US 3662689 A
Superconducting high speed train system comprising a rail including at least one elongated hard superconducting member disposed horizontally along the running direction of the train and having a hollow or gap portion extending in the elongated direction, and a train body including a superconducting magnet for generating a magnetic field perpendicular to the hard superconducting member, thereby floating the body from the rail by the magnetic force acting between the superconducting magnet and the hard superconducting member.
Description (OCR text may contain errors)
United States Patent Kawabe et al.
[ 51 May 16, 1972 HIGH SPEED TRAIN UTILIZING HARD SUPERCONDUCTOR Ushio Kawabe; Hiroshi Kimura; Toshio Doi, all of Tokyo, Japan 7 Hitachi, Ltd., Tokyo, Japan July 10, 1970 Inventors:
Foreign Application Priority Data July 23, 1969 Japan .,.44/57702 US. Cl. ..l04/148 SS Int. Cl ...B6lb 13/08, HOlf9/O0 Field of Search 104/148 MS, 148 SS  References Cited UNITED STATES PATENTS 3,470,828 10/1969 Powell, Jr. et a1. 104/148 Primary Examiner-Arthur L. La Point Assistant Examiner-George H. Libman Attorney--Craig, Antonelli & Hill  ABSTRACT Superconducting high speed train system comprising a rail including at least one elongated hard superconducting member disposed horizontally along the running direction of the train and having a hollow or gap portion extending in the elongated direction, and a train body including a superconducting magnet for generating a magnetic field perpendicular to the hard superconducting member, thereby floating the body from the rail by the magnetic force acting between the superconducting magnet and the hard superconducting member.
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SHEET 8 [IF 6 INVENTORS usmo RPM ABE Hmosm MMURH Tosmo om ATTORNEYS HIGH SPEED TRAIN UTILIZING HARD SUPERCONDUCTOR BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a high speed train utilizing the properties of a superconductor and more particularly to a hovercraft high speed train utilizing the magnetic shielding effect of an inhomogeneous hard superconductor.
2. Description of the Prior Art In recent years, keeping pace with the development in various forms of transportation, researches are being proceeded in the field of trains to provide larger capacities and higher speeds. Although a high speed train of about 200 Km/hr is realized, higher speed trains of above 300 Km/hr cannot be realized practically according to conventional structures.
Namely, according to the conventional method, the wheels of a train are driven by a motor and the train moves due to the friction between the wheels and the rails. But above a certain speed, vibrations of the body become so large as to cause the possibility of running off the rails and also problems of skid occurs. Thus it becomes necessary to float a train from the rail and to drive it in such a floated state to provide a speed above 300 Km/hr. But since the weight of a train is so large, there have been no appropriate means to float a train from the rail and thus it has been impossible to realize a train which can run at a speed above 300 Km/hr.
Considering these points, an object of the invention is to provide a novel hovercraft high speed train.
SUMMARY OF THE INVENTION More specifically, an object of the invention is to provide a high speed train utilizing the magnetic floating effect to float the train above the ground and drive it in a floated state to provide a speed higher than 300 Km/hr.
For this purpose, an inhomogeneous hard superconductor is used according to this invention to provide a sufficiently large floating force by the magnetic shielding effect.
Other object, advantages and features of this invention will be apparent from the following detailed description when read in conjunction with accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 are magnetization curves of a soft and a hard superconducting material, respectively.
FIG. 3 illustrates the principle of magnetic floating according to the invention.
FIG. 4 illustrates the magnetic shielding effect.
FIG. 5 is a schematic diagram for illustrating the driving principle according to the invention.
FIG. 6 is a schematic diagram of a driving system according to the invention.
FIG. 7 is a schematic partial cross section of a rail according to the invention.
FIGS. 8 and 9 are schematic cross-sectional views of embodiments of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT Firstly, the known principle of magnetic floating utilizing a soft superconductor will be described.
FIG. 1 shows a magnetization curve with the abscissa representing external magnetic field H, and the ordinate representing magnetization (-M). As is apparent from the figure, upon the application of an external magnetic field a soft superconductor is magnetized in the opposite direction (showing a diamagnetic characteristic) with a magnitude in proportion to that of H However, at a certain magnetic field H the magnetization suddenly reduces to zero and the superconducting state is broken. This value H,., is called the lower critical magnetic field and the region of H, H is called the perfect diamagnetic region or the Meissner region. In this region, current flows in a surface layer of the soft superconductor in a thickness of about several angstroms and thus the external field cannot penetrate into the interior of the said soft superconductor any further, keeping the internal magnetic field zero. When a body the internal magnetic field of which is zero is placed in a magnetic field having a certain gradient, certain force acts on the body and it has become possible to float the body in the direction along which said magnetic field decreases. Thus, the body of a train can be floated from the ground by the use of this principle.
In the case of utilizing the Meissner effect of a soft superconductor as is described above, however, the maximum floating force is expressed by H /81iand this is limited by the magnitude of the critical magnetic field H Although it is possible to obtain a superconductor having a rather large critical magnetic field H there still exists a restriction and practically it is quite difficult to float a very heavy body such as a train.
Whereas, the present invention is based on the use of the magnetic shielding effect of an inhomogeneous hard superconductor which can provide a floating force several thousand times greater than that in the case of utilizing the Meissner effect.
Among inhomogeneous hard superconductors, there are Nb-Zr-Ti, Nb Sn, V -,Ga, Nb (Al Ge etc. each of which shows a magnetization characteristic as shown in FIG. 2. Namely, with the increase of an applied magnetic field, the intensity of the magnetization (M) of a hard superconductor placed in the magnetic field increases in linear proportion therewith up to the lower critical magnetic field H but above H the rate of increase of the magnetization (-M) gradually decreases with a certain point forming a peak and then the magnetization begins to decrease. Finally, at the upper critical magnetic field H the superconducting state is broken for the first time. While the region of H, 11,, is called the Meissner region similar to the preceding case, the region of l-l H, H is called the magnetic shielding region. In this magnetic shielding region, a spatial region of less magnetic field, i.e. magnetic field diluted space, is formed in a hard superconductor placed in the field due to a completely different principle from said Meissner effect. Namely, a magnetic field penetrates into a hard superconductor to such an extent where the pinning force due to dislocations and/or precipitation defects in the hard superconductor is balanced by the Lorentz's force that the magnetic flux due to an external field tends to penetrate into the hard superconductor. Consequently, an induction current flows in a surface region, to the inner boundary of which said magnetic flux could penetrate. By this induction current, the magnetic flux due to the external field is prevented from penetrating into the hard superconductor further to form a region of extremely less magnetic flux in the hard superconductor. In this case, the depth of penetration of the magnetic flux into the hard superconductor depends on the intensity of the external field and is about 10 times larger than that of the surface layer in which current flows by the meissner effect. Thus, the magnetic shielding effect produces a region of less magnetic field in a hard superconductor, while the Meissner effect produces a region of no magnetic field in a superconductor. Thus, the magnetic characteristics of the two are quite different, but in both cases a superconductor placed in a magnetic field having a uniform gradient receives a force in the direction along which the magnetic field decreases.
The magnetic shielding effect of an inhomogeneous hard superconductor will become more apparent from the following experiment.
Now, discs 1 and 2 formed of inhomogeneous hard superconductor are disposed parallel to each-other by supporting members 3 and 4, as is shown in FIG. 3. And a superconducting solenoid 5 is disposed in such a position to produce a magnetic field H substantially perpendicular to the disc surfaces. With such a structure, the relation of the change of the external magnetic field H and the magnetic field H at the center of the gap of the parallel discs is studied and the result is shown in FIG. 4. As is shown in FIG. 4, when the intensity of an applied magnetic field H is increased from zero, the internal magnetic field H is almost unchanged in the first stage and keeps small values near zero. That is, the penetration of the magnetic flux is prevented by the shielding characteristic of the superconductor discs 1 and 2. When the intensity of the external magnetic field H reaches the critical point H of the hard superconductor, the superconducting state is broken and the internal magnetic field H takes a value almost equal to the external magnetic field H. Then, the intensity of the external field H is gradually decreased. Even when the external field H is decreased to zero, the internal field H does not reduce to zero and a certain magnetic field H remains between the parallel discs. Namely, a hard superconductor has a magnetic capturing characteristic.
The former property of a hard superconductor, i.e., the magnetic shielding property, is utilized in this invention. For example, when the external magnetic field is 20 kilogauss, the magnetic field in the gap of .the discs is about 2 kilogauss showing that the magnetic field is very weak between the discs. Thus, if there exists a gradient 4) in the magnetic field H as is shown in FIG. 3, the structure 1 to 4 is floated upward to the direction along which the magnetic flux decreases. In this case, the structure is stable in the radial direction. And in the gravitational direction it is stable at a position where the floating force is balanced with the gravitational force. This is completely contrary to the case of a ferro-magnetic body. When the structure 1 to 4 is fixed, a force acts on the superconducting solenoid 5 to move it downward.
The high speed train according to the present invention is floated by the above-described principle with the maximum floating force expressed by (l'y)H/8 1r (dyne/cm (H,., H H Here, 'y is the magnetic shielding factor and in FIG. 4 'y H'lH. H is the upper critical magnetic field as shown in FIG. 2 and has a value about 100 times larger than the usual lower critical magnetic field of a soft superconductor. The factor 'y can be brought to a value very near to zero by the geometrical configuration and the material. Thus, an apparatus-utilizing the magnetic shielding characteristic can afford a floating force about several thousand times larger than that of the conventional apparatus utilizing the Meissner effect.
Next, the principle of driving a train according to the invention will be described. Since the driving force of the conventional train is due to the friction between the wheels and rails, a new type of drive becomes necessary for a friction-less train such as this invention. FIG. 5 illustrates the principle of the driving system, in which reference numeral 5 indicates a saddle-shaped solenoid, 6 a ladder-shaped conductor, and 7 a DC source. The saddle-shaped solenoid 5' works with the superconducting coil 5 of FIG. 3 for generating a magnetic field H in the direction indicated by an arrow H in the figure. In the ladder-shaped conductor 6, a current I is allowed to flow by the DC source 7 in the direction indicated by an arrow I. Thus, a force acts on the saddle-shaped solenoid in the direction indicated by an arrow F.
Letting the magnetic field generated by the saddle-shaped solenoid be H (gauss), the distance between the conducting rails 1 (cm), the current flowing from the dc source 7 to the ladder-shaped conductor I (ampere), the number of crosstieshaped conductors providing reaction to said generated magnetic field p, and the total weight of a train M (gram weight), the driving acceleration dv/dt of the saddle-shaped solenoid 5 is expressed by:
Thus, for example, ifP=l0, I= 10 (A), I= 1.5 (m), H= 50 (KG) and M 50 (ton), the hovercraft superconducting train is theoretically driven with an acceleration of l5-g (cm/sec an acceleration fifteen times larger than gravitational acceleration. Further, if the effective cross section of the magnetic field of the saddle-shaped solenoid is arranged to be 1(m) X 5(m) and the magnetic shielding factor 7 0.2, the maximum floatable weight is 5,000 (ton). These values are sufliciently large for practical purposes. In the practical form, a multiplicity of ladder-shaped conductors I, II, III, are
formed in the rail for a train and supplied with a current from power lines 8 through respective control switches 93, 92, 91, as is shown in FIG. 6. In the figure, a train is supposed to be running on the region II in the direction indicated by an arrow. In this state, the control switch 91 is turned off and the switch 92 is on. When the control switch 93 is connected in such a way that current is allowed to flow in the opposite direction as is shown in FIG. 6, a train passing above this region receives a braking force. By the control of the intensity and the direction of the current flow in the respective ladder-shaped conductors, a train can easily be started, stopped or reversed in its running direction.
Next, an embodiment of a high-speed hovercraft superconducting train according to this invention utilizing the abovedescribed magnetic floating and driving method will be described.
In FIG. 8, curved plates 10, 11, 12 and 13 formed ofa hard superconducting material such as an Nb Sn sintered body are placed to form opposing pairs by 10 and 12, and 11 and 13, and are supported by supporting structure 14 to 17 at the four corners. The use of curved plates facilitates the effective use of the applied magnetic field in such a manner that the external field is wholly applied perpendicular to these curved plates. The portion 18 surrounded by these curved hard superconductor plates forms a refrigerant passage. For example, liquid helium or helium gas at a very low temperature is allowed to flow through this passage to keep the plates 10 to 13 in the superconducting state. These structures are contained in a rail 19 formed of concrete. In the upper surface of said rail 19, ladder-shaped conducting circuits 6 are formed along the running direction of the train.
FIG. 7 is a partially cross-sectional schematic perspective view of a rail for a high speed train in which similar parts as those of FIG. 8 are indicated by similar reference numerals.
The body of a high speed train is, for example, divided into the upper and the lower part. In the upper part, seats 20 are disposed in double-layered chambers and double-glassed windows 21A to 21D are formed in the wall of both chamber. On the other hand, the lower part has a reversed U shaped corss section and rides on the rail 19. A saddle shaped coil 5 such as shown in FIG. 5 is disposed in the lower part in a position facing the ladder-shaped conducting circuit of the rail. Further in positions facing against the hard superconducting plates 11 and 13, control solenoids for guiding the rail 22 and 23 are respectively provided. On the bottom portion of the body, safety tires are provided.
When a current is allowed to flow through the saddleshaped solenoid 5 to produce magnetic flux 11 in such a structure, there is formed beneath the solenoid a magnetic field having a certain gradient. Whereas, in the portion 18 surrounded by the hard superconducting plates 10 to 13, an extremely weak magneticfield can only exist due to the magnetic shielding effect of the superconducting plates. Thus, the structure comprising the plates 10 to 13 receives a force in the direction of the magnetic field. But since the structure is fixed to the ground, the body receives a lifting force and floats to a height where the weight of the body and the floating force balance. Further, when a current I is allowed to flow through the ladder-shaped circuit 6, the body of the train receives a force and begins to move in the direction of the front side of the figure. The greater the intensity of the magnetic field by the solenoid 5 is, the higher will be the speed at which the train runs and the greater the floating force so obtained. When the intensity of the magnetic field is decreased, the speed of the train decreases and the floating force decreases. If the magnetic field is further decreased to zero, the train runs on safety tires 24 and 25 for some distance and halts.
Further, a current allowed to flow through the solenoids 22 and 23 produces magnetic fluxes 41 and The solenoids 22 and 23 receive a force by the interaction with the lesser magnetic field region 18 to a direction along which the magnetic flux decreases. This interaction prevents rolling of the body.
Thus, by the above construction, an extremely large floating force can be provided by the use of the magnetic shielding characteristic of a hard superconductor and a train can be driven at a very high speed.
F IG. 9 shows another embodiment of the invention in which the body of a train is hung down from concrete rails.
In the concrete rails 41 and 42, discs to 32 and 33 to 35 formed of curved hard superconductors are supported by supporting members 36 and 37 to be mutually parallel, respectively. These discs 30 to 35 are immersed in liquid helium and held in the superconducting state. On the upper surface of said rails 41 and 42, ladder-shaped circuits 61 and 62 are formed.
The body of the train is separated into a double structured passenger car portion in which seats 20A to 20F are disposed and a portion containing field coils 51 and 52. These two portions are connected by a connecting shaft 38. Liquid helium is also contained in the upper portion to keep the field coils 51 and 52 in the superconducting state. There are also provided safety tires 39 and 40.
In the above system, a train is floated by the interaction of the magnetic field established by superconducting field coils 51 and 52 and the weak magnetic field in the gap of the curved discs 30, 31, 32 and 33, 34, 35 and is further driven by the interaction of the field by the field coils 51 and 52 and the currents flowing through the ladder-shaped circuits 61 and 62 to run above the rails at a very high speed.
This embodiment provides an advantage in that the stability of the rail guiding of a train is very large.
In the above embodiments the Lorentzs force acting on the magnetic field and the current in the ladder-shaped conductor is utilized to drive a train, but other means such as a linear motor or jet propelling can also be employed in place of the Lorentzs force.
As is apparent from the foregoing description, a large floating force needed for floating a train can be easily provided with less power consumption by the utilization of the magnetic shielding effect of a hard superconductor according to the invention. Further, the magnetic field established by the field coil for floating the train can also be utilized for propelling a train to reduce the manufacturing cost. Further, the control of starting, halting, or varying the speed of a train can be extremely easily done by controlling the magnitude and the direction of the current flowing through the ladder-shaped circuit.
1. A superconducting high speed train system comprising:
train rail means including at least a pair of inhomogeneous hard superconducting plates disposed along the running direction of a train, vertically facing to one another, and means for cooling said superconducting plates to keep them in the superconducting state;
a body of a train accommodating thereon a superconducting field coil, means for operating said coil to generate a magnetic field perpendicular to the surface of said hard superconductor plates and means for cooling said coil to keep the same in the superconducting state, whereby floating the train body by the interaction of the magnetic field established by said superconducting coil means and the weak magnetic field formed in the gap of said pair of hard superconductor plates; and means for driving said train body in the floated state.
2. A superconducting high speed train system comprising:
train rail means including at least a pair of inhomogeneous hard superconductor plates disposed in vertically facing relation to each other along the running direction of a train, means for cooling said superconductor plates to keep them in the superconducting state, and laddershaped circuit means for allowing a current to fiow perpendicularly to the running direction of the train;
a body of a train including superconducting coil means for generating a magnetic field perpendicular to the surfaces of said hard superconductor plates and said laddershaped circuit, and means for cooling said coil means to keep the same in the superconducting state, whereby floating the train by the interaction of the magnetic field generated by said superconducting coil means and the weak magnetic field formed in the gap of said pair of hard superconductor plates; and means for controlling the current flowing through the ladder-shaped circuit means whereby propelling the train by the force caused by the magnetic field generated by said superconducting coil means and the current flowing through said laddershaped circuit means.
3. A superconducting high speed train system according to claim 2, in which said ladder-shaped circuit means includes a number of ladder-shaped unit circuits, each having an appropriate length and said control means includes switch means provided to the respective unit circuits for controlling the magnitude and the direction of the flow of current, thereby controlling the starting, braking or speed of the train.
4. A superconducting high speed train system comprising:
train rail means including two pairs of inhomogeneous hard superconductor plates disposed in horizontally and vertically facing relation to one another along the running direction of a train, means for cooling said superconductor plates to keep them in the superconducting state, and ladder-shaped circuit means for allowing current to flow perpendicularly to the running direction of the train;
a body of a train including first superconducting coil means for generating a magnetic field perpendicularly to the surfaces of a pair of said hard superconductor plates facing vertically and said ladder-shaped circuit means, second superconducting coil means for generating a magnetic field perpendicularly to the surface of another pair of said hard superconductor plates facing horizontally, whereby the train is floated by the interaction of the magnetic field generated by said first superconducting coil and the weak magnetic field in the gap of said pair of hard superconductor plates facing vertically, and controlled the position thereof by the interaction of the magnetic field generated by said second superconducting coil and the weak magnetic field formed in the gap of said another pair of hard superconductor plates facing horizontally; and means for controlling the current flowing through said laddershaped circuit means whereby the train is propelled by the force caused by the magnetic field generated by said first superconducting coil means and the current flowing through said ladder-shaped circuit means.