DESC:FIELD OF THE INVENTION
The present invention relates to an electric power assisted steering gear for advantageous use in automobiles and in particular, for use in off-highway vehicles and more particularly to provide an integrated electrically assisted power steering system along with steering gear as a single unit. More specifically, the present invention relates to an integrated electric power assisted steering system, which has reduction gear, torque and angle sensor within main housing of mechanical gear box and attachment of electric motor on the main housing at any orientation convenient to packaging on the off highway vehicles and automobiles.

BACKGROUND OF THE INVENTION
Generally, Electric Power Assisted Steering (EPS or EPAS) uses an electric motor to assist the driver of a vehicle. Sensors detect the position and torque of a steering column and a computer-on-module applies assistive torque via motor. The motor connects to either the steering gear or steering column, which allows varying amounts of assistance to be applied depending on driving conditions.

The conventional steering arrangement is to turn the front wheels of an off-highway vehicle such as tractors, forklifts, cranes, backhoes, bulldozers, and golf carts or automobile using a hand–operated steering wheel which is positioned in front of driver, via the steering column. The basic aim of steering is to ensure that the wheels are turned in the desired directions, which is achieved by a series of linkages, rods, pivots and gears. The steering linkages connecting the steering box and the wheels usually conform to a variation of Ackermann steering geometry to account for the fact that in a turn, the inner wheel travels a path of smaller radius than the outer wheel, so that the degree of automotive suitable for driving in a straight path is not suitable for turns.

Most of the off-highway vehicles are fitted with box type manual steering gears. The force required on the steering wheel to steer the tractor is dependent on the steering ratio and type of the mechanism used in the manual steering gears. Some models of off-highway vehicles are fitted with a hydrostatic power steering system to reduce the steering effort, in said vehicles, the assistance at the road wheels is provided by hydraulic force through cylinders which are actuated by a rotary directional control hydraulic valve connected to the steering wheel. There is no positive mechanical connection in this type of steering system.

Cost of the hydrostatic steering system is relatively higher and from a functional point of view, hydraulic pump used in the system draws considerable power from the engine. In the case of low powered vehicles, this affects the draw bar pull and thus intended performance suffers. Hence, not used in lower powered vehicles. Conventionally in the automotive vehicles with pay load exceeding 0.75 ton are fitted with fully integrated box type hydraulic power steering gears. In these vehicles hydraulic pump, which is the source of energy draws power continuously from the engine, thereby consuming more fuel.

In the conventional automobile, electric power assisted system is mounted on the output shaft or outer column inside the passenger compartment to protect it from dust, water, heat etc. In the case of the off-highway vehicles as there is no cabin, exposure to atmosphere is high and thereby chances of malfunctioning of the system due to water and dust entry are predominant. Packaging of conventional column mounted electric power assisted system on the off-highway vehicle is more difficult and it may require major changes in the fuel tank and cluster assembly.

Some of the prior arts are:
US8485305 discloses an all terrain vehicle includes a vehicle body frame, a rotatable steering shaft supported by the vehicle body frame, a power steering device including an electric motor, the power steering device being configured to exert an auxiliary rotational force to the steering shaft by a driving power generated in the electric motor, a radiator disposed in front of the electric motor, and a shield member mounted to the vehicle body frame and positioned between the radiator and the electric motor to cover the electric motor from a forward direction. However the shield member protects only the electric motor and not sensors.

US7789191 discloses an electric power assist module for a steering system has an integrated housing for accommodating the torque sensor, motor and electronic control unit. A helical gear train including a pinion gear, an intermediate gear and steering gear are provided to transfer the motion from the motor to an output shaft that is coupled to an input shaft by way of a torsion bar. The drawback is, the motor only partially contained by the integrated housing and reduction gear is not positioned in the integrated housing of the electric power assist module.

US8684128 discloses a steering gear, which comprises a helical pinion and a helical gear which are mounted in the gear housing and driven by an electric motor. A control unit and a sensor system connected thereto are also disposed in or on the steering gear so as to detect and control the rotor position and/or rotation of the rotor of the electric motor. However, the connection of the electric motor in combination with the helical pinion and a helical gear requires a large installation space.

Electric Power Steering (EPS) system which comprises main components such as an electric control unit (E.C.U.), a torque sensor, an electric motor and an intermediate gear with clutch, said components are integrated into one unit which can be placed on any part of steering column. (Vishal N. Sulakhe Et al. International Journal of Engineering Research and Applications, ISSN: 2248-9622, Vol. 3, Issue 6, Nov-Dec 2013, pp.661-666)

Accordingly, there exists a need for an integrated electric power assisted steering system, which has reduction gear, torque and angle sensor within main housing of mechanical gear box and attachment of electric motor on the main housing at any orientation convenient to packaging on the off highway vehicles and automobiles.

OBJECTS OF INVENTION
One or more of the problems of the conventional prior art may be overcome by various embodiments of the system and method of the present invention.

Accordingly, it is the primary object of the present invention to provide an integrated electrically assisted power steering system along with steering gear as a single unit for an off-highway vehicle.

It is another object of the present invention to integrate electric power assisted steering system in the existing off highway vehicle without major, minor / minimum modification in fuel tank and cluster assembly.

It is another object of the present invention to provide an integrated electric power assisted steering system, which has reduction gear, torque and angle sensor within main housing of mechanical gear box and attachment of electric motor on the main housing at any orientation convenient to packaging on the off highway vehicles and automobiles.

It is another object of the present invention to provide an integrated electric power assisted steering system, which has minimal number of parts and thereby reduce the overall cost compared with existing hydrostatic steering system.

It is another object of the present invention to provide a high torque handling capability in the electric power assisted steering system required for the off-highway vehicles and the gear set is fully located inside the main housing.

It is another object of the present invention to provide solid column construction without using universal joints to use directly on the off highway vehicle with existing base mounting.

It is another object of the present invention, wherein the off-highway vehicles includes but not limited to tractors, forklifts, cranes, backhoes, bulldozers, and golf carts.

SUMMARY OF THE INVENTION
Thus according to the basic aspect of the present invention there is provided an integrated electric power steering system along with steering gear as a single unit comprising:
one or more bearings;
main nut assembly;
at least one rocker shaft;
worm end;
worm wheel;
sensing unit;
worm shaft;
input shaft; and
Electronic Control Unit (ECU),
wherein said components are assembled within an housing and filled with lubricant,
wherein the main nut assembly is a translational member provided on the worm end with support of one or more balls, said balls are re-circulated through transfer tube of the main nut assembly,
wherein the bearings support the worm end which is being axially pre-loaded by a screw plug to rotate in the steering box assembly,
wherein the sensing unit comprising of torque and angle sensor is mounted over the worm end and input shaft,
wherein when the input shaft is rotated, the deflection in position of orientation between the worm end and input shaft is measured by the sensor unit and data is transmitted to the ECU,
wherein the ECU drives a motor until the worm end rotates with coupling of the worm shaft and worm wheel to get the original position of orientation with the input shaft, and
wherein the worm shaft with the worm wheel form a gear set capable of reducing the RPM and amplifying the torque from the motor output end, said motor is mounted on the housing.

It is another aspect of the present invention, wherein the main nut assembly has a nut on one side which is coupled to the rocker shaft to convert linear movement of the main nut assembly to rotational movement of the rocker shaft as output.

It is another aspect of the present invention, wherein a drop arm connects the rocker shaft output end to external steering linkages for converting rotational movement of the rocker shaft to oscillatory movement to steering linkage.

It is another aspect of the present invention, wherein in the event of electric system malfunctioning the vehicle can be driven with the mechanical system available in the gear.

It is another aspect of the present invention, wherein assembly of the sensing unit within the housing protects from atmospheric ingress of dust and/or water.

It is another aspect of the present invention, wherein a seal and one or more oil seals and positioned on the rocker shaft and worm end are used to prevent the entry of dirt and the leakage of the lubricant.
BRIEF DESCRIPTION OF THE DRAWING
Figure 1: illustrates the exploded view of the integrated electric power assisted steering system according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWING
The present invention as discussed hereinbefore relates to an integrated electrically assisted power steering system along with steering gear as a single unit. More specifically, the present invention relates to an integrated electric power assisted steering system, which has reduction gear, torque and angle sensor within main housing of mechanical gear box and attachment of electric motor on the main housing at any orientation convenient to packaging on the off highway vehicles and automobiles.

Referring to Figure 1, the integrated electric power steering system comprising one or more bearings [3] and [8]; main nut assembly [5]; at least one rocker shaft [27]; a worm end [4]; worm wheel [7]; sensing unit [10]; worm shaft [19]; input shaft [12]; and Electronic Control Unit (ECU), said components are assembled within an housing [1] and filled with lubricant for smoother working of the system. The bearings [3] and [8] are used to support the worm end [4] which is being axially pre-loaded by a screw plug [9] to rotate in the steering box assembly. A cover plate [2] is mounted with the housing [1] with the help of one or more spring washers [37] and bolts [38]. The housing [1] is made up of material which includes but not limited to machined cast iron.

The main nut assembly [5] is a translational member provided on the worm end [4] with support of one or more balls, said balls are re-circulated through transfer tube of the main nut assembly [5]. The main nut assembly [5] has either a tooth or dome profile nut on one side, said tooth or dome profile nut is coupled to the rocker shaft [27] to convert linear movement of the main nut assembly [5] to rotational movement of the rocker shaft [27] as output. In case of dome profiled nut, fork type rocker shaft [27] with spherical roller [6] is used for coupling to prevent the gear tooth or dome of the main nut assembly [5] and gear tooth or dome of the rocker shaft [27] get engaged. The rocker shaft [27] is supported by one or more bushings [26] or one or more needle bearings, or a combination of the two. The rocker shaft [27] is retained in position using a spring [28], locator [29], spring seat [30], adjuster screw [31] and lock nut [32].

A drop arm [34] is fitted with the rocker shaft [27] by spline seating and lock nut [36] with a spring washer [35], said drop arm [34] is a forged metal linkage connecting the rocker shaft [27] output end to external steering linkages for converting rotational movement of the rocker shaft [27] to oscillatory movement to steering linkage. Since the rocker shaft [27] output end is connected with external steering linkages in the event of electric system malfunctioning, the vehicle can be driven with the mechanical system available in the gear. A seal [33] and one or more oil seals [41] and [42] positioned on the rocker shaft [27] and worm end [4] are used to prevent the entry of dirt and the leakage of the lubricant.

A worm wheel [7] is press fitted to the worm end [4] and engaged to a worm shaft [19] whose ends are supported by bearings [20] and [21], the linear movement of said worm shaft [19] is arrested by a circlip [22] and end plug [18]. The worm shaft [19] in combination with the worm wheel [7] form a gear set capable of reducing the RPM and amplifying the torque from the motor output end. The worm shaft [19] is coupled with a motor [25] through coupling [23] and spider [24]. The motor [25] is mounted on the housing with the help of allen screws [40]. When the motor [25] runs it rotates the worm shaft [19] and the worm end [4] rotates simultaneously through the worm wheel [7] which is engaged with the worm shaft [19].

The worm end [4] and input shaft [12] are pinned with a torsion bar [11] using one or more dowel pins [13], said torsion bar [11] is a thin member preferably made of spring steel material having elastic property for pre-defined degree of twist. The pinning takes place when protruded end of the worm end [4] goes inside the internal flat drive end of the input shaft [12] and step diameter of the worm end [4] is guided by the bore of the input shaft [12]. The input shaft [12] can be rotated alone by twisting the torsion bar [11] until the closing of clearance between the protruded end of the worm end [4] and flat drive end of the input shaft [12].

The input shaft [12] starts driving the worm end [4] when the clearance between the protruded end of the worm end [4] and flat drive end of the input shaft [12] gets closed. The clearance angle gap between the protruded end of the worm end [4] and flat drive end of the input shaft [12] is approximately 6°. The torsion bar [11] gets twisted due to differential load acting on the input shaft [12] and worm end [4], said torsion bar [11] retain the position of orientation between the worm end [4] and input shaft [12] when there is no load on the input shaft [12] side.

The sensing unit [10] comprising of torque and angle sensor is mounted over the worm end [4] and input shaft [12]. The sensor unit [10] measures the twist experienced by the worm end [4] and input shaft [12] and also measures the number of steering rotations from straight ahead position (SAP) to the Left Hand [LH] / Right Hand [RH] end.

When the input shaft [12] is rotated, the deflection in position of orientation between the worm end [4] and input shaft [12] is measured by the sensor unit [10] and sensed data is fed to the motor [25] through the ECU. The ECU drives the motor [25] until the worm end [4] rotates with coupling of the worm shaft [19] and worm wheel [7] to get the original position of orientation with the input shaft [12]. The orientation of the motor [25] can be positioned suitably to the requirement of the off highway vehicle. The motor [25] drives the worm shaft [19] unlike the column driven type used in passenger cars. The motor [25] used includes but not limited to brushed/brushless DC motor.

A steering wheel is splined to an inner column assembly [14] which is located in centre of outer column assembly [15] and supported by a bearing [16] at top of the outer column assembly [15]. The linear movement of the inner column assembly [14] is arrested by circlip [17]. The outer column assembly [15] is mounted on the housing [1] using one or more screws [39] and one or more spring washers [37]. A rigid coupling is positioned between the inner column assembly (14) and splined end of the input shaft [12]. The steering wheel is engaged to wheel end shaft which is metal shaft with spline and thread cut across to enable the driver’s steering function i.e., to transmit steering torque to the input shaft [12]. An outer tube with a bearing at the top and welded flange at the bottom is bolted to the steering box housing [1]. The outer tube acts as a protective shield and reinforcing structure to the wheel end shaft.

Since precise part of the sensors are fully protected from atmospheric ingress of dust/water, to use the integrated electric power assisted steering system on the off highway vehicles where there is no cabin. The off-highway vehicles include but not limited to tractors, forklifts, cranes, backhoes, bulldozers, and golf carts.

,CLAIMS:WE CLAIM:
1. An integrated electric power steering system along with steering gear as a single unit comprising:
one or more bearings [3] and [8];
main nut assembly [5];
at least one rocker shaft [27];
worm end [4];
worm wheel [7];
sensing unit [10];
worm shaft [19];
input shaft [12]; and
Electronic Control Unit (ECU),
wherein said components are assembled within an housing [1] and filled with lubricant,
wherein the main nut assembly [5] is a translational member provided on the worm end [4] with support of one or more balls, said balls are re-circulated through transfer tube of the main nut assembly [5],
wherein the bearings [3] and [8] support the worm end [4] which is being axially pre-loaded by a screw plug [9] to rotate in the steering box assembly,
wherein the sensing unit [10] comprising of torque and angle sensor is mounted over the worm end [4] and input shaft [12],
wherein when the input shaft [12] is rotated, the deflection in position of orientation between the worm end [4] and input shaft [12] is measured by the sensor unit [10] and data is transmitted to the ECU,
wherein the ECU drives a motor [25] until the worm end [4] rotates with coupling of the worm shaft [19] and worm wheel [7] to get the original position of orientation with the input shaft [12], and
wherein the worm shaft [19] with the worm wheel [7] form a gear set capable of reducing the RPM and amplifying the torque from the motor [25] output end, said motor [25] is mounted on the housing [1].

2. The integrated electric power steering system as claimed in claim 1, wherein the main nut assembly [5] has a nut on one side which is coupled to the rocker shaft [27] to convert linear movement of the main nut assembly [5] to rotational movement of the rocker shaft [27] as output.

3. The integrated electric power steering system as claimed in claim 2, wherein a drop arm [34] connects the rocker shaft [27] output end to external steering linkages for converting rotational movement of the rocker shaft [27] to oscillatory movement to steering linkage.

4. The integrated electric power steering system as claimed in claim 3, wherein in the event of electric system malfunctioning the vehicle can be driven with the mechanical system available in the gear.

5. The integrated electric power steering system as claimed in claim 1, wherein assembly of the sensing unit [10] within the housing [1] protects from atmospheric ingress of dust and/or water.

6. The integrated electric power steering system as claimed in claim 1, wherein a seal [33] and one or more oil seals [41] and [42] positioned on the rocker shaft [27] and worm end [4] are used to prevent the entry of dirt and the leakage of the lubricant.