JP4978767B2 - Steering device - Google Patents

Description

  The present invention relates to a rack and pinion type steering apparatus.

The rack-and-pinion steering device includes a rack bar that is slidably supported by a housing (see, for example, Patent Document 1). The rack bar moves in the axial direction by the operation of the steering wheel. Thereby, a knuckle arm can be rotated via the tie rod provided in the both ends of a rack bar, and the steered wheel attached to the knuckle arm can be steered.
Japanese Patent Laid-Open No. 2004-10956

  Some of the above steering devices generate a steering assist force using a hydraulic cylinder. Specifically, a cylindrical cylinder main body that is fixed to the housing and surrounds a part of the rack bar, and a piston that is fitted in a ring-shaped groove of the rack bar are provided. Oil chamber is defined. Due to the differential pressure between the two oil chambers, the piston is moved to give a steering assist force to the rack bar. Oil seals are provided at both ends of the cylinder body to seal between the cylinder body and the rack bar.

When the rack bar moves in the axial direction, it slides frictionally with the lip of the oil seal, so wear resistance is required. Further, since the rack bar receives a bending moment due to the input from the tire (reverse input), a sufficient bending strength that can withstand this bending moment is required.
Therefore, it is conceivable to improve the wear resistance and to secure a sufficient bending strength by performing a heat treatment on the surface of the rack bar to form a hardened layer having a sufficient thickness. However, when the hardened layer is thickened, the rack bar is distorted due to the heat treatment. This problem is likely to occur particularly when the rack bar is made hollow for weight reduction.

Similar problems exist not only in power steering devices using hydraulic cylinders, but also in power steering devices and manual steering devices that apply the power of an electric motor to a rack bar via a speed reduction mechanism.
The present invention has been made under such a background, and an object of the present invention is to provide a steering device that is excellent in wear resistance and bending strength of a rack bar and that is less distorted in the rack bar.

In order to achieve the above object, the present invention is formed in a hollow shape, and is slidably supported in the axial direction (S) by the cylindrical housing (30), and moves in the axial direction (S) in response to steering. rack comprising a bar (14), the surface (40) of said rack bar (14), over the entire region, the cured layer formed is subjected to a heat treatment (41) is formed, the end of the rack bar in part vicinity, case depth comprises (B) continuously changes region (R2), the region (R2) of the hardened layer depth (B) is continuously changed, the rack bar (14) taken but the maximum case depth (B) is in the housing a predetermined supported portion which is received by the end (33) of the housing (30) when the most prominent from (30) (42) and (Bmax) the from the predetermined supported portion (42) Rakkuba (14) end of the case depth toward the (35) (B) is to provide a steering device, wherein a gradually decreases.

In addition, the alphanumeric characters in parentheses represent corresponding components in the embodiments described later. The same applies hereinafter. Moreover, as a hardened layer depth, the effective hardened layer depth and the total hardened layer depth can be illustrated.
When an input (reverse input) from a tire or the like is generated at the end of the rack bar and a bending moment is generated in the rack bar, the bending moment becomes the largest in the portion of the rack bar received by the end of the housing. Further, the bending moment at the portion received by the end of the housing becomes the largest when the rack bar protrudes most from the housing (that is, when the moment length becomes maximum). Therefore, the bending moment generated in the rack bar is maximized at the portion received by the end portion of the housing when the rack bar protrudes most from the housing.

  According to the present invention, by providing the hardened layer on the surface of the rack bar, the wear resistance of the surface can be sufficiently ensured. For example, in the case of a configuration that generates a steering assist force using a hydraulic cylinder, the rack bar is required to have wear resistance that can withstand sliding with an oil seal provided in the hydraulic cylinder. Sufficient wear resistance can be ensured. Moreover, when the stroke amount of the rack bar is maximized, the depth of the hardened layer is maximized at the portion where the bending moment generated in the rack bar is the largest. Thereby, it is possible to sufficiently ensure the bending strength of the portion where the bending moment is the largest. As a result, a sufficient bending strength of the rack bar can be ensured. Further, in the region where the hardened layer depth changes, the hardened layer depth is gradually reduced toward the end of the rack bar where the bending moment gradually decreases. Thereby, necessary and sufficient bending strength can be ensured according to a site | part. In addition, the amount of heat applied to the rack bar during the heat treatment can be reduced, and the distortion caused by the heat treatment can be reduced.

In the present invention, since the rack bar (14) is formed in a hollow shape , the rack bar can be reduced in weight. The hollow rack bar is likely to be distorted due to the heat treatment, but in the case of the present invention, the occurrence of distortion can be satisfactorily suppressed.

Preferred embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a conceptual diagram showing a basic configuration of a power steering apparatus according to an embodiment of the present invention. This power steering device is provided in association with the steering mechanism 1 of the vehicle, and is for applying a steering assist force to the steering mechanism 1.
The steering mechanism 1 includes a steering wheel 11 that is operated by a driver, a steering shaft 12 coupled to the steering wheel 11, a pinion gear 13 provided at a tip portion of the steering shaft 12, and a left-right direction of the vehicle. And a rack bar 14.

A rack gear 14a is formed on the rack bar 14, and the pinion gear 13 is engaged with the rack gear 14a. Further, tie rods 15 are coupled to both ends of the rack bar 14, and the tie rods 15 are coupled to knuckle arms 16 that support the steered wheels 2 and 3, respectively.
The knuckle arm 16 is rotatably provided around the kingpin 17. With this configuration, when the steering wheel 11 is operated and the steering shaft 12 is rotated, this rotation is converted into a linear motion along the left-right direction of the vehicle by the pinion gear 13 and the rack bar 14, and this linear motion is converted into the knuckle arm 16. The turning of the steered wheels 2 and 3 is achieved by converting the rotation around the kingpin 17.

That is, the rack bar 14 moves in the axial direction S in accordance with the steering of the steering wheel 11, and the steered wheels 2 and 3 are steered as shown in FIG. 2 (in FIG. 2, the rack bar 14 is pivoted). The full stroke state most advanced in one of the directions S is shown (only the steered wheel 2 of the steered wheels 2 and 3 is shown).
Referring again to FIG. 1, a torsion bar 21 that twists in accordance with the direction and magnitude of the steering torque applied to the steering wheel 11, and the direction of twisting of the torsion bar 21, in the middle of the steering shaft 12. In addition, an oil pressure control valve 22 whose oil feeding direction and opening degree change according to the size is provided.

The hydraulic control valve 22 is provided with four ports 221, 222, 223, and 224, and hydraulic oil pumped from the reservoir tank 24 by the oil pump 23 is supplied to the port 221 through the oil pipe 251. It has come to be.
The port 222 communicates with the reservoir tank 24 via the oil pipe 252. The ports 223 and 224 are connected to oil chambers 261 and 262 of the cylinder body 260 of the power cylinder 26 that generates a steering assist force through oil pipes 253 and 254, respectively.

Between the oil chambers 261 and 262 of the cylinder main body 260, a piston 263 that moves in the vehicle width direction (axial direction S) due to a hydraulic pressure difference in the oil chambers 261 and 262 is provided. The piston 263 is fitted in an annular groove (not shown) formed in the rack bar 14 and can move integrally with the rack bar 14 in the axial direction S.
The cylinder body 260 has a cylindrical shape and is attached to the housing 30. The cylinder body 260 surrounds a part of the rack bar 14 in the axial direction S. Annular oil seals 31 and 32 are attached to both ends of the cylinder body 260 in the axial direction S, respectively, and seal between the cylinder body 260 and the rack bar 14. The surface of the rack bar 14 slides with the lips of these oil seals 31 and 32 when moving in the axial direction S.

  When the steering wheel 11 is rotated in either the left or right direction, the torsion bar 21 is twisted, and the corresponding one of the cylinder body 260 from the hydraulic control valve 22 by an amount corresponding to the twist of the torsion bar 21. The hydraulic oil is supplied to the oil chamber 261 or the oil chamber 262. As a result, a hydraulic pressure difference is generated between the oil chambers 261 and 262, and the piston 263 of the power cylinder 26 is moved in accordance with the hydraulic pressure difference, so that the steering assist force is applied to the rack bar 14.

  At this time, the excess hydraulic oil from the other oil chamber 262 or the oil chamber 261 is returned from the hydraulic control valve 22 to the reservoir tank 24 via the oil pipe 252. When the torsion bar 21 is hardly twisted, the hydraulic control valve 22 is in an equilibrium state, and the hydraulic oil supplied from the oil pump 23 to the hydraulic control valve 22 is not supplied to the power cylinder 26. The oil is returned to the reservoir tank 24 through the oil pipe 252.

The oil pump 23 is a gear pump that performs pumping action by rotation of a drive gear and a driven gear (not shown), and the rotational force of the electric motor 27 is input to the drive gear. The electric motor 27 is driven and controlled by an electronic control unit 8 including a microcomputer.
The electronic control unit 8 includes a steering angle sensor 4 for detecting the steering angle of the steering wheel 11, a vehicle speed sensor 5 for detecting the speed of the vehicle, and a current (motor current) flowing through the electric motor 27. The output signal of the motor rotation speed sensor 7 for detecting the rotation speed of the motor current detection circuit 6 and the electric motor 27 is given.

  The electronic control unit 8 responds to, for example, that the ignition key switch of the vehicle is turned on based on signals given from the steering angle sensor 4, the vehicle speed sensor 5, the motor current detection circuit 6, the motor rotation speed sensor 7, and the like. Then, the electric motor 27 is activated, and after the electric motor 27 is activated, the driving of the electric motor 27 is controlled so that an appropriate steering assist force according to the operation of the steering wheel 11 is applied to the steering mechanism 1.

The housing 30 has a long cylindrical shape in the axial direction S and surrounds an intermediate portion of the rack bar 14. Corresponding ends 35 and 36 of the rack bar 14 protrude from the pair of ends 33 and 34 of the housing 30 in the axial direction S, respectively.
The housing 30 supports the rack bar 14 so as to be slidable in the axial direction S via rack bushes 37 and 38 provided at a pair of end portions 33 and 34 of the housing 30, respectively.

FIG. 3 is an enlarged cross-sectional view of a main part around one end portion 33 of the housing 30 in FIG. 2, and shows a state where the rack bar 14 has made a full stroke in one of the axial directions S. Since the configuration around the one end portion 33 of the housing 30 and the configuration around the other end portion 34 of the housing 30 are the same, the configuration around the one end portion 33 of the housing 30 will be mainly described below.
With reference to FIGS. 2 and 3, the rack bush 37 is fixed to the inner peripheral surface 39 of the one end portion 33 of the housing 30. The inner peripheral surface of the rack bush 37 is in slidable contact with the surface 40 (outer peripheral surface) of the rack bar 14.

  The rack bar 14 is a hollow cylindrical member made of metal (for example, carbon steel such as S45C) and has a thickness A of about 5 mm, for example. One end 35 of the rack bar 14 is closed, and the tie rod 15 is attached to the one end 35. A hardened layer 41 is formed on the surface 40 of the rack bar 14 by heat treatment over the entire region in the axial direction S. As a result, the rack bar 14 is provided with wear resistance against sliding with the oil seals 31 and 32, and is provided with sufficient bending strength against input (reverse input) from the steered wheels 2 and the like. .

A feature of the present embodiment is that a region R2 in which the hardened layer depth B of the hardened layer 41 (effective hardened layer depth. The whole hardened layer depth may be sufficient) varies on the surface 40 of the rack bar 14. The region R1 and the region R3 where the hardened layer depth B does not change are included.
In the region R2, the hardened layer depth is increased by a predetermined supported portion 42 received by the rack bush 37 (one end portion 33 of the housing 30) when the one end portion 35 of the rack bar 14 protrudes most in the axial direction S from the housing 30. The thickness B takes the maximum value Bmax, and the hardened layer depth B decreases from the predetermined supported portion 42 toward the one end portion 35 of the rack bar 14. In the region R2, the hardened layer depth B decreases from the predetermined supported portion 42 toward the other end of the rack bar 14 (region R1).

Regarding the first axial direction S1 from the other end of the rack bar 14 toward the one end 35 in the axial direction S, the regions R1 to R3 are arranged in the order of the regions R1, R2, and R3.
In the region R1, the hardened layer depth B is a minimum value Bmin and is constant with respect to the axial direction S. The minimum value Bmin is preferably 0.5 mm or more. This is because if the minimum value Bmin is less than 0.5 mm, it is difficult to form a substantially hardened layer.

One end 44 of the region R2 (the boundary between the region R1 and the region R2) is continuously (smoothly) continuous with the region R1, and the other end 45 of the region R2 (the boundary between the region R2 and the region R3). ) Is continuously connected to the region R2. In the region R2, with respect to the first axial direction S1, the hardened layer depth B gradually increases as it proceeds from the one end portion 44 to the predetermined supported portion 42.
The one end portion 44 is a portion where a bending moment does not substantially act even if a reverse input occurs in the one end portion 35 when the predetermined supported portion 42 is received by the rack bush 37, and the hardened layer depth B is The minimum value is Bmin. The hardened layer depth B of the other end 45 is set to a minimum value Bmin.

The hardened layer depth Bmax in the predetermined supported portion 42 is preferably 50% or less of the thickness A, and more preferably 40% or less. In the present embodiment, since the wall thickness A is 5 mm, Bmax is preferably 2.5 mm or less, and more preferably 2.0 mm or less. In the present embodiment, Bmax is set to 2.0 mm.
If the maximum value Bmax of the hardened layer depth B is deeper than 50% of the wall thickness A, the amount of heat given to the rack bar 14 during heat treatment of the hardened layer 41 tends to increase and distortion tends to increase. The upper limit of the maximum value Bmax was set in this way, because it becomes easier to burn over the entire region in the thickness direction of 14.

When one end 35 of the rack bar 14 protrudes most in the axial direction S, if a reverse input is input to the one end 35 of the rack bar 14, a bending moment acts on the region R2, but the hardened layer depth in the region R2 The distribution of B corresponds to the distribution of the bending moment at this time.
Specifically, when one end portion 35 of the rack bar 14 protrudes most from the housing 30, in the protruding region R <b> 2, the hardened layer depth B is substantially in the axial direction S substantially corresponding to the bending moment distribution. Has changed. As a result, a uniform strength can be obtained in each part with respect to bending.

The region R3 is provided from the other end 45 to one end 35 of the rack bar 14, and the hardened layer thickness B is constant at the minimum value Bmin.
In the region R2, the change in the hardened layer depth B is continuous and does not change rapidly.
With respect to the axial direction S, the rate of change of the hardened layer depth B from the predetermined supported portion 42 to the other end 45 in the region R2 is relatively moderate, and the predetermined rate from the one end 44 of the region R2 is predetermined. The rate of change of the hardened layer depth B over the supported portion 42 is relatively steep.

The formation of the hardened layer 41 is performed by, for example, induction hardening. The quenching method at this time is so-called moving baking in which at least one of the heating time and the heating temperature is changed according to the hardened layer depth B.
In the power steering apparatus having the above-described schematic configuration, when a reverse input from the steered wheels 2 or the like is generated at one end portion 35 of the rack bar 14 and a bending moment is generated on the one end portion 35 side of the rack bar 14, this bending moment is The rack bar 14 has the largest portion received by the rack bush 37 (one end portion 33 of the housing 30).

  Further, the bending moment at the portion received by the rack bush 37 becomes the largest when the rack bar 14 protrudes most from the one end portion 33 of the housing 30 (that is, when the moment length becomes maximum). Therefore, the bending moment generated in the rack bar 14 is maximized at a portion (predetermined supported portion 42) received by the rack bush 37 when the rack bar 14 protrudes most from the housing 30 in the axial direction S.

As described above, according to the present embodiment, by providing the hardened layer 41 on the surface 40 of the rack bar 14, the wear resistance of the surface 40 can be sufficiently ensured. The rack bar 14 is required to have abrasion resistance that can withstand sliding with the oil seals 31 and 32. Even in this case, sufficient abrasion resistance can be ensured.
Further, when the stroke amount of the rack bar 14 is maximized, the hardened layer depth B of the hardened layer 41 at the predetermined supported portion 42 at which the bending moment generated in the rack bar 14 is maximized is maximized. . Thereby, it is possible to sufficiently secure the bending strength of the predetermined supported portion 42 in which the bending moment is the largest. As a result, the bending strength of the rack bar 14 can be sufficiently secured.

Further, in the region R2 of the surface 40 of the rack bar 14, the hardened layer depth B is gradually reduced toward the one end portion 35 of the rack bar 14 where the bending moment gradually decreases. Thereby, necessary and sufficient bending strength can be ensured according to a site | part. Further, the amount of heat applied to the rack bar 14 during the heat treatment can be reduced, and the distortion caused by the heat treatment can be reduced.
Further, when one end portion 35 of the rack bar 14 protrudes most from the housing 30 in the axial direction S, the hardened layer depth B corresponds to the change in the bending moment received by the rack bar 14 in the protruding region R2. Has changed. Thereby, the hardened layer depth B can be set according to the bending strength required for the rack bar 14. Therefore, the hardened layer depth B of the hardened layer 41 can be minimized, and the amount of heat applied to the rack bar 14 can be reduced. The distortion generated in the rack bar 14 can be further reduced.

Furthermore, since the rack bar 14 is formed hollow, the rack bar 14 can be reduced in weight. The hollow rack bar 14 is likely to be distorted due to heat treatment, but by optimizing the hardened layer depth B, the occurrence of distortion can be satisfactorily suppressed.
The present invention is not limited to the above embodiment. For example, the rack bar 14 may be formed in a solid bar shape. Further, the region R3 may be eliminated and the region R2 may be provided up to the one end portion 35 of the rack bar 14. Furthermore, the present invention can be applied to an electric power steering device that generates the steering assist force by applying the power of the electric motor via the speed reduction mechanism, and can also be applied to a manual steering device that does not generate the steering assist force.

It is a conceptual diagram which shows the basic composition of the power steering apparatus which concerns on one embodiment of this invention. A full stroke state in which the rack bar has advanced most in one axial direction is shown. FIG. 3 is an enlarged cross-sectional view of a main part around one end of the housing of FIG. 2, showing a state in which the rack bar has made a full stroke in one axial direction.

Explanation of symbols

14 ... rack bar, 30 ... housing, 33 ... one end of (housing), 35 ... one end of (rack bar), 40 ... surface of (rack bar), 41 ... hardened layer, 42 ... predetermined supported part, B: Hardened layer depth, Bmax: Maximum value of hardened layer depth, R2: Region where hardened layer depth changes, S: Axial direction.

Claims (1)

It is formed in a hollow, is supported by a cylindrical housing so as to be slidable in the axial direction, and includes a rack bar that moves in the axial direction according to steering,
The surface of the rack bar, over the entire region, the cured layer formed is subjected to heat treatment is formed,
In the vicinity of the end of the rack bar, including a region where the hardened layer depth continuously changes,
In the region where the depth of the hardened layer is continuously changed, the rack bar takes a maximum value hardened layer depth supported portion of the predetermined which is received by the end of the housing when the most prominent from the housing, steering apparatus characterized by hardened layer depth is gradually decreased toward the end of the rack bar from said predetermined supported portion.

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