FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See Section 10; rule 13)
TITLE OF THE INVENTION
Vehicle Steering Assembly For Directional Stability And Returnability Of Steering Wheel


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
Charu Saxena and Amol Majgaonkar
Both are 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 specification particularly describes the invention and the manner
in which it is to be performed.

FIELD OF INVENTION
The present invention relates to power steering and mechanical steering system of a vehicle. The present invention more particularly relates to a vehicle steering assembly for directional stability and returnability of steering wheel.
BACKGROUND OF INVENTION
Generally, vehicles such as passenger cars, utilizes rack and pinion gear and collapsible steering column. Some vehicles may have different gear but all vehicles, including LCV, MCV, and HCV, have steering column in the steering system. The steering system provides directional stability and driver control on the vehicle, which may be mechanical systems. In addition to primary requirement of directional stability, the steering sysm should have good returnability within short duration. Such steering returnability is desired because after executing a turn, the vehicle should move in straight path or the steering wheel should come to neutral position for straight driving. In other words, when driver releases the steering wheel after taking a turn, the steering wheel should automatically return to the centre position.
Furthermore, the self centering of steering is essential because of wide variety of external forces acts on a vehicle steering system. Steering geometry balances it up to certain extent, where it should be dealt with satisfactorily in order to provide stable and controllable steering of the vehicle. As the vehicle speed increases, the effects of any spurious steering inputs are magnified, which makes it necessary for the driver to exercise precise and careful driving control. In ideal driving situation, the steering system should inherently cause the vehicle to travel in straight line unless the driver intentionally turns the vehicle. The ideal steering system should require little attention from the driver as the vehicle progresses along a straight line path down the roadway.
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Conventionally automobile steering systems achieves steering wheel returnability by slanting KPI (King Pin Inclination) or the steering axis of wheels, which provides the directional stability as well as balances the centrifugal forces of the vehicle at the time of turning. The positive caster is provided by caster offset. The pivot axis of the steerable wheel of the motor vehicle is usually provided by a "King Pin'. Since the contact point of the steerable wheel with positive caster trails the pivot line point of the wheel, side forces can cause the wheel to turn in the direction that the force is being applied.
Moreover, the patent application WO 2008/120231A2 describes the spring operated return device, which is provided with a spiral spring connected internally to the steering column shaft. The returnability and directional stability are the two important parameters in the vehicles, which can be affected due to various reasons like vehicle performance and manufacturing defects, geometry disturbance and others.
With reference to the conventional steering systems, it has been designed that the system should eliminate clogging of spring particles or pieces, which can cause due to the failure of spring and friction arising due to interaction between the two coils of springs with easy manufacturing and assembling process. The system should also provide better elasticity to help in better returnabilty and directional stability of the steering wheel.
In order to overcome the deficiency of the prior art, the elasticity of spring should satisfy the requirement of number of turns of steering wheel, i.e. it should come on its original position after leaving the steering wheel. Hence, it is necessary to provide a vehicle steering assembly, which can address the issue of failure of spring, stiffness of spring and friction related issues. Also, it should have good elasticity and provide safety in case of spring break and no trapping of spring in arbour that leads to jamming of the steering system which can cause accidents.
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OBJECTS OF INVENTION
An object of the present invention is to provide a vehicle steering assembly, which improves directional stability and retumability of the steering wheel with less number of parts and steering inputs.
Another object of the present invention is to provide a vehicle steering assembly for directional stability and retumability of a steering wheel, which self compensates any loss in spring characteristics.
Yet another object of the present invention is to provide a vehicle steering assembly for directional stability and retumability of a steering wheel, which is compact, cost effective and easy to assemble and manufacture.
SUMMARY OF INVENTION
According to one aspect, the present invention, which achieves the objectives, relates to of a vehicle steering assembly for directional stability and retumability of a steering wheel comprising a steering column mounted on a steering column mounting bracket that is welded on a cross member. The steering wheel is mounted on the steering column, and a torsion spring is assembled on a stationary tube of the steering column. The torsion spring is fixed in a rotary shaft of the steering column to produce return torque when the steering wheel is turned so that the steering wheel is returned to its actual centre position after releasing the steering wheel. Such torsion spring provides better elasticity to eliminate spring failure, spring stiffness issues and spring friction related issues, which improves directional stability and retumability of the steering wheel. The basic property of torsion spring is elasticity, due to slip angles, wheel misalignment or the disturbance in toe, causes to pull the steering wheel in one side, either left or right and it may cause accidents, so torsion spring will provide dual torque to avoid pulling of steering wheel.
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At straight ahead condition, there is no role of torsion in the torsion spring, but when the vehicle is turned at left or right, the torsion spring can be twisted respectively and work according to the spring stiffness. Thereafter, when the steering wheel is released, the steering wheel can come back to its original position due to elasticity of the torsion spring and also creates vibration in system so, damper is required for the same, but in given invention due to direct connection of spring with road wheels the spring itself damped the vibrations and acts as a damper in this invention. In this way definitely, the vehicle steering assembly can achieve straight ahead recovery of steering along with maintaining the mean position of the steering wheel.
STATEMENT OF INVENTION
This invention relates to A vehicle steering assembly for directional stability and returnability of a steering wheel, comprising; a steering column mounted on a steering column mounting bracket welded on a cross member, said steering column on which a steering wheel is mounted; and a torsion spring assembled on a stationary tube of said steering column, wherein said torsion spring is fixed in a rotary shaft of said steering column to produce return torque when said steering wheel is turned so that said steering wheel is returned to its actual centre position after releasing said steering wheel.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 shows a schematic view of a vehicle steering assembly mounted on a steering system, in accordance with an exemplary embodiment of the present invention;
FIG. 2 shows construction of locking points for a torsion spring on a steering column, in accordance with an exemplary embodiment of the present invention;
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FIG. 3 shows an exploded view of the vehicle steering assembly, in accordance with an exemplary embodiment of the present invention; and
FIG. 4 shows an isometric and side view of the torsion spring of the vehicle steering assembly, in accordance with an exemplary embodiment of the present invention.
DETAILED DESCRIPTION OF INVENTION
The invention will be discussed in greater detail with reference to the accompanying Figures.
Referring to FIG. 1, a schematic view of a vehicle steering assembly mounted on a steering system is illustrated, in accordance with an exemplary embodiment of the present invention. The vehicle steering assembly comprises a steering column (3) that is mounted on a steering column mounting bracket (2) welded on a cross member (4) of a vehicle. A steering wheel (1) is mounted on a rotary shaft (8) of the steering column (3). A torsion spring (5) is assembled and mounted on the steering column (3) by suitable assembly tool, where one end of the torsion spring (5) is fixed to a stationary tube (7) of the steering column (3) and other end of the torsion spring (5) is engaged on the arbor and/or rotary shaft (8) of the steering column (3).
During turning of the steering wheel (1) in either direction, the torsion spring (5) provides return torque so that the wheel (1) comes back to neutral position. Therefore, while releasing the steering wheel (1), the steering wheel (1) can come back to its original position due to elasticity of the torsion spring (5), and also cause some vibrations that can be overcome by the tyre forces. In this way definitely, the vehicle steering assembly can achieve straight ahead recovery of steering and also maintain the mean position of the steering wheel. Thus, it provides steering returnability in response to large steering wheel inputs and directional stability in response to spurious steering inputs.
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Such vehicle steering assembly is compact, since it has only single additional part with respect to existing steering assembly. Moreover, the design of the vehicle steering assembly can compensate any loss in spring characteristics. Accordingly, the advantages of the vehicle steering assembly includes improved directional stability and returnability of vehicles, thereby reducing accidents and set back effect in heavy vehicles, and keeping steering feel good in a cost effective manner.
FIG. 2 shows construction of locking points for the torsion spring (5) on the steering column (3), in accordance with an exemplary embodiment of the present invention. The torsion spring (5) is initially assembled in free condition, i.e. free from torsion, such that one end of the torsion spring (5) is fixed in a rectangular slot of the column tube (7) and other end is engaged on the arbor (8) of the steering column (3). The torsion spring (5) can be slightly preloaded While assembling the torsion spring (5). After the torsion spring (5) is assembled on the steering column (3), the torsion spring (5) can be externallly shown, which prevents coming out of the torsion spring (5) from the steering assembly. The steering column tube (7) acts as a guide shaft for the torsion spring (5).
Referring to FIG. 3, an exploded view of the vehicle steering assembly is illustrated, in accordance with an exemplary embodiment of the present invention. The torsion spring (5) is assembled on the steering column tube (7) and the rotary shaft (8) while mounting the steering column (3) on the mounting bracket (2). A steering lock (6) should be assembled before mounting the torsion spring (5) on the steering column tube (7). Finally, the steering wheel (1) is assembled on the rotary shaft (8) of the steering column (3). The rotary shaft (8), the torsion spring (5) and the steering column (3) are rigidly fixed on the steering column mounting bracket (2). Hence, the rotary shaft (8) is connected to the steering wheel (1).
Referring to FIG. 4, an isometric and side view of the torsion spring (5) of the vehicle steering assembly is illustrated, in accordance with an exemplary embodiment of the present invention. The torsion spring (5) can be designed as low
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torsional stiffness with high deflection, where the elasticity of the torsion spring (5) should satisfy the requirement of number of turns of the steering wheel (1), i.e. it should come to its original position after releasing the steering wheel (1). When the steering wheel (1) is turned in clockwise or anticlockwise direction from mean position, the torsion spring (5) can be twisted respectively and work according to the spring stiffness.
Since the torsion spring (5) is fixed in the rotary shaft (8) of the steering column (3), the torsion spring (5) produces return torque when the steering wheel (1) is turned so that the steering wheel (1) is returned to its actual centre position after releasing the steering wheel (1). Thus, the torsion spring (5) provides better elasticity to eliminate spring failure, spring stiffness issues and spring friction related issues, which facilitates good directional stability and returnability of the steering wheel (1) of the vehicle. As a result, accident cases can be avoided due to pulling of steering at one side.
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WE CLAIM
1. A vehicle steering assembly for directional stability and returnability of a
steering wheel, comprising:
a steering column mounted on a steering column mounting bracket welded on;
a cross member, said steering column on which a steering wheel is mounted; and
a torsion spring assembled on a stationary tube of said steering column, wherein said torsion spring is fixed in a rotary shaft of said steering column to produce return torque when said steering wheel is turned so that said steering wheel is returned to its actual centre position after releasing said steering wheel.
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2. The assembly as claimed in claim 1, wherein said stationary tube of said steering column acts as a guide shaft for said torsion spring.
3. The assembly as claimed in claim 1, wherein said torsion spring is assembled externally on said steering column.
4. The assembly as claimed in claim 1, wherein said torsion spring is twisted when said steering wheel is turned in clockwise or anticlockwise direction.
5. The assembly as claimed in claim 1, wherein said torsion spring is assembled on a stationary tube of said steering column.