Linear motor supporting apparatus for vehicles

Field of the Invention

The present invention relates to an apparatus to support a linear-induction motor used for propelling vehicles such as railway cars.

Description of the Prior Art

In a linear motor-propelled railroad whose track facility consists of rails on which the train runs and a linear motor reaction plate, there are some dimensional errors in laying the rails and reaction plate and their combined relative errors are large. And these errors result in variations in distance between the primary coil and reaction plate of the linear motor. To keep the primary coil on the bogie from contacting the reaction plate, there is provided a standard gap of ten odd millimeters between them. To maintain this gap requires accurate laying work and also frequent adjustments, making the system costly.

The gap of ten odd millimeters provided between the primary coil and the reaction plate is very large compared to the gap of 1 or 2 millimeters formed between the armature and stator of a rotary motor. The large gap reduces the efficiency of the linear motor.

For installing the linear motor, a structure is proposed in the Japanese Unexamined Publication No. 64251/1987, which has a dedicated support wheel to make the gap small and constant. In this prior art, the primary coil is supported by the gap-setting support wheel, which runs on both sides of the reaction plate laid on the ground. Although this construction is simple, there is a drawback that the support wheel is acted upon by the attractive force of the linear motor and thus must be robust enough to withstand that force.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a linear motor supporting apparatus for vehicles, which can make small and maintain the gap between the on-board coil of the linear motor such as a primary coil and the ground stator - another constituent member of the linear motor - such as a reaction plate with inherent laying errors, to minimize a reduction in the linear motor efficiency, without using the linear motor support wheel that can withstand high loads, without requiring a special work to enhance the laying accuracy of the reaction plate and rails, or a maintenance work to maintain the high level of dimensional accuracy of the reaction plate and rails.

To achieve the above objective, the linear motor supporting apparatus according to this invention comprises: an on-board coil mounted on a bogie; a ground stator laid on ground along the track on which the vehicles travel, the on-board coil and the ground stator together comprising a linear-induction motor; a means for measuring the distance between the on-board coil and the ground stator, the distance measuring means being mounted on the bogie; and a means for vertically driving the on-­board coil in response to the output of the distance measuring means to keep the distance between the on-board coil and the ground stator at a predetermined value.

The apparatus of the invention also comprises: an on-board coil mounted on a bogie; a ground stator laid on ground along the track on which the vehicles travel, the on-board coil and the ground stator together comprising a linear-induction motor; a sensor member placed in contact with the ground stator and adapted to move up or down following the contour of the ground stator; and a servo device, the servo device comprising: a valve body connected to the sensor member; a valve box secured to the on-board coil, the valve box accommodating the valve body in such a way that the valve body can be moved vertically therein; and a servo device body for accommodating the valve box in such a way that the valve box can be moved vertically therein, the body being mounted to the bogie and adapted to cause, through hydraulic pressure, the valve box to move up or down following the vertical motion of the valve body.

The apparatus of the invention further comprises: a means for restricting the lower-limit position of the servo device body with respect to the bogie; and a spring preloaded to urge the servo device body downward from the bogie.

Moreover, the apparatus of the invention comprises:

a plurality of bogies making up a train; an on-board coil mounted on each bogie; a ground stator laid on ground along the track on which the train travels, the on-board coil and the ground stator together comprising a linear-­induction motor; a means for measuring the distance between the on-board coil and the ground stator, the distance measuring means being provided to the front bogie; a means for vertically driving the on-board coil in response to a control signal to keep the distance between the on-board coil and the ground stator at a predetermined value, the drive means being provided in each bogie; a means for measuring the speed of the train; and a control means for receiving outputs from the distance measuring means and the speed measuring means and then applying the output of the distance measuring means to the drive means as a control signal with a time delay of T=L/V where V is the speed of the train and L is the distance in the direction of travel between the distance measuring means and the drive means.

According to this invention, the on-board coil such as a primary coil is mounted on the bogie and the ground stator such as a reaction plate is laid on the ground along the track, to form a linear motor. The distance between the on-board coil and the ground stator is measured, and the on-board coil is vertically moved so that the distance is kept to a predetermined value. This eliminates the need to improve the laying accuracy of the ground stator and of the rails on which the bogies travel, to an unnecessarily high level. The invention also allows the distance between the on-board coil and the ground stator to be set as small as possible, improving the efficiency of the linear motor. Furthermore, since the on-board coil is mounted to the bogie, there is no need to provide a wheel on which to support the on-board coil.

According to the invention, the distance between the on-board coil and the ground stator is measured by a sensor member that moves up and down in contact with the ground stator and, according to the displacement of the sensor member, the on-board coil position is vertically regulated by the servo device.

Moreover, according to the invention, a plurality of bogies are connected to form a single train with a distance measuring means provided only to the front bogie. The second and succeeding bogies behind the distance measuring means are given, with a time delay T, a control signal for keeping the on-board-coil-to-ground-­stator distance to a predetermined value. This construction needs only one distance measuring means. It is also possible to provide a means for driving the on-­board coil up and down in connection with the distance measuring means mounted on the first bogie.

BRIEF DESCRIPTION OF THE DRAWINGS

• Figure 1 is a cross-sectional view of a part of one embodiment of this invention;
• Figure 2 is a simplified plan view of the embodiment shown in Figure 1;
• Figure 3 is a cross-sectional view of a servo device 9;
• Figure 4 is a simplified schematic diagram of another embodiment of this invention;
• Figure 5 is a block diagram showing the electrical configuration of the embodiment shown in Figure 4;
• Figure 6 is a cross-sectional view of a servo device 9a employed in the embodiment of Figures 4 and 5;
• Figure 7 is a graph explaining the operation of a processing circuit 59; and
• Figure 8 is a graph explaining the operation of the processing circuit 59 of another embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure 1 shows a simplified side elevation of a part of one embodiment of this invention. Figure 2 is a simplified plan view of Figure 1. A bogie or truck 1 is mounted, through springs, with wheels 2 that travel on a pair of rails 3 laid on ground in the direction of travel 57. Mounted on the bogies 1 through air springs 4 is a vehicle body 5 that carries passengers. The bogies 1 and the vehicle body 5 constitute the vehicle. Under the bogie 1 is provided an on-board primary coil 7, which comprises a part of the linear-induction motor 6. Immediately below the primary coil 7 is a reaction plate 8 laid on the ground in the direction of travel 57. The on-board primary coil 7 is mounted to the bogie 1 through three servo devices, of which one 9 is installed at the front of the bogie with respect to the direction of travel and two 10 are mounted at the rear, laterally spaced apart. The on-board primary coil 7 magnetically interacts with the reaction plate 8 to generate a force to propel the bogie 1 forward. Displacement between the primary coil 7 and the bogie 1 along the direction of travel is blocked by a means not shown. In Figure 2, the bogie 1 is omitted.

Figure 3 is a cross-sectional view of the servo device 9. As shown in the figure, the reaction plate 8 consists of a rigid base material 11, a plate 12 of ferromagnetic material placed on the base material 11, and a plate 13 made of such metals as aluminum or copper other than ferromagnetic material, these three components being secured together.

A wheel 14 running on the upper surface of the reaction plate 8 and a support rod 15 that rotatably supports the wheel 14 constitute a sensor member 16, which measures the distance ℓ1 between the primary coil 7 and the reaction plate 8.

The support rod 15 is rigidly connected to a vertically movable valve body 17 that has a vertical axis of the servo device 9. The valve body 17 is installed inside a valve box 18 which can be vertically displaced. The valve box 18 in turn is accommodated in a servo device body 19 in such a manner that it can be moved vertically in the body 19. The body 19 has an end member 20 securely attached to the lower end thereof through thread. The valve body 17 has lands 21, 22 spaced apart in axial direction, with annular small-diameter portions 23, 24, 25 formed axially adjacent to the lands. The valve box 18 is formed with annular grooves 26, 27 corresponding to the lands 21, 22, and these annular grooves 26, 27 are connected with oil holes 28, 29. The valve box 18 is formed with a piston portion 30 along the axis between the oil holes 28 and 29. The servo device body 19 is formed with an annular groove 32, which communicates with an oil hole 31 formed in the valve box 18 corresponding to the small-diameter portion 23 of the valve body 17. The body 19 is also formed with an oil passage 33 communicating with the annular groove 32. The oil passage 33 is supplied with pressurized oil from a pipe 34. The body 19 has another oil passage 37, which is connected through an annular groove 36 to an oil hole 35 formed in the piston portion 30, the oil hole 35 communicating with a space defined by the small-diameter portion 24 of the valve body 17. The oil passage 37 is connected with a pipe 38, which in turn is connected to an oil tank. The valve body 17 has an axially extending oil passage 48 formed therein that communicates the small-diameter portions 23 and 25 with each other.

The upper end portion 39 of the body 19 is formed cylindrical and fitted into a guide cylinder 40 secured to the bogie 1 in such a way that it is vertically movable. The guide cylinder 40 has a support plate 41 integrally formed therein. Support members 43 with a large-diameter head 42 are passed vertically movable through the support plate 41, and its lower end portion 44 is threaded and screwed into the upper end portion 39 of the body 19. A spring 45 encloses the guide cylinder 40 and the upper end portion 39 of the body 19 and is preloaded to urge the body 19 downwardly from the bogie 1. The head 42 of the support member 43 engages the support plate 41 thus blocking the downward displacement of the body 19 to restrict the lower limit position of the body 19 with respect to the bogie 1.

Another spring 46 is installed in the body 19 between the end member 20 and the piston portion 30 to urge the valve box 18 upwardly with respect to the body 19.

The axial length of the land 21 of the valve body 17 (in the vertical direction in Figure 3) is set slightly larger than the axial length of the annular groove 26 so that a blind zone is formed. This construction is also employed for the other land 22 and the corresponding annular groove 27. In the state of Figure 3, the lands 21, 22 close the annular grooves 26, 27.

Let us consider a situation in which, during operation, the sensor member 16 is lifted up from the state of Figure 3 due to laying errors of the reaction plate 8. As the valve body 17 moves up, the working oil from the pipe 34 flows through the oil passage 33 and annular groove 32 in the body 19, the oil passage 31 in the valve box 18, the small-diameter portion 23 of the valve body 17 and the axially extending oil passage 48 formed in the valve body 17 and to the small-diameter portion 25 of the valve body 17, from which the oil further flows through the oil passage 29 into a chamber 47 where the spring 46 is installed. As a result, the piston portion 30 is pushed up by the hydraulic pressure. The piston portion 30 moves up following the motion of the valve body 17 until the annular grooves 26, 27 are closed by the lands 21, 22. Therefore, the upward displacement of the valve box 18 equals the upward displacement of the valve body 17. As the valve box 18 moves up, the primary coil 7 which is integral with the valve box 18 also moves up. In this way, the primary coil 7 follows the vertical variations in the reaction plate 8, thus keeping the distance ℓ1 between the primary coil 7 and the reaction plate 8 constant. The reaction force of the servo device is sustained by the bogie 1 through the body 19, spring 45 and support member 43.

Should there be an abnormal projection on the reaction plate 8 or when the primary coil 7 comes into contact with the reaction plate 8, the servo device 9 may not be able to respond quickly enough. In this case, the upper end portion 49 of the valve body 17 may abut the upper end portion 50 of the valve box 18, the oil pressure in a chamber 51 on the upper side of the piston portion 30 may increase, or the upper end portion of the valve box 18 may strike the upper end portion of the body 19, exerting an excess force on the sensor member 16 and the valve body 17. The spring 45 solves this problem. When the valve box 18 abruptly moves up, the body 19 also moves up compressing the spring 45. The spring 45 is preloaded and, when applied with a compressive force in excess of the preloading force, is compressed. If the spring 45 was not given any precompression, it would easily be compressed even with a slight vibrating load, making the servo device unstable. With this construction, the sensor member 16 and the valve body 17 are prevented from being burdened with an excessive force.

When there is an oil leakage, the reduced oil pressure will render it impossible for the servo device 9 to drive the valve box 18 following the motion of the valve body 17. In such a case, the hydraulic oil in the chamber 51 above the piston portion 30 is discharged through the oil passage 28 and the force of the spring 46 causes the valve box 18 and therefore the primary coil 17 to move upward, thus preventing the sensor member 16 from being burdened with a reaction force of supporting the primary coil 7. As for the remaining servo devices 10, their constructions are similar to that of the above servo device 9. The combined use of these three servo devices 9, 10 for a single primary coil 7 ensures that a torsion moment is prevented from being applied to the primary coil 7 when there is a twist in the reaction plate 8, or when there is a relative deviation between the rails 3 and the reaction plate 8, or when the vehicle is running on a curved track. As another embodiment of the invention, it is possible to provide four or more servo devices 9, 10. When four servo devices are used, it is necessary to make the forces between any two servo devices equal by an equalizer that works as a balance.

In another embodiment of the invention, there is provided a displacement sensor 52 in connection with the servo device 9. The displacement sensor 52 is rigidly mounted to the support plate 41 of the guide cylinder 40 and passes through the valve box 18 and the body 19. The displacement sensor 52 is intended to detect the amount of vertical displacement of the valve body 17 relative to the bogie 1 and convert it into electric signal. The distance ℓ1 between the primary coil 7 and the reaction plate 8 therefore can be measured by the displacement sensor 52.

Figure 4 is a simplified schematic diagram of yet another embodiment of this invention equipped with the displacement sensor 52. A train 54 consists of a plurality of cars 55, 56 (in this case two) connected together and travels in the direction of arrow 57. At the front (with respect to the direction of travel) of the car 55, the bogie 1, which has been described with reference to Figures 1 to 3, is installed. At the rear of the car 55 another bogie 1a is provided. The second car 56 is provided with bogies 1b, 1c. In this embodiment, the output of the displacement sensor 52 in the servo device 9 for the bogie 1 has a waveform W1 of Figure 4.

Figure 5 is a block diagram showing the electrical configuration of the embodiment of Figure 4. The speed of the train 54 is detected by a speed sensor 58. The outputs of the displacement sensor 52 and the speed sensor 58 are fed to a processing circuit 59, which is made up of a microcomputer. The processing circuit 59 then drives motors 69a, 69b, 69c installed in the bogies 1a, 1b, 1c, respectively. The control signals applied to these motors 69a, 69b, 69c are indicated by reference symbols W2, W3 and W4 in Figure 4. Let L1 stand for the distance from the displacement sensor 52 of the bogie 1 to the corresponding position of the bogie 1a. Likewise, let L2 and L3 stand for the distances from the displace­ment sensor 52 of the bogie 1 to the corresponding positions of the bogies 1b, 1c. Also let the speed of the train detected by the speed sensor 58 be V. The waveforms W2, W3, W4 are delayed from the waveform W1 of the displacement sensor 52 by times T1, T2, T3, respectively before being applied to the motors 69a, 69b, 69c.

T1 = $\frac{\text{L1}}{\text{V}}$      (1)

T2 = $\frac{\text{L2}}{\text{V}}$      (2)

T3 = $\frac{\text{L3}}{\text{V}}$      (3)

Figure 6 is a cross-sectional view of a servo device 9a mounted on the bogie 1a which corresponds to the servo device 9 on the bogie 1. This servo device 9a resembles the abovementioned servo device 9 of Figure 3, with the corresponding parts represented by the same numerals attached with a subscript a. It should be noted that in this embodiment the valve body 17a is connected to a drive shaft 61, which is driven vertically by the motor 69a.

Figure 7 is a graph showing the relationship between a displacement ΔA of the valve body 17a driven by the motor 69a, which is controlled by the processing circuit 59, and a displacement δ of the same as detected by the displacement sensor 52 with respect to the state of Figure 3, which is taken as a reference. The displace­ment δ detected by the displacement sensor 52 is proportional to the displacement ΔA of the valve body 17a driven by the motor 69a. It should be noted, however, that the control signal for the motor 69a to produce the displacement ΔA is delayed by the time duration T1 from the moment the displacement sensor 52 has detected the deviation. The spring 45a prevents the primary coil 7a from being burdened with an excessive force when the primary coil 7a contacts the reaction plate 8. The time duration T1 may include such delay factors as the time required by hydraulic oil to flow into the servo device 9a and the operation delay of the motor 69a. The same also applies to the time durations T2, T3.

Although the foregoing description concerns the servo device 9 for the bogie 1 and the similar servo device 9a for the bogie 1a, the same construction can be used with the servo device 10 for the bogie 1 and with the similar servo device 10a for the bogie 1a. All these also apply to the bogies 1b, 1c.

With these embodiments, it is possible to keep constant the gap ℓ1 between the primary coil 7a and the reaction plate 8 regardless of the weight of passengers boarding the cars 55, 56. Referring again to Figure 5, the weight of passengers is measured by the weight sensor 63 provided in the car 55. When the passenger weight or the current value changes after the first bogie has passed a given point, the second and succeeding bogies will compensate for that change when they pass the same point. These sensor signals are supplied to the processing circuit 59 which generates a control signal to be applied to the motor 69a. As shown in Figure 8, the compensation or correction value ΔB is set to increase in proportion to an increase in the passenger weight. The compensation value ΔB is added to the control signal, which is given to the motor 69a. Then, the primary coil 7a will be shifted up toward the bogie 1a, keeping the gap ℓ1 constant.

As still another embodiment of the invention, the following compensation method is also possible. The current fed to the primary coil 7a is measured by a current sensor 64. When the current increases, the control signal to the motor 69a is modified to cause the primary coil 7a to move up toward the bogie 1a. As the current of the primary coil 7a increases, the bogie 1a will be shifted downwardly by the magnetic attraction of the primary coil 7a and reaction plate 8. However, since the motor 69a causes the primary coil 7a to move up toward the bogie 1a as mentioned above, the distance ℓ1 is kept at a predetermined constant value. The same also applies to the second car 56.

In the above embodiments, four bogies 1, 1a, 1b, 1c are used for a single train. In the case of a long train hauling many bogies, for example, 20 bogies, it is possible to divide them into two groups, each consisting of ten bogies and to provide a displacement sensor 52 to the first bogie of each group in order to achieve the abovementioned compensation control. This helps simplify the construction of the servo devices.

As explained above, since this invention can maintain at a small and almost constant value the gap between the on-board coil and the ground stator (reaction plate), both constituting the linear-induction motor, the reduction in linear motor efficiency can be minimized. Furthermore, even when there are variations in distance between the rails on which the bogies travel and the reaction plate, the gap between the on-board coil and the ground stator can be kept constant. This eliminates the need for a complicated control to enhance the accuracy of laying the rails and reaction plate, which in turn eliminates the maintenance service and reduces cost.