Technical Field The present invention relates to window regulators. The present invention particularly relates to a lifting plate of a window regulator with retainers that are operably interconnected by means of a motion-transmitting element for a tilt-free operation of a window screen. Background and prior art Automotives usually have window regulators which are operable either manually or powered. The window regulator is designed to facilitate the up-down movement of window screen. Window regulators are of common usage in all vehicles. Its functions are to raise and lower the window screen. This is guided into the side channels mounted on the vehicle body. The function of the lifting plate is to hold the window screen& carrying the same during upward & downward movement of the window screen on actuation of the mechanism. Normally, in the motion transmitting element type of window regulators the lifting plate is moved up & down by a motion transmitting element fixed to it. The motion transmitting element is usually made of tensile material. The position of the motion transmitting element ends with respect to the lifting plate is very much important. If the motion transmitting element ends are crossing each other, particularly at extreme top & bottom position of the window screen, the functional movement of crossed motion transmitting element ends creates unwanted noise. To avoid this in some window regulators the motion transmitting element ends are moved apart from each other causing a sharp bend in the cable, because of this the motion transmitting element gets stressed resulting in fatigue failure. The usual method in motion transmitting element type of window regulators is to mount the window screen on a lifting plate, which slides on guide rail. The guide rail is provided with mounting brackets, which is mounted on the door. The lifting plate which slides on the guide rail in turn actuates the window screen upward & downward. Therefore, the design of the lifting plate is crucial for functioning of the window regulator without failure. The common problems encountered in window regulators because of lifting plate are jumping of the motion transmitting element out of the roller pulley, motion transmitting element tension force acting on the roller pulley which eventually causes its failure, rubbing noise due to crossing of motion transmitting element, window screen pop out due to excess play in the lifting plate and lifting plate breakage due to improper material and strength. Object of the present invention The primary object of the present invention is to provide a window regulator with lifting plate with retainers that are operably interconnected by means of a motion-transmitting element for a tilt-free operation of a window screen. An object of the present invention is to provide a window regulator with a tilt-free lifting plate movement. Another object of the present invention is to provide a window regulator with a lifting plate to prevent fatigue-failures of the motion-transmitting element. Yet another object of the present invention is to provide a window regulator with a lifting plate to prevent fatigue-failures of roller-pulleys of the guide rails. Summary of the invention The present invention particularly provides a lifting plate of a window regulator with retainers that are operably interconnected by means of a motion-transmitting element for a tilt-free operation of a window screen. The window regulator comprising a slidable lifting plate mounted on a vertical guide rail, a pair of flanges disposed on the rear side of lifting plate to mate with said guide rail and to provide a tilt -free sliding support to the lifting plate. A pair of retainers with locking means is operably connected by means of a motion-transmitting element. The motion transmitting element is disposed to form a contact-free crossover of said motion-transmitting element on the rear side of the lifting plate. Brief description of the accompanied diagrams Fig 1 is a schematic diagram of a window regulator mounted on the door of an automotive depicting the window screen in the closed position. Fig 2 is a schematic diagram of a window regulator mounted on the door depicting the window screen in open position. Fig 3 is a rear view of the lifting plate depicting contact-free crossover of motion transmitting element. Fig 4 is a sectional view of the lifting plate along the section A-A' of the lifting plate shown in Fig 3 Fig 5 illustrates the front view of the lifting plate showing the ends of motion transmitting elements. Fig 6 depicts the guide rail-guide with flanges of the lifting plate. Fig 7 is a sectional view of the lifting plate with guide rail along the section 'B-B' as shown in Fig 6. Detailed description of the drawings The present invention provides a window regulator with a lifting plate for automotives. The invention is now described with reference to the accompanied diagrams. Initially referring to Figs 1& 2, said figures depict the window regulator of the present invention with a window screen 1, said window regulator mounted on a door panel 3 of a vehicle- door. These Figures also depict the position of the window screen 1 in closed and open positions respectively. The door channels 2 on either side of the door, guides the window screen 1 in the door frame 3a during upward and downward movement of the window screen 1. The window regulator of the present invention comprises a guide rail 4 said guide rail is vertically mounted on the door with some inclination with respect to horizontal. A slidable lifting plate 5 is disposed on the guide rail 4. A motion transmitting element 6 'traversing the full length of the guide rail 4 is disposed on the lifting plate 5 by means of its ends. The motion transmitting element 6 of the present inyention is cable made of flexible and tensile material, preferably steel and metallic alloys. The guide-rail 4 with an 'L-shaped' section 4a (as shown in Fig 6), is fastened to the vehicle-door, by means of mounting brackets 12 & 12a. The mounting brackets 12 & 12a made from suitable metallic material are used to fix the window regulator onto the door of an automotive. The lifting plate 5 of the present invention is a winged-shape device. However, the shape of the lifting plate can be selected from other shapes like rectangle, oval or a capsule or any shapes that are suitable to the present application. The lifting plate 5 of the present invention is dual-sided viz., the rear side and the front side. The rear side of the lifting plate 5 is slidably fitted onto the 'L-shaped' section 4a of the guide-rail 4. The window screen 1 is fastened to the front side of the lifting plate 5 by conventional means 9. A'drum cover 16 receives the motion transmitting element 6 from a roller pulley 7, winds on a drum pulley (not shown in figures) and transmits to another roller pulley 8 through tension springs 19. The motion transmitting element is selected from a tensile material preferably a metallic material. The drum cover 16 is mounted of the vehicle door by means of bolts 17. A pair of roller brackets 10 & 11 is welded to the top and bottom positions of the guide- rail 4. A pair of roller pulleys 7 & 8 are disposed on the roller brackets 10 & 11. The roller pulleys 7 & 8 are made from suitable material, preferably, plastic materials. The motion transmitting element 6 that is extending from the guide rail 4 is further extended to roller pulleys 7 & 8. The wire rope assembly 14 comprises inner and outer core (not shown in Fig 1 & 2). An anti-rattle sleeve 15 made up of suitable rubber material is wrapped around the wire rope pulley assembly 14 to avoid a contact between * the window screen 1 and wire rope assembly 14.The Wire rope assembly 14 is fitted to the roller bracket 10 on top using a bush adjuster 13. Bush adjuster 13 has three slots, which help to maintain the tension in the wire rope assembly 14. The tension in the motion transmitting element 6 is varied by utilizing the three slots of the bush adjuster 13. An O-ring 22 is fitted over the bush adjuster 13 to ensure the firm contact between the bush adjuster 13 and the wire rope assembly 14. Referring to Figs 3, 4 & 5, the motion-transmitting element 6 which is allowed to pass through the pulley 7 comprises two ends 28 & 29. The ends are crimped, these crimping are made of suitable profile. A pair of retainers 25 & 26 disposed on rear and front sides of the lifting plate 5 to house the locking means by way of forming hollow cavities. The retainers 25 & 26 comprise locking means 5b disposed at the outer portion of the tapered seating area. These locking means 5b are provided to prevent the motion-transmitting element ends 28 & 29 from popping out of the retainers 25 & 26. The ends 28 & 29 of the motion transmitting element 6 are press-fitted into said retainers 25 & 26 to enable the locking of the ends with said retainers 25 & 26. This The one end 28 of the motion transmitting element 6, which is operably locked in the retainer 25 is extended either through the pulley 7 or 8 depending upon the extension of the motion transmitting element either towards pulley 7 or 8. The motion-transmitting element 6 accounts for the smooth and tilt-free movement of the window screen 1 during upward and downward movement of the lifting plate 5. Front and rear sides (dual sides) of the lifting plate 5 are shown in Figs 3, 4 & 5. The lifting plate 5 of the present invention is strengthened by providing a strong- ribbed surface. The surface of the lifting plate 5 having the meshing of ribs constitutes the front side 31 of the lifting plate 5 and the non-ribbed surface constitutes the rear side 30 of the lifting plate 5. The retainers 25 & 26 are diagonally disposed on the rear and front sides 30 & 31 of the lifting plate 5 respectively. The retainers 25 & 26 are made of hollow rectangular passages with tapered seating area. An opening 27 is disposed on the lifting plate 5, in close proximity to the front retainer 26. The opening 27 is a pass-through passage extending from one side of the lifting plate > 5 to the other. The motion transmitting element end 28 originating from the retainer 25 is extended through the full length of the guide-rail 4, roller 8 and wound around a drum pulley (not shown in Figures) to reach the other side of the guide rail 4 and terminates as another end 29 into the front retainer 26, through the opening 27. The retainers 25 & 26 are positioned on sides of the lifting plate 5 to enable the motion transmitting element 6 to form a loop extending from one retainer to the other to provide a lifting motion to the window screen 1 in conjunction with the vertical movement of the lifting plate 5. During the process of this movement of window screen 1, the loop thus formed of the motion transmitting element 6 does not have any criss-cross contact of the motion transmitting element 6. As a result total lack of friction in the motion transmitting element 6, the window regulator of the present invention does not emit any noise during the normal operation of the regulator. The locking of motion transmitting element ends 28 & 29 on opposite sides of the lifting plate 5 is to enable contact-free separation of motion transmitting element. This separation eliminates the movement of one end of the motion transmitting element relative to other end, thereby eliminating the operating noise. Supporting surface members 5a carved out of the lifting plate 5 are disposed adjacent to the point of criss-cross of motion transmitting element 6, to provide a slip-free passage arid tangential exit to the motion transmitting element 6 from the lifting plate 5 with respect to the roller pulleys 7 & 8. The stress on the motion transmitting element 6 is reduced by making its exit more or less straight. This prevents the fatigue failure of the motion transmitting elements. Both the motion transmitting element ends from retainers 25 & 26 are always fall tangentially into the roller pulley 7 & 8 groove. This reduces the load on the roller pulley 7 at extreme top and bottom positions of the window screen. This prevents the fatigue failure of the roller pulley 7 & 8. The Lifting plate 5 has a pair of flanges 24 on either side of the rear side of the lifting plate to mate with guide-rail 4 to provide a tilt-free sliding. The flanges 24 are inserted into the 'L' section 4a of the guide-rail 4. The flanges 24 of the lifting plate 5 are having an 'L-shaped' reciprocating profile of the guide rail 4. The lifting plate 5 slides over. the guide section 'L' during upward & downward of the window screen on being actuated. The flanges 24 are placed on two-sides of the longitudinal axis of the lifting plate 5. The flanges 24 in the lifting plate 5 are defined with curvaceous curves; the radii of the curves are selected to match the profile of the guide rail 4. This curvaceous profile of the flanges 24 plays the key role in minimizing the tilt of the window screen 1 in long usage of the window regulator. The width of the flanges 24 is suitably selected to prevent popping up of the window screen 1 after long usage of the window regulator. The lifting plate 5 comprises a pair of centrally located oppositely placed tongues 23 disposed on the rear & front side of the lifting plate 5 to provide a sliding path to the lifting plate 5 on the guide-rail 4. The thickness of the guide-rail 4 deteπυines the gap between the tongues 23. The curvaceous profile of the tongues 23 ensures firm contact during the long run of the window regulator. The pair of tongues 23 provides a firming support to guide rail 4 during the slide of the lifting plate on the guide rail 4. Referring to Fig 4, a section is cut along the axis A-A' as visible in Fig 3. Fig 4 shows a sectional view of the lifting plate, this view is mainly to emphasize the crossing-over of the motion transmitting element 6 as well as the separation of the motion transmitting element 6 at the juncture of criss-crossing. The separation of the motion transmitting element 6 at the juncture of criss-crossing ensures elimination of operating noise thus incrementing the longevity of the motion transmitting element 6. Referring to Fig 6, which depicts the guide rail-guide 4a with flanges of the lifting plate. Fig 7 is a sectional view of the lifting plate with guide rail 4 along the section 'B-B' as shown in Fig 6. Fig 7 shows a pair of centrally located oppositely placed tongues 23 is shown on the rear and front side of the lifting plate 5 to provide a sliding path to the lifting plate 5 on the guide-rail 4. Operation of the window regulator: The operation of the window regulator can be best understood from the Figs 1 & 2. The upward and downward motion of the window screen 1 is achieved by actuating the drum pulley (not shown in the figures) of the window regulator. On actuation of the drum pulley (not shown in the figures) the motion transmitting element 6 which is locked onto the drum pulley (not shown in the figures) is actuated. The movement of the motion transmitting element 6 in turn moves the lifting plate 5 up & down on the guide rail 4. The upward movement of the window screen 1 is stopped by ,the upper channel in the door frame 3a shown in Fig 1. Downward movement of the window screen is stopped by rubber stopper 18 as shown in Fig 2. Rubber stopper 18 is inserted into the bottom roller bracket 11. The reverse transmission of motion is stopped by the brake spring mechanism present in the drum cover 16. In the lifting plate of the present invention, the motion transmitting element ends 28 & 29 are locked at diagonally opposite retainers 25 & 26 on opposite sides of the lifting plate 5 which results in a contact-free crossover. As the motion transmitting element ends 28 & 29 are separated from each other, there is no relative movement of one motion transmitting element end relative to other which eliminates noise. Advantages 1. The curvaceous profile of the flanges on the lifting plates minimizes the tilt of the window screen during long usage of the window regulator mechanism. 2. The lifting plate of the present invention is provided with a meshing of ribs, thereby making the plate very strong and durable. 3. The operating noise has been eliminated due to use lifting plates with non-touching motion transmitting cables by virtue of lifting plate design. 4. Profile of the Flanges in the lifting plate prevents window screen pop-out after long usage of the window regulator. 5. Stress on the motion transmitting element reduced by making the motion transmitting element exit from the lifting plate more or less straight, due to the design of the lifting plate. 6. The fatigue failure of the roller pulley is prevented; this is achieved by ensuring the exit of the motion transmitting element from the lifting plate is tangential.