"Power Saver Hydraulic Power Steering Gear"

Field of Invention :

Present invention relates to hydraulic power steering gear. More particularly, it relates to pressure developed in it to provide torque to the output shaft.

Background and Prior Art:

Existing integral hydraulic power steering gear device comprises of input shaft to which steering wheel is connected. The input shaft is called worm which is a ball screw. On the ball screw a piston is assembled with the help of re-circulating balls. The piston has rack cut on it, which meshes with output shaft, which is called sector shaft. When the steering wheel is turned, the input shaft (worm) rotates and moves the piston linearly in the housing and rotates the sector shaft. On the sector shaft a pitman arm is mounted which is connected to road wheels via drag link and steering arm. The piston divides the housing in two chambers, say left chamber and right chamber. Therefore, when we turn steering wheel clockwise, piston either moves to left or to right, depending upon kinematic linkages mounted on chassis. Let us say, piston is moving to right. In this situation, adequate pressure is developed on the left side of the piston and piston is helped to move.

The pressure acting on the piston face creates a force and a moment is transmitted to the sector shaft through the gearing formed by rack teeth and sector shaft teeth. Thus torque is created at sector shaft which is just sufficient to move road wheels. The torque created depends upon piston area and pressure. If area is increased, pressure reduces and vice versa.

Difficulty is experienced by designers in increasing both area of cylinder and maximum pressure of the system. Increase in area of piston by increasing its diameter disproportionate its relationship with gear tooth size it wears on. And, increase in maximum pressure setting demands higher strength of pump, higher strength of pipings, and higher amount of fuel from the engine which drives the pump. And, possibilities of deformations of various components need considerations for high strength. Off all the reasons, higher fuel consumption by engine assumes priority as it leads to higher CO ₂ and NOX emissions by the engine. The system operated at lower pressure will be economical and environment friendly.

Fig (1) shows cross section of existing integral hydraulic power steering gear.

Object of Invention:

The invention has two objects..

i) To reduce operating pressure in the integral hydraulic system, and

ii) Thereby, reducing fuel consumption of the vehicle, this results in lower emissions of CO ₂ and NOx.

Summary of Invention:

Integral hydraulic power steering gear comprises piston assembly which has rack teeth cut on it. These teeth mesh with sector shaft teeth. Another piston is accommodated in the second bore of the housing which has similar teeth cut on it and they mesh with the same sector shaft which has another set of teeth meshing. Therefore, when we operate steering wheel, two pistons will move linearly in two separate bores, parallel to each other, but in opposite direction. A couple of forces is made to act upon the sector shaft, with dual set of teeth, there by generating higher torque at lower pressures.

Brief Description of drawings:

Fig.1 : Describes cross section of existing power steering ear assembly.

Fig.2 : Describes cross section of proposed power steering Gear assembly.

Following table No.1 describes the legends used in the drawings and their description. Table No.1

Detail Description of Drawing:

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.1) 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). One end is formed by the end cover (5). 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.

Nut (12) is assembled on the worm (3) with re-circulation balls (10) and "driver" (11) is press-fitted on the nut. The "driver" (11) engages with the valve (6). This valve movement to the left or to the right is responsible for the generation of pressure in the system.

The piston (2) is engaged by suitable gearing with the sector shaft (4) which is supported on roller bearing (17) on which drop arm is mounted (not shown). The valve (5) controls the flow as the worm (3) is turned, otherwise, in neutral position, allows oil to go to tank (18). When the worm (3) is turned, piston moves left or right, depending on the hand of the worm (3) and chambers (13) or (14) is at low pressure and visa-versa. Pressure level depends upon load on the tire which is communicated to the valve (6) via sector shaft (4). The sector shaft (4) develops the necessary torque to move the road wheel as it (sector shaft (4) is connected to it via pitman arm, drag link and steering arm (not shown). This is the way a normal power steering gear operates.

Fig.2 shows the proposed invention, wherein, an additional piston (7) is accommodated in second bore (9) of the housing (1). This bore (9) is parallel to first bore (8) and is of equal size in diameter of the first bore (8). As the worm (3) is rotated by the steering wheel (not shown), the piston assembly (2) moves linearly in the bore (8) of the housing (1). It drives sector shaft (4) angularly to one direction whereas piston (7) moves in opposite direction. If piston assembly (2) has higher pressure in chamber (13) then piston (7) has same pressure in chamber (15). The chambers (14) and (16) remain connected to oil tank (18) and have low pressure. Thus a couple acts on sector shaft (4). In "prior art" force acts only on one side of sector shaft (4). Torque gets doubled at the same pressure. This means that we get same torque at the sector shaft (4), as was obtained in prior art, at 50% of pressure level. Reduction in maximum pressure setting by 50% implies reduction in fuel from the engine and, hence, emission reduction.

Working of Invention :

Fig.2 shows the proposed invention.

As the imput shaft 3 is moved clockwise or anticlockwise, piston (2) moves to right or left; and piston (7) moves left or right. It means, the movements of pistons are opposite to each other. If piston (2) is going to right, the chamber (14) and chamber (16) are presssurised and help the piston (2) to move to right and piston (7) is helped to move to left. Similarly, when piston (2) is going to left, the chamber (13) and chamber (15) are pressurised and help the piston (2) to move to left and piston (7) is helped to move to right. Hence, a couple acts on the sector shaft. This implies that you get the required torque at 50% of pressure level. In other words, torque capacity of the "prior art" steering gets doubled.

As the pressure is reduced, vane pump which draws power from the engine also gets reduced. Thereby, consumption of fuel reduces. This reduces C02 emissions.

Following table (2) shows actual observations on the prototype on the Endurance Test Rig.

31

PCT/IN2013/000815

Table 2