FORM 2
THE PATENT ACT, 1970
(39 of 1970)
&
THE PATENTES RULES, 2005
COMPLETE SPECIFICATION
(See section 10, rule 13)
1. TITLE OF THE INVENTION
"System for Differential Wheel Speed Based Bend Lighting"
2. APPLICANT(S)
a) Name : MAHINDRA & MAH1NDRA LIMITED
b) Nationality : Indian Company registered under the provisions
of the Companies Act, 1956
c) Address : R&D Center, Automotive Sector,
89, M.I.D.C, Satpur, Nashik - 422 007 Maharashtra State, India
3. PREAMBLE OF THE DESCRIPTION
COMPLETE
The following specification particularly describes the invention and the manner in which it is to be performed.

System for Differential Wheel Speed Based Bend Lighting
Field of the invention
The present invention relates to a lighting system for a vehicle and more particularly, to a system for differential wheel speed based bend lighting for the vehicle.
Background of the invention
The bend-lighting function enables the verges of the road, on the nearside of a vehicle, close to which the vehicle is travelling when passing round a bend, to be illuminated in front and to the side of the vehicle. The bend lighting in the vehicle is achieved in two ways, for example, static/fixed bend lighting and dynamic bend lighting. In both the cases, a turning angle of the vehicle is required to enable bend lighting. The turning angle is calculated from a steering angle sensor in most of the present day vehicles. The method of calculation of the turning angle using the steering angle sensor has a drawback as the method is dependent on the type of steering like mechanical, hydraulic or electrical and hence, the method cannot be used universally. Further, the method is not cost effective.
Furthermore, the use of steering angle sensor does not work properly in case of tyre pressure difference in front two wheels of the vehicle. The difference in tyre pressure may cause the tyres to rotate at different speed which may in turn delay the lights to turn 'ON' or the light might turn 'ON' on straight roads also.
Accordingly, there is a need of a system for differential wheel speed based bend lighting for a vehicle without using a steering angle sensor.
Summary of the invention

Accordingly, the present invention provides a system for differential wheel speed based bend lighting. The system comprises a plurality of wheel speed sensors, an anti-lock braking system (hereinafter "the ABS"), a plurality of tyre pressure sensors, a body control module and a pair of bend lamps.
Each wheel speed sensor of the plurality of wheel speed sensors is positioned in each wheel of the vehicle. The ABS is operably connected to each wheel speed sensor of the plurality of wheel speed sensors. The ABS comprises an electronic control unit. The electronic control unit collects all the wheel speeds. Each tyre pressure sensor of the plurality of tyre pressure sensors is positioned in each wheel of the vehicle and calculates an individual tyre pressure. The body control module receives all the wheel speeds from the electronic control unit and the individual tyre pressures from the plurality of tyre pressure sensors. The pair of bend lamps is capable of switching ON and OFF based on the individual wheel speed, the individual tyre pressure and the vehicle speed.
The system uses a differential speed of front two wheels to calculate a turning angle of the vehicle without using a steering angle sensor. The system further comprises a tyre pressure monitoring unit to compensate a tyre pressure difference in the front two wheels. When the front tyres have different circumferences because of different pressure levels or due to wear, the wheel speed values are added for the rear tyres in order to calculate whether the vehicle is steered towards left or right. Also, when the rear wheel speeds do not match with each other, the system determines the circumference variation in the rear wheel speeds in order to determine the timing to switch ON the pair of bend lamps.
Brief description of the drawings
Other features as well as the advantages of the invention will be clear from the following description.

In the appended drawings:
Figure 1 shows a block diagram of a system for differential wheel speed based
bend lighting for a vehicle, in accordance with the present invention;
Figure 2 shows a flowchart for measurement of a turning angle of the vehicle by using a tyre pressure monitoring unit in one aspect of the present invention;
Figure 3 shows a flowchart for measurement of the turning angle of the vehicle in accordance with another aspect of the present invention; and
Figure 4 shows a flowchart for measurement of the turning angle of the vehicle in accordance with yet another aspect of the present invention.
Detailed description of the invention
The foregoing objects of the present invention are accomplished and the problems and shortcomings associated with the prior art, techniques and approaches are overcome by the present invention as described below in the preferred embodiments.
Accordingly, the present invention provides a system for differential wheel speed based bend lighting for a vehicle without using a steering angle sensor. The system calculates a turning angle of the vehicle more accurately as the system is independent of a steering angle sensor, ratio of steering angle, steering shaft and other related gears.
The present invention is illustrated with reference to the accompanying drawings, throughout which reference numbers indicate corresponding parts in the various figures. These reference numbers are shown in bracket in the following description.

Referring to figure 1, a block diagram of a system (100) for differential wheel speed based bend lighting of a vehicle in accordance with the present invention is shown. Specifically, the system (100) is designed for the vehicle having four wheels and provides development of static or dynamic bend lighting without using a steering angle sensor. However, it is understood that the system (100) can be utilized to accomplish similar performance results for a two wheel vehicle such as in the case of a motorcycle and for any other vehicle having more wheels.
The system (100) comprises a plurality of wheel speed sensors (10), an anti-lock braking system (20) (hereinafter "the ABS (20)"), a plurality of tyre pressure sensors (30), a body control module (40) and a pair of bend lamps (50).
Each speed sensor (not numbered) of the plurality of speed sensors (10) is positioned in each wheel (not shown) that is a front right wheel, a front left wheel, a rear right wheel and a rear left wheel.
Each speed sensor of the plurality of speed sensors (10) is operably connected to the ABS (20). The ABS (20) includes an electronic control unit (not shown). The electronic control unit (hereinafter "the ECU") monitors the rotational speed of each wheel. In an embodiment, the ECU is programmed to disregard differences in rotational speed of the wheels below a critical threshold. The ECU collects all the wheel speeds and transmits to the body control module (40) over a Controller Area Network (hereinafter "the CAN").
Each tyre pressure sensor (not numbered) of the plurality of tyre pressure sensors (30) are positioned in each tyre (not shown) and calculates an individual tyre pressure. The body control module (40) also receives the individual tyre pressures from the plurality of tyre pressure sensors (30) via a radio frequency communication. In an embodiment, the body control module (40) switches the

pair of bend lamps (50) ON and OFF based on the individual wheel speed, individual tyre pressure and the vehicle speed.
The system (100) uses a differential speed of front two wheels (not numbered) to calculate a turning angle (9) of the vehicle as shown by a flowchart in figure 2. If V1 is speed of the front left wheel and V2 is speed of the front right wheel then following relational expressions are obtained:
V2-V1=dθ/t,
θ=(((v2-v1)t)/d,)
Since, V2 = (2πr2n2)/t, Vl= (2πr1n1)/t,
θ= (((2πr2n2/t) - (2πr1n1/t))t)/d,
Since, r1 = r2 = r and cancelling t we get,
θ=(n2-n1)(2πr/d),
Since (2πr/d) is constant, hence (2πr/d) = k
Then,θ=k(n2-n,) (1),
Similarly for left turn, θ= k(m -n2) (2)
where,
d = distance between the front two wheels,
t = total time of the turn,
n = radius of the left wheel,
r2 = radius of the right wheel,
r = radius of the vehicle's wheel,
k = constant,
m = number of rotations of the left wheel,
n2 = number of rotations of the right wheel.
In accordance with the present invention, when all the wheels are at the same circumference then expressions (1) and (2) are used to determine the turning angle (9).

In one aspect, the system (100) uses a tyre pressure monitoring unit (not shown) to compensate a tyre pressure difference in the front two wheels.
In accordance with the present invention, below mentioned equations are used to compensate the tyre pressure difference:
Let, speed percentage difference of unit pressure level of tyre is V3%. Therefore, if a difference of n pressure level is the speed corresponding to the opposite tyre then the speed differs by n x V3%. If the tyre pressure level is lower, the speed gets reduced by the above percentage and if the tyre pressure is more, the speed gets increased by the same percentage.
If V1 has 'n' lower tyre pressure than V2 then by compensating for the tyre pressure, new V2 becomes:
V2 = V2 + (nV3/100) (3)
Then new turning angle (9) is calculated using the expressions (1) and (2).
In another aspect, the system (100) determines the way in which the vehicle is steered. In accordance with the present invention, all the four wheel speeds are continuously monitored by the system (100) and if there is a difference in the front wheel speeds then the rear wheel speeds are taken into consideration as shown by a flowchart in figure 3 to determine the way in which the vehicle is steered.
If the front tyres have different circumferences because of different pressure levels or due to wear, the wheel speed values are added for rear tyres (not numbered) in order to calculate whether the vehicle is steered towards left or right.
If the vehicle is steered towards a left side then the left side wheels rotate on a lesser speed compared to right side wheels. Similarly, for a right steering, the

right side wheels rotate on a lesser speed compared to the left side wheels.
Assuming that the front left wheel circumference is lesser than other three wheels circumference in normal driving conditions then there is a drag towards the left side of the vehicle. In order to compensate, the driver tilts the steering wheel towards the right side to move straight. This increases the front left wheel speed causing a variation in the calculation. This is cancelled if the rear wheel speeds are matching with the front right wheel speed.
If the rear left wheel speed is greater than the right side wheel speeds then the vehicle is steered towards right and the pair of bend lamps (50) are switched ON after G+ct angle of the vehicle tilt. If the rear left wheel speed is lesser than the right side wheel speeds then the vehicle is steered towards left and the pair of bend lamps (50) are switched ON after -θ+a angle of the vehicle tilt. Similarly, the right side calculations are obtained.
In yet another aspect, the system (100) determines a circumference variation in the rear wheel speeds as shown by a flowchart in figure 4. If the front wheel speeds are matching with each other and the rear wheel speeds are not matching with each other then the system (100) determines the circumference variation in the rear wheel speeds in order to determine the timing to switch ON the pair of bend lamps (50).
In accordance with the present invention, the total distance covered by the sum of diagonal wheels should match. If there is a match then the steps described in figure 2 is used for the switching ON of the pair of bend lights (50). If there is mismatch then the method described in figures 3 and 4 is used to determine the timing to switch ON the pair of bend lamps (50).
Advantages of the invention

1. The system (100) is cost effective in the vehicle equipped with the front wheel speed sensors for example, the system (100) having the ABS (20).
2. The system (100) saves valuable time during vehicle production and service unlike the steering angle sensor that requires calibration.
3. The turning angle (θ) is calculated more accurately as the system (100) is independent of the steering angle, ratio of steering angle, steering shaft and other related gears.
The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, to thereby enable others skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omission and substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but such are intended to cover the application or implementation without departing from the spirit or scope of the present invention.

We Claim:
1. A system for differential wheel speed based bend lighting, the system comprising:
a plurality of wheel speed sensors, each wheel speed sensor of the plurality of wheel speed sensors being positioned in each wheel of the vehicle;
an anti-lock braking system operably connected to each wheel speed sensor of the plurality of wheel speed sensors, the anti-lock braking system having an electronic control unit, the electronic control unit being capable of collecting all the wheel speeds;
a plurality of tyre pressure sensors, each tyre pressure sensor of the plurality of tyre pressure sensors being positioned in each wheel of the vehicle and being capable of calculating an individual tyre pressure;
a body control module being capable-of receiving all the wheel speeds from the electronic control unit and the individual tyre pressures from the plurality of tyre pressure sensors; and
a pair of bend lamps being capable of switching ON and OFF based on the individual wheel speed, the individual tyre pressure and the vehicle speed,
wherein, the differential speed of front two wheels is used to calculate a turning angle of the vehicle without using a steering angle sensor.
2. The system as claimed in claim 1, wherein the system further comprises a tyre pressure monitoring unit to compensate a tyre pressure difference in the front two wheels.
3. The system as claimed in claim 1, wherein when the front tyres have different circumferences because of different pressure levels or due to wear, the wheel speed values are added for the rear tyres in order to calculate whether the vehicle is steered towards left or right.

4. The system as claimed in claim 1, wherein when the rear wheel speeds are not matching with each other then the system determines the circumference variation in the rear wheel speeds in order to determine the timing to switch ON the pair of bend lamps.