JP7053336B2 - Power steering device - Google Patents

Description

The present invention relates to a power steering device.

A rack-assisted power steering device in which a rotational force (power) of a motor is input to a rack shaft as an assist force is known (see Patent Document 1). In such a power steering device, the rotational force of the motor is converted into a reciprocating motion by a ball screw and input to the rack shaft.

Japanese Unexamined Patent Publication No. 2006-69517

However, in Patent Document 1, in the nut constituting the ball screw, a convex portion is projected on the radial outer side of the circulation path, and the convex portion engages with the concave portion formed on the inner peripheral surface of the sleeve. Therefore, the outer diameters of the nut and sleeve were large. The assist force from the motor is input to the sleeve.

Therefore, it is an object of the present invention to provide a power steering device in which a nut and a sleeve have a small diameter.

As a means for solving the above-mentioned problems, the present invention includes a motor for generating power, a rack shaft for steering steering wheels, and a power transmission mechanism for transmitting power from the motor to the rack shaft. In the steering device, the power transmission mechanism includes a screw rod that is integrated with the rack shaft and has a first thread groove formed on the outer peripheral surface, and a second screw centered on the screw rod and on the inner peripheral surface. A nut having a groove formed therein, a plurality of tumblers for rolling on a rolling path composed of the first threaded groove and the second threaded groove, and a sleeve centered on the nut are provided. The nut includes a nut body having a circulation path for circulating the tumbler inside, and one end of the nut on one end side of the nut body, and the sleeve is arranged radially outside the nut body. A sleeve main body to which power from the motor is input and a sleeve one end portion on one end side of the sleeve main body are provided, and a convex portion protruding outward in the radial direction is provided on the outer peripheral surface of the nut one end portion. A concave portion is formed on the inner peripheral surface of the sleeve end portion to engage with the convex portion, and the first length from the central axis of the screw rod to the apex of the convex portion is the central axis to the convex portion. It is a power steering device characterized in that it is shorter than the second length to the radial outer end of the circulation path.

According to such a configuration, since the convex portion of one end of the nut and the concave portion of one end of the sleeve are engaged with each other in the circumferential direction, the power of the motor is transmitted from the sleeve to the nut. Further, the first length from the central axis to the apex of the convex portion, that is, the first length from the central axis to the engagement position of the convex portion and the concave portion is shorter than the second length from the central axis to the circulation path. .. In this way, since the nut and the sleeve are engaged at positions deviated from the circulation path in the axial direction, an engaged portion with the sleeve becomes unnecessary on the radial outer side of the nut body in which the circulation path is formed. , The outer diameter of the nut body and the sleeve body is smaller than that of Patent Document 1.

According to the present invention, it is possible to provide a power steering device in which a nut and a sleeve have a small diameter.

It is a block diagram of the power steering apparatus which concerns on this embodiment. It is sectional drawing of the main part of the power steering apparatus which concerns on this embodiment. FIG. 2 is a cross-sectional view taken along the line X1-X1 of FIG. It is sectional drawing of the power steering apparatus which concerns on the modification. It is sectional drawing of the power steering apparatus which concerns on the modification.

An embodiment of the present invention will be described with reference to FIGS. 1 to 3.

≪Structure of power steering device≫
The power steering device 100 according to the present embodiment is a rack assist type in which the assist force (power) generated by the electric motor 140 is input to the rack shaft 130.

The power steering device 100 includes a steering wheel 110, a steering shaft 120, a rack shaft 130, a motor 140, a power transmission mechanism 1 that transmits the assist force of the motor 140 to the rack shaft 130, an angle sensor 191 and the like, and an ECU 200. (Electronic Control Unit) and.

The steering wheel 110 is an operating member operated by the driver.

The steering shaft 120 is an elongated cylindrical member, and is rotatably supported by a vehicle body via a bearing (not shown). The upper end of the steering shaft 120 is connected to the steering wheel 110, and the steering shaft 120 and the steering wheel 110 rotate integrally.

A pinion gear 121 is formed at the lower end of the steering shaft 120, and the pinion gear 121 meshes with the rack 132 described later. A torsion bar (not shown) that twists in the circumferential direction is provided in the middle of the steering shaft 120, and the torsion bar twists in response to the operating torque.

The rack shaft 130 is an elongated rod-shaped member extending in the vehicle width direction, and is a member that steers the front wheels 302 by sliding. The rack shaft 130 is slidably housed in a cylindrical housing 131 (see FIG. 2) via a bush (not shown). A rack 132 is formed on the rack shaft 130.

Rack ends 133 are fixed to both ends of the rack shaft 130. Each rack end 133 is connected to a front wheel 302 (steering wheel) via a tie rod 301. Then, when the rack shaft 130 slides in the vehicle width direction, the front wheels 302 and 302 are steered.

The motor 140 is an electric motor that generates an assist force according to a command from the ECU 200. However, a hydraulic motor may be used.

The angle sensor 191 detects the operating angle of the steering shaft 120 and outputs it to the ECU 200. The torque sensor 192 detects the operating torque input to the steering shaft 120 by the driver and outputs it to the ECU 200. The vehicle speed sensor 193 detects the vehicle speed and outputs it to the ECU 200.

The ECU 200 is a control device that electronically controls the power steering device 100, and is configured to include a CPU, ROM, RAM, various interfaces, electronic circuits, etc., and controls various devices according to a program stored therein. However, various processes are executed.

Specifically, the ECU 200 drives the motor 140 based on the operating angle, operating torque, and vehicle speed. For example, as the operating torque increases, the driving torque of the motor 140 increases.

≪Power transmission mechanism≫
The power transmission mechanism 1 is a mechanism for transmitting the assist force of the motor 140 to the rack shaft 130. The power transmission mechanism 1 includes a belt mechanism 60 and a ball screw 10.

<Belt mechanism>
The belt mechanism 60 is a mechanism that transmits the assist force (rotational force) of the motor 140 to the nut 20 described later. The belt mechanism 60 includes a drive pulley 61 fixed to the output shaft of the motor 140, a passive pulley 70 (sleeve) fixed to the nut 20, and a belt 62 spanned by the drive pulley 61 and the passive pulley 70. I have. The passive pulley 70 will be described in detail later.

<Ball screw>
The ball screw 10 is a conversion mechanism that converts the rotational force from the motor 140 into a linear motion in the vehicle width direction. The ball screw 10 includes a screw rod 11, a nut 20, and a plurality of balls 58 (rollers).

<Screw rod>
The screw rod 11 is a rod-shaped portion integrated with the rack shaft 130, and is centered on the central axis O1. In the present embodiment, the screw rod 11 is configured by processing a part of the rack shaft 130, but the screw rod 11 as a separate member may be connected to the rack shaft 130. A first thread groove 12 having a semicircular cross section is threaded on the outer peripheral surface of the screw rod 11.

<Nut>
The nut 20 is a cylindrical member arranged around the screw rod 11 so as to surround the screw 11. The nut 20 includes a nut body 30, a nut left end 40 (nut one end) formed on the left end side (one end side) of the nut body 30, and a nut formed on the right end side (end end side) of the nut body 30. It is provided with a right end portion 50.

A second thread groove 31 having a semicircular cross section is threaded on the inner peripheral surface of the nut body 30. The second thread groove 31 constitutes a rolling path 15 having a circular cross section for rolling the ball 58 with the first thread groove 12.

Inside the nut body 30, more specifically, a circulation path 32 that opens to the outer peripheral surface and extends in the axial direction is formed. The circulation path 32 is a passage that communicates both ends of the rolling path 15 and circulates the ball 58 so as to pass through the rolling path 15. The radial outer opening of the circulation path 32 is closed by the passive pulley 70.

Deflectors 22 are provided on the left side and the right side of the circulation path 32, respectively. Each deflector 22 is a member that transfers and guides the ball 58 between the circulation path 32 and the rolling path 15. That is, the deflector 22 scoops up the ball 58 from the rolling path 15 and guides it to the circulation path 32, or guides the ball 58 from the circulation path 32 to the rolling path 15.

The left end portion 40 of the nut and the right end portion 50 of the nut are formed to be thinner than the nut body 30, and the outer peripheral surface of the nut 20 is different at the boundary portion between the nut body 30 and the left end portion 40 of the nut or the right end portion 50 of the nut. It has become.

On the outer peripheral surface of the left end portion 40 of the nut, one ridge 41 (convex portion) that protrudes outward in the radial direction and extends in the axial direction is formed (see FIG. 3). In the present embodiment, the ridge 41 and the circulation path 32 are formed at the same position in the circumferential direction. That is, the ridge 41 and the circulation path 32 are in the same phase.

The ridge 41 is press-fitted into the concave groove 81 (recess) described later, and the ridge 41 and the concave groove 81 are engaged in the circumferential direction and are not easily displaced in the axial direction. As a result, the nut 20 rotates integrally with the passive pulley 70. The left end portion 40 of the nut is also press-fitted into the left end portion 80 of the pulley, which will be described later, so that the nut 20 and the passive pulley 70 are less likely to shift in the axial direction. A C-shaped clip 49 for preventing the left end portion 80 of the pulley from falling off is attached to the left end portion 40 of the nut.

The right end portion 50 of the nut is a self-aligning type and is rotatably supported by a ball bearing 51 with a shield. A lock nut 52 screwed into the right end portion 50 of the nut is in contact with the inner ring 51a of the ball bearing 51, and the ball bearing 51 is positioned. The outer ring 51b of the ball bearing 51 is internally fitted in the housing 131.

<Ball>
The ball 58 rolls on a rolling path 15 formed between the screw rod 11 and the nut 20, thereby facilitating the relative rotation between the screw rod 11 and the nut 20. In addition, in FIG. 2, only one ball 58 is described in the circulation path 32, and the others are omitted.

<Passive pulley>
The passive pulley 70 of the belt mechanism 60 will be described. The passive pulley 70 is a cylindrical member arranged around the nut 20 so as to surround the nut 20. The passive pulley 70
It includes a pulley main body 71 (sleeve main body) and a pulley left end portion 80 (sleeve one end portion) formed on the left end side (one end side) of the pulley main body 71.

The pulley body 71 is a portion arranged on the outside of the nut body 30. A belt 62 is hung on the pulley main body 71, and power from the motor 140 is input to the pulley main body 71. An annular restricting member 72, 72 having an L-shaped cross section that regulates the belt 62 in the axial direction is fixed to the outer peripheral surface of the pulley main body 71.

The left end portion 80 of the pulley is formed to be thicker than the pulley main body 71, and the inner peripheral surface of the left end portion 80 of the pulley projects radially inward (on the central axis O1 side) from the inner peripheral surface of the pulley main body 71. That is, the inner peripheral surface of the passive pulley 70 is stepped at the boundary portion between the pulley main body 71 and the left end portion 80 of the pulley.

One concave groove 81 (recess) extending in the axial direction is formed on the inner peripheral surface of the left end portion 80 of the pulley (see FIG. 3). As described above, the ridge 41 is fitted in the concave groove 81, and the concave groove 81 is engaged with the ridge 41.

The first length L1 from the central axis O1 to the apex of the ridge 41 is shorter than the second length L2 from the central axis O1 to the top wall surface (diameter outer end) of the circulation path 32. That is, in the radial direction, the engagement position between the ridge 41 and the concave groove 81 is radially inside the circulation path 32.

≪Effects of power steering device≫
The operation and effect of the power steering device 100 will be described.
Since the convex strip 41 of the nut 20 and the concave groove 81 of the passive pulley 70 are engaged with each other at a position deviated from the circulation path 32 in the axial direction, the passive pulley is radially outward of the circulation path 32 in the nut body 30. The engaged portion with 70 becomes unnecessary. As a result, the outer diameters of the nut 20 and the passive pulley 70 become smaller than those of Patent Document 1.

≪Variation example≫
Although one embodiment of the present invention has been described above, the present invention is not limited to this, and may be modified as follows, for example.

In the above-described embodiment, the configuration in which the power transmission mechanism 1 includes the belt mechanism 60 as a mechanism for transmitting the rotational force of the motor 140 to the nut 20 is exemplified, but in addition, for example, a chain mechanism for transmitting power via a chain is provided. It may be provided. The chain mechanism includes a drive sprocket fixed to the output shaft of the motor 140, a passive sprocket (sleeve) fixed to the nut 20, and a drive sprocket and a chain spanned to the passive sprocket.

Alternatively, for example, the power transmission mechanism 1 may be configured to include a gear mechanism. The gear mechanism includes a drive gear fixed to the output shaft of the motor 140 and a passive gear (sleeve) that meshes with the drive gear and is fixed to the nut 20.

In the above-described embodiment, the configuration in which the ridge 41 and the concave groove 81 and the circulation path 32 are at the same position (same phase) in the circumferential direction is exemplified, but the positions of the ridge 41 and the concave groove 81 can be freely changed. Is. For example, the ridge 41 and the groove 81 may be formed on the opposite side of the circulation path 32 by 180 °.

In the above-described embodiment, the configuration in which one ridge 41 and one concave groove 81 are engaged is exemplified, but the number of the ridge 41 and the concave groove 81 can be freely changed. That is, the power steering device 100 includes at least one protrusion 41 (convex portion) and at least one concave groove 81 (concave portion), which are fitted and engaged with each other in the circumferential direction. Any configuration may be used.

Specifically, for example, as shown in FIG. 4, four ridges 41 and concave grooves 81 may be provided at equal intervals (90 °) in the circumferential direction. Further, as shown in FIG. 5, a serration shaft portion 42 is formed on the outer peripheral surface of the nut left end portion 40, a serration hole portion 82 is formed on the inner peripheral surface of the pulley left end portion 80, and the nut left end portion 40 and the pulley left end portion are formed. A configuration in which 80 and 80 are serrated may be used. In this case, the serration shaft portion 42 is provided with a plurality of convex portions, the serration hole portion 82 is provided with a plurality of concave portions, and the plurality of convex portions and the plurality of concave portions are fitted and engaged in the circumferential direction.

In the above-described embodiment, as shown in FIG. 3, the width of the ridge 41 in the circumferential direction is narrow, and the central angle of the ridge 41 when centered on the central axis O1 is about 10 °. However, the width of the ridge 41 can be changed freely. For example, the width of the ridge 41 may be a half arc or more, that is, the central angle of the ridge 41 may be 180 ° or more. The same applies to the concave groove 81.

In the above-described embodiment, the power steering device 100 exemplifies a configuration in which the steering wheel 110 and the rack shaft 130 are mechanically connected, but in addition, for example, SBW (Steer By Wire,) which is not mechanically connected. The configuration may be a steering-by-wire) method.

1 Power transmission mechanism 10 Ball screw 11 Thread rod 12 1st thread groove 15 Rolling path 20 Nut 30 Nut body 31 2nd thread groove 32 Circulation path 40 Nut left end (nut end)
41 Convex (convex part)
58 balls (rollers)
60 Belt mechanism 70 Passive pulley (sleeve)
71 Pulley body (sleeve body)
80 Pulley left end (sleeve end)
81 concave groove (recess)
100 Power steering device 130 Rack axle 140 Motor 302 Front wheel (steering wheel)
O1 Central axis L1 1st length L2 2nd length

Claims (2)

A motor that generates power and
The rack axle that steers the steering wheel and
A power transmission mechanism that transmits power from the motor to the rack shaft,
It is a power steering device equipped with
The power transmission mechanism includes a screw rod that is integrated with the rack shaft and has a first thread groove formed on the outer peripheral surface, and a nut centered on the screw rod and having a second thread groove formed on the inner peripheral surface. A plurality of tumblers that roll on a rolling path composed of the first thread groove and the second thread groove, and a sleeve centered on the nut.
The nut includes a nut body having a circulation path for circulating the tumbler inside, and one end of the nut on one end side of the nut body.
The sleeve includes a sleeve body that is arranged radially outside the nut body and to which power from the motor is input, and one end of the sleeve on one end side of the sleeve body.
A convex portion protruding outward in the radial direction is formed on the outer peripheral surface of one end of the nut.
A concave portion that engages with the convex portion is formed on the inner peripheral surface of one end of the sleeve.
A power steering device characterized in that the first length from the central axis of the screw rod to the apex of the convex portion is shorter than the second length from the central axis to the radial outer end of the circulation path. The power steering device according to claim 1, wherein the convex portion is press-fitted into the concave portion.

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