FORM 2
THE PATENTS ACT-1970
(39 of 1970) &
The Patent Rules, 2006
COMPLETE SPECIFICATION
(See Section 10 and Rule 13)
1. TITLE OF THE INVENTION
Auto setting limiters for integral hydraulic power steering gear
2. APPLICANT
a) Name ZF Steering Gear (India) Limited
b) Nationality Indian
C) Address 1242/44, village Vadu Budruk taluka-Shirur, dist. Pune-412216
3. PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention
and the manner in which it is to be performed

Title:
Auto setting limiters for integral hydraulic power steering gear-Field of Invention:
Present invention relates to hydraulic limiters used in power steering gears. More particularly, it relates to automatic hydraulic limiters used in Power steering gears
Background and Prior art:
Integral hydraulic power steering gear devices have pistons installed in it. They work as working piston that moves linearly in the housing. It also has cut-off devices that cut off the hydraulic pressure in the high pressure chamber formed by the piston and the housing when axle stops . are reached on the vehicle. When driver turns the steering wheel, piston moves linearly in the housing bore, sector shaft meshed with the piston, turns around itselffeither clockwise or anticlockwise) along with the cam machined as its integral part and approaches needles of the limiter valves which have been accommodated in the housing cover. The needle with the sealing seat in the body of the limiter valve holds pressurized fluid. As the needle is lifted, pressurized fluid enters the cavity of the housing cover to lift the other needle which is connected to low pressure fluid. This causes drop in pressure as the axle stop is reached. This saves waste of energy of the engine and parts, linked in the process of turning of road wheels, are saved from unnecessary stresses. But, these limiters are required to be adjusted by the assemblers on the assembly line as the position of the limiter, if preset while assembling the steering gear, can not guaranty its positional accuracy to cause pressure drop. This is caused by the tolerances on the various parts, which are linked between steering gear and the road wheel, of the chassis. As it consumes time on the assembly line, the assembler does not adjust the limiters.
US5086864 describes auto setting limiters for power steering gears. In this patent a hole parallel to working piston is drilled and two cut-off pistons with push rods are fixed in the said hole. When working piston is moved to either side, respective cut-off piston gets pushed by push rod and connects surge chamber which is under working pressure with other surge chamber which is relieved of pressure through the said drilled hole.
Fig. 2 shows existing piston cross section in which it is clear that there is no scope to drill such hole which communicates with two surge chambers.
Object of Invention:
Object of the invention is to provide auto setting limiters for existing hydraulic power steering gears.

Summary of Invention:
Integral hydraulic power steering gear comprises piston assembly accommodated in housing. The piston has machined longitudinal cavities, where from oil is brought in the piston, on either side. Two passages are drilled from the faces of the piston and are made to communicate with the longitudinal cavities. The said drilled passages house the needles which are pressing against valve seat with the help of springs and the oil pressure prevailing in the machined cavities. Two bushings are positioned, one in the housing and the other one on the end cover, to face these needle valves. When steering approaches axel stop, needle come in contact with the bush, gets pressed allowing oil to flow from longitudinal cavities to the area between piston and housing wall. Thus pressure is reduced.
Brief description of drawings
Fig 1- Describes cross section of Integral hydraulic power steering gear assembly Fig. 2- Describes cross section of existing piston
Detail description of drawings
Description and examples described below is for the sake of understanding and it does not limit the invention.
Fig. 1 describes the integral hydraulic power steering gear (Fig.l) comprises of housing (1) which has suitable bore to accommodate piston assembly (2). The piston assembly has worm (3) running through it. It is supported in the housing (1) at two ends. One end is formed by the end cover (5) and other end by bearing bush (11). Nut (12) is fixed in the cavity of piston and is responsible for reciprocation of piston (2) in the bore of housing (1) as the worm (3) is turned by the driver either clockwise or anticlockwise. The piston (2) is engaged by suitable gearing with the sector shaft (4) on which drop arm is mounted (not shown). The valve (not shown) controls the flow as the worm (3) is turned, otherwise, in neutral position, allows oil to go to tank. When the worm (3) is turned, piston moves left or right, depending on the hand of the worm (3), and chambers (13) or (14) are pressurized to help piston move. If chamber (13) is pressurized chamber (14) is at low pressure and visa-versa. Pressure level depends upon load on the tire which is communicated to the valve (not shown) via sector shaft (4). Whatever pressure is built up in the steering gear, same pressure is available in the slot (10) milled in the body of the piston (2).

When the driver is not actuating the steering wheel (not shown), the pressure in chamber (13), chamber (14) and in the slot (10) is same and is called system pressure. The needle valves (6)
and (7) remain closed due to weak spring (15).
As the steering wheel is actuated by rotating worm (3), the needle valves remain closed due to springs (15) and differential pressure prevailing in chamber (13) and (14) and slot (10).
As the driver, while steering, approaches axle stop on the axle, piston (2) forces the cap on the screw and gets set there permanently. While this is happening, it has already pressed the needle valve lifting the seat and allowing high pressure oil to mix with low pressure oil in chamber. Same operation happens with the piston narrowing the chamber (13) in other direction of travel of piston. E.g when worm (3) rotates clockwise, piston assembly moves to left side. When steering approaches axel stop on the axel needle (7) touches bush (16) and gets pressed. Due to the pressing of the needle, seat (21) lifts allowing oil in slot 10 to move in the chamber 14. This oil pressurizes the piston and helps the said piston to move to opposite direction.

Claims:
We claim,
1) Integral hydraulic power steering gear comprising,
a) piston assembly accommodated in housing, worm (3) supported by end cover (5) at one end and bearing bush(ll) at opposite end;
b) Working chambers (13,14) on opposite sides of piston assembly for accommodating oil required to build pressure at either side;
c) hydraulic circuit for providing pressurized oil to said chambers
d) bush (16), screw(17); wherein,
piston assembly comprising slot (10) in the body of piston(2) having access to oil supplied from said oil reservoir (18); needle valve which gets pressed when said piston (2) forces bush(16) on the screw(17) at the axel stop resulting in lifting the seat up allowing high pressure oil from said slot (10)to mix with oi! in chamber building high pressure to move piston in opposite direction.
2) Piston assembly as claimed in claim lcomprising spring (15) which closes needle valves (6, 7) until steering approaches axel stop.
3) Piston assembly as claimed in claim lcomprising nut (12) fixed in the cavity of piston (2) engaged with worm (3); as the said worm rotates at either side, said nut (12) reciprocates piston.
4) Piston assembly as claimed in claim 1 comprising, sector shaft (4) engaged with piston (2), steering valve controlling the flow of oil depending on the rotation of the worm.
5) Sector shaft (4) as claimed in claim 3 communicates load on the tire to valve (20) controlling the oil flow