FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See Section 10; rule 13)
TITLE OF THE INVENTION Steering wobble reduction mechanism
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
Mr. Praful Bonde
An Indian national
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 manner in which it is performed.

FIELD OF INVENTION
The present invention relates to a steering wobble reduction mechanism, and more particularly, to a device for suppressing vibrations in the steering system of a vehicle that may otherwise be transmitted to the steering wheel.
BACKGROUND OF INVENTION
The steering wheel of an automotive vehicle is a member for allowing an operator of the vehicle to steer the vehicle. The operator of the vehicle always handles directly the steering wheel during driving the vehicle, and typically develops sensitivity to even minute vibrations excited in the steering wheel. Such vibration may be caused by brake roughness, tyre/wheel imbalance, road input etc. and are often transmitted to the steering wheel from the wheels of the automotive vehicle.
Rack and pinion steering for vehicles have been recognized for steering precision and reduction in objectionable forces. That is why rack and pinion steering is particularly desirable in high performance vehicles. In a typical rack & pinion steering unit according to prior art, an elongated flat rack is engaged with a pinion gear. The steering shaft is connected to the pinion gear so that steering movement is converted in to rotation of pinion gear and a reciprocal translation of the rack. The rack and pinion steering system is giving such a better performance. But still steering wobble in rack and pinion steering is one of the major issues faced by the customers which is a big discomfort and worry for automobile engineers.
Steering wobble is caused mainly due to lateral force variation at wheel assembly which is getting transmitted to rack through the tie rod. This lateral force is either generated at ground, which generates torque above vertical axis or the wheel assembly imbalance. Part of this torque is absorbed by the suspension bushes and remaining is transmitted to the steering rack. Further this cyclic torque feedback is transmitted to steering wheel which driver perceives as steering wobble.

Majority of times steering wobble issues are related to speed-sensitive vibrations due to an out-of-balance wheel. For remaining cases major root causes responsible are bent rim, an out-of-round rim or tire, an off-center wheel or hub, or a bent or imbalanced driveshaft. Sometimes the problem is worn shocks or a loose part in the suspension or steering linkage. Most tire/wheel imbalance problems will make themselves evident at speeds above 80kmph. A back-and-forth shimmy in the steering wheel means one or both front wheels are dynamically imbalanced. Even during vehicle running, improper steering geometry, braking application and maneuvers results in tyre uneven wear which further results in to lateral force variation. The present invention describes a mechanism by which the steering wobble is minimized or abolished.
OBJECTS OF INVENTION
The main object of the invention is to obviate above mentioned drawbacks by providing steering wobble reduction mechanism in a vehicle.
Another object of the invention is to provide a defined torque threshold, beyond which the torque transmission is permitted.
Yet another object of the invention is to provide a mechanism which provides positive torque transmission from wheel of the vehicle to the steering wheel.
SUMMARY OF INVENTION
The present invention relates to a wobble reducing device for a vehicle steering system provided on either side of vehicle rack, each of said device comprises a reservoir for storing a dampening fluid, a cylindrical casing disposed between the vehicle rack and inner ball joint of vehicle tie rod, a fluid vibration dampener hydraulically connected to the reservoir for suppressing vibration of said vehicle steering system, said fluid vibration dampener is disposed within said enclosure and is operatively connected to said vehicle rack and said inner ball joint, a first

linkage having its first end operatively connected to said vehicle rack and its second end operatively connected to said dampener, a second linkage having its first end operatively connected to said inner ball joint and its second end operatively connected to said dampener, and a spring loaded valve disposed between said reservoir and said dampener for maintaining constant hydraulic pressure of said dampener.
According to a preferred embodiment, said enclosure is a cylindrical casing having curved surface and two faces. The cylindrical casing is adapted to retain the spring loaded valve.
Preferably, said fluid vibration dampener is formed by the second end of said first linkage, the second end of said second linkage and the curved surface of said cylindrical casing.
According to another preferred embodiment, said spring loaded valve comprises a fixing member attached to the outer side of said curved surface, valve closing member resiliency suspended from said fixing member and extending into said dampener through the walls of said dampener, and resilient means disposed between the fixing member and the valve closing member.
Preferably, said second end of the second linkage is threaded and is fixed to the inner walls of said dampener.
Most preferably, said second end of the first linkage is configured in the form of a piston.
Preferably, said first linkage (403) is provided with leak proof seal to prevent fluid leakage during operation.
According to another preferred embodiment, said first linkage is a rigid rod connecting to the vehicle rack with said dampener.

According to yet another preferred embodiment, said second linkage is a rigid rod connecting to the inner ball joint of the vehicle tie rod with said dampener.
BRIEF DESCRIPTION OF DRAWINGS
Referring to the accompanying drawing, 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.
Figure 1 shows Hysteresis graph of steering inverse friction
Figure 2 shows the conventional rack and pinion assembly with part details.
Figure 3 shows the schematic lay out of the rack and pinion and proposed
mechanism location.
Figure 4 is a perspective view of steering wobble reduction mechanism.
Description of reference numbers for the major component of the present invention in the drawings:
301-Outer ball joint 302- Inner ball joint 303-Rack 304-Pinion
305- Steering wobble reduction mechanism
306- Tie rod
100- Device for vibration damping
401- Fluid storage means/Reservoir
402- Damping means/ Spring loaded valve
403- Rod connecting to rack (303) 404-Rod connecting to inner ball joint (302)

405- Cylinder
406- Spring
407- Closing member

408- Piston
409- Threaded portion 410-Fluid vibration dampner
DETAILED DESCRIPTION
For any steering system there is minimum torque at ground / lateral force at tie rod which will be delivered to steering wheel. If the torque / force is less than this threshold value then the input from ground or wheel should not be sensed by the steering wheel. This is measured as inverse friction with steer wheel angle and steer torque measurement. The graph of a measurement is shown in fig. 1.
Hysteresis derived from above graph is the threshold value for the steered wheel torque. During moving of the vehicle, if the torque at ground or due to imbalance wheel exceed the threshold value this torque gets transmitted to the steering wheels and steering wheels starts to oscillate. To overcome this wobble issue the system is proposed to absorb the input torque generated at steer wheel at Tie rod or connecting member between master gear and Inner ball joint. Proposed system will absorb the input torque to a limit defined by the user, for any torque input till the desired torque will not be transmitted to master gear.
The present invention discloses a mechanism which enables to reduce the steering wobble phenomenon. The disclosed invention increases the threshold of lateral force or torque values beyond which the input from wheel assembly or ground gets transmitted to the steering wheel. In the present invention, a device (400) is disposed between the vehicle rack and inner ball joint of vehicle tie rod, The device (400) act as a torque limiter disables torque transmission from the ground to be carried over to steering wheel for certain set torque value. Vehicle run on uneven surface and wheel assembly imbalance generates variation in lateral force. This generated force further transmitted to the steering wheel through rack pinion and steering column structure. The apparatus proposed with this invention works as threshold and filters these inputs and limits the torque transmission to a set value.

The invention describes the mechanism by which the steering wobble phenomenon can be reduced and brought to the acceptable for any vehicle without concerning the tyre imbalance and suspension detonation effects. The invention is about adding a torque filter which constrains the torque feedback from grounds and restrict the torque to be transmitted to the steering wheel. Torque input generated from the contact patch [ground] or wheel rotation transmits the lateral load to the rack and pinion. This input from ground partially absorbed by suspension and remaining is transmitted to rack and pinion as lateral load. Lateral load at rack and pinion does not completely carried over to steering wheel, if the load exceed the inverse friction for the rack and pinion then only the input to the rack and pinion is given to the steering wheel. Steering wheel wobble and kickback is the result of this lateral load transmission to the steering wheel.
As explained the invention proposed is made for the objective of preventing or
reducing the steering wobble phenomenon. There are several causes which
generates the steering wobble. During vehicle running mass imbalance at tire
amplifies and result lateral force variation. The calculation of how tyre imbalance
causes the lateral force generation are mention below.
m =Tyre imbalance
r = Tyre radius
w = Rotational velocity
Lateral force = mrw2
This force transmitted to the outer ball joint and subsequent to steering wheel. If this force generated exceeds the threshold value, derived from the steering inverse friction then only steering wheel have input and start wobbling. To reduce the wobble if this threshold value is increased, force generated at wheels will not be able to steering wobble. This increased threshold value will result in higher force to

generated steering wobble. To achieve the higher threshold value and steering wobble reduction mechanism is proposed at short gear region.
Referring now to the drawings wherein the showings the steering wobble reduction mechanism location and detailed arrangement.
Fig. 2 shows the steering rack and pinion conventional assembly and part comprising the assembly.
Various parts of the present invention are shown with their arrangement in the accompanying figure-3 and figure-4.
Fig. 3 is a schematic diagram sowing the present mechanism position. A steering wobble reduction mechanism (305) is disposed between a vehicle rack (303) and inner ball joint (302)of tie rod (306) of the vehicle. The steering wobble reduction mechanism (305) is provided on either side of the vehicle rack (303). The rack is connected to the wheels of the vehicle via tie rod (306) and a pinion (304) which engages continuously in the rack. The pinion is connected to the manual steering wheel via steering shaft.
Referring to Fig. 4, the mechanism location shown in fig 2 is described with the sketch. The mechanism is placed in between the rack and inner ball joint. The mechanism consist of a cylinderical member (405) connected to the rod (403) connecting thevehicle rack and inner Ball Joint (IBJ) rod (404). A reservoir (401) is placed above the cylinder (405). The reservoir (401) is filled with fluid to required level and vent or breather is provided on the top of the reservoir for breathing purpose. A rod (404) connecting to IBJ is threaded and has fixed joining. Whereas on other side of cylinder the rod (403) connecting to the rack have piston (408). Leak proof joining is given for this rod which will insure oil leakage or seepage will not occur during operation. A spring loaded valve (402) is attached at the top of the cylindrical casing (405).. When wheel will give any force to outer

ball joint this force will be transmitted to the inner ball joint from there to the proposed mechanism. There is relative movement of rod (403) connecting to rack and rod (404) connecting to IBJ, this will result in increase in pressure of the cylindrical casing (405).
The increase in pressure of the cylindrical casing will life the spring and raise the base of the valve. At designed value of pressure the valve will be closed and the motion starts getting transferred from IBJ to rack through the rods (404) and (403). This torque is transmitted to the steering wheel. The force required for motion transfer from rods (403) and (404) in addition to the steering system inverse friction is the threshold value for the steering system. For adjusting the threshold force following adjustment is available.
1) Spring (406)of valve (402)
2) Inner diameter of cylindrical casing (405)
3) Valve (402) base dimension
To achieve desired threshold value with vehicle packing constraints above mentioned parameters tuning options are available.
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.

WE CLAIM
1. A wobble reducing device for a vehicle steering system provided on either side of vehicle rack (303), each of said device comprising:
a reservoir (401) for storing a dampening fluid;
an enclosure (405) disposed between said vehicle rack (303) and inner ball joint (302) of vehicle tie rod (306);
a fluid vibration dampener (410) hydraulically connected to said reservoir (401) for suppressing vibration of said vehicle steering system ; said dampener (410) is disposed within said enclosure (405) and is operatively connected to said vehicle rack (303) and said inner ball joint (302);
a first linkage (403) having its first end operatively connected to said vehicle rack and its second end operatively connected to said dampener (410);
a second linkage (404) having its first end operatively connected to said inner ball joint (302) and its second end operatively connected to said dampener (410); and
a spring loaded valve (402) disposed between said reservoir (401) and said dampener (410) for maintaining constant hydraulic pressure of said dampener (410).
2. The device as claimed in claim 1, wherein said enclosure (405) is a cylindrical casing having a curved surface and two end faces.
3. The device as claimed in claim 1, wherein said fluid vibration dampener (410) is formed by the second end of said first linkage (403), the second end of said second linkage (404) and the curved surface of said cylindrical casing (405).
4. The device as claimed in claims 1 to 3, wherein said cylindrical casing is adapted to retain the spring loaded valve (402).

5. The device as claimed in claims 1 to 4, wherein said valve (402) comprises a fixing member (411) attached to the outer side of said curved surface, valve closing member (407) resiliency suspended from said fixing member (411) and extending into said dampener (410) through the walls of said dampener (410), and a resilient means (406) disposed between said fixing member (411) and said valve closing member (407).
6. The device as claimed in claim 1, wherein said second end of the second linkage (404) is threaded and is fixed to the inner walls of said dampener (410).
7. The device as claimed in claim 1, wherein said second end of the first linkage (403) is configured in the form of a piston (408).
8. The device as claimed in claim any of the above claim, wherein said first linkage (403) is provided with leak proof seal to prevent fluid leakage during operation.
9. The device as claimed in any of the above claims, wherein said first linkage (403) is a rigid rod connecting to the vehicle rack (303) with said dampener (410).

10. The device as claimed in any of the above claims, wherein said second linkage (404) is a rigid rod connecting to the inner ball joint (302) of the vehicle tie rod (306) with said dampener (410).