FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
PROVISIONAL SPECIFICATION
(See Section 10; rule 13)
TITLE OF THE INVENTION
Method Of Reducing Power Consumption By Using Low Flow Hydraulic Power Steering Pump For Vehicles
APPLICANTS
TATA MOTORS LIMITED, an Indian company
Having its registered office at Bombay House,
24 Homi Mody Street, Hutatma Chowk,
Mumbai 400 001 Maharashtra, India
INVENTOR
Jagtap Santosh L
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.

FIELD OF INVENTION
This invention is related to power steering system and more particularly it is related to hydraulic power steering pump for power steering in vehicles
BACKGROUND OF INVENTION
Generally hydraulic Power steering pump draws power from engine to pressurize hydraulic oil which in turn is supplied to rack and pinion hydraulic cylinder to assist steering action on vehicle.
Power steering power consumption happens because of two major reasons.
Pressure developed in system during Steering action and thereby power drawn
by Power Assisted Steering (PAS) pump from engine through auxiliary drive.
Power Assisted Steering (PAS) Pump churning losses during straight ahead
driving.
The conventional way of reducing power consumption from hydraulic power
steering are as follows
By increasing pulley ratio between pump to crank shaft pulley thereby reducing
the pump speed w r t engine speed and reducing hydraulic churning losses.
Other way is to control flow of fluid by electronic orifice valve
Further way is by using the controlled variable displacement PAS pump.
Disadvantages of the above different types are as follows Need more packaging space. Bigger pulley. High inertia weight. Need Electronic feedback control system and valve. Costly solution.
OBJECTS OF INVENTION
The main object of the present invention is to provide low flow hydraulic power steering pump for vehicles to reduce power consumption.


Another object of the present invention is to provide low flow hydraulic power steering pump by reducing the pump displacement and thereby reducing the churning losses.
Still yet another object of the present invention is to provide low flow hydraulic power steering pump for vehicles which increases fuel efficiency.
BRIEF DESCRIPTION OF INVENTION
In accordance with the present invention Low flow hydraulic power steering pump for vehicles to reduce power consumption comprises the Following steps;
(a) Deciding lowest possible pump displacement considering steering catch-up to accomplish the flow requirement in extreme avoidance maneuver,
(b) Using available displacement pump,
(c) Selecting lowest possible decided flow rate for the trials,
(d) Choosing rotary spool valve characteristics in Hydraulic rack and pinion, wherein said step of choosing rotary spool valve characteristics in Hydraulic rack and pinion further comprises;
-Selecting the valve curve, fixing/putting the torsion bar inside the said valve, -Selecting oil flow at high speed,
(e) Finalizing the pump flow characteristics,
(f) Getting the desired flow pump with final flow characteristics,
(9) Signing off ride and handling with final rotary spool valve characteristics.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure -1 shows the speed vs. power characteristics of pump having 7.2cc/rev and 6cc/rev displacement thereby saving power using low flow. Figure-2 shows Power rack and pinion valve curve (example)


Figure-3 shows Power rack and pinion valve curve (Measurement on vehicle) example
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,
Power steering power consumption happens because of two major reasons. Pressure developed in system during Steering action and thereby power drawn by PAS pump from engine through auxiliary drive. PAS Pump churning losses during straight ahead driving. Hydraulic power assist steering (PAS) pump displacement specification in majority of the benchmark vehicles is found to be around 7cc per revolution. PAS pump displacement is reduced to 6cc per revolution as basic specification for the new generation passenger car. Thereby, ensured that during the straight ahead driving power consumption is reduced due to less churning losses.
It is important that for optimizing the hydraulic power steering system the Rotary spool valve assembly have to be tuned in Hydraulic power rack and pinion. This is to achieve right steering effort and feel on vehicle.
Conventional way of tuning hydraulic power steering for ride and handling of vehicle has following steps
1. Deciding pump displacement based on the standard spool available and benchmark information.
2. Deciding rotary spool valve characteristics in Hydraulic rack and pinion.
a. To get /decide valve curve
b. To select/decide torsion bar inside the valve


3. Selecting/decide oil flow of power steering pump in static and parking maneuver.
4. Selecting/decide oil flow at high speed. Finalizing/Finalize pump flow characteristics.
Now referring to figure 2 and 3, method of reducing power consumption by
using low flow pump to reduce the power consumption and tuning rotary spool
valve in rack and pinion together so that by meeting the steering feel
requirements the power saving can be achieved.
In accordance with the present invention Low flow hydraulic power steering
pump for vehicles to reduce power consumption comprises the Following
steps;
a. Deciding lowest possible pump displacement considering steering catch
up to accomplish the flow requirement in extreme avoidance maneuver,
b. Using available displacement pump,
c. Selecting lowest possible decided flow rate for the trials,
d. Choosing rotary spool valve characteristics in Hydraulic rack and
pinion, wherein said step of choosing rotary spool valve characteristics
in Hydraulic rack and pinion further comprises;
• Selecting the valve curve, fixing/putting the torsion bar inside the said valve,
• Selecting oil flow at high speed,
e. Finalizing the pump flow characteristics,
f. Getting the desired flow pump with final flow characteristics,
g. Signing off ride and handling with final rotary spool valve
characteristics.
To decide oil flow of Power Assisted Steering (PAS) pump
The Criterion for deciding the said oil flow of power Assisted Steering (PAS)
is To check catch-up


Rack and Pinion C/S Area = fl[ - 4) * [(cylinder ID)2-(rack shaft OD)2] =
718.7mm2
Maximum Steering speed consideration for avoidance maneuver = 720 deg per
min
C factor = Rack travel per rotation of pinion shaft = 50 mm per revolution
Min flow required to avoid catch-up = steering rate in rpm * Rack cylinder
volume displacement in liters = 4.31pm
Considering margin minimum flow required = 61pm — (I)
PAS pump minimum RPM
= min. pulley ration between engine to PAS pulley * min. engine idle RPM
= 1000rpm — (II)
Minimum displacement of PAS pump in cc/ rev = I + II = 6cc per revolution.
Existing available pump has 7.2 cc per revolution pump. Starting development
with optional 7.2 cc / rev and 6 cc/rev specification.
Flow rate 61pm @ 1000 rpm specified after trial with 61pm pump
Conducting Trial with different rack and pinion spool valve as per following
table as Iteration 1 and Iteration 2.(refer table given bellow) Subjective ratings
are given for the iterations. Finalizing the Rotary spool valve of the Rack and
Pinion.
Finalizing droop flow characteristic, after high speed Ride and Handling
iteration 4 and iteration 5 (refer table given bellow).
Getting 6cc /rev flow pump with final flow characteristic and
Signing off ride and handling with final rotary spool valve characteristic.