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 energy efficient hydraulic power steering system
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. KULKARNI ANAND VIJAY, Mr. GAJANKUSH JAYAPAL 1, Mr. SONCHAL
CHIRAG P, Mr. PAWAR SANDEEP C and Ms. WAKCHAURE PRADNYA S
All 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 describes the invention and the manner in which it is performed.

FIELD OF INVENTION
This invention relates to electronically controlled power steering pump and more particularly relates to energy efficient methodology to control power steering pumps.
BACKGROUND OF THE INVENTION
Primary function of a steering system in a vehicle is to achieve angular motion of the front wheels to negotiate a turn. This is done through linkages and steering gear that convert the rotary motion of the steering hand wheel into angular motion of the front road wheels. Additionally, steering system
a) Provides directional stability to the vehicle when traveling in straight line.
b) Ensures perfect rolling motion of the road wheels at all times
c) Facilitates steering returnability after completing a turn
Based on handwheel torque study, it is observed that steering effort required is highest in parking manoeurvres and at slower speeds, wherein actually assistance for steering is required. In order to enhance driving comfort, assisting leverage is provided to the steering so that driving fatigue can be eliminated. Such systems are classified as "Power steering system". Typically power assistance to steering can be provided using hydraulic system, electric system or electromechanical system.
A hydraulic assisted power steering system (HPAS) has a steering pump which is directly driven from the engine continuously. During a typical highway drive which usually consists travelling on straight roads for large portion, assistance from steering pump remains unused for 76% of the time. However, the constantly rotating steering pump continues to consume the energy from the prime mover i.e. engine. Thus, the present HPAS system is not energy efficient and keeps on drawing power from the primary source which leads to more fuel burning and emitting exhaust gas.
OBJECT OF THE INVENTION
The main object of the present invention is to make the conventional power steering systems more energy efficient.
Another object of the present invention is to reduce the emission of harmful exhaust gases. Yet another object of the present invention is to control the power steering system based on a driver input.

Yet another object of the present invention is to control the power steering system based on
the steering angle.
Yet another object of the present invention is to control the power steering system based on
the vehicle speed and steering angle.
The objectives are achieved by providing an electronically controlled means to the power steering system that provides leverage only on driver demand. Thus, it ensures that unnecessary dissipation of valuable energy generated from IC engine is saved whenever traveling on straight ahead roads. This enables reduction of parasitic auxiliary load on the engine thereby not only saving valuable fossil fuel but also reducing the emissions.
SUMMARY OF THE INVENTION:
Energy efficient HPAS system consists of an electronically controlled hydraulic pump which provides leverage to the driver only when demanded. System consists of a microcontroller that continuously monitors demand for any steering assistance by the driver based on the vehicle speed and/or steering angle and /or driver input and provides control signal to turn on / off the paired leverage mechanism.
This invention discloses an energy efficient hydraulic power steering system comprising at least one handwheel (1) connected to the rack and pinion (4) through a pinion gear on steering column (2);
at least one controller (17) for receiving and analyzing vehicle speed and input signals from the steering angle sensor (3) mounted on the steering column (2) for producing a controlsignal for controlling the engaging device for engagement or disengagement; wherein said controller (17) is configured for scanning and/or selecting plurality of operating modes on the basis of predetermined/preset values and programme;
at least one power steering pump (7) controlled through said controller (17) is driven by the engine (13) to pump fluid from the fluid reservoir (5) to energize valve spool inside the rack housing.
An energy efficient hydraulic power steering system also comprising
at least one handwheel (1) connected to the rack and pinion (4) through a pinion gear on
steering column (2);

at least one power steering pump (7) driven by the engine (13) to pump fluid from the fluid reservoir (5) to energize valve spool inside the rack housing and returns back to said fluid reservoir;
at least one controller (17) configured for direct initial activation of said power steering pump (7) for a predetermined time interval form each engine start timing and after said predetermined time interval receiving and analyzing vehicle speed and input signals from the steering angle sensor (3) mounted on the steering column (2) for producing a control signal for controlling the engaging device for engagement or disengagement; wherein said controller (17) is configured for scanning and/or selecting plurality of operating modes on the basis of predetermined/preset values and programme for subsequent activation / deactivation of said power steering pump (7).
The steering system having plurality of operating modes comprises of at least three manual selection modes and at least one default/automatic selection mode.
The engaging device is a electromagnetic pairing device. The controller (17) is an electronic controller. The power steering pump (7) draws fluid from the fluid reservoir (5) and the pressurized fluid is supplied to the rack through a high pressure hose (8) to energize the valve spool inside the rack housing and said fluid from the spool returns to the reservoir through the return hose (9).
The power steering pump (7) is directly activated by selection of first manual mode skipping scanning by said controller (17) and overriding all other modes.
The controller (17) deactivates said power steering pump (7) on receiving the feedback of the second manual mode selection.
The controller (17) is configured for deactivating said power steering pump (7) when the steering angle is found within the preset range of threshold band and activating said power steering pump (7) when the steering angle is found outside the preset range of threshold band on detection of third manual mode.

The controller (17) is configured for switching to default/automatic selection mode when none of the manual mode is detected and scanning for vehicle speed and steering angle for comparing the vehicle speed with predetermined vehicle speed value and steering angle input signal with predetermined threshold band; wherein when said vehicle speed is found below a predetermined vehicle speed value and/or said steering angle is not found within the specified range then said power steering pump (7) is activated and when said vehicle speed is found above a predetermined vehicle speed value then said power steering pump (7) is controlled on basis of said steering angle values alone.
The controller (17) is configured for switching to default/automatic selection mode when none of the manual mode is detected and scanning for vehicle speed and steering angle for comparing the vehicle speed with predetermined vehicle speed value and steering angle input signal with predetermined threshold band range; wherein when said vehicle speed is found zero for a predetermined period and constant steering angle is recorded then said power steering pump (7) is deactivated and when any consequent change in steering angle and/or vehicle speed is detected then said power steering pump (7) is activated.
The controller (17) is configured for deactivating said power steering pump (7) after a predetermined time if said vehicle speed is found above a predetermined vehicle speed value and said steering angle is found within the specified threshold band range
STATEMENT OF INVENTION:
Accordingly the present invention discloses an energy efficient hydraulic power steering system comprising
at least one handwheel (1) connected to the rack and pinion (4) through a pinion gear on steering column (2);
at least one controller (17) for receiving and analyzing vehicle speed and input signals from the steering angle sensor (3) mounted on the steering column (2) for producing a control signal for controlling the engaging device for engagement or disengagement; wherein said controller (17) is configured for scanning and/or selecting plurality of operating modes on the basis of predetermined/preset values and programme;

at least one power steering pump (7) controlled through said controller (17) is driven by the engine (13) to pump fluid from the fluid reservoir (5) to energize valve spool inside the rack housing.
The present invention further discloses an energy efficient hydraulic power steering system comprising
at least one handwheel (1) connected to the rack and pinion (4) through a pinion gear on steering column (2);
at least one power steering pump (7) driven by the engine (13) to pump fluid from the fluid reservoir (5) to energize valve spool inside the rack housing and returns back to said fluid reservoir;
at least one controller (17) configured for direct initial activation of said power steering pump (7) for a predetermined time interval form each engine start timing and after said predetermined time interval receiving and analyzing vehicle speed and input signals from the steering angle sensor (3) mounted on the steering column (2) for producing a control signal for controlling the engaging device for engagement or disengagement; wherein said controller (17) is configured for scanning and/or selecting plurality of operating modes on the
basis of predetermined/preset values and programme for subsequent activation / deactivation
of said power steering pump (7).
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is schematic illustration of the hydraulic power steering system including the electronically controlled paired device
Figure 2 shows the flowchart as per the first method for controlling power steering pump. Figure 3 shows the flowchart as per the second method for controlling power steering pump.
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
The invention presented herein refers to the hydraulically assisted steering system and more particularly to such a system in which a hydraulic power steering pump can be selectively

driven from the engine, as a function of driver demand in terms of handwheel rotation and/or vehicle speed and/or mode of selection.
Referring to the figure 1, shows schematic illustration of the hydraulic power steering system, a typical system consists of a handwheel 1, which is connected to the rack and pinion 4, through a steering column 2. The pinion gear at the base of the steering column 2 is mated to the rack in the rack and pinion housing 4. This meshing transforms the rotary motion of handwheel 1 into linear motion of the rack 4. Each end of the rack 4 has tie rod 10 which is connected with the steering knuckle 11, through ball joint. The wheel assembly 12 is mounted on to the steering knuckle 11 using wheel mounting bolts.
In this system, power assistance is provided by the power steering pump 7, which is driven from the engine 13, through a Poly V-belt. The power steering pump 7 draws fluid from the fluid reservoir 5. The pressurized fluid from the pump is supplied to the rack through a high pressure hose 8. The valve spool inside the rack housing is energized by the pressurized fluid and the fluid from the spool returns to the reservoir through the return hose 9. The electronic controller receives input signal generated from the steering angle sensor 3 which is mounted on the steering column 2 and the vehicle speed. The controller analyzes the signals using the designed algorithm and produces a control signal for controlling the electromagnetic pairing device for engagement or disengagement.
This Controller has 4 modes in total. Of this 3 modes are available for manual selection by individual drivers as per their preference.
a) FPAS: This mode enables full time activation of the assistance to the steering irrespective of any drive condition based on speed or handwheel position.
b) ECONOMY: This mode permanently disables assistance to the steering thereby offering option to harness best fuel efficiency.
c) SMART: In this mode, driver gets assistance to the steering based on demand. Virtually, in this mode the vehicle is as good as normally assisted vehicle for the normal driver. Operation in SMART mode: Once the controller receives the information about the engine start condition, it starts scanning steering hand wheel movement. Once the steering hand wheel movement is above a predetermined threshold value in clockwise or anticlockwise direction, the algorithm produces an output control signal for the electromagnetic pairing device to engage with the pump shaft & supply pressurized fluid

to the rack and pinion for providing required power assistance to the steering. During the course of time, as the driver completes negotiating the steering maneuver, the controller awaits and if no handwheel movement is diagnosed within a certain predetermined time interval, the controller releases the control signal for disengaging the pairing device thereby stopping the steering assistance when not required.
As indicated previously, with the help of the electronically controlled operation of the power steering pump, the pump functions infrequently i.e. during parking manoeuvers, turning and on rare occasions like evasive manoeuvers or lane changing. Thus, majority of the time, particularly during highway driving which consists of travelling on straight roads for longer duration, the steering pump remains off thereby reducing parasitic load on the engine. This in turn results in reduction in fuel consumption as well as reduced emissions. d) CITY: If none of the above 3 modes is selected, the controller intelligently slips into this default mode. The driver gets the assistance to steering not only based on demand but also based on vehicle speed.
Operation in CITY mode: In this mode, the controller scans two conditions continuously which are vehicle speed and handwheel angle. The assistance to the steering remains constantly on below the vehicle speed of V kmph, preferably 40 kmph. The assistance gets cut off once the vehicle speed exceeds that limit. In this high speed zone the steering assistance is provided based on the angle movement similar to SMART mode.
Figure 2 exhibits the process diagram of the control process for the electronic controller. o If FPAS is ON it will turn ON the power steering pump and will not scan for any further switch / signal input. This can be called as Master Override.
o IF FPAS is not pressed it will scan the next mode switch i.e. ECONOMY. If ECONOMY is ON, it will directly switch OFF the power steering pump & not scan for any further signal input except the Master Override i.e. FPAS. ECONOMY can be called as 2nd Manual Override.
o If both FPAS & ECONOMY are not pressed then controller will scan for next mode selection switch i.e. SMART mode. If this operational mode is selected, controller directly starts scanning the Steering angle input signal. It keeps on comparing the

instantaneous steering angle values with the threshold band. If the steering angle value comes between the threshold band, it will wait for 4 seconds & then switches OFF the Power steering Pump & goes again to check whether one of the Override is activated ( FPAS / ECONOMY), and keeps on scanning the steering angle input values. At any point of time steering angle value crosses the threshold band; controller immediately turns on the power steering pump & again keeps on scanning steering angle value & comparing with the threshold.
o CITY: If none of the above 3 modes is selected, the controller intelligently slips into this default mode. The driver gets the assistance to steering not only based on demand but also based on vehicle speed, i.e when the vehicle is speed is below a predetermined value (\|/ kmph) it activate the pump. Otherwise it check for the steering angle and if the steering angle is not between threshold i.e -6° & +8° it activate the pump. If the steering angle is between the above mentioned threshold it wait for predetermined time period before switching of the assistance pump.
Figure 3 represents a broader application of this system to further improve vehicle fuel economy. Each time engine is started from OFF condition the controller before going to mode scan or analyzing any input signal, directly activates the power steering pump for a predetermined period preferably first 3 minutes. This step is necessary to take care of assistance in parking maneuvers and will be more clarified after explaining the full logic. • Once 3 minute is over, Controller now Start scanning for the mode selection switches.
o If FPAS is ON it will turn ON the power steering pump and will not scan for any further switch / signal input. This can be called as Master Override.
o IF FPAS is not pressed it will scan the next mode switch i.e. ECONOMY. If ECONOMY is ON, it will directly switch OFF the power steering pump & not scan for any further signal input except the Master Override i.e. FPAS. ECONOMY can be called as 2nd Manual Override.
o If both FPAS & ECONOMY are not pressed then controller will scan for next mode selection switch i.e. SMART mode. If this operational mode is selected, controller directly starts scanning the Steering angle input signal. It keeps on comparing the

instantaneous steering angle values with the threshold band. If the steering angle value comes between the threshold band (-8° & +5°), it will wait for a predetermined time period, preferably 4 seconds and then switches OFF the Power steering Pump and goes again to check whether one of the Override is activated ( FPAS / ECONOMY), and keeps on scanning the steering angle input values. At any point of time steering angle value crosses the threshold band; controller immediately turns on the power steering pump and again keeps on scanning steering angle value and comparing with the threshold.
• IF none of the operational mode is selected, Controller automatically goes to a default mode called a CITY MODE.
o City Mode: - once controller enters into this mode it first scan the vehicle speed input signal and checks whether vehicle is at stationary condition. If it detects that the vehicle speed is zero for more than a predetermined period, preferably 3 seconds, the controller switches off the power steering pump and records the steering wheel position at that moment as θ0 and starts comparing next instantaneous steering wheel position say θ1 with θO. if the controller detects any change in steering wheel position, it switches on the power steering pump and then continues scanning switch position. During this entire operation even if vehicle starts moving, controller will switch on the power steering pump. Thus this mode enables control of pump operation in both conditions as to whether the vehicle is at traffic signal or in stationary condition and consequently contributes in reducing idle fuel consumption.
The foregoing description is a specific methodology of the present invention. It should be appreciated that these methodologies are described for purpose of illustration only, and that numerous alternatives 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 alternatives be included insofar as they come within the scope of the invention as claimed or the equivalents thereof

We Claim:
1. An energy efficient hydraulic power steering system comprising
at least one handwheel (1) connected to the rack and pinion (4) through a pinion gear on steering column (2);
at least one controller (17) for receiving and analyzing vehicle speed and input signals from the steering angle sensor (3) mounted on the steering column (2) for producing a control signal for controlling the engaging device for engagement or disengagement; wherein said controller (17) is configured for scanning and/or selecting plurality of operating modes on the basis of predetermined/preset values and programme; at least one power steering pump (7) controlled through said controller (17) is driven by the engine (13) to pump fluid from the fluid reservoir (5) to energize valve spool inside the rack housing.
2. An energy efficient hydraulic power steering system comprising
at least one handwheel (1) connected to the rack and pinion (4) through a pinion gear on steering column (2);
at least one power steering pump (7) driven by the engine (13) to pump fluid from the fluid reservoir (5) to energize valve spool inside the rack housing and returns back to said fluid reservoir;
at least one controller (17) configured for direct initial activation of said power steering pump (7) for a predetermined time interval from each engine start timing and after said predetermined time interval receiving and analyzing vehicle speed and input signals from the steering angle sensor (3) mounted on the steering column (2) for producing a control signal for controlling the engaging device for engagement or disengagement; wherein said controller (17) is configured for scanning and/or selecting plurality of operating modes on the basis of predetermined/preset values and programme for subsequent activation / deactivation of said power steering pump (7).
3. The steering system as claimed in claim 1 or 2 wherein said plurality of operating modes
comprises of at least three manual selection modes and at least one default/automatic
selection mode.

4. The steering system as claimed in claim 1 or 2 wherein said engaging device is a electromagnetic pairing device.
5. The steering system as claimed in claim 1 or 2 wherein said controller (17) is an electronic controller.
6. The steering system as claimed in claim 1 or 2 wherein said power steering pump (7) draws fluid from the fluid reservoir (5) and the pressurized fluid is supplied to the rack through a high pressure hose (8) to energize the valve spool inside the rack housing and said fluid from the spool returns to the reservoir through the return hose (9).
7. The steering system as claimed in claim 3 wherein said power steering pump (7) is directly activated by selection of first manual mode skipping scanning by said controller (17) and overriding all other modes.
8. The steering system as claimed in claim 3 wherein said controller (17) deactivates said power steering pump (7) on receiving the feedback of the second manual mode selection.
9. The steering system as claimed in claim 3 wherein said controller (17) is configured for deactivating said power steering pump (7) when the steering angle is found within the preset range of threshold band and activating said power steering pump (7) when the steering angle is found outside the preset range of threshold band on detection of third manual mode.
10. The steering system as claimed in claim 1 or 3 wherein said controller (17) is configured for switching to default/automatic selection mode when none of the manual mode is detected and scanning for vehicle speed and steering angle for comparing the vehicle speed with predetermined vehicle speed value and steering angle input signal with predetermined threshold band; wherein when said vehicle speed is found below a predetermined vehicle speed value and/or said steering angle is not found within the specified range then said power steering pump (7) is activated and when said vehicle speed is found above a predetermined vehicle speed value then said power steering pump (7) is controlled on basis of said steering angle values alone.

11. The steering system as claimed in claim 2 or 3 wherein said controller (17) is configured for switching to default/automatic selection mode when none of the manual mode is detected and scanning for vehicle speed and steering angle for comparing the vehicle speed with predetermined vehicle speed value and steering angle input signal with predetermined threshold band range; wherein when said vehicle speed is found zero for a predetermined period and constant steering angle is recorded then said power steering pump (7) is deactivated and when any consequent change in steering angle and/or vehicle speed is detected then said power steering pump (7) is activated.
12. The steering system as claimed in claim 3 wherein said controller (17) is configured for deactivating said power steering pump (7) after a predetermined time if said vehicle speed is found above a predetermined vehicle speed value and said steering angle is found within the specified threshold band range.
13. The energy efficient hydraulic power steering system substantially as herein described with reference to accompanying drawings.