Abstract:
The present invention includes a track ( 1, 101 ) of a track system with straight, transition, curved, and switch track sections. The invention further comprises bogies ( 40 ) for vehicle cabins suspended under the track. Track sections of the track have an upper rail ( 1 ) and one or two lower rails ( 101, 201 ). Further, a bogie ( 40 ) has fore and aft sets of upper guide and switch wheels ( 151, 251, 154, 254 ), and one set of lower guide and switch wheels ( 152, 153, 252, 253, 156, 157, 256, 257 ). The bogies ( 40 ) also have one left and/or one right load bearing wheel ( 150, 250 ) and one drive wheel facing upwards and engaging a downwards directed drive wheel running surface ( 15 ) of the upper rail. Each set of lower guide wheels consist of left and right wheel pairs ( 152, 153, 252, 253 ) so that transition sections can be passed without moving any parts of the bogie ( 40 ). Switch wheels ( 154, 254, 156, 157, 256, 257 ) are separated from guide wheels so that they can be positioned according to the preferred direction of travel well before reaching a switch.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a track and bogie for wheel based suspended vehicles. Vehicles provided with at least two of said bogies form together with said track a transportation system. In particular the invention is useful for public transportation often denoted as PRT (personal rapid transit). 
       BACKGROUND OF THE INVENTION 
       [0002]    The problems with transporting the large and increasing number of people living in cities are well known. Public transportation with large vehicles in the form of metro, trolley and buses all have the problem with people having to wait for vehicles to arrive and then stop at all stations during the trips. Cars offer the flexibility of a personal trip but have problems with pollution, accidents, congestion and land use. A transit system which offers the flexibility of the car without its drawbacks is widely known as PRT. 
         [0003]    Many PRT systems have been described and patented. These systems can be characterized as having rotating motors driving on wheels or linear motors. The wheel traction based systems have problems with loss of traction in some weather conditions while the linear electric motor systems have an economic and efficiency problem, as linear electric motors are in general more expensive and less efficient than rotating electric motors. For large vehicle systems like trains the uncertain traction can be compensated with long headways, i.e. inter-vehicle times. This is not possible for a system with small vehicles as the reduced track capacity would make the system economically infeasible. 
         [0004]    Vehicles of PRT systems can further be characterized as either supported on the track or suspended under the track. One main advantage with a suspended system is to avoid accumulation of snow, water or debris on the running surfaces of the track. A suspended system can achieve this by having only one track opening, facing downwards, greatly reducing the risk of foreign particles entering the track. 
         [0005]    Many previous PRT systems have been designed with cabins suspended under the track. One main problem with this type of configuration is that the running surfaces on each side of the track opening must be kept at a constant lateral distance. This is structurally complicated as the track usually has a rather high U-shape internally to allow vehicles to pass. This problem is compounded by the fact that a vehicle is subjected to lateral forces acting on the cabin. These lateral forces translate to torsional moments which tend to pry the track open, i.e. to increase the width of the track opening. To avoid this the track must be made stiff, which increases its weight, cross-section size and cost. 
         [0006]    To implement a PRT system a possibility to individually switch each vehicle to a selected track at switch points is required. Many systems having an on board switch mechanism have been designed and patented. Such designs have the advantage of allowing switching without moving parts in the track. A problem with this type of switch mechanism, particularly for a suspended vehicle configuration, is to maintain the possibility to transfer above mentioned torsional moments from the vehicle cabin to the track at all times when negotiating switches. 
         [0007]    U.S. Pat. No. 3,830,163 describes a PRT system. A vehicle of said prior art PRT system does not have separate guide and switch wheels, which means that switching movement must be performed when the guide/switch wheels are under pressure from torsional moments, causing wear of wheels and tracks, noise and excessive energy use. In addition the system has drive wheels bearing down on an upwards facing surface of the track, an arrangement which does not provide a safe traction as stated above. Furthermore the switch mechanism of said disclosure has a downwards facing central rail which prevents the use of upwards facing drive wheels. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention includes a transportation system track with straight, transition, curved, and switch sections. The invention further comprises bogies for vehicle cabins suspended under said track. Track sections of the track have an upper rail referred to as first track member and one or two lower rails referred to as second track members. Straight and curved track sections have one lower rail on the left or right side, as made appropriate by the side preferred for placing cantilevered posts upholding the track. Transition sections have two lower rails, left and right, and are used between two straight or curved track sections having opposite side lower rails. Switches have two lower rails on the common route and one each on the two alternate routes of the switch. Furthermore, in switch sections, these lower rails are special in that while maintaining engagement with respective load bearing wheels of a bogie guided by said track they no longer engage the lower guide wheels of the bogie. This arrangement allows the bogie to select a left or a right alternate route out of the switch by positioning switch wheels of the bogie appropriately, as will be described below. 
         [0009]    Bogies of a preferred configuration have two sets of upper guide and switch wheels, and one set of lower guide and switch wheels. They also have one left and one right load bearing wheel and one drive wheel facing upwards, engaging a downwards facing running surface of the first track member. Each set of lower guide wheels consist of left and right wheel pairs so that transition sections can be passed without moving any parts of the bogie. Switch wheels are separate from guide wheels so that they can be positioned according to the preferred direction of travel well before reaching a switch. 
         [0010]    According to one aspect of the invention a track with the characteristics of the enclosed claim  1  is presented. 
         [0011]    According to a further aspect of the invention a suspended bogie with the characteristics of the enclosed independent claim  8  is presented. 
         [0012]    According to a further aspect of the invention a vehicle based on said suspended bogie is presented in claim  20 . 
         [0013]    According to a further aspect of the invention a transportation system comprising said track and said suspended bogie is presented as claim  21 . 
         [0014]    Further aspects and embodiments of the invention are presented in the dependent claims. 
         [0015]    The present invention preferably uses rotating electric motors and ensures the most reliable friction possible by locating the running surface receiving the drive wheel facing downwards inside a mostly enclosed first track member provided with a downward facing opening. The contact force of a drive wheel of a bogie when engaging the drive wheel running surface can be adjusted using a servo mechanism. The contact force is adjusted to accommodate different drive/brake force requirements and coefficients of friction, thus preventing any significant slippage of the drive wheels while minimizing the rolling resistance in each drive wheel. 
         [0016]    A vehicle being guided along the track of the track system comprises a cabin suspended from two or more of the bogies described herein, said bogies arranged in line, one after the other, wherein the two or more bogies of a vehicle are coupled to each other. 
         [0017]    Advantages accomplished by means of the invention are:
       a minimization of the drawback with respect to possible loss of friction when using a rotating electric motor so that short inter-vehicle headways can be achieved with maintained system safety in all weather conditions.   a minimization of energy loss due to rolling resistance.   a reduction of the risk of accumulation of snow, water or debris inside the track.   elimination of the above mentioned adverse effects of torsional moments, whereby a reduction of track weight, cross-section size and cost compared to other systems is achieved.   allowing a network or mesh type of track layout where vehicles can select paths at each switch using an on board switch mechanism, this switch mechanism being able to transfer torsional moments from the vehicle cabin to the track at all times when negotiating switches.       
 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0023]      FIG. 1  is a sectional view of a bogie on a straight track section. 
           [0024]      FIG. 2  is a perspective view of a bogie on a straight track section with the switch in a neutral position. 
           [0025]      FIG. 3  is a perspective view of a switch showing a bogie set to run in a left direction out from the switch. 
           [0026]      FIG. 4  is a perspective view of switch showing a bogie set to run in a right direction out from the switch. 
           [0027]      FIG. 5  is a perspective view from below of a bogie in the switch, bound left as shown in  FIG. 3 . 
           [0028]      FIG. 6  is a perspective view from below of a bogie in the switch, bound right as shown in  FIG. 4 . 
           [0029]      FIG. 7  is a side view of a bogie showing the upwards facing drive unit. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0030]    In the following embodiments of the invention will be described more in detail with reference to the enclosed drawings. 
         [0031]    In  FIG. 1  a preferred embodiment of a bogie is shown on a straight track section consisting of an upper u-shaped track member, the first track member  1 , and a lower track member, referred to as the second track member  101 , in this case arranged to the left in the direction of travel. These first  1  and second  101  track members are fixedly connected to each other, for instance using ribs ( 110 , see  FIG. 2 ) and preferably enclosed in a u-shaped cover with a downwards facing opening (not shown). 
         [0032]    A bogie  40  has a bogie frame  50  holding left and right load bearing wheels  150 ,  250 . In the shown embodiment, the left load bearing wheel  150  is in contact with the upwards facing surface  101   a  of the left second track member  101 , thus transferring the downwards directed force from the bogie to the track. The bogie  40  is provided with upper guide wheels  151   a ,  151   b ,  251   a ,  251   b  carried by the bogie frame  50 . The purpose of said upper guide wheels  151   a ,  151   b ,  251   a ,  251   b  is to keep the bogie aligned with the track at an upper level, i.e. at the level of the first track member  1 . Attached to the bogie is, further, a set of left lower guide wheels  152 ,  153  including a left inner guide wheel  152  and a left outer guide wheel  153  with the purpose of keeping the bogie aligned with the track at a lower level, i.e. at the level of the second track member. Correspondingly, attached to the bogie is a set of right lower guide wheels  252 ,  253  including a right inner guide wheel  252  and a right outer guide wheel  253  with the purpose of performing the same task as the set of left lower guide wheel  152 ,  153  in a track section where a right second track member (not shown) is present. Alternatively, the track may be provided with a right second track member along the main part of the track and the bogie then being guided by said right lower guide wheels  252 ,  253  along the main part of the track and guided by said left lower guide wheels  152 ,  153  in a track section where a left second track member  101  is present. 
         [0033]    The first track member  1  of the track provides an upper set of a first  16  wheel running surface and a second  17  wheel running surface facing each other in an inwards direction. Said wheel running surfaces  16 ,  17  are the inner surfaces of the flanges of a downwards facing U-shaped beam. The web of said U-shaped beam connecting said flanges has a downwards directed drive wheel running surface  15  for receiving the drive wheel of a bogie  40 . 
         [0034]    The second track member  101  of the track provides a lower set of wheel running surfaces including an upwards facing surface  101   a , a first outwards directed surface  101   b  on a lateral side of said second track member  101  and a second inwards directed surface  101   c  on an opposite lateral side of said second track member  101 , wherein said lower set of wheel running surfaces are offset in relation to a vertical plane intersecting a centre line between the upper set of wheel running surfaces. The term “centre line” is herein meaning a line which along the track is located between the wheel running surfaces  16 ,  17  of the first track member  1  at an equal distance to said wheel running surfaces  16 ,  17 . This fact is herein referred to simply that the second track member  101  is laterally offset in relation to the first track member  1 . 
         [0035]    The first  1  and second  101  track members are rigidly connected to each other by means of ribs  110  (shown schematically in  FIG. 2 ) at regular distances along the track. Said ribs keep the first and second track members at an equal distance along the track. Preferably, the first and second track members are made of steel and welded or bolted to the ribs. 
         [0036]    A vehicle made for running along said track has a cabin suspended from at least two bogies  40 , where said bogie on its part is suspended from the track having said first  1  and said second  101  track member. 
         [0037]    A set of left lower guide wheels  152 ,  153  include said first lower guide wheel  153  located to run along a first lateral surface  101   b  of said second track member  101  and said second lower guide wheel  152  located to run along a second lateral surface  101   c  of said second track member  101 . 
         [0038]    A set of right lower guide wheels  252 ,  253  include said first lower guide wheel  253  located to run along a first lateral surface  201   b  of said second track member  201  and said second lower guide wheel  252  located to run along a second lateral surface  201   c  of said second track member  201 . 
         [0039]    A set of upper guide wheels includes: said first upper guide wheels  151   a ,  151   b  being located to run along a first inwards directed running surface, herein called a first guide surface  16  of said first track member  1  and second upper guide wheels  251   a ,  251   b  being located to run along a second inwards directed running surface, herein called a second guide surface  17  of said first track member  1 , wherein as stated said first  16  and second  17  guide surfaces face each other. 
         [0040]    In a transportation system including a vehicle and the track for said vehicle, it is often a requirement to have the ability to switch the vehicle into different track routes at a switch section of the track. Hereinafter switching a vehicle bogie  40  in a switch section will be described. In  FIG. 2  an aft switching shaft  51   b  (in the direction of bogie travel) can be seen. A corresponding fore switching shaft  51   a  can be seen in  FIG. 7 . The shaft  51   b  is pivotally connected to the bogie frame  50  by upper and lower bearings  55   b ,  56   b  (in  FIG. 1 ) and holds an aft upper switch wheel holder  52   b  on which a left upper switch wheel  154   b  and a right upper switch wheel  254   b , are mounted. Corresponding components in the fore can be seen in  FIG. 7 , wherein it is disclosed that the shaft  51   a  is pivotally connected to the bogie frame  50  by upper and lower bearings  55   a ,  56   a , and wherein the fore shaft  51   a  holds a fore upper switch wheel holder  52   a  on which, in the fore end of the bogie, a left upper switch wheel  154   a  and a right upper switch wheel  254   a , are mounted. The fore and aft switching shafts  51   a ,  51   b  can thus control engagement of the upper switch wheels by rotation of said shafts. The shafts  51   a ,  51   b  are forced to rotate by a switch drive (not shown), both shafts being connected to a switch plate  54  which performs an arc shaped mostly lateral movement, left or right, to perform switching. As a consequence of the arrangement, fore and aft shafts  51   a ,  51   b  will rotate in opposite directions upon movement of the switch plate  54 . Lower switch wheel swingers  155 ,  255  are also engaged by the switch plate  54  so that they rotate synchronously with the lower switch cranks  53   a ,  53   b , and also with the upper switch wheel holders  52   a ,  52   b  via the switch shafts  51   a ,  51   b . Accordingly, upper switch wheels  154   a ,  254   a ,  154   b ,  254   b  are also rotated synchronously with the switching shafts  51   a ,  51   b . Outer lower switch wheels  156 ,  256  are mounted on their respective lower switch wheel swingers  155 ,  255  while inner lower switch wheels  157 ,  257  are mounted directly on the bogie frame  50 . The switch plate  54  can perform the arched movement as it is attached to three equal length crank functions at  301 ,  302 ,  303 . The switch crank  53   b  is connected to the switch plate  54  by a pin in a slot arrangement  304  of the switch plate forcing the crank  53   b  and, via the switching shaft  51   b , also the upper switch holder  52   b  to rotate in the opposite direction to the aforementioned three cranks functions  301 ,  302 ,  303  (See also  FIG. 7 ). 
         [0041]    The lower switch wheels include a left outer switch wheel  156  attached to a left swinger  155  and a right outer switch wheel  256  attached to a right swinger  255 , wherein said left and right swingers are pivotally attached to said switch plate  54  by means of a crank functions  301 ,  303  and pivotally attached to the frame  50 , whereby the left outer switch wheel  156  will rotate inwards towards the frame  50  when the right outer switch wheel  256  rotates outwards away from the frame  50 , and vice versa, upon a movement of the switch plate  54 . 
         [0042]    In  FIG. 3  a bogie is approaching a switch from an entry point  305  and has its switch mechanism positioned to go to the left switch exit  306 . When the bogie  40  reaches the starting point of lower switch rails  102 ,  202  the left lower outer switch wheel  156  will continue on the outer (left) side of the left lower switch rail  102  while the right lower outer switch wheel  256  will continue on the inside of the right lower switch rail  202 , thus forcing the bogie to continue towards the left switch exit  306  at the lower vertical level. At the same time the upper left switch wheels  154   a ,  154   b  engage the left side of a downwards extended left flange  103  of the first track member  1  while the upper right switch wheels  254   a ,  254   b  continue on the inside of a downwards extended right flange  203 , thus forcing the bogie to continue towards the left switch exit  306  at the higher vertical level. As the right lower switch rail  201  has a notch at position  204  lower right guide and switch wheels  253 ,  256 ,  257  are not blocked from following the straight path to the left switch exit  306 . The fact that both upper and lower switch wheels work together to force the bogie towards the left switch exit  306  ascertains that any torsional moments that may be acting on the bogie  40  while it passes the switch can be transferred to the track, i.e. that the bogie is not allowed to rotate around a longitudinal axis even in the presence of such moments. Despite the denominations entry and exit used it is as feasible for a bogie to enter the switch from opposite directions at position  306  or position  307  and continue towards position  305  as well as going in the direction described here. 
         [0043]    The lower switch rails  102 ,  202  are rigidly connected to the lower track members  101 ,  201  and the upper track member  1  by means of ribs similar to  110  at regular intervals within the switch section (not shown). 
         [0044]      FIG. 4  is very similar to  FIG. 3  but in this figure the bogie  40  has its switch mechanism positioned to go to the right exit  307  of the switch. The right lower switch wheel swinger  255  has been rotated such that it has become positioned further away outwards from the centre of the bogie so that the right lower outer switch wheel  256  will pass on the outer (right) side of the right lower switch rail  202 . As the right lower switch rail  202  is formed as a curve bending away, in a direction to the right, from the longitudinal direction of the track, the bogie is forced to follow the track towards the right exit  307  at the lower vertical level. At the same time the upper switch wheel holders  52   a ,  52   b  have been synchronously rotated, whereby the right upper switch wheels  254   a ,  254   b  have become correspondingly positioned further away outwards, to the right, from the centre of the bogie, so that said right upper switch wheels  254   a ,  254   b  will pass on the outside of a downwards extended right flange  203  of the first track member  1 , thus forcing the bogie  40  to continue towards the right switch exit  307  at the higher vertical level. As the left lower rail  101  has a notch at position  104  of the drawing, lower left guide and switch wheels  153 ,  156 ,  157  are not blocked from following the curved path towards the right switch exit  307 . 
         [0045]      FIG. 5  shows a bogie  40  on its way towards the left switch exit  306 . In this position the left upper switch wheels  154   a ,  154   b  are on the outside of the downwards extended left flange  103  of the upper track member  1  and together with the left upper guide wheels  151   a ,  151   b  they force the bogie to continue towards the left switch exit  306  at an upper level. The right upper switch wheels  254   a ,  254   b  are on the inside of the downwards extended right flange  203  of the upper track member  1  and can travel unhindered towards the left switch exit  306 . The left lower outer switch wheel  156  is on the outside of the left lower switch rail  102  and together with the left lower inner switch wheel  157  it forces the bogie to continue towards the left switch exit  306  at a lower level. At this longitudinal position the lower guide wheels  153 ,  253  are disengaged from the lower track members  101 ,  201  thanks to the notches at positions  104  and  204  and can pass towards the left switch exit  306  without being engaged by said lower track members. The right lower outer switch wheel  256  has been rotated inwards, so that it can pass through the notch at position  204  towards the left switch exit  306  along with the right lower inner switch wheel  257 . 
         [0046]      FIG. 6  shows a bogie  40  on its way towards the right switch exit  307 . In this position the right upper switch wheels  254   a ,  254   b  have been rotated as described above in relation to  FIG. 4 , so that they are running on the outside of the downwards extended right flange  203  of the upper track member  1  and together with the right upper guide wheels  251   a ,  251   b  they force the bogie towards the right switch exit at  307  in the upper level. The left upper switch wheels  154   a ,  154   b  pass on the inside of the downwards extended left flange  103  of the upper track member  1  and can travel unhindered towards the right switch exit  307 . The right lower outer switching wheel  256  is correspondingly positioned on the outside of the lower right switch rail  202  and together with the right lower inner switch wheel  257  it forces the bogie  40  to continue towards the right switch exit  307  at the lower level. The lower guide wheels  153 ,  253  are disengaged from the lower track members  101 ,  201  in this longitudinal position thanks to their notches at positions  104 ,  204  and can thus pass towards the right switch exit  307 . The left lower switch wheel  156  has been rotated inwards to the right by means of left switch wheel swinger  155  so that it can pass through the notch at position  104  towards the right switch exit  307  along with the left lower inner switch wheel  157 . 
         [0047]      FIG. 7  shows one preferred drive mechanism utilizing a so called wheel motor symbolized by a drive wheel  57  which engages the downwards facing drive wheel running surface  15  (in  FIG. 1 .) of the first track member  1 . The periphery of the wheel motor has a rubber coating or similar intended to increase friction. The normal force between the wheel motor and said drive wheel running surface  15  can be adjusted using a pressurizer actuator  59  here shown in the shape of a hydraulic cylinder, although the function could just as well be performed by an electric motor with some kind of gear box and a crank or excenter function. The force exerted by the pressurizer actuator is transferred to the wheel motor by means of a drive wheel pressurizer  58  shown here as a lever mechanism. The pressurizer  58  rotates around a first joint at  308  when the pressurizer actuator  59  moves it. This movement is transferred to the wheel motor by a second joint at  309 , thus (mainly) changing the compression of the rubber coating of the wheel motor, which in turn affects the normal force of the drive wheel against the running surface  15  as intended.