WO1992000862A1

WO1992000862A1 - Linear motor in-track transit system

Info

Publication number: WO1992000862A1
Application number: PCT/CA1991/000232
Authority: WO
Inventors: Pierre Veraart
Original assignee: Utdc Inc.
Priority date: 1990-07-05
Filing date: 1991-07-02
Publication date: 1992-01-23
Also published as: AU8051291A

Abstract

A linear induction motor in-track transit system (10) includes a guideway (12) supporting at least one vehicle (20) movable along the guideway. The guideway extends between a baggage loading station (28) and a baggage unloading station (30). Stopping zones (S) having primary and secondary brakes (18, 60) are located at the loading and unloading station. The secondary brakes (60) remain inactive unless a vehicle is detected as passing a predetermined stopping point (SP) within the stopping zone. Vertical and horizontal curves (32, 34) are present in the guideway between the stations. Deceleration zones (D) are positioned along the guideway prior to the curves to ensure that a vehicle exiting the deceleration zone does so at a desired velocity chosen to ensure that the vehicle safely negotiates the curve. The guideway is sub-divided into blocks (B), with each block including a plurality of LIM primaries (18). Controllers (44) are associated with the LIM primaries and communicate with sensors which detect the presence of a vehicle in the block. The controllers receive signals from their downstream counterparts and operate the LIM primaries to stop a vehicle in the block if a vehicle is present in the downstream block. This prevents two vehicles from being located in the same block. A transformer (165) is associated with the power supply (PDS) and scales the power supply voltage when the controller operates the LIM primaries to stop a vehicle so that current drawn from the power supply by the LIM primaries remains at a level similar to that drawn when the primaries are operated to supply forward thrust to the vehicles.

Description

LINEAR MOTOR IN-TRACK TRANSIT SYSTEM

TECHNICAL FIELD

The present invention relates to a linear motor in-track transit system.

BACKGROUND ART

Transit systems are well known in the art. Some conventional transit systems implement linear induction motors (LIM's) wherein the LIM primaries are located at spaced intervals between the rails of a track and wherein the LIM secondaries or reaction rails are secured to the undercarriage of vehicles travelling along the track. These transit systems are conventionally designated as LIM in-track transit systems. In these in-track transit systems and as in all transit systems, when more than one vehicles are travelling along the track, it is important to avoid collisions between vehicles. This of course requires the speed of all vehicles travelling along the track to be accurately controlled to ensure that vehicle spacing is maintained. In many systems, to increase vehicle throughput, the vehicles are propelled at high speeds. However, in certain segments of the track such as loading and unloading stations, it is necessary to stop the vehicles with high precision. In other sections of the track such as merge locations, it may also be necessary to stop the vehicles to avoid potential vehicular collisions. Also in many systems, it is necessary to decelerate vehicles at certain sections of the track to ensure that when vehicles enter the following sections of the track such as curves or grades, they do so below a certain speed in order to minimize the chance of derailment.

In some of the conventional in-track transit systems, a single linear motor primary in combination with an expensive controller is used in the stopping zones to stop the vehicles along the track within the stopping zones. Although this type of stopping mechanism typically functions satisfactorily, problems can arise in the event of failure of the LIM primary or controller therefor. This is due to the fact that if the LIM primary or controller fails, the vehicle will pass through the stopping zones unimpeded.

The problem of uncontrolled travel of a vehicle due to power failure has been considered by U.S. Patent 4,819,564 to Brandis et al which shows a track installation having a continuous stator disposed between the rails of a track. The track is divided into a plurality of sections with each section having a brake associated therewith. The brakes receive the supply current applied to the stator and remain inoperative as long as current is supplied to the stator. However, when the current supply to the stator is interrupted, the brakes move to an operative position. A vehicle coasting along the track due to a power supply failure will be stopped by one of the brakes as the vehicle passes thereover since the brakes function to engage frictionally the vehicle located within their associated track section. This prevents vehicles from moving uncontrolled along the track in the event of a power failure.

Although this design is satisfactory for stopping vehicles during power system failure, it is not suitable for repeatedly stopping vehicles under normal operating procedures or for stopping vehicles in the event of stator malfunction.

In conventional deceleration zones used in conventional in-track transit systems, closed loop control has been implemented using multiple LIM primaries and associated controllers therefor. Although these components provide excellent vehicle control, a problem exists in that if the linear induction motor primaries and/or controllers fail, vehicles are not slowed at all (except due to friction and drag) in the deceleration zone and thus, may enter the following sections of the track at unsafe speeds. Furthermore, another problem exists in that the controllers and LIM primaries are expensive and thus, conventional systems using multiple LIM primaries increase construction and operation costs of the transit system. A prior art in-track transit system is shown in U.S. Patent 4,716,346 to Matsuo which discloses a conveying apparatus including a track having a curve and a carriage movable along the track. The track is provided with a plurality of LIM stators disposed along the straight portions of the track. A reaction rail is secured to the chassis of the carriage and communicates with the stators. Carriage detection sections are also located on the track and are positioned before and after the curved segment of the track. The carriage detection sections co-operate with the LIM stators and detect the speed and mass of the carriage. When a moving carriage passes over a carriage detection section, the speed of the carriage is calculated. A predetermined reverse thrust is then provided to the carriage via an energizing LIM stator and the speed of the carriage is once again calculated. This allows the mass of the carriage to be determined so that the maximum speed of the carriage over the curved section of track can be calculated. Once the maximum speed has been calculated, it is compared with the speed of the carriage so that the necessary thrust can be applied to the carriage before it enters the curved segment of the track to ensure that the vehicle travels at the correct maximum speed over the curved segment of track.

As can be seen, the carriage detection sections in the Matsuo system require two controllers and two LIM stators to permit the mass of the carriage to be calculated so that the second LIM stator can be operated to supply the necessary thrust to the carriage, thereby ensuring the carriage. It should be apparent that if the controllers or LIM stators in the Matsuo system fail, the carriage is not slowed prior to entering the curved section of the track. Furthermore, the cost of the multiple controllers and LIM stators makes this type of velocity control zone expensive.

Outside of the stopping and deceleration zones, conventional in-track transit systems are operated in a manner so that vehicles are propelled at high speeds to increase vehicle throughput. However, the increased speed requires increased headway between vehicles to avoid collisions. Collisions can be avoided by ensuring that the spacing between successive vehicles is large but this substantially reduces vehicle throughput in the transit system. Collisions can also be avoided by increasing the number of LIM primaries positioned along the track and by providing high precision controllers for each of the LIM primaries. However, this type of collision avoidance scheme increases substantially construction and operating costs of the transit system.

Also in these in-track transit systems, an extensive power system is used to supply all of the LIM primaries disposed between the rails of the track. During vehicle braking operations, current drawn from the power system by the LIM primaries can be large thereby increasing costs due to the assessed penalties from the hydro utility. When vehicles are propelled at high speeds and braking thrusts increase, costs are increased further.

It is therefore an object of the present invention to obviate or mitigate the above disadvantages by providing novel zones in a linear motor in-track transit system and a controller therefor.

DISCLOSURE OF THE INVENTION

According to one aspect of the present invention, there is provided a stopping zone in a linear motor in-track transit system, said transit system including a guideway and at least one vehicle moveable along said guideway, said stopping zone comprising: primary braking means disposed along said guideway and being operable to stop a vehicle entering said stopping zone; and secondary braking means disposed along said guideway and being spaced from said primary braking means, said secondary braking means being conditioned to stop the vehicle upon failure of said primary braking means. Preferably, the primary braking means is in the form of a linear motor primary having a controller associated therewith, the controller being operable to condition the linear motor primary to provide sufficient reverse thrust to the vehicle entering the stopping zone to stop the vehicle at a designated stopping point within the stopping zone.

It is also preferred that the secondary braking means is conditioned to an operative condition in response to outputs signals generated by a position sensor disposed along the guideway downstream from the primary braking means, the position sensor detecting excess travel of the vehicle beyond the designated stopping point.

In one embodiment, it is preferred that the secondary braking means in the form of a mechanical brake located downstream from the primary braking means, the mechanical brake being responsive to output signals generated by an overshoot sensor. The overshoot sensor provides an enable signal to the mechanical brake when the vehicle is detected as travelling past the desired stopping point. Preferably, a second linear motor primary is included in the stopping zone and is positioned between the mechanical brake and the first linear motor primary. The second linear motor primary is used to restart vehicles that have been stopped by the mechanical brake.

In another embodiment, it is preferred that the mechanical brake is disposed between the first linear motor primary and the second linear motor primary.

In still yet another embodiment, it is preferred that the primary and secondary braking means are in the form of first and second linear motor primaries respectively, the second linear primary motor of which is located upstream from the first linear motor primary. In this embodiment, the second linear motor primary is operable to slow a vehicle to a predetermined speed when the vehicle enters the stopping zone. The first linear motor primary is operable to stop the vehicle slowed by the second linear motor primary. However, the second linear motor primary operates to stop the vehicle when the vehicle is detected as travelling beyond the designated stopping point.

According to another aspect of the present invention there is provided a voltage controller for a linear motor primary disposed along a guideway comprising: switch means operable between first and second conditions, in said first condition, said switch means connecting said linear motor primary to the positive phase sequence of a three phase power supply and in said second condition, said switch means connecting said linear motor primary to the negative phase sequence of said power supply; control means operable to actuate said switch means to one of said conditions so that said linear motor primary is operable to generate thrust in a desired direction; and scaling means interconnecting said power supply and said switch means when said switch means is in said second condition to reduce the current drawn from said power supply by said linear motor primary.

In another aspect of the present invention there is provided a transit system comprising: a guideway; at least one vehicle movable along said guideway, said guideway being divided into a plurality of blocks; at least two linear motor primaries disposed along said guideway within said block at spaced intervals and being operable to supply thrust to a vehicle within said block; a three phase power supply connectable to said linear motor primaries; switch means interposed between said power supply and at least one of said linear motor primaries, said switch means being actuable between first and second conditions to connect said linear motor primary to one of the positive and negative phase sequences of said power supply respectively; control means operable to actuate said switch means to said first condition in normal operation and to said second condition when it is desired to stop said vehicle in said block; and scaling means interconnecting said power supply and said switch means when said switch means is in said second condition to reduce the current drawn from said power supply by said linear motor primary.

Preferably, the control means conditions one of the linear motor primary means to slow a vehicle to a speed below a pre-determined value and the other linear motor primary means located downstream from the one linear motor primary means to stop the vehicle when a sensing means in the adjacent downstream block of the guideway detects the presence of a vehicle. It is also preferred that each block includes a plurality of the one linear motor primary means, each of which is operable to supply a pre-determined forward thrust to a vehicle passing thereover in normal operation if the vehicle is detected as travelling below a pre-determined speed and each of which is operable to supply a pre-determined reverse thrust to a vehicle upon conditioning thereof by the control means without stopping the vehicle.

Preferably, the scaling means reduces the voltage of the power supply so that the current drawn by the linear motor primary when operating to generate a reverse thrust is substantially the same as when operating to generate a forward thrust. It is also preferred that the scaling means is in the form of an auto-transformer, the transformer reducing the voltage of the power supply by about 20% prior to supplying the linear motor primary. Preferably, the switch means in the form of a reversible contact switch responsive to the control means and operates to reverse the phase sequence of the power supplied to the linear motor primary means to cause the linear motor primary means to provide a reverse thrust to a vehicle upon conditioning by the control means.

According to yet another aspect of the present invention there is provided a transit system comprising: a guideway; a plurality of vehicles movable along said guideway and including linear motor secondary means secured thereto, said guideway being sub-divided into a plurality of blocks, each of said blocks including at least two linear motor primary means disposed along said guideway at spaced intervals for communicating with said linear motor secondary means and being operable to provide a forward thrust thereto in normal operation; sensing means for detecting the presence of a vehicle in each of said blocks; and control means operable to condition said linear motor primary means to stop a vehicle in a block when a sensing means in the adjacent downstream block detects the presence of a vehicle therein.

According to still yet another aspect of the present invention there is provided a high speed zone in a linear motor in-track transit system, said transit system including a guideway and a plurality of vehicles movable along said guideway, said high speed zone being defined by a section of said guideway and being sub-divided into a plurality of blocks, each of said blocks including: at least two linear motor primary means disposed along said guideway at spaced intervals for communicating with linear motor secondary means secured to said vehicles and being operable to provide a forward thrust thereto in normal operation; sensing means for detecting the presence of a vehicle in each of said blocks; and control means operable to condition said linear motor primary means to stop a vehicle in a block when a sensing means in the adjacent downstream block detects the presence of a vehicle.

Preferably, the control means conditions one of the linear motor primary means to slow a vehicle to a speed below a pre-determined value and the other linear motor primary means located downstream from the one linear motor primary means to stop the vehicle when a sensing means in the adjacent downstream block detects the presence of a vehicle. It is also preferred that each block includes a plurality of the one linear motor primary means, each of which is operable to supply a pre-determined forward thrust to a vehicle passing thereover in normal operation if the vehicle is detected as travelling below a pre-determined speed and each of which is operable to supply a pre¬ determined reverse thrust to a vehicle upon conditioning thereof by the control means without stopping the vehicle.

Preferably, switch means in die form of a reversible contact switch is connected between the plurality of one linear motor primary means and a power distribution system and operates to reverse the phase sequence of the power supplied to the linear motor primary means to cause the linear motor primary means to provide a reverse thrust to a vehicle upon conditioning by the control means.

It is also preferred that the sensing means includes a plurality of proximity sensors disposed along the guideway in a manner so that at least one of the sensors will always detect the presence of a vehicle located within the block. Preferably, a pair of sensors are positioned on opposite sides of each of the plurality of one linear motor primary means and the other linear motor primaries means, each sensor providing signals to the control means upon detection of a vehicle. Preferably, the control means is in the form of a programmable controller electrically connected to the sensors, the reversible contact switch and the programmable controller in the adjacent upstream and downstream blocks.

According to still yet another aspect of the present invention there is provided a deceleration zone in a linear motor in-track transit system, said transit system including a guideway and at least one vehicle movable along said guideway, said vehicle including linear motor secondary means secured thereto, said deceleration zone being located along a section of said guideway and having a vehicle entrance end and a vehicle exit end, said deceleration zone comprising: magnetic braking means positioned along said guideway adjacent said vehicle entrance end; and linear motor primary means positioned along said guideway adjacent said vehicle exit end wherein said magnetic braking means operates independently of said linear motor primary means and interacts with the linear motor secondary means secured to a vehicle to provide a substantially constant retarding thrust thereto to slow said vehicle and wherein said linear motor primary means interacts with the linear motor secondary means secured to said vehicle and provides thrust thereto, said thrust being of a magnitude and direction so that said vehicle exits said deceleration zone having a velocity substantially equal to a desired velocity.

Preferably, the magnetic braking means includes at least one permanent magnet decelerator (PMD) and the deceleration zone is positioned in the transit system so that vehicles entering the deceleration zone have a speed in the constant force range of the permanent magnet decelerator. It is also preferred that the linear motor primary is in the form of a synchronous linear induction motor. Preferably the permanent magnet decelerators are arranged to slow vehicles of a high mass to a velocity above the synchronous speed of the LIM primary and to slow vehicles of lower mass to a velocity less than the synchronous speed of the linear induction motor primary.

In still yet another aspect of the present invention, there is provided a decelerator for use in a linear motor in-track transit system comprising: magnetic braking means for disposition along a guideway and operable to provide a substantially constant retarding thrust to a vehicle having a reaction element secured thereto and passing thereover; and a synchronous linear motor primary for disposition along said guideway downstream from said magnetic braking means, said synchronous linear motor primary being operable to supply a thrust to said vehicle having a magnitude and direction so that said vehicle assumes a velocity substantially equal to the synchronous speed of said synchronous linear motor primary.

Preferably, the deceleration zones are located in the transit system adjacent and upstream of track switches, curves and downgrades to slow vehicles before they enter these sections of the track.

The present invention provides advantages in that the time taken for vehicles having different mass passing through a deceleration zone in the transit system remains substantially constant thereby maintaining vehicle separation. This allows the throughput of vehicles in the transit system to be increased as compared with conventional systems. Moreover, other advantages exist in that even if the linear motor primary or controller therefor fails, the permanent magnet decelerators provide a retarding thrust to the vehicles ensuring that the vehicles are slowed prior to entering the following section of track. Also, since a synchronous linear motor primary is used, a complex controller for the motor is not required thereby reducing costs. In addition, the collision avoidance scheme used in the present invention provides advantages in that high vehicle throughput is achieved while reducing vehicular collisions and costs. Also, the reduced voltage braking scheme provides advantages in that high vehicle throughput is achieved while reducing large current from being drawn from the power supply when braking is required. This of course simplifies the requirements of the power system and reduces costs.

Moreover, the provision of two braking mechanisms in each stopping zone provides advantages by ensuring that vehicles are stopped in the stopping zone even in the event of failure of the primary brake. Furthermore, since vehicles are stopped in the stopping zone even in the event of failure of one of the brakes, linear motor primaries can be conveniently located for restarting vehicles regardless of which brake is used to stop the vehicle within the stopping zone.

BRIEF DESCRIPTION OF THE DRAWING

Embodiments of the present invention will now be described more fully with reference to the accompanying drawings in which:

Figure 1 is a top plan view of a transit system;

Figure 2 is a side view of a portion of the transit system shown in Figure 1.

Figure 3 is a side view of a stopping zone in the transit system shown in Figure 1;

Figure 4 is a side view of another stopping zone in the transit system shown in Figure 1;

Figure 5 is a side view of still yet another stopping zone in the transit system shown in Figure 1; Figure 6 is a perspective view of a mechanical brake used in the stopping zones shown in Figures 3, 4 and 5; and

Figure 7 is an end view of the mechanical brake shown in Figure 6 together with a portion of a vehicle.

Figure 8 illustrates two adjacent blocks within a high speed zone in the transit system shown in Figure 1;

Figure 9 illustrates the typical velocity of a vehicle moving through one of the blocks illustrated in Figure 8;

Figure 10 shows operating characteristics of linear motor primaries used in the blocks shown in Figure 8;

Figure 11 shows additional operating characteristics of a linear motor primary used in the blocks shown in Figure 8;

Figure 12 shows graphs illustrating characteristics of permanent magnet decelerators used in the deceleration zone shown in Figure 2;

Figure 13 shows a graph illustrating the response of vehicles passing over the permanent magnet decelerators shown in Figure 2;

Figure 14 shows a response curve of a synchronous linear induction motor used in the deceleration zone shown in Figure 2; and

Figure 15 shows response curves of vehicles passing through the deceleration zone shown in Figure 2.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to Figures 1 and 2, a transit system is shown and is generally indicated by reference numeral 10. The transit system 10 includes a track 12 having a pair of rails 14,16. Linear induction motor (LIM) primaries 18 are located between the rails of the track 12 at spaced intervals. Freight-carrying vehicles 20 are supported by the track 12 and are movable therealong. Each vehicle 20 includes a reaction rail 22 or LIM secondary secured to its chassis which cooperates with the linear induction motor primaries 18 in a known manner to propel the vehicles 20. Since the operation of linear induction motors is well known to those of skill in the art, a detailed description thereof will not be discussed herein.

As can be seen, the track 12 extends between a manual freight loading station 28 and an automatic freight unloading station 30. The majority of the track 12 extending between the two stations 28, 30 is generally horizontal and straight. These sections of the track are designated by reference numerals 36 and 38 and are sections of the track where vehicles are propelled at high speeds to increase vehicle throughput. However, the track also experiences a downgrade 32 (best seen in Figure 2) and a curve 34 (best seen in Figure 1) along a portion of its length. Deceleration zones D_x and D₂ are designated along portions of the track 12 adjacent the vehicle entrance end of the downgrade 32 and the vehicle entrance end of the curve 34 respectively. The deceleration zones Dj and D₂ are identical and function to slow vehicles 20 travelling along the track between the stations 28,30 to a desired speed before the vehicles leave the deceleration zones and enter the following sections of track.

A merging section of track 40 intersects the main track 12 at a location adjacent the bottom of the downgrade 32. Similarly, the merging section of track 40 has linear induction motor primaries 18 disposed between the rails thereof at spaced intervals to propel vehicles 20.

Vehicle stopping zones Sj and S₃ are designated along the track 12 in the loading and unloading stations 28,30 respectively and function to stop the vehicles 20 at the stations so that freight can be placed on the vehicles and removed therefrom. A stopping zone S₂ is also designated along a section of the merge track 40 so that vehicles travelling therealong are automatically stopped before entering the main track 12. The stopping zones S_, S₂ and S₃ include a primary brake and a secondary brake, each brake of which is operable to stop the vehicle. However, the secondary brake remains in an inoperative condition unless the vehicle 20 has been detected as passing a designated stopping point within the stopping zone due to failure or malfunction of the primary brake.

To increase throughput in the transit system 10, it is desired to move the vehicles 20 along the track 12 between the loading and unloading stations 28,30 respectively as fast as possible with accurate control to avoid high speed collisions. This collision avoidance is achieved by dividing the track into fixed segments or blocks Bj to B^. When a vehicle 20 is detected as being present in a block B_x by sensors positioned along the track, a block occupied signal BLO is generated by a controller 44 in the block B_x and is applied to the controller 44 in the previous or upstream block B_x.,. If a vehicle enters the previous block B_x_j while the controller 44 therein is receiving the block occupied signal BLO from the adjacent downstream block B_x, the LIM primaries 18 in the block B_x.j are operated by the controller 44 in a manner to cause the vehicle 20 to be stopped within the block B_x.j. This prevents two vehicles from being located within the same block and thus, avoids collisions between vehicles and maintains vehicle spacing. This operation is achieved by ensuring that the length of each block B_x is sufficient to stop a vehicle completely or at least to slow a vehicle to a speed such that even if the vehicles collide in the block B_x, the impact resulting from the collision can be withstood by the vehicles without any resulting damage.

Referring now to Figures 3, 6 and 7, the stopping zone Sj in the manual loading station 28 is better illustrated. As can be seen, the stopping zone S_j includes two spaced linear induction motor primaries 18a, 18b disposed between the rails of the track 12. The LIM primaries 18a, 18b are positioned in a manner so that the reaction rail 22 secured to a vehicle 20 extends over both LIM primaries at certain positions in the stopping zone. A mechanical wayside "fail-safe" brake assembly 60 (best illustrated in Figure 6) is also disposed along the track 12 within the stopping zone Si and is positioned between the two LIM primaries 18a, 18b respectively. The brake assembly 60 includes a housing 60a in which an air actuated drive (not shown) is contained. A pair of spaced brake clamps 60b project upwardly through an opening in the housing 60a and are biased towards one another by four coil springs located within the housing. An air cylinder 60c connected to a suitable compressed air supply is operable to actuate a drive within the housing by supplying compressed air thereto upon actuation of a solenoid 60d mounted on the housing. The drive in turn reverse biases the springs to move the brake clamps 60b apart and thus, release the brake assembly 60. An exhaust valve 60e is also provided to decompress the air cylinder 60c so that brake clamps 60b spring back to the closed position when desired. The brake clamps 60b are operable to engage a brake rail 21 secured to the chassis of the vehicles 20 when moved to the closed position. Typically, the brake clamps are maintained in the open position but are returned to the closed position when required. This design is preferred in that the brake clamps automatically move to the closed position upon power failure or isolation from the compressed air supply.

The LIM primary 18a is controlled by a linear voltage control module (LVCM) 64 which is capable of connecting the LIM primary 18a to a power distribution system PDS in a manner so that the LIM primary supplies thrust to the vehicles having a desired magnitude and direction. LVCM sensors 65 are positioned along the track on opposite sides of the LIM primary 18a and communicate with the LVCM 64 so that the position and speed of the vehicle in the stopping zone S_x can be determined by the LVCM.

The other LIM primary 18b is controlled by a synchronous speed starter (SSS) 66 which is operable to connect the LIM primary 18a to the positive phase sequence of the power distribution system PDS at full voltage. Thus, the LIM primary 18b is only capable of supplying a predetermined forward thrust to a vehicle 20 located within the control zone of the LIM primary 18b. An overshoot sensor 68 in the form of a proximity switch is positioned along the track 12 adjacent the LIM primary 18b and is operable to detect travel of a vehicle beyond a designated stopping point Pj within the stopping zone. The sensor 68 and the LVCM sensors 65 are arranged so that at least one of the sensors always detects the presence of a vehicle located within the stopping zone Sj. The sensors 65,68 are in communication with a programmable controller 44 and provide signals thereto upon detection of a vehicle 20. The controller 44 is also in communication with the LVCM 64, the solenoid 60d of the brake assembly 60, the synchronous speed starter 66 and the programmable controller 44 in the adjacent downstream section Bj of the track 12. The programmable controller 44 is also in communication with the programmable controller 44 in the adjacent upstream section B₀ of the track 12 and provides a signal BLO thereto when a vehicle is located within the stopping zone S_t. This signal is used by the upstream programmable controller 44 to prevent another vehicle from entering the stopping zone Sj when it is already occupied by a vehicle 20.

Figure 4 shows the low speed stopping zone S₂ located at the intersection formed between the merge section 40 and the main section of track 12. As mentioned previously, the stopping zone S₂ functions to stop vehicles 20 prior to vehicles merging onto the main section 12 of the track. As can be seen, the stopping zone S₂ also includes a pair of spaced LIM primaries 18c, 18d disposed between the rails of the track. An LVCM 80 is operable to connect one of the LIM primaries 18c to the power distribution system PDS while a synchronous speed starter 82 is operable to connect the other LIM primary 18d to the power distribution system. LVCM sensors 81 in communication with the LVCM 80 are positioned between the rails of the track on opposite sides of the LVCM 80. An overshoot sensor 84 is located along the track downstream of the second LIM primary 18d and detects excess travel of a vehicle 20 beyond a designated stopping point P₂ within the stopping zone S₂. The overshoot sensor 84 and the LVCM sensors 81 are in communication with a programmable controller 44 and are spaced along the track in a manner so that at least one of the sensors always detects the presence of a vehicle in the stopping zone.

Another brake assembly 88 identical to brake assembly 60 is located along the track 12 slightly downstream from the overshoot sensor 84. The brake assembly 88 is similarly operable to engage frictionally the brake rail 21 secured to a vehicle to stop the vehicle. The solenoid of the brake assembly 88 is also in communication with the programmable controller 44 and is actuated to an inoperative position by the programmable controller 44 upon detection of a vehicle 20 within the stopping zone S₂. The programmable controller 44 is also in communication with the programmable controllers 44 located in the adjacent upstream and downstream segments of track, with the LVCM 80 and with the synchronous speed starter 82.

Figure 5 illustrates the high precision stopping zone S₃ used in the automatic freight unloading station 30. The stopping zone S₃ includes a pair of spaced LIM primaries 18e,18f located between the rails of the track 12, each of which is controlled by an LVCM 90,92 respectively. A plurality of LVCM sensors 94 are located along the track 12 at spaced intervals and communicate with the LVCMs 90,92. The sensors are located along the track 12 in a manner so that any vehicle located within the stopping zone S₃ is always detected by at least one sensor. Similar to the other stopping zones, the LVCMs 90,92 are operable to connect the LIM primaries 18e,18f to the power distribution system PDS. A brake assembly 96 identical to the brake assembly 60 is located downstream from the LIM primary 18f and is operable to engage fictionally the brake rail 21 secured to the chassis of the vehicles 20. An overshoot detector 98 in the form of a proximity switch is located downstream from the brake assembly 96 and communicates with a programmable controller 44. The programmable controller 44 also commumcates with the brake assembly 96, the two LVCM's 90,92 and the LVCM sensors 94 to effect high precision stopping of vehicles at a designated stopping point P₃ within the stopping zone S₃. The programmable controller 44 also communicates with the programmable controllers 44 in the in adjacent upstream and downstream sections of the track 12.

The operation of the three stopping zones will now be described. In operation, when a vehicle 20 enters the loading station 28, it is desired to stop the vehicle so that freight can be placed thereon. In this instance, since the loading of freight is performed manually, high precision stopping of the vehicle in the stopping zone at the designated stopping point ¥• is not critical, since small variations in the stopping point can be tolerated by personnel loading the freight on the vehicle. When the vehicle 20 enters the stopping zone Si, the LVCM sensors 65 detect the presence of the vehicle and supply signals to the LVCM 64 and to the programmable controller 44. Since the sensors 65 are arranged so that a vehicle 20 within the stopping zone Si is always detected by at least one sensor, the controller 44 always receives a signal from at least one sensor when a vehicle is present in the stopping zone. The controller 44 in response to the signals received from the sensors, generates a BLO signal which is conveyed to the controller 44 in the previous section BQ of track 12. The BLO signal is used by the upstream controller 44 to inhibit another vehicle 20 from entering the stopping zone S_ when it is already occupied by a vehicle. When the LVCM 64 receives the signals generated by the sensors 65, the LVCM 64 calculates the speed of the vehicle and in turn connects the linear induction motor primary 18a to the power distribution system PDS in a manner so that the LIM primary 18a supplies a reverse thrust to the vehicle to bring the vehicle to a stop with its centre over the designated stopping point Pj. Once the vehicle 20 has been stopped, an output signal is generated by the LVCM 64 and is conveyed to the programmable controller 44. The controller 44 in turn disables the LVCM 64 to prevent the LIM primary 18a from being energized and enables the brake assembly 60 by supplying a conditioning signal to the solenoid 60d and to the exhaust valve 60e. When this occurs, the solenoid triggers to disconnect the air cylinder 60c from the compressed air supply and to release the air pressure within the drive. This causes the drive to release so that the springs move the brake clamps 60b together and clamp onto the brake rail 21 secured to the chassis of the vehicle 20. This prevents the chassis of the vehicle 20 from rolling during loading. At this time, the vehicle 20 can be manually loaded with freight.

Once tiie vehicle 20 has been loaded with freight, a signal is provided to the controller 44 by the operating personnel. The controller 44 in turn energizes the brake assembly 60 by activating the solenoid 60d allowing the air cylinder 60c to supply the drive. This reverse biases the springs so that the brake clamps 60b move apart and disengage the brake rail 21. Once this has been done, the controller 44 enables the LVCM 64 if a block occupied signal BLO is not being received by the programmable controller 44 from the downstream block B₂. When the LVCM 64 is enabled, the LVCM connects the LIM primary 18a to the power distribution system PDS so that the LIM primary supplies a forward propulsive force to the vehicle 20 causing the vehicle to leave the stopping zone Si and enter the next segment Bj of track on its way to the unloading station 30. Once the vehicle 20 leaves the stopping zone Si, the output of the sensors therein go low thereby causing the programmable controller 44 to remove the BLO signal applied to the upstream controller 44. This allows the upstream controller to direct another vehicle 20 into the stopping zone S During normal operation, the LIM primary 18a operates to stop the vehicle 20 at the designated stopping point Pj and the vehicle does not trigger the brake engage sensor 68. However, since the sensor 68 is located slightly downstream from the typical stopping point P_x of the leading edge of the reaction rail 22, some overshoot past the designated stopping point by the vehicle 20 is permitted in typical operation without activating any secondary braking mechanism. If overshoot occurs and the reaction rail 22 lies in the control zone of both LIM primaries 18a, 18b without triggering the sensor 68, the programmable controller 44 enables the LVCM 64 and the synchronous speed starter 66 so that both LIM primaries are used to restart the vehicle 20 after the brake assembly 60 has been released.

However, if the LIM primary 18a or LVCM 64 completely fail or malfunction and the vehicle 20 is not stopped within the tolerated overshoot interval, the sensor 68 detects the presence of the reaction rail 22 secured to the vehicle 20 and supplies a signal to the controller 44. When this occurs, the controller 44 disables the LVCM 64 and activates the brake assembly 60 in the same manner previously described. The brake assembly 60 in turn operates to engage frictionally the brake rail 21 secured to the vehicle 20 causing the vehicle to stop with its centre located within the stopping interval SIj. This operation minimizes vehicle overshoot past the designated stopping point P_j. The exact stopping point of the vehicle within the stopping interval Sl_x is of course dependant on the speed and mass of the vehicle when it passes over the sensor 68. Once the vehicle has been stopped by the brake assembly 60, the vehicle 20 can be loaded with freight. Once loaded, a signal is supplied to the programmable controller 44 by the operating personnel. The controller 44 in turn energizes the brake assembly 60 in the manner described previously and operates the starter 66. Once operated, the synchronous speed starter 66 connects the LIM primary 18b to the positive phase sequence of the power distribution system PDS at full voltage so that the LIM primary 18b supplies a predetermined forward thrust to the vehicle 20 causing the vehicle to leave the stopping zone S_t and enter the following segment Bj of track 12.

After the vehicle has left the stopping zone Sj, the LIM primaries 18 in each block B_x are successively operated to propel the vehicle 20 along the track towards the unloading station 30 in a manner to avoid collisions by ensuring that only one vehicle is located within each block and to ensure that vehicles enter curves in the track at desired speeds as will be more fully described. When the vehicle enters the unloading station 30, the high precision stopping zone S₃ brings the vehicle 20 to a stop so that the centre of the vehicle overlies the designated stopping point P₃. This allows automated freight unloading equipment to unload the vehicle.

In particular, as the vehicle 20 enters the stopping zone S₃, the first LVCM sensor 94 detects the presence of the vehicle 20 and provides signals to the LVCM 90 and to the controller 44. The LVCM 90 in turn connects the LIM primary 18e to the power distribution system PDS in a manner to cause the LIM primary 18e to provide a reverse thrust to the vehicle 20 so that the vehicle is slowed to a desired speed but not stopped. At the same time, the controller 44 generates a BLO signal in response to the signals received from the sensors 94 and conveys the BLO signal to the upstream block B₉. This prevents another vehicle from entering the stopping zone S₃ while it is occupied by a vehicle. Once this occurs and the vehicle is detected as passing over the second LVCM sensor 94, the sensor 94 provides a signal to the controller 44 which in turn disables the LVCM 90 and enables the other LVCM 92. Once enabled, the LVCM 92 connects the LIM primary 18f to the power distribution system PDS in a manner so that the LIM primary 18f applies a reverse thrust to the vehicle 20 causing the vehicle to stop with its centre over the designated stopping point P₃. Since the speed of the vehicle 20 is reduced substantially prior to entering the control zone of the second LIM primary 18f, precision stopping of the vehicle at the stopping point P₃ is permitted while reducing the maximum current drawn from the power distribution system PDS by the LIM primaries 18e and 18f respectively.

Once the vehicle 20 has been stopped, a signal is conveyed to the controller 44 by the LVCM 92. The controller 44 in response to the signal disables the LVCM 92 and supplies a signal to the brake assembly 96 so that the brake assembly 60 inhibits any further movement of the vehicle 20 in the same manner previously described. At this time, the automatic freight removal equipment is operated. Once the freight has been removed from the vehicle, a signal is applied to the controller 44 from the freight removal equipment. The controller 44 in turn engages the brake assembly 96 in the same manner as described for brake assembly 60 and enables the LVCM 90 so that the first LIM primary 18e can be operated to restart the vehicle provided the following section of the track 12 is not occupied by another vehicle 20. If the last LVCM sensor 94 detects the presence of the vehicle without the overshoot sensor 98 being triggered, the controller 44 enables both LVCM's 90,92 so that both LIM primaries 18e,18f are used to restart the vehicle 20 provided the following section of the track 12 is not occupied by another vehicle 20.

If the LVCM 90 or LIM primary 18e fails so that the vehicle 20 is not slowed by the LIM primary 18e, the excess speed of the vehicle is detected by the LVCM 92 using the output signals generated by the sensors 94. The LVCM 92 in turn connects the second LIM primary 18f to the power distribution system PDS in a manner so that the vehicle is still stopped with its centre over the designated stopping point P₃ without the vehicle passing over the overshoot sensor 98. Once the vehicle 20 has been stopped, the LVCM 92 is disengaged by the controller 44 and the brake assembly 96 is released to permit freight removal. After this occurs, the brake assembly 96 is connected to the compressed air supply and the LVCM 92 is engaged by the controller 44 so that the LIM primary 18f can be operated to restart the vehicle provided the following section of the track 12 is not occupied by another vehicle 20.

In the event that the second LJM primary 18f or LVCM 92 foils after the first LIM primary 18e has slowed the vehicle 20, the excess travel of the vehicle beyond the designated stopping point P₃ is detected via the overshoot sensor 98. When this occurs, the sensor output is conveyed to the controller 44 which in turn enables the LVCM 90. The LVCM 90 in turn connects the LIM primary 18e to the power distribution system PDS so that the necessary reverse thrust is applied to the vehicle 20 thereby bringing the vehicle to a stop with the centre of the vehicle lying within a stopping interval SI₃. When this occurs, the LVCM 90 continues to operate the LIM primary 18e so that the vehicle reverses direction and is stopped with its centre over the stopping point P₃. After this, the controller 44 disengages the LVCM 90 and supplies a signal to the brake assembly 96 so that the brake assembly inhibits any further movement of the vehicle 20 thereby allowing the freight to be removed from the vehicle. Following this, the controller 44 energizes the brake assembly 96 and engages the LVCM 90 to permit restarting of the vehicle provided the following section of the track 12 is not occupied by another vehicle 20.

The stopping zone Sj is included in the transit system 10 to stop all vehicles before they enter the main section of the track 12 from the merge section 40 of track. When a vehicle 20 enters the stopping zone Sj, the presence of the vehicle is detected by at least one LVCM sensor 81. The sensors 81 in turn provide signals to the LVCM 80 as well as to the controller 44 when they detect the presence of a vehicle 20. The LVCM 80 in turn connects the LIM primary 18c to the power distribution system PDS so that a reverse thrust is applied to the vehicle 20 causing the vehicle 20 to stop with its centre over the designated stopping point P₂. At the same time, the controller 44 releases the brake assembly 88 in the same manner as described for brake assembly 60 to a closed position and provides a BLO signal to the block B_π to prevent another vehicle from entering the stopping zone while it is occupied. In normal operation, the LVCM 80 and LIM primary 18c operate to stop the vehicle 20 at a designated stopping point P₂ before it reaches the brake assembly 88 and thus, the brake assembly 88 although operated to close the brake clamps does not engage the brake rail 21 of the vehicle. Therefore, the brake assembly 88 effectively remains inoperative. After the vehicle 20 has stopped, a signal is conveyed to the programmable controller 44 by the LVCM 80 causing the controller 44 to energize the brake assembly 88. Thereafter, the LVCM 80 operates the LIM primary 18c to restart the vehicle provided the following section of track is clear. If the following section of track is occupied, the controller 44 operates in the same manner as in the other stopping zones and inhibits the LVCM 80 from operating until the track becomes clear.

If the LIM primary 18c or LVCM 80 fail and the vehicle 20 travels beyond the designated stopping point P₂, the brake assembly 88 engages the brake rail 21 secured to the vehicle 20 causing it to stop with its centre lying within a stopping interval SI₂. When this occurs, the overshoot sensor 84 detects the presence of the vehicle and provides signals to the controller 44. The controller 44 in turn disables the LVCM 80 to prevent the LIM primary 18c from generating thrust against the braking force of the brake assembly 88.

Once the vehicle 20 has been stopped by the brake assembly 88 and the following section of the track is detected as being clear, the brake assembly 88 is energized by the controller 44. Thereafter, the synchronous speed starter 82 is enabled by the controller 44 so that the second LIM primary 18d restarts the vehicle. With the vehicle 20 restarted, the vehicle enters the main segment of track 12 and proceeds to the unloading station 30. Referring now to Figure 8, a portion of the "high speed zone" section 36 of the track 12 including two complete segments or blocks B; and B₃ respectively is shown. The length of the two adjacent blocks B₂ and B₃ is labelled as DVF while the length of each block is indicated by DBL. As can be seen, each block is substantially identical and is divided into two sections, namely a speed conditioning section 50 and an end section 52. The speed conditioning sections 50 include three cruise linear induction motor (LIM) primaries 18g located at spaced intervals between the rails of the track 12 within the blocks. The cruise LIM primaries 18g are chosen to have characteristics to enable a "worst case" vehicle 20 to be slowed to a speed below a pre-determined value, if necessary, before the vehicle enters the end section 52 while allowing the vehicle 20 to be propelled through the section 50 at a desired average speed v_W8 if it is not necessary to stop the vehicle within the block. The cruise OM primaries typically operate at 75% to 80% of the synchronous speed of the LIM primary 18g and supply thrust to vehicles in the forward mode accordingly.

Since the blocks B₂ and B₃ are identical, a detailed description of block B₂ will only be provided herein. Each of the cruise LIM primaries 18g is connected to the three phase power distribution system PDS via a non- reversible solid state relay 158. The power distribution system PDS is extensive and supplies all of the LIM primaries 18 in the transit system when they are required to provide thrust to a vehicle. The relays 158 are operable to connect the cruise LIM primaries 18g to the power distribution system PDS at full voltage in response to enable signals received from a programmable controller 44. A reversible contact switch 160 which typically remains in the position shown in Figure 8 is also connected between the relays 158 and the power distribution system PDS. Thus, the reversible contact switch 160 is normally positioned to connect the cruise LIM primaries 18g to the positive phase sequence of the power distribution system PDS but is actuable to connect the cruise LIM primaries 18g to the negative phase sequence of the power distribution system PDS via an auto-transformer 165 in response to signals from the programmable controller 44. The auto-transformer 165 operates to step the nominal full voltage of the power distribution system PDS down so that current drawn by the LIM primaries 18g during reverse thrust operation are reduced. The use of the auto-transformer and its advantages will be described in more detail hereinafter.

A plurality of sensors 164a to 164g in the form of proximity switches are also located along the track 12 at spaced intervals within speed conditioning section 50 of the block Bj. The sensors are positioned between successive LIM primaries 18g and are arranged so that at least one sensor 164 in the section 50 detects the presence of a vehicle 20 located within the conditioning section 50. The programmable controller 44 receives output signals generated by the sensors 164 in response to vehicle detection as well as block occupied signals BLO from the programmable controller 44 located in the adjacent downstream block B₃ via a block occupied conductor 166. The programmable controller 44 in turn provides output signals to a data bus 168 interconnecting all programmable controllers 44 in the transit system 10 and extending to a central computer (not shown) so that transit system diagnostics can be carried out and to another block occupied conductor 166 extending to the programmable controller 44 in the adjacent upstream segment B_t.

The end section 52 includes a single LIM primary 18h which is controlled by a linear voltage control module (LVCM) 172. The LVCM 172 is capable of connecting the LIM primary 18h to the power distribution system PDS in a manner so that the LIM primary supplies thrust to vehicles passing over the LIM primary 18h having a desired magnitude and direction. Thus, the LVCM 172 can operate the LIM primary 18h so that reverse and forward thrusts of different magnitudes can be applied to different vehicles depending on the desired motion profile of the vehicle passing through the end section 52. The LVCM 172 is also connected to the programmable controller 44 via a stop conductor 180 and controls the operation of the UM primary 18h in response to signals received from the controller 44 via the conductor 180 as will also be described herein.

LVCM sensors 174 are positioned between the rails of the track 12 on opposite sides of the LIM primary 18h and function to detect the presence and direction of movement of a vehicle 20 located within the end section 52. The sensors 174 provide signals to the LVCM 172 so that the LVCM 172 is capable of determining the speed and position of a vehicle 20 as it passes through the end section 52. The LVCM sensors 174 also provide signals to the programmable controller 44. Thus, at least one of the sensors 164 and 174 will always detect the presence of a vehicle within the block 1^ and will provide signals to the programmable controller 44 as along as a vehicle 20 is detected within the block.

Since the transit system 10 includes high speed zones 36,38, the operation of the transit system 10 is carried out on the basis that under normal operating conditions there will be no need to stop a vehicle 20 in the designated high speed zones 36,38 to avoid collisions. Minimum occurrence of collisions is therefore controlled by ensuring that the travel time of a vehicle 20 over a block B_x plus the "worst case" stopping distance of a vehicle is at all times less than the minimum headway value, this being the inverse of vehicle throughput expressed as vehicles per minute.

To achieve this, the block length DBL must be equal to or greater than the "worst case" stopping distance of a vehicle. This "worst case" stopping distance of a vehicle is of course determined by the characteristics of the LIM primaries 18 being used to stop the vehicle, the maximum possible mass of the vehicle and the minimum vehicle drag. Another parameter which affects the stopping distance of a vehicle 20 is the spacing between successive LIM primaries 18 in a block. For smooth vehicle travel, the spacing between successive LIM primaries 18 should be equal to the length of the reaction rail 22 secured to each vehicle 20. If non-critical loads such as freight are being transported, the LIM primary spacing can be increased. This introduces higher vehicle accelerations and jerk rates but decreases the costs of the transit system 10. Since the present transit system 10 operates with a LIM primary spacing in the high speed zones greater than the length of the reaction rail 22, the "worst case" stopping distance is greater than the control zone of a single LIM primary. As such, each block B_x requires at least two LIM primaries to stop a vehicle. This requirement is satisfied by providing the cruise LIM primaries 18g in section 50 and the LIM primary 18h in end section 52. Maximizing vehicle throughput in the transit system 10 is achieved by maintaining the separation between two consecutive vehicles travelling through the high speed zones equal to the length of two consecutive blocks DVF. In this manner, a vehicle will never enter a block B_x which is receiving a BLO signal from the adjacent downstream block B_x+1 and thus, the vehicles will never be required to be stopped in a block unless it is a stopping zone.

In operation, when a vehicle 20 has been manually loaded with freight at the loading station 28, the stopping zone Si operates to restart the vehicle 20 provided that the following section of track Bj is clear. Once the vehicle 20 has departed from the loading station 28, another vehicle can be brought into the station for loading.

When the vehicle 20 leaves the loading station 28 and enters the second segment Bj of track 12, it is detected by the first sensor 164a in the conditioning section 50. The sensor 64a generates a signal as long as the vehicle 20 is detected thereover and supplies it to the programmable controller 44. As soon as the programmable controller 44 receives a signal from the sensor 164a, it generates a block occupied signal BLO. The BLO signal is then conveyed to the previous block in this case the stopping zone S_x via conductor 166. The BLO signal received by the programmable controller 44 in the stopping zone S_x causes the programmable controller 44 in the stopping zone to inhibit operation of the LIM primaries in the stopping zone. This prevents the stopping zone from propelling a vehicle into the block Bj while it is occupied by another vehicle 20.

When the vehicle 20 reaches the control zone of the first cruise LIM primary 18g, a signal is generated by the second sensor 164b and is conveyed to the controller 44. When the controller 44 receives the signal generated by the second sensor 164b, the time taken for the vehicle 20 to travel between the sensors 164a and 164b respectively is determined. Since the distance between the sensors 164a and 164b is known, the speed of the vehicle 20 entering the control zone of the first cruise LIM primary 18g can be determined. If the vehicle 20 is detected as travelling above a preset speed V_WB, the controller 44 does not operate the relay 158. This maintains the relay 158 in a disabled condition so that the LIM primary 18g is not energized. Thus, the vehicle 20 coasts along the track 12 over the first cruise LIM primary 18g and decelerates due to friction and drag.

However, if the vehicle 20 is detected as travelling along the track 12 between the two sensors 164a and 164b respectively below the preset speed Y„_g, the controller 44 provides an enable signal to the relay 158 causing it to connect the first cruise LIM primary 18g to the positive phase sequence of the three phase distribution system PDS at full voltage via the contact switch 60. This in turn results in the LIM primary 18g supplying a predetermined forward thrust to the vehicle 20 while the vehicle 20 is located in the control zone of the LIM primary. After the vehicle 20 continues along the track 12 and is detected by the next sensor 164c, the programmable controller 44 disables the relay 158 so that the first cruise LIM primary 18g is de-energized. The controller 44 also determines the time taken for the vehicle to travel between sensors 164c and 164d.

When the vehicle is detected by the third sensor 164c, one of two operations is implemented. If the programmable controller 44 is not receiving a block occupied signal BLO from the programmable controller 44 in the adjacent downstream segment B₃ via the conductor 166, the elements in the block Ba operate in the same manner described above. Thus, the programmable controller 44 allows the second cruise LIM primary 18g to be energized by enabling the relay 158 when the vehicle 20 is detected by sensor 164d as being within the control zone of that LIM primary 18g and if the vehicle 20 is travelling below the preset speed V,^. Otherwise, the relay 158 is maintained in a disabled condition so that the vehicle 20 coasts towards the third cruise LIM primary 18g in the section 50 and decelerates due to friction and drag.

If the programmable controller 44 is still not receiving a BLO signal from the controller 44 in the adjacent downstream block B₃ when the vehicle 20 is detected by sensor 164f, the same operation, as described above, is performed. Thus, the third cruise LIM primary lδg is operated to provide a forward thrust to the vehicle 20 if it is detected as travelling below the preset speed. Similarly, third cruise LIM primary will remain inactive if the vehicle is detected as travelling above the preset speed. In either case, the vehicle will pass over the third cruise LIM primary 18g and enter the end section 52 at a speed substantially equal to the preset speed V^.

When the vehicle 20 enters the end section 52, it is detected by the first LVCM sensor 174. The sensor 174 in turn provides a signal to the programmable controller 44 so that the BLO signal is maintained on conductor 166 and applied to the programmable controller 44 in the adjacent upstream block Si. The LVCM sensor 174 also provides signals to the LVCM 172 so that the speed and position of the vehicle 20 can be determined. When the vehicle 20 reaches the control zone of LIM primary 18h, the LVCM 172 selects a motion profile and connects the UM primary 18h to the power distribution system PDS so that the UM primary 18h operates in the same manner as the cruise LIM primaries 18g. Thus, if the vehicle 20 is detected as travelling below the preset speed V_WΪ, a predetermined forward thrust is applied to the vehicle before it leaves the block B₂ and enters the next block B₃. However, if the vehicle is detected as travelling above the preset speed, it is allowed to coast along the track and enter the next segment B₃ of track 12.

This operation of the LIM primaries 18g and 18h and the resulting thrust supplied to a vehicle 20 passing through the block Bj by the LIM primaries 18g,18h is shown in Figure 9. As can be seen, as a vehicle travelling at the desired preset speed V_wg enters the block Bj, it coasts and decelerates (200) until it reaches the control zone CZj of the first cruise LIM primary 18g. The cruise LIM primary is then connected to the power system PDS at full voltage so that the vehicle 20 is accelerated rapidly as indicated at 202 to a speed above the average speed. When the vehicle 20 leaves the control zone of first cruise LIM primary 18g, it again coasts and decelerates (204) so that the vehicle 20 reaches the control zone C j of the second LIM primary travelling at a speed less than the preset speed V,^. This process is continued throughout the block resulting in successive accelerations and decelerations of the vehicle as it passes through a block while maintaining an average speed. This rapid acceleration and deceleration of the vehicle within the block is acceptable in this transit system 10 since non-critical loads such as baggage are typically carried by the vehicles 20. However, if the vehicle 20 is detected by the sensor 164c while the programmable controller 44 is receiving a BLO signal from the controller 44 in the block B₃, the cruise LIM primaries 18g are operated in a different manner as will be described. The position of sensor 164c along the track 12 in the block , is designated as the brake decision point BDP. In particular, upon receipt of vehicle detection signals from the sensor 164c and the BLO signal from the controller 44 in block B^ the programmable controller 44 in block B₂ generates a switching signal which is conveyed to the reversible contact switch 160. The reversible contact switch 160 in turn is actuated to connect the negative phase sequence of the power distribution system PDS to each of the relays 158 in the block B₂ via the auto-transformer 164 which steps the power distribution system PDS voltage down, the reasons for which will be described hereinafter.

When the sensor 164d associated with the second cruise LIM primary 18g detects the presence of the vehicle 20, a signal is conveyed to the controller 44 which in turn operates the relay 158. The negative phase sequence of the stepped-down power distribution system voltage is then conveyed to the second cruise LIM primary 18g causing the cruise LIM primary 18g to supply the vehicle 20 with a reverse thrust of a pre-determined magnitude so that the vehicle 20 is slowed but not stopped. When the vehicle 20 leaves the control zone of the second cruise LIM primary 18g and is detected by sensor 164e, the second cruise LIM primary 18g is disabled due to the removal of the enabling signal supplied to the relay 158 by the controller 44. When the slowed vehicle 20 reaches the control zone of the third cruise LIM primary 18g and is detected by sensor 164f, the controller 44 energizes the relay 158. This connects the third cruise LIM primary 18g to the power distribution system PDS so that the third cruise LIM primary 18g supplies the predetermined reverse thrust to the vehicle 20 thereby slowing but not stopping the vehicle 20. When the vehicle 20 leaves the control zone of the third cruise LIM primary 18g and is detected by sensor 164g, the controller 44 disables the relay 158 associated therewith so that the third cruise LIM primary 18g is de- energized. The controller 44, at this time, also generates a stop signal and applies it to conductor 180. The signal on conductor 180 is conveyed to the LVCM 72 which in turn operates to select another motion profile. This motion profile is selected so that the voltage and phase sequence supplied to the LIM primary 18h via the power distribution system PDS causes the LIM primary 18h to generate a reverse thrust sufficient to bring the vehicle 20 to a stop at stopping point SP over the LIM primary 18h. Accordingly, when the vehicle 20 enters end section 52 and is detected by the LVCM sensors 174, the LVCM 172 calculates the speed of the vehicle and energizes the LIM primary 18h in a manner so that the vehicle is slowed and stopped within the control zone of the LIM primary 18h at the stopping point SP.

When the vehicle 20 in the adjacent downstream block B₃ departs therefrom, the BLO signal applied to the controller 44 via conductor 166 is removed. In turn, the controller 44 removes the stop signal applied to conductor 180 and the signal applied to the reversible contact switch 160. This of course, actuates the switch 160 to connect the positive phase sequence of the power distribution system PDS to the relays 158. The detection of the removal of the stop signal from conductor 180 by the LVCM 172 and the fact the vehicle 20 is detected by the LVCM 172 as being stopped over the LIM primary 18h, causes the LVCM 172 to select another motion profile suitable for re-starting the vehicle 20 so that the vehicle 20 enters the next block B₃ of track at a desired speed V^. When the vehicle enters the next block of track 12, the same sequence of operations are performed to avoid collisions by preventing more than one vehicle from entering the same block B_x of track 12. It should be realized that if a vehicle 20 has passed the braking decision point BDP and hence, the third sensor 164c and is being propelled forward by the second cruise LIM primary 18g before a BLO signal is received by the controller 44 (an occurrence which is very rare), the programmable controller 44 operates the reversible contact switch 160 and the relays 158 and conditions the LVCM 172 via the stop signal so that all further operation of the LIM primaries 18g,18h located in the block is in a manner to stop the vehicle in the block at the stopping point. Conversely, if a BLO signal is removed before a vehicle 20 is stopped in the block, the reversible contact switch 160 and LVCM 172 are reconditioned so that the LIM primaries 18g and 18h are operated to supply forward thrust to the vehicle 20.

The LVCM 172 is used in the end section 52 and the LIM primary 18h is chosen to have characteristics so that a vehicle 20 can be stopped in the block B₂ under normal conditions even if the vehicle 20 is accelerated by the third cruise LIM primary 18g. However, this operation is not desirable due to the large current drawn from the power distribution system PDS by the LIM primary 18h to provide the necessary reverse thrust to the vehicle 20 to achieve this result. Under abnormal conditions wherein the LIM primary 18h is not capable of stopping the vehicle 20 within the block, it is generally capable of slowing the vehicle 20 to a speed insufficient to cause damage should two vehicles collide in the next block B₃.

Although a specific arrangement of three cruise LIM primaries and one LVCM controlled LIM primary have been shown in the blocks B_j and B₃ respectively, in general, the length DBL of each block is related to the length of the high speed zone and the travel time tolerance over the zone. Based on this and given the LIM primary spacing criteria (in this case, greater than the length of a reaction rail 22), the required block length DBL can be determined as well as the minimum number of LIM primaries within each block that are required to bring a vehicle to a stop within the block. Using design procedures, it is possible to obtain a LIM primary with characteristics such that the forward thrust required to maintain the average speed of a vehicle is matched to the braking requirement for the quantity of LIM primaries per block. Thus, the number of blocks of length DBL for a given high speed zone length L can be given by L/DBL which must be an integer value.

In many cases, however, the braking thrust of the LIM primaries cannot be matched to the cruising thrust and thus, the braking thrust may be well in excess of the normal operating cruising thrust. To illustrate this, Figure 10 shows characteristic curves for two LIM primaries having similar cruise operating regions. However, as can be seen, the braking thrust of the different LIMs are significantly different. Thus, a block having LIM primaries spaced sufficient to maintain the average forward velocity of a vehicle, may have excess braking thrust. This results in the reduction of the brake zone length DBD in each block, i.e. it moves the brake decision point BDP closer to the end section 52. Alternatively, the block length DBL can be increased. When increasing the block length DBL or reducing the brake zone length DBD, the minimum vehicle following distance DVF must be equal to or greater than DBD + DBL to avoid collisions. Since the block length DBL can be increased due to the excess braking thrust, a reduction in the number of blocks required in a given high speed zone can be reduced. Since each block B_x requires an LVCM 72 which is expensive, the reduction in the required number of blocks provides advantages in that costs of the transit system are reduced.

In addition to allowing the length of the blocks in the high speed zones to be increased, the excess braking thrust typically available in the blocks provides additional advantages as will be described. Since operation of a linear induction motor primary to provide reverse thrust to a vehicle typically results in large current being drawn from the power distribution system PDS, it is desirable to reduce current drawn so that penalties for excessive peak loads on the power distribution system are not assessed by the hydro utility.

To reduce further peak current drawn from the power distribution system PDS by the cruise LIM primaries 18g, the auto-transformer 165 is provided. The auto-transformer 165 functions to step down the voltage of the power system applied to the LIM primaries 18g via the relays 158 during reverse thrust operation of the LIM primaries 18g. Since the multiple cruise LIM primaries 18g used in the conditioning section 50 of the block B_x provide the segment with excess braking thrust, the input voltage supplied to the LIM primaries 18g can be reduced to 80% of the nominal value without adversely affecting vehicle braking within the block. The reduction in the applied voltage to the LIM primaries 18g results in the magnitude of the reverse thrust being supplied to the vehicles 20 by the LIM primaries 18g to be reduced as compared with full voltage reverse thrust operation. Figure 11 shows a "compound" cruise LIM primary characteristic illustrating positive thrust 300 and current 302 drawn by the LIM primary at full voltage and braking thrust 306 and current 308 drawn by the LIM primary at 80% of the full voltage. As should be apparent, the current drawn by the LIM primary when operated in this manner, remains substantially constant over the entire range of operation.

Accordingly, by employing a voltage reduction during reverse thrust operation of the cruise LIM primaries 18g, the power distribution system current requirements used in the transit system 10 are simplified thereby reducing costs. Also, since maximum peak current drawn is reduced, additional cost savings are achieved. It should also be apparent to those of skill in the art that the length of the blocks can be increased or decreased and include fewer or more cruise LIM primaries. In addition it should be realized that other sections of the track not designated as high speed zones have a programmable controller 44 and sensors associated therewith to permit BLO signals to be generated and conveyed to upstream controllers so that only one vehicle is permitted in each block of the transit system.

It should also be apparent to those of skill in the art that the brake decision point BDP can be located at alternative locations in the conditioning section 50 of the block. If the BDP point is located at sensor 164a, the voltage supplied to the cruise LIM primaries during reverse thrust can be further reduced since all three cruise LIM primaries will be operated to provide reverse thrust if it is needed to stop a vehicle. Alternatively, if peak current draw is not a concern, the BDP point can be located adjacent sensor 164e so that only the third cruise LIM primary 18g and the LIM primary 18b supply reverse thrust to the vehicle when it is necessary to stop the vehicle.

Figure 2 best illustrates the deceleration zone D_x positioned upstream from the downgrade 32. Since the deceleration zones D_ and D₂ are identical, only the deceleration zone D_x will be described in detail herein. As can be seen, the deceleration zone D_! is located within the blocks B₄ and is divided into two sections, namely a passive section 250 located adjacent the vehicle entrance end of the deceleration zone D_ and an active section 252 located adjacent the vehicle exit end of the deceleration zone. The passive section 250 includes a plurality of permanent magnets decelerators (PMD's) 254 such as those manufactured by Northern Magnetics Inc. The PMD's 254 are located between the rails 14,16 of the track 12 at spaced intervals. The active section 252 includes a synchronous linear induction motor primary 18i. The PMD's 254 in conjunction with the synchronous LIM primary 18i function to reduce the speed of vehicles 20 as they pass through the deceleration zone D_t while ensuring that vehicles carrying payloads of different mass pass through the deceleration zone in substantially the same amount of time and enter the following section of track 12 at substantially the same speed. The operation of the deceleration zone in this manner, maintains vehicle spacing thereby reducing the probability of vehicular collisions. This, of course, also allows vehicle throughput in the transit system to be maximized. In addition, since the deceleration zone functions to slow vehicles to a predetermined speed, the probability of vehicle derailment in the following sections of track is greatly reduced.

The arrangement of the PMD's 254 within the deceleration zone Dj and the selection of the synchronous linear motor primary 18i can be made to optimize the deceleration zones in terms of the maximum allowable exit speed and minimum speed of a vehicle in the zone as well as travel time differentials between vehicles of different mass passing through the deceleration zone. Although optimization is often desired, in actual practice, the synchronous linear motor primary is typically selected based on devices available and used in other segments of the transit system which although do not result in an optimized deceleration zone, will provide an acceptable level of performance.

Referring now to Figure 12, the thrust vs speed characteristics of two types of PMD's 254 are shown, namely "D" type and "G" type permanent magnet decelerators. As can be seen, both "D" or "G" type decelerators provide a somewhat constant braking force to vehicles 20 travelling thereover in the speed range of 4m/s to lOm/s although the magnitudes of the braking forces are different. The constant braking force applied to the vehicles in this speed range results in the deceleration of the vehicles becoming primarily a function of their mass and to a far lesser extent drag. Thus, vehicles of different mass passing over these decelerators will be decelerated differently. This condition is illustrated in Figure 13 which shows response curves for a 250kg and a 400kg vehicle respectively travelling along the track 12 and passing over the passive section 250 of the deceleration zone D_t. As can be seen, the passive section 250 includes five "D" type PMD's 254 spaced along the track. The spacing between consecutive PMD's is chosen so that the centre to centre spacing of consecutive PMD's is equal to the length Lg of the reaction rail 22 secured to the vehicles 20.

In this instance, both vehicles entered the passive section 250 of the deceleration zone D_! having a velocity of 8m/s. The 400kg vehicle took approximately two (2) seconds to pass over the passive section 250 and was slowed to an exit velocity of approximately 5m/s. In contrast, the 250kg vehicle took approximately four-and-one-half (4.5) seconds to pass over the passive section 250 and was slowed to an exit velocity of approximately lm/s. In transit systems where high vehicle throughput is required, the above difference in time taken for vehicles of different mass to travel thereover is unsatisfactory. This is due to the fact that the time difference delta T must be compensated for by increasing vehicle spacing to avoid collisions which of course decreases vehicle throughput. Thus, these types of decelerators are unacceptable when used on their own.

To compensate for the operational nature of the PMD's 254, the synchronous linear induction motor (LIM) primary 18i is also provided in the deceleration zone D. As is well known to those of skill in the art, the synchronous LIM primary 18i operates to supply thrust having a magnitude and direction to a vehicle so that the vehicle leaves the control zone of the synchronous LIM primary at substantially the synchronous speed of the LIM primary. Figure 14 illustrates the characteristics of a synchronous LIM primary having a synchronous speed of approximately 5.7m/s. As can be seen, the synchronous LIM primary 18i applies a retarding thrust to vehicles 20 travelling above the synchronous speed and a propulsive thrust to vehicles travelling below the synchronous speed. In the present system, the synchronous LIM primary 18i is chosen to have a synchronous speed close to that of the desired exit speed of the vehicles from the deceleration zone Dj and to have a peak thrust approximately equal to the retarding thrust of the PMD's 254.

Although in the present in-track transit system 10, the synchronous linear motor primary lδi is chosen to have a peak thrust substantially equal to the thrust of the PMD's 254, it should be apparent that synchronous linear motors having different thrust characteristics may be employed. In general given a specific arrangement of PMD's 254, a synchronous linear motor having a greater peak thrust than the PMD's will result in improved performance, namely, decreasing speed and lower time differentials between vehicles of different mass passing through the deceleration zones.

The operation of the deceleration zones will be now be described. After a vehicle 20 has been loaded at the loading station 28, the LIM primaries in each of the blocks B_x are energized in succession by their controllers so that the vehicle 20 travels towards the unloading station 30 at the desired speed. When the vehicle 20 enters block B₃ upstream from the deceleration zone Di, the vehicle 20 is propelled by the LIM primaries 18 therein so that the vehicle enters the deceleration zone Dj having a speed in the constant force range of the PMD's 254 and at a speed so that the reverse thrust applied to the vehicle 20 by the PMD's 254 is insufficient to stop the vehicle 20. When the vehicle enters the deceleration zone D_l5 the magnetic interaction between the PMD's 254 and the reaction rail 22 secured to the vehicle 20 causes eddy current to flow in the reaction rail 22. This results in a reverse thrust being applied to the vehicle 20 thereby slowing the vehicle before the vehicle enters the active section 252 of the deceleration zone D_1# To reduce the difference in the time taken for vehicles of different mass to pass through the deceleration zone D_l5 the number and type of PMD devices 254 used in the passive section 250 are chosen so that a vehicle of average mass in the transit system 10 will leave the passive section 250 having a speed substantially equal to the synchronous speed of the LIM primary 18i. Vehicles of lower mass than the average will leave the passive section 250 at a speed less than the synchronous speed while vehicles of greater mass than the average will leave the passive section 250 at a speed greater than the synchronous speed.

When the vehicles enter the active section 252, the synchronous LIM primary 18i functions to accelerate the vehicles of lower mass and decelerate the vehicles of higher mass while allowing the averaged mass vehicles travelling at the synchronous speed to pass so that each of the three types of vehicles leaves the deceleration zone Dj at substantially the same speed, this speed being substantially equal to the synchronous speed of the LIM primary 18i. In addition, since the synchronous LIM primary 18i decelerates heavier vehicles and accelerates lighter vehicles, heavier vehicles take longer to pass over the active section 252 than do lighter vehicles. This difference in time taken for the heavier vehicles to pass over the active section 252 somewhat offsets the difference in time taken for the different massed vehicles to pass over passive section 250, thereby reducing the overall difference in the time taken for vehicles of different mass to pass through the deceleration zone D_x.

The above-described operation is illustrated in Figure 14 which shows response curves for a 400kg vehicle and a 250kg vehicle passing through the present deceleration zone D_x. As can be seen, both vehicles entered the deceleration zone O_ having a velocity of 8m/s. The 400kg vehicle took two (2) seconds to pass through the deceleration zone Dj and had an exit velocity of approximately 5.7m/s. The 250kg vehicle took two-and-a-half (2.5) seconds to pass through the deceleration zone D_x and had an exit velocity of approximately 4.5m/s. Accordingly, the difference in time taken for the two substantially different mass vehicles to pass through the deceleration zone was only 0.5 seconds. The difference in the exit velocity between the two vehicles was approximately 1.25m/s.

In comparing the above-described vehicular travel through the deceleration zone Di with vehicular travel over only PMD's 254 as shown in Figure 13, it can be seen that the difference in exit velocity of the two different mass vehicles was reduced from 4.9m/s to 1.25m/s. Furthermore, the travel time for the vehicles to pass through the deceleration zone was reduced from 2.5 seconds to 0.5 seconds. If a synchronous linear motor primary 18i having a higher peak thrust is chosen for use in the deceleration zone, the time and speed differentials can be further reduced.

Thus, as a vehicle enters the deceleration zone Dj, it is slowed to a desired speed before travelling along the downgrade 32. Once the vehicle leaves the downgrade, it is propelled by the LIM primaries 18 towards the curve 34. The deceleration zone D₂ which is positioned just upstream from the curve 34, functions in the same manner described above to slow the vehicle before it enters the curve. After the vehicle 20 has been slowed in the deceleration zone D₂ and navigates the curve, it is propelled to the unloading station 30 and stopped so that the freight carried by the vehicle 20 can be removed.

Although, the present deceleration zone shows the use of permanent magnet devices to slow the vehicle in the passive section, it should be realized that electro-magnet devices can also be used, with the electro-magnets being supplied by a power supply that is preferably independent of the synchronous LIM primary. The present deceleration zone provides advantages in that the use of the PMD devices in conjunction with the synchronous LEM primary provides an inexpensive decelerator which permits vehicles of different mass to be slowed in the deceleration zone to substantially the same exit speed and to travel through the deceleration zone in substantially the same amount of time. Moreover, the use of the PMD devices to provide the initial retarding thrust ensures that all vehicles are slowed even if the synchronous LIM primary fails or in the event of a general power failure.

The present stopping zones provide advantages in that the redundant braking schemes provided therein ensure that a vehicle is stopped within the stopping zone in the event of failure or malfunction of the primary brake. Furthermore, the arrangement of the sensors and the additional LIM primaries permits the secondary brakes to operate timely to reduce vehicle overshoot past the designated stopping points in the stopping zones and to facilitate restarting of the vehicles once they have been stopped.

The present transit system also provides advantages in that high vehicle throughput is achieved while minimizing vehicular collisions and increasing block lengths thereby reducing the required number of expensive controllers, simplifying power system requirements and reducing peak current drawn from the power distribution system PDS.

Claims

What is claimed is:

1. A stopping zone in a linear motor in-track transit system, said transit system including a guideway and at least one vehicle movable along said guideway, said stopping zone comprising: primary braking means disposed along said guideway and being operable to stop a vehicle entering said stopping zone; and secondary braking means disposed along said guideway and being spaced from said primary braking means, said secondary braking being conditioned to stop said vehicle upon failure of said primary braking means.

2. A stopping zone as defined in claim 1 wherein said secondary braking means is positioned downstream from said primary braking means.

3. A stopping zone as defined in claim 2 wherein said primary braking means is in the form of a first linear motor primary operable to supply a reverse thrust to a vehicle carrying a linear motor secondary entering said stopping zone, said reverse thrust being sufficient to stop said vehicle at a designated stopping point within said stopping zone.

4. A stopping zone as defined in claim 3 wherein said first linear motor primary is operable to restart a vehicle stopped thereby.

5. A stopping zone as defined in claim 4 further comprising restart means disposed along said guideway adjacent said secondary braking means, said restart means being operable to restart a vehicle stopped by said secondary braking means.

6. A stopping zone as defined in claim 5 wherein said restart means is in the form of a second linear motor primary.

7. A stopping zone as defined in claim 6 further comprising: control means in communication with said first and second linear motor primaries; and vehicle sensing means disposed along said guideway adjacent said secondary braking means for detecting travel of said vehicle beyond said designated stopping point, said control means disabling said first linear motor primary upon detection of said vehicle by said sensing means.

8. A stopping zone as defined in claim 5 wherein said secondary braking means is in the form of a mechamcal brake operable to engage frictionally a portion of said vehicle.

9. A stopping zone as defined in claim 8 wherein said mechamcal brake is positioned along said guideway between said first linear motor primary and said restart means, said mechanical brake being actuable between inoperative and operative conditions, said mechanical brake remaining in said inoperative condition and being actuable to said operative condition upon detection of a vehicle entering said stopping zone.

10. A stopping zone as defined in claim 9 further comprising: control means in communication with said first linear motor primary and said mechanical brake; and vehicle sensing means disposed along said guideway adjacent said restart means for detecting travel of said vehicle beyond said designated stopping point, said control means actuating said mechanical brake to said operative condition upon detection of a vehicle entering said stopping zone and further disabling said first linear motor primary upon detection of said vehicle by said vehicle sensing means.

11. A stopping zone as defined in claim 10 wherein said restart means is in the form of a second linear motor primary, said control means actuating said mechanical brake to said inoperative condition and enabling said second linear motor primary to restart a vehicle after a vehicle has been stopped by said mechamcal brake.

12. A stopping zone as defined in claim 8 wherein said mechanical brake is positioned along said guideway downstream from said restart means, said mechanical brake being actuable between inoperative and operative conditions, said mechanical brake remaining in said inoperative condition and being actuable to said operative condition upon detection of a vehicle travelling beyond said designated stopping point.

13. A stopping zone as defined in claim 12 further comprising control means in communication with said first linear motor primary and said mechanical brake; and vehicle sensing means disposed along said guideway adjacent said mechanical brake for detecting travel of said vehicle beyond said designated stopping point, said control means actuating said mechanical brake to said operative condition upon detection of a vehicle by said vehicle sensing means.

14. A stopping zone as defined in claim 13 wherein said control means further disables said first linear motor primary upon actuation of said mechanical brake to said operative condition.

15. A stopping zone as defined in claim 14 wherein said vehicle sensing means is positioned between said restart means and said mechamcal brake and wherein said restart means is in the form of a second linear motor primary.

16. A stopping zone as defined in claim 15 wherein said control means actuates said mechamcal brake to said inoperative condition and enables said second linear motor primary to restart a vehicle after a vehicle has been stopped by said mechamcal brake.

17. A stopping zone as defined in claim 16 wherein said first and second linear motor primaries are spaced along said guideway in a manner so that said linear motor secondary secured to said vehicle extends over both of said linear motor primaries at least at one position within said stopping zone, said one position being located upstream from said vehicle sensing means and wherein said control means enables said first and second linear motor primaries to restart said vehicle when said first linear motor primary stops said vehicle in said one position.

18. A stopping zone as defined in claim 13 wherein said control means disables said first linear motor primary and actuates said mechamcal brake to said operative condition upon stopping of a vehicle by said first linear motor primary and actuates said mechamcal brake to said inoperative condition and enables said first linear motor primary when it is desired to restart said vehicle.

19. A stopping zone as defined in claim 1 wherein said secondary braking means is located upstream from said primary braking means and is operable to stop said vehicle upon detection of a vehicle travelling beyond a designated stopping point within said stopping zone.

20. A stopping zone as defined in claim 19 wherein said primary and secondary braking means are in the form of first and second linear motor primaries respectively.

21. A stopping zone as defined in claim 20 wherein said second linear motor primary is operable to slow a vehicle carrying a linear motor secondary entering said stopping zone to a predetermined speed and is conditioned to stop said vehicle upon detection of said vehicle travelling beyond said designated stopping point.

22. A stopping zone as defined in claim 21 further comprising control means in communication with said first and second linear motor primaries, said control means enabling said first and second linear motor primaries upon detection of a vehicle within said stopping zone.

23. A stopping zone as defined in claim 22 wherein said control means disables said second linear motor primary and enables said second linear motor primary to stop said vehicle upon detection of said vehicle travelling beyond said designated stopping point.

24. A stopping zone as defined in claim 23 further comprising vehicle holding means disposed along said guideway downstream from said first linear motor primary, said control means disabling said first and second linear motor primaries and enabling said holding means upon stopping of said vehicle in said stopping zone, said control means disabling said holding means and re-enabling said first and second linear motor primaries when it is desired to restart said vehicle.

25. A stopping zone as defined in claim 24 further comprising a vehicle overshoot sensor disposed along said guideway downstream from said holding means, said sensor being in communication with said control means and detecting travel of said vehicle beyond said designated stopping point.

26. A stopping zone as defined in claim 25 wherein said holding means is in the form of a mechanical brake.

27. A deceleration zone in a linear motor in-track transit system, said transit system including a guideway and at least one vehicle movable along said guideway, said vehicle including linear motor secondary means secured thereto, said deceleration zone being located along a section of said guideway and having a vehicle entrance end and a vehicle exit end, said deceleration zone comprising: magnetic braking means positioned along said guideway adjacent said vehicle entrance end; and linear motor primary means positioned along said guideway adjacent said vehicle exit end wherein said magnetic braking means operates independently of said linear motor primary means and interacts with the linear motor secondary means secured to a vehicle to provide a substantially constant retarding thrust thereto to slow said vehicle and wherein said linear motor primary means interacts with the linear motor secondary means secured to said vehicle and provides thrust thereto, said thrust being of a magnitude and direction so that said vehicle leaves said deceleration zone having a velocity substantially equal to a desired velocity.

28. A deceleration zone as defined in claim 27 wherein said magnetic braking means is in the form of at least one permanent magnet decelerator disposed along said guideway.

29. A deceleration zone as defined in claim 28 wherein said magnetic braking means includes a plurality of permanent magnet decelerators, said decelerators being located at spaced intervals along said guideway, consecutive decelerators being spaced so that the centre to centre spacing therebetween is equal to the length of a linear motor secondary means secured to a vehicle.

30. A deceleration zone as defined in claim 29 wherein said linear motor primary means is in the form of a synchronous linear motor primary.

31. A deceleration zone as defined in claim 30 wherein said synchronous linear motor primary is chosen to have a peak thrust equal to or greater than said constant retarding thrust generated by said magnetic braking means.

32. A deceleration zone as defined in claim 31 wherein said permanent magnet decelerators are arranged to decelerate vehicles having a mass less than a predetermined mass to a speed less than the synchronous speed of said linear motor primary and to decelerate vehicles having a mass greater than said predetermined mass to a speed greater than said synchronous speed, said synchronous linear primary motor accelerating said vehicles travelling below said synchronous speed and decelerating said vehicles travelling above said synchronous speed so that said vehicles leave said deceleration zone at substantially said synchronous speed.

33. A deceleration zone as defined in claim 32 wherein said predetermined mass is equal to the mass of an average vehicle carrying an average payload in said transit system.

34. A decelerator for use in an in-track transit system comprising: magnetic braking means for disposition along a guideway and operable to provide a substantially constant retarding thrust to a vehicle having a reaction element secured thereto and passing thereover; and a synchronous linear motor primary for disposition along said guideway downstream from said magnetic braking means, said synchronous linear motor primary being operable to supply a thrust to said vehicle having a magnitude and direction so that said vehicle assumes a velocity substantially equal to the synchronous speed of said synchronous linear motor primary.

35. A decelerator as defined in claim 34 wherein said magnetic braking means includes at least one permanent magnet decelerator.

36. A deceleration as defined in claim 35 wherein said magnetic braking means includes a plurality of permanent magnet decelerators, said decelerators being located at spaced intervals along said guideway, consecutive decelerators being spaced so that the centre to centre spacing therebetween is equal to the length of a linear motor secondary means secured to a vehicle.

37. A transit system comprising: a guideway; a plurality of vehicles movable along said guideway and including linear motor secondary means secured thereto, said guideway being sub-divided into a plurality of blocks, each of said blocks including at least two linear motor primary means disposed along said guideway at spaced intervals for communicating with said linear motor secondary means and operable to provide a forward thrust thereto in normal operation; sensing means for detecting the presence of a vehicle in each of said blocks; and control means operable to condition said linear motor primary means to stop a vehicle in a block when a sensing means in the adjacent downstream block detects the presence of a vehicle.

38. A transit system as defined in claim 37 wherein said control means conditions one of said linear motor primary means to slow a vehicle to a speed below a pre-determined value and conditions the other of said linear motor primary means downstream from said one linear motor primary means to stop said vehicle when a sensing in the adjacent downstream block detects the presence of a vehicle.

39. A transit system as defined in claim 38 wherein said segment includes a plurality of said one linear motor primary means, each of said one linear motor primary means being operable to supply a pre-determined forward thrust to a vehicle passing thereover in normal operation and being operable to supply a pre-determined reverse thrust to a vehicle upon conditioning thereof by said control means.

40. A transit system as defined in claim 39 wherein said linear motor primary means supply said pre-determined forward thrust to said vehicle when said vehicle is detected as passing thereover below a pre-set speed.

41. A transit system as defined in claim 40 wherein said control means conditions said plurality of one linear motor primary means to provide said reverse thrust at substantially the same time.

42. A transit system as defined in claim 41 further comprising switch means connected between said plurality of one linear motor primary means and a three phase power supply, said switch means being operable to reverse the phase sequence of said power supply connected to said one linear motor primary means to cause said one linear motor primary means to provide a reverse thrust upon conditioning by said control means.

43. A transit system as defined in claim 42 wherein said switch means is in the form of a reversible contact switch.

44. A transit system as defined claim 41 wherein said sensing means includes a plurality of proximity sensors disposed along said guideway, said sensors being positioned so that at least one sensor always detects the presence of a vehicle located in said block, each of said sensors providing signals to said control means upon detection of a vehicle thereover.

45. A transit system as defined in claim 44 wherein said control means includes second switch means interconnecting each of said one linear motor primary means and said power supply, said second switch means being operable to connect said power supply to said one linear motor primary means upon detection of a vehicle by said sensing means adjacent said one linear motor primary means.

46. A transit system as defined in claim 45 wherein said second switch means is in the form of a plurality of non-reversible relays, each relay interconnecting one of said one linear motor primary means and said power supply.

47. A transit system as defined in claim 46 wherein said control means further includes a programmable controller electrically connected to said relays, said sensors, said reversible contact switch and a programmable controller in the adjacent downstream block.

48. A transit system as defined in claim 39 wherein said control means permits a vehicle to pass over at least one of said one linear motor primary means before conditioning said linear motor primary means to stop a vehicle in said block when a vehicle is detected in the adjacent downstream block.

49. A transit system as defined in claim 48 wherein said control means permits said vehicle to pass over only one of said one linear motor primary means before conditioning said linear motor primary means to stop a vehicle in said block, said only one linear motor primary means being positioned adjacent the vehicle entrance end of said block.

50. A transit system as defined in claim 42 wherein said switch means is actuable between first and second conditions, in said first condition, said switch means connecting each of said one linear motor primary means to the positive phase sequence of said power supply in normal operation and in said second condition, said switch means connecting each of said one linear motor primary means to the negative phase sequence of said power supply, said transit system further including scaling means for reducing the voltage of said power supply applied to each of said one linear motor primary means when said switch means is in said second condition.

51. A transit system as defined in claim 50 wherein said scaling means reduces the voltage to a level so that the current drawn by said one linear motor primary means during reverse thrust is approximately equal in magnitude to the current drawn by said one linear motor primary means during forward thrust.

52. A transit system as defined in claim 51 wherein said scaling means is in the form of an auto-transformer.

53. A transit system as defined in claim 52 wherein said voltage is reduced to a level equal to approximately 80% of the voltage level applied to said one linear motor primaries when said switch means is in said first condition.

54. A transit system as defined in claim 53 wherein said switch means is in the form of a reversible contact switch responsive to said control means.

55. A high speed zone in a linear motor in-track transit system, said transit system including a guideway and a plurality of vehicles movable along said guideway, said high speed zone being defined by a section of said guideway and being sub-divided into a plurality of blocks, each of said blocks including: at least two linear motor primary means disposed along said guideway at spaced intervals for communicating with linear motor secondary means secured to said vehicles and operable to provide a forward thrust thereto in normal operation; sensing means for detecting the presence of a vehicle in each of said blocks; and control means operable to condition said linear motor primary means to stop a vehicle in a block when a sensing means in the adjacent downstream block detects the presence of a vehicle.

56. A high speed zone as defined in claim 55 wherein said control means conditions one of said linear motor primary means to slow a vehicle to a speed below a pre-determined value and conditions the other of said linear motor primary means downstream from said one Unear motor primary means to stop said vehicle when a sensing in the adjacent downstream block detects the presence of a vehicle.

57. A high speed zone as defined in claim 56 wherein said segment includes a plurality of said one linear motor primary means, each of said one linear motor primary means being operable to supply a pre-determined forward thrust to a vehicle passing thereover in normal operation and being operable to supply a pre-determined reverse thrust to a vehicle upon conditioning thereof by said control means.

58. A high speed zone as defined in claim 57 wherein said linear motor primary means supply said pre-determined forward thrust to said vehicle when said vehicle is detected as passing thereover below a pre-set speed.

59. A high speed zone as defined in claim 58 wherein said control means conditions said plurality of one linear motor primary means to provide said reverse thrust at substantially the same time.

60. A high speed zone as defined in claim 59 further comprising switch means connected between said plurality of one linear motor primary means and a three phase power supply, said switch means being operable to reverse the phase sequence of said power supply connected to said one linear motor primary means to cause said one linear motor primary means to provide a reverse thrust upon conditioning by said control means.

61. A high speed zone as defined in claim 60 wherein said switch means is in the form of a reversible contact switch.

62. A high speed zone as defined claim 61 wherein said sensing means includes a plurality of proximity sensors disposed along said guideway, said sensors being positioned so that at least one sensor always detects the presence of a vehicle located in said block, each of said sensors providing signals to said control means upon detection of a vehicle thereover.

63. A high speed zone as defined in claim 62 wherein said control means includes second switch means interconnecting each of said one linear motor primary means and said power supply, said second switch means being operable to connect said power supply and said one linear motor primary means upon detection of a vehicle by said sensing means adjacent said one linear motor primary means.

64. A high speed zone as defined in claim 63 wherein said second switch means is in the form of a plurality of non-reversible relays, each relay interconnecting one of said one linear motor primary means and said power supply.

65. A high speed zone as defined in claim 64 wherein said control means further includes a programmable controller electrically connected to said relays, said sensors, said reversible contact switch and a programmable controller in the adjacent downstream block.

66. A high speed zone as defined in claim 55 wherein said control means permits said vehicle to pass over at least one of said one linear motor primary means before conditioning said linear motor primary means to stop a vehicle in said block when a vehicle is detected in the adjacent downstream block.

67. A high speed zone as defined in claim 66 wherein said control means permits a vehicle to pass over only one of said one linear motor primary means before conditioning said linear motor primary means to stop a vehicle in said block, said one linear motor primary means being positioned adjacent the vehicle entrance end of said block.

68. A high speed zone as defined in claim 59 wherein said switch means is actuable between first and second conditions, in said first condition, said switch means connecting each of said one linear motor primary means to the positive phase sequence of said power supply in normal operation and in said second condition, said switch means connecting each of said one linear motor primary means to the negative phase sequence of said power supply, said high speed zone further including scaling means for reducing the voltage of said power supply applied to each of said one linear motor primary means when said switch means is in said second condition.

69. A high speed zone as defined in claim 68 wherein said scaling means reduces the voltage to a level so that the current drawn by said one linear motor primary means during reverse thrust is approximately equal in magnitude to the current drawn by said one linear motor primary during forward thrust.

70. A high speed zone as defined in claim 69 wherein said scaling means is in the form of an auto-transformer.

71. A high speed zone as defined in claim 70 wherein said voltage is reduced to a level equal to approximately 80% of the voltage level applied to said one linear motor primaries when said switch means is in said first condition.

72. A high speed zone as defined in claim 71 wherein said switch means is in the form of a reversible contact switch responsive to said control means.

73. A voltage controller for a linear motor primary disposed along a guideway comprising: switch means operable between first and second conditions, in said first condition, said switch means connecting a linear motor primary to the positive phase sequence of a three phase power supply and in said second condition, said switch means connecting the linear motor primary to the negative sequence of said power supply; control means operable to actuate said switch means to one of said conditions so that said linear motor primary is operable to generate thrust in a desired direction; and scaling means interconnecting said power supply and said switch means when said switch means is in said second condition to reduce the current drawn from said power supply by said linear motor primary.

74. A voltage controller as defined in claim 73 wherein said scaling means reduces the voltage of the power supply so that the current drawn by said linear motor primary during reverse thrust is substantially the magnitude as the current drawn by said linear motor primary during forward thrust.

75. A voltage controller as defined in claim 73 wherein said scaling means is in the form of an auto-transformer, said auto-transformer reducing the voltage of said power supply to a level equal to approximately 80% of the voltage applied to the linear motor primary when said switch means is in the first condition.

76. A voltage controller as defined in claim 75 wherein said switch means is in the form of a reversible contact switch responsive to said control means.

77. A voltage controller as defined in claim 76 wherein said control means is in the form of a programmable controller, said programmable controller being responsive to vehicle operation instruction signals and conditioning said contact switch to one of said conditions in accordance with said instruction signal.

78. A voltage controller as defined in claim 77 further comprising second switch means interconnecting said linear motor primary and said first switch means, said second switch means being operable to connect said linear motor primary to said first switch means in response to signals from said programmable controller.

79. A voltage controller as defined in claim 78 wherein said programmable controller is operable to control the movement of a vehicle along a pre-defined section of said guideway and is operable to control said linear motor primaries to stop a vehicle in said section upon detection of a vehicle in an adjacent downstream section of said guideway, said programmable controller being responsive to signals from said downstream segment and operable to condition said first switch means to said one condition when said downstream segment is clear and to condition said first switch means to said second condition when said downstream segment is occupied by another vehicle.

80. A voltage controller as defined in claim 79 wherein a plurality of linear motor primaries are associated with said guideway in said pre-defined segment, said first switch means being operable to connect each of said plurality of linear motor primaries to said power supply in both of said conditions.

81. A transit system comprising: a guideway; at least one vehicle movable along said guideway, said guideway being divided into a plurality of blocks; at least two linear motor primaries disposed along said guideway within said block at spaced intervals and being operable to supply thrust to a vehicle within said block; a three phase power supply connectable to said linear motor primaries; switch means interposed between said power supply and at least one of said linear motor primaries, said switch means being actuable between first and second conditions to connect said linear motor primary to the positive and negative phase sequence of said power supply respectively; control means operable to actuate said switch means to said first condition in normal operation and to said second condition when it is desired to stop said vehicle in said block; and scaling means interconnecting said power supply and said switch means when said switch means is in said second condition to reduce the current drawn from said power supply by said linear motor primary.

82. A transit system as defined in claim 81 wherein said scaling means reduces the voltage of the power supply so that the current drawn by said linear motor primary during reverse thrust is substantially the magnitude as the current drawn by said linear motor primary during forward thrust.

83. A transit system as defined in claim 82 wherein said scaling means is in the form of an auto-transformer, said auto-transformer reducing the voltage of said power supply to a level equal to approximately 80% of the voltage applied to the linear motor primary when said switch means is in the first condition.

84. A transit system as defined in claim 83 wherein said switch means is in the form of a reversible contact switch responsive to said control means.

85. A transit system as defined in claim 84 wherein said control means is in the form of a programmable controller, said programmable controller being responsive to vehicle operation instruction signals and conditioning said contact switch to one of said conditions depending on said instruction signal.

86. A transit system as defined in claim 85 further comprising second switch means interconnecting said linear motor primary and said first switch means, said second switch means being operable to connect said linear motor primary to said first switch means in response to signals from said programmable controller.