FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See Section 10; rule 13)
TITLE OF THE INVENTION 5-Axis Servo-hydraulic Steering System Level Test Apparatus
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. Hari Srinivas Babu Aggarapu,
Mr. Swapnil R. Salunkhe and Mr. Manoj S. Walkikar
AH 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
The present invention relates to the testing apparatus of a steering system, in particular to a testing apparatus in which a full vehicle can be mounted on a test bed with suitable mounting fixtures having loading devices for applying to the steering system, driver's steering torque and a loading device for generation of road surface reaction forces arising out of the vehicle tire interaction with the road and the movement of tires with respect to the suspension system being considered.
BACKGROUND OF INVENTION
Conventionally, Steering system testing apparatus is basically required to simulate the interaction of not only various steering system components with each other but also other systems' interaction. It also shall provide the possible deterioration in steering component performance over a period of time as in real world usage conditions. However, most of the existing steering system testing apparatus available are capable of either testing the steering system as an aggregate or as an individual component. When tested as an individual component, the influence of other systems on the subject steering components cannot be understood, also with predicted level of reliability as a component, steering system level validation needs to be done on a full vehicle on actual road. In view of the above:
• Steering System Design sufficiency cannot be predicted as a whole, unless tested on a vehicle on actual roads / test tracks.
• Accommodation of design changes during vehicle development phase is time consuming, since cross-talk of one system's design change cannot be predicted unless tested as a complete system, which as of now is to be done on a vehicle on actual roads / test tracks.
• For most of the original equipment manufacturers (OEMS), where the complete steering system is not sourced from a single supplier, it becomes responsibility of the OEMs to test the complete steering system as a whole.

In view of the above, a steering system testing apparatus capable of simulating the full vehicle loading and its interactions with various systems was required. Also, a steering system testing apparatus which can reduce the design validation time by simulating the actual road load conditions as in field was required to be developed. In the past, various attempts have been made to address the above drawbacks in steering system testing. Mr.Tatsuya Sagiyama,Mr.Fumihiko Baba,Mr.William J Lenger,Mr.Niel R Petersen ,Mr.Paul S Petersen & Mr. Joseph W .Daley etc teaches testing apparatus, wherein various methods of testing steering systems & various methods of loading & constraining a vehicle under various simulated conditions are proposed. But none of these refers to any method/s for testing of a steering system as a whole considering the vehicle approach on a test bed.
OBJECTS OF INVENTION
The main object of this invention is to provide a steering system testing apparatus for simulating full vehicle loading and its interactions with various systems. Another object is to provide a testing apparatus for steering system with 5-axis of loading, wherein the first axis being the Steering torque, second and third axis being a loading system which applies load /force to the steering system simulating the road-surface interactions, fourth and fifth axis being the actuators for simulating vertical suspension/tyre vertical movements.
Yet another object is to provide a testing apparatus of steering system, capable of simulating the complete road profile collected during various steering manoeuvring
events.
Yet another object is to provide a testing apparatus, capable of accommodating a complete vehicle on the test bed.
Yet another object is to provide a testing apparatus, which can accommodate vehicles ranging from a very small passenger car to the biggest available truck.

Yet another object is to provide a generic testing apparatus, which can be used to test the vehicle steering system at a much accelerated way (how) but yet provide the same loads as the system undergoes during actual road testing.
Yet another object is to provide a generic testing apparatus, which can be suitably adopted for testing of any chassis mounted parts to simulate the actual road profile.
Yet another object is to provide a generic testing apparatus, which can be suitably adopted as a 2-poster for testing of complete vehicle front portion for structural durability by simulating the actual road load data.
Yet another object of the present invention is to asses the structural performance of the steering system of the vehicle in terms of fatigue and durability.
Yet another object is to simulate the service load on complete vehicle steering system, aggregates or components of steering system on a single test bed.
SUMMARY OF INVENTION
In order to overcome above drawbacks, a vehicle steering system mainly concentrating on steering system testing is devised. The embodiments herein provide a 5-axis servo-hydraulic steering testing apparatus in which a complete vehicle is mounted on a test bed with suitable mounting fixtures having loading devices for applying to the steering system, driver's steering torque and a loading device for generation of road surface reaction forces arising out of the vehicle tire interaction with the road and the movement of tires with respect to the suspension system being considered. For the purpose of mounting the vehicle on the test bed, suitable vehicle mounting structures are provided as described in the embodiments.
A testing apparatus for steering system for simulating actual road conditions and interaction with various subsystems, comprising a test bed having plurality of mounting structures and loading devices for applying load to steering system. A first axis loading device having a rotary actuator connected to the steering wheel

through an extension rod at one end, said extension rod is located on a pedestal unit of vehicle. One end of the rotary actuator is connected to an extended split unit (9) & (28), the other end is coupled to a vehicle steering wheel. A torque generating unit 28 is provided on a support structure 6 of said testing apparatus. A second and third axis loading device includes vertical actuators 15 and 16 for connecting to the vehicle steering arm ends with vertical adaptors 20 and 21. A vertical actuators (15) & (19) are connected to said vertical adaptors (20) & (21) provided with the steering arm ends (31) & (32) on the inner side and connected to the tie rod members (11) & (24) respectively on the other end. A rack and pinion end of the steering system is connected said vertical adopters. A fourth and fifth axis loading device includes a pair of lateral actuators 2 and 29 connected to other end of tie rod members 11 and 24 by means of which the steering reaction forces are applied during the tests.
However the test bed according to present invention can be suitably adopted for various other component/system testing which are also parts of the said invention and will become apparent from the description and claims.
The above and other objects ,test methods, special features, advantages of the present invention becomes apparent from the following descriptions and claims, taking in to consideration the attached drawings.
BRIEF DESCRIPTION OF DRAWINGS
Fig. 1 shows a perspective view of 5-axis Servo-Hydraulic Steering System,
according to present invention.
FIG. 2 shows a graph illustrating a steering stiffness with respect to input torque.
FIG. 3 shows a graph illustrating coherence and cross talk between signals during
simulation of service load on the steering system test apparatus, according to
present invention.
FIG. 4 and FIG. 5 shows a graph illustrating a reference signal and response signal .

to analyze the simulation accuracy for every signal and subsequently all signals in the target time series.
DETAILED DESCRIPTION OF INVENTION
Referring now to the drawing 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 embodiments herein provide a testing apparatus for steering system for simulating actual road conditions and interaction with various subsystems is as shown in FIG. 1. The steering testing apparatus comprising a test bed 16 having plurality of mounting structures and loading devices for applying load to steering system. A first axis loading device having a rotary actuator 7 connected to the steering wheel 3 through an extension rod at one end, said extension rod is located on a pedestal unit 26 of vehicle. One end of the rotary actuator 7 is connected to an extended split unit (9) & (28), the other end is coupled to a vehicle steering wheel. A torque generating unit 28 is provided on a support structure 6 of said testing apparatus. A second and third axis loading device includes vertical actuators 15 and 16 for connecting to the vehicle steering arm ends with vertical adaptors 20 and 21. A vertical actuators (15) & (19) are connected to said vertical adaptors (20) & (21) provided with the steering arm ends (31) & (32) on the inner side and connected to the tie rod members (11) & (24) respectively on the other end. A rack and pinion end of the steering system is connected said vertical adopters. A fourth and fifth axis loading device includes a pair of lateral actuators 2 and 29 connected to other end of tie rod members 11 and 24 by means of which the steering reaction forces are applied during the tests.
As shown in the Fig.l, a testing apparatus of a steering system includes a test bed or surface Plate 16 on which the entire set-up is located upon. The vertical actuators (15) & (19) are mounted on mounting structures (14) & (18). The lateral actuators (2) & (29) are mounted on the mounting structures (1) & (23). A rotary actuating

unit (7) is provided on mounting structure (27) & (25). The vehicle support structures (12) & (13) and a rotary unit (28) to the Steering wheel connecting module along with a pedestal (26).
A steering torque generating unit (28) (in this case, a rotary servo Actuator) is provided on a support structure (6) is capable of rotating with a motor at an angle of 90°.The rotary actuator (7) is equipped with Angle and torque sensors (30) for controlling the steering angle and torque during testing. The end of the rotary actuator is connected to an extended split unit (9) & (28), other side of which is coupled to a vehicle steering wheel. The subject test vehicle (10) is clamped on vehicle clamping structures (12) & (13) using suitable method to arrest vehicle movements during loading (i.e. torque application and lateral loading on the steering wheel and tie rods respectively) of the vehicle. The vehicle support structures (12) & (13) are clamped on the surface plate (16) as indicated in the figure. The 2-vertical actuators (15) & (19) are connected to the vertical adaptors
(20) & (21) as shown in the FIG. 1. In turn, the end of the vertical adaptors (20) &
(21) are provided with the steering arm ends (31) & (32) on the inner side and connected to the tie rod members (11) & (24) respectively on the other end. The end of the tie rod members are connected to the two lateral actuators (2) & (29) by means of which the steering reaction forces are applied during the tests.
Method of Mounting of Vehicle & preparation for testing comprises of comprises steps of placing the vertical actuator structures (14) & (15) by maintaining a distance (actuator centre to centre) equal to the steering rack and pinion tie rod outer ball joints centre distance. Mounting vehicle (10) on the support structures (12) & (13) and clamping suitably with the rear portion of the vehicle freed so that the extension rod passes through the vehicle from the rotary actuator (7). Finalizing rotary actuator (7) location based on the drive of the vehicle (i.e. Left / Right hand side) and locking the output shaft angle (9) & (28) to the driver steering wheel. Mounting lateral actuators (2) & (29) along with the load sensors (33) & (34) on extended tie rods (11) & (24) one side of which is connected to the actuators (2) &

(29)and other side connected to the vertical adopters ( 20) & (21) respectively and applying load on the steering system for testing a complete vehicle or aggregate or sub-system or components.
Shown below is a table 1.1 illustrating different tests that can be performed using the said test apparatus: Test apparatus as specified can be used for performing the following tests on either a complete vehicle or as an aggregate or a sub-system.

S.no. Type of Test Test Description On Complete Vehicle / Aggregate / Sub-System/ Component Level
1 Performance Steering Effort at Various vehicle conditions Vehicle / Aggregate
2
Steering System Friction Cascading Vehicle
3
Rack & Pinion Gear Characterization & Finalization. Vehicle
4
System Dead Band / Backlash measurement Vehicle
5
Power Steering Oil
Temperature Measurement Vehicle / Aggregate
6
Steering System level Stiffness measurement

7
Steering Wobble Simulation, Measurement Vehicle
8 Durability Steering System Level Endurance Test based on Road profile Vehicle / Aggregate / Sub-System / Component
9
Steering System Level Fatigue Test

10 Any other Chassis part Durability based on road profile
11 Strength Steering System Input torque strength test

The object of the present invention is to asses the structural performance of the steering system of the vehicle in terms of fatigue & durability. The loading conditions are typically determined from measurements on actual vehicle road tests. Object is to simulate the service load on complete vehicle steering system, aggregates or components of steering system (both passenger cars and commercial vehicles) on a claimed single test bed. The methodology enables us to determine the service load environment which corresponds to a predefined number of kilometers of customer usage. The description of some the tests that are performed are as follows:
Performance of the steering system:
Test set up: The subject vehicle (10) as mentioned in FIG. 1 is clamped on the claimed steering system test apparatus constraining vehicle movements during loading. The steering arm (31 & 32) is mounted on the pair of vertical adaptors 20 & 21 at LH & RH side of front wheels to which two vertical actuators 15 & 16 are connected. The tie rod members/linkages of steering system are connected to the steering arm ends to which on other side two lateral actuators (2 & 29) are connected for steering reaction forces. The rotary actuator (7) with torque generating unit (28) with steering angle and torque sensor is connected to steering wheel of test vehicle. In case of Power steering, Rated Hydraulic power assistance is given from external supply.

a) Steering system level stiffness measurement:
Both the front wheel ends (LH & RH) side coupled with vertical adaptors (20 &21)
are blocked by Lateral actuators (2 & 29) with a known loading requirement in tension and compression mode. The steering wheel is rotated from one end to other end through rotary actuator (7) equipped with steering angle and torque sensors (30). Steering angle / steering torque values are measured /recorded as shown in fig-2
b) Steering system friction cascading:
Test vehicle is mounted as mentioned above on the steering test apparatus. Both the front wheel ends (LH & RH) side coupled with vertical adaptors (20 &21) are kept in no load condition. The steering wheel input is given through rotary actuator (7) coupled with torque generating unit as shown in fig. 1. The steering wheel is rotated from one end to other. Steering angle / steering torque values are recorded. Steering column is removed from steering gear unit. Input to the steering wheel is given and respective values of steering angle and torque are recorded. The difference between the two values (with steering gear coupled and without steering gear coupled) gives the frictional resistance of a system.
C) Structural Durability / Endurance test:
Vehicle instrumentation: Two accelerometers are placed on the steering arm or at suitable location on both front wheels of the vehicle (LH and RH) to measure the wheel accelerations under different conditions of the road track. The strain gauges are located on the tie rod / linkages of the steering system to measure the strains / load generated on the road track on the tie rod / linkages. The strain gauges are kept at mid of tie rod / linkages for stress concentration. These strain value define the load in the tie rod. However, in addition these strains will be related to steering angle and friction between tires. The vehicle components are instrumented and load data containing different steering maneuvers for laboratory tests can now be obtained from test vehicles on customer- correlated proven ground. The loading environment is obtained in a statistical sense. The mix of proving ground surfaces

that produces the same loading environment can be determined. For good response of the data, Load data captured on road profiles consist of different maneuvers. Vehicle life is determined by the fatigue of the individual components of the steering system, and fatigue is proportional to cyclic strain levels. The road load data are then analyzed with commercially available software. An accelerated durability program is developed with this commercially available damage editing software. This accelerated program is used as a target time series for the simulation on the test rig.
Simulating service load on the steering system test rig apparatus:
The subject vehicle (10) as mentioned in FIG. 1 is clamped on the claimed steering test apparatus constraining vehicle movements during loading. The steering arm (31 & 32) is mounted on the 2 vertical adaptors (20 & 21) at LH and RH side of front wheels to which 2 vertical actuators (15 & 16) are connected. The tie rod members / linkages of steering system (with strain gauging) are connected to the steering arm ends to which on other side 2 lateral actuators (2 & 29) are connected to simulate steering reaction forces. The rotary actuator (7) with torque generating unit (28) with steering angle and torque sensor is connected to steering wheel of test vehicle. To simulate the wheel acceleration, 2 accelerometers are placed in the same location (on wheel spindle) as placed while collecting data on the vehicle on customer correlated proven ground. The 5 actuators ( 2 lateral actuators ( for tie rod forces, 2 vertical actuators for wheel displacement and rotary actuator for steering angle and torque ) are used as a drives to achieve the accelerated target time series. These drives are controlled through PID control (proportional gain derivative gain, integral gain) of the servo actuators. The PID tuning of these actuators are kept constant throughout the durability test program of the test vehicle .The transducers / data channels (strain gauge, steering angle, steering torque, accelerometers) are calibrated to get the proper response from the individual sensor. Understanding the test system and the response from the test vehicle is important and it is achieved through Frequency response function of the test system and the test vehicle (steering system). Drives to the signal are given considering loading requirements

of the vehicle aggregates / components for the safety of aggregates while deriving the test rig response. The frequency response function is achieved by giving a known excitation and a measure a subsequent response from the signals. The steering system consists of the steering linkages which are correlated to each other. As every drive signal has correlation with each other, non linearity exists in the systems which result in high Coherence between two transducer / signal. To establish the steady behavior of the system, a transfer function is established between test apparatus and the test vehicle by giving a random signal. The accuracy of this transfer function is based on coherence of every data channel. For a good transfer function, coherence of every data channel is kept more than 0.7 as shown in FIG. 3.
Once the transfer function is formed between steering test apparatus and vehicle, the target time series is kept as a reference signal for the drive signals by the servo actuators. These reference signals is achieved through iterative software. Since high correlation exist between the steering system, number of iterations are carried out to achieve the target signals. FIG. 4 and FIG. 5 shows an graph illustrating an overlay of reference signal and response signal to analyze the simulation accuracy for every signal and subsequently all signals in the target time series.
Accuracy of these derived drive signal is specified by comparing the relationship with the customer correlated proven ground. These drive signals is used as a durability test program of the vehicle. The above test method can be used for performing fatigue test till the life of the vehicle. The steering reaction forces on each tie rod are related to wheel acceleration and the lateral load coming on the steering arm while cornering/braking. The steering forces are also the effect of steering torque / steering angle input given by the driver. The steering reaction forces are achieved through both vertical and lateral actuators on both sides of the front wheels. The drive given by each actuator is in consisting with the steering functionalities.

Level of acceptance:
There should not be any crack / failure to the steering system . All the components in the steering system shall meet functional requirements at the end of the test, d) Steering system input torque strength test:
Test vehicle is mounted as mentioned above on the steering test apparatus. In case of power steering, Power assistance port is kept open to atmosphere. Rotation of the steering gear is restricted in straight head position of a vehicle by blocking the front wheel ends by giving suitable loading conditions by both lateral actuators (2 &29) in tension and compression mode. Input Torque to the Steering wheel is given through rotary actuator (7) with torque generating unit both in clockwise and anticlockwise direction till failure occurs.
ADVANTAGE:
The present invention provides a testing apparatus for steering system for simulating the complete road profile collected during various steering manoeuvring events. The generic testing apparatus can be used for testing of any chassis mounted parts to simulate the actual road profile.
• The testing apparatus according to present invention includes 5-axis of loading, wherein the first axis is the Steering torque, second and third axis being a loading system which applies load /force to the steering system simulating the road-surface interactions, fourth and fifth axis being the actuators for simulating vertical suspension/tyre vertical movements.
• The testing apparatus according to present invention accommodates a complete vehicle on the test bed ranging from a very small passenger car to the biggest available truck.
• The testing apparatus according to present invention tests the vehicle steering system at a much accelerated way and applies loads in such a way as the system undergoes during actual road testing.

• It provides a generic testing apparatus, which can be suitably adopted as a 2-poster for testing of complete vehicle front portion for structural durability by simulating the actual road load data.
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.

WE CLAIM
1. A testing apparatus for steering system for simulating actual road conditions and
interaction with various subsystems, comprising;
a test bed having plurality of mounting structures and loading devices for applying load to steering system;
a first axis loading device having a rotary actuator connected to the steering wheel through an extension rod at one end, said extension rod is located on a pedestal unit of vehicle; one end of the rotary actuator is connected to an extended split unit (9) & (28), other end is coupled to a vehicle steering wheel, a torque generating unit 28 is provided on a support structure 6 of said testing apparatus,
a second and third axis loading device having a vertical actuators 15 and 16 for connecting to the vehicle steering arm ends with an vertical adaptors 20 and 21 an vertical actuators (15) & (19) connected to said vertical adaptors (20) & (21) provided with the steering arm ends (31) & (32) on the inner side and connected to the tie rod members (11) & (24) respectively on the other end, a rack and pinion end of the steering system is connected said vertical adopters,
a fourth and fifth axis loading device having a pair of lateral actuators 2 and 29 connected to other end of tie rod members 11 and 24 by means of which the steering reaction forces are applied during the tests.
2. The testing apparatus according to claim 1, wherein said first axis loading device includes a steering angle and torque controllers.
3. The testing apparatus according to claim 1, wherein said extension rod is located on a pedestal unit of vehicle to avoid the load of extension rod on the steering wheel.
4. The testing apparatus according to claim 1, wherein said steering torque
generating unit (28) rotates at an angle of 90 ° by a motor.

5. The testing apparatus according to claim 1, wherein said rotary actuator (7) is equipped with an angle and torque sensors (30) for controlling the steering angle and torque during testing.
6. The testing apparatus according to claim 1, wherein said test vehicle (10) is clamped on vehicle clamping structures (12) & (13) on test bed 16 to arrest vehicle movements during loading (i.e. torque application and lateral loading on the steering wheel and tie rods respectively) of the vehicle.
7. The testing apparatus according to claim 1, wherein said vertical adapters are provided for simulating the lateral forces on the steering system arising out of the vehicle's tyre interaction with the road surface during Various manoeuvring events with very high frequencies.
8. The testing apparatus according to claim 1, wherein said second and third axis loading system is provided for applying load /force to the steering system for simulating the road-surface interactions;
9. The testing apparatus according to claim 1, wherein said fourth and fifth axis loading device is provided for simulating vertical suspension/tyre vertical movements.

10. The testing apparatus according to claim 1, wherein said fourth and fifth axis loading system includes an lateral actuators 2 and 29 for connecting to the vehicle steering system to simulate the vertical loads / movements generated during various events of steering / cornering.
11. The testing apparatus according to claim 1, wherein, said plurality of mounting structures includes vehicle support structure 12 and 13 for supporting the vehicle to be tested, a mounting structure 14 and 18 with vertical actuators 15 and 19, a mounting structures 1 and 23 with lateral actuators 1 and 29 and a mounting structure 27 and 25 with rotary actuator 7.

12. The testing apparatus according to claim 1, wherein the second and third loading devices are connected respectively to the vehicle tie rods to detect the steering loads which are identical but opposite in sings when compared.
13. The testing apparatus according to claim 1, wherein the steering torque applied to the steering wheel is opposite to the direction of loading of the second and third actuators.
14. The testing apparatus according to claim 1, wherein said steering testing apparatus can accommodate vehicles ranging from a very small passenger car to the biggest available truck.
15. The apparatus according to claim 1, wherein various tests such as performance, durability and strength test etc can be preformed by using said test apparatus
16. The testing apparatus according to claim 1, wherein accelerometers are
provided on the steering arm or at suitable location on both front wheels of the
vehicle (LH and RH) to measure the wheel accelerations under different conditions
of the road track.
17. The testing apparatus according to claim 1, wherein strain gauges are located on the tie rod / linkages of the steering system to measure the strains / load generated on the road track on the tie rod / linkages.
18. The testing apparatus according to claim 1, wherein said test apparatus can be used for testing a complete Vehicle or Aggregate or Sub-System or Component Level.
19. A method for testing of a steering system, comprising steps of;
Placing the vertical actuator structures (14) & (15) by maintaining a distance' (actuator centre to centre) equal to the steering rack and pinion tie rod outer ball joints centre distance;

Mounting vehicle (10) on the support structures (12) & (13) and clamping suitably
with the rear portion of the vehicle freed so that the extension rod passes through
the vehicle from the rotary actuator (7);
Finalizing rotary actuator (7) location based on the drive of the vehicle (i.e. Left /
Right hand side) and locking the output shaft angle (9) & (28) to the driver steering
wheel;
Mounting lateral actuators (2) & (29) along with the load sensors (33) & (34) on extended tie rods (11) & (24) one side of which is connected to the actuators (2) &
(29)and other side connected to the vertical adopters ( 20) & (21) respectively and
Applying load on the steering system for testing a complete vehicle or aggregate or
sub-system or components.
20. The testing apparatus for steering system as herein described with reference to accompanying drawings.