Field of Invention
The present invention relates to the drive mechanism of a Sliding Type Plug Door System for automatic opening and closing of a door panel installed at the entrance portal of the car-body sidewall of a railway coach. The mechanism supports the weight of door panel while providing smooth and jerk free movement during opening and closing. The drive mechanism enables the plug-in/plug-out action during the closing/opening of door panel.
Background of the Invention
A sliding type plug door system is used as an entrance system in vehicles which require a flush external surface. The sliding type plug door system constitutes a drive mechanism for opening and closing a door panel, the operating sequence of which is as follows:
During the opening sequence, the door panel plugs out of the entrance portal such that a gap is created between the door panel and car-body. It is then followed by the sliding movement so that the portal is completely opened for the passengers to board or de-board. In the closing sequence, door panel slides back to cover the portal and plugs in, to seal off the entrance portal. The drive mechanism for the sliding type plug door system is operated by an electrical motor. It should be robust and compact while at the same time provide a smooth opening and closing function.
Some prior arts disclose plug door systems and their drive mechanisms towards smooth opening and closing function of said door.

One prior art KR20120027805A, having priority date 19/03/2012, discloses a plug door system is disclosed. Such a system includes a frame providing an entrance, a transfer screw rotatable mounted in the frame in a forward / reverse direction, a sliding hanger screwed to the transfer screw to reciprocate in the longitudinal direction of the transfer screw according to the rotation of the transfer screw, and sliding. One side is connected to the hanger and the other side is connected to the door body includes a plugging hanger for moving the door body according to the movement of the sliding hanger, and a first guide rail portion for guiding the movement of the plugging hanger. The first guide rail portion includes a straight portion that guides the lateral movement of the door body and a curved portion that guides the movement for the plugging operation of the door body.
Another prior art CN201428357Y, having priority as 14/07/2009, discloses A linear guide momentary plug door, it includes left and right doors, doorframes, guide bearing means, the drive mechanism, the central locking mechanism, characterized in that: said top and bottom of each door leaf are provided on the two guide rollers and two lower guide rollers, the top of each door is provided with a plurality of the slider, the upper fixing groove of each door drive axle; guide means mounted on the carrier vehicle cabin outer wall surface, which includes an upper slotted rail, a lower rail groove, right and left linear guide bearing, the bearing block, short linear guide, the linear guide bearing positioned within an upper channel-shaped rails, each carrying two linear guides fitted on the carrier block, a linear guide of the fixed short of the bottom of each carrier trolley each slider at the top of the door leaf rails are fitted with each of the short line, a vertical guide door leaf rollers respectively rolling groove of the upper rail and a lower rail groove; the drive mechanism by two right angle rack mounted over the inner wall of the cabin door, which includes a motor, a

toothed pulley, a toothed belt around the drive slide, the drive slider is provided The latch and the slider are respectively fixed to right and left driving the loose side of the toothed belt tight side edges, left and right drive slider slidably connected to the drive axle on the door leaf, respectively; the central locking mechanism is attached to the outer drive mechanism housing middle of the upper surface, comprising unlocking a motor, to unlock the push rod, the latch hook, the latch hook return spring, said latch hook can be snapped on the left and right drive slide bolt, the latching hook can be unlocked and the motor driver to unlock the push ram unlock.
The present invention is a novel effort towards achieving a simple and highly reliable electrically driven sliding type plug door system that provides a synchronous plugging movement of the door panel, without jamming at the entrance portal in railway vehicle.
Objectives of the Invention
Primary objective of this invention is to provide a simple and highly reliable electrically driven sliding type plug door system that provides a synchronous plugging movement of the door panel, without jamming at the entrance portal in railway vehicle.
Another object of the invention is to provide a novel drive mechanism of a Sliding Type Plug Door System for automatic opening and closing of a door panel installed at the entrance portal of the car-body sidewall of a railway coach; wherein the said drive mechanism enables the plug-in/plug-out action during the closing/opening of door panel and effectively supports the weight of door panel towards providing smooth and jerk free movement during opening and closing.

Another object of the present invention is to provide a drive mechanism which consists of a main support shaft, threaded spindle, threaded nut, door connector and synchronizer shaft.
Another object of the present invention is to provide a drive mechanism, wherein, wherein said door connector, on which the door panel is mounted, slides on the main support shaft in the vehicle longitudinal direction during the opening and closing operations, and particularly the sliding motion of the said door connector is provided by the threaded nut engaged with the threaded spindle.
Another object of the present invention is to provide a drive mechanism, wherein the synchronizer shaft which is connected to main support shaft through mechanical components, ensures the application of equal forces at both ends of main support shaft and therefore said synchronizer shaft is characterized in performing its smooth functioning even during manual operation.
Summary
The sliding type plug door system contains a door panel which is installed at the entrance portal of a railway vehicle and a drive mechanism. The drive mechanism, along with bottom guide, supports the door panel such that it always remains longitudinally parallel to the vehicle car-body sidewall and ensures smooth movement of door panel during opening and closing operations.
The drive mechanism consists of a main support shaft, threaded spindle, threaded nut, door connector and synchronizer shaft. The door connector, on which the door panel is mounted, slides on the main support shaft in the vehicle longitudinal

direction during the opening and closing operations. The sliding motion of the door connector is provided by the threaded nut engaged with the threaded spindle.
The synchronizer shaft which is connected to main support shaft, ensures the application of equal forces at both ends of main support shaft. If un-even forces are applied at both ends of the main support shaft, then door panel does not remain longitudinally parallel to vehicle car-body sidewalk This results in jamming of door panel at the entrance portal. The connection between main support shaft and synchronizer shaft is done through mechanical components. Hence, the synchronizer shaft will perform its function even during manual operation.
As mentioned earlier, a bottom guide is present to support the bottom portion of door panel and keep it aligned with the vehicle body, always during the opening/closing operation. The bottom guide consists of 3 rollers which are engaged with a bottom guide rail mounted on the door panel. On engagement, the 3 rollers form a pivot arrangement that does not allow the door panel to deflect about the vehicle's longitudinal direction (X axis) and touch the vehicle walls at the bottom, when plugged out. During the plugging action the profile of bottom guide rail allows the 3 rollers to move freely and assist in smooth movement of door panel.
The sliding type plug door system also includes 3 locking units, which are mounted to the vehicle body. These locking units perform the function of keeping the door locked and secured when the door panel is in fully closed position, by supporting it in the upper, middle and lower positions. They also protect the door panel from any sort of deflection or distortion caused due to various loads such as structural loads, aerodynamic loads, loads applied by passengers etc.

Brief Description of the Drawings
The invention along with its advantages will be understood with reference to the accompanying drawings in which:
Fig. 1 shows the isometric view of sliding type plug door system;
Fig. 2 shows the view of sliding type plug door system from inside the coach;
Fig. 3 is the top view of drive mechanism in the closed position;
Fig. 4 is the top view of drive mechanism in the open position;
Fig. 5 is the side view of drive mechanism in the closed position;
Fig. 6 is the side view of drive mechanism in the open position;
Fig. 7 is an isometric view of the assembly of main shaft, synchronizer shaft,
side plates and end pieces corresponding to the open (dashed line) and
closed position (solid lines) of the door panel.
Fig. 8 is an isometric view of the drive mechanism, without synchronizer shaft
and end pieces.
Part List

Part No. (being used in Drawings as numeric reference therein) Description
1 Sliding Type Plug Door System
2 Railway Vehicle
3 Door Panel
4 Drive Mechanism
5 Main Support Shaft
6 Threaded Spindle

7a Right Mounting Bracket
7b Left Mounting Bracket
8 Threaded Nut
9 Motor
10 Door Connector
11 Roller
12 Top Guide
13 Connecting Link 1
14 Connecting Link 2
15 Synchronizer Shaft
16 Side Plate
17 End Piece
Detailed Description of the Invention
A sliding type plug door system (1) installed on a railway vehicle (2) is shown in Fig. 1 and 2. Direction references of the sliding type plug door system installed on a railway vehicle will be followed as per the coordinate system shown in Fig. 2, where X refers to the vehicle longitudinal direction, Y refers to the vehicle lateral direction and Z refers to the vehicle height direction, respectively. In case of door panel, the side in which door panel closes i.e. the positive X direction will be referred as the leading edge and the other side as trailing edge as shown in Fig. 1.
The structure and working of the drive mechanism (4) will now be described.

As shown in Fig. 3 and 4, the drive mechanism (4) consists of a main support shaft
(5) which carries the complete weight of the door panel (3) and a threaded spindle
(6) which provides movement to it for opening and closing. The main support shaft (5) and threaded spindle (6) are mounted on the mounting brackets (7a) and (7b). The threaded spindle (6) is connected to the motor (9) through a coupling (not shown). By engaging the threaded spindle (6) with a threaded nut (8), the rotational motion is converted into linear motion. This threaded nut (8) is installed on the inner diameter of a nut housing, which is further connected to the door connector (10) via the connecting link 1 (13) and connecting link 2 (14). Thus, when powered the rotational motion of the threaded spindle (6) is converted into linear motion through the threaded nut and spindle pair, and it drives the door connector (10) which is mounted on the main support shaft (5), along the longitudinal direction i.e. X axis.
The door panel (3) is mounted on the door connector (10) which has a roller (11) at the centre. This roller (11) rolls on the vertical surface of a top guide (12) when the door connector (10) moves along the longitudinal direction of the vehicle. The top guide (12) consists of a straight portion and an inclined portion, which extend towards the vehicle outside wall at an angle with respect to longitudinal direction (X-axis) of the vehicle. The inclined portion guides the motion of the door panel (3) during the plugging action. The main support shaft (5) moves in the slots provided in mounting brackets (7) (as shown in Fig. 5 and 6), in the vehicle width direction during the plugging action along with the door connector (10) and door panel (3).
Side Plate (16) is mounted between the main support shaft (5) and mounting brackets (7) at both the ends to avoid the wear of main support shaft (5). As clearly visible in Fig. 2, the straight and inclined portion of the top guide (12) meets at a

curved path, provided to assist in smooth transition from sliding motion to plugging motion.
Slots are also provided in connecting link 1 (13) to assist during the plugging movement of the door panel (3). As shown in Fig. 8, the extended arms of nut housing fits inside the slots of connecting link 1 (13). During the closed position, once the threaded spindle (6) starts to rotate, the nut housing tries to push the connecting link 1 (13) in linear direction i.e. vehicle's longitudinal direction.
However, because of the geometry of top guide (12), a plugging action is created which results in movement of door panel (3) in lateral and longitudinal direction simultaneously. The slots provided in mounting brackets (7) and connecting link 1 (13) aid in the smooth movement of door panel (3) in vehicle's lateral direction.
As shown in Fig. 7 the drive mechanism (4) also includes an additional shaft called synchronizer shaft (15). The synchronizer shaft (15) is located above the main support shaft (5) and is connected to it through an end piece (17) from both sides. The top part of end piece (17) is mounted on the synchronizer shaft (15) and fixed with the help of a split pin (not shown). The bottom part of the end piece is mounted on the side plate (16) which is further connected with main support shaft (5). As the name suggests, synchronizer shaft (15) prevents jamming of the main support shaft (5), by ensuring its synchronized movement, along the width of the vehicle during plug-in or plug out.
In the absence of synchronizer shaft (15), during closing operation when the roller (11) of door connector (10) approaches the inclined portion of the top guide (12) and starts plugging in, an inward force acts on the main support shaft (5) towards the

leading side of door panel (3), thus creating a moment about the vertical Z-axis. Due to this moment the door panel (3) will also rotate about the vertical Z-axis during plug in and would jam without complete closure.
To prevent this phenomenon the synchronizer shaft (15) comes into effect. Due to the coupling between the main support shaft (5) and synchronizer shaft (15), when the main support shaft (5) moves along the width of the vehicle from the leading side, the synchronizer shaft (15) will rotate about its own axis as shown in Fig. 7, and thus will pull the trailing side of the main support shaft (5) along with it, thus resulting in a synchronized or balanced movement.
As the main support shaft (5) slides in the slots of mounting brackets (7) during plugging action, the end piece (17) starts to rotate about the centre axis of synchronizer shaft (15). In order to satisfy all the geometrical constraints to have a smooth plugging action, a slot is also provided at the bottom part of end piece (17).
It is very important to arrest the rotational play between the synchronizer shaft (15) and end piece (17), as this results in un-even distribution of forces at the leading edge and trailing edge of main support shaft (5) which will cause jamming of door panel (3) in the entrance portal.
The flat surface made on the internal and external surface of end piece (17) and synchronizer shaft (15) respectively, eliminates the possibility of any play between both the parts which ensures smooth plugging action.
Advantages of the Invention

Various advantages offered by this invention in the field of sliding type plug door system are as follows:
• A more reliable system due to a smaller number of moving parts in the drive mechanism (4).
• Smaller number of moving parts also results in lighter weight of the entire system.
• Easy and quick installation of the entire drive mechanism (4).
• No lubrication required between threaded spindle (6) and threaded nut (8) for environmental operation.
• Synchronized movement of door panel (3) during entire opening/closing operation which avoids jamming at the entrance portal.
• The opening/closing operation of the sliding type plug door system (1) can be performed even in the absence of electric power.
• Less maintenance required due its simple and robust design.
• Lower frictional resistance offered by the drive mechanism (4) due to smaller number of moving parts. This increases the smoothness of door panel (3) operation.
• Since there are no hinge connections between nut housing and door connector (10), the force is more effectively transferred from threaded nut (8) to door connector (10). This enhances the overall efficiency of door operation.
• Due to the modular design, majority of the components can be removed and replaced individually, if required, during maintenance activities.
Although the present disclosure has been illustrated and described herein with reference to preferred embodiments and specific examples thereof, it will be

readily apparent to those of ordinary skill in the art that other embodiments and examples may perform similar functions and/or achieve like results. All such equivalent embodiments and examples are within the spirit and scope of the present disclosure, are contemplated thereby, and are intended to be covered by the following claims.

We claim

1. Drive mechanism of a sliding type plug door system, comprises of:
a. A door connector which holds the door panel,
b. A top guide which guides the movement of the door connector along
the vehicle longitudinal direction and lateral direction,
c. A door mounting bracket which carries the main support shaft and
allow its movement along the vehicle lateral direction, and
d. A mechanism which only allows synchronized movement of main
support shaft along the width of the vehicle;
wherein
said drive mechanism for sliding type plug door operation is characterized in:-
• automatic opening and closing of a door panel installed at the entrance portal of the car-body sidewall of a railway coach;
• a synchronous plugging movement of the door panel, without jamming at the entrance portal in railway vehicle; and
• simple and highly reliable electrically driven sliding type plug door system.
2. Drive mechanism of a sliding type plug door system, as claimed in claim 1, wherein the said drive mechanism for synchronized movement of main support shaft includes:
a. A synchronizer shaft which extends along the length of the vehicle,

b. An end piece which connects the main support shaft and the synchronizer shaft and only allow the synchronized movement of the main support shaft along the width of vehicle.
3. A sliding type plug door system, as claimed in claim 1 or 2, wherein the flat surface provided on the internal and external surface of end piece and synchronizer shaft respectively, avoids any rotational play and hence creating a smooth plugging action.
4. Drive mechanism of a sliding type plug door system, as claimed in claims 1-3, wherein the connecting link 1 and connecting link 2, assembled with door connector, are so engaged with the pair of threaded nut and threaded spindle that upon the rotation of said threaded spindle, the threaded nut moves linearly along the longitudinal direction of vehicle and thereby drives the door connector.
5. Drive mechanism of a sliding type plug door system, as claimed in claim 1, wherein the said drive mechanism, installed at the entrance portal of the car-body sidewall of a railway coach, mainly consists of a main support shaft, threaded spindle, threaded nut, door connector and synchronizer shaft, and wherein said drive mechanism enables the plug-in/plug-out action during the closing/opening of door panel and effectively supports the weight of door panel towards providing smooth and jerk free movement during opening and closing.
6. Drive mechanism of a sliding type plug door system, as claimed in claim 1, wherein the said drive mechanism, along with bottom guide, supports the door

panel such that it always remains longitudinally parallel to the vehicle car-body sidewall and ensures smooth movement of door panel during opening and closing operations.
Drive mechanism of a sliding type plug door system, as claimed in claim 1, wherein said door connector, on which the door panel is mounted, is provisioned to slide on the main support shaft in the vehicle longitudinal direction during the opening and closing operations, and particularly the sliding motion of the said door connector is provided by the threaded nut, engaged with the threaded spindle.
Drive mechanism of a sliding type plug door system, as claimed in claim 1, wherein the synchronizer shaft is connected to main support shaft through mechanical components and ensures the application of equal forces at both ends of main support shaft and therefore said synchronizer shaft is characterized in performing its smooth functioning even during manual operation.
Drive mechanism of a sliding type plug door system, as claimed in claim 1, wherein said bottom guide employed in the said drive mechanism, consists of 3 rollers, engaged with a bottom guide rail mounted on the door panel to form a pivot arrangement therein to refrain the door panel from deflecting about the vehicle's longitudinal direction (X axis) and/or touching the vehicle's wall(s) at the bottom, once plugged out; wherein said bottom guide is characterized in providing support to the bottom portion of door panel and keeping the said bottom portion of door panel aligned with the vehicle body, particularly during the opening/closing operation.

10. Drive mechanism, as claimed in claims 1-9, wherein the preferred embodiment of said drive mechanism of a slide type plug door system, is characterized in following structural and operational provisions:
• the drive mechanism (4) consists of a main support shaft (5) which carries the complete weight of the door panel (3) and a threaded spindle (6) which provides movement to it for opening and closing.
• The main support shaft (5) and threaded spindle (6) are mounted on the mounting brackets (7a) and (7b).
• The threaded spindle (6) is connected to the motor (9) through a coupling and by engaging the threaded spindle (6) with a threaded nut (8), the rotational motion is converted into linear motion.
• Said threaded nut (8) is installed on the inner diameter of a nut housing, which is further connected to the door connector (10) via the connecting link 1 (13) and connecting link 2 (14).
• When powered, the rotational motion of the threaded spindle (6) is converted into linear motion through the threaded nut and spindle pair, and it drives the door connector (10), which is mounted on the main support shaft (5), along the longitudinal direction i.e. X axis.
• The door panel (3) is mounted on the door connector (10) which has a roller (11) at the centre.
• Said roller (11) rolls on the vertical surface of a top guide (12), when the door connector (10) moves along the longitudinal direction of the vehicle.

• The top guide (12) consists of a straight portion and an inclined portion, which extend towards the vehicle outside wall at an angle with respect to longitudinal direction (X-axis) of the vehicle.
• The inclined portion guides the motion of the door panel (3) during the plugging action.
• The main support shaft (5) moves in the slots provided in mounting brackets (7), in the vehicle width direction during the plugging action along with the door connector (10) and door panel (3).
• Side Plate (16) is mounted between the main support shaft (5) and mounting brackets (7) at both the ends to avoid the wear of main support shaft (5).
• The straight and inclined portion of the top guide (12) meets at a curved path, provided to assist in smooth transition from sliding motion to plugging motion.
• Slots are also provided in connecting link 1 (13) to assist during the plugging movement of the door panel (3).
• The extended arms of nut housing fits inside the slots of connecting link 1 (13).
• During the closed position, once the threaded spindle (6) starts to rotate, the nut housing tries to push the connecting link 1 (13) in linear direction i.e. vehicle's longitudinal direction.
• However, because of the geometry of top guide (12), a plugging action is created which results in movement of door panel (3) in lateral and longitudinal direction simultaneously.

• The slots provided in mounting brackets (7) and connecting link 1 (13) aid in the smooth movement of door panel (3) in vehicle's lateral direction.
• Said drive mechanism (4) also includes an additional shaft called synchronizer shaft (15), which is located above the main support shaft (5) and is connected to it through an end piece (17) from both sides.
• The top part of end piece (17) is mounted on the synchronizer shaft (15) and fixed with the help of a split pin (not shown).
• The bottom part of the end piece (17) is mounted on the side plate (16) which is further connected with main support shaft (5).
• Said synchronizer shaft (15) prevents jamming of the main support shaft (5), by ensuring its synchronized movement, along the width of the vehicle during plug-in or plug out.
• Due to the coupling between the main support shaft (5) and synchronizer shaft (15), when the main support shaft (5) moves along the width of the vehicle from the leading side, the synchronizer shaft (15) rotates about its own axis and pulls the trailing side of the main support shaft (5) along with it, thus resulting in a synchronized or balanced movement.
• As the main support shaft (5) slides in the slots of mounting brackets (7) during plugging action, the end piece (17) starts to rotate about the centre axis of synchronizer shaft (15).
• In order to satisfy all the geometrical constraints to have a smooth plugging action, a slot is also provided at the bottom part of end piece (17).

• To avoid jamming of door panel (3) in the entrance portal, it is very important to arrest the rotational play between the synchronizer shaft (15) and end piece (17), as this results in un-even distribution of forces at the leading edge and trailing edge of main support shaft (5).
• The flat surface made on the internal and external surface of end piece (17) and synchronizer shaft (15) respectively, eliminates the possibility of any play between both the parts which ensures smooth plugging action.