JPH0225834B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gear mechanism for a steering device, and more specifically, a rack formed on a piston that moves forward and backward in conjunction with an input shaft, and a taper formed on an output shaft that meshes with the rack. The present invention relates to a gear mechanism of a steering device including a sector gear.

In order to increase the output of a power steering device equipped with this type of gear mechanism, it is necessary to strengthen each part, but in the gear mechanism mentioned above, it is especially important to increase the wall thickness of the bottom part of the rack. required. Furthermore, in order to increase the ratio in a variable gear ratio steering device, it is necessary to lengthen the teeth of the sector gear. In either case, the distance between the axes of the piston and the output shaft must be increased, resulting in an increase in the size of the entire device.

By the way, in the above gear mechanism, the rack is generally engaged with the axis of the output shaft at an angle equal to the conical angle of the tapered sector gear, but the meshing line of the teeth of both gears is not parallel to the axis of the output shaft. It is also not parallel to the conical surface of the tapered sector gear.
For this reason, the two teeth start contacting each other, for example, at one point on the tooth tip of the rack and end at one point on the tooth tip of the tapered sector gear. This kind of engagement is
Since one tooth comes into point contact with the other tooth at the beginning and end of the meshing, this is undesirable because it causes damage to the gear and also applies a force that causes the piston to rotate. For this reason, a steering device has been proposed in which the tips of the teeth are cut along the meshing line so that the meshing of the teeth is always in line contact (Japanese Patent Application No. 53-154876 (Japanese Unexamined Patent Publication No. 154876) −
83668), Japanese Patent Application No. 155758 (1982),
No. 83669)). However, even in a steering device that is cut along the engagement line of the tooth tips, the above-mentioned problems occur when the above-mentioned high output is achieved or when the variable ratio is increased.

The present invention utilizes and develops the above-mentioned technology of cutting the tooth tips along the line of engagement, and involves cutting the tips of at least one of the gears, the rack and the taper sector gear, along the line of engagement between the two. At the same time,
In addition, by cutting the tooth bottom of at least one of the rack and taper sector gear that faces the cut surface of the cut tooth tip to form a clearance part, the distance between the shafts can be avoided without increasing the distance between the shafts. The present invention provides a gear mechanism for a steering device that can achieve high output and increase variable gear ratio.

The present invention will be described below with reference to the illustrated embodiments.
Reference numeral 1 denotes a piston that is slidably fitted in the casing of a steering device (not shown), and 2 is a ball screw shaft fitted to the axis of the piston.The ball screw shaft 2 and the piston 1 are a circulating ball screw. They are linked through a mechanism. Further, the ball screw shaft 2 is linked to a steering wheel via an input shaft such as a steering shaft, and is rotated in response to rotational operation of the steering wheel so that the piston 1 can reciprocate in the axial direction. It's getting old. A rack 3 is formed on one side of the outer peripheral surface of the piston 1, and a tapered sector gear 5 formed integrally with the output shaft 4 is meshed with this rack 3. This output shaft 4 is rotatably supported by the above-mentioned casing (not shown), and is interlocked with steering wheels via a pitman arm (not shown) or the like.

The tooth tip 3a of a commonly used rack and the tooth tip 5a of a tapered sector gear are shown by dashed lines, and the tooth tip 3a of the rack is parallel to the tooth bottom 5b of the taper sector gear, which is shown by a two-dot chain line. In addition, the tooth tip 5a of the taper sector gear is the easy tooth bottom 3.
It is parallel to b. However, in this type of gear mechanism, as described above, point contact occurs at points A and B at the beginning and end of meshing of both teeth, which is not preferable. Therefore, by cutting both tooth tips along the meshing line of both teeth, the occurrence of the point contact is prevented. In the figure, the cut surface 3A of the rack 3 after cutting is shown by a solid line and a dotted line, and the cut surface 5A of the taper sector gear 5 after cutting is shown by a solid line. This results in contact with the tooth surface all at once in the width direction, that is, in line contact.

However, in this embodiment, each cutting surface 3A, 5A indicated by a solid line and each tooth bottom 3b, 5b indicated by a two-dot chain line are
The relief portions 6 and 7 are formed by cutting the narrowest portions of the tooth bottoms 3b and 5b of the respective gaps between the teeth. These relief portions 6 and 7 provide an allowance for the gap at the narrowest portion, respectively.
While keeping the distance L between the axis of the ball screw shaft 2 and the axis of the output shaft 4 constant, the tooth bottom of the rack 3 can be lowered by the above margin, and the insertion of the tooth bottom and the ball screw shaft 2 is possible. The wall thickness between the regular hole and the main hole is increased to accommodate higher output. Alternatively, in the case of a variable gear ratio type steering device, the teeth of the tapered sector gear 5 or the rack 3 can be lengthened by the above margin to increase the variable ratio.

It goes without saying that the inter-axle distance L may be reduced by the above-mentioned margin to reduce the size of the steering device. Further, in the above embodiment, the relief portions 6 and 7 are formed on both the tooth bottoms 3b and 5b, but only one of them may be provided. Further, in the above embodiment, both the tooth tips 3A and 5A are cut along the meshing line, but if necessary, only one of them may be cut. In this case, the relief part is also cut. It is only necessary to install it on the side.

As described above, according to the present invention, it is possible to increase output and variable gear ratio while keeping the distance between the shafts constant, or to downsize the device by reducing the distance between the shafts. This has the effect of being able to.

[Brief explanation of drawings]

The figure is a sectional view showing one embodiment of the present invention. 1... Piston, 3... Rack, 4... Output shaft, 5... Taper sector gear, 6, 7... Relief portion, 3A, 5A... Cutting surface, 3b, 5b... Tooth bottom.

Claims (1)

[Claims] 1. A rack formed on a piston that moves forward and backward in conjunction with an input shaft, and a taper sector gear provided on an output shaft and meshing with the rack, the tooth tip of at least one of the rack and the taper sector gear being In the gear mechanism of the steering device, which is cut along the meshing line of both teeth, a relief portion is formed by cutting the bottom of at least one of the gears of the rack and the taper sector gear, which are opposed to the cut surface of the cut tooth tip. A gear mechanism for a steering device characterized by: