JP4548095B2 - Steering device - Google Patents

Description

  The present invention relates to a steering device, and more particularly to a steering shaft that transmits rotation of a steering wheel to a steering gear.

  Since the steering shaft that transmits the rotation of the steering wheel to the steering gear requires a certain torsional strength to transmit the rotational torque of the steering wheel, a steering shaft made of a solid material has been conventionally used. However, in recent years, in order to reduce the weight of the vehicle body and reduce the cost, a hollow pipe material has been used for the steering shaft.

  The steering shaft must be provided with an annular groove for a stopper ring that stops the bearing for pivotally supporting the steering shaft on the steering column, a male screw for fixing the steering wheel, and serration processing for shock absorption. For this reason, the strength is lowered and a portion where the stress is concentrated is generated. Therefore, when a hollow pipe material is used, some measure for the strength is required.

  Therefore, conventionally, measures such as using a hollow material having a thick wall or cutting a male screw and stopping a bearing with a nut instead of cutting an annular groove where stress is concentrated have been taken. In addition, the steering shaft shown in Patent Document 1 is designed to simultaneously obtain weight reduction and strength by fitting a header made of a solid shaft formed with a male screw or an annular groove into a shaft body made of a hollow pipe material. ing. However, there is a demand for further weight reduction and compactness, and there is a need for a steering shaft made of a hollow pipe material that can obtain sufficient strength even when a groove or the like is processed.

JP-A-9-202245

  It is an object of the present invention to provide a steering device that secures collision safety and strength against torsional deformation and has good workability even when a thin hollow pipe material is used.

The above problem is solved by the following means. That is, in the first invention, the steering shaft for transmitting the rotation of the steering wheel to the steering gear is calculated by the following formula, where H is Vickers hardness (HV) and YS is yield strength (MPa). The steering device is characterized by being formed of a steel material having a yield coefficient KV of 1400 or more and a Vickers hardness H of HV250 or less.
KV = (H + YS ² ) / H

  A second invention is the steering device according to the first invention, wherein the steering shaft is formed of a hollow pipe material.

Third invention is a steering apparatus of the second aspect, the pipe member of the steering shaft is a steering device characterized by Oh Rukoto in welded steel pipe.

  A fourth invention is the steering device according to the third invention, wherein the yield coefficient KV is 1500 or more.

A fifth invention is the steering device according to the fourth invention, wherein the Vickers hardness H is HV230 or less.

  In the steering device of the present invention, it is possible to select a shaft made of a material having both strength against torsional deformation, workability, and processing accuracy of the steering shaft using the concept of yield coefficient calculated from hardness and yield strength. Therefore, even when a thin hollow pipe material is used, it is possible to manufacture a steering device that ensures collision safety and strength against torsional deformation.

  The steering device requires that the shock absorbing system operates normally at the time of a collision, and for that purpose, the steering device needs to have sufficient strength so that the steering shaft is not deformed at the time of the collision. Further, even when a twisting force several times that of normal use is applied due to a collision with a curb or a steering wheel operation in a stationary state, the steering shaft needs to have sufficient strength to prevent plastic deformation.

  One way to increase the strength of steering devices is to increase the hardness. It is known that the yield strength of steel is proportional to the hardness (Takayoshi Murakami, “Effects of Metal Fatigue Microdefects and Inclusions” “In 1993, Yokendo). However, if the hardness is increased more than necessary in order to increase the strength, the processing accuracy of the steering shaft is lowered due to the lowering of workability, and the weld crack sensitivity is increased. That is, when considering use as an actual product, it is understood that the balance between hardness and yield strength is important.

  Therefore, the present inventors selected a welded steel pipe from which materials having various hardness and yield strength can be easily obtained as a material for the steering shaft in order to derive an empirical formula that can determine the strength of the steering shaft from the hardness and the yield strength. Then, the processing accuracy of the steering shaft and the strength against torsional deformation were tested.

  In other words, welded steel pipes have very small wall thickness fluctuations, good dimensional accuracy and surface condition, and work hardening by cold forming, but depending on the choice of material components and heat treatment conditions, A high-quality welded steel pipe with yield strength is an advantageous material that can be easily obtained at an appropriate cost, and is therefore a preferable material for both experiments and actual products. (For example, JISG3445)

  Hereinafter, an experimental apparatus, an experimental method, and an experimental result for deriving an empirical formula for determining the strength of the steering shaft of the present invention will be described. FIG. 1 is a front view showing a steering device used in an experiment of the present invention. FIG. 2 is a view taken in the direction of arrow P in FIG. FIG. 3 is a front view showing an outer shaft and an inner shaft that are rotatably supported in the column of FIGS. FIG. 4 is a front view of the torsional deformation angle experiment device for the steering device. FIG. 5 is an explanatory diagram showing the dimensions of the outer shaft and the inner shaft that were tested with the torsional deformation angle experiment apparatus of FIG.

  FIG. 6 shows the shape of the inner shaft, and is an explanatory view showing a portion where the processing accuracy is evaluated after the drawing processing is performed on the tip portion. FIG. 7 is a table showing results of experiments on machining accuracy and torsional deformation angle for inner shafts of various hardnesses and yield strengths. FIG. 8 is a graph showing the relationship between the yield coefficient and the torsional deformation angle in the table of FIG.

  As shown in FIGS. 1 to 3, the steering device used in the experiment is a steering device capable of adjusting the tilt / telescopic position, and is pivotally supported by the bracket 1 so as to be swingable around a pivot pin 11. An outer column 3 is fitted on the inner column 2 so as to be slidable telescopically. A friction plate 31 having a telescopic adjustment groove is fixed on both side surfaces of the outer column 3, and a tilt adjustment groove is formed on the side plate 12 of the bracket 1. The tightening rod 13 passes through the telescopic adjustment groove and the tilt adjustment groove, and at the time of clamping, the outer column 3 is clamped by clamping to the side plate 12 via the friction plate 31, and the operation lever 14 is operated when adjusting the tilt / telescopic position. Then, the force for clamping the outer column 3 to the side plate 12 is released, and the tilt position and the telescopic position of the steering wheel 4 can be adjusted.

  In the outer column 3 and the inner column 2, an inner shaft 5 and an outer shaft 6 shown in FIG. 3 are rotatably supported by bearings (not shown). A steering wheel 4 is attached to the right end (vehicle body rear side) of the outer shaft 6, and a universal joint 51 is attached to the left end (vehicle body front side) of the inner shaft 5. The universal joint 51 is connected to a steering gear (not shown) via an intermediate shaft 52, and a wheel (not shown) can be steered by rotating the steering wheel 4.

  A female serration (not shown) is formed on the inner periphery of the outer shaft 6, and the male serration formed on the outer periphery of the inner shaft 5 is engaged so that telescopic adjustment is possible. In the experiments of hardness, yield strength, processing accuracy evaluation, and torsional deformation angle (torsional deformation strength) described below, the inner shaft 5 that tends to be disadvantageous in the torsional deformation experiment because of its small diameter was used.

  FIG. 4 shows an experimental apparatus for testing the torsional deformation angle of this steering apparatus. As shown in FIG. 4, the bracket 1 of the steering device is fixed to the fixing portion 71 of the experimental device, a fixing jig 81 is connected to the universal joint 51 at the left end of the inner shaft 5, and the fixing jig 81 is connected to the torque measuring device 82. To fix. And this torque measuring device 82 is fixed to the fixing | fixed part 72 of an experimental apparatus.

  In this state, the steering wheel 4 is rotated, and the rotational torque applied to the steering wheel 4 is released when the torque display of the torque measuring device 82 displays 250 N · m. When the rotational torque applied to the steering wheel 4 was released, the angle (degree) of torsional deformation in which the inner shaft 5 was plastically deformed was measured to obtain the value of torsional deformation strength.

  FIG. 5 is an explanatory diagram showing a dimensional relationship between the outer shaft 6 and the inner shaft 5 used in the torsional deformation angle experiment apparatus of FIG. The inner shaft 5 has a total length of 270 mm, the male serration 53 has a length of 65 mm, an outer diameter of φ18 mm, and an inner diameter of φ13 mm. The outer shaft 6 has a total length of 370 mm, an outer diameter of φ27 mm, and an inner diameter of φ20 mm. The total length when the outer shaft 6 and the inner shaft 5 are assembled is 500 mm. The steel types of the outer shaft 6 and the inner shaft 5 are SAE1030 equivalent, and electric welding steel pipes were used.

  FIG. 6 shows the shape of the inner shaft 5 and is an explanatory view showing the location for evaluating the processing accuracy of the inner shaft 5. A steel pipe having a hollow circular cross section shown in FIG. 6 (1) and an oval die portion 54 for connecting the universal joint 51 as shown in FIG. 6 (2) are formed by drawing at the left end of the inner shaft 5. ing.

  After the drawing process, the dimension L between the flat parts of the oval mold part 54 and the dimension R of the cylindrical part were measured, and an error with respect to a predetermined dimension of 50 μm or more was evaluated as defective. A case where both the dimension L and the dimension R are defective is indicated by x, and a case where either the dimension L or the dimension R is defective is indicated by Δ. The half angle of the die for drawing the oval die portion 54 is 8 to 10 degrees, and the processing force is 20 tons.

  Hardness measured the hardness of the cross-sectional center part of the inner shaft 5. FIG. The measuring instrument was a micro Vickers hardness tester, measuring a measurement load of 1 kg and measuring 30 points, and taking the average value as hardness (HV). The weld zone is also included in the hardness measurement range.

  The yield strength was measured by removing the drawn portion of the inner shaft 5 and the male serration 53. Insert a core into the hollow part on both the left and right sides of the inner shaft 5 and hold it with a chuck of a tensile tester (tensile tester 5585 manufactured by INSTRON). The yield strength (MPa) was defined as the stress when The conditions of the tensile test such as the speed at which the force was applied were performed according to JISZ2241.

FIG. 7 is data showing the results of experiments on evaluation of processing accuracy and torsional deformation angles for 18 types of inner shafts 5 having various hardness and yield strength. From this data, the present inventors derived the concept of a yield coefficient that can determine the strength of the steering shaft (the strength against torsional deformation). That is, when H is Vickers hardness (HV) and YS is yield strength (MPa), the yield coefficient KV is a coefficient calculated by the following equation.
KV = (H + YS ² ) / H

  FIG. 7 shows the values obtained by calculating the yield coefficient KV by the above formula for the 18 types of inner shafts 5. The graph of FIG. 8 shows the relationship between the yield coefficient KV and the torsional deformation angle for 18 types of inner shafts 5.

  As shown in FIG. 7 to FIG. It can be seen that the inner shafts 5, 16, and 17 have a torsional deformation angle of 10 degrees or more, so that the operability of the steering wheel 4 deteriorates and is not suitable as a material for the inner shaft 5. On the other hand, No. with a yield coefficient KV of 1400 or more and a hardness H of 250 (HV) or less. 1-No. 14, the torsional deformation angle is suppressed to 5 degrees or less, so that the operability of the steering wheel 4 is good and the inner shaft 5 is suitable as the material of the inner shaft 5.

  In the case of further pursuing the strength against torsional deformation, it is more preferable that the yield coefficient KV is 1500 or more because the torsional deformation angle can be further reduced. However, No. with a hardness H of 250 (HV). In the inner shaft 5 of No. 14, the dimension R may be defective in the machining accuracy evaluation. Therefore, when the machining accuracy is further pursued, the hardness H is preferably 230 (HV) or less.

  Further, when the yield coefficient KV is 1400 or more, the hardness H exceeds 250 (HV). It can be understood that the inner shaft 5 of 18 is not suitable as the material of the inner shaft 5 because the processing accuracy deteriorates. That is, when the hardness H exceeds 250 (HV), not only molding with a die becomes difficult due to the high hardness, but also the elastic limit increases due to an increase in yield strength, and a predetermined shape dimension can be obtained with a springback. The result was gone.

  In the above embodiment, using the concept of the yield coefficient KV calculated from the hardness H and the yield strength YS, it is possible to select a shaft made of a material having both strength against torsional deformation of the steering shaft and processing accuracy. Therefore, even when a thin hollow pipe material is used, it is possible to manufacture a steering device that secures collision safety and strength against torsional deformation.

  In the above-described embodiment, an example is shown in which the present invention is applied to a hollow steering shaft that telescopically moves. However, the present invention may be applied to a solid shaft, a shaft that does not telescopically move, a shaft that does not collapsibly move, an intermediate shaft, and the like. Further, the present invention may be applied to a steering device having a steering force assisting device that assists the steering force applied to the steering wheel and facilitates the operation of the steering wheel.

It is a front view showing a steering device of an embodiment of the present invention. It is a P arrow view of FIG. FIG. 3 is a front view showing an outer shaft and an inner shaft that are rotatably supported in the column of FIGS. 1 and 2. It is a front view of the twist deformation angle experiment apparatus of a steering device. It is explanatory drawing which shows the dimensional relationship of the outer shaft and inner shaft which were experimented with the torsional deformation angle experiment apparatus of FIG. It is explanatory drawing which shows the shape of an inner shaft, and shows the location which evaluates a processing precision, after giving a drawing process to the front-end | tip part. It is a table | surface which shows the result of having experimented the processing precision and the torsional deformation angle about the inner shaft of various hardness and yield strength. It is a graph which shows the relationship between the yield coefficient KV of the table | surface of FIG. 7, and a twist deformation angle.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Bracket 11 Pivoting pin 12 Side plate 13 Clamping rod 14 Operation lever 2 Inner column 3 Outer column 31 Friction plate 4 Steering wheel 5 Inner shaft 51 Universal joint 52 Intermediate shaft 53 Male serration 54 Oval type part 6 Outer shaft 71, 72 fixed part 81 Fixing jig 82 Torque measuring device

Claims (5)

When the steering shaft that transmits the rotation of the steering wheel to the steering gear has H as Vickers hardness (HV) and YS as yield strength (MPa), the yield coefficient KV calculated by the following formula is 1400 or more, and Vickers A steering apparatus characterized by being formed of a steel material having a hardness H of HV250 or less.
KV = (H + YS ² ) / H The steering apparatus according to claim 1, wherein
A steering apparatus, wherein the steering shaft is formed of a hollow pipe material. The steering apparatus according to claim 2, wherein
Steering system pipe of the steering shaft, characterized in Oh Rukoto in welded steel pipe. In the steering apparatus according to claim 3,
A steering apparatus, wherein the yield coefficient KV is 1500 or more. The steering apparatus according to claim 4, wherein
The steering apparatus according to claim 1, wherein the Vickers hardness H is HV230 or less.

Images