Belt-type drive train and rack-and-pinion type electric power steering device having the same

Abstract

Belt type drive train with: a ball nut (220) engaged with a rack bar (155) and configured to slidably move the rack bar (155); a nut pulley (305) engaged with an outer peripheral surface of the ball nut (220) and configured to transmit a driving force of a belt (210); and support members (310) formed in an inner peripheral surface of the nut pulley (305); characterized in that the support members (310) are configured to add a supporting force while being elastically deformed when the nut pulley (305) engages the ball nut (220); and the support elements (310) comprise: a fixed part (311) inserted into the inside of the nut pulley (305) and integrally fixed thereto; and an elastically deformable member (313) projecting outwardly from the inner peripheral surface of the nut pulley (305) and being elastically deformed when the nut pulley (305) is engaged with the ball nut (220); and the elastically deformable part (313) comprises: Side edges (313a) connected to the fixed parts (311) extend in a radial direction, portions of the side edges (313a) being bent in a circumferential direction and connected to each other, and a projection (313c) projecting in the radial direction and formed in a region (313b) in which the side edges (313a) of the elastically deformable part (313) are connected to each other; and the elastically deformable part (313) has curvatures with different signs in the circumferential direction.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention

[0001] The present invention relates to a belt-type drive train and a rack-assist type electric power steering apparatus having the belt-type drive train. More specifically, the present invention relates to a belt-type drive train and a rack-assist type electric power steering apparatus having the belt-type drive train, which can increase durability while preventing non-traction spinning of a ball nut and a nut pulley due to slippage between the ball nut and the nut pulley during operation of a drive belt by driving a motor, and provide a user with comfortable steering by minimizing vibration and noise generated by a rack bar, ball nut, nut pulley, etc., transmitted when the rack bar slides while the nut pulley and ball nut rotate. 2. Description of the state of the art

[0002] A general rack and pinion type electric power steering apparatus includes a steering system connected to wheels on both sides from a steering wheel, and an assist mechanism for supplying an assist steering force to the steering system.

[0003] Fig. 1 is a partially cross-sectional view schematically illustrating a general rack-assist type electric power steering apparatus, and Fig. 2 is a cross-sectional view schematically illustrating a belt type drive train in the general rack assist type electric power steering apparatus.

[0004] The general rack-and-pinion type electric power steering apparatus includes a steering system 100 connected to wheels 150 on both sides from a steering wheel 105, and an assist mechanism 160 for supplying an assist steering force to the steering system 100.

[0005] The steering system 100 includes a steering shaft 110, an upper end of which is connected to the steering wheel 105 for rotation with the steering wheel 105, and a lower end of which is connected to a pinion shaft 120 through a pair of universal joints 115. Furthermore, the pinion shaft 120 is connected to a rack bar 155 through a rack and pinion mechanism part 135, and both ends of the rack bar 155 are connected to wheels 150 through a steering tie rod 140 and a tie rod arm 145.

[0006] A pinion gear 125 formed in a lower end of the pinion shaft 120 is engaged with a rack gear 130 formed on one side of an outer peripheral surface of the rack bar 155, so that the rack / pinion mechanism part 135 is formed.

[0007] An assist mechanism 160 includes a torque sensor 117 for measuring a torque applied by a driver to the steering wheel 105 and outputting an electrical signal proportional to the measured steering torque, an electronic control unit (ECU) for generating a control signal based on the electrical signal transmitted from the torque sensor 117, a motor (electric motor) 165 for generating an assist steering force based on the control signal transmitted from the ECU, and a belt-type drive train 170 for transmitting the assist force generated in the motor 165 to the rack and pinion 155 through a belt 210.

[0008] The belt-type drive train 170 includes a motor 165 controlled by the ECU, a motor pulley 205a fixed to a shaft 165a of the motor 165, the belt 210 wound around the motor pulley 205a, a ball nut 220 for supporting the rack bar 155 in a rack housing 200 surrounding the rack bar 155, and a nut pulley 205b coupled to an outer peripheral surface of the ball nut 220.

[0009] The ball nut 220 rotates while engaging with the rack bar 155 through a ball to cause the rack bar 155 to slide on an inner side of the rack housing 200. A bearing 340 for supporting the rotation of the ball nut 220 is mounted on the outer peripheral surface of the ball nut 220.

[0010] However, according to the conventional art, the ball nut and the nut pulley spin without traction due to the generation of slippage, so that power transmission efficiency is deteriorated and the auxiliary steering force cannot be transmitted accurately.

[0011] Furthermore, there is a problem that when the rack rod slides while the ball nut rotates, noise and vibration are generated by the rack rod, the ball nut, the nut pulley, the bearing, the rack housing, and the like, and the vibration and noise are transmitted to other components, thereby causing loosening of fastened or tightened components.

[0012] In addition, the transmitted noise and vibrations are transmitted to a driver along with vibrations and noise from other components, thereby impairing the driver's smooth steering.

[0013] The generic document US 2009 / 0 191 995 A1 describes a pulley comprising an outer cylindrical portion having an outer peripheral surface on which a belt is to be wound, an inner cylindrical portion disposed radially inward of and concentric with the outer cylindrical portion, and a plurality of ribs connecting an inner peripheral surface of the outer cylindrical portion and an outer peripheral surface of the inner cylindrical portion.

[0014] DE 10 2008 014 402 A1 describes an electromechanical steering system with a transmission having a belt drive with a first pulley, a second pulley, and a belt coupling them. At least one of the pulleys has an outer ring and an inner ring, with a damping medium arranged in a space formed between the outer ring and the inner ring, torsionally elastically coupling the outer ring to the inner ring.

[0015] JP 2011- 105 075 A describes another conventional electric power steering device. SUMMARY OF THE INVENTION

[0016] Accordingly, the present invention has been created to solve the above-mentioned problems encountered in the prior art, and the present invention provides a belt-type drive train and a rack-assist type electric power steering apparatus having the belt-type drive train, which can enhance durability while preventing non-traction spinning of a ball nut and a nut pulley due to slippage between the ball nut and the nut pulley during operation of a drive belt by a motor, and provide a user with comfortable steering by minimizing vibration and noise transmitted through a rack bar, the ball nut, the nut pulley, etc., when the rack bar slides while the nut pulley and the ball nut rotate.

[0017] In accordance with the present invention, there is provided a belt type power train having the features of claim 1 and a rack assist type electric power steering apparatus having the features of claim 3.

[0018] Advantageous further training results from the dependent subclaims.

[0019] Accordingly, the present invention has an effect of enhancing durability while preventing non-traction spinning of a ball nut and a nut pulley due to slippage between the ball nut and the nut pulley during operation of a drive belt by driving a motor, and providing a user with comfortable steering by minimizing vibration and noise transmitted through a rack bar, the ball nut, the nut pulley, etc. when the rack bar slides while the nut pulley and the ball nut rotate. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a partially cross-sectional view schematically illustrating a general rack assist type electric power steering apparatus. Fig. 2 is a cross-sectional view schematically illustrating a belt type drive train in the general rack assist type electric power steering apparatus. Fig. 3 is an exploded perspective view illustrating a portion of a belt drive train in accordance with an embodiment of the present invention. Fig. 4 is a front view illustrating a mother pulley in a belt drive train. Fig. 5 is a front view illustrating a mother pulley in a belt drive train in accordance with an embodiment of the present invention. Fig. 6 is a front view illustrating a coupling state of a nut pulley and a ball nut in a belt drive train according to an embodiment of the present invention. Fig. 7 is an exploded perspective view illustrating a portion of a belt drive train. Fig. 8 and Fig. 9 are front views illustrating a mother pulley in a belt drive train. DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0020] Exemplary embodiments of the present invention will be described below with reference to the accompanying drawings. In the following description, like elements will be denoted by the same reference numerals even though they are shown in different drawings. Furthermore, in the following description, a detailed explanation of known related functions and configurations may be omitted to avoid unnecessarily obscuring the subject matter of the present invention.

[0021] Furthermore, in describing the structural elements of the present invention, terms such as a first, a second, A, B, (a), (b), or the like may be used. Such a term is used merely to distinguish one structural element from another structural element and does not limit the essential feature, order, or sequence of the structural element, or the like. When a structural element is "coupled," "joined," or "connected" to another structural element, a structural element is directly coupled or connected to another structural element, but it can also be understood that another, different structural element may be "coupled," "mounted," or "connected" between each structural element.

[0022] Fig. 3 is an exploded perspective view illustrating a portion of a belt drive train in accordance with an embodiment of the present invention. Fig. 4 is a front view illustrating a mother pulley in a belt drive train. Fig. 5 is a front view illustrating a mother pulley in a belt drive train in accordance with an embodiment of the present invention. Fig. 6 is a front view illustrating a coupling state of a nut pulley and a ball nut in a belt drive train according to an embodiment of the present invention. Fig. 7 is an exploded perspective view illustrating a portion of a belt drive train. Fig. 8 and Fig. 9 are front views illustrating a mother pulley in a belt drive train.

[0023] With reference to Fig. 3 to Fig. 9 in conjunction with Fig. 1 and Fig. 2, a belt-type drive train includes a ball nut 220 engaged with a rack bar 155 to cause the rack bar 155 to slide, a nut pulley 305 engaged with an outer peripheral surface of the ball nut 220 to transmit a driving force of a belt 210, and support members 310 provided in an inner peripheral surface of the nut pulley 305 and adding a supporting force while being elastically deformed upon engagement with the ball nut 220.

[0024] The belt-type drive train includes a drive device and a driven device. The drive device includes a motor 165 controlled by the ECU, a motor pulley 205a coupled to a shaft 165a of the motor 165, the belt 210, etc.

[0025] Furthermore, the output device has the ball nut 220 for supporting the rack bar 115 inside a rack housing 200 surrounding the rack bar 115, and the nut pulley 305 is engaged with the outer peripheral surface of the ball nut 220.

[0026] The motor pulley 205a, which is connected to the motor 165, and the nut pulley 305, which is connected to the rack and pinion 155, are arranged parallel to each other. The belt 210 is attached to the motor pulley 205a and the nut pulley 305 so that a rotational force of the motor 165 is transmitted to the rack and pinion 155 through the ball nut 220, and the rack and pinion 155 moves horizontally upon operation of the ball nut 220, thereby generating an auxiliary steering force.

[0027] The ball nut 220 rotates while engaging with the rack bar 155 through the ball 230, causing the rack bar 115 to slide on an inner side of the rack housing 200 and a gear case (not shown). The nut pulley 305 for rotating the ball nut 220 and a bearing 240 for supporting the rotation of the ball nut 220 are provided on the outer peripheral surface of the ball nut 220.

[0028] A power transmission structure capable of generating an auxiliary steering force by sliding the rack bar 155 in the shaft direction is provided in an inner peripheral surface of the ball nut 220 and the outer peripheral surface of the rack bar 155. The power transmission structure includes an outer peripheral screw groove 155a having a hemispherical or arcuate cross section and formed in a spiral shape in the outer peripheral surface of the rack bar 155, with the ball 230 inserted into the outer peripheral screw groove 155a, and an inner peripheral screw groove 220a having a hemispherical or arcuate cross section and formed in a spiral shape in the inner peripheral surface of the ball nut 220, which fits with the outer peripheral screw groove 155a.

[0029] The ball nut 220 is a hollow tube provided with the inner peripheral screw groove 220a in its inner peripheral surface. The nut pulley 305 is tightly installed on one side of the outer peripheral surface of the ball nut 220, and the bearing 240 is installed on an opposite side of the outer peripheral surface of the ball nut 220. A set screw (not shown) is screwed to an inner peripheral surface of the rack housing 200 to be fixed to a distal end of an arcuate ridge and one end of the outer peripheral surface of the bearing 240, while supporting the bearing 240.

[0030] Furthermore, the support members 310 provided in or on an inner peripheral surface of the nut pulley 305 add the support force while being elastically deformed when the nut pulley 305 engages or is engaged with the ball nut 220, thereby absorbing vibrations and noises while preventing the nut pulley 305 from spinning without traction.

[0031] The support elements 310 can be Fig. 3 to Fig. 6 or according to Fig. 7 to Fig. 9 must be implemented.

[0032] The support member 310 is formed of a metal material, a plastic material, a rubber material, or the like. As shown in Fig. 4, the plurality of support members 310 may be inserted into and engaged with the mother pulley 305, or may be formed integrally with the mother pulley 305 by an insert technique.

[0033] In the present case, the support member 310 has a projection 313c projecting in a radial direction, ie, toward the inner center of the ball nut 220, and the nut pulley 305 has a coupling recess 305a to which the support members 310 are coupled in the inner peripheral surface of the nut pulley 305.

[0034] Furthermore, the support element 310, as shown in Fig. 5 and Fig. 6, has a cylindrical shape formed by bending a thin plate made of a metal material, a plastic material, or a rubber material, and is integrally formed with the mother pulley 305 by the insert molding technique. The support member 310 may generally include a fixed part 311 and an elastically deformable part 313.

[0035] The fixed part 311 is a fixed part inserted into the inside of the mother pulley 305 and integrally formed therewith by the insert molding technique, and it assists the elastic deformation and recovery of the elastically deformable part 313.

[0036] The elastically deformable part 313 is a part that protrudes from the inner peripheral surface of the nut pulley 305 and adds the supporting force to the nut pulley 305 and the ball nut 220 while being elastically deformed upon engagement of the nut pulley 305 and the ball nut 220, thereby preventing the slippage without traction of the nut pulley 305.

[0037] In an embodiment described in Fig. 5 and Fig. 6, both side edges 313a of each of the elastically deformable parts 313 connected to the fixed parts 311 extend and protrude in the radial direction, are then bent in the circumferential direction, and are then connected to each other.

[0038] Furthermore, the elastically deformable part 313 has a projection 313c formed at a portion 313b where the side edges 313a of the elastically deformable part 313 are joined to each other after being bent in the circumferential direction, the projection 313c projecting in the radial direction, ie, toward the inner center of the ball nut 220.

[0039] Accordingly, when the nut pulley 305 engages with the outer peripheral side of the ball nut 220, the projection 313c of the elastically deformable part 313 is elastically deformed as shown in Fig. 6, and adds the supporting force to the ball nut 220 and the nut pulley 305 by an elastic restoring force, so that it is possible to absorb and dampen vibrations and noises generated in the nut pulley 305 and the ball nut 220 and vibrations and noises transmitted through the ball and the rack bar 155 upon rotation of the ball nut 220, while at the same time preventing the ball nut 220 and the nut pulley 305 from spinning without traction.

[0040] Here, a deep support part 220b may be provided in the outer peripheral surface of the ball nut 220, by which the elastically deformable part 313 is supported.

[0041] The support member 310 may also be formed of a metal material, a plastic material, a rubber material, etc. As shown in Fig. 8, the plurality of support members 310 may be individually inserted into the mother pulley 305 or may be integrally formed with the mother pulley 305 by the insert technique.

[0042] In this case, the support member 310 is formed to have a curved surface that is convex in the radial direction while protruding outward from the inner peripheral surface of the nut pulley 305. The nut pulley 305 has coupling recesses 305a to which the support members 310 are coupled in the inner peripheral surface thereof.

[0043] Furthermore, the support member 310 has a cylindrical shape formed by bending a thin plate made of a metal material, a plastic material, or a rubber material, as shown in Fig. 9, and is formed integrally with the mother pulley 305 using the insert technique. The support element 310 may generally include the fixed or immovable part 311 and the elastically deformable part 313.

[0044] In this case, the elastically deformable part 313 is formed to have a curved surface that is convex in the radial direction while protruding outward from the inner peripheral surface of the nut pulley 305.

[0045] As described above, the elastically deformable part 313 is formed to have the curved surface which is convex in the radial direction, so that the elastically deformable part 313 adds the supporting force to the ball nut 220 and the nut pulley 305 while being elastically deformed, similarly to the projection 313c in Fig.4, thereby absorbing and damping vibrations and noises generated in the nut pulley 305 and the ball nut 220, and vibrations and noises transmitted through the ball and the rack bar 155 upon rotation of the ball nut 220, while simultaneously preventing the ball nut 220 and the nut pulley 305 from spinning without traction.

[0046] The elastically deformable parts 313 may be arranged at a predetermined interval in the circumferential direction in the inner circumferential surface of the nut pulley 305, and the plurality of elastically deformable parts 313 may also be arranged at a predetermined interval in the shaft direction.

[0047] The number of elastically deformable parts can be determined or set according to the type of vehicles or a magnitude of the auxiliary steering force required in the rack assist type electric power steering device.

[0048] The belt-type drive train constitutes the rack-assist type electric power steering apparatus together with the torque sensor for outputting the electric signal proportional to the steering torque, the ECU for generating the control signal based on the electric signal transmitted from the torque sensor, and the motor 165 for generating the assist steering force based on the control signal transmitted from the ECU.

[0049] Accordingly, the above-mentioned present invention improves power transmission efficiency and durability by preventing the non-traction spinning of the ball nut and the nut pulley due to the slippage between the ball nut and the nut pulley during operation of the belt by the engine, and provides a driver with comfortable steering by minimizing vibrations and noises transmitted through the rack bar, the ball nut, the nut pulley, etc. when the rack bar slides while the nut pulley and the ball nuts rotate.

[0050] Although it has been described above that all components of an embodiment of the present invention are connected as a single unit or coupled so as to be operatively operated as a single unit, the present invention is not necessarily limited to such an embodiment. That is, one or more of the components may be selectively coupled to be operatively operated as one or more units.

[0051] Furthermore, since terms such as "containing," "comprising," and "having" imply that one or more corresponding components may be present, unless expressly stated otherwise, they should be interpreted to include one or more other components. All terminology containing one or more technical or scientific terminologies has the same meaning as normally understood by those skilled in the art, unless defined differently. A commonly used term, such as a term defined by a dictionary, should be interpreted to have a meaning equivalent to that in the context of a relevant, pertinent description and should not be interpreted in an idealized or overly formal sense unless clearly defined in the present patent specification.

Claims

[1] Belt type drive train with: a ball nut (220) engaged with a rack bar (155) and configured to slidably move the rack bar (155); a nut pulley (305) engaged with an outer peripheral surface of the ball nut (220) and configured to transmit a driving force of a belt (210); and support members (310) formed in an inner peripheral surface of the nut pulley (305); characterized by , that the support members (310) are configured to add a supporting force while being elastically deformed when the nut pulley (305) engages the ball nut (220); and the support elements (310) comprise: a fixed part (311) inserted into the inside of the nut pulley (305) and integrally fixed thereto; and an elastically deformable member (313) projecting outwardly from the inner peripheral surface of the nut pulley (305) and being elastically deformed when the nut pulley (305) is engaged with the ball nut (220); and the elastically deformable part (313) comprises: Side edges (313a) connected to the fixed parts (311) extend in a radial direction, portions of the side edges (313a) being bent in a circumferential direction and connected to each other, and a projection (313c) projecting in the radial direction and formed in a region (313b) in which the side edges (313a) of the elastically deformable part (313) are connected to each other; and the elastically deformable part (313) has curvatures with different signs in the circumferential direction. [2] A belt-type drive train according to claim 1, wherein each support member (310) is formed integrally with the mother pulley (305) by insert molding. [3] Rack and pinion type electric power steering device comprising: a torque sensor for outputting an electrical signal proportional to the steering torque; an electronic control unit (ECU) for generating a control signal based on the electrical signal transmitted from the torque sensor; a motor (165) for generating an auxiliary steering force based on the control signal transmitted from the ECU; and a belt-type drive train for transmitting an auxiliary power generated in the motor (165) to a rack bar (155), wherein the belt type drive train comprises: a ball nut (220) engaged with the rack bar (155) and configured to slidably displace the rack bar (155); a nut pulley (305) engaged with an outer peripheral surface of the ball nut (220) and configured to transmit a driving force of a belt (210); and Support members (310) formed in an inner peripheral surface of the nut pulley (305); characterized by , that the support members (310) are configured to add a supporting force while being elastically deformed when the nut pulley (305) engages the ball nut (220); and the support elements (310) comprise: a fixed part (311) inserted into the inside of the nut pulley (305) and integrally fixed thereto; and an elastically deformable member (313) projecting outwardly from the inner peripheral surface of the nut pulley (305) and being elastically deformed when the nut pulley (305) is engaged with the ball nut (220); and the elastically deformable part (313) comprises: Side edges (313a) connected to the fixed parts (311) extend in a radial direction, portions of the side edges (313a) being bent in a circumferential direction and connected to each other, and a projection (313c) projecting in the radial direction and formed in a region (313b) in which the side edges (313a) of the elastically deformable part (313) are connected to each other; and the elastically deformable part (313) has curvatures with different signs in the circumferential direction.

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