Description:FIELD OF THE INVENTION
The present invention relates to an electric power steering system of an automobile and more particularly the present invention relates to the roller screw actuator for electric power steering system. Further the invention provides compact in size, higher output torque, ease in manufacturing, flexibility in ratio change.

BACKGROUND OF THE INVENTION
Generally, an electric power steering comprises of reduction gear unit and mechanical gear unit, wherein reduction gear unit transmit the torque from electric motor to mechanical gear. Mechanical gear provides torque transmission between steering hand wheel to road wheel through steering linkage mechanism.

CN208868130U discloses an electric power steering gear and a commercial vehicle. The lead screw is sleeved with the rack nut, and the rack nut is meshed with one end of the output shaft through a gear and a rack; The at least one pin roller is arranged between the screw rod and the rack nut and is in threaded connection with the screw rod and the rack nut; The two inner gear rings are arranged between the rack nut and the lead screw, and the two ends of each pin roller are meshed with the inner gear rings respectively, so that no relative sliding exists between the rack nut and the pin rollers; And the power-assisted steering motor is used for driving the screw rod to rotate. According to the utility model, the rotation of the screw rod is converted into the axial movement of the rack nut through the pin roller which is simultaneously in threaded engagement with the screw rod and the rack nut, and the rotation of the output shaft is realized by the rack nut and the output shaft through gear and rack engagement; A roller structure is adopted to replace an existing circulating ball type structure, steering force is provided through a steering power-assisted motor, the magnitude of the steering force applied to a steering wheel is reduced, a steering pump does not need to be arranged, the structure is compact, the size is small, and the occupied installation space is small.

US20210237795A1 discloses a Steer-by-wire steering system having a spindle drive. A spindle drive for an actuator of a steer-by-wire steering system. The spindle drive has a linearly displaceable threaded spindle. The spindle drive is in the form of a roller screw drive. The roller screw driver has a first efficiency in the driving direction and a second different efficiency in the reverse-driving direction.

CN216269501U discloses a double-motor planetary roller screw type electric power steering gear for heavy-load commercial vehicle. The method comprises the following steps: the double-motor power-assisted steering device consists of a torque corner sensor, double motors, a speed reducing mechanism and a controller; the planetary roller screw type steering gear is provided with a planetary roller screw transmission pair and a rack and sector transmission pair, the output end of the double-motor power-assisted steering device is connected with a screw rod in the planetary roller screw transmission pair, and the rack and sector transmission pair is connected with a rocker shaft; the power-assisted torque output by the double-motor power-assisted steering device is superposed with the hand torque of the steering wheel and then output to the rocker shaft through the planet roller screw transmission pair and the rack and- pinion transmission pair. The utility model has the beneficial effects that: when a single motor fails, the other motor can still normally act, so that the normal steering of the steering system is ensured; the steering power assistance can be shared by the two motors, and the steering pure electric requirement of the heavy-load commercial vehicle can be met under the current situation of a 24V voltage system.

The following are the deficiencies in the existing prior art:
• Complexity in manufacturing.
• More Number of parts used.
• Occupies an enormous space.

Accordingly, there exists a need for an actuator for electric power steering system, which provides compact in size, improved output torque to weight ratio, ease of manufacturing and flexible ratio change.

OBJECT OF THE INVENTION
It is the primary object of the present invention to provide a compact steering gear for higher output torque electric power steering system.

It is the primary object of the present invention to provide ease in manufacturing.

SUMMARY OF THE INVENTION
One or more of the problems of the conventional prior art may be overcome by various embodiments of the present invention.

It is primary aspect of the present invention to provide an electric power steering system with improved steering gear actuator, comprising:
a housing;
an input shaft;
an output shaft;
a reduction input gear;
a reduction output gear;
a roller screw unit;
a motor;
a coupler; and
one or more adjuster cover,
wherein the roller screw actuator comprises a screw shaft, one or more roller shaft, one or more bearings, a carrier ring, a rack nut, and one or more adjuster cover,
wherein the roller shaft has a straight axial groove with circular shape,
wherein the screw shaft has one or more helical threads with triangle profile form,
wherein the carrier ring has a straight axial groove with triangle form,
wherein the input shaft is connected with the screw shaft and the thread of the screw shaft is engaged with groove of roller shaft, and the groove of the roller shaft is engaged with the groove of carrier ring, and the carrier ring is connected with the rack nut through the bearing and the adjuster cover.

It is another aspect of the present invention to provide the electric power steering system with improved steering gear actuator, wherein the roller screw unit can be flexible to any ratio change.

It is another aspect of the present invention to provide the electric power steering system with improved steering gear actuator, wherein the rack nut has gear tooth engaged with the output shaft of a steering gear.

It is another aspect of the present invention to provide the electric power steering system with improved steering gear actuator, wherein the adjuster cover is for arresting the axial movement of the roller screw set.

It is another aspect of the present invention to provide the electric power steering system with improved steering gear actuator, wherein the driver torque is applied to the screw shaft through the input shaft.

It is another aspect of the present invention to provide the electric power steering system with improved steering gear actuator, wherein the assist torque transmits from the motor coupled with the reduction input gear, the reduction input gear transfers the torque to the reduction output gear and the torque transmits from the reduction output gear connected with the input shaft and the input shaft transfers to the screw shaft.

It is another aspect of the present invention to provide the electric power steering system with improved steering gear actuator, wherein the torque of the input shaft is transmitted to the screw shaft.

It is another aspect of the present invention to provide the electric power steering system with improved steering gear actuator, wherein the torque of the screw shaft is transmitted into the roller shaft and the torque of the roller shaft is transmitted as the torque of the carrier ring.

It is another aspect of the present invention to provide the electric power steering system with improved steering gear actuator, wherein the torque of carrier ring is transmitted as axial force of the rack nut through the bearing.

It is another aspect of the present invention to provide the electric power steering system with improved steering gear actuator, wherein the axial force of the rack nut delivers as an output torque to the output shaft.

It is another aspect of the present invention to provide the electric power steering system with improved steering gear actuator, wherein the roller screw unit includes one of a planetary roller screw, an inverted roller screw, a recirculating roller screw and a bearing ring roller screw.

It is another aspect of the present invention, wherein the system provides a provision for arresting axial play on screw shaft and the roller shaft, a provision for arresting axial play also between the roller shaft and carrier ring, and a provision for adjusting the backlash between the reduction input gear and reduction output gear.

It is another object of the present invention to provide an actuator for electric power steering system, wherein the motor is connected with reduction input gear and reduction output gear through coupler.

It is another object of the present invention to provide an actuator for electric power steering system, wherein the gear pair arrangement is flexible to motor shaft orientation with respect to the output shaft.

It is another object of the present invention to provide an actuator for electric power steering system, wherein the roller screw set may include any type of roller screw mechanism. For example, the roller screw may include a planetary roller screw, an inverted roller screw, a recirculating roller screw, or a bearing ring roller screw.

It is another object of the present invention to provide an actuator for electric power steering system, wherein, for example, the electric motor comprises a torque of 14 Newton meters during operation. For example, the reduction gear has a gear ratio of 20.5 and the mechanical gear ratio has a gear ratio of again 20.1. In order to that, sum of total torque requires at the output shaft with an efficiency of 60% as 3000 Newton meters, with an efficiency of 85% as 4270 Newton meters, and with an efficiency of 100% as 5025 Newton meters.

It is another object of the present invention to provide an actuator for electric power steering system, wherein, for example, the electric motor comprises a torque of 20 Newton meters during operation. For example, the reduction gear has a gear ratio of 20.5 and the mechanical gear ratio has a gear ratio of again 24.4. In order to that, sum of total torque requires at the output shaft with an efficiency of 60% as 6000 Newton meters, with an efficiency of 85% as 8500 Newton meters, and with an efficiency of 100% as 10000 Newton meters.

It is another object of the present invention to provide an actuator for electric power steering system, wherein, for example, the electric motor comprises a torque of 28 Newton meters during operation. For example, the reduction gear has a gear ratio of 20.5 and the mechanical gear ratio has a gear ratio of again 24.7. In order to that, sum of total torque requires at the output shaft with an efficiency of 60% as 8500 Newton meters, with an efficiency of 85% as 10200 Newton meters, and with an efficiency of 100% as 14170 Newton meters.

BRIEF DESCRIPTION OF THE DRAWINGS:
So that the manner in which the features, advantages and objects of the invention, as well as others which will become apparent, may be understood in more detail, more particular description of the invention briefly summarized above may be had by reference to the embodiment thereof which is illustrated in the appended drawing, which form a part of this specification. It is to be noted, however, that the drawing illustrates only a preferred embodiment of the invention and is therefore not to be considered limiting of the invention's scope as it may admit to other equally effective embodiments.
Figure 1: illustrates the cross-sectional view of the actuator with roller screw set according to the present invention.
Figure 2: illustrates another cross-sectional view of the actuator with roller screw set according to the present invention.
Figure 3: illustrates the cross-sectional view of the actuator with motor according to the present invention.

DESCRIPTION FOR DRAWINGS WITH REFERENCE NUMERALS:
[1] Main Housing
[2] Input shaft
[3] Screw shaft
[4] Roller shaft
[5] Carrier ring
[6] Rack nut
[7] Bearing
[8] Roller bearing
[9] Adjuster Cover
[10] Output shaft
[11] Reduction output gear
[12] Reduction input gear
[13] Coupler
[14] Motor

 
DETAILED DESCRIPTION OF INVENTION
The present invention relates to an electric power steering system of an automobile and more particularly the present invention relates to the roller screw actuator for electric power steering system.

The roller screw actuator for electric power steering system, comprising one or more housings [1], an input shaft [2], an output shaft [10], a screw shaft [3], one or more roller shaft [4], one or more bearings [7], a carrier ring [5], a rack nut [6], one or more adjuster covers [9], a motor [14], a coupler [13], a reduction input gear [12] and a reduction output gear [11]. The roller screw set comprises a screw shaft [3], roller shaft [4], bearings [7], a carrier ring [5], a rack nut [6] and an adjuster cover [9].

The system adjuster cover [9] provides a provision for arresting axial play on screw shaft and the roller shaft, and a provision for arresting axial play also between the roller shaft and carrier ring.

The screw shaft has one or more helical threads with triangle profile form. Roller shaft [4] has a straight axial groove with circular concave form. Carrier ring [5] has a straight axial groove with triangle form.

The input shaft [2] is connected with the screw shaft [3] and the thread of screw shaft [3] is engaged with groove of roller shaft [4] and the groove of roller shaft [4] is engaged with the groove of carrier ring [5]. The carrier ring [5] is connected with rack nut [6] through bearing [7] and adjuster cover [9].

The rack nut [6] has gear tooth engaged with the output shaft [10] of the steering gear. The motor is connected with reduction input gear [12] and reduction output gear [11] through coupler [13]. The adjuster cover [9] provides a provision for arresting axial movement of the roller screw set.

The driver torque applied to the screw shaft [3] through input shaft [2]. The required torque obtained from the input shaft [2] connected with the roller screw set transferred the torque to the output shaft [10]. The assist torque transmits from the motor [14] coupled with the reduction input gear [12], the reduction input gear [12] transfers the torque to the reduction output gear [11] and the torque transmits from the reduction output gear [11] connected with the input shaft [2] and the input shaft [2] transfers to the screw shaft [3].

The torque of screw shaft [3] is transmitted into the roller shaft [4] and the torque of the roller shaft [4] is transmitted as the torque of carrier ring [5]. The axial force of rack nut [6] delivers as an output torque to the output shaft [10].

The roller screw set may include any type of roller screw mechanism. For example, the roller screw may include a planetary roller screw, an inverted roller screw, a recirculating roller screw, or a bearing ring roller screw.

The gear pair arrangement is provided to improve output torque to weight ratio. The gear pair arrangement can be flexible to any ratio change. The gear pair arrangement is flexible to motor shaft orientation with respect to the output shaft [10].

According to one exemplary embodiment of the present invention, for example, the electric motor comprises a torque of 14 Newton meters during operation. For example, the reduction gear has a gear ratio of 20.5 and the mechanical gear ratio has a gear ratio of again 20.1. In order to that, sum of total torque requires at the output shaft with an efficiency of 60% as 3000 Newton meters, with an efficiency of 85% as 4270 Newton meters, and with an efficiency of 100% as 5025 Newton meters. According to another exemplary embodiment of the present invention, the electric motor comprises a torque of 20 Newton meters during operation. For example, the reduction gear has a gear ratio of 20.5 and the mechanical gear ratio has a gear ratio of again 24.4. In order to that, sum of total torque requires at the output shaft with an efficiency of 60% as 6000 Newton meters, with an efficiency of 85% as 8500 Newton meters, and with an efficiency of 100% as 10000 Newton meters. According to another exemplary embodiment of the present invention, the electric motor comprises a torque of 28 Newton meters during operation. For example, the reduction gear has a gear ratio of 20.5 and the mechanical gear ratio has a gear ratio of again 24.7. In order to that, sum of total torque requires at the output shaft with an efficiency of 60% as 8500 Newton meters, with an efficiency of 85% as 10200 Newton meters, and with an efficiency of 100% as 14170 Newton meters.

Advantages:
• Ease of manufacturing
• Compact in size
• Higher Output torque
• Flexibility in ratio change can be achieved by changing worm screw lead parameter.
• Ease in axial play and backlash control
, Claims:WE CLAIM:
1. An electric power steering system with improved steering gear actuator, comprising:
a housing [1];
an input shaft [2];
an output shaft [10];
a reduction input gear [12];
a reduction output gear [11];
a roller screw unit;
a motor [14];
a coupler [13]; and
one or more adjuster cover [9],
characterized in that, the roller screw unit comprises a screw shaft [3], one or more roller shaft [4], one or more bearings [7], a carrier ring [5], a rack nut [6], and one or more adjuster cover [9],
wherein the roller shaft [4] has a straight axial groove with circular shape,
wherein the screw shaft [3] has one or more helical threads with triangle profile form,
wherein the carrier ring [5] has a straight axial groove with triangle form,
wherein the input shaft [2] is connected with the screw shaft [3] and the thread of the screw shaft [3] is engaged with groove of roller shaft [4], and the groove of the roller shaft [4] is engaged with the groove of carrier ring [5], and the carrier ring [5] is connected with the rack nut [6] through the bearing [7] and the adjuster cover [9].
2. The electric power steering system with improved steering gear actuator as claimed in claim 1, wherein the roller screw unit can be flexible to any ratio change.

3. The electric power steering system with improved steering gear actuator as claimed in claim 1, wherein the rack nut [6] has gear tooth engaged with the output shaft [10] of a steering gear.

4. The electric power steering system with improved steering gear actuator as claimed in claim 1, wherein the adjuster cover [9] is for arresting the axial movement of the roller screw set.

5. The electric power steering system with improved steering gear actuator as claimed in claim 1, wherein the driver torque is applied to the screw shaft [3] through the input shaft [2].

6. The electric power steering system with improved steering gear actuator as claimed in claim 1, wherein the assist torque transmits from the motor [14] coupled with the reduction input gear [12], the reduction input gear [12] transfers the torque to the reduction output gear [11] and the torque transmits from the reduction output gear [11] connected with the input shaft [2] and the input shaft [2] transfers to the screw shaft [3].

7. The electric power steering system with improved steering gear actuator as claimed in claim 1, wherein the torque of the input shaft [2] is transmitted to the screw shaft [3].

8. The electric power steering system with improved steering gear actuator as claimed in claim 1, wherein the torque of the screw shaft [3] is transmitted into the roller shaft [4] and the torque of the roller shaft [4] is transmitted as the torque of the carrier ring [5].

9. The electric power steering system with improved steering gear actuator as claimed in claim 1, wherein the torque of carrier ring [5] is transmitted as axial force of the rack nut [6] through the bearing [7].

10. The electric power steering system with improved steering gear actuator as claimed in claim 1, wherein the axial force of the rack nut [6] delivers as an output torque to the output shaft [10].

11. The electric power steering system with improved steering gear actuator as claimed in claim 1, wherein the roller screw unit includes one of a planetary roller screw, an inverted roller screw, a recirculating roller screw and a bearing ring roller screw.