FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See Section 10; rule 13)
TITLE OF THE INVENTION
Method of testing brake steer on vehicle
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
Vinay Upadhyay, K. Gopalakrishna both Indian national
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 Complete specification particularly describes the invention and the manner in which it is to be performed.

Field of Invention:
This invention relates to testing of brake steer on vehicle and more particularly it relates to a method of testing of brake steer on vehicle by evaluating axle twist.
Background of Invention
Tuning of the steering components in relation to the suspension components is very much essential on the vehicle. If this tuning is not done then repercussions like brake pulling or abnormal tyre wear and low tyre life can result. One of the reasons why brake pulling occurs is "Brake Steer".
Brake Steer is a phenomenon which occurs when brake is applied, load transfer from rear to front of vehicle occurs causing leaf spring to wind-up, this in turn twist the axle. Hence a moment occurs on the steering arm - drag link ball joint, which pushes the drag link (and further steering linkages) but as steering wheel is held stationary tight the moment causes the stub axle (wheel) to turn on LH side, thus causing vehicle pulling on Left Hand side (LH) direction.
Conventional methods used for tuning and integration of said components on the vehicle being done with the help of Kinematics and Compliance (KnC) test rig or Suspension Parametric Measuring Machine (SPMM) test rig. In this method the wheels of the test vehicle (with required instrumentation) are rigidly clamped to the turn pads of the rig. Testing on the rig requires huge investment of resources in terms of money and space. More-over the test conducted through the test rig is in stationary condition, which does not give accurate picture of vehicle in dynamic condition.
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Objects of Invention
The main object of this invention is to provide a method of testing brake steer on vehicle in dynamic conditions which will be able to give more realistic testing conditions than the test rig.
Another objective is to provide a method of testing brake steer on vehicle which requires less time.
Yet another object of this invention is to provide a method of testing of brake steer to optimize steering components in tune with suspension components.
Yet another object of this invention is to provide a method of testing of brake steer which is simple and cost effective.
Statement of Invention
Method of testing brake steer on vehicle comprising of following steps:
a) Identifying the vehicle having front rigid axle suspension on which testing to be performed;
b) Mounting height sensor fixture on front axle;
c) Instrumentation of vehicle for measuring various parameters;
d) Acquiring data by running vehicle and applying the pedal force up to just before limit of adhesion at various speeds with engine disconnected state;
e) Removing the spikes from the raw data;
f) Plotting graph time Vs. height;
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g) Calculating axle twisting angle by known method from the heights
obtained;
g) Plotting graph time Vs. twist angle on the same graph of step (f);
i) Drawing the trend line of the graph of step (h) and finding the slope or
finding the maximum twist angle;
j) Determining brake steer by Adam's Analysis by using twist angle
obtained by step (i).
Method of testing brake steer on vehicle, wherein said height sensor fixture is fitted in such a way that the axis of height sensor fixture is perpendicular to the axis of front axle beam.
Method of testing brake steer on vehicle, wherein said height sensors are placed at equal distance from the center-line of the base plate of said fixture.
Method of testing brake steer on vehicle, wherein instrumentation of the vehicle involves provision of height sensor, speed sensor, brake switch and data acquisition system.
Method of testing brake steer on vehicle, wherein vehicle is running at 40 to 80 KMPH.
Method of testing brake steer on vehicle, wherein said brake force should be applied instantaneously.
Method of testing brake steer on vehicle, wherein steering wheel should be held stationary tight at the time of brake application till the vehicle becomes stand still.
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Fine tuning of the steering components in relation to suspension components by using results obtained by a method of testing brake steer on vehicle.
Brief Description of Invention
Method of testing of brake steer in accordance with this invention by evaluation of axle twist due to leaf spring wind-up comprises instrumentation of the vehicle to acquire height measurements of the front axle with respect to ground (at fixed point on the front and fixed point on the rear of the front axle) continuously by real time data collection (RTDC) technique in dynamic running condition and when brakes are applied. In addition to this, instrumentation of vehicle is also required for acquisition of data for time, speed and deceleration. The heights obtained are plotted on the graph time Vs height and with the help of difference in heights at the time when the vehicle is under braking condition, axle twist is calculated by known method. Above said axle twisting is used to calculate brake steer by using ADAM'S analysis. Finally, fine tuning of suspension and steering components is done by using brake steer value.
Higher the amount of brake steer more is the amount of vehicle pulling. Hence in order to reduce brake steer, tuning (change in the dimensions of the components to reduce brake steer) of suspension and steering components is done.
Brief Description of Drawings
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
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Figure 1 shows typical arrangement of front rigid axle suspension system with steering
linkages.
Figure 2 shows fixture for mounting of the height sensors.
Figure 3 A shows mounting of the height sensors on the front axle of vehicle.
Figure 3B shows instrumentation of the vehicle
Figure 4 shows graph of Time Vs height (at front of the front axle and at rear of front
axle) and angle through with axle twists.
Detailed Description of Invention
Referring to figures 1 to 4;
Method of testing of brake steer on vehicle consists of following major steps -
1. Identifying the vehicle (front rigid axle suspension) on which evaluation to be done. Specifications of components including stiffness and compliance characteristics of the steering and suspension system should be available before the start of the test, in order to re-check the values measured.
2. Drill holes on the front axle beam (10) for mounting of the fixture (12) or remove the shock absorber and its bottom mounting and its two holes can be used for mounting of fixture (12). Mounting of the fixture (12) is done by fastening the base plate (13) on front axle beam (10). Height sensors (16) are mounted at the mounting holes (14, 15) on the fixture (12).
3. Instrument the vehicle for acquiring heights, speed, and deceleration.
4. Driving the instrumented vehicle for at about 50 to 60 kmph, to warm up the vehicle and apply 8 to 10 snub braking during this running so that brakes reaches its normal operating temperature.
5. For the test, drive the vehicle on the straight patch at a constant speed of 50kmph and apply the brake in such a way that pedal force should generates maximum
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MFDD (Mean Fully Developed Deceleration). Applying the pedal force up to the limit of adhesion and keeping engine in disconnected state and ensuring that all the brake circuits are in healthy condition.
6. Triggering the instrument for collection of the data by using brake switch.
7. Acquiring the data at sufficient resolution frequency preferably at 40Hz from the moment brakes are applied till the time when the vehicle speed reaches 0kmph.
8. Repeat the tests with 40 to 80 kmph speed with laden and unladen condition of the vehicle.
9. Filtering the data for spikes (which come due to noise in the system).
10. Plot a graph of time Vs height obtained from the height sensors. Data will show variation in the heights at the time of brake application which is shown clearly in fig.4. Calculate from the difference in the heights the axle twisting by known method. Here the forward movement (in X-direction towards vehicle front) of the front axle is neglected as the values obtained are very minimal. Plot the values of axle twisting (as data acquired in RTDA) on the graph.
11. Draw a trend line for the axle twisting obtained (preferably with polynomial expression) for avg (average value obtained) and max value of the axle twisting for max (maximum value obtained). These values are used for calculation or analysis in Adam's Analysis to obtain brake steer value as (0avg) for average brake steer of the vehicle or (0max) for maximum brake steer of the vehicle in degrees.
12. Average brake steer of the vehicle (0avg) and maximum brake steer of the vehicle (0max) values further to be used for fine tuning of suspension components like stiffness of leaf spring (3), spring span, dimensions of spring mounting bracket(ll), or steering components like position of gearbox mounting(7), length/offset of pitman arm(6), length of draglink(4), position of
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draglink-pitman ball joint(5), position of steering arm-draglink ball joint(9), offset of steering arm(2) etc.
In method of testing of brake steer by evaluation of axle twist due to leaf spring wind-up height sensor fixture (12) is fitted in such a way that the axis of height sensor fixture is perpendicular to the axis of front axle beam (10), and both the height sensors should be placed at a equal distance from the center-line of the base plate of fixture (12).
Method of testing of brake steer by evaluation of axle twist due to leaf spring wind-up involves instrumentation of the vehicle with height sensor (L sensor), speed sensor, brake switch and data acquisition system like micro EEP-11.
Method of testing of brake steer by evaluation of axle twist due to leaf spring wind-up involves deriving straight line trends or parabolic trends or logarithmic trends or exponential trends or polynomial trends, most preferably polynomial trend are used for the purpose.
The test method is simple and cost effective and can be performed on front rigid axle suspension vehicle. In this method a fixture is developed to mount the height sensors on the front axle. Two height sensors are used and mounted on the fixture (where the fixture projects height sensor - one in front of the front axle and one at the rear of the front axle). In initial condition height sensed by the two sensors are equal from the ground surface. At the time of braking due to leaf spring wind-up front axle twists causing change in the heights, which is sensed by the height sensors. This change is calculated in terms of axle twist and by using Adam's analysis brake steer is calculated.
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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.
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WE CLAIM
1. Method of testing brake steer on vehicle comprising of following steps:
a) Identifying the vehicle having front rigid axle suspension on which testing to be performed;
b) Mounting height sensor fixture on front axle;
c) Instrumentation of vehicle for measuring various parameters;
d) Acquiring data by running vehicle and applying the pedal force up to just before limit of adhesion at various speeds with engine disconnected state;
e) Removing the spikes from the raw data;
f) Plotting graph time Vs. height;
g) Calculating axle twisting angle by known method from the heights obtained;
h) Plotting graph time Vs. twist angle on the same graph of step (f);
i) Drawing the trend line of the graph of step (h) and finding the slope or
finding the maximum twist angle;
j) Determining brake steer by Adam's Analysis by using twist angle
obtained by step (i).
2. Method of testing brake steer on vehicle as claimed in claim 1 wherein said
height sensor fixture is fitted on front axle beam in such a way that the axis of
height sensor fixture is perpendicular to the axis of front axle beam.
3. Method of testing brake steer on vehicle as claimed in claims 1 and 2wherein
said height sensors are placed at equal distance from the center-line of the base
plate of said fixture.
4. Method of testing brake steer on vehicle as claimed in claims 1 to 3 wherein
instrumentation of the vehicle involves provision of height sensor, speed sensor,
brake switch and data acquisition system.
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5. Method of testing brake steer on vehicle as claimed in claim 1 wherein vehicle is running at 40 to 80 Kmph.
6. Method of testing brake steer on vehicle as claimed in claim 1 wherein said brake force should be applied instantaneously.
7. Method of testing brake steer on vehicle as claimed in claims 1 and 6 wherein steering wheel should be held stationary tight at the time of brake application till the vehicle becomes stand still.
8. Fine tuning of the steering components in relation to suspension components by using results obtained by a method of testing brake steer on vehicle as claimed in claims 1 to 7.
9. Method of testing brake steer on vehicle substantially as herein described with reference to accompanying drawings.
Date this 11th day of July 2007

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Abstract
Method of testing brake steer on vehicle
This invention relates to method of testing of brake steer on vehicle by evaluation of axle twist due to leaf spring wind-up, comprises instrumentation of the vehicle to acquire height measurements of the front axle w.r.t ground (at fixed point on the front and fixed point on the rear of the front axle) continuously by real time data collection (RTDC) technique in dynamic running condition and when brakes are applied. In addition to this, instrumentation of vehicle is also required for acquisition of data for time, speed and deceleration. The heights obtained are plotted on the graph time Vs height and with the help of difference in heights at the time when the vehicle is under braking condition, axle twist is calculated by known method. Above said axle twisting is used to calculate brake steer by using Adam's Analysis. Finally fine tuning of suspension and steering components is done by using brake steer value.