FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See Section 10; rule 13)
TITLE OF INVENTION
Apparatus For Calibrating Wheel Force Transducers
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
INVENTOR
Shailesh P Badadhe, an 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 specification particularly describes the invention and the
manner in which it is to be performed.

FIELD OF INVENTION
The present invention relates to calibration rig set up for Wheel force transducer.
BACKGROUND OF INVENTION
Wheel Force Transducer or the WFT is a device that is used to measure the various forces acting on the wheel during the motion of the vehicle. Its purpose is to analyze the various forces coming on the wheel during the vehicle motion. This used to analyze the forces on the wheel so that the vehicles can be designed optimally according to these actual forces.
The forces acting on the wheel change continuously during the motion the vehicle. The wheel experiences three forces and three moments namely Fx, Fy, Fz, Mx, My and Mz. The WFT setup is used to determine these forces and moments and a graph is obtained between those and time, for a particular time interval. These values from the WFT are fed into softwares like ADAMS, etc which are used to design the vehicle optimally as the actual forces coming on the various components can be known.
The WFT setup has a recommended service life of 2 years after which it is to be calibrated so that it continues to measure the force accurately. It is a very important process because the prototype of a vehicle is being designed on the basis of the forces given by the WFT. If these are not accurate, it would lead to a faulty prototype and hence all slaves would be designed faultily. To prevent this, it is of utmost importance to calibrate the setup once every 2 years.
The basic principle being used in the calibration operation of the WFT setup is that we are applying some forces on the wheel which we are obtaining with the help of tri-axial master load cells and then we are comparing it with the forces being shown


by the actual WFT setup. Hence, a calibration curve can be obtained between the known applied forces and those obtained from the WFT.
The point of application of all the forces and moments is taken as the bottom-most part of the tyre so as to provide a condition close to the actual road setup and apply the forces on the wheel as they come in actual conditions.
The applied forces Fx, Fy and Fz can be obtained directly from then load cells while the moments Mx, My and Mz can be calculated as follows:
Mx (moment about the direction in which Fx force is being applied) = FyxR
My (moment about the direction in which Fy force is being applied) = FxxR
Mz (moment about the direction in which Fz force is being applied) = FyxR
(Mz is same as Mx because we calculate Mz by changing the calibration of the encoder by fixing the datum as 90 degrees away from the original datum) Here R is the effective radius at which the forces are being applied with respect to axis of the tyre.
The above 6 components are being compared with those shown by the WFT and hence WFT can be calibrated.
A single WFT setup has 4 load cells which sense the total load coming on the wheel in all the three directions. Each load cell gives three force outputs. The net force in a single direction is found out by their resultant on each load cell.


SUMMERY OF INVENTION
According to present invention an apparatus for calibrating Wheel force transducers comprising, a wheel force transducer (WFT) attached to a wheel, said WFT connected to a first adaptor, a second adaptor rotatably connected to a vertical supporting member using a connecting means, a tri-axial load cell attached to said second adaptor, said first adaptor with WFT screwed to said load cell, a loading system having a vertical moving platform, a horizontally slidable table resting on said vertical moving platform and at least one hydraulic jack to apply force on said platforms.
BRIEF DESCRIPTION OF DRAWINGS
Figure 1. Cross sectional view of the apparatus
Figure 2. Cross sectional plan view
Figure 3. Sectional detail of rotating arrangement
DETAILED DESCRIPTION OF INVENTION
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.
The setup has been prepared for the static calibration of the WFT. Various standard size of wheels of car to truck with WFT can be calibrated in the mentioned setup been used. The wheel with WFT has been mounted to a vertical member using adaptors. Two adaptors are used to connect the WFT to vertical member. A tri axial master load cell is disposed between said adaptors. Referring to the figures, a WFT assembly (1) mounted on tire rim (14) connected to first adaptor (2). The WFT (1) with adaptor (2) is rotatably mounted on a vertical support member(6). For rotatably mounting the WFT with adaptor a mounting arrangement (5) is used. The rotatable mounting arrangement is having an outer circular plate (20), intermediate ring plate


(21) and inner circular plates (22) respectively. The outer plate is having a stepped ring portion (24) and a bearing (23) is fitted outer diameter of the stepped portion. The intermediate ring plate (21) is rotating on the bearing (24) located on the outer plate (20) and outer periphery is having a flange (25) to accommodate the inner circular plate (22). The bearing (23) located inside of the intermediate ring plate. Inner circular plate (22) is having a steeped portion (26). The inner circular plate
(22) is located inside the flange (25) of intermediate ring plate (21) and stepped portion (26) of inner plate located in inside of stepped ring portion (24) of the outer plate. The inner plate is connected to the outer plate thereby holding the bearing and intermediate plate. The flanged portion of intermediate plate is connected to a second adaptor (3). Through holes are provided on the outer plate to insert alien bolt to connect the intermediate plate to step adaptor. A tri-axial load cell (4) is connected to the second adaptor (3). The adaptor (2) with WFT (1) is screwed to the load cell (4) so that the load cell is sandwiched between said adaptors. By the above arrangement the tire with WFT can be rotated to fix in four different positioned to test all load cell located in the WFT. For fixing in different locations the second adaptor is fixed to the outer plate using connectors (27).
For applying loads, a loading platform is located below the tire for applying vertical loads (Z direction). The loading platform includes a horizontally sliding table (8) and vertically movable platform (7). The table is mounted in the slots (10) provided on the platform to slide horizontally (X and Y direction). To avoid slip on the tyre a rough zig-zag surface (11) is made on top of sliding table. The loading platform is supported on three hydraulic cylinders (12) located 120 degree to each other and guided by four vertical pillars (9) at corners. These cylinders are fitted to single hand pump so as to maintain equal stroke length of all the cylinder in Z-axis. Three cylinders are used to balancing the vertical force acting on the tire. Another hydraulic cylinder (13) is located horizontally on the sliding table of the loading platform to apply horizontal loads in X and Y direction. The vertical member (6), the vertical cylinders (12), vertical pillars (9) and support for horizontal cylinder (13) are support on a base plate rigidly fixed to the ground (15). For twin wheel


WFT calibration different adaptor is used to connect WFT to the rotatable mounting arrangement.
Method of calibrating WFT
The rotatable mounting arrangement is fixed according to the tyre radius such that the bottom portion of the tyre will be located above loading platform keeping a minimum clearance distance between each other so as to rotate wheel freely for WFT calibratation. The WFT is mounted on the wheel rim. The roller bearings are attached to the outer dia of stepped portion of the outer plate. Intermediate plate is fixed to the bearing such that the bearing is located inside the bore of the intermediate plate. Now the outer plate is located inside the flanges of the intermediate plate and screwed to the outer plate. A stepped adaptor is screwed to flanged area of intermediate plate. The intermediate plate locked between outer and inner plate and rotating on bearing located in outer diameter of the stepped outer plate. A tri-axial load cell is attached to the stepped adaptor. The stepped adaptor can rotate to any angle and can be fixed in position by screwing to the outer plate. The WFT with adaptor is now connected to the tri-axial load cell. Orient the WFT to remove the angle error. At this position the WFT with rotatable arrangement is fixed to the vertical member. Actuating vertical cylinder thereby the loading platform apply load on the tyre vertically. The WFT values compared with mater load cell force value for different varying loads in increasing and decreasing order. For calibrating the X and Y force the sliding table is actuated horizontally in X and Y direction using a horizontal cylinder accordingly and the loading acting on WFT and the load cell are compared. The calibration procedure is repeated on the four point of WFT by rotating the wheel in 90° at each time.
Calibrating Force (Fx) and Torque (My)
The longitudinal force i.e. Fx had been applied by the arrangement as described above. For this, the hydraulic jack has been mounted on a fixture so as to align its axis horizontally in the longitudinal direction. The amount of force applied had been measured with the help of a tri-axial load cell which had been mounted between


step adaptor & wft adaptor. The applied force, Fx can thus be known and compared with the corresponding value of the WFT.
The applied moment My can be made known by the formula,
My = Fx x R
This gave the value of My which had been compared by the value shown by the WFT and the calibration curve was thus obtained for My.
Setup measuring the Force (Fy) and Torque (Mx & Mz)
The above setup is done to calculate the lateral force, Fy and moments Mx and Mz.
The application and determination of this force is similar to that of the Fx force
except that its orientation is different. In this, the force is applied in the direction as
shown in the above arrangement i.e. directed perpendicular to the plane of the
wheel.
The moments Mx and Mz were given by the formula,
Mx = Mz = Fy x R
The moments obtained here were compared with their corresponding values by the WFT and hence a calibration curve had been obtained.
Setup measuring the Force (Fz)
For the application of the vertical force Fz, components. So to get accurate Fz value,
the setup such that in the above arrangement is free from lateral & longitudinal
forces by dismantling hydraulic jack from sliding table. The force is measured from
the tri-axial load cell.
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 in so far as they come within the scope of the invention as claimed or the equivalents thereof.


WE CLAIM
1. An apparatus for calibrating wheel force transducers comprising, a wheel force transducer (WFT) attached to a wheel, said WFT connected to a first adaptor, a second adaptor rotatably connected to a vertical supporting member using a connecting means, a tri-axial load cell attached to said second adaptor, said first adaptor with WFT screwed to said load cell, a loading system having a vertical moving platform, a horizontally slidable table resting on said vertical moving platform and at least one hydraulic jack to apply force on said platforms.
2. The apparatus for calibrating wheel force transducers as claimed in claim 1, wherein said connecting means includes a outer circular plate having a stepped ring, a bearing located at the periphery of outer side of said stepped ring, an intermediate ring plate having a flange located at the periphery of outer side, said bearing located inside said intermediate ring plate, an inner circular plate having a stepped portion, said inner circular plate located inside of said flange of intermediate ring and said stepped portion located inside of stepped ring of said outer circular plate, and said second adaptor connected to the flange of said intermediate ring plate.
3. The apparatus for calibrating wheel force transducers as claimed in claim 2, wherein said intermediate plate located between said outer and inner circular plate and rotating on said bearing.
4. The apparatus for calibrating wheel force transducers as claimed in claim 2, wherein said inner circular plate connected to said outer circular plate.
5. An apparatus for calibrating wheel force transducers as claimed in claim 2, wherein said outer circular plate is connected to the vertical supporting member.


6. The apparatus for calibrating wheel force transducers as claimed in claim 1, wherein said vertical moving platform guided on vertical pillars and said horizontally sliding platform moving on slots provided on said vertical moving platform.
7. The apparatus for calibrating wheel force transducers as claimed in claim 1, wherein three hydraulic cylinders are located below said loading system for applying vertical loads and a hydraulic cylinder located horizontally and applying load on sliding table.
8. The apparatus for calibrating wheel force transducers as claimed in any one of the preceding claims wherein said vertical supporting member, vertical pillars and hydraulic jacks are fixed to ground.
9. The apparatus for calibrating Wheel force transducers substantially as herein described with reference to accompanying drawings.


ABSTRACT
Apparatus For Calibrating Wheel Force Transducers
An apparatus for calibrating Wheel force transducers comprising, a wheel force
transducer (WFT) attached to a wheel, said WFT connected to a first adaptor, a second
adaptor rotatably connected to a vertical supporting member using a connecting means,
a tri-axial load cell attached to said second adaptor, said first adaptor with WFT
screwed to said load cell, a loading system having a vertical moving platform, a
horizontally slidable table resting on said vertical moving platform and at least one
Figure 1
hydraulic jack to apply force on said platforms.