Title of Invention	A DEVICE FOR STEERING RETURNABILITY AND CENTERING OF A VEHICLE
Abstract	This invention relates to a device for steering returnability and centering of vehicle comprises of at least two spiral springs, an arbor, case assembly and mounting means. Wherein said spiral are provided on said arbor coaxially assembly. Said arbor is adopted to be rotatably engaged with steering column/wheel and said casing assembly is mounted on mounting means. When steering wheel is turned in either direction the springs provide return torque so that the wheel comes back to neutral position. The invention thus provides steering returnability in response to large steering wheel inputs and steering centering in response to spurious steering inputs, thus eliminating the need of providing positive caster in the suspension. The invention is compact and has least number of parts. Apart from that the device is easy to assemble and manufacture.

Title of Invention

A DEVICE FOR STEERING RETURNABILITY AND CENTERING OF A VEHICLE

Abstract

This invention relates to a device for steering returnability and centering of vehicle comprises of at least two spiral springs, an arbor, case assembly and mounting means. Wherein said spiral are provided on said arbor coaxially assembly. Said arbor is adopted to be rotatably engaged with steering column/wheel and said casing assembly is mounted on mounting means. When steering wheel is turned in either direction the springs provide return torque so that the wheel comes back to neutral position. The invention thus provides steering returnability in response to large steering wheel inputs and steering centering in response to spurious steering inputs, thus eliminating the need of providing positive caster in the suspension. The invention is compact and has least number of parts. Apart from that the device is easy to assemble and manufacture.

Full Text	FORM 2 THE PATENTS ACT 1970 (39 of 1970) & THE PATENTS RULES, 2003 PROVISIONAL SPECIFICATION (See Section 10; rule 13) TITLE OF THE INVENTION A Device for Steering Returnability and Centering of a Vehicle APPLICANTS TATA MOTORS LIMITED, an Indian company having its registered office at Bombay House, 24 Homi Mody Street, Hutatma Chowk, Mumbai 400 001 Maharashtra, India INVENTORS Soheb Ahmed, Abhay Deshpande both Indian nationals of TATA MOTORS LIMITED, an Indian company having its registered office at Bombay House, 24 Homi Mody Street, Hutatma Chowk, Mumbai 400 001 Maharashtra, India PREAMBLE TO THE DESCRIPTION The following provisional specification particularly describes the invention and the manner in which it is to be performed. FIELD OF INVENTION This invention relates to a device for steering returnability and centering of vehicle and more particularly relates to a mechanical device for steering return ability and centering of vehicle. BACKGROUND OF INVENTION Primary function of the steering system in automobiles is to provide driver control on the vehicle. These systems may be conventional mechanical systems or steer by wire systems. In addition to the primary requirement of driver control, these systems have provisions for steering centering and returning. Steering return ability is desired because after executing a turn, the vehicle should move in a straight path or the steering wheel should come to a neutral position for straight driving. In other words, when the vehicle driver releases the steering wheel after turning the steering wheel to change the direction of the vehicle, the steering wheel should automatically return to the center position. Steering centering or center feel is also essential, because wide variety of extraneous forces can act on a vehicle steering system and spurious steering inputs caused by these forces must be dealt with satisfactorily in order to provide stable and controllable steering of a vehicle. As vehicle speed increases, the effects of any spurious steering inputs are magnified, making it necessary for 2 the driver to exercise more precise and careful driving control. The ideal driving situation is therefore one where the steering system inherently causes the vehicle to travel in an unswerving straight line unless the driver intentionally turns the vehicle in another direction. The ideal steering system should therefore require relatively little attention from the driver as the vehicle progresses along a straight line path down the roadway. From a steering standpoint, the vehicle should not respond to anything but the driver's steering commands and these must be of sufficient magnitude to overcome a significant resistance to turning away from center. In the absence of a steering input by the driver, the vehicle should literally do nothing but progress straight ahead. Conventionally, automobile steering systems have steering wheel return ability by slanting the king pins of the steer wheels. Such positive caster is provided by positive caster offset, which is also known as mechanical trail. Caster offset is the distance from the ground intersection point of a pivot line drawn through the pivot axis of a steerable wheel to a contact point at the center of the area over which the wheel contacts the ground. The pivot axis of a steerable wheel of a motor vehicle is usually provided by a "king pin". Because the contact point of a steerable wheel with positive caster trails the pivot line point of the wheel, side forces cause the wheel to turn in the direction that the force is being applied. But this provision has its disadvantages like effects of strong gusty cross winds are more pronounced with large amounts of positive caster offset. The vehicle tends to caster towards the side of the roadway to which it is being pushed by the wind. Any small amount of stability gained on a non-windy day from 3 slanting the steer wheel king pins may be paid for many times over when driving in a crosswind because of the destabilizing castering effect of the crosswind. Similarly, a high crown at the center of the roadway or a slanted roadway tends to cause vehicles with castered steer wheels to turn toward the edge of the roadway, that is, in the downhill direction. Castered steer wheels also allow steering inputs from rutted and other imperfect roadway surfaces to steer back against the driver and thereby cause road wander. Keeping a vehicle tracking straight and under control currently requires an inordinate amount of driver steering corrections to counteract the adverse side effects of castered steer wheels. The repetitive task of making numerous precise steering corrections mile after mile weighs heavily on a driver's physical and mental well-being, and may result in extreme driving fatigue. In addition, due to increased turning-lift effects, generous positive king pin angles provide significant resistance to small radius turns, which can make city driving quite fatiguing. Moreover, positive caster generates camber gain in a corner which may also cause the tires to heat up, lose grip, and wear out prematurely. These adverse effects are some of the negative aspects of attempting to achieve steering system stability through generous amounts of caster angle. In short, steer wheel castering is directly responsible for road wander, crowned road steering wheel pull and cross wind steering problems. Hence, there is critical need to provide directional stability by replacing castered wheels with another method of achieving steer wheel return ability. In other words there is need of providing directional stability of steer wheels with no positive caster, i.e., a caster angle of zero degree. The replacement of steerable wheel castering with 4 the power centering technology of the present invention has a number of additional advantages. These include precision on-center directional stability of the steerable wheels that make the vehicle more comfortable to drive a corresponding reduction in accident potential due to the considerable reduction in driving fatigue, improvement in steerable wheel blowout protection and related safety, improvement in the tire wear pattern of the steerable wheels that increases tire life and reduces maintenance costs, a stable non-swaying ride that improves passenger comfort particularly in buses and other large vehicles, and lower insurance costs due to significant improvements in overall vehicle safety. Instead of relying on positive castering, steering wheel returnability after a turning movement is provided by steering centering/returning assemblies. Some of the relevant ones are discussed as under. US 5050443 describes a spring operated return assist device which permits a limited degree of free rotation of the steering shaft before activation of the mechanism. The return assist device urges the shaft and the steering wheel to a near central neutral position after rotation of the steering wheel. The invention suffers from the shortcoming that it will have poor center feel due to presence of aperture as a design feature. Apart from that the system is backlash prone. In addition the system has great many parts and the assembly is complicated and costly to manufacture. U.S. 6694839 describes springs designed to apply a return torque on the rotating ring to return it to the neutral point and means for limiting in two directions the 5 rotation of the rotating ring. The device comprises a plate mounted rotatable relative to the fixed element and two helical springs, a first spring being arranged on one side of the plate and fixed thereon by its internal end, a second spring being arranged on the other side of the plate and fixed by its internal end on the fixed element, the external end of the first spring being linked, in a first direction, to the rotation of the rotating ring and the external end of the second spring being linked, in a second direction opposite to the first, to the rotation of the plate. The invention suffers from the shortcoming that there are no provisions to address the issue of permanent set of springs, resulting in backlash over the period of use resulting in poor center feel. U.S. 6705419 describes a steering shaft and a center feel mechanism. The center feel mechanism comprises a cam face, an urging member and a second geared portion. The cam face and the urging member are configured to generate a retuning torque to the center feel mechanism. The returning torque has a direction opposite the second angular displacement. Similarly, U.S. 6820703 also describes a mechanical steering feel enhancement device which provides a return-to-center function. The invention suffers from the drawback that the system has great many parts and the assembly is not compact as well as complicated and costly to manufacture. Secondly the cam and roller assembly in conjunction with gears will result in friction related issues. A study of the prior art related to steering returnability and steering centering devices reveals a long felt need for a system that, 6 1. Comprises of less no. of parts 2. Is coaxial with the steering wheel / steering column and compact 3. Is easy to manufacture and assemble 4. Eliminates friction arising due to mechanical interaction between two or more parts 5. Self compensates any loss in spring characteristics or permanent set OBJECTS OF INVENTION The main object of this invention is to provide a device for steering returnability of vehicle which eliminates the requirement of positive caster in the suspension. Another object of the invention is to provide steering centering (improved center feel) in response to small/spurious steering inputs. Another object of the invention is to provide steering returnability and steering centering device with least number of parts. Another object of the invention is to provide steering returnability and steering centering device which is compact, easy to assemble and manufacture. Yet another object of the invention is to provide steering returnability and steering centering device with least system level friction. 7 Yet another object of the invention is to provide steering returnability and steering centering device which self compensates any loss in spring characteristics or permanent set. Yet another object of the invention is to provide steering returnability and steering centering device which substantially matches the return torque requirements vis-à-vis steering wheel angle. SUMMARY OF INVENTION The device comprises of means to provide steering return ability and steering centering device for use in a vehicle steering system. It consists of arbor and case assembly for two spiral springs. The arbor is rotatably engaged with steering column/wheel. The arrangement is such that when steering wheel is turned in either direction the springs provide return torque so that the wheel comes back to neutral position. The invention thus provides steering return ability in response to large steering wheel inputs and steering centering in response to spurious steering inputs, thus eliminating the need of providing positive caster in the suspension. The invention is compact and has least number of parts. Apart from that the device is easy to assemble and manufacture. Moreover, the design of the system is such that it self compensates any loss in spring characteristics or permanent set. 8 DETAILED DESCRIPTION OF DRAWINGS Referring now to the drawings wherein the showings are for the purpose of illustrating a preferred embodiment of the invention only, and not for the purpose of limiting the same, Fig.l shows the mounting of the steering return ability and centering device on the steering system Fig.2 shows steering returnability and centering device on the steering wheel assembly Fig. 3 shows the exploded view of the steering return ability and centering device mounting arrangement steering column Fig. 4 shows the steering return ability and centering device in isometric view Fig. 5 shows isometric and plan view spiral springs Fig. 6 shows constructional details of unitary arbor Fig. 7 shows constructional details of unitary casing Referring to Fig. 1 and Fig. 2 the steering return ability and centering device 2 is mounted on mounting bracket 8 using bolts 14. The mounting bracket 8 is welded to column tube 4 which is mounted on steering system cross member 6 using mounting bracket 5. Referring to Fig. 3 and Fig. 4 it can be noticed that invention comprises of unitary arbor 13, unitary casing 11 and a set of similar spiral springs 9 and 10. The unitary casing 11 is mounted on mounting bracket 8 using assembly bolts 14 and mounting legs 12. The mounting bracket 8 is welded to steering column 9 tube 4. The steering column 7 consists of multiple keys 15 on its outer periphery. The spiral spring 9 is assembled in the unitary casing 11 and unitary arbor 13 such that the outer ends of the spiral spring 9 are seated in the rectangular slots 18 and 20. Similarly, the spiral spring 10 is assembled in the unitary casing 11 and unitary arbor 13 such that the outer ends of the spiral spring 10 are seated in the rectangular slots 17 and 19. The unitary arbor 13 is rotatably engaged with steering column 7 by seating steering column keys 15 in key slots 16 of unitary arbor. The unitary casing 11 is bolted to the mounting bracket 8 using bolts 14. Fig.5 shows isometric and plan view of spiral spring 9 and 10 Referring to Fig.6, unitary arbor 13 has multiple key slots 16 on its inner periphery and two rectangular cut slots 17 and 18 on its outer periphery. Referring to FIG 7, unitary casing 11 comprises of two rectangular cut slots 19 and 20 on its inner periphery, and bolting legs 12 welded on outer periphery. Assembly procedure for the steering return ability and centering device Referring to FIG 3, spiral spring 9 is first assembled in free condition such that outer ends of spiral spring 9 are seated in the rectangular slots 18 and 20. This yields an assembly of spiral spring 9, unitary casing 11 and unitary arbor 13. Now the unitary casing 11 is held in a fixture/vice and unitary arbor 13 is rotated such that spiral spring 9 is wound to solid state. After this the spiral spring 10 is assembled in free condition such that outer ends of spiral spring 10 are seated in the rectangular slots 17 and 19. When the unitary casing 11 is released from fixture, the spiral spring 9 unwounds half the no. of turns to solid and spiral 10 spring 10 wounds for half the number of turns to solid. At equilibrium state both spiral springs 9 and 10 exert equal torques and achieve steady state. The invention comprises of unitary arbor 13, unitary casing 11 and a set of similar spiral springs 9 and 10, The unitary casing 11 is rigidly fixed onto the steering mounting frame 6 via mounting bracket 8. The unitary arbor 13 is rotatably engaged with steering column 7. Hence the Unitary arbor 13 rotates in response to steering wheel movement. When steering wheel 3 is turned in clockwise direction by vehicle driver as viewed from driver side unitary arbor 13 rotates such that spiral spring 10 wounds and spiral spring 9 unwounds. This creates torque imbalance in the steering returnability and centering device 2. The device 2 exerts reaction torque onto the steering wheel 3. When the driver releases steering wheel 3 the reaction torque exerted by steering returnability and centering device 2 returns the steering wheel 3 to its central/neutral position. . When steering wheel 3 is turned in anti-clockwise direction by vehicle driver as viewed from driver side unitary arbor 13 rotates such that spiral spring 9 wounds and spiral spring 10 unwounds. This creates torque imbalance in the steering returnability and centering device 2. The device 2 exerts reaction torque onto the steering wheel 3. When the driver releases steering wheel 3 the reaction torque exerted by steering returnability and centering device 2 returns the steering wheel 3 to its central/neutral position. Thus the steering returnability and centering device 2 not only provides steering returnability in response to large steering wheel inputs but also ensures steering centering (improved center feel) in response to small/spurious steering inputs. In case either of the spiral springs 9 or 10 has permanent set or load loss after usage over a period of time 12 the torque balance point shifts which can be corrected by resetting toe characteristics of the vehicle by method known in the art. The foregoing description is a specific embodiment of the present invention. It should be appreciated that this embodiment is described for purpose of illustration only, and that numerous alterations and modifications may be practiced by those skilled in the art without departing from the spirit and scope of the invention. It is intended that all such modifications and alterations be included insofar as they come within the scope of the invention as claimed or the equivalents thereof. Dated this 29th day of March 2007

Full Text

FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
PROVISIONAL SPECIFICATION
(See Section 10; rule 13)
TITLE OF THE INVENTION
A Device for Steering Returnability and Centering of a Vehicle
APPLICANTS
TATA MOTORS LIMITED, an Indian company
having its registered office at Bombay House,
24 Homi Mody Street, Hutatma Chowk,
Mumbai 400 001 Maharashtra, India
INVENTORS
Soheb Ahmed, Abhay Deshpande both Indian nationals
of TATA MOTORS LIMITED,
an Indian company having its registered office
at Bombay House, 24 Homi Mody Street, Hutatma Chowk,
Mumbai 400 001 Maharashtra, India
PREAMBLE TO THE DESCRIPTION
The following provisional specification particularly describes the invention and the manner in which it is to be performed.

FIELD OF INVENTION
This invention relates to a device for steering returnability and centering of vehicle and more particularly relates to a mechanical device for steering return ability and centering of vehicle.
BACKGROUND OF INVENTION
Primary function of the steering system in automobiles is to provide driver control on the vehicle. These systems may be conventional mechanical systems or steer by wire systems. In addition to the primary requirement of driver control, these systems have provisions for steering centering and returning.
Steering return ability is desired because after executing a turn, the vehicle should move in a straight path or the steering wheel should come to a neutral position for straight driving. In other words, when the vehicle driver releases the steering wheel after turning the steering wheel to change the direction of the vehicle, the steering wheel should automatically return to the center position.
Steering centering or center feel is also essential, because wide variety of extraneous forces can act on a vehicle steering system and spurious steering inputs caused by these forces must be dealt with satisfactorily in order to provide stable and controllable steering of a vehicle. As vehicle speed increases, the effects of any spurious steering inputs are magnified, making it necessary for
2

the driver to exercise more precise and careful driving control. The ideal driving situation is therefore one where the steering system inherently causes the vehicle to travel in an unswerving straight line unless the driver intentionally turns the vehicle in another direction. The ideal steering system should therefore require relatively little attention from the driver as the vehicle progresses along a straight line path down the roadway. From a steering standpoint, the vehicle should not respond to anything but the driver's steering commands and these must be of sufficient magnitude to overcome a significant resistance to turning away from center. In the absence of a steering input by the driver, the vehicle should literally do nothing but progress straight ahead.
Conventionally, automobile steering systems have steering wheel return ability by slanting the king pins of the steer wheels. Such positive caster is provided by positive caster offset, which is also known as mechanical trail. Caster offset is the distance from the ground intersection point of a pivot line drawn through the pivot axis of a steerable wheel to a contact point at the center of the area over which the wheel contacts the ground. The pivot axis of a steerable wheel of a motor vehicle is usually provided by a "king pin". Because the contact point of a steerable wheel with positive caster trails the pivot line point of the wheel, side forces cause the wheel to turn in the direction that the force is being applied.
But this provision has its disadvantages like effects of strong gusty cross winds are more pronounced with large amounts of positive caster offset. The vehicle tends to caster towards the side of the roadway to which it is being pushed by the wind. Any small amount of stability gained on a non-windy day from
3

slanting the steer wheel king pins may be paid for many times over when driving in a crosswind because of the destabilizing castering effect of the crosswind. Similarly, a high crown at the center of the roadway or a slanted roadway tends to cause vehicles with castered steer wheels to turn toward the edge of the roadway, that is, in the downhill direction. Castered steer wheels also allow steering inputs from rutted and other imperfect roadway surfaces to steer back against the driver and thereby cause road wander. Keeping a vehicle tracking straight and under control currently requires an inordinate amount of driver steering corrections to counteract the adverse side effects of castered steer wheels. The repetitive task of making numerous precise steering corrections mile after mile weighs heavily on a driver's physical and mental well-being, and may result in extreme driving fatigue. In addition, due to increased turning-lift effects, generous positive king pin angles provide significant resistance to small radius turns, which can make city driving quite fatiguing. Moreover, positive caster generates camber gain in a corner which may also cause the tires to heat up, lose grip, and wear out prematurely.
These adverse effects are some of the negative aspects of attempting to achieve steering system stability through generous amounts of caster angle. In short, steer wheel castering is directly responsible for road wander, crowned road steering wheel pull and cross wind steering problems. Hence, there is critical need to provide directional stability by replacing castered wheels with another method of achieving steer wheel return ability. In other words there is need of providing directional stability of steer wheels with no positive caster, i.e., a caster angle of zero degree. The replacement of steerable wheel castering with
4

the power centering technology of the present invention has a number of additional advantages. These include precision on-center directional stability of the steerable wheels that make the vehicle more comfortable to drive a corresponding reduction in accident potential due to the considerable reduction in driving fatigue, improvement in steerable wheel blowout protection and related safety, improvement in the tire wear pattern of the steerable wheels that increases tire life and reduces maintenance costs, a stable non-swaying ride that improves passenger comfort particularly in buses and other large vehicles, and lower insurance costs due to significant improvements in overall vehicle safety.
Instead of relying on positive castering, steering wheel returnability after a turning movement is provided by steering centering/returning assemblies. Some of the relevant ones are discussed as under.
US 5050443 describes a spring operated return assist device which permits a limited degree of free rotation of the steering shaft before activation of the mechanism. The return assist device urges the shaft and the steering wheel to a near central neutral position after rotation of the steering wheel. The invention suffers from the shortcoming that it will have poor center feel due to presence of aperture as a design feature. Apart from that the system is backlash prone. In addition the system has great many parts and the assembly is complicated and costly to manufacture.
U.S. 6694839 describes springs designed to apply a return torque on the rotating ring to return it to the neutral point and means for limiting in two directions the
5

rotation of the rotating ring. The device comprises a plate mounted rotatable relative to the fixed element and two helical springs, a first spring being arranged on one side of the plate and fixed thereon by its internal end, a second spring being arranged on the other side of the plate and fixed by its internal end on the fixed element, the external end of the first spring being linked, in a first direction, to the rotation of the rotating ring and the external end of the second spring being linked, in a second direction opposite to the first, to the rotation of the plate. The invention suffers from the shortcoming that there are no provisions to address the issue of permanent set of springs, resulting in backlash over the period of use resulting in poor center feel.
U.S. 6705419 describes a steering shaft and a center feel mechanism. The center feel mechanism comprises a cam face, an urging member and a second geared portion. The cam face and the urging member are configured to generate a retuning torque to the center feel mechanism. The returning torque has a direction opposite the second angular displacement. Similarly, U.S. 6820703 also describes a mechanical steering feel enhancement device which provides a return-to-center function. The invention suffers from the drawback that the system has great many parts and the assembly is not compact as well as complicated and costly to manufacture. Secondly the cam and roller assembly in conjunction with gears will result in friction related issues.
A study of the prior art related to steering returnability and steering centering devices reveals a long felt need for a system that,
6

1. Comprises of less no. of parts
2. Is coaxial with the steering wheel / steering column and compact
3. Is easy to manufacture and assemble
4. Eliminates friction arising due to mechanical interaction between two or more parts
5. Self compensates any loss in spring characteristics or permanent set
OBJECTS OF INVENTION
The main object of this invention is to provide a device for steering returnability of vehicle which eliminates the requirement of positive caster in the suspension.
Another object of the invention is to provide steering centering (improved center feel) in response to small/spurious steering inputs.
Another object of the invention is to provide steering returnability and steering centering device with least number of parts.
Another object of the invention is to provide steering returnability and steering centering device which is compact, easy to assemble and manufacture.
Yet another object of the invention is to provide steering returnability and steering centering device with least system level friction.
7

Yet another object of the invention is to provide steering returnability and steering centering device which self compensates any loss in spring characteristics or permanent set.
Yet another object of the invention is to provide steering returnability and steering centering device which substantially matches the return torque requirements vis-à-vis steering wheel angle.
SUMMARY OF INVENTION
The device comprises of means to provide steering return ability and steering centering device for use in a vehicle steering system. It consists of arbor and case assembly for two spiral springs. The arbor is rotatably engaged with steering column/wheel. The arrangement is such that when steering wheel is turned in either direction the springs provide return torque so that the wheel comes back to neutral position. The invention thus provides steering return ability in response to large steering wheel inputs and steering centering in response to spurious steering inputs, thus eliminating the need of providing positive caster in the suspension. The invention is compact and has least number of parts. Apart from that the device is easy to assemble and manufacture. Moreover, the design of the system is such that it self compensates any loss in spring characteristics or permanent set.
8

DETAILED DESCRIPTION OF DRAWINGS
Referring now to the drawings wherein the showings are for the purpose of illustrating a preferred embodiment of the invention only, and not for the purpose of limiting the same,
Fig.l shows the mounting of the steering return ability and centering device on
the steering system
Fig.2 shows steering returnability and centering device on the steering wheel
assembly
Fig. 3 shows the exploded view of the steering return ability and centering
device mounting arrangement steering column
Fig. 4 shows the steering return ability and centering device in isometric view
Fig. 5 shows isometric and plan view spiral springs
Fig. 6 shows constructional details of unitary arbor
Fig. 7 shows constructional details of unitary casing
Referring to Fig. 1 and Fig. 2 the steering return ability and centering device 2 is mounted on mounting bracket 8 using bolts 14. The mounting bracket 8 is welded to column tube 4 which is mounted on steering system cross member 6 using mounting bracket 5.
Referring to Fig. 3 and Fig. 4 it can be noticed that invention comprises of unitary arbor 13, unitary casing 11 and a set of similar spiral springs 9 and 10. The unitary casing 11 is mounted on mounting bracket 8 using assembly bolts 14 and mounting legs 12. The mounting bracket 8 is welded to steering column
9

tube 4. The steering column 7 consists of multiple keys 15 on its outer periphery. The spiral spring 9 is assembled in the unitary casing 11 and unitary arbor 13 such that the outer ends of the spiral spring 9 are seated in the rectangular slots 18 and 20. Similarly, the spiral spring 10 is assembled in the unitary casing 11 and unitary arbor 13 such that the outer ends of the spiral spring 10 are seated in the rectangular slots 17 and 19. The unitary arbor 13 is rotatably engaged with steering column 7 by seating steering column keys 15 in key slots 16 of unitary arbor. The unitary casing 11 is bolted to the mounting bracket 8 using bolts 14.
Fig.5 shows isometric and plan view of spiral spring 9 and 10
Referring to Fig.6, unitary arbor 13 has multiple key slots 16 on its inner periphery and two rectangular cut slots 17 and 18 on its outer periphery. Referring to FIG 7, unitary casing 11 comprises of two rectangular cut slots 19 and 20 on its inner periphery, and bolting legs 12 welded on outer periphery.
Assembly procedure for the steering return ability and centering device
Referring to FIG 3, spiral spring 9 is first assembled in free condition such that outer ends of spiral spring 9 are seated in the rectangular slots 18 and 20. This yields an assembly of spiral spring 9, unitary casing 11 and unitary arbor 13. Now the unitary casing 11 is held in a fixture/vice and unitary arbor 13 is rotated such that spiral spring 9 is wound to solid state. After this the spiral spring 10 is assembled in free condition such that outer ends of spiral spring 10 are seated in the rectangular slots 17 and 19. When the unitary casing 11 is released from fixture, the spiral spring 9 unwounds half the no. of turns to solid and spiral
10

spring 10 wounds for half the number of turns to solid. At equilibrium state both spiral springs 9 and 10 exert equal torques and achieve steady state.
The invention comprises of unitary arbor 13, unitary casing 11 and a set of similar spiral springs 9 and 10, The unitary casing 11 is rigidly fixed onto the steering mounting frame 6 via mounting bracket 8. The unitary arbor 13 is rotatably engaged with steering column 7. Hence the Unitary arbor 13 rotates in response to steering wheel movement. When steering wheel 3 is turned in clockwise direction by vehicle driver as viewed from driver side unitary arbor 13 rotates such that spiral spring 10 wounds and spiral spring 9 unwounds. This creates torque imbalance in the steering returnability and centering device 2. The device 2 exerts reaction torque onto the steering wheel 3. When the driver releases steering wheel 3 the reaction torque exerted by steering returnability and centering device 2 returns the steering wheel 3 to its central/neutral position. . When steering wheel 3 is turned in anti-clockwise direction by vehicle driver as viewed from driver side unitary arbor 13 rotates such that spiral spring 9 wounds and spiral spring 10 unwounds. This creates torque imbalance in the steering returnability and centering device 2. The device 2 exerts reaction torque onto the steering wheel 3. When the driver releases steering wheel 3 the reaction torque exerted by steering returnability and centering device 2 returns the steering wheel 3 to its central/neutral position. Thus the steering returnability and centering device 2 not only provides steering returnability in response to large steering wheel inputs but also ensures steering centering (improved center feel) in response to small/spurious steering inputs. In case either of the spiral springs 9 or 10 has permanent set or load loss after usage over a period of time
12

the torque balance point shifts which can be corrected by resetting toe characteristics of the vehicle by method known in the art.
The foregoing description is a specific embodiment of the present invention. It should be appreciated that this embodiment is described for purpose of illustration only, and that numerous alterations and modifications may be practiced by those skilled in the art without departing from the spirit and scope of the invention. It is intended that all such modifications and alterations be included insofar as they come within the scope of the invention as claimed or the equivalents thereof.
Dated this 29th day of March 2007

Documents:

592-mum-2007-abstract(8-1-2008).pdf

592-mum-2007-claims(8-1-2008).pdf

592-MUM-2007-CLAIMS(AMENDED)-(22-11-2013).pdf

592-MUM-2007-CLAIMS(AMENDED)-(26-4-2012).pdf

592-MUM-2007-CLAIMS(AMENDED)-(6-1-2014).pdf

592-MUM-2007-CLAIMS(MARKED COPY)-(26-4-2012).pdf

592-MUM-2007-CLAIMS(MARKED COPY)-(6-1-2014).pdf

592-MUM-2007-CORRESPONDENCE(24-07-2008).pdf

592-mum-2007-correspondence(29-3-2007).pdf

592-mum-2007-correspondence(8-2-2008).pdf

592-mum-2007-correspondence-received.pdf

592-mum-2007-descripiton (provisional).pdf

592-mum-2007-description(complete)-(8-1-2008).pdf

592-mum-2007-drawing(8-1-2008).pdf

592-mum-2007-drawings.pdf

592-mum-2007-form 1(8-1-2008).pdf

592-MUM-2007-FORM 13(22-11-2013).pdf

592-mum-2007-form 18(8-2-2008).pdf

592-mum-2007-form 2(complete)-(8-1-2008).pdf

592-mum-2007-form 2(title page)-(complete)-(8-1-2008).pdf

592-mum-2007-form 2(title page)-(provisional)-(29-3-2007).pdf

592-MUM-2007-FORM 3(24-07-2008).pdf

592-mum-2007-form 3(29-3-2007).pdf

592-MUM-2007-FORM 5(22-11-2013).pdf

592-mum-2007-form 8(8-2-2008).pdf

592-mum-2007-form 9(8-2-2008).pdf

592-MUM-2007-FORM PCT-IB-373(24-10-2011).pdf

592-MUM-2007-FORM PCT-ISA-210(24-10-2011).pdf

592-mum-2007-form-1.pdf

592-mum-2007-form-2.doc

592-mum-2007-form-2.pdf

592-mum-2007-form-26.pdf

592-mum-2007-form-3.pdf

592-MUM-2007-GENERAL POWER OF ATTORNEY(26-4-2012).pdf

592-MUM-2007-MARKED COPY(22-11-2013).pdf

592-mum-2007-petition under rule 137(8-1-2008).pdf

592-MUM-2007-PETITION UNDER RULE-137(22-11-2013).pdf

592-MUM-2007-REPLY TO EXAMINATION REPORT(24-10-2011).pdf

592-MUM-2007-REPLY TO EXAMINATION REPORT(26-4-2012).pdf

592-MUM-2007-REPLY TO HEARING(22-11-2013).pdf

592-MUM-2007-REPLY TO HEARING(6-1-2014).pdf

592-MUM-2007-SPECIFICATION(AMENDED)-(22-11-2013).pdf

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Patent Number

258459

Indian Patent Application Number

592/MUM/2007

PG Journal Number

03/2014

Publication Date

17-Jan-2014

Grant Date

10-Jan-2014

Date of Filing

29-Mar-2007

Name of Patentee

TATA MOTORS LIMITED

Applicant Address

BOMBAY HOUSE, 24 HOMI MODY STREET, HUTATMA CHOWK, MUMBAI-400 001,

Inventors:

#	Inventor's Name	Inventor's Address
1	SOHEB AHMED	Bombay House, 24 Homi Mody Street, Hutatma Chowk, Mumbai-400 001,
2	ABHAY DESHPANDE	Bombay House, 24 Homi Mody Street, Hutatma Chowk,Mumbai-400 001

PCT International Classification Number

B62D5/08

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA