Helical tooth broach

Details Helical tooth broach Helical tooth broach

2001-07-11

2003-03-04

Banks, Derris H. (Department: 3712)

Cutters, for shaping

Rectilinear broach

C407S018000, C407S019000, C407S016000, C407S017000

Reexamination Certificate

active

06527484

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a gear tooth broach for forming internal helical gears or splines.
2. Description of the Related Art
Internal helical gears or splines widely used in transmissions for motor cars are machined by using helical gear tooth broaches each having a series of axially aligned and spaced teeth disposed thereon, tooth spaces or traces of the teeth in a longitudinally extending helical alignment along the axis of the body at a helical angle the same as that of the internal helical gear or spline to be machined and gullets of the teeth in a general side by side circumferentially extending helical arrangement.
Generally, the helical gear tooth broach has an elongate body having a roughing broach section disposed thereon having a series of teeth having substantially the same width and increasing height to perform deep cuts for the tooth spaces and a finishing broach section formed on a shell integrated with the elongate body and having a series of teeth having substantially full height and increasing width to perform finish cuts of the sides of each tooth of a work piece.
A helical gear tooth broach, such as shown in Japanese Industrial Standard (J IS) B 0175 No. 1622, is of the so called right-angled-to-the-axis gullet broach, wherein each tooth space or trace of the teeth is formed so that it longitudinally extends at a helical angle which is the same as that of the internal helical gear or work to be machined, and each gullet of the teeth in a general side by side circumferentially extending helical arrangement is made to form an annular groove. Such a right-angled-to-the-axis gullet broach performs an intermittent cutting action against a horizontal plane of the work to be machined, and generates vibrations and deteriorates machining accuracy.
Further, as shown in FIG. 4 of U.S. Pat. No. 2,986,801, a helical gear tooth broach is known which has a series of axially helically aligned and spaced thread-like teeth along the axis of the broach body and gullets of the teeth each of which extends at a helical angle perpendicular to the helix angle of a tooth space or trace. More precisely, in FIG. 4 of U.S. Pat. No. 2,986,801, the direction of the arrow 7 of a tooth space or trace crosses at a right angle to the direction of the arrow 6 of a gullet. This type of broach is called right-angled-to-the-tooth-trace gullet broach.
Furthermore, Japanese Unexamined Patent Publication (TOKKAI) Hei 2(1990)-15915 and TOKKAI Hei 1(1989)-271119 both disclose helical gear tooth broaches having gullets each of which extends at a helical angle not perpendicular to the helix angle of a tooth space or trace. Also, in Japanese Examined Utility Model Publication Hei 8(1996)-8019 and TOKKAI Hei 10(1998)-309622, helical tooth broaches are disclosed in which the number of each of its helical-splined gullet(s) is changed.
However, in the above described conventional helical gear tooth broaches, as shown in
FIG. 4
, in which a portion of the surface of the conventional broach is projected on a plane, the direction of the tooth spaces or traces
14
of teeth
12
in the longitudinally extending helical alignment and the direction of the gullets
13
in the general side by side circumferentially extending helical arrangement are revesely oriented with respect to each other. That is, the tooth spaces or traces
14
of teeth
12
orient to a right hand of a helix angle (right-upward oriented) and on the contrary, the gullets
13
are directed to a left hand of a helix angle (left-upward oriented). Stated another way, the teeth
12
and tooth spaces
14
are oriented in
FIG. 4
along a line
14
′ on the projection of the broach surface having a positive slope whereas the gullets
13
are oriented along a line having an opposite or negative slope. That is, the signs of the slopes of the lines defining the orientation of the teeth
12
and gullets
13
are opposite to each other in the conventional broach of FIG.
4
.
Setting the helix angle &bgr; of a tooth space or trace
14
of the teeth
12
to be equal to that of the work to be broached, and assuming that the helix angle of a gullet
13
is (90°−&agr;′), by selecting the helix angles &bgr;, &agr;′ and the number of helically splined gullets) the cutting dimension of the broach is determined. In the above described right-angled-to-the-axis gullet broach, the angle &agr;′ is set equal to 0 (&agr;′=0), and in the above described right-angled-to-the-tooth-trace gullet broach, &agr;′=&bgr;. Further, the helix angle &bgr; of the tooth space or trace
14
is called “a helix angle to the axis of the broach”, and the helix angle (90°−&agr;′) of the gullet
13
is called “a helix angle to the circumferential direction of the gullet
13
”.
When an internal helical gear or a work is broached using a helical gear tooth broach, a twisting movement is applied to the work along the direction of the helix angle &bgr; of the tooth spaces or traces
14
of the broach. As a result, the work to be broached is rotated in a direction in which the twisting movement is applied to the broach.
In such a situation, in the above described conventional helical gear tooth broach having the conventional helical gullet, such as shown in
FIG. 4
, a component of the force generated by the cutting resistance force of the teeth of the broach in an axial direction along an axis
5
presses the work to be broached in the circumferential direction and in addition, causes the work to rotate to a greater or lesser extent. To cope with this component of the force, the work to be broached should be strongly clamped to limit its rotating movement.
On the other hand, in the above described right-angled-to-the-axis gullet broach, since the angle &agr;′=0, no axial component of the force is generated by the cutting resistance force of the teeth and no circumferential additional rotational force is applied to the work to be broached. However, such broach performs an intermittent cutting action against the work and deteriorates machining accuracy compared with the above described right-angled-to-the-tooth-trace gullet broach.
Therefore, in the above described conventional helical gear tooth broaches, in order to limit the rotating movement of the work to be broached, a strong clamp on the work is required. On the contrary, in the above described right-angled-to-the-axis gullet broach, although no axial component of the force is applied, the cutting action against the work is intermittent, and the accuracy of machining is not sufficient.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a helical gear tooth broach which does not require strong clamping of the work to be broached by a special clamping device, and which does not perform an intermittent cutting action against the work.
These and other objects of the present invention are solved by a gear tooth broach for broaching internal helical gears or splines comprising an elongate body having a series of axially aligned and spaced teeth disposed thereon, tooth spaces or traces of the teeth in a longitudinally extending helical alignment along an axis of the body and gullets of the teeth in a side by side circumferentially extending helical arrangement. The gear tooth broach is characterized in that a first direction of the tooth spaces or traces of the teeth in the longitudinally extending helical alignment and a second direction of the gullets of the teeth in the side by side circumferentially extending helical arrangement are both oriented at a right-upward or left-upward helix angle in common with each other.
In the above described conventional helical gear tooth broaches, as shown in
FIG. 4
, the direction of the tooth spaces or traces in the longitudinally extending helical alignment and the direction of the gullets in the side by side circumferentially extending helical arrangement are revesely oriented with respect to each other. Thus, the rotational force applied to the

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