FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, rule 13] "POWER ASSISTED STEERING SYSTEM"
INVENTOR
Vaibhav Rawat
Indian national of TATA MOTORS LIMITED
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 disclosure and the manner in which it is to be performed.

TECHNICAL FIELD
The present disclosure generally relates to steering systems and more particularly relates a power assisted steering system for a vehicle.
BACKGROUND OF THE DISCLOSURE
Vehicles are provided with power steering systems to reduce the steering efforts put in by drivers for steering the vehicle. Accordingly in vehicles equipped with power steering systems, the driver needs to apply a modest effort, which is augmented by a hydraulic or electric system, for steering the vehicle. Currently, most of the passenger vehicles incorporate hydraulic or electric power assist steering system. Hydraulic power assist systems, due to their low efficiency and high maintenance cost, are being rapidly replaced by electric power assist steering (also referred to as "EPAS" or "EPS"). A full fledged EPAS consists of too many parts, such as, electric motor, gear system, microcontroller, torque sensor etc. The development of EPAS for any vehicle therefore, also requires extensive calibration, and hence substantial time for development.
There have been several solutions to electric power assist steering system, but most incorporate following elements as base design, i.e. motor gear reduction, a microcontroller, a torque sensor, a motor RPM sensor etc. These EPAS may work for overall vehicle speed range, and may also incorporate vehicle speed dependency in the algorithm. However, all these systems suffer the basic problem of cost and long development time, particularly due to complexity of the elements involved.
Patent No 2,756,605 discloses a design which is based on only steering rotation direction (Clockwise / Counterclockwise), and takes no input of steering torque, rotation speed or vehicle speed. Such a system may not be suitable for high speed operations, since steering torque demand varies with vehicle speed and road conditions.

OBJECTS OF THE DISCLOSURE
The objective of disclosure is to provide a reliable, simple and cost effective, power assisted steering system.
Another object of the disclosure is to provide a power assisted steering system, that over comes the limitation associated with cost, development time, and vehicle safety.
Another object of the present disclosure is to provide a power assisted steering system that works without a torques sensor.
Another object of the present disclosure is to provide a power assisted steering system that uses vehicle speed and EPAS motor speed signals.
Further objects and features of the disclosure will become apparent from the following detailed description when considered in conjunction with the drawings.
SUMMARY OF THE DISCLOSURE
The various embodiments of the present disclosure disclose an electric power assisted steering system for a vehicle. The system comprising a steering wheel, a first coupler connected concentrically to the steering wheel, a second coupler connected to a steering shaft. The second coupler is adapted to be engaged with the first coupler for rotating with the first coupler rotation. A resilient member is associated with each of the first coupler and the second coupler to restrict transfer of a predefined movement from the first coupler to the second coupler. A first set of switch plates is carried by the first coupler, and a second set of switch plates is carried by the second coupler. A slip ring mechanism is electrically coupled to the second set of switch plates, such that when one or more of the first set of switch plates get electrically engaged with one or more of the second set of switch plates, a predetermined electrical signal is transferred by the slip ring mechanism, and a steering motor engaged with the steering shaft and adapted to receive the electrical signal from the slip ring mechanism to steer the vehicle

BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a perspective view of a steering input mechanism of the power assisted steering system, according to an embodiment of the disclosure,
FIG. 2 illustrates an exploded perspective view of a steering input mechanism of the power assisted steering system, according to an embodiment of the disclosure,
FIG. 3 illustrates a perspective view of a power assisted steering system, according to an embodiment of the disclosure,
FIG. 4 illustrates an exploded perspective view of the power assisted steering system, according to an embodiment of the disclosure,
FIG. 5 illustrates a block diagram for a method of steering a vehicle, by steering input mechanism of the power assisted steering system, according to an embodiment of the disclosure, and
FIG. 6 illustrates a flow diagram for the power assisted steering system, according to an embodiment of the disclosure.
DETAILED DESCRIPTION OF THE DISCLOSURE
Referring now to the drawings wherein the showings are for the purpose of illustrating a preferred embodiment of the disclosure only, and not for the purpose of limiting the same.
FIG. 1 and 2 illustrate a perspective and an exploded perspective view of a steering input mechanism 100 for a power assisted steering system 102, according to an embodiment of the disclosure. The power assisted steering system 102 may be utilized in a variety of vehicles, such as passenger cars, commercial or heavy duty economic, slow moving

vehicles, such as lawn-mowers, farm equipments, in-factory vehicles, golf-carts, limited field electric vehicles and the like.
The power assisted steering system 102 (best shown in FIG. 3 and 4), includes the steering input mechanism 100, a steering wheel 104, a steering shaft 106, and drive unit 108 coupled to the steering shaft 106.
The steering input mechanism 100 of the present disclosure includes a first coupler 10 (also referred to as "upper coupling hub") and a second coupler 12 (also referred to as "lower coupling hub"). The first coupler 10 and the second coupler 12 are best shown in FIG. 2 and 4. The first coupler 10 may be an integral integrated part of base-plate (not numbered) of the steering wheel 104. The first coupler 10 and a second coupler 12 are kept together in vertical direction using an elongated nut 14 which engages with first coupler 10 through a bearing and locks on the steering shaft 104 threads just above the second coupler splines. The bearing on first coupler 10 is locked using a circlip 16, seated just above the bearing outer face. The first coupler 10, when engaged with the second coupler 12, forms a love-joy coupling.
The steering input mechanism 100 further includes a resilient member 18 (not visible in FIG I and 3). When the first coupler 10 is connected to the second coupler 12 a seat or a cavity for receiving the resilient member 18, is defined. The resilient member 18 is adapted to be received in the seat. The resilient member 18 may be a rubber spider. It may herein be noted that the resilient member 18, may alternatively by any other compressible members, without deviating from the spirit of the present disclosure.
The resilient member 18 is associated with each of the first coupler 10 and the second coupler 12. The resilient member 18 allows restricted rotation transfer from the first coupler 10 to the second coupler 12. More specifically, when a user, such as, a driver of the vehicle applies torque on the steering wheel 104, the steering wheel 104 along with the first coupler 10, rotates. During initial rotation of the first coupler 10, i.e. up till a torque less than a threshold torque (also referred to as "activation threshold torque") is applied, the resilient member 18 gets compressed. During such initial rotation of the first coupler 10, due to the compression of the resilient member 18, the movement of the first

coupler 10 is not transferred to the second coupler 12, therefore the movement of the first coupler 10 is relative to the second coupler 12. Such movement of the first coupler 10 relative to the second coupler 12 may be in clock-wise or clockwise direction, depending on the direction in which torque was applied at the steering wheel 104.
In one embodiment of the present disclosure, up till the steering torque is less than or equal to two Newton meters (2 Nm), only the first coupler 10 moves and compresses the resilient member 18 by up to two degrees, with respect to its original uncompressed position.
It may herein be noted that, the value of torque before which first coupler rotation is not transferred to the second coupler 12, may be altered based on requirement by changing the material, shape, size or kind of the resilient member 18, and without deviating from the spirit of the present disclosure.
As shown in various figures, the steering input mechanism 100 also includes a first set of conducting members carried by the first coupler 10 and a second set of conducting members carried by the second coupler 12. The conducting members, also collectively referred to as, "direction switches." The first set of conducting members includes a first switch plate 20 and a second switch plate 22. Likewise, the second set of conducting members includes a third switch plate 24 and a second switch plate 26.
In alternative embodiments of the present disclosure, there may be fewer or more switch plates in the first set of conducting members, and the second set of conducting members, without deviating from the spirit of the present disclosure.
The first switch plate 20 and the second switch plate 22 may be mounted on the first coupler 10 by a ring of non-conducting material. Likewise, the third switch plate 24 and the fourth switch plate 26 may be mounted on the second coupler 12 by another identical ring of non-conducting material. The first switch plate 20 and the second switch plate 22 on the first coupler 10 are connected to a vehicle ground/earth.
The first switch plate 20 and the second switch plate 22 come in electrical contact with the third switch 24 and fourth switch plate 26, when the when the first coupler 10 has

moved by at least a predefined threshold distance with respect to the second coupler 12 in either clockwise or anticlockwise direction. That is to say that, the first switch plate 20 and the second switch plate 22 comes in electrical contact with the third switch 24 and fourth switch plate 26, when a predefined threshold torque, say up to 2 Nm, is applied at the steering wheel, and the resilient member 18 compresses by the predefined angle, say 2 degrees.
A slip ring mechanism 28 is electrically coupled to the second set of switch plates. When one or more of the first set of switch plates get electrically engaged with one or more of the second set of switch plates, a predetermined electrical signal is transferred by the slip ring mechanism 28 to a controller (not shown) of a drive unit 108 of the power assisted steering system 102. In one embodiment of the present disclosure, the drive unit 108 or steering motor may be like an inline electric motor carried by the steering shaft 106.
In accordance to one embodiment of the present disclosure, the slip ring mechanism 28 includes a first slip ring 30 having a spring loaded plunger 32, a second slip ring 34 also having a spring loaded plunger 36. The first slip ring 30 and the second slip ring 34 are electrically coupled with the third switch plate 24 and the fourth switch plate 26 respectively, of the second set of conducting members. A drive controller is electrically connected to each of the spring loaded plungers 32, 36 and the motor steering motor 108 for controlling the motor 108 based on the input from the one of the spring loaded plungers.
More specifically, the when the first switch plate 20 comes in connection with the third switch plate 24 (when a torque of at least 2 Nm is applied on the first coupler 10, in clockwise direction), ground signal is passed from the first switch plate 20 to the third switch plate 24, and from third switch plate 24 to the first slip ring 30 via spring loaded the plunger 32. These signals are transferred to the motor controller and the motor controller may direct the motor unit to rotate the steering shaft in clockwise direction. Clearly, with such movement of the steering shaft, the first switch plate 20 is removed from electrical contact from the third switch plate 24, and thus the signal in broken. A

similar process, but in opposite direction, happens for steering in counter clockwise direction.
The power assisted steering system 102 may optionally also include an EPAS override switch, to disable the power assisted steering system 102, when desired.
The present disclosure also relates to a method of steering a vehicle using a power steering system, such as the power assisted steering system 102. The method of steering the vehicle includes the following steps. At the step one, the steering input on a first coupler 10 of steering wheel obtaining. The steering input may be identified as either below or beyond a predetermined threshold. In the present embodiment, the steering input may be identified as either below 2 Nm or beyond 2 Nm.
Subsequently, at step two, input about speed of the vehicle is obtained. Based on that input, the speed of the vehicle is obtained as below or beyond a predetermined speed threshold. This input may be obtained from a vehicle ECU. At step three, input about status of the engine is obtained. Based on that input the engine is identified at turned on or off. This input may be also obtained from the vehicle ECU. The steering input from the first coupler to a second coupler is restricted until the steering input is beyond a predetermined threshold, in terms of steering torque. The steering input from the first coupler to a second coupler transferred as the steering input is beyond the predetermined threshold.
Simultaneously, the first coupler is electrically coupled to the second coupler, when the steering input is beyond the predetermined threshold. The coupling of the first coupler with the second coupler may be a clockwise or anticlockwise, based on the direction in which steering input is given. In case of clockwise coupling, completing electrical circuit of a first clip ring, and in case of anticlockwise coupling , completing the electrical circuit of the second clip ring. Thereafter, the motor controller is signal abut about of completing of electrical circuit, speed threshold, and status of the engine. The motor controller based on the completion of electrical circuit, speed threshold, and status of the engine, operates the controlling the steering motor. Based on above signals, motor controller is able to decide the direction and amount of torque assist required at steering shaft, and controls

the motor current accordingly. Few signals are required to decide direction and amount and torque assist, while other signals are used for activating the EPAS system. The algorithm makes sure that the road wheels never get steered more than the driver's intension, and turns the torque assist to zero whenever steering hand wheel torque is less than the activation threshold torque.
The advantage of the power assisted steering system 102 lies in the fact that it is torque-sensor-less which reduces system's cost as well as calibration development time. The system utilizes naturally available signals, provides stable steering assist, and also incorporates an override switch for emergencies. System does not include any worm-gear arrangement; hence in case of EPAS system failure, it does not get locked and behaves tike manual steering. The system also does not require any major modifications in the exiting vehicle system, in terms of steering column, shaft, combi-switch, steering mounting structure and the like.
FIG. 6 illustrates another flow diagram for the power assisted steering system 102.
The foregoing description provides specific embodiments of the present disclosure. It should be appreciated that these embodiment are described for purpose of illustration only, and that numerous other alterations and modifications may be practiced by those skilled in the art without departing from the spirit and scope of the disclosure. It is intended that all such modifications and alterations be included insofar as they come within the scope of the disclosure as claimed or the equivalents thereof.

Referral Numerals Description
100 Steering input mechanism
102 Power assisted steering system
104 Steering wheel
106 Steering shaft
108 Drive unit
10 First coupler
12 Second coupler

14 Elongated nut
16 Circlip
18 Resilient member
20 First switch plate
22 Second switch plate
24 Third switch plate
26 Second switch plate
28 Slip ring mechanism
30 First slip ring
32 Spring loaded plunger
34 Second slip ring
36 Spring loaded plunger

We claim:
1. A steering input mechanism for a power assisted steering system, the steering
input mechanism comprising:
a first coupler connected to a steering wheel for rotating with the steering wheel rotation,
a second coupler connected to a steering shaft, the second coupler adapted to be engaged with the first coupler for rotating with the first coupler,
a resilient member associated with each of the first coupler and the second coupler to allow restricted rotation transfer from the first coupler to the second coupler,
a first set of conducting members carried by the first coupler,
a second set of conducting members carried by the second coupler, one or more of the first set of conducting members get electrically engaged with one or more of the second set of conducting members when the first coupler has moved by at least a threshold distance with respect to the second coupler in one of a clockwise and anticlockwise direction,
a slip ring mechanism electrically coupled to the second set of conducting members, such that when one or more of the first set of conducting members get electrically engaged with one or more of the second set of conducting members, a predefined electrical signal is transferred to a controller of a drive unit of the power assisted steering system.
2. The steering input mechanism as claimed in claim 1, wherein the drive unit is coupled with the steering shaft to drive the steering shaft whereby one or more of the first set of conducting members get disengaged from one or more of the second set of conducting members.
3. The steering input mechanism as claimed in claim 1, wherein the first coupler is integral to the base plate of the steering wheel, and the second coupler is connected to the steering shaft through splines.

4. The steering input mechanism as claimed in claim 1, wherein the first coupler, when connected to the second coupler, defines a seat for receiving the resilient member.
5. The steering input mechanism as clamed in claim 1, the first coupler and the second coupler for a love-joy coupling.
6. The steering input mechanism as claimed in claim 1, wherein the resilient member compresses till the first coupler moves by up to two degrees.
7. The steering input mechanism as claimed in claim 1, wherein the resilient member is a rubber spider.
8. The steering input mechanism as claimed in claim 1, wherein the first set of conducting members includes a first switch plate and a second switch plate; and the second set of conducting members includes a third switch plate and a fourth switch plate.
9. The steering input mechanism as claimed in claim 7, wherein one of first switch plate and second switch plate connects with one of the third switch plate and the fourth switch plate, when the first coupler is moved beyond a predetermined angle in one of a clock wise and an anti clockwise direction.
10. The steering input mechanism as claimed in claim 8, the connection of the first switch plate with the third switch plate triggers the drive unit controller to operate the drive unit in a clockwise direction.
11. The steering input mechanism as claimed in claim 9, the connection of the second switch plate with the fourth switch plate triggers the drive unit controller to operate the drive unit in an anti-clockwise direction.
12. The steering input mechanism as claimed in claim 10, wherein the both anticlockwise direction and clockwise operation of the drive unit moves the second coupler, thereby disengaging the first set of conducting members from the second set of conducting members.

13. The steering input mechanism as claimed in claim 1, wherein the slip rings
mechanism further includes
a first slip ring having a spring loaded plunger,
a second slip ring also having a spring loaded plunger, the first slip ring and the second slip ring being electrically coupled with the third switch plate and the fourth switch plate respectively, of the second set of conducting members, and
a drive controller electrically connected to each of the spring loaded plungers and an motor for controlling the motor based on the input from the one of the spring loaded plungers.
14. An electric power assisted steering system for a vehicle, the electronic power
assisted steering system comprising;
a steering wheel,
a first coupler connected concentrically to the steering wheel for rotating with the steering wheel rotation,
a second coupler connected to a steering shaft, the second coupler adapted to be engaged with the first coupler for rotating with the first coupler rotation,
a resilient member associated with each of the first coupler and the second coupler to restrict transfer of a predefined movement from the first coupler to the second coupler,
a first set of switch plates carried by the first coupler,
a second set of switch plates carried by the second coupler, one or more of the first set of switch plates get electrically engaged with one or more of the second set of switch plates when the first coupler has moved by at least a threshold distance with respect to the second coupler in one of a clockwise and anticlockwise direction,
a slip ring mechanism electrically coupled to the second set of switch plates, such that when one or more of the first set of switch plates get electrically engaged with one or more of the second set of switch plates, a predetermined electrical signal is transferred by the slip ring mechanism, and
a steering motor engaged with the steering shaft and adapted to receive the electrical signal from the slip ring mechanism to steer the vehicle,

15. The electric power assisted steering system as claimed in claim 9, wherein the steering motor is an inline motor.
16. A method of steering a vehicle, the method comprising;
obtaining a steering input on a first coupler of steering wheel, the steering input being either below or beyond a predetermined threshold,
obtaining input about speed of the vehicle as below or beyond a predetermined speed threshold.
obtaining input about status of the engine, as turned on or off,
restricting transfer of steering input from the first coupler to a second coupler until the steering input is beyond a predetermined threshold,
transferring the steering input from the first coupler to a second coupler when the steering input is beyond the predetermined threshold,
coupling, electrically, the first coupler to a second coupler when the steering input is beyond the predetermined threshold in one of a clockwise and anticlockwise direction,
identifying the coupling of the first coupler with second coupler as one of a clockwise coupling and an anticlockwise coupling,
completing electrical circuit of a first clip ring in case of a clockwise coupling, and a second clip ring in case of anti clockwise coupling,
communicating to a motor controller about of completing of electrical circuit, speed threshold, and status of the engine, and
controlling the steering motor based on the completion of electrical circuit, speed threshold, and status of the engine.