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. Ashfaque Ahmed Ansari and
Mr. Manoj S. Walkikar
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.

This application discloses an improvement and/or modification of the invention described and disclosed in the complete specification filed together with the patent application numbered as 2864/MUM/2009 and is filed with an intent of obtaining a patent of addition.
FIELD OF INVENTION
This 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. This invention also relates to the testing apparatus in which Electronic Control Unit (ECU) for any Electric Power Steering System can be simulated and data generation can be carried out for development & fine-tuning purposes based on actual road load simulations.
BACKGROUND OF THE 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 manufactures (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 and hence is very complex scenario.
• This complexity is widened if the Steering system under consideration is Electric Power Steering system (EPS), for the reason that different OEMs would like to have their own control strategies based on various Input electronic signal requirements and the actuation mechanisms.
In view of the above, a steering system testing apparatus capable of simulating the full vehicle loading and its interactions with various vehicle hardware & control 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 order to overcome the said drawbacks, full vehicle steering system mainly concentrating on steering system testing is devised. However, the same test bench when adopted suitably can be used for various other component / system testing which are also parts of the said invention and will become apparent from the description and claims.
OBJECTS OF INVENTION
The main object of this invention is to provide a full vehicle steering system level testing apparatus.

Yet another object is to provide a testing apparatus of a steering system with 5-axis of loading, wherein the first axis being the Steering torque, second & third being a loading system which applies load /force to the steering system simulating the road-surface interactions ,fourth & fifth being the actuators for simulating vertical suspension/tyre vertical movements.
Yet another object is to provide a testing apparatus of steering system, wherein the second & third actuators are being connected to the vehicle steering arm ends with suitable adaptors 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.
Yet another object is to provide a testing apparatus of steering system, wherein the fourth & fifth actuators are connected to the vehicle system to simulate the vertical loads / movements generated during various events of steering / cornering.
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 generic testing apparatus, which can be used to test the vehicle steering system at a much accelerated way 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 is to simulate various control signals to be sent to vehicle EPS ECU so that ,steering system functionalities can be simulated similar to the ones noticed on vehicle during road load data collection.
Yet another object is to generate various vehicle signals to be sent to vehicle EPS ECU to understand the behaviour of the steering system under different control strategies.
Yet another object is to acquire the electronic signals from EPS ECU and motor controlling the steering assistance in either case i.e. during electronic signal generation or simulation for further processing on the data used to develop the EPS control strategies.
SUMMARY OF INVENTION
The present invention describes a testing apparatus of a steering system, in which a full vehicle (10) can be mounted on a test bed (16) 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 (10) on the test bed, suitable vehicle mounting structures are provided as described in the embodiments. For the purpose of simulating actual road load conditions in vehicle having Electric Power Steering System, a generic Controller, Data Acquisition System & Signal Generator is provided.
The combination of a Generic controller (38), Data acquisition system (36), Signal generator (37) and power supply (35) with the existing 5-axis Servo-Hydraulic Steering System is capable of:
• Simulating various control signals that can be sent to EPS ECU (Electronic control unit) so that, steering system functionalities can be simulated similar to the ones noticed during actual vehicle running.

• Generate vehicle signals to understand the behavior of EPS system under different EPS ECU control strategies and hence finalize / optimize the algorithm.
• Helps in understanding the behavior of EPS ECU under various fault conditions (eg. Over-voltage, under-voltage, reverse polarity, etc.).
BRIEF DESCRIPTION OF DRAWINGS
The elements of the present invention will be explained in greater detail herein-after with reference to an illustrative embodiment shown in the accompanying drawings, in which:
FIG. 1 shows a perspective view of 5-axis Servo-Hydraulic Steering System,
according to present invention.
FIG. 2 Schematic block of system level test Rig for EPS system.
FIG. 3 shows a graph illustrating a steering stiffness with respect to input torque.
FIG. 4 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. 5 shows a graph illustrating overly of target signal and response signal.
FIG. 6 shows a graph illustrating overlay of road data and the rig simulated time
series data.
FIG. 7 shows a graph illustrating EPS Torque sensor output voltage vs. Motor
current.
FIG. 8 shows a graph illustrating EPS Torque Sensor Output Voltage, Motor
Current against time series data
DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENTS:
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, Fig.l View of 5-axis Servo-Hydraulic Steering System.

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 & Fig.2, a testing apparatus of a steering system in accordance to the present invention consists of a surface Plate or test bed (16) on which the entire set-up is located upon. At least two vertical actuators (15, 16) are mounted on mounting structures (14, 18) and at least two lateral actuators (2, 29) are mounted on mounting structures (1, 23). A rotary actuating unit (7) is provided on mounting structure (27) & (25). The testing apparatus also comprises vehicle support structures (12, 13) and a rotary unit (28) to the Steering wheel connecting module along with a pedestal (26). The system further comprises a generic controller (38) along with a data acquisition system (36), signal generator (37) and power supply unit (35).

A steering torque generating unit (28) (in this case, a rotary servo Actuator) is provided on a support structure (6) 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 figure. 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. In case of the electronic steering system, the entire set-up as explained above is connected to the generic controller (38), power supply unit (35) and data acquisition system (36) as specified in Fig .2.
The generic controller (38) with data acquisition system (36) and power supply (35) is capable of generating various vehicle level signals that are used in operation of Electric power steering system (EPS). Human machine interfacing (HMI) (39) input is connected to the data acquisition system (36).
Data acquisition system (36) is coupled with existing Servo-hydraulic rig controller with input channels & output channels. The Independent power supply unit (35) is used to simulate the actual vehicle battery conditions.
The generic testing apparatus can simulate and/or generate various control signals to be sent to the vehicle EPS ECU so that the steering system functionalities can be simulated on a test bench similar to the ones obtained during road load data collection.

The generic testing apparatus, is capable of acquiring the electronic signals from EPS ECU and motor controlling the steering assistance during electronic signal generation or simulation for further processing on the data used to develop the EPS control strategies. Based on the above, the data obtained from the test rig can be used for finalizing the ways the EPS system shall behave to inputs from the driver. By doing so, the behavior of the steering system can be predicted well before fitting on the vehicle and any anomalies arising out during different maneuvering events can be corrected / modified. This helps in safety of not only the test engineers but also the safety of various electronic parts.
The generic testing apparatus is capable of determining the various faults that can be simulated and its effect on steering system performance.
The method of mounting of vehicle and preparation for testing comprises the steps of placing the vertical actuator structures (14, 15) by maintaining a distance (actuator centre to centre) equal to the steering rack & pinion tie rod outer ball joints centre distance. The vehicle (10) is located on the structures (12, 13) as shown and clamped suitably with the rear portion of the vehicle freed so that the extension rod passes through the vehicle from the rotary actuator (7). The rotary actuator (7) location is determined based on the drive of the vehicle (i.e. Left / Right hand side) and the output shaft angle (9, 28) is locked to the driver steering wheel as shown. Lateral actuators (2, 29) along with the load sensors (33, 34) are mounted on extended tie rods (11, 24) one side of which is connected to the actuators (2, 29) and other side is connected to the vertical adapters (20, 21) respectively. The entire set-up as explained above is connected to generic controller (38), power supply unit (35) and data acquisition system (36). The generic controller (38) is coupled with a signal generator (37) capable of simulating various kinds of vehicle level signals. The data acquisition system (36) is coupled with an existing Servo-hydraulic rig controller with input channels & output channels. The independent power supply unit (35) is to simulate the actual vehicle battery conditions.

The test apparatus as described above 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
Motor Current, Motor Voltage & EPS Torque sensor voltage measurement at various vehicle conditions Vehicle / Aggregate
9 Durability Steering System Level Endurance Test based on Road profile Vehicle / Aggregate / Sub-System / Component
10
Steering System Level Fatigue Test

11
Any other Chassis part Durability based on road profile

12 Strength Steering System Input torque strength test

Performance of the steering system:
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.
Test set up: The subject vehicle (10) as mentioned in Fig. 1 is clamped on the claimed steering test apparatus constraining vehicle movements during loading . Steering arm (31, 32) is mounted on the 2 vertical adaptors (20, 21) at LH & RH side of front wheels to which 2 vertical actuators (15, 16) are connected. Tie rod members / linkages of steering system are connected to the steering arm ends to which on other side 2 lateral actuators (2, 29) are connected for steering reaction forces. 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). 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 measure /recorded as shown in fig. 3.
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. Steering wheel input is given through rotary actuator (7) coupled with torque generating unit as shown in fig. 1. 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. 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:
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.
Strain gauges were 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. Location of the strain gauge was kept at mid of tie rod / linkages in view of 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. 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 programme was developed with this commercially available damage editing software. This accelerated programme 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 Steering arm (31 & 32) is mounted on the 2 vertical adaptors ( 20 & 21) at LH & RH side of front wheels to which 2 vertical actuators (15 & 16) are connected. 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. 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. PID tuning of these actuators kept constant throughout the durability test program of the test vehicle .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) . A drive to the signal is given considering loading requirements of the vehicle aggregates / components for the safety of aggregates while deriving the test rig response. Frequency response function is achieved by giving a known excitation and a measure a subsequent response from the signals. Steering system consist of the steering linkages which are correlated to each other. As every drive signal has correlation with each other, non linearity exists in the system which results 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. Accuracy of this transfer function based on coherence of every data channel. For a good transfer function, coherence of every data channel kept more than 0.7 as shown in fig. 4.
Once the transfer function form between steering test apparatus and vehicle, the target time series kept as a reference signal for the drive signals by the servo actuators. These reference signals are achieved through iterative software. Since high correlation exist between the steering systems, nos. of iteration carried out to

achieve the target signals. Refer Fig. 5 & Fig. 6 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 programme of the vehicle.
Steering reaction forces on each tie rod is related to wheel acceleration and the lateral load coming on the steering arm while cornering/braking. Steering forces are also effect of the steering torque / steering angle input given by the driver. Steering reaction forces is achieved through both vertical and lateral actuators on both sides of the front wheels. 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.
e) EPS Motor Current Characterization: Using the test set-up in Figure 1 &
Figure 2, EPS Motor Current and EPS Torque Sensor output voltage can be
measured and plotted to understand the EPS functionality. Refer Fig. 7.

Also, in Fig. 8 shows the EPS Motor Current & EPS Torque Sensor output voltage w.r.t. time. This plot shows whether the motor current signal is following the torque sensor signal signature. If motor current is following the torque sensor signal signature, then torque sensor signal could be used as a reference for motor current in the control algorithm. Otherwise, effect of other signals on motor current needs to be evaluated for control algorithm.

WE CLAIM
1. A testing apparatus for steering system for simulating actual road conditions and interaction with various subsystems, 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 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), 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 (19) connected to a vertical adaptors (20) & (21) provided with the steering arm ends (31) & (32) on the inner side and connected to tie rod members (11) & (24) respectively on the other end, a rack and pinion end of the steering system is connected to 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,
a generic controller (38) with data acquisition system (36), signal generator (37) and power supply (35) are coupled to said testing apparatus.
said data acquisition system (36) is coupled with a servo-hydraulic rig controller with input channels & output channels of said testing apparatus.
2. The testing apparatus according to claim 1, wherein generic controller is coupled with a signal generator to simulate and/ or generate various control signals to be sent to vehicle EPS ECU.
3. The testing apparatus according to claim 1, wherein the generic controller coupled with a signal generator acquires the electronic signals from EPS ECU and

motor controlling the steering assistance during electronic signal generation or simulation for further processing on the data used to develop the EPS control strategies.
4. The testing apparatus according to claim 1, wherein the generic controller is coupled with a signal generator to generate vehicle signals to understand the behavior of EPS system under different EPS ECU control strategies and hence finalize / optimize the algorithm.
5. The testing apparatus according to claim 1, wherein generic controller is coupled with a signal generator to determine the behavior of EPS ECU under various fault conditions.
6. The testing apparatus according to claim 1, wherein the generic controller is coupled with a signal generator to test the vehicle steering system under high acceleration and to provide the same loads as the system undergoes during actual road testing.
7. The testing apparatus according to claim 1, wherein the generic controller coupled with a signal generator is capable of testing of any chassis mounted parts to simulate the actual road profile.
8. The testing apparatus according to claim 1, wherein the generic controller coupled with a signal generator is capable of simulating the complete road profile collected during various steering manoeuvring events.

9. The testing apparatus according to claim 1, wherein the generic controller coupled with a signal generator can be suitably adapted as a 2-poster for testing of complete vehicle front portion for structural durability by simulating the actual road load data.