FORM 2
THE PATENT ACT 1970 (as amended)
[39 OF 1970]
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
[See Section 10 and Rule 13]
TITLE: “AN ELECTRIC POWER STEERING SYSTEM OF A VEHICLE AND METHOD THEREOF”
Name and address of the Applicant:
TATA MOTORS LIMITED, an Indian company having its registered office at
Bombay house, 24 Homi Mody Street, Hutatma Chowk, Mumbai 400 001, Maharashtra,
INDIA.
Nationality: INDIAN
The following specification particularly describes the nature of the invention and the manner in which it is to be performed.

TECHINCAL FIELD
Embodiments of the present disclosure relate to a power steering system of a vehicle. More particularly, the embodiments relate to an electric power steering system to provide steering assistance to the driver at a low speed of the vehicle.
BACKGROUND OF DISCLOSURE
The conventional electric power steering system for an automobile comprises of steering wheel, an electric motor along with reduction mechanisms, a controller, various sensors, steering column, and steering rack & pinion. The electric motor is coupled to the steering column through a gear mechanism.
Conventional electric power steering system requires expensive sensors namely torque sensor & steering wheel angle sensor and electronic control unit with high processing capabilities to take care of power assistance at all maneuvering events. The conventional steering assistance system provides assistance at all maneuvering events and till the maximum speed is achieved which increases the complexity and overall cost of the system.
For the vehicles with comparatively less front axle weight it is found that, steering effort required by the driver is considerably high when the vehicle is in parking condition or at very low speeds only. However, the steering effort reduces drastically as the vehicle speed increases. Hence, for such vehicles with lower front axle weight, full fledge and high cost electronic power steering system with assistance at all maneuvering events is not necessary and is also complex in terms of functionality and development.
In light of forgoing discussion, there is a need to provide an electronic power steering system to provide steering assistance at low speed of the vehicle.
STATEMENT OF THE DISCLOSURE
Accordingly, the present disclosure provides an electric power steering system (100) of a vehicle comprising; a vehicle speed sensor (101) mounted in a predetermined location of the steering system (100) for measuring speed of the vehicle; a rotation sensor

(102) attached to a steering column (103) of the steering system (100) for measuring a direction of rotation of the steering column (103); a torque measuring means (110), mounted on a predetermined location of the steering column (103), for measuring the torque applied on the steering column (103); an electric motor (104) with a reduction gearbox (105) mounted on the steering column (103) for rotating the said column (103) in predetermined direction; a control unit (106) interfaced with the sensors (101 and 102) and torque measuring means (110) to compare the measured values of torque and speed respectively with a predetermined values and to provide signal to the electric motor (104) to rotate the steering column (103) in the predetermined direction based on outcome of the comparison, and also provides a method of operating an electric power steering system (100) of a vehicle, said method comprising acts of: measuring a speed of the vehicle using a speed sensor (101); sensing the direction of rotation of steering column
(103) using a direction rotation sensor (102) when the speed of vehicle measured by the speed sensor (101) is less than predetermined value; measuring a torque applied on a steering column (103) using a torque measuring means (110); and comparing the measured values of speed and torque respectively with predetermined values, for providing signal to an electric motor (104) through an electronic control unit (106) to rotate the steering column (103) in a predetermined direction, when the torque measured by the torque measuring means (110) exceeds the predetermined limit, and also provides for an arrangement to measure a torque applied on steering column (103) of an electric power steering system (100) of a vehicle, said arrangement comprising; at least one electric contact (C) mounted on an upper column shaft (107) of the steering system (100); and pair of electric contacts (A and B) mounted on a lower column shaft (108) of the steering system (100), wherein at least one electric contact (A or B) makes contact with electric contact (C) when torque applied on the steering column (103) exceeds a predetermined value of torque.
SUMMARY OF DISCLOSURE
The shortcomings of the prior art are overcome and additional advantages are provided through the provision of a system and a method as claimed in present disclosure.

Additional features and advantages are realized through the techniques of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered a part of the claimed disclosure.
One embodiment of the present disclosure provides an electronic power steering system (100) of a vehicle. The steering system (100) comprises a speed sensor (101) is mounted in the predetermined location of the steering system (100). Said speed sensor (101) measures the speed of the vehicle. A rotation sensor (102) attached to a steering column (103) of the steering system (100) senses a direction of rotation of the steering column (103). A torque measuring means (110) mounted on the predetermined location of the steering column (103) measures a torque applied in the steering column (103). An electric motor (104) with reduction gear (105) mechanism mounted on the steering column (103) configured to rotate the said column (103) in predetermined direction; a control unit (106) interfaced with the sensors (101 and 102) and torque measuring means (110) to compare the measured values of torque and speed respectively with a predetermined torque and speed values and to provide signal to the electric motor (104) to rotate the steering column (103) in the predetermined direction based on outcome of the comparison.
In one embodiment of the present disclosure, the electric motor (104) rotates the steering column (103) in clock wise direction or in anti clock wise direction upon receiving the signal from the rotation sensor (102).
Another embodiment of the present disclosure provides a method of operating an electric power steering system (100) of a vehicle. The said method comprises acts of; measuring a speed of the vehicle using a speed sensor (101). Sensing the direction of rotation of steering column (103) using a direction rotation sensor (102) when the speed of vehicle measured by the speed sensor (101) is less than predetermined value. Now measuring a torque applied on a steering column (103) using a torque measuring means (110). Then comparing the measured values of speed and torque respectively with predetermined values, for providing signal to an electric motor (104) through a control

unit (106) to rotate the steering column (103) in a predetermined direction, when the torque measured by the torque measuring means (110) exceeds the predetermined limit.
Another embodiment of the present disclosure provides an arrangement to measure a torque applied on steering column (103) of an electric power steering system (100) of a vehicle. The arrangement comprises at least one electric contact (C) mounted on an upper column shaft (107) of the steering system (100). And pair of electric contacts (A and B) mounted on a lower column shaft (108) of the steering system (100). At least one of electric contact (A or B) makes contact with electric contact (C) when torque applied on the steering column (103) exceeds a predetermined value of torque.
In one embodiment of the present disclosure, the electric contact (A) makes contact with the electric contact (C) when the steering column (103) rotates in anti clock wise direction, else the electric contact (B) makes contact with the electric contact (C) when the steering column (103) rotates in clock wise direction.
The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.
OBJECTIVES OF THE DISCLOSURE
One object of the present disclosure is to provide an electric power steering system which provides a steering assistance to the driver at low vehicle speeds and to stop the assistance once the vehicle speed exceeds predetermined limit.
One object of the present disclosure is to provide an arrangement to measure a torque applied on steering column of the electronic power steering system.
One object of the present disclosure is to provide a control unit which provides signals to the electric motor, by comparing values of torque and speed measured by the sensor and torque measuring means respectively with the predetermined values, for rotating the steering column in predetermined direction.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
The novel features and characteristic of the disclosure are set forth in the appended claims. The disclosure itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying figures. One or more embodiments are now described, by way of example only, with reference to the accompanying figures wherein like reference numerals represent like elements and in which:
FIG. 1 illustrates an electric power steering system of the present disclosure.
FIG. 2 illustrates an upper column shaft, lower column shaft, torsion bar and torque measurement means of an electric power steering system of the present disclosure.
FIG. 3a and 3b illustrates torque measuring means of the present disclosure.
FIG. 4 illustrates a flow chart to operate an electronic power steering system of the present disclosure.
FIG. 5 illustrates a control unit of the present disclosure.
The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.
DETAILED DESCRIPTION
In the following detailed description, reference is made to the accompanying figures, which form a part hereof. In the figures, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, figures, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without

departing from the spirit or scope of the subject matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, and designed in a wide variety of different configurations, all of which are explicitly contemplated and make part of this disclosure.
This disclosure is drawn, inter-alia to a power steering system of a vehicle. More particularly, the embodiments relate to an electric power steering system to provide steering assistance to the driver at low speed of the vehicle.
FIG. 1 is an exemplary embodiment which illustrates an electric power steering system (100). The steering system (100) comprises a speed sensor (101) for measuring the speed of the vehicle. The speed sensor (101) is mounted in predetermined location of the steering system (100) and is interfaced with a control unit (106) to provide a speed input to the control unit (106). A rotation sensor (102) inbuilt in a steering column (103) of the steering system (100) for sensing the direction of rotation of the steering column (103). The rotation sensor (102) is interfaced with the control unit (106) to provide a signal of direction of rotation of the steering column (103) to the control unit (106). A steering wheel (112) is mechanically connected to the steering column (103) at its one end and the rack and pinion arrangement (111) is connected at the other end of the steering column (103). An electric motor (104) with reduction gear (105) mechanism is coupled to the steering column (103). The said electric motor (104) receives signal from the control unit (106) to rotate the steering column (103) in predetermined direction.
The steering wheel (112) is connected to the steering column (103) through universal joint and is used to apply the torque on the steering column (103) for turning the vehicle in either of the directions and the rack and pinion mechanism (112) is used to convert a rotary motion of steering column (103) to reciprocating motion. This achieves in turning of the vehicle in desired direction. The electric motor (104) with reduction gear mechanism (105) is provided in the steering system (100) to provide assistance to the driver for turning the vehicle in desired direction. The steering assistance is provided by the electric motor (104) as disclosed in the present disclosure if the vehicle speed is less

than the predetermined value. The electric motor (104) rotates the steering column (103) in clock wise or anti clock wise direction depending on the signal provided by rotation sensor (102) through the control unit (106).
In one embodiment of the present disclosure, the predetermined value of vehicle speed is stored in the control unit (106). The predetermined value of speed varies from vehicle to vehicle and preferably the value is 15 Km/hr.
In one embodiment of the present disclosure, the rotation sensor (102) senses the direction of rotation of steering column (103) and provide signal to the electric motor (104) through the control unit (106) to rotate the steering column either right or left direction.
FIG. 2 is an exemplary embodiment which illustrates arrangement of an upper column shaft (107), lower column shaft (108), torsion bar (109) and a torque measuring means (110) of the electric power steering system (100). The upper column shaft (107) is mechanically connected to one end of the steering column (103) through a suitable means. And the lower column shaft (108) connected to the other end of the steering column (103) mechanically by a suitable means. The shafts (107 and 108) are connected to the steering column (103) such that the torque is applied on steering column (103) transmits through the shafts (107 and 108). The torsion bar (109) is connected positively between the shafts (107 and 108). And said torsion bar (109) is free to deflect between the upper column shaft (107) and the lower column shaft (108) depending on the torque difference between them.
The torsion bar (109) is connected to the upper column shaft (107) and lower column shaft (108) by a means selected from a group comprising but not limited to pins, screws, or any other fasteners which serve the purpose. The diameter of the torsion bar (109) varies from vehicle to vehicle and preferably the diameter of bar (109) is above 3mm.
The torsion bar (109) used in the present disclosure is selected from a group comprising but not limited to flexible spring, flexible rod and flexible bar.

The torque measuring means (110) is illustrated in the FIG.2. Said means comprises, an electric contact (C) mounted on the upper column shaft (107) in predetermined location. And a pair of electric contacts (A and B) mounted on lower column shaft (108) in predetermined location. At least one of said contacts (A or B) makes contact with the electric contact (C) when torque applied on the steering column (103) exceeds the predetermined value of torque. The torque measuring means (110) is interfaced with the control unit (106) to rotate the electric motor (104) in predetermined direction if the torque applied on the steering column (103) exceeds the predetermined value.
In one embodiment of the present disclosure, an insulating material is applied at the bottom of the electrical contacts (A, B and C) while mounting on upper and lower column shafts (107 and 108) to prevent short circuit.
In one embodiment of the present disclosure, predetermined value of torque varies from vehicle to vehicle and it is set based on the diameter of the torsion bar (109). The torque value in the present disclosure varies between 6-8 N/m.
In one embodiment of the present disclosure, the dead band value of the steering system (100) can be set by the required deflection of measurement. Said value can be adjusted by varying the space between the main electric contact (C) and other two electric contacts (A and B)
FIGS. 3a and 3b are exemplary embodiments which illustrates an arrangement to measure the torque in an electric power steering system (100). The arrangement comprises an electric contact (C) mounted on the upper column shaft (107) in predetermined location. And a pair of electric contacts (A and B) mounted on lower column shaft (108) in predetermined location. At least one of said contacts (A or B) makes contact with the electric contact (C) when torque applied on the steering column (103) exceeds the predetermined value of torque.

FIG. 3a illustrates torque measuring arrangement in which the electric contact (B) is making contact with the electric contact (C). When the steering wheel (112) is rotated in clockwise direction the steering column (103) starts rotating in same direction. If the torque applied on the steering column (103) exceeds the predetermined torque value then the electric contact (B) mounted on lower column shaft (107) makes contact with the electric contact (C) mounted on upper column shaft (108). This triggers the control unit (106) to provide signal to the electric motor (104) to rotate steering column (103) in clockwise direction.
In one embodiment of the present disclosure, if the steering wheel rotated in anticlockwise direction the steering column (103) starts rotating in same direction. If the torque applied on the steering column (103) exceeds the predetermined torque value then the electric contact (A) mounted on lower column shaft (107) makes contact with the electric contact (C) mounted on upper column shaft (108). This triggers the control unit (106) to provide signal to the electric motor (104) to rotate steering column in anticlockwise direction.
FIG. 3b illustrates torque measuring arrangement in which the electric contacts (A or B) are not in contact with the electric contact (C). The torque applied on the steering wheel (112) is transferred to the steering column (103). If the applied torque is sufficient to turn the vehicle in desired direction, then the electric contacts (A or B) will not make contact with electric contact (C). Hence, no signal is provided to the electric motor (104) by the control unit (106).
FIG.4 is an exemplary embodiment which illustrates a flow chart to operate an electronic power steering system (100). When vehicle ignition key is inserted, the control unit (106) is powered ON. Also, the vehicle signal like vehicle speed is fed to the control unit (106) through the vehicle speed sensor (101). When a driver intends to turn the vehicle, he/she starts rotating the steering wheel (112) in desired direction [step 301]. Since the steering wheel (112) and a steering column (103) are mechanically connected with each other the torque on the steering wheel (112) transfers to the steering column (103) [step 302]. Then the same torque is transferred to the torsion bar (109) which has a

positive connection with upper column shaft (107) & lower column shaft (108) [step 303]. However, torsion bar (109) is free to deflect in between upper column shaft (107) and lower column shaft (108) depending on the torque difference between them. Then, torque is measured using a torque measuring means (110). Once torque is measured, decision is taken whether to provide steering assistance to driver or not based on result of measured torque [step 312]. Now, the direction of ration of the steering column (103) is sensed using rotation sensor (102) [step 305]. If the steering column (103) rotates in left direction, the electric contact (A) of the torque measuring means makes contact with electric contact (C) [step 306]. Then the electric contact (C) activates the control unit (106) to provide signal to the electric motor (104) to rotate the steering column in anticlockwise direction to provide steering assistance to the driver to the driver while taking the left turn [step 307]. If the steering column (103) rotates in right direction, the electric contact (B) of the torque measuring means makes contact with electric contact (C) [step 309]. Then the electric contact (C) activates the control unit (106) which inturn provide signal to the electric motor (104) to rotate the steering column in clockwise direction to provide steering assistance to the driver while taking the right turn [step 310 and step 311].
FIG. 5 is an exemplary embodiment which illustrates a control unit (106). The control unit (106) interfaced with the sensors (101 and 102) and torque measuring means (110) to compare the measured values of torque and speed respectively with a predetermined values and to provide signal to the electric motor (104) to rotate the steering column (103) in the predetermined direction based on outcome of the comparison.
Advantages:
The present disclosure provides an electric power steering system which is simple in construction and easy to assemble.
The present disclosure provides an electric power steering system which is low cost.

The present disclosure provides an electric power steering system which uses available signals from the vehicle.
The present disclosure provides an electric power steering system which provides steering assistance to the driver only in low speed of the vehicle and stooping the assistance when vehicle speed exceeds predetermined limit.
Equivalents
With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.
It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as "open" terms (e.g., the term "including" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "includes" should be interpreted as "includes but is not limited to," etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an" (e.g., "a" and/or "an" should typically be interpreted to mean "at least one" or "one or more"); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the

recited number (e.g., the bare recitation of "two recitations," without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to "at least one of A, B, and C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, and C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to "at least one of A, B, or C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, or C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase "A or B" will be understood to include the possibilities of "A" or "B" or "A and B."
While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.
Referral Numerals:

Reference number Description
100 Electronic power steering system
101 Speed sensor
102 Rotation sensor
103 Steering column
104 Electric motor

105
Reduction gear
106 Control unit
107 Upper column shaft
108 Lower column shaft
109 Torsion bar
110 Torque measuring means
111 Rack and pinion arrangement
A and B Electric contacts
mounted on lower
column shaft
C Electric contact
mounted on upper
column shaft

We claim:
1. An electric power steering system (100) of a vehicle comprising:
a vehicle speed sensor (101) mounted in a predetermined location of the steering system (100) for measuring speed of the vehicle;
a rotation sensor (102) attached to a steering column (103) of the steering system (100) for measuring a direction of rotation of the steering column (103);
a torque measuring means (110), mounted on a predetermined location of the steering column (103), for measuring the torque applied on the steering column (103);
an electric motor (104) with a reduction gearbox (105) mounted on the steering column (103) for rotating the said column (103) in predetermined direction;
a control unit (106) interfaced with the sensors (101 and 102) and torque measuring means (110) to compare the measured values of torque and speed respectively with a predetermined values and to provide signal to the electric motor (104) to rotate the steering column (103) in the predetermined direction based on outcome of the comparison.
2. The system (100) as claimed in claim 1, wherein the electric motor (104) rotates the steering column (103) in clock wise direction or in anti clock wise direction upon receiving the signal from the rotation sensor (102).
3. The system as claimed in claim 1, wherein the predetermined value of speed is stored in the control unit (106) and predetermined value of torque is set in the torque measuring means (110).
4. The system as claimed in claim 1, wherein the torque measuring means (110) is selected from at least one of torque sensor and an electric contact mounted on upper shaft and lower shaft for measuring the torque.

5. A method of operating an electric power steering system (100) of a vehicle, said
method comprising acts of:
measuring a speed of the vehicle using a speed sensor (101);
sensing the direction of rotation of steering column (103) using a direction rotation sensor (102) when the speed of vehicle measured by the speed sensor (101) is less than predetermined value;
measuring a torque applied on a steering column (103) using a torque measuring means (110); and
comparing the measured values of speed and torque respectively with predetermined values, for providing signal to an electric motor (104) through an control unit (106) to rotate the steering column (103) in a predetermined direction, when the torque measured by the torque measuring means (110) exceeds the predetermined limit.
6. The method as claimed in claim 5, wherein the control unit (104) activates the electric motor (104) to rotate the steering column (103) in predetermined direction if the speed measured by the speed sensor (101) is less than the predetermined limit.
7. The method as claimed in claim 5, wherein rotating the steering column (103) in clock wise or anti clock wise direction depending on the signal received by the electronic control unit (106) from the direction rotation sensor (102).
8. An arrangement to measure a torque applied on steering column (103) of an electric power steering system (100) of a vehicle, said arrangement comprising;
at least one electric contact (C) mounted on an upper column shaft (107) of the steering system (100); and
pair of electric contacts (A and B) mounted on a lower column shaft (108) of the steering system (100),
wherein at least one electric contact (A or B) makes contact with electric contact (C) when torque applied on the steering column (103) exceeds a predetermined value of torque.

9. The arrangement as claimed in claim 8, wherein a torsion bar (109) is provided in between the upper column shaft (107) and lower column shaft (108), said torsion bar (109) deflects depending on torque difference between shafts (107 and 108).
10. The arrangement as claimed in claim 8, wherein the predetermined value of torque varies upon change in a diameter of the torsion bar (109).
11. The arrangement as claimed in claim 8, wherein the electric contact (A) makes contact with the electric contact (C) when the steering column (103) rotates in anti clock wise direction, else the electric contact (B) makes contact with the electric contact (C) when the steering column (103) rotates in clock wise direction.
12. An electric power steering system (100) comprising a torque measuring arrangement as claimed in claim 8.
13. A vehicle comprising an electric power steering system (100) as claimed in claim 1.
14. An electric power steering system (100) of a vehicle, a method of operating an electric power steering system (100) of a vehicle and an arrangement to measure a torque applied on steering column (103) of an electric power steering system (100) of a vehicle are substantially as herein above described and as illustrated in accompanying drawings.