EP0704364B1

EP0704364B1 - Damper for damping transverse deflection of a railway vehicle and damping system

Info

Publication number: EP0704364B1
Application number: EP19950306897
Authority: EP
Inventors: Kenichi c/o Railway Techn. Res. Inst. Kasai; Kimiaki c/o Railway Techn. Res. Inst. Sasaki; Takayuki c/o Railway Techn. Res. Inst. Shimomura; Shougo c/o Railway Techn. Res. Inst. Kamoshita; Haruhiko c/o Kayaba Kogyo K. K. Kawasaki; Yasuo c/o Kayaba Kogyo K. K. Tuyuki; Masakazu c/o Kayaba Kogyo K. K. Nakazato; Toshiaki c/o Kayaba Kogyo K. K. Kamei
Original assignee: Railway Technical Research Institute; Kayaba Industry Co Ltd
Current assignee: Railway Technical Research Institute; KYB Corp
Priority date: 1994-09-30
Filing date: 1995-09-29
Publication date: 2001-11-28
Anticipated expiration: 2015-09-29
Also published as: DE69524173D1; DE69524173T2; EP0704364A1

Description

This invention relates to a damping damper of a semiactive control for damping a transverse deflection generated in a body of a railway vehicle, and a system for damping a transverse deflection of the body using said damping damper.
Generally, in running vehicles such as railway vehicles, automobiles and the like, hydraulic dampers are interposed between a truck and a vehicle body or wheels and the vehicle body, and vertical vibrations and transverse vibrations generated in the body during running are attenuated by these hydraulic dampers so as to suppress the vertical and transverse deflections of the body.
These hydraulic dampers merely make use of a flow resistance of internal working oil to attenuate the vertical and transverse vibrations of the body.
Accordingly, the attenuation action of the vertical and transverse vibrations of the body by way of the hydraulic dampers merely depends upon the relative vibration speed between mounting points of the vertical and transverse vibrations generated in the body, and the attenuation action takes place irrespective of the behavior of the body, thus failing to obtain a sufficient comfortableness to ride-in.
For the above-described reason, in the automobiles, there has been used a damping system of a so-called active control which detects the behavior of the vehicle body to positively damp the body by oil pressure in order to further improve the comfortableness to ride-in.
However, in the damping system of an active control, a hydraulic pump as a power source and special control valves are necessary to suppress the vertical and transverse vibrations of the body, and in addition a controller is also necessary to control and operate these control valves.
As described above, since the damping system of the active control is provided with the hydraulic pump as a power source, on the contrary, it does harm the comfortableness to ride-in if an erroneous operation should occur.
Further, the controller requires a complicated electronic circuit to control the control valves. This leads to a complicated structure of the controller itself and a higher cost accordingly.
From the foregoing, recently, in the automobiles, attention has been paid to a damping system of a so-called semiactive control which is in response to the amplitude or frequency of vibrations of the vehicle body to control the damping force without using a power source.
This damping system of the semiactive control is simple in both soft aspect and hard aspect and so has an advantage in that it can be easily used in operation and in maintenance.
However, on the other hand, the damping system of the semiactive control as described above poses problems mentioned below if it is applied to damp a transverse deflection, of a railway vehicle which is extremely large in the body mass on the damping side different from the automobile, without modification.
That is, the damping force variable damper used as the damping system of the semiactive control expands and contracts even when the truck is abruptly transversely vibrated at a high speed in the same direction as that of the vehicle body, and produces damping forces accordingly.
Therefore, the body is pressed by these truck or wheels through the damping force variable damper, as a result of which the transverse deflection of the body is increased rather than the transverse deflection of the body is suppressed to not only impair the running stability as the vehicle but also greatly lower the comfortableness to ride-in.
Besides, it is necessary to diligently turn on and off the control valves for the damping force variable control in the damping force variable damper in response to the magnitude of the amplitude of the transverse deflection generated in the body and high or low frequency to regulate the damping force. This poses a problem of durability because the control valves for the control of the damping force are frequently turned on and off.
Moreover, when the variable control of the damping-force by the damping force variable damper was disabled due to the occurrence of the turning-off of the power supply or the abnormal conditions, the damping force variable damper is abruptly actuated to the stroke end due to the inertia of the truck or the body and as a result a great impact force is generated at the stroke end.
According to a first aspect of the present invention, there is provided a variable damping force damper for damping transverse deflection of a railway vehicle by suppressing the transverse deflection of a vehicle body while using semiactive control which controls the generated damping force of the damper when the damper is transversely interposed between a vehicle truck and the vehicle body and which adjusts to the state of the transverse deflection between the vehicle truck and the vehicle body, said variable damping force damper comprising:
a stroke sensing cylinder;
a flowpassage for allowing only a flow of working fluid from a head side chamber toward a rod side chamber of said stroke sensing cylinder;
a reservoir in communication with the head side chamber of said stroke sensing cylinder through a suction valve;
an unload valve for a pressure side having the head side chamber, disposed in a flowpassage for bringing the head side chamber into communication with the reservoir;
an unload valve for an expansion side likewise disposed in the flowpassage for bringing the rod side chamber into communication with the head side chamber; and
a damping force control circuit disposed between the rod side chamber and the reservoir, wherein said damping force control circuit has a plurality of damping force generating elements arranged in series and on-off valves for bypass-controlling the damping force generating elements, said on-off valves being turned on and off to control the generated damping force in the damping force control circuit.
According to a second aspect of the present invention, there is provided a variable damping force damper for damping transverse deflection of a railway vehicle by suppressing the transverse deflection of a vehicle body while using semiactive control which controls the generated damping force of the damper when the damper is transversely interposed between a vehicle truck and the vehicle body and which adjusts to the state of the transverse deflection between the vehicle truck or wheels and the vehicle body, said variable damping force damper comprising:
a stroke sensing cylinder;
a flowpassage for allowing only a flow of working fluid from a head side chamber toward a rod side chamber of said stroke sensing cylinder;
a reservoir in communication with the head side chamber of said stroke sensing cylinder through a suction valve;
an unload valve for a pressure side having the head side chamber, disposed in a flowpassage for bringing the head side chamber into communication with the reservoir;
an unload valve for an expansion side likewise disposed in the flowpassage for bringing the rod side chamber into communication with the head side chamber; and
a damping force control circuit disposed between the rod side chamber and the reservoir, wherein said damping force control circuit has a maximum damping force generating element and a normally open proportional flow rate control valve or proportional pressure control valve arranged in parallel, said proportional flow rate control valve or the proportional pressure control valve being operated to continuously control the generated damping force in the damping force control circuit.
According to a third aspect of the present invention, there is provided a system for damping transverse deflection of a railway vehicle in which a variable damping force damper under semiactive control is transversely interposed between a vehicle truck and a vehicle body to suppress the transverse deflection of the vehicle body, wherein:
said variable damping force damper comprises a stroke sensing cylinder; a flowpassage for allowing only a flow of working fluid from a head side chamber toward a rod side chamber of said stroke sensing cylinder; a reservoir in communication with the head side chamber of said stroke sensing cylinder through a suction valve; an unload valve for a pressure side having the head side chamber, disposed in a flowpassage for bringing the head side chamber into communication with the reservoir; an unload valve for an expansion side likewise disposed in the flowpassage for bringing the rod side chamber into communication with the head side chamber; and a damping force control circuit disposed between the rod side chamber and the reservoir; and
said system is arranged such that a damper signal detected by the stroke sensing cylinder is divided into a damper displacement signal and a damper speed signal, an optimum damping force value is computed by a computer on the basis of said damper displacement signal and said damper speed signal and a vehicle speed signal from detection means provided on the vehicle body, the generated damping force in the damping force control circuit is controlled on the basis of said result of computation, and the deflection direction of the vehicle body at that time is determined by the computer according to the vehicle speed signal from said detection means to selectively switch and control the unload valves for pressure side and expansion side.
In the preferred embodiments, the transverse deflection damping damper with its semiactive control has improved durability without increasing transverse deflection of the vehicle body due to transverse deflection of the truck and reduces the frequency of on/off switching of control valves for controlling the damping force.
The transverse deflection damping damper can function as a normal hydraulic damper even at the time of disablement of control due to an occurrence of abnormal conditions such as turn-off of power supply, so as to be fail-safe.
The transverse deflection damping damper can simplify flowpassage construction by common use of flowpassages and shorting the length of the flowpassage to thereby reduce the flow resistance of a working fluid.
In the preferred embodiments, the stroke sensing cylinder constituting the damper body of the damping damper serves as a damper in a unidirectional flow for circulating a working fluid in the rod side chamber through a damping force control circuit and a reservoir even at the time of operation in either direction of the extension side or compressed side by the function of a flowpassage for allowing only a flow of working fluid from the head side chamber toward the rod side chamber and a suction valve.
Thereby, in the stroke sensing cylinder, a ratio of sectional area between a piston and a piston rod is set to 2 : 1 whereby the flow rate of working fluid, on the expanded side, which is extruded into the damping force control circuit as the stroke sensing cylinder expands and compresses is the same as the compressed side.
On the other hand, at the time of occurrence of the transverse deflection when the stroke sensing cylinder expands and compresses in correspondence to the deflecting direction of the body, the computer determines the transverse deflection state of the body on the basis of the damper signal from the stroke sensing cylinder and the body speed signal from the detection means.
The computer computes the value of the damping force closest to the optimum value to be generated in the damping force control circuit on the basis of the results of determination to switch and control the on-off valve or the proportional flow rate control valve or the proportional pressure control valve incidental to the damping force generating element so as to adjust to the results of computation, control the damping force generated in the damping force control circuit and effectively damp the transverse deflection of the body.
In addition to the above, the computer detects that, when a situation occurs where the stroke sensing cylinder reaches the operating end, the stroke sensing cylinder reaches near the operating end in response to a damper displacement signal on the basis of the damper signal from the stroke sensing cylinder.
Then, the on-off valve or the proportional flow rate valve or the proportional pressure control valve is switched to control the generated damping force to the maximum in the damping force control circuit so as to relieve the impact generated in the operating end of the stroke sensing cylinder.
In the case where the truck is deflected at higher speed in the same direction as that of the body, the operating direction of the stroke sensing cylinder is reversed, and the working fluid pressure on the basis of the damping force generated in the damping force control circuit is applied to the stroke sensing cylinder.
The working fluid pressure acting on the stroke sensing cylinder causes the body to be pressed in the direction of transverse deflection at that time through the stroke sensing cylinder so as to increase the transverse deflection of the body by the transverse deflection of the truck.
However, the computer determines the direction of the transverse deflection of the body every time on the basis of the body speed signal from the detection means provided on the body to selectively output a switching signal to the unload valve for the pressure side and the unload valve for the expansion side.
These switching signals selectively switch the unload valve for the pressure side or expansion side in the direction opposite to the operating direction of the stroke sensing cylinder which expands and compresses to the unload state.
Thereby, when the stroke sensing cylinder expands, the unload valve for the pressure side is switched to an on position by a switching signal from the computer to bring the head side chamber into communication with the reservoir, whereas,when the stroke sensing cylinder compresses, the unload valve for the expansion side is switched to an on position by a switching signal from the computer to bring the rod side chamber into communication with the head side chamber.
As a result, the working fluid pressure acting on the stroke sensing cylinder automatically escapes to the reservoir or the head side chamber through the unload valve for the pressure side or expansion side which has been switched to the on position corresponding to the deflecting direction of the body.
Therefore, the working fluid pressure applied to the head side chamber or the rod side chamber of the stroke sensing cylinder due to the occurrence of the situation as described above is automatically discharged into the reservoir or the head side chamber through the unload valve for the pressure side or the expansion side to prevent the transverse deflection of the body from being increased due to the transverse deflection of the truck.
Thus, the above-described situation does not use the on-off valve for controlling the damping force or the proportional flow rate control valve or the proportional pressure control valve but uses the unload valves for the pressure side and the expansion side to be on-off controlled in correspondence to the deflecting direction of the body which is low in frequency.
Accordingly, the frequency of operation of the on-off valve or the proportional flow rate control valve or the proportional pressure control valve in the damping force control circuit is reduced and the durability of the control valves is materially improved.
Furthermore, when the control becomes disabled due to the occurrence of the abnormal condition such as power off, the stroke sensing cylinder always causes the working fluid to extrude toward the damping force control circuit as it extends and compresses in order to keep the unload valves for the pressure side and expansion side at an off position despite the fact that the transverse deflection occurs in the body.
Moreover, in the damping force control circuit, the on-off valve for controlling the damping force or the proportional flow rate control valve or the proportional pressure control valve arranged in the aforementioned circuit automatically returns to its off position.
Thereby, the damping damper secures a preset damping force by the function of the on-off valve for controlling the damping force or the proportional flow rate control valve or the proportional pressure control valve to damp the transverse deflection of the body, and the damping damper serves as a normal hydraulic damper to perform a fail-safe.
Preferred non-limiting embodiments of the invention will now be described with reference to the accompanying drawings, in which:-
FIG. 1 is a block diagram showing one embodiment of a damper system for damping a transverse deflection of a railway vehicle;
FIG. 2 is a schematic view showing a structural example of the damping damper used for the damper system for damping a transverse deflection;
FIG. 3 is a schematic view showing a modified embodiment of the damping damper;
FIG. 4 is a schematic view showing a further structural embodiment of the damping damper; and
FIG. 5 is a schematic view showing a further modified embodiment of the damping damper.
In FIG. 1, damping dampers 3 and 4 of a semiactive control type according to this invention are horizontally arranged opposedly each other between a truck 1 and a vehicle body 2.
While, in these damping dampers 3 and 4 of a semiactive control system, only one out of them may be used, it is to be noted that, if the two dampers are used as in this embodiment, a fail-safe effect can be obtained when one of them is out of order.
On the body 2 is provided a detector 5 formed from an accelerometer or a speedometer for detecting a state of transverse vibration of the body 2.
The damping damper 3 and 4 comprise a stroke sensing cylinder 6, a reservoir 7 and a damping force control circuit 8, as shown in FIG. 2.
The stroke sensing cylinder 6 has a cylinder 9 the interior of which is divided by a slidable piston 10 into a head side chamber 11 and a rod side chamber 12, and a piston rod 13 extends from the piston 10 towards outside.
The piston rod 13 has scale memories 14 incised thereon in a predetermined spaced relation, and a displacement sensor 15 is fixed opposite to the scale memories 14.
The damping dampers 3 and 4 keep positions to have check valves 16 and 17 at their respective off positions and are provided with an unload valve 18 for a pressure side and an unload valve 19 for an expansion side which become conductive at a position at which the dampers are turned on.
The unload valve 18 for the pressure side is provided in the midst of a flowpassage 20 for bringing the head side chamber 11 of the cylinder into communication with the reservoir 7 of the head side chamber 11, and is arranged so that,at its off position, a flow of working fluid flowing from the head side chamber 11 towards the reservoir 7 is checked by the check valve 16 whereas,at its on position, the head side chamber 11 is placed in communication with the reservoir 7 through the flowpassage.
On the other hand, the unload valve 19 for the expansion side is provided in the midst of a flowpassage 21 which extends from an inlet side of the unload valve 18 for the pressure side towards the rod side chamber 12, and is arranged so that, at its off position, a flow of working fluid flowing from the rod side chamber 12 towards the head side chamber 11 is checked by the check valve 17 whereas, at its on position, the rod side chamber 12 is placed in communication with the head side chamber 11.
The head side chamber 11 is also communicated with the reservoir 7 through a suction flowpassage 23 having a suction valve 22, and the rod side chamber 12 is communicated with the reservoir 7 from the damping force control circuit 8 through an oil filter 24.
The damping force control circuit 8 comprises three throttles 25, 26 and 27 which are damping force generating elements connected in series, three on-off valves 28, 29 and 30 for selecting the use of the three throttles 25, 26 and 27, a high pressure relief valve 32 which is a damping force generating element disposed in the midst of a flowpassage 31 for bringing the rod side chamber 12 into communication with the reservoir 7, and a low pressure relief valve 34 which is likewise a damping force generating element disposed in the midst of a flowpassage 33 for bringing a portion between the throttles 26 and 27 into communication with the reservoir 7.
In the case of this embodiment, the on-off valve 28 intermittently controls a bypass flowpassage 35 which bypasses the throttles 25 and 26, the on-off valve 29 intermittently controls a bypass flowpassage 36 of the throttle 26, and the on-off valve 30 intermittently controls a bypass flowpassage 37 of the throttle 27.
Out of these three on-off valves 28, 29 and 30, particularly, the on-off valve 30 is constituted by a normally closed valve so that, at its off position, the bypass flowpassage 37 is kept in a cutoff state, different from other on-off valves 28 and 29.
With this arrangement, when only the on-off valve 30 is switched to an on position, the on-off valve 30 causes the bypass flowpassage 37 to open so that the inlet side of the throttle 25 is directly brought into communication with the reservoir 7 through the bypass flowpassage 37 from the bypass flowpassage 35.
Therefore, the working fluid passing through the damping force control circuit 8 bypasses the throttles 25, 26 and 27 and flows into the reservoir 7 through the bypass flowpassage 37 from the bypass flowpassage 35. The damping force control circuit 8 is maintained in the lowest damping force generating state on the basis of the flowpassage resistance of the bypass flowpassages 35 and 37.
On the other hand, when the on-off valves 28 and 29 are switched to an on position, the bypass flowpassage 37 as well as the bypass flowpassages 35 and 36 are placed in the closed state, and the working fluid passing through the damping force control circuit 8 sequentially flows through the throttles 25, 26 and 27.
As a result, the damping force control circuit 8 is switched to the state where the highest damping force is generated while cooperating with the high pressure relief valve 32 with pressure losses of the throttles 25, 26 and 27 superimposed.
When the on-off valve 28 as well as the on-off valve 30 are switched to an on position, the bypass flowpassage 35 is closed, and the inlet side of the throttle 26 is communicated with the reservoir 7 through the bypass flowpassages 36 and 37.
Thereby, the working fluid passing through the damping force control circuit 8 flows from the throttle 25 to the reservoir 7 through the bypass flowpassages 36 and 37, and the damping force control circuit 8 generates the damping force on the basis of the pressure loss of the throttle 25.
When all the on-off valves 28, 29 and 30 are kept at an off position (the state shown in FIG. 2), the inlet side of the throttle 25 is communicated with the inlet side of the throttle 27 while bypassing the throttles 25 and 26 through the bypass flowpassage 35.
Therefore, the working fluid passing through the damping force control circuit 8 flows from the bypass flowpassage 35 to the reservoir 7 through only the throttle 27, and the damping force control circuit 8 generates the damping force on the basis of the pressure loss of the throttle 27 under a restriction of a low pressure relief valve 34.
When all the on-off valves 28, 29 and 30 are switched to an on position from the state shown in FIG. 2, only the inlet side of the throttle 27 is communicated with the reservoir 7 through the bypass flowpassage 37.
As a result, the working fluid passing through the damping force control circuit 8 flows from the throttles 25 and 26 to the reservoir 7 through the bypass flowpassage 37, and the damping force control circuit 8 generates the damping force with pressure loss of the throttle 26 superimposed to pressure loss of the throttle 25.
On the other hand, when only the on-off valve 28 is switched to an on position, the bypass flowpassage 35 is closed while the inlet side of the throttle 26 remains communicated with the reservoir 7 through the throttle 27 from the bypass flowpassage 36.
Thereby, the working fluid passing through the damping force control circuit 8 flows into the reservoir 7 through the bypass flowpassage 36 and the throttle 27 from the throttle 25, and the damping force control circuit 8 generates the damping force with pressure loss of the throttle 27 superimposed to pressure loss of the throttle 25.
As described above, the damping force generated in the damping force control circuit 8 is controlled in six stages by suitably selecting the on-off valves 28, 29 and 30 to turn them on and off.
Needless to say, the damping force generated in the damping force control circuit 8 can be also controlled in six stages or more or less by increasing or decreasing the number of the throttles and the on-off valves, or changing the construction of the bypass flowpassage.
On the other hand, the vehicle body 2 is relatively displaced in the transverse direction between it and the truck 1 due to the transverse deflection during the running and,as such relative displacement in the transverse direction occurs, the stroke sensing cylinder 6 extends and contracts.
When the stroke sensing cylinder 6 extends, it extrudes the working fluid within the rod side chamber 12 towards the damping force control circuit 8 through the oil filter 24 while sucking the working fluid in the reservoir 7 into the head side chamber 11 through the suction flowpassage 23 from the suction valve 22.
On the contrary, when the stroke sensing cylinder 6 contracts, the suction valve 22 is closed to cause the working fluid in the head side chamber 11 to flow into the rod side chamber 12 through the unload valve 19 for the expansion side irrespective of on/off of the unload valve 19 for the expansion side from the flowpassage 20, and the working fluid in quantity corresponding to an integration of an entered body of the piston rod 13 from the rod side chamber 12 is extruded to the damping force control circuit 8 through the oil filter 24.
Because of this, the flow rate of the working fluid extruded towards the damping force control circuit 8 is ┌(A - a) x L┘ at the time of extension and ┌a x L┘ at the time of compression, wherein A is a sectional area of the cylinder 9, a is a sectional area of the piston rod 13, and L is a stroke of the stroke sensing cylinder 6.
From the foregoing, the stroke sensing cylinder 6 can select a ratio ┌A : a = 2 : 1┘ between the sectional area A of the cylinder 9 and the sectional area a of the piston rod 13 to thereby make the flow rate of the working fluid extruded towards the damping force control circuit 8 at the time of extension equal to that at the time of compression or can suitably select the ratio of flow rate by changing the first mentioned ratio.
The working fluid having been extruded towards the damping force control circuit 8 flows into the reservoir 7 under the selection of the throttles 25, 26 and 27 as the on-off valves 28, 29 and 30 are turned on and off to generate a predetermined damping force as a relative displacement occurs between the truck 1 and the vehicle body 2, thus effectively suppressing the transverse deflection of the vehicle body 2.
The displacement sensor 15 provided on the stroke sensing cylinder 6 cooperates with the scale memories 14 of the piston rod 13 to detect a relative displacement between the cylinder 9 and the piston rod 13 to output it as a damper signal S from an amplifier 38.
Turning back to FIG. 1, the damper signal S is processed into a plus damper displacement signal W1 (extension side) and a minus damper displacement signal W2 (compression side) by a sensor signal processing circuit 39 for conversion of a computer signal, and processed into a plus damper speed signal V1 (extension side) and a minus damper speed signal V2 (extension side) calculated on the basis of the damper displacement signal W1 and W2, which are thereafter input into a computer 40.
On the other hand, the detector 5 provided on the vehicle body 2 detects a deflection of the vehicle body 2 as a vehicle body signal T, the vehicle body signal T being also processed to the plus vehicle body speed signal U1 and the minus vehicle body speed signal U2 according to the transverse deflection direction of the vehicle body 2 by a processing circuit 41 for converting a computer signal, said signals U1 and U2 being input into the computer 40.
In the case where the detector 5 is a speedometer, the signal is processed into a plus vehicle speed signal U1 and a minus vehicle speed signal U2 by a processing circuit 41, whereas in the case where the detector 5 is an accelerometer, the acceleration is once converted into a speed, after which it is processed into a plus vehicle speed signal U1 and a minus vehicle speed signal U2.
The computer 40, on one hand, determines the direction of the transverse deflection of the vehicle body 2 at that time according to the vehicle speed signals U1 and U2 being transmitted from the detector 5 on the side of the vehicle body 2 and outputs a switching signal P or Q to the unload valve 18 or 19 for pressure side or extension side through a valve driver circuit 42 to selectively turn them on or off.
Further, the computer 40 computes the control logic of the damping force generated by the damping dampers 3 and 4 on the basis of the damper speed signals V1 and V2 and the damper displacement signals W1 and W2 being transmitted from the displacement sensor 15 of the stroke sensing cylinder 6 together with the vehicle speed signals U1 and U2.
The computer 40 then outputs the results of computation as switching signals X, Y and Z to the on-off valves 28, 29 and 30 of the damping force control circuit 8 in the damping dampers 3 and 4 through the valve driver circuit 42 to turn on or off the on-off valves 28, 29 and 30 on the basis of the results of computation.
The damping dampers 3 and 4 perform the damping operation while being operated under the control as will be described below with respect to the transverse relative displacement generated between the truck 1 and the vehicle body 2.
In this case, the damping dampers 3 and 4 merely perform their damping operation in a reversed direction but perform similar function in connection with the operation.
Accordingly, if only one operation of these damping dampers 3 and 4 is described, the other operation will be easily understood. Here, for the sake of preventing the complexity of description, the damper system using the damping damper 3 will be described hereinafter.

1 ○ [When vehicle body 2 is deflected leftward]

When the vehicle body 2 is deflected leftward during running, the detector 5 operates to input the plus vehicle speed signal U1 into the computer 40 through the processing circuit 41.
The computer 40 then determines that the vehicle body 2 is deflected leftward on the basis of the plus vehicle speed signal U1, and outputs the switching signal P to the unload valve 18 for pressure side to switch it to an on position.
If the truck 1 is deflected leftward at a lower speed than that of the vehicle body 2 or if it is deflected rightward contrary to the former, the stroke sensing cylinder 6 is operated on the extension side to extrude the internal working fluid to the damping force control circuit 8.
On the other hand, the displacement sensor 15 of the stroke sensing cylinder 6 operates to input the plus damper displacement signal W1 and the plus damper speed signal V1 to the computer 40 through the sensor signal processing circuit 39.
The computer 40 determines the extension speed of the stroke sensing cylinder 6 at that time on the basis of the plus damper speed signal V1 and the previously mentioned plus vehicle speed signal U1 and computes the damping force value closest to the optimum valve from the extension speed.
The computer 40 then selectively outputs the switching signals X, Y and Z to the on-off valves 28, 29 and 30 accordingly, and adequately controls the generated damping force of the damping force control circuit 8 while on-off controlling the on-off valves 28, 29 and 30 to effectively suppress the leftward transverse deflection of the vehicle body 2.
And yet, when the situation occurs in which the stroke sensing cylinder 6 reaches the extended end, the computer 40 determines it on the basis of the plus damper displacement signal W1 from the displacement sensor 15.
When reaching the neighborhood of the extended end, the computer 40 outputs the switching signals X and Y to switch the on-off valves 28 and 29 to an on position while keeping the on-off valve 30 at an off position so that the generated damping force of the damping force control circuit 8 is kept at the maximum value to relieve the impact at the extended end.
Even so, the situation in which the stroke sensing cylinder 6 reaches the extended end occurs, in many cases, when the vehicle body 2 is abruptly subjected to the transverse deflection at a high speed.
Therefore, even if the damping force control circuit 8 is merely placed in the state where the maximum damping force is generated, pressure of the working fluid being extruded from the stroke sensing cylinder 6 to the damping force control circuit 8 possibly abnormally rises.
At this time, however, the high pressure relief valve 32 is actuated to return the working fluid being extruded from the stroke sensing cylinder 6 to the reservoir 7 through the flowpassage 31 and the flowpassage 20 to prevent the damping dampers 3 and 4 from being damaged by the high pressure working fluid while limiting the pressure of the working fluid by the high pressure relief valve 32.
In this manner, the damping force control circuit 8 effectively suppresses the transverse deflection of the vehicle body 2 to perform the damping operation while generating the damping force according to the magnitude of the extension speed of the stroke sensing cylinder 6.
Suppose now that when the vehicle body 2 is deflected leftward, for example, the truck 1 is deflected leftward at a higher speed than that of the transverse deflection of the vehicle body 2 leftward due to a dislocation of the rails or the like. The stroke sensing cylinder 6 is compressed so that a fluid pressure corresponding to the generated damping force of the damping force control circuit 8 is generated also in the head side chamber 11 of the stroke sensing cylinder 6.
The fluid pressure generated in the head side chamber 11 acts as a force to press the stroke sensing cylinder 6 in the extending direction due to a difference in pressure receiving area between the head side chamber 11 and the rod side chamber 12 generated by the presence of the piston rod 13 to greatly deflect the vehicle body leftward. It is therefore necessary not to produce the fluid pressure.
However, even in this case, since the vehicle body 2 itself still deflects leftward, the computer 40 continues to output the switching signal P to the unload valve 18 for pressure side on the basis of the plus vehicle speed signal U1 from the detector 5 to keep holding the unload valve 18 for pressure side at an on position.
Thereby, the working fluid of the head side chamber 11 escapes to the reservoir 7 through the unload valve 18 for pressure side from the flowpassage 20.
As a result, the fluid pressure is not generated in the head side chamber 11 of the stroke sensing cylinder 6, and the stroke sensing cylinder 6 prevents the vehicle body 2 from being more greatly deflected leftward.

2 ○ [When vehicle body 2 is deflected rightward]

When the vehicle body 2 is deflected rightward contrary to the former, the detector 5 operates to input the minus vehicle speed signal U2 into the computer 40 through the processing circuit 41.
The computer 40 then outputs the switching signal Q to the unload valve 19 for extension side on the basis of the minus vehicle speed signal U2 to switch it to an on position.
Here, when the truck 1 is deflected leftward at a lower speed than that of the vehicle body 2, or when it is deflected leftward reversely to the vehicle body 2, the stroke sensing cylinder 6 is operated on the compression side to extrude the internal working fluid towards the damping force control circuit 8.
By the operation of the stroke sensing cylinder 6 towards the compression side, the displacement sensor 15 causes the computer 40 to receive the minus damper speed signal V2 and the minus damper displacement signal W2.
The computer 40 determines the compression speed of the stroke sensing cylinder 6 at that time on the basis of the minus damper speed signal V2 and the minus vehicle speed signal U2, in the same manner as the previous case where the vehicle body 2 is deflected leftward, to compute the damping force value closest to the optimum value from the compression speed.
The computer selectively outputs the switching signals X, Y and Z to the on-off valves 28, 29 and 30 accordingly to adequately control the generated damping force of the damping force control circuit 8 while on-off controlling the on-off valves 28, 29 and 30 to effectively suppress the transverse deflection of the vehicle body 2 rightward. And yet, when the situation occurs in which the stroke sensing cylinder 6 reaches the extended end, the computer 40 determines it on the basis of the minus damper displacement signal W2 from the displacement sensor 15.
When reaching the neighborhood of the extended end, the computer 40 outputs the switching signals X and Y to switch the on-off valves 28 and 29 to an on position while keeping the on-off valve 30 at an off position so that the generated damping force of the damping force control circuit 8 is kept at the maximum value to relieve the impact at the extended end.
Further, when the vehicle body 2 is abruptly subjected to the transverse deflection at a high speed, the high pressure relief valve 32 is actuated to return the working fluid being extruded to the flowpassage 21 through the unload valve 19 on the extension side from the stroke sensing cylinder 6 to the reservoir 7 by the flow passages 31 and 20, in the same manner as the previous case where the vehicle body 2 is subjected to the transverse deflection leftward, to prevent the damping dampers 3 and 4 from being damaged by the high pressure working fluid.
In this manner, the damping force control circuit 8 effectively suppresses and reduces the transverse deflection of the vehicle body 2 while generating the damping force according to the magnitude of the extension speed of the stroke sensing cylinder 6.
Even in the above case, when the truck 1 is deflected rightward at a higher speed than that of the transverse deflection of the vehicle body 2 rightward due to a dislocation of the rails or the like, the stroke sensing cylinder 6 is extended so that a fluid pressure corresponding to the generated damping force of the damping force control circuit 8 is generated in the rod side chamber 12 of the stroke sensing cylinder 6.
The fluid pressure generated in the rod side chamber 12 acts as a force to press the stroke sensing cylinder 6 in the compressing direction to increase the transverse deflection of the vehicle body 2 rightward. It is therefore necessary not to produce the fluid pressure.
However, even in this case, since the vehicle body 2 itself still deflects rightward, the computer 40 continues to output the switching signal Q to the unload valve 19 for extension side on the basis of the minus vehicle speed signal U2 from the detector 5 to keep holding the unload valve 19 for extension side at an on position.
Thereby, the working fluid of the rod side chamber 12 escapes to the head side chamber 11 of the stroke sensing cylinder 6 through the unload valve 19 for extension side and the flowpassage 20 from the flowpassage 21.
As a result, the fluid pressure is not generated in the rod side chamber 12 of the stroke sensing cylinder 6, and the stroke sensing cylinder 6 prevents the vehicle body 2 from being more greatly deflected rightward.

3 ○ [At the time of disablement of control due to occurrence of power-off and abnormal situation]

Even in this case, since the stroke sensing cylinder 6 repeats its extension and compression operation as the vehicle body 2 is subjected to the transverse deflection leftward and rightward, the working fluid in the stroke sensing cylinder 6 is extruded towards the damping force control circuit 8.
However, at the time of power off or when a standby signal is extinguished, the switching signals Q, X, Y and Z from the computer 40 are cut off simultaneously therewith. Therefore, the unload valves 18 and 19 for pressure side and extension side and the on-off valves 28, 29 and 30 are maintained at an off position shown in FIG. 2.
Thereby, the working fluid extruded to the damping force control circuit 8 from the stroke sensing cylinder 6 flows into the reservoir 7 through the throttle 27 under the control of the low pressure relief valve 34, and acts as a normal damper while generating a predetermined damping force at pressure loss of the throttle 27 to damp the transverse deflection of the vehicle body 2 leftward and rightward.
FIG. 3 shows a modified example in which a part of the construction of damping dampers 3a and 4a is changed. In the embodiment shown in FIG. 2 so far mentioned, when the stroke sensing cylinder 6 is compressed, the flowpassage for causing the working fluid to flow from the head side chamber 11 towards the rod side chamber 12 is constituted by the flowpassages 20 and 21 provided outside and the check valve 17 provided at an off position of the unload valve 19 for extension side.
On the other hand, in the modified embodiment shown in FIG. 3, check valves are not provided at an off position of an unload valve 18a for pressure side and an unload valve 19a for extension side, respectively, but said off position is made to be a block position.
Instead, the stroke sensing cylinder 6 is provided with a flowpassage 21a for bringing the head side chamber 11 and the rod side chamber 12 into mutual communication through the piston 10. A check valve 17a for allowing only a flow of working fluid from the head side chamber 11 to the rod side chamber 12 is disposed in the flowpassage 21a, which point is different from the embodiment shown in FIG. 2.
Even with this arrangement, the stroke sensing cylinder 6, when compressed, closes the suction valve 22 and opens the check valve 17a to cause the working fluid in the head side chamber 11 to flow to the rod side chamber 12 from the flowpassage 21a.
The working fluid in the quantity corresponding to a part for entered volume of the piston rod 13 through the oil filter 24 from the rod side chamber 12 is extruded towards the damping force control circuit 8.
Thus, also in the embodiment shown in FIG. 3, the stroke sensing cylinder 6 acts as a unidirectional flow damper. Accordingly, it can perform the operation similar to the case of the FIG. 2 embodiment as previously mentioned, as can be easily understood from the previous description.
In the damping dampers 3, 4 and 3a, 4a so far mentioned, the transverse deflection of the vehicle body 2 was suppressed while digitally controlling the generated damping force of the damping force control circuit 8 in six stages.
On the other hand, in damping dampers 3b and 4b shown in FIG. 4, the transverse deflection of the vehicle body 2 is suppressed while continuously analogically controlling the damping force generated in a damping force control circuit 8b, as in the embodiment shown in FIG. 4.
The damping force control circuit 8b in these damping dampers 3b and 4h is different from the previous embodiment and modified embodiment in construction wherein the throttle 26, the on-off valve 29 and the bypass flowpassage 36 are removed from the damping force control circuit 8 and a proportional flow rate control valve 28b is employed in place of the on-off valve 28.
The proportional flow rate control valve 28b comprises a normally open valve similar to the previous on-off valve 28, and as the proportional flow rate control valve 28b operates, it serves as a device for controlling an opening degree of the throttle of a bypass flowpassage 35 of the throttle 25.
On the contrary, an on-off valve 30 comprises a normally closed valve as previously mentioned in connection with the embodiment shown in FIG. 2, in which,at an on position, the throttle 27 and the low pressure relief valve 34 are maintained in a bypass state by a bypass flowpassage 37.
Thereby, when the opening degree of the throttle of the proportional flow rate control valve 28b is operated into a zero state, the working fluid extruded from the rod side chamber 12 of the stroke sensing cylinder 6 to the damping force control circuit 8b sequentially passes the throttles 25 and 27 and flows into the reservoir 7.
As a result, the damping force control circuit 8b is maintained in the state where the highest damping force is generated while cooperating with a high pressure relief valve 32 with pressure losses caused by the throttles 25 and 27 superimposed each other.
On the other hand, when the opening degree of the throttle of the proportional flow rate control valve 28b is operated to the maximum, the total opening degree of the throttle of the throttle 25 and the proportional flow rate control valve 28b assumes the maximum and the pressure loss caused by the opening degree of the throttle assumes the minimum. The working fluid extruded to the damping force control circuit 8b results in only the pressure loss caused by the throttle 27 under the control of the low pressure relief valve 34 and is maintained in the state where the minimum damping force is generated.
From the foregoing, if the opening degree of the throttle of the proportional flow rate control valve 28b is analogically continuously changed between the zero and the maximum opening degree, the opening degree of the throttle of the proportional flow rate control valve 28b is added to the opening degree of the throttle of the throttle 25, and the pressure loss at the portions of the throttle 25 and the proportional flow rate control valve 28b continuously lowers accordingly.
Moreover, since the pressure loss caused by the total opening degree of the throttle of the throttle 25 and the proportional flow rate control valve 28b is superimposed to the pressure loss caused by the opening degree of the throttle of the throttle 27, the generated damping force in the damping force control circuit 8b continuously changes between the maximum state and the minimum state.
The on-off valve 30 is opened whereby the throttle 27 and the inlet side and outlet side of the low pressure relief valve 34 are short -circuited and maintained at the same pressure. Thus, the generated damping force at the damping force control circuit 8b is controlled merely by the pressure loss caused by the throttle 25 and the proportional flow rate control valve 28b.
Accordingly, when the proportional flow rate control valve 28b is operated from this state to the maximum opening degree, the generated damping force at the damping force control circuit 8b becomes a damping force which is further lower than the previous minimum damping force.
Thus in the case where a variable region of the generated damping force at the damping force control circuit 8b is used in the maximum and minimum damping force generating region through the operation of the proportional flow rate control valve 28b, the on-off valve 30 need not always be provided and there can be dispensed with it.
So, if the transverse deflection speed of the vehicle body 2 is within a normal range, the computer 40 sends the switching signal X corresponding to the transverse deflection speed to the proportional flow rate control valve 28b to control the opening degree of the throttle thereof.
Thereby, the working fluid extruded to the damping force control circuit 8b from the stroke sensing cylinder 6 flows into the reservoir 7 through the throttle 25, the proportional flow rate control valve 28b and the throttle 27, and the generated damping force is controlled by the controlling operation of the proportional flow rate control valve 28b to suppress the transverse deflection of the vehicle body 2.
At the same time, the computer 40 outputs the switching signal Z also to the on-off valve 30 according to the transverse deflection speed of the vehicle body 2 to effectively suppress the transverse deflection of the vehicle body 2 while on-off controlling the on-off valve 30 by way of the switching signal Z.
Moreover, when the situation occurs wherein the stroke sensing cylinder 6 reaches the neighborhood of the extension end or the compression end, the computer 40 determines it on the basis of the plus or minus damper displacement signals W1 and W2 from the displacement sensor 15 and,when reaching the neighborhood of the extension end or the compression end, the opening degree of the throttle of the proportional flow rate control valve 28b is made small by the switching signal X from the computer 40.
Thereby, the working fluid extruded to the damping force control circuit 8 from the stroke sensing cylinder 6 flows into the reservoir 7 through the throttles 25, 27 and the proportional flow rate control valve 28b under the control of the high pressure relief valve 32 to keep high the generated damping force of the damping force control circuit 8b to relieve the impact at the extension end and the compression end.
Further, in the case where the vehicle body 2 is abruptly subjected to the transverse deflection at a high speed, the proportional flow rate control valve 28b is closed by the switching signal X from the computer 40, and the damping force control circuit 8 assumes the state where the maximum damping force is generated.
At this time, however, the high pressure relief valve 32 is actuated to return the working fluid extruded from the stroke sensing cylinder 6 to the reservoir 7 through the flowpassage 21, the flowpassage 31 and the flowpassage 20 to prevent the damping damper 3 from being damaged by the high pressure working fluid while limiting the working fluid pressure by the high pressure relief valve 32.
Further, damping dampers 3c and 4c shown in FIG. 5 are modified examples of the damping dampers 3b and 4b shown in FIG. 4, and the only difference therebetween is the provision of a proportional pressure control valve 28c in place of the proportional flow rate control valve 28b shown in FIG. 4.
That is, the value of the damping force acting on the stroke sensing cylinder 6 is originally determined by a pressure difference between both the working fluids of the head side chamber 11 and the rod side chamber 12.
In the FIG. 4 embodiment, the proportional flow rate control valve 28b for continuously proportion-controlling the opening degree of the throttle is disposed in the damping force control circuit 8. The proportional flow rate control valve 28b is proportionally operated according to the transverse deflection speed of the vehicle body 2 to thereby control the working fluid pressure of the rod side chamber 12, and the value of the damping force acting on the stroke sensing cylinder 6 is controlled while adjusting to the transverse deflection speed of the vehicle body 2.
Thus, even if the proportional pressure control valve 28c is used in place of the proportional flow rate control valve 28b, as in the modified example shown in FIG. 5, the proportional pressure control valve 28c is proportionally operated according to the transverse deflection speed of the vehicle body 2 whereby the working fluid pressure of the rod side chamber 12 in the stroke sensing cylinder 6 can be controlled.
Accordingly, also in the FIG. 5 modified example, the proportional pressure control valve 28c is proportionally operated according to the transverse deflection speed of the vehicle body 2 whereby the value of the damping force acting on the stroke sensing cylinder 6 can be controlled while adjusting to the transverse deflection speed of the vehicle body 2, in the same manner as the FIG. 4 embodiment.
In the damping dampers 3b, 4b and 3c, 4c shown in FIG. 4 and FIG. 5, respectively, the unload valves 18 and 19 for pressure side and extension side are totally the same as those shown in the FIG. 2 embodiment, and in addition the damping force control means in the damping force control circuits 8b and 8c are also not fundamentally different from those shown in FIG. 2.
Accordingly, it is obvious that in the case where the truck 1 is subjected to the transverse deflection in the same direction at higher speed than that of the vehicle body 2 due to a dislocation or the like, the transverse deflection of the vehicle body 2 can be prevented from being increased by the function of the unload valve 18 or 19, and that, at the time of disablement of control due to the power off or the occurrence of abnormal situation, the valves are returned to their off position to achieve a fail-safe while performing the normal damper operation. According to the damping dampers 3b, 4b and 3c, 4c shown in FIG. 4 and FIG. 5, respectively, not only it is possible to reduce one (switching signal Y) of the switching signals from the computer 40 to control the generated damping force but also it is possible to diligently suppress the transverse deflection of the vehicle body 2 to effectively damp the deflection while analogically continuously controlling the generated damping force.
Though not particularly shown, needless to say, modification similar to FIG. 3 with respect to FIG. 2 can be applied to the damping dampers 3b, 4b and 3c, 4c shown in FIG. 4 and FIG. 5, respectively, and the scale memories 14 in the stroke sensing cylinder 6 may be provided externally of the stroke sensing cylinder 6.
As described above, the stroke sensing cylinder is used as the damper for damping the transverse deflection whereby the transverse deflection of the vehicle body can be suppressed while adequately controlling the generated damping force of the damping force control circuit by using the damper signal from the stroke sensing cylinder while adjusting to the state of the relative displacement between the truck and the vehicle body.
Moreover, the generated damping force in the damping force control circuit is continuously proportional-controlled by the proportional flow rate control valve or the proportional pressure control valve whereby the transverse deflection of the vehicle body can be effectively suppressed in the diligent and shockless state.
Furthermore, the unload valves for pressure side and extension side for switching the unload to the onload or vice versa are separate from the damping force control circuit. These unload valves are selectively switched to the on position in advance opposite to the operating direction of the stroke sensing cylinder which is extended and compressed according to the deflecting direction of the vehicle body. With this, even if a situation should occur in which the truck is deflected transversely at higher speed in the same direction as the vehicle body so as to increase the transverse deflection of the vehicle body, the damping force control circuit can be automatically placed in the unload state by these unload valves to prevent the transverse deflection of the vehicle body from being increased due to the transverse deflection of the truck.
As a result, when the situation as described above occurs, the generated damping force of the damping force control circuit is merely controlled, and the unload valves are selectively on-off controlled according to the direction of the transverse deflection of the vehicle body which is low in the vibrational frequency. Therefore, the frequency of switching the valves for controlling the damping force is reduced accordingly, and the durability of these valves can be also improved.
Further, at the time of disablement of control due to the power off or the occurrence of abnormal situation, the controlling valves in the damping force control circuit along with the unload valves are automatically returned to the off position. Therefore, the generated damping force of the damping force control circuit in the off state of these valves is adequately selected whereby the fail-safe effect can be also obtained while causing the damping damper to serve as a normal damper when the aforementioned situation should occur.Particularly, in the case where,as the valves for controlling the damping force, the proportional flow rate control valve or the proportional pressure control valve is used, the on-off valves for on-off controlling the throttles and the bypass flowpassages of the throttles are disposed in series along with these the proportional flow rate control valve or the proportional pressure control valve, whereby a region for controlling the generated damping force of the damping force control circuit can be spread downward to effect the diligent control of the damping force.
Further, the check valve which is opened from the head side chamber towards the rod side chamber of the stroke sensing cylinder is provided at the off position of the unload valve for extension side, which leads to merit in which the stroke sensing cylinder can be constituted as a unidirectional flow cylinder making use of the flowpassage of the unload valve for pressure side.
On the other hand, if the above-described check valve is provided on the piston of the stroke sensing cylinder, there can exhibit the merit in which the length of the flowpassage from the head side chamber towards the rod side chamber can be shortened to decrease the flowpassage resistance of the working fluid flowing through the flowpassage.
Furthermore, the control operation of the valves provided on the damping force control circuit and the selective on-off switching of the unload valves for pressure side and extension side are controlled by the computer using the damper speed signal and the damper displacement signal from the stroke sensing cylinder whereby the generated damping force of the damping force control circuit can be automatically controlled effectively and adequately while adjusting to the transverse deflection speed of the vehicle body.
Thus, there can be provided a damper system suited for use of damping the transverse deflection of railway vehicles.

Claims

A variable damping force damper (3, 4, 3a, 4a) for damping transverse deflection of a railway vehicle by suppressing the transverse deflection of a vehicle body (2) while using semiactive control which controls the generated damping force of the damper (3, 4, 3a, 4a) when the damper is transversely interposed between a vehicle truck (1) and the vehicle body (2) and which adjusts to the state of the transverse deflection between the vehicle truck and the vehicle body, said variable damping force damper (3, 4, 3a, 4a) comprising:

a stroke sensing cylinder (6);

a flowpassage (20, 21) for allowing only a flow of working fluid from a head side chamber (11) toward a rod side chamber (12) of said stroke sensing cylinder (6);

a reservoir (7) in communication with the head side chamber (11) of said stroke sensing cylinder (6) through a suction valve (22);

an unload valve (18) for a pressure side having the head side chamber (11), disposed in a flowpassage (20, 21) for bringing the head side chamber (11) into communication with the reservoir (7);

an unload valve (19) for an expansion side likewise disposed in the flowpassage (20, 21) for bringing the rod side chamber (12) into communication with the head side chamber (11); and

a damping force control circuit (8) disposed between the rod side chamber (12) and the reservoir (7), wherein said damping force control circuit has a plurality of damping force generating elements (25, 26, 27) arranged in series and on-off valves (28, 29, 30) for bypass-controlling the damping force generating elements, said on-off valves being turned on and off to control the generated damping force in the damping force control circuit
The damper according to Claim 1, wherein the on-off valves for bypass-controlling the plurality of damping force generating elements comprise a combination of a normally open valve (28) and a normally closed valve (30).
A variable damping force damper (3b, 4b, 3c, 4c) for damping transverse deflection of a railway vehicle by suppressing the transverse deflection of a vehicle body (2) while using semiactive control which controls the generated damping force of the damper (3b, 4b, 3c, 4c) when the damper is transversely interposed between a vehicle truck (1) and the vehicle body (2) and which adjusts to the state of the transverse deflection between the vehicle truck or wheels and the vehicle body, said variable damping force damper (3b, 4b, 3c, 4c) comprising:

a stroke sensing cylinder (6);

a flowpassage (20, 21) for allowing only a flow of working fluid from a head side chamber (11) toward a rod side chamber (12) of said stroke sensing cylinder (6);

a reservoir (7) in communication with the head side chamber (11) of said stroke sensing cylinder (6) through a suction valve (22);

an unload valve (18) for a pressure side having the head side chamber (11), disposed in a flowpassage (20, 21) for bringing the head side chamber (11) into communication with the reservoir (7);

an unload valve (19) for an expansion side likewise disposed in the flowpassage (20, 21) for bringing the rod side chamber (12) into communication with the head side chamber (11); and

a damping force control circuit (8b, 8c) disposed between the rod side chamber (12) and the reservoir (7), wherein said damping force control circuit has a maximum damping force generating element (25) and a normally open proportional flow rate control valve (28b) or proportional pressure control valve (28c) arranged in parallel, said proportional flow rate control valve (28b) or the proportional pressure control valve (28c) being operated to continuously control the generated damping force in the damping force control circuit.
The damper according to Claim 3, wherein the damping force control circuit (8b, 8c) has a minimum damping force generating element (27) disposed in series with the maximum damping force generating element (25) and a normally closed on-off valve (30) for bypass controlling the minimum damping force generating element (27).
The damper according to Claim 1, 2, 3 or 4, wherein the flowpassage for allowing only a flow of working fluid from the head side chamber (11) toward the rod side chamber (12) of said stroke sensing cylinder (6) comprises an unload flowpassage (20, 21) for expansion side and a check valve (17) provided at an off position of the unload valve (19) fur expansion side disposed in said flowpassage.
The damper according to Claim 1, 2, 3 or 4, wherein the flowpassage for allowing only a flow of working fluid from the head side chamber (11) toward the rod side chamber (12) of said stroke sensing cylinder (6) comprises a flowpassage (21a) provided in a piston (10) of the stroke sensing cylinder (6) and a check valve (17a) disposed in said flowpassage (21a).
A system for damping transverse deflection of a railway vehicle in which a variable damping force damper (3, 4, 3a, 4a, 3b, 4b, 3c, 4c) under semiactive control is transversely interposed between a vehicle truck (1) and a vehicle body (2) to suppress the transverse deflection of the vehicle body, wherein:

said variable damping force damper (3, 4, 3a, 4a, 3b, 4b, 3c, 4c) comprises a stroke sensing cylinder (6); a flowpassage (20, 21) for allowing only a flow of working fluid from a head side chamber (11) toward a rod side chamber (12) of said stroke sensing cylinder (6); a reservoir (7) in communication with the head side chamber (11) of said stroke sensing cylinder (6) through a suction valve (22); an unload valve (18, 18a) for a pressure side having the head side chamber (11), disposed in a flowpassage (20, 21) for bringing the head side chamber (11) into communication with the reservoir (7); an unload valve (19, 19a) for an expansion side likewise disposed in the flowpassage (20, 21) for bringing the rod side chamber (12) into communication with the head side chamber (11); and a damping force control circuit (8, 8b, 8c) disposed between the rod side chamber (12) and the reservoir (7); and

said system is arranged such that a damper signal (S) detected by the stroke sensing cylinder (6) is divided into a damper displacement signal (W1, W2) and a damper speed signal (V1, V2), an optimum damping force value is computed by a computer (40) on the basis of said damper displacement signal (W1, W2) and said damper speed signal (V1, V2) and a vehicle speed signal (U1, U2) from detection means (5) provided on the vehicle body (2), the generated damping force in the damping force control circuit (8, 8b, 8c) is controlled on the basis of said result of computation, and the deflection direction of the vehicle body (2) at that time is determined by the computer (40) according to the vehicle speed signal (U1, U2) from said detection means to selectively switch and control the unload valves (18, 19, 18a, 19a) for pressure side and expansion side.