Gear grinding unit

A gear grinding unit, capable of grinding a tooth flank of a gear to have fine surface roughness without requiring any special shaping work such as dressing, includes a threaded grinding part which is rotatable around a rotation axis (S1) and engages with a tooth of a gear to be ground. Through a rotational motion of the threaded grinding part, a tooth flank of the gear is ground. The threaded grinding part includes a plurality of flexible abrasive sheets each including a virtual circle having a diameter that equals a root diameter (DA) of the threaded grinding part and a bulge part bulging radially outward from the virtual circle. With the bulge parts of the abrasive sheets mutually shifted around the rotation axis (S1), the abrasive sheets are overlapped along the rotation axis (S1) to form the threaded grinding part.

TECHNICAL FIELD

The present invention relates to a gear grinding unit which grinds a tooth flank of a gear by bringing a threaded grinding function part into contact with a gear tooth.

BACKGROUND ART

Recently, in the field of automobiles that places importance on comfortability and fuel efficiency, fine surface roughness of a gear used for a transmission or the like to achieve less noise, less vibration and lower fuel consumption has been increasingly demanded.

To achieve fine surface roughness of a gear, a conventional technique is such that the gear and a threaded grindstone are mutually rotated in engaging relation for generation grinding of a tooth flank of the gear (refer to, for example, Patent Document 1).

RELATED ART DOCUMENT

Patent Document

As an example of the threaded grindstone mentioned above, there has been proposed a grindstone which has a threaded grinding surface formed on a surface of a base metal throughout an axial direction of the base metal with a precise pitch and has, for example, electrodeposited CBN abrasive grains on the threaded grinding surface via a plating layer.

The above-described threaded grindstone, however, cannot be made with ease. In order to grind the tooth flank of the gear to have fine surface roughness, the above-described threaded grindstone itself must be shaped with high accuracy to match a tooth profile of the gear, thus problematically requiring advanced working technique.

Moreover, the threaded grindstone occasionally requires shaping work called dressing for maintaining fine surface roughness of a gear to be ground because the surface of the threaded grindstone is shaved off with use, thereby requiring a machine exclusively for dressing. In addition, not only does time for the grinding work need to be spared, but time for the dressing work also needs to be spared. Thus, the incidental equipment problematically increases, and production efficiency problematically decreases.

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

In view of the problems discussed above, the present invention aims to provide a gear grinding unit which can be made with ease and can grind a tooth flank of a gear to have fine surface roughness without requiring any special shaping work such as dressing.

Means for Solving the Problems

To achieve the above object, a gear grinding unit according to the present invention comprises:

a threaded grinding part that is rotatable around a rotation axis and engages with a tooth of a gear to be ground,

wherein a tooth flank of the gear is ground through a rotational motion of the threaded grinding part,

the gear grinding unit further comprising:

a plurality of flexible abrasive sheets each including a bulge part bulging radially outward from a virtual circle whose diameter equals a root diameter of the threaded grinding part,

wherein the threaded grinding part is formed by overlapping the abrasive sheets along the rotation axis with the bulge parts mutually shifted around the rotation axis (First Invention).

In the present invention, it is preferable that each of the abrasive sheets further include a backing including a curved part outlining the bulge part, and an abrasive layer be provided only in the vicinity of the curved part on a surface of the backing so as to contact the tooth flank of the gear (Second Invention).

In the present invention, it is preferable that a spacer be interposed between adjacent abrasive sheets of the plurality of the abrasive sheets for providing a predetermined space (Third Invention).

Advantages of the Invention

In the gear grinding unit of the first invention, the threaded grinding part is formed by overlapping the plurality of flexible abrasive sheets along the rotation axis with the bulge parts of the abrasive sheets mutually shifted around the rotation axis, so that when the threaded grinding part is pressed against the gear tooth, the abrasive sheets bend according to the profile of the tooth, thereby allowing the threaded grinding part to be in close contact with the tooth flank. Accordingly, the tooth flank can be ground uniformly and is not subjected to localized grinding. As a result, the tooth flank can be ground so as to have fine surface roughness. Moreover, the threaded grinding part does not require high-precision shaping so as to fit the profile of the gear tooth and can thus be made with ease.

Furthermore, the bending abrasive sheets exert their restoring force for returning to their respective original positions, so that the abrasive sheets are always pressed against the tooth flank. For this reason, even if the abrasive sheets wear away with use, the abrasive sheets can maintain their contact with the tooth flank, thereby eliminating the need for special shaping work such as dressing that a threaded grindstone requires.

In the gear grinding unit of the second aspect of the invention, the abrasive layer is provided only in the vicinity of the curved part on the surface of the backing of each of the abrasive sheets to be able to contact the tooth flank of the gear. Providing abrasive only to a part of each abrasive sheet that substantially comes into contact with the tooth flank allows the abrasive sheet to have a required grinding function and can reduce consumption of the abrasive or the like by a substantial amount.

Since the abrasive layer is not provided to a part other than in the vicinity of the curved part of the backing of the abrasive sheet, the abrasive sheet bends more flexibly than the abrasive sheet having the abrasive layer on the entire surface of the backing, thereby allowing the threaded grinding part to contact the tooth flank more closely. Thus, finer surface roughness can be obtained.

Moreover, centrifugal force associated with the rotational motion of the threaded grinding part can effectively act on the abrasive sheets, thereby causing the bending abrasive sheets to rise so as to return to their respective original positions. In this way, the abrasive sheets can be pressed against the tooth flank. Pressing force of the abrasive sheets with respect to the tooth flank can be adjusted by adjusting the centrifugal force, that is to say, adjusting rotational speed of the threaded grinding part.

In the gear grinding unit of the third aspect of the invention, the spacer is interposed between the adjacent abrasive sheets of the plurality of the abrasive sheets for providing the predetermined space, so that the degree of bending of the abrasive sheets can be adjusted with ease by adjusting spacer thickness, spacer diameter, the number of spacers and others.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Concrete exemplary embodiments of a gear grinding unit according to the present invention are demonstrated hereinafter with reference to the accompanying drawings.

First Exemplary Embodiment

Description of a Gear Grinding Device

A gear grinding device1shown inFIGS. 1 (a)and1(b) is equipped with, in a three-axis control system formed of an X axis, a Y axis and a Z axis which are orthogonal to one another, a main spindle2rotatively driven around a rotation axis S1extending along the X axis, and a table shaft3rotatively driven around a rotation axis S2. The rotation axis S2is positioned at a predetermined distance from the rotation axis S1along the Y axis orthogonal to the X axis to be perpendicular to the rotation axis S1and extends along the Z axis.

The main spindle2is movable along the X, Y and Z axes.

The main spindle2is mounted with a detachable worm-shaped gear grinding unit4A. It is to be noted that reference mark5denotes a fastener for holding the gear grinding unit4A firmly on the main spindle2.

As the main spindle2is rotatively driven, the gear grinding unit4A rotates around the rotation axis S1together with the main spindle2.

The table shaft3is mounted with a detachable external gear6which is an object to be ground. It is to be noted that reference mark7denotes a fastener for holding the gear6firmly on the table shaft3.

As the table shaft3is rotatively driven, the gear6rotates around the rotation axis S2together with the table shaft3.

The gear grinding device1changes a position of an engagement between the gear grinding unit4A and the gear6for grinding the gear6by synchronizing rotational driving of the main spindle2with rotational driving of the table shaft3and moving the main spindle2along each of the axes.

(Description of the Gear Grinding Unit)

As shown inFIG. 2, the gear grinding unit4A has such a threaded grinding part8A as to form two threads8a,8brunning along two parallel, virtual spiral curves (not shown), respectively.

The threaded grinding part8A has such dimensions as to be able to engage with a tooth9of the gear6. While engaging with the tooth9of the gear6, the threaded grinding part8A is rotated around the rotation axis S1, thereby grinding a tooth flank9aof the gear6.

As shown inFIG. 3, the gear grinding unit4A includes a plurality of flexible abrasive sheets10A arranged along the rotation axis S1with their respective rotation centers aligned. These abrasive sheets10A are overlapped along the rotation axis S1to form the threaded grinding unit4A.

(Description of the Abrasive Sheets)

As shown inFIGS. 4 (a)to4(c), each abrasive sheet10A is formed of a backing11that constitutes a base of the sheet10A, and an abrasive layer12provided on an entire surface of one side (the left side inFIG. 4 (b)) of the backing11. It is to be noted here that the abrasive layer12is formed by applying an abrasive to the backing11via an adhesive layer.

As shown inFIG. 4 (a), the abrasive sheet10A includes bulge parts10aeach bulging radially outward from a virtual circle13whose diameter equals a root diameter DAof the threaded grinding part8A (refer toFIG. 2).

The number of the bulge parts10aprovided for the abrasive sheet10A corresponds to the number of threads of the threaded grinding part8A. In this embodiment, the number of the threads is two, so that two bulge parts10aare provided. These bulge parts10aare circumferentially evenly spaced (every 180 degrees in this case) having the center point O1as their center through which the rotation axis S1passes.

As shown inFIGS. 4 (a)and4(c), the abrasive sheet10A has an insertion hole14having the center point O1as its center.

To position the plurality of the abrasive sheets10A with the bulge parts10aof the sheets10A mutually shifted by a predetermined angle around the rotation axis S1, one of the abrasive sheets10A has a positioning hole15at an angle of, for example, 0 degrees with the center point O1being as its center (refer toFIG. 4 (a)), while another abrasive sheet10A has the positioning hole15at an angle of, for example, 10 degrees with the center point O1being as its center (refer toFIG. 5 (a)). In such a way, with the center point O1being as their center, the plurality of the abrasive sheets10A have respective positioning holes15at the different predetermined angular positions, respectively.

As shown inFIG. 3, the plurality of the abrasive sheets10A of the gear grinding unit4A are arranged with their rotation centers aligned along the rotation axis S1in order of decreasing or increasing angle at which the positioning hole15of each abrasive sheet10A is positioned, and a positioning shaft16is inserted to pass through the respective positioning holes15of the abrasive sheets10A, whereby the abrasive sheets10A can be overlapped along the rotation axis S1with their bulge parts10apositioned to be mutually shifted by the predetermined angle around the rotation axis S1.

The plurality of the abrasive sheets10A thus positioned by the positioning shaft16are fixed in place by a holder17, or more specifically, by passing a hollow shaft17aof the holder17(refer toFIG. 2) through the respective insertion holes14of the abrasive sheets10A and holding the sheets10A collectively from both sides by means of flanges17bprovided at respective ends of the hollow shaft17a.

As shown inFIG. 4 (c), the backing11includes a main body11awhich is an inner part of the virtual circle13having the center point O1as its center, curved parts11boutlining the respective bulge parts10a, and crescent-shaped parts11c, each of which is formed between the main body11aand the curved part11b.

Here, each of the curved parts11bcomprises a first curved part18that is in a first predetermined angle region around the center point O1(between 0 degrees and 90 degrees and between 180 degrees and 270 degrees, seeFIG. 4 (c)) and a second curved part19that is in a second predetermined angle region around the center point O1(between 90 degrees and 180 degrees and between 270 degrees and 360 degrees, seeFIG. 4 (c)). In the first predetermined angle region, the distance from the center point O1to the first curved part18increases as an angle around the center point O1increases, and in the second predetermined angle region, the distance from the center point O1to the second curved part19decreases as an angle around the center point O1increases. Therefore, the curved part11bis a combination of parts of the spiral curve.

The backing11may be appropriately selected from flexible sheet materials such as cotton cloth, synthetic fiber cloth, kraft paper, nonwoven fabric cloth, metal mesh and a synthetic resin sheet.

The adhesive layer used for providing adhesion between the backing11and the abrasive comprises a binder for binding the abrasive materials together, and an adhesive for bonding the abrasive to the backing.

The binder used for binding the abrasive materials together may be appropriately selected from commonly used metal, electrodeposition, vitrification, resin and others.

Glue and synthetic resin etc. may be used as the adhesive for bonding the abrasive to the backing. Main examples of the synthetic resin to be used are polyimide resin, phenol resin and epoxy resin. It is to be noted that there are cases where a filler such as calcium carbonate is combined.

A description is provided hereinafter of grinding operation on the gear6that is performed by the gear grinding device1using the gear grinding unit4A having the above-described structure.

As shown inFIGS. 1 (a)and1(b), the position of the main spindle2along the X, Y and Z axes is controlled first to move the threaded grinding part8A of the gear grinding unit4A into engagement with the tooth9of the gear6.

Next, the main spindle2and the table shaft3are rotatively driven in synchronization with each other such that the threaded grinding part8A is pressed against the tooth flank9a.

As shown inFIGS. 2 and 3, the threaded grinding part8A of the gear grinding unit4A is formed by overlapping the plurality of the flexible abrasive sheets10A along the rotation axis S1, with their bulge parts10amutually shifted by the predetermined angle around the rotation axis S1, so that when the threaded grinding part8A is pressed against the tooth9of the gear6, as shown inFIGS. 6 (a)and6(b), the abrasive sheets10A bend according to the profile of the tooth9, thereby allowing a thread8aof the threaded grinding part8A to be in close contact with the tooth flank9a.

In the gear grinding unit4A of this embodiment, the abrasive sheets10bend to allow the thread8aof the threaded grinding part8A to come into close contact with the tooth flank9a, so that the tooth flank9acan be ground uniformly and localized grinding can be avoided. As a result, the tooth flank9acan be ground with finer surface roughness. Moreover, the threaded grinding part8A can be made with ease by overlapping the plurality of the abrasive sheets10in the manner described above, thereby eliminating the need for high-precision shaping so as to fit the profile of the tooth9of the gear6.

The bending abrasive sheets10exert their restoring force for returning to their respective original positions, so that the abrasive sheets10are always pressed against the tooth flank9a. For this reason, even if the abrasive sheets10wear away with use, the sheets10can maintain their contact with the tooth flank9a, thereby eliminating the need for special shaping work such as dressing that a conventional threaded grindstone requires.

In the conventional threaded grindstone, a threaded grinding part has an increased diameter to relatively reduce the influence of its wear associated with grinding, whereas in the gear grinding unit4A of the present embodiment, the influence of the wear of the threaded grinding part8A that is associated with the grinding is offset by the above-mentioned restoring force of the abrasive sheets10, so that the threaded grinding part8A can have a relatively small diameter.

In such a feed operation of the gear grinding unit4A along the Z axis in relation to the gear6as shown inFIGS. 7 (a)to7(c), when the gear grinding unit4A moves along the tooth flank9aof the gear6from left to right in the drawings, contact between a leading portion of the moving gear grinding unit4A and the tooth flank9aresults in formation of, as shown inFIG. 7 (a), downward-sloping arc-shaped grinding lines21aalong rotating direction R of the gear grinding unit4A on the tooth flank9a, and contact between a following portion of the moving gear grinding unit4A and the tooth flank9aresults in formation of, as shown inFIG. 7 (b), upward-sloping arc-shaped grinding lines21balong rotating direction R of the gear grinding unit4A on the previously formed downward-sloping grinding lines21aon the tooth flank9a.

In this way, the tooth flank9aof the gear6is formed with, as shown inFIG. 7 (c), grinding lines21in a cross-hatching pattern in which two kinds of the arc-shaped grinding lines21a,21bof different directions cross each other. At an intersection of the arc-shaped grinding lines21a,21bof the grinding lines21having the cross-hatching pattern, an oil reserving part22is formed, and when the gear6is used in, for example, a transmission of an automobile, lubricating oil stored in this oil reserving part22can suppress wear of the tooth flank9amore effectively.

Second Exemplary Embodiment

FIG. 8 (a),FIG. 8 (b)andFIG. 8 (c)illustrate an abrasive sheet of a gear grinding unit in accordance with the second exemplary embodiment of the present invention, withFIGS. 8 (a)to8(c) being a front view, a side view and a rear view of the abrasive sheet, respectively.FIG. 9 (a)is an enlarged view of an essential part showing the gear grinding unit of the second embodiment and a gear in an engaging condition, andFIG. 9 (b)is an enlarged view of part F inFIG. 9 (a).

It is to be noted that in the second embodiment, elements which are the same as or similar to those in the first embodiment have the same reference marks in the drawings, and the detailed descriptions of those elements are omitted. Emphasis is placed hereinafter on distinctive characteristic of the second embodiment, (and the same goes for a third exemplary embodiment which will be described later).

The abrasive sheet10A of the first embodiment has, as shown inFIGS. 4 (a)to4(c), the abrasive layer12provided on the entire surface of one side (the left side inFIG. 4 (b)) of the backing11, whereas an abrasive sheet10B of the second embodiment has, as shown inFIGS. 8 (a)to8(c), a minimally required abrasive layer12provided only in the vicinity of the curved part11bon a surface (the left surface inFIG. 8 (b)) of one side of the backing11.

It goes without saying that gear grinding unit4B of the second embodiment can obtain the same effects as the gear grinding unit4A of the first embodiment. Moreover, since the minimally required abrasive layer12is provided only in the vicinity of the curved part11bon the surface of the one side of the backing11, the provided abrasive layer12corresponds only to a part of the abrasive sheet10B that substantially comes into contact with the tooth flank9a, whereby the abrasive sheet10B can have a required grinding function, while consumption of abrasive or the like can be reduced by a substantial amount.

Since the abrasive layer12is not provided to a part other than in the vicinity of the curved part11bof the backing11of the abrasive sheet10B, the abrasive sheet10B bends more flexibly than the abrasive sheet having the abrasive later 12 on the entire surface of the backing11, thereby allowing the thread8aof a threaded grinding part8B to contact the tooth flank9amore closely as shown inFIGS. 9 (a)and9(b). Consequently, finer surface roughness can be obtained.

Furthermore, centrifugal force associated with a rotational motion of the threaded grinding part8B can effectively act on the abrasive sheet10B, thereby causing the bending abrasive sheet10B to rise so as to return to its original position. Thus, the abrasive sheet10B can be pressed against the tooth flank9a. Pressing force of the abrasive sheet10B with respect to the tooth flank9acan be adjusted by adjusting the centrifugal force, that is to say, adjusting rotational speed of the threaded grinding part8B.

Third Exemplary Embodiment

FIG. 10is an enlarged view of an essential part showing a gear grinding unit of the third exemplary embodiment and a gear in an engaging condition.

In the gear grinding unit4A of the first embodiment, the plurality of the abrasive sheets10A are arranged close to one another as shown inFIG. 6 (a)andFIG. 6 (b), whereas in a plurality of the abrasive sheets10A of a gear grinding unit4C of the third embodiment, a spacer23is interposed between the adjacent abrasive sheets10A for providing a predetermined space, and with the spacers23interposed, the plurality of the abrasive sheets10A are overlapped along the rotation axis S1, thus forming a threaded grinding part8C.

It goes without saying that the gear grinding unit4C of the third embodiment can obtain the same effects as the gear grinding unit4A of the first embodiment. Moreover, the spacer23interposed between the adjacent abrasive sheets10A of the plurality of the abrasive sheets10A provides the predetermined space, so that the degree of bending of the abrasive sheets10A can be adjusted with ease by adjusting thickness and diameter of the spacer23, the number of the spacers23and others.

The embodiments of the gear grinding unit according to the present invention have been described above. However, the present invention is not limited to the structures described in the above embodiments and allows appropriate variations on each of the structures without departing from its spirit, such as, appropriately combining the structures of the foregoing embodiments.

For example, when the number of the threads of the threaded grinding part8A is three, the abrasive sheet10C having, as shown inFIG. 11 (a), three bulge parts10awhich are circumferentially evenly spaced around the center point O1(every 120 degrees) may be used, and when the number of the threads is four, the abrasive sheet10D having four bulge parts10awhich are circumferentially evenly spaced around the center point O1(every 90 degrees) as shown inFIG. 11 (b)may be used (the same goes for the threaded grinding parts8B,8C).

In place of the positioning hole15provided in the abrasive sheet10A (refer toFIGS. 4 (a)and4(c)), a notch24may be provided at a periphery of the insertion hole14as shown inFIGS. 12 (a)and12(c), and the shaft17aof the holder17may be provided with a projection (not shown) corresponding to this notch24for positioning the abrasive sheet10A (and the same goes for abrasive sheets10B,10C and10D).

Although the abrasive sheets10A to10D each have the abrasive layer12provided on the surface of the backing11, the present invention is not limited to this. For example, a sheet of synthetic resin into which abrasive (abrasive grains) is kneaded may be used instead as the abrasive sheet10A,10B,10C or10D.

It is also to be noted that the curved part11bof the backing11that outlines the bulge part10aof each of the abrasive sheets10A to10D is not necessarily required to be a perfect curve and may instead be a series of many lines connected to shape into a curve as a whole.

With regard to the abrasive sheets10A to10D, the example in which the abrasive layer12is provided only to one side of the backing11has been shown. In such a case, however, in order to grind a tooth flank9bon the opposite side, the gear grinding unit4A,4B or4C needs to be temporarily disengaged from the gear6, and thereafter mounting direction of the gear grinding unit4A,4B or4C with respect to the main spindle2needs to be changed, or engagement position of the gear grinding unit4A,4B or4C with respect to the gear6needs to be shifted.

For this reason, the other side of the backing11of the abrasive sheet10A,10B,10C or10D is also provided with the abrasive layer12, that is to say, the both sides of the backing11have the abrasive layers12, respectively. Thus, the tooth flank9aon one side and the tooth flank9bon the opposite side can both be ground in one chuck without disengagement of the gear grinding unit4A,4B or4C from the gear6, thereby improving work efficiency. To grind the tooth flank9bthat is on the opposite side of the tooth flank9aon the one side, the main spindle2and the table shaft3are controlled in synchronization with each other so as to press the threads8a,8bof the threaded grinding part8A,8B or8C against the tooth flank9b.

INDUSTRIAL APPLICABILITY

A gear grinding unit according to the present invention is easy to make and has the characteristic of grinding a tooth flank of a gear to have fine surface roughness without requiring any special shaping work such as dressing and therefore, is suitable for achieving finer surface roughness of a gear used, for example, in a transmission or the like in the field of automobiles that places importance on comfortability and fuel efficiency.

DESCRIPTION OF REFERENCE MARKS IN THE DRAWINGS