FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See Section 10; rule 13)
TITLE OF THE INVENTION
An improved power steering system for higher fuel efficiency and steering
performance.
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. Benz Pa u lose Mr. Sumit Panigrahi
Both 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 describes the invention and the manner in which it is
performed.

Field of invention:
This invention related to the power steering system used in passenger vehicles and more particularly energy efficient power steering system.
Summary of the invention:
The invention is aimed at improving fuel efficiency and CO2 emission of an automobile. The improvement is achieved through optimization of power steering performance in different speeds and reducing the overall parasitic load on engine drive ultimately. The working principle involves an electro viscous clutch in a hydraulic system which transfers optimum drive to power steering pump from engine driven belt. At low speed, when the power steering performance is more important, it allows maximum drive to the pump to generate less steering effort. At high speed, where power steering performance is relatively redundant, it reduces the drive to pump for minimum power assistance and thereby reduces the parasitic load on engine abruptly. In summary, the improvement in fuel efficiency and CO2 emission can be achieved without any compromise in power steering performance.
The actuation of viscous couple is done though a PWM (pulse width modulator) controller device which receives electrical signals from vehicle speed sensor, steering angle sensor and lateral acceleration sensor. Based on the requirement of power assistance at different speed, steering input and vehicle dynamics input, logic is fed to controller which determines the required slip characteristics of viscous clutch. Power steering pump receives the drive from engine belt as per the slip determined by the controller logic.
The present invention discloses an improved power steering system for higher fuel efficiency and steering performance comprising at least one belt drive system (5) connecting engine pulley (1) and an auxiliary drive pulley (2); at least one power steering pump (9) connected to said auxiliary drive pulley (2) through viscous coupling device (6) for transferring the drive; at least one input drive means (7) of said viscous coupling (6) is connected to the engine drive (1) and at least one output drive means (8) of said viscous coupling (6) is connected to the power steering pump (9); at least one

engaging device in said viscous coupling device (6) for engaging said input drive means (7) with output drive means (8) of said viscous coupling device (6); and plurality of sensing means for sensing various parameters and supplying the input signals to at least one controller (14) configured for selecting and controlling the desired action of said viscous coupling device (6).
Various sensing means comprises of speed sensor (11) to determine the vehicle speed, the steering angle senor (12) attached to said steering wheel (10) for measuring the steering angle and Yaw rate sensor (13) to provide lateral acceleration (latac) of the vehicle to monitor the vehicle dynamics input, provides input signals to a pulse width modulator (PWM) controller (14) for controlling the desired action of said electro viscous coupling (6).
The PWM controller (14) is configured for assessing drive pattern through the measured signals from all the said sensors and generating and providing necessary electronic signals to electro viscous coupling (6) to trigger the electrical actuation of the electromagnetic clutch of said viscous coupling device (6).
The driver's intended action as steering angle input is identified by the steering wheel (10) and column units attachment. The PWM controller (14) is configured to vary the electrical signal at the electro viscous coupling (6) for corresponding variation of viscous fluid travel to working chamber inside the viscous coupling casing on the basis of different form of drive patterns, to generate different slip conditions/ efficiencies between input (7) and output (8) drives of said viscous coupling (6).
The input drive (7) is coupled to said engine drive (1) for continuous rotation with engine rpm and said output drive (8) rotates at a relatively reduced rpm as determined by the assigned slip characteristics of the coupling device to reduce the overall load on engine to increase fuel efficiency and reduce C02 emission.
The engaging device is a electro-magnetic clutch is configured to be electrically actuated when triggered by the output signal from the controller (14). The PWM

controller (14) is configured to receive input signals from speed sensor (11), steering angle sensor (12), yaw rate sensor (13), EMS ECU (15) and battery terminal by electronic communication (16) through hard wiring harness or CAN system.
The Method for higher fuel efficiency and steering performance comprises of following steps
• capturing all the signals by the micro controller and determining different drive patterns of the vehicle;
• generating a unique signal for each drive pattern as per the predefined logic fed in microcontroller;
• selecting and controlling the desired action of said viscous coupling device (6) through
said controller (14);
generating necessary slip between input drive (7) and output drive (8) of electro viscous coupling (6) used for transferring engine drive to power steering pump on the basis of the captured input signals as per plurality of predetermined slip characteristics established in increasing order based on varying speed and steering angle of the automobile in order to generate the highest power assistance in the low speed conditions by varying the load on the engine.
Object of the invention:
The main object of this invention is to provide a system for improving fuel
efficiency and reducing CO2 emission with the reduction in parasitic load on the
engine,
Another object of this invention is to provide a system for optimizing power steering
performance based on different driving maneuvers and driver's needs.
Yet another object of this invention is to provide a system for smoother and safer
control of steering due to dampening effect of hydraulic fluid inside electro viscous
coupling.
Additionally, another object of this invention is to provide a system comprising
electro viscous coupling and controller unit for reducing the parasitic loads on all

engine auxiliary devices such as alternator and further increasing fuel efficiency of the automobile.
Statement of Invention;
Accordingly the present invention discloses an improved power steering system for
higher fuel efficiency and steering performance comprising
at least one belt drive system (5) connecting engine pulley (1) and an auxiliary drive
pulley (2);
at least one power steering pump (9) connected to said auxiliary drive pulley (2) through
viscous coupling device (6) for transferring the drive;
at least one input drive means (7) of said viscous coupling (6) is connected to the engine
drive (1) and at least one output drive means (8) of said viscous coupling (6) is
connected to the power steering pump (9);
at least one engaging device in said viscous coupling device (6) for engaging said input
drive means (7) with output drive means (8) of said viscous coupling device (6); and
plurality of sensing means for sensing various parameters and supplying the input
signals to at least one controller (14) configured for selecting and controlling the desired
action of said viscous coupling device (6).
The Method for higher fuel efficiency and steering performance comprises of following steps of
• capturing all the signals by the micro controller and determining different drive patterns of the vehicle;
• generating a unique signal for each drive pattern as per the predefined logic fed in microcontroller;
selecting and controlling the desired action of said viscous coupling device (6) through said controller (14);
generating necessary slip between input drive (7) and output drive (8) of electro viscous coupling (6) used for transferring engine drive to power steering pump on the basis of the captured input signals as per plurality of predetermined slip characteristics established in increasing order based on varying speed and steering angle of the

automobile in order to generate the highest power assistance in the (ow speed conditions by varying the load on the engine.
Brief description of the invention:
In accordance with the present invention, the set-up involves introduction of an electro magnetic viscous coupling connected to power steering pump. The free rotating end of the clutch of coupling is fitted to the engine driven belt.
When the vehicle is driven at low speed (measured by speed sensor), the electromagnetic coil is deactivated and there is a maximum fluid travel to working chamber of coupling. Thus it generates maximum slip in the coupling. It leads to maximum torque transfer with maximum efficiency and there is maximum drive to PS pump from engine driven belt through the clutch. The power assistance is maximized which results in less steering effort. At higher speed, the electro-magnetic coil is energized and fluid travel to working chamber ceases. It leads to minimum slip (up to @ Xl%) condition and there is a limited drive transfer possible to PS pump. Thus power assistance to steering is reduced which results in reduction in parasitic load on engine. This in-effect improves fuel efficiency. Similarly, multiple slip generation is possible for different speed condition other than idling and maximum speed as boundary conditions. Higher sfip or efficiency will generate higher power assistance. The fuel efficiency will be improved when the vehicle runs with lower power assistance. The change in steering effort for varying speeds is dampened due to hydraulic viscous fluid system resulting in smoother, safer and controlled steering-ability even at higher speeds. But the response time for the change is not perceived by the driver.
The engagement of the clutch can be controlled by a PWM controller unit interfaced to the engine EMS, steering angle , yaw angle (for latac generation) or any other related system. Based on the requirement of power assistance at different speed and steering input, logic is fed to controller which determines the required slip characteristics of viscous clutch. This logic determines the slip or transmission efficiency required for the electro viscous clutch. Power steering pump receives the drive from engine corresponding to the assigned slip or transmission efficiency and revolves in specific

rpm based on the intended logic. The inputs of the logic are drawn from speed sensor, steering angle sensor and yaw rate sensor. The logic determines the required slip value from the predefined slip reference table for entire speed range and steering angle input. The controller sends the signal to electro viscous couple to generate the slip corresponding to the slip reference table. The logic involves both the major parameters (speed and steering angle) to determine the required slip of viscous fluid, hence driver intended power assistance can be closely translated through this logic. In order to have a safety override, yaw rate sensor provides vehicle dynamics input in terms of lateral acceleration.
Brief description of drawings:
According to the present invention,
Figure 1 shows the layout of power steering system with viscous coupling in accordance
with the invention
Figure 2 shows the PWM (Pulse Width Modulator) controller diagram
Figure 3 shows the flow chart of the logic for required power assistance/slip of viscous
coupling at different drive patterns
Detailed description of the 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.
Now referring to fig 1, in accordance with the present invention, the system layout of power steering system with electro viscous coupling mainly comprises; a belt drive (5) system connecting engine pufley (I) with alternator pulfey (3), idler pulley (4) and an auxiliary drive pulley (2). A power steering pump (9) is fitted with the said auxiliary drive pulley (2) via an electro viscous coupling device (6). The steering wheel (10) and column units are attached to identify the driver intended action as steering angle input. The vehicle speed is determined by speed sensor (11) and the steering angle is measured by steering angle senor (12) attached to said steering wheel (10). Yaw rate sensor (13)

is required to provide lateral acceleration (latac) of the vehicle to monitor the vehicle dynamics input. Ail the measured parameters provide input signal to a pulse width modulator (PWM) controller (14) which controls the desired action of said viscous coupling (6). The PWM controller (14) assesses drive pattern through the measured signals from all the said sensors and generates necessary electronic signal to viscous coupling (6). The output signal from the controller (14) triggers the electrical actuation of the electro-magnetic clutch present in the viscous coupling device (6). Based on different form of drive patterns, the PWM controller (14) varies the electrical signal at the electro viscous coupling (6) and accordingly the viscous fluid travel to working chamber inside the viscous coupling casing varies. This in effect generates different slip conditions/ efficiencies between input (7) and output (8) drives of said viscous coupling (6). The input drive (6) is always connected to said engine drive (1) and rotates continuously with engine rpm. However, the output drive (8) of electro-viscous coupling (6) rotates at a relatively reduced rpm as determined by the assigned slip characteristics of the coupling device. As the power steering pump (9) is connected to said output drive (6), it also rotates at the desired reduced rpm. Thus the overall load on engine due to the rotation of the power steering pump reduces effectively and fuel efficiency is improved. Improved fuel efficiency results in reduction in CO2 emission.
Referring to fig 2,
The said PWM controller (14) takes input signal from speed sensor (11), steering angle sensor (12), yaw rate sensor (13), EMS ECU (15) and battery terminal by electronic communication (16) through hard wiring harness or CAN system. PWM controller consists of a programmable micro controller unit which operates as per defined logic and sends output signal to its driver unit. The same signal is transferred to viscous coupling to generate the desired slip characteristics. Micro controller unit should be selected to have the least response time to transfer the desired signals. The unit can also be integrated to engine management system (EMS) to associate with vehicle input parameters. In this case, the signals which are already available in EMS ECU (15) need not be separately captured from independent sensor units. Based on different driving patterns, logic is created and fed into the micro controller chip. The same logic prescribes the desired signals to generate different slips in the electro viscous coupling

(6). The range of slips generated is from XI (preferably 20%) to X6 (preferably 85%). XI is decided by the viscous loss present in the viscous coupling. The slip or efficiency of the viscous coupling (6) for a conventional power steering pump with drooping flow characteristics is defined by (N1-N2)/N1 where N1 and N2 are the maximum rpm and actual rpm of the pump. All the said slip vales (XI, X2, ..., X6) have been assigned based on the above formula.
The maximum slip values are assigned for low pump rpm and minimum for high pump rpm. This characteristic is typical for drooping flow effect. Here the slip is meant for the volume working fluid transfer inside the working chamber. If there is less slip then there will be less volume of transfer of fluid and torque rransferd will be less. The loss is basically utilized for high speed maneuvers where power assistance can be kept minimized. Similarly, X6 is decided by the maximum efficiency of the viscous coupling. In this state, there is highest possible fluid travel to provide maximum torque transfer to output drive (8) of viscous coupling (6). Hence, this state generates the highest power assistance which is utilized in the low speed conditions. The above mentioned slip range(Xl to X6%) is entirely dependent on the design of electro viscous coupling (6), Also, the program in the micro controller is completely calibrateable for different range of automobiles performing varied drive scenarios.
Referring to fig 3,
The micro controller captures all the signals and determines different drive patterns of the vehicle. For each drive pattern, a unique signal is generated as per the defined logic and electro viscous coupling (6) generates necessary slip accordingly. Based on varying speed and steering angle of the automobile, 6 different slip characteristics (XI, X2, ..., X6) have been established in increasing order (preferable in step of+15%). The intermediate slips are also calibrateable and defined by the design of the fins on the electro viscous coupling (6).
The entire logic has been demonstrated through the flow chart shown in the figure. If either battery state or ignition state of the automobile is OFF, then PWM controller (14) does not operate and generates no output signal through its driver unit. If both the states are ON, then engine rpm and vehicle speed should be checked. If the vehicle is

stationary and engine rpm is at idling condition, then electro viscous coupling (6) generates X6 % slip for steering angle more than 50 deg, because in this state, maximum power assistance is desired. For steering angle less than 50 deg, the vehicle is not intended to move further and does not require power assistance, hence XI% slip i.e. slip equivalent to viscous loss is assigned. If the vehicle speed is less than 20 kph, maximum slip (X6 %) is assigned irrespective of steering angle input. This pattern resembles to city driving conditions where maximum assistance is always desired. For speed range (20 to 49 kph) where the steering angle input is less than 100 deg, a relatively lesser assistance is desired compared to maximum assistance (X6 % slip) because the rolling friction is relatively less. Hence, a slip of X4 % is assigned for this pattern. But if the steering input is higher than 100 deg, a higher assistance is required to smoothly maneuver the vehicle. However, the assistance need not be the maximum (X6 % slip) considering higher speed of the car, but it should be definitely higher than the assistance corresponding to X4 % slip. Therefore, X5 (higher than X4, but less than X6) %slip is assigned for this condition. On the similar ground, X3 (X3 < X4) % slip is assigned for steering angle more than 200 deg and speed range (50 to 79 kph). And X4% slip for angle less than 200 deg is defined. If the vehicle is driven in a speed more than 80 kph, minimum assistance (XI % slip) is desired for the least rolling friction condition and the slip is assigned irrespective of the steering input. This demonstrates the highway drive pattern where adequate steering assistance is already available. All the above strategies hold true only when the latac of the vehicle is less than Y (preferably 0.5g). In this condition, the vehicle is assumed to be in control of the driver and the driver is able to adjust with the change in steering parameters. However, if latac exceeds Y, then a relatively lesser and adequate assistance corresponding X2 (greater than XI, but less than X3) % slip is required. This condition overrides all the above conditions and restrains the slip to X2 % irrespective of vehicle speed and steering angle input. This is important and necessary considering the overall safety of the driver. In this condition, the vehicle does not tend to over steer and the driver is expected to control the vehicle with improved steer ability (X2 % slip). This logic is based on the drive experience and can be tuned for different driving behaviors. In accordance with this invention, the slip characteristics can be programmed for different flow Vs RPM curves. Even a positive displacement pump can also be proposed

for this invention and a simpler logic can be established. Thus the additional cost for drooping flow effect and time for tuning the flow characteristics can also be saved.
Advantages
Improvement in fuel efficiency can be achieved as the power assistance is based on requirement only and the engine is not always loaded with the power steering pump. Power steering performance can be optimized based on assistance requirements at different speeds. Driver's intended power assistance can be closely translated through the extensive controller logic.
The logic for determining required slip characteristics also receives vehicle dynamics input. In unsafe maneuvers, the logic gives priority to slip characteristics assigned for high lateral acceleration. This logic overrides all other speed dependent and comfort parameters and provides overall safety for the driver. Electro viscous coupling can provide multiple slip characteristics. Hence it will provide wide & vast options while tuning the power assistance based on different vehicle inputs.
The losses and maximum efficiency of electro-viscous coupling can be used as the boundary conditions for high and low speed power assistance respectively resulting in maximum utility.
In no condition, the vehicle is driven without any assistance to steering compared to conventional electro magnetic clutch arrangement. The power steering feel is not compromised.
Damping effect observed in steering effort for varying speeds due to hydraulic viscous fluid system, resulting in smoother, safer and controlled steering-ability even at higher speeds, unlike conventional ON/OFF logic in electromagnetic clutch coupled power steering system.
At very high speed, the issue of steering lightness leading to unsafe maneuvers is observed on most cars fitted with conventional power steering. If the steering is tuned to higher effort for high speed performance, there is a compromise in on-center and parking effort performance. However, steering lightness at high speed can be addressed with calibration, without implementing drooping flow characteristics.

The electro viscous coupling can be used as an additional device to the convention power steering pump or as an engine accessory along with a positive displacement hydraulic pump. The logic can be established differently for both the systems. As power steering pump does not need to run always, the pump life increases and cost of ownership of power steering fluid reduces compared to conventional power assisted pump.
Similar concept can be applied for all auxiliary devices driven by engine belt so that it can further benefit in reducing overall fuel efficiency of the automobile. Separate logics can be established for different devices to perform independent of engine rpm and based on requirement only.
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. An improved power steering system for higher fuel efficiency and steering
performance comprising
at least one belt drive system (5) connecting engine pulley (1) and an auxiliary drive
pulley (2);
at least one power steering pump (9) connected to said auxiliary drive pulley (2)
through viscous coupling device (6) for transferring the drive;
at least one input drive means (7) of said viscous coupling (6) is connected to the
engine drive (1) and at least one output drive means (8) of said viscous coupling (6)
is connected to the power steering pump (9);
at least one engaging device in said viscous coupling device (6) for engaging said
input drive means (7) with output drive means (8) of said viscous coupling device
(6); and
plurality of sensing means for sensing various parameters and supplying the input
signals to at least one controller (14) configured for selecting and controlling the
desired action of said viscous coupling device (6).
2. The power steering system as claimed in claim 1 wherein various sensing means comprises of speed sensor (11) to determine the vehicle speed, the steering angle senor (12) attached to said steering wheel (10) for measuring the steering angle and Yaw rate sensor (13) to provide lateral acceleration (latac) of the vehicle to monitor the vehicle dynamics input, provides input signals to the pulse width modulator (PWM) controller (14) for controlling the desired action of said electro viscous coupling (6).
3. The power steering system as claimed in any one of the preceding claims wherein the PWM controller (14) is configured for assessing drive pattern through the measured signals from all said sensors and generating and providing necessary electronic signals to electro viscous coupling (6) to trigger the electrical actuation of the electro-magnetic clutch of said viscous coupling device (6).

4. The power steering system as claimed in any one of the preceding claims wherein the driver's intended action as steering angle input is identified by the steering wheel (10) and column unit attachment.
5. The power steering system as claimed in any one of the preceding claims wherein said PWM controller (14) is configured to vary the electrical signal at the electro viscous coupling (6) for corresponding variation of viscous fluid travel to working chamber inside the viscous coupling casing on the basis of different form of drive patterns, to generate different slip conditions/ efficiencies between input (7) and output (8) drives of said viscous coupling (6).
6. The power steering system as claimed in any one of the preceding claims wherein said input drive (7) is coupled to said engine drive (1) for continuous rotation with engine rpm and said output drive (8) rotates at a relatively reduced rpm as determined by the assigned slip characteristics of the coupling device to reduce the overall load on engine to increase fuel efficiency and reduce CO2 emission.
7. The power steering system as claimed in any one of the preceding claims wherein said engaging device is a electro-magnetic clutch is configured to be electrically actuated when triggered by the output signal from the controller (14).
8. The power steering system as claimed in any one of the preceding claims wherein said PWM controller (14) is configured to receive input signals from speed sensor (11), steering angle sensor (12), yaw rate sensor (13), EMS ECU (15) and battery terminal by electronic communication (16) through hard wiring harness or CAN system.
9. The Method for higher fuel efficiency and steering performance comprises of following steps
• capturing all the signals by the micro controller and determining different drive patterns of the vehicle;

• generating a unique signal for each drive pattern as per the predefined logic fed in microcontroller;
• selecting and controlling the desired action of said viscous coupling device (6) through said controller (14);
• generating necessary slip between input drive (7) and output drive (8) of electro viscous coupling (6) used for transferring engine drive to power steering pump on the basis of the captured input signals as per plurality of predetermined slip characteristics established in increasing order based on varying speed and steering angle of the automobile in order to generate the highest power assistance in the low speed conditions by varying the load on the engine.
10. The improved power steering system for higher fuel efficiency and steering performance substantially as herein described with reference to accompanying drawings.