correspond to the electric zero. That is, in a real servovalve (i.e. of the type fitted to railroad cars), the hydraulic zero is reached with a drive current of other than zero (bias current), and at any rate does not correspond to a zero drive current. Consequently, if regulating circuit 22 were not provided with integrating circuit 40, a zero drive current would be generated when the error is eliminated (balanced position of the system), servovalve 15, for the above reasons, would not be set to the hydraulic zero position, the pressure of actuators 13r, 13l would not be the same, and a position error of other than zero would remain. Circuit 40, however, provides for eliminating the above drawback by continually forming the integral of error signal ϑe and generating a signal increasing continually as long as error signal ϑe is present. Upon the balanced position being reached, the error is zeroed, the output of circuits 31, 37 is zero, but node 34 is supplied with the output signal of integrator 40. A drive current is thus generated which, by appropriately sizing gain Gi, forms the bias current for correctly positioning the slide valve and achieving hydraulic zero in the balanced position of the system. Clearly, changes may be made to the control system as described and illustrated herein without, however, departing from the scope of the present invention.

Claims: A system for controlling rotation of a railroad car body to reduce the non-compensated acceleration to which the passengers are subjected; the railroad car comprising a body (11) housing the passengers, and a rotation device (12, 13r, 13l, 15, 14) for rotating the body (11) about at least one longitudinal axis (G) of the car (3); said rotation device (12, 13r, 13l, 15, 14) rotating said body (11) by a given angle (ϑ) as a function of a drive signal (I); said control system (1) comprising electronic computing means (14, 22) for generating said drive signal (I); said electronic computing means (22) comprising: reference means (26) for generating a reference signal (ϑc) indicating the required pattern of said angle; first node means (23) supplied at the input (23a) with said reference signal (ϑc) and a feedback signal (ϑz) indicating the actual value of said angle; said first node means (23) generating at the output an error signal (ϑe) equal to the difference between said reference signal (ϑc) and said feedback signal (ϑz); proportional means (31) supplied with said error signal (ϑe) and generating at the output (31u) a signal equal to the product of said input signal (ϑe) multiplied by a proportional gain (Gp); differentiating means (37) presenting an input (37a) supplied with said error signal (ϑe), arid generating at the output (37u) a signal equal to the derivative of the input signal (ϑe) multiplied by a derivative gain (Gd); second node means (34) supplied with the output signal (31u) of said proportional means (31) and the output signal (37u) of said differentiating means (37); said second node means (34) generating at the output (34u) said drive signal; characterized in that said differentiating means (37) present a derivative gain (Gd) which is a function of the derivative in time (d|ϑe|/dt) of the modulus of said error signal (ϑe). A system as claimed in Claim 1, characterized in that said derivative gain (Gd) decreases alongside a reduction in the derivative in time of the modulus of said error signal (ϑe). A system as claimed in Claim 1 or 2, characterized in that said derivative gain (Gd) presents a pattern presenting at least three portions: a first portion (K) between a first value (0) and a second value (0.2 degrees/seconds) of the derivative of the error signal modulus (d|ϑe|/dt), and wherein the derivative gain (Gd) is substantially zero; a second portion (L) between the second value (0.2 degrees/seconds) and a third value (2.2 degrees/seconds) of the derivative of the error signal modulus (d|ϑe|/dt), and wherein the derivative gain (Gd) increases steadily with a constant slope; and a third portion (M) wherein the derivative of the error signal modulus (d|ϑe|/dt) exceeds the third value (2.2 degrees/seconds), and the derivative gain (Gd) assumes a constant value (0.5 mA/°/second). A system as claimed in any one of the foregoing Claims, characterized in that said reference means (26) generate a reference signal (ϑc) indicating the ideal pattern of said given angle (ϑ) as a function of time (t); said pattern comprising a first portion (A) wherein said angle (ϑ) increases steadily, and a second portion (B) adjacent to the first portion (A) and wherein said angle (ϑ) assumes a constant value (ϑlim). A system as claimed in any one of the foregoing Claims, characterized in that it comprises integrating means (40) presenting an input (40a) communicating with the output (23u) of said first node means (23), and an output (40u) communicating with an input (34c) of said second node means; said integrating means (40) generating at the output (40u) a signal equal to the integral of the input signal (ϑe) multiplied by an integral gain (Gi). A system as claimed in any one of the foregoing Claims, characterized in that said rotation device (12, 13r, 13l, 15, 14) comprises at least first and second actuators (13r, 13l) for rotating said body (11) in opposite directions; and a servovalve (15) for supplying said actuators (13r, 13l); said servovalve (15) presenting at least one inlet (15a) supplied with pressurized fluid (16); and a first and second outlet (15r, 15l) communicating respectively with said first and second actuators (13r, 13l); characterized in that said servovalve is an open-center type.

Inventors: BALOSSINI GUALTIERO, BOZZOLA PIERO, JACAZIO GIOVANNI, BALOSSINI, GUALTIERO, BOZZOLA, PIERO, JACAZIO, GIOVANNI
Applicants: FIAT FERROVIARIA SPA, MICROTECNICA, FIAT FERROVIARIA S.P.A., MICROTECNICA S.P.A.
Application year: 1995
Main classification: B61F5
IPC codes: B61F5