1. Field of the Invention
This invention relates to the structive of a truck to be used for an attraction type magnetically levitated vehicle.
2. Description of the Prior Art
An attraction type magnetically levitated vehicle is levitated by the action of the attraction between electromagnets (or a group of electromagnets assigned different functions) and armature rails; and, while being guided laterally, is caused to travel by a thrusting power obtained from propelling means separately provided.
In an example of the conventional construction of such a vehicle, which is illustrated in FIGS. 1(a) and 1(b) of the accompanying drawings, electromagnets 2 having iron cores of a U-shaped cross-section are disposed on the lower part of the vehicle in such a way as to confront a pair of left and right armature rails 1 having also a U-shaped cross-section. The vehicle 3 is levitated when the electromagnets 2 are attracted by the magnetic power toward the armature rails which are made of a ferromagnetic material.
An example in which control means for the exciting power is employed to maintain a preset gap between the armature rails and the electromagnets for stable levitating of the vehicle is as illustrated in FIG. 2. This means for maintaining the preset gap comprises a gap detector 4 which detects the amount of the gap between each confronting pair of an armature rail 1 and an electromagnet 2, and an amplifier 5 which causes a controlled exciting current to flow to the magnet 2 according to variation in the output signal of the gap detector 4. In order to stably levitate a vehicle 3 that has a given length and a given width, four electromagnets 2, each subjected to such exciting power control by the means for maintaining a preset gap, must be disposed at the vertexes of a rectangular plane figure formed by the bottom of the vehicle 3.
The foregoing is the basic constructional arrangement of an attraction type magnetically levitated vehicle. In cases where such a vehicle is to be propelled by a linear motor or the like, the following must be taken into consideration:
The left and right armature rails on the ground preferably have no local uneven surfaces and are laid in parallel with each other in smooth straight lines or curved lines.
Practically speaking, however, it is hardly possible to have the flatness or parallelism of such armature rails above a certain level of precision because of various problems encountered in terms of laying technique and maintenance work. Hence, for running such a vehicle 3, the fact that these armature rails have more or less unevenness must be taken into account. Assuming that four electromagnets 2 provided for levitation are secured directly to a vehicle which is a rigid body, as illustrated in FIGS. 1(a) and 1(b), there arises two problems. One problem is that if the left and right armature rails 1 and 1 are not perfectly parallel with each other as shown in FIG. 3(b), when the vehicle passes the point A shown in FIG. 3a, a large electric controlling current for reducing the large gaps flows to each of the electromagnets 2a and 2d while the electric controlling current flowing to each of the other electromagnets 2b and 2c decreases to widen the gaps; and this results in the weight of the vehicle being supported chiefly by the electromagnets 2a and 2d. Then, if the vehicle is stationary at the point A, this tends to bring about overheating of the electromagnets 2a and 2d. Further, the rotational movement of the vehicle on the electromagnets 2a and 2d becomes less controllable and, accordingly, the electromagnets 2b and 2c come closer to the armature rails. Therefore, under such a condition, the electromagnets tend to come into contact with the armature rails due to the shaking of the vehicle that takes place while it is on the run. The other problem relates to the following capability of the electromagnets. Namely, when the vehicle is travelling along uneven rails, the electromagnets must be capable of quickly following vertical displacement of the rails to control and prevent the gaps between the electromagnets and the armature rails from excessively deviating from the preset value. This is very important, particularly in high speed travel, for preventing the electromagnets from coming into contact with the armature rails.
In the case where electromagnets are secured directly to a vehicle as shown in FIG. 1, however, inertia that resists quick movement of the electromagnets is present due to the large mass of the vehicle. In order to enhance the following capability of the electromagnets, therefore, a large amount of controlling power is required. Furthermore, with this configuration, the movement of one electromagnet (or a group of magnets) induces the movement of other electromagnets (or groups of magnets) through the great mass of the vehicle which is a rigid body. In other words, these four electromagnets are dynamically linked with each other. For ideal control over such a system, it is necessary to control the electric current of each electromagnet by a signal which is obtained by mixing signals representing displacements of all electromagnets instead of controlling each electromagnet independently. However, such a control system inevitably becomes complex.
As one method of solving the above stated problems, it is most desirable to have the electromagnets (or groups of electromagnets) connected to the vehicle through shock absorbers which are independently suspended (hereinafter called an "independent suspension system"). Such an arrangement improves the riding quality of the vehicle to a great extent. However, the use of such an independent suspension system in general results in a complex structure with considerable increase in weight. An alternative form of this connection is one in which the four electromagnets (electromagnet groups) are rigidly attached to the truck and the truck is then connected to a vehicle through a shock absorber. Such a method, however, is not only incapable of solving the above stated first problem but also inferior to the independent suspension system which is provided for solving the second problem in terms of controllability and its following capability because of the mass of the rigid truck.
However, if were possible to replace such a rigid truck with a truck having a construction that does not restrict torsion relative to a longitudinal or transverse axis of the truck, the position of the four electromagnets (or electromagnet groups) would no longer be restricted to the same plane. Then, with such an arrangement, almost the same effect as that of the independent suspension system can be achieved. For example, a system can be conceived of which is illustrated in FIGS. 4(a) and 4(b) wherein a pair of left and right electromagnets 2 in the front part of a vehicle 3 are secured to a rigid body a while another pair of electromagnets 2 in the rear part of the vehicle are also secured to another rigid body b. These rigid bodies a and b are arranged to be rotatable on a longitudinal axis. Then the truck which is arranged in this manner is connected to a vehicle through shock absorbers 7.
In the structural arrangement as illustrated in FIGS. 4(a) and 4(b), when the position of one electromagnet changes, such a change brings about only a slight pitching movement of the other electromagnets disposed ahead of or after it and only a slight rolling movement of other electromagnets disposed on the left or right side thereof while no vertical positional movement is caused by such a change.
When such arrangement is employed, a preset gap can be easily maintained between the electromagnets and the armature rails even when these rails are not perfectly parallel with each other, thus overcoming the above stated first problem. As for the following cability, since the mass that is involved in the required movement is limited to the electromagnets and the associated structural arrangement, the characteristic can be considerably improved. Furthermore, with this arrangement, the dynamic linkage among these electromagnets is reduced to a great degree, enabling stable control over the levitation of the vehicle.
For this reason, a system having four electromagnets (or groups of electromagnets) disposed on a truck that permits torsional deformation has many advantages as a truck for an attraction type magnetically levitated vehicle. In such a case, however, it is important to note that an electromagnet has an intrinsic property which tends to cause unstable rolling movement in relation to an opposed armature rail. Further, where one electromagnet or even a group of electromagnets is controlled by a gap detector, such an electromagnet or electromagnets also tend to bring about unstable pitching movement in relation to the opposed armature rail. In view of this tendency, such a twistable truck must be designed not to cause such rolling or pitching. The structural arrangement of the truck shown in FIGS. 4(a) and 4(b) satisfies such conditions.
However, such a design does not permit sufficient reduction in weight because of the mechanical moving parts involved.