FORM 2
THE PATENTS ACT 1970 (as amended)
[39 OF 1970]
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
[See Section 10 and Rule 13]
TITLE OF THE INVENTION
SYSTEM AND METHOD FOR DYNAMICALLY CHANGING STEERING RATIO OF A MOTORIZED VEHICLE
APPLICANT
TATA MOTORS LIMITED
Bombay house, 24 Homi Mody Street,
Hutatma Chowk, Mumbai 400001,
Maharashtra, India.
Nationality: Indian
And
TATA MOTORS EUROPEAN TECHNICAL CENTRE Plc
18 Grosvenor Place, London, SW1X 7HS, United Kingdom. Nationality: United Kingdom
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in
which it is to be performed.

SYSTEM AND METHOD FOR DYNAMICALLY CHANGING STEERING RATIO OF A MOTORIZED VEHICLE
Field of invention:
The present invention relates to a steering control mechanism for a motorized vehicle which facilitates a variety of inputs and driving mechanisms to control the angle of driven wheel. More particularly this invention provides a dynamically changing steering ratio for steer-by-wire steering system at various conditions of driving.
Background of the invention:
It is known in the art to turn wheels of a vehicle by a direct mechanical linkage between a steering wheel, steering gears, and the actual wheels. With such systems, the operator turns the steering wheel to request that the steering gear turn the vehicle wheels. Feedback of the torque encountered by the steering system as the wheels are turned is provided to the operator through the mechanical linkage. This torque feedback can provide the operator with a sense of the road conditions, such as the traction of the vehicle wheels with the road surface. In addition, the feedback provides the operator with some sense of the condition of the components of the steering system.
It has been proposed that direct mechanical linkages be replaced by steer-by-wire systems. In a steer-by-wire system, a position encoder monitors the amount of turning of a steering wheel. A position encoder translates the amount of turning of the wheel into a desired amount of turning of the vehicle wheels. An electric signal is sent to the steering system, and the wheels are turned in response to the signals.

Although steer by wire systems are seen as having great potential in that they eliminate a number of required mechanical connections and components, significant further benefits can be obtained by the ability to change steering ratio dynamically based on various condition of the vehicle and road.
Additionally, the steering controller modules that are known to the prior arts either involve a conventional joystick or steering wheel which needs an upgrade in a view to the modern steer-by-wire techniques.
With a view therefore to overcome the drawbacks associated with conventional steering systems used in steer-by-wire technique, the inventors felt the need to develop a novel steering mechanism for the same. The present invention proposes to provide a solution to the existing difficulties in said field of invention by providing multiple novel features in said steering mechanism.
Summary of the invention:
Accordingly, the present invention provides, a system for dynamically changing steering ratio of a motorized vehicle in order to control the angle of driving wheels, comprising:
- a steering controller unit,
- at least one steering angle generator unit,
- a steering control mechanism,
- at least one pair of steering motors, and
- a torque feedback unit
wherein said steering angle generator unit is operably linked with said steering control mechanism, to collect data from sensors provided within said vehicle and thereupon generates steering angle signal to feed said steering controller unit and changes the steering ratio based on said collected data and pre-calibrated lookup tables,

wherein said steering controller unit, upon receiving the signal generated by said steering angle generator unit, determines the amount of current to be passed to each of said steering motors,
wherein said pair of steering motors is fed with the output from said steering controller unit. Said pair of steering motors thereby controls the angle of driven wheels,
said torque feedback unit provides steering feedback force to said steering control mechanism based on the input received from said steering motors.
Preferably the invented system is provided with two steering angle generator units having a first steering angle generator unit and a second steering angle generator unit, wherein each of said steering angle generator units works independent of each other to generate the steering angle for movement of the wheels and said steering controller unit upon fed with said steering angle data, checks whether the data of said steering angle are plausible.
Each steering angle generator unit will be provided with vehicle parameters (speed, gear position, mode and wheel speeds) and steering mechanism movement. They will then use these data in order to determine the required angle of movement for the road wheels. These angles are then provided to the steering controller which checks that the values are plausible. For instance the case that one steering angle generator were to request a right steer and the other requested a left steer, would be considered implausible.
Alternatively two separate processors may be provided in one steering angle generator unit to generate the steering angle for movement of the wheels and said steering controller unit upon fed with said steering angle data, checks whether the data of said steering angle are plausible.

In the invented system, sensors are provided within the vehicle. Said sensors provided within the vehicle, measure angle and rate of change of said steering mechanism along with vehicle speed, detect gear position, wheel speed, load on steering motors and selected drive mode to provide corresponding data output to the steering angle generator unit.
Preferably, the drive modes, provided within the invented system include sporty mode, normal mode and city mode.
According to one embodiment of the invented system, steering control mechanism can be an arm rest steering mechanism. Wherein, said arm rest steering mechanism includes a seat steering unit. Said seat steering unit comprises a seat, movable arm rests, a mechanism to measure the arm rest movement and a mechanism to provide steering feedback.
According to another embodiment of the invented system, steering control mechanism can be a touch pad mechanism.
According to yet another embodiment of the invented system, steering control mechanism can be handle bar steering mechanism wherein said handle bar rotates around a central axis and thereby determines the direction of vehicle movement.
According to a further embodiment of the invented system, steering control mechanism can be joystick steering mechanism.
According to a further embodiment of the invented system, steering control mechanism can be carried out by a steering wheel.
The present invention also provides a method for dynamically changing steering ratio of a motorized vehicle in order to control the angle of driven wheels, comprising the steps of:

- obtaining plurality of input data by means of at least one steering angle generator unit, operably linked with a steering control mechanism, from sensors provided with the said vehicle;
- developing a steering angle and changing the steering ratio by means of said steering angle generator unit based on said plurality of input data and pre-calibrated lookup tables;
- determining current to be passed to each of steering motors by means of a steering controller unit based on said steering angle developed by said steering angle generator unit;
- controlling the angle of driven wheels by means of said steering motors based on the current passed by said steering controller unit; and
- improving the feel of steering and feeding information of the condition of the road to the operator by providing a steering feedback force to said steering control mechanism by means of a torque feedback unit.
This summary is provided to introduce a selection of concepts that are further described below in the illustrative embodiments. Further embodiments, forms, objects, features, advantages, aspects, and benefits shall become apparent from the following description and drawings.
Brief description of the drawings:
Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which:
Figure 1 depicts the box diagram of the invented system for dynamically changing steering ratio of a motorized vehicle with arm rest steering mechanism.
Figure 2 depicts the box diagram of the invented system for dynamically changing steering ratio of a motorized vehicle with touch pad steering mechanism.

Figure 3 depicts the box diagram of the invented system for dynamically changing steering ratio of a motorized vehicle with handle bar steering mechanism.
Figure 4 depicts the box diagram of the invented system for dynamically changing steering ratio of a motorized vehicle with joystick steering mechanism.
Figure 5(a), 5(b) and 5(c) illustrates the steering mechanisms provided in the present invention.
Detailed description of the invention:
The claimed subject matter has been provided here with reference to one or more features or embodiments. Those skilled in the art will recognize and appreciate that, despite of the detailed nature of the exemplary embodiments provided here; changes and modifications may be applied to said embodiments without limiting or departing from the generally intended scope. These and various other adaptations and combinations of the embodiments provided here are within the scope of the disclosed subject matter as defined by the claims and their full set of equivalents. Like numbers refer to like elements throughout.
Figure 1 depicts one embodiment of the invented system (100) for dynamically changing steering ratio of a motorized vehicle in order to control the angle of driving wheels (112,114).
The invented system (100) comprises: a steering controller unit (106), at least one steering angle generator unit (102 or 104), a steering control mechanism (118), at least one pair of steering motors (108,110), and a torque feedback unit (116).
Steering control mechanism used in this embodiment is an arm rest steering mechanism (118).

Preferably, said arm rest steering mechanism (118) includes a seat steering unit (120). The seat steering unit (120) comprises a seat, movable arm rests (122,124), a mechanism to measure the arm rest movement and a mechanism to provide steering feedback. Wherein the vehicle is steered by lifting and lowering of the arm rests (122,124) viz. lifting the left arm (122) whilst lowering the right arm (124) will steer the vehicle towards right and vice versa, which is illustrated in figure 5(a). Since this mechanism is similar to that of any standard steering wheel, it is quite easy to adopt.
The steering angle generator unit (102 or 104) is operably linked with the steering control mechanism (118). The steering angle generator unit (102 or 104) collects data from sensors provided in said vehicle. Said steering angle generator unit (102 or 104) thereupon generates steering angle signal to feed said steering controller unit (106) and changes the steering ratio dynamically based on said collected data and pre-calibrated lookup tables.
The steering controller unit (106) receives a signal generated by said steering angle generator unit (102 or 104) and determines the amount of current to be passed to each of said steering motors (108,110) provided within the invented system (100).
The pair of steering motors (108,110) is fed with the output from said steering controller unit (106) to control the angle of driven wheels (112,114).
Then said torque feedback unit (116) provides steering feedback force to the steering control mechanism (118) based on the input received from said steering motors (108,110).
Preferably, said system (100) is provided with two steering angle generator units (102,104). Said steering angle generator units (102,104) comprise of a first steering angle generator unit (102) and a second steering angle generator unit

(104). These two steering angle generator units (102,104) work independent of each other to determine the steering angle of the driven wheels (112,114) for the movement of the vehicle. Thereon said data of angles are fed to the steering controller unit (106) that checks and confirms plausibility of said data of steering angles in order to avoid any unintended change in direction of vehicle movement.
For instance, if one steering angle generator unit (102) gives an output steering angle to steer in left direction and the other steering angle generator unit (104) gives and output steering angle to steer in the right direction then that set of data of steering angles will be implausible.
Alternatively, two separate processors may be provided in one of the steering angle generator units (102 or 104) to carry out the above mentioned functionality of the steering angle generator units (102,104).
The system (100) is configured to use a range of said pre-calibrated lookup tables which are based upon selected vehicle drive mode (sporty, city, relaxed and reverse), steering parameters (wheel angle change, rate of wheel angle change) and speed (wheel speed) in order to determine the angle which the wheels (112,114) are turned by around their axes.
The lookup tables are calibrated at the start of each operation, so that the steering feel can be tuned to each vehicles requirement. Typical lookup tables are shown below:

Table 1:
Selected mode: City ride mode
Vehicle
speed (Kmph) 0 0 0 0 0 0 Steering wheel angle

4 5 10 20 50 75
0
8 10 20 35 35 35
10
8 10 20 35 35 35
25
8 10 20 35 35 35
50
8 10 20 35 35 35
100
4 5 10 20 35 35

Table2:
Selected mode: Sport drive mode
Vehicle
speed (Kmph) 0 0 0 0 0 0 Steering wheel angle

4 5 10 20 50 75
0
8 10 20 35 35 35
10
8 10 20 35 35 35
25
8 10 20 35 35 35
50
8 10 20 35 35 35
100
4 5 10 20 35 35

In the invented system (100), sensors are provided within the vehicle. Said sensors measures plurality of input data comprising angle and rate of change of said steering mechanism (S1.2, S1.3) along with vehicle speed (S1.1), gear position (S1.4), wheel s234peed (S1.6), load on steering motors (S1.7) and selected drive mode (S1.5).
The drive mode (S1.5) provided in the invented system (100) includes sporty mode, normal mode and city mode.
Figure 2 depicts another embodiment of the invented system (200) for dynamically changing steering ratio of a motorized vehicle in order to control the angle of driving wheels (112,114). Steering control mechanism provided in this particular embodiment is a touch pad steering mechanism (218). Wherein the vehicle is steered by sliding hands on the touch pad viz. sliding the left hand forward whilst sliding the right arm backward will steer the vehicle to the right and vice versa which is illustrated in figure 5(b).
Figure 3 depicts yet another embodiment of the invented system (300) for dynamically changing steering ratio of a motorized vehicle in order to control the angle of driving wheels (112,114). Steering control mechanism provided in this particular embodiment is a handle bar steering mechanism (318). Wherein the handle bar (320) rotates around a central axis and thereby determines the direction of vehicle movement which is illustrated in figure 5(c). This mechanism is similar to that of standard steering wheel operation.
Figure 4 depicts a further embodiment of the invented system (400) for dynamically changing steering ratio of a motorized vehicle in order to control the angle of driving wheels (112,114). Steering control mechanism provided in this particular embodiment is a joystick steering mechanism (418). Wherein, the vehicle is steered by movement of the joystick which is carried out in conventional side to side movement of said joystick.

The invented system (200,300,400) for dynamically changing steering ratio of a motorized vehicle in order to control the angle of driving wheels (112,114) differs from the invented system (100) with regard to using different steering control mechanism only. Rest of the members of the invented system (200,300,400) work in similar fashion as the invented system (100) as has already been explained in reference to figure 1.
The present invention also provides a method for dynamically changing steering ratio of a motorized vehicle in order to control the angle of driven wheels (112,114).
First, plurality of input data are obtained by means of at least one steering angle generator unit (102 or 104) from sensors provided with the said vehicle. The steering angle generator unit (102 or 104) is operably linked with a steering control mechanism (118,218,318,418).
Next, a steering angle is developed and the steering ratio is changed by means of said steering angle generator unit (102 or 104) based on said plurality of input data and pre-calibrated lookup tables.
Then the amount of current to be passed to each of steering motors (108,110) is determined by means of a steering controller unit (106) based on said steering angle developed by said steering angle generator unit (102 or 104). Thereby angle of driven wheels (112,114) are controlled by means of said steering motors (108,110) based on the current passed by said steering controller unit (106).
Finally, a torque feedback unit (116) provides a steering feedback force to said steering control mechanism (118,218,318,418) for improving the feel of steering and feeding information of the condition of the road to the operator.

As already mentioned, the foregoing description is illustrative of the invention and not limitative to its scope, because it will be apparent to persons skilled in the art to devise other alternative embodiments without departing from the broad ambit of the disclosures made herein.

We Claim:
1. A system (100,200,300,400) for dynamically changing steering ratio of a
motorized vehicle in order to control the angle of driving wheels (112,114),
comprising:
- a steering controller unit (106),
- at least one steering angle generator unit (102 or 104),
- a steering control mechanism (118,218,318,418),
- at least one pair of steering motors (108,110), and
- a torque feedback unit (116)
wherein said steering angle generator unit (102 or 104), operably linked with said steering control mechanism (118,218,318,418), collects data from sensors provided within said vehicle and thereupon generates steering angle signal to feed said steering controller unit (106) and thereupon changes the steering ratio based on said collected data and pre-calibrated lookup tables;
wherein said steering controller unit (106), upon receiving the signal generated by said steering angle generator unit (102 or 104), determines the amount of current to be passed to each of said steering motors (108,110);
wherein said pair of steering motors (108,110), fed with the output from said steering controller unit (106), controls the angle of driven wheels (112,114); and
wherein said torque feedback unit (116) provides steering feedback force to said steering control mechanism (118,218,318,418) based on the input received from said steering motors (108,110).
2. The system (100,200,300,400) as claimed in claim 1, wherein said system
(100,200,300,400) is provided with two steering angle generator units (102,104)

having a first steering angle generator unit (102) and a second steering angle generator unit (104), wherein each of said steering angle generator units (102,104) works independent of each other to generate the steering angle for movement of the wheels (112,114) and said steering controller unit (106) upon fed with said steering angle data, checks whether the data of said steering angle are plausible.
3. The system (100,200,300,400) as claimed in claim 1, wherein two
separate processors are provided in one steering angle generator unit (102,104) to
generate the steering angle for movement of the wheels (112,114) and said
steering controller unit (106) upon fed with said steering angle data, checks
whether the data of said steering angle are plausible.
4. The system (100,200,300,400) as claimed in any of the above claims 1 to
3, wherein said sensors provided within the vehicle:
measure angle and rate of change of said steering mechanism (S1.2, S1.3) along with vehicle speed (S1.1), detect gear position (S1.4), wheel speed (S1.6), load on steering motors (S1.7) and selected drive mode (S1.5) to provide corresponding data output to the steering angle generator unit (102,104).
5. The system (100,200,300,400) as claimed in claim 4, wherein said drive mode (S1.5) includes sporty mode, normal mode and city mode.
6. The system (100) as claimed in any of the above claims 1 to 5, said steering control mechanism is an arm rest steering mechanism (118).
7. The system (100) as claimed in claim 6, wherein said arm rest steering mechanism (118) includes a seat steering unit (120) comprising a seat, movable arm rests (122,124), a mechanism to measure said arm rest movement and a mechanism to provide steering feedback.

8. The system (200) as claimed in any of the above claims 1 to 5, wherein said steering control mechanism (218) is a touch pad mechanism (218).
9. The system (300) as claimed in any of the above claims 1 to 5, said steering control mechanism (318) is a handle bar steering mechanism (318), wherein said handle bar (320) rotates around a central axis and thereby determines the direction of vehicle movement.
10. The system (400) as claimed in any of the above claims 1 to 5, said steering control mechanism is a joystick steering mechanism (418).
11. A method for dynamically changing steering ratio of a motorized vehicle in order to control the angle of driven wheels (112,114), comprising the steps of:
obtaining plurality of input data by means of at least one steering angle generator unit (102 or 104), operably linked with a steering control mechanism (118,218,318,418), from sensors provided with the said vehicle;
developing a steering angle and changing the steering ratio by means of said steering angle generator unit (102 or 104) based on said plurality of input data and pre-calibrated lookup tables;
determining current to be passed to each of steering motors (108,110) by means of a steering controller unit (106) based on said steering angle developed by said steering angle generator unit (102 or 104);
controlling the angle of driven wheels (112,114) by means of said steering motors (108,110) based on the current passed by said steering controller unit (106); and

improving the feel of steering and feeding information of the condition of the road to the operator by providing a steering feedback force to said steering control mechanism (118,218,318,418) by means of a torque feedback unit (116).