FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
PROVISIONAL SPECIFICATION
(See Section 10; rule 13)
TITLE OF THE INVENTION
Advanced Steering System with Low Speed Assist

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. Ashfaque Ahmed Ansari, Mr. Hari Srinivas Babu Aggarapu,
Mr. Preesty Thomas J, Mr. Shirguppe Abhijeet A
All are Indian Nationals
of TATA MOTORS LIMITED,
an Indian company having its registered office
at Bombay House, 24 Homi Mody Street, Hutatma Chowk,
Mumbai 400 001 Maharashtra, India

PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed.


Field of invention
This invention relates to the Power Steering system used in vehicles and more particularly to the Electric Power Steering system.
Background of the Invention
Electric Power Steering (EPS) 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 (ECU) with high processing capabilities to take care of power assistance at all manoeuvring events. This increases the complexity and overall cost of the system. For the vehicles with comparatively less Front Axle Weight (FAW) 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 FAW (in the range of 250 ~ 350 kg), full fledge & high cost EPS system with assistance at all manoeuvring events is not necessary and is also complex in terms of functionality & development.
Objects of invention
The main object of this invention is to provide steering assist in parking condition and at very low vehicle speeds.
Yet another object of this invention is to provide assistance to driver with a simple and low cost system.
Statement of invention
Low cost Electric Power Steering system with Park-Assist feature active only at low vehicle speeds and decoupling as soon as high vehicle speeds are achieved.
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Park-Assist Electric Power Steering System comprises a Steering Column, Reversible Electric DC Motor, ECU, sensor capturing steering rates, Left & Right turn signals and Vehicle speed signal, wherein said Electric Motor is coupled to a reduction gearbox which gives output on both the sides. The output of the reduction gearbox is coupled to the upper portion of the column on one side; where as the other end is connected to the lower end of the column. The steering angle sensor is mounted on the steering column. Left & Right turn signals from the combination switch, vehicle speed sensor, steering angle sensor and vehicle battery is fed to the controller. Depending on the programmed logic in the ECU (given in Fig.2 below), motor will rotate in clockwise or counter clockwise directions and thus provides required power assistance in desired direction.
Brief Description of Drawings
Figure 1 show the assembly of "Park-Assist Electric Power Steering System Assembly", in accordance with this invention.
Figure 2 show the "Park-Assist Electric Power Steering System Control Algorithm", in accordance with this invention.
Detail description of Invention w.r.t. drawing
Referring now to the drawings 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.
Park-Assist Electric Power Steering System comprises a Steering Column, Reversible Electric DC Motor, ECU, sensor capturing steering rates, Left & Right turn signals and Vehicle speed signal, wherein said Electric Motor is coupled to a reduction gearbox which gives output on both the sides. The output of the reduction gearbox is coupled to the upper portion of the column on one side; where as the other end is connected to the lower end of the column. The steering angle sensor is mounted on the steering column. Left & Right turn signals from the combination
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switch, vehicle speed sensor, steering angle sensor and vehicle battery is fed to the controller. Depending on the programmed logic in the ECU (given in Fig.2 below), motor will rotate in clockwise or counter clockwise directions and thus provides required power assistance in desired direction.
In one of the embodiment when the vehicle ignition key is inserted, ECU is powered ON. Also other vehicle signals like Vehicle speed, turn signals from Combi switch and steering rate are detected by the ECU. In static vehicle condition or at very low vehicle speeds (10 ~ 15 Kmph), if driver intend to turn to Left/Right, he shall switch ON the Left / Right turn switch on combi switch. The ECU after receipt of this signal, check for vehicle speed value & steering angle value, then based on programmed logic in the ECU as shown in Figure 2 below, the motor will start rotating in clockwise or counter clockwise direction, thus providing required steering assist to the driver. The motor assistance seizes in the following 3-situations:
1. Vehicle Speed 15 Kmph.
2. Turn Switch is OFF.
3. Steering Rate becomes '0'.
The criteria of vehicle speed to start the proposed Advanced Steering System for Low Speed Assist can be varied as desired. The speed should be below 15kmph if the weight of the vehicle is less such as small cars and commercial vehicles with low weight, the speed can be below 25 kmph in case the vehicle weight is medium like sedan, sports utility vehicle etc. and the criteria of vehicle speed can be less than 40kmph if the weight of the vehicle is high. However, for all the vehicles to decrease complex control system the criteria of speed can be less than 15kmph.
Advantages of the instant invention over the prior art are: Simple in construction and assembly. Low Cost. Low weight.
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Use of available signals from vehicle.
Selection of Low capacity motor with 3-4 times overload possibility (as the duty cycle is found to be only 5%).
Energy conservation due to selective use of the system.
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.
2 3 SEP 2009